CN107110492A - Side feed forced ventilation formula biomass combustion cooking furnace - Google Patents

Abstract

Disclosed herein is helping to reduce the granular material discharged system and device of biomass stove, such as by using being ejected at gas in the zoneofoxidation of combustion chamber or neighbouring.In addition disclose to help gas injection and/or collect system and device that the pump or air blower of waste gas provide electric energy.It is the thermoelectric generator that can also be used for energizing for other devices there is provided the device of electric energy in certain embodiments.In many examples, gas injection at or near the zoneofoxidation of system and device in the combustion chamber of biomass stove.The gas being injected into the area can be fresh air, burning waste gas or its combination.It is pumped into gas propulsive may also aid in the help of the pump of waste gas or air blower into combustion chamber.

Description

Side Feed Forced Draft Biomass Burning Cooking Oven

Cross References to Related Applications

This application claims the benefit of priority under 35 U.S.C. § 119(e), U.S. Provisional Patent Application no. 62/048,884, filed September 11, 2014, the entire contents of which application are hereby incorporated by reference.

technical field

The present invention discloses systems and devices that help reduce emissions from biomass furnaces, for example, by utilizing gases that are injected into a combustion chamber, at or near an oxidation zone. Also disclosed are systems and devices for generating electrical power from a biomass furnace to operate pumps or blowers that assist in injecting gases and/or collecting exhaust gases.

Background technique

The global commercial market for improved cooking stoves is a nascent market. While furnace improvement programs have been used for decades, these programs have had limited impact due to poor durability and performance, or lack of understanding of the market (such as price points), misplaced subsidies, and lack of incentives and education. A number of anticipated public benefits of improved cooking stoves are discussed below.

Health Impacts on Rural Populations

Ambient concentrations of airborne pollutants such as CO and particulate matter (PM ₁₀ , PM _2.5 ) smaller than about 10 or 2.5 microns have been observed in dwellings in rural areas of developing countries exceeding World Health Organization (WHO) exposure limits Up to 30X and exceeds the EPA limit of 100X. This indoor air pollution (IAP) has been linked to nearly 3% of the global disease burden and is a major contributor to as many as 2 million premature deaths each year. Advanced gasifying cooking stoves have demonstrated their potential to reduce PM and CO emissions associated with three-stone stoves.

Exhaust gas recirculation (EGR) can further reduce emissions, benefiting hundreds of thousands of users in general.

Description of drawings

Figure 1 illustrates various embodiments of the presently disclosed EGR cooking ovens and devices.

Figure 2 shows the emissions improvement for one embodiment of the disclosed EGR prototype compared to a three stone furnace.

Figure 3 shows discreet PM emissions data for one embodiment of an EGR furnace.

Figure _{4 shows} the _{soot volume fraction} , _primary Particle size and number concentration of the primary particle distribution. These are cross-sectional "pictures" (taken with time-resolved laser-induced incandescence (TIRE-LII) and TEM) of co-flowing non-premixed flames. The fuel flows coaxially with three different gas mixtures, the composition of which is marked in the subscript of the figure.

FIG. 5 illustrates various embodiments of a power supply for a fan-driven EGR system disclosed herein.

Figure 6 shows a photograph of an example of an EGR permitting biomass stove used for testing.

Figure 7 shows a schematic diagram of an embodiment of an EGR permitting biomass furnace (top) and a cutout of the EGR device.

Figure 8 is an example of an EGR enabled furnace used to test emission reduction parameters.

Fig. 9 is the embodiment of Fig. 8 shown from the front with two injection nozzles located in the mouth of the furnace.

Figure 10 depicts an EGR device for addition to a biomass stove.

FIG. 11 depicts an embodiment of the disclosed apparatus with a preferred location for the injection nozzles located in the EGR permitting furnace.

Figure 12 depicts an embodiment of the disclosed apparatus in which the injection nozzles located in the EGR permit furnace have a preferred geometry.

Figure 13 is a photograph of one embodiment of the disclosed system and apparatus used to test the effect of gas temperature on emissions.

Figure 14 shows the results of a start-up phase flow rate analysis performed on one embodiment of the disclosed furnace.

Figure 15 shows the results of a steady state fire phase flow rate analysis performed on one embodiment of the disclosed furnace.

Figure 16 shows various positions of nozzles for use with the disclosed devices and systems.

Figure 17 shows the analysis of a study testing emissions as a function of temperature.

Figure 18 shows start-up and steady state discharge as a function of flow rate for various nozzle positions.

Figure 19 shows the results of air jet flow rate optimization for side jet nozzles.

Figure 20 shows test results for optimized PM _2.5 emissions for side jet nozzles as a function of nozzle diameter.

Figure 21 shows the results for steady state flow rates and optimized discharges for various diameter jet orifices.

Figure 22 shows the local peak discharge for a 3.2 mm nozzle.

Figure 23 shows the local peak discharge for a 5.7 mm nozzle.

Figure 24 shows the flow distribution in the combustion chamber and the effect on emissions at different air injection flow rates.

Figure 25 shows the various injection positions tested in the G3300.

Figure 26 shows several pictures of an embodiment of a chimney ring nozzle.

Figure 27 shows the effect of air flow velocity at the top injection location.

Figure 28 shows the spray angles tested at the bottom of the chimney.

Figure 29 shows an embodiment of an angled chimney ring nozzle.

Figure 30 shows start-up and steady state PM and flow rate for a G3300 with a side jet nozzle having a 1.5 mm diameter jet orifice.

Figure 31 shows start-up and steady state PM and flow rates for a G3300 with a side jet nozzle having a 2.3mm diameter jet orifice.

Figure 32 shows start-up and steady state PM and flow rates for a G3300 with a 1.5 mm diameter injection orifice at the chimney annulus at the bottom of the upper combustion chamber.

Figure 33 shows start-up and steady state PM and flow rates for a G3300 with a 1.5mm diameter injection orifice and a chimney annulus in the middle of the upper combustion chamber.

Figure 34 shows the start-up and steady state PM and flow rates for a G3300 with a 1.5 mm diameter injection orifice in the chimney annulus high in the upper combustion chamber.

Figure 35 shows start-up and steady state PM and flow rates for a G3300 with a 1.5mm diameter injection orifice at the chimney annulus at the bottom of the upper combustion chamber.

Figure 36 shows start-up and steady state PM and flow rate for a G3300 with a 3.0 mm diameter injection orifice at the chimney annulus at the bottom of the upper combustion chamber

Contents of the invention

Disclosed herein are systems and devices for reducing emissions from biomass combustion devices, such as furnaces. The disclosed systems and devices may include exhaust gas recirculation (EGR) and/or fresh air injection systems to reduce particulate emissions. The disclosed systems and devices can also be used to increase the thermal efficiency of biomass combustion devices, such as furnaces. In many embodiments where exhaust is used for injection, a portion of the biomass combustion system emissions (combustion exhaust) is captured and re-injected into the combustion zone. In some embodiments, exhaust may be combined with fresh air prior to re-injection. Use of the disclosed systems and devices can help reduce emissions (e.g., CO and particulate matter) from biomass burning devices and, in some embodiments, can provide electrical power to power jet fans/blowers and other electronic devices (e.g., phones or batteries) can.

Disclosed herein is an apparatus for reducing emissions from a biomass furnace, the apparatus comprising: a fluid inlet orifice; an inlet conduit having an outer surface and an inner surface, the inner surface defining an inlet chamber via the An inlet port is in fluid communication with the outer surface, an inner chamber for introducing a fluid (eg, a gas, such as air, which may include greater than about 15% oxygen, O ₂ ); located within the inlet chamber and located in the inlet hole a fan at the distal end of the mouth for drawing fluid through the inlet orifice and into the chamber, and into an outlet conduit having an inner surface defining an outlet chamber, the an outlet chamber in fluid communication with the inlet chamber; having one or more nozzles inside in fluid communication with the outlet chamber for directing fluid into a combustion chamber of the biomass furnace; and defined within the A plurality of outlet orifices on the surface of the nozzle designed to allow fluid to exit the interior of the nozzle. In some embodiments, the nozzle is located at or near the top of the lower combustion chamber. In some embodiments, the outlet orifice has an average diameter between 0.5 and 3.5 mm and defines a circle, square, triangle or ellipse as measured through the center of the circle, square, triangle or ellipse. The average diameter. In some embodiments, the volume of gas escaping from the one or more nozzles is greater than about 10 standard liters per minute and less than about 100 standard liters per minute, and the gas can flow from the orifice at about 5-25 m/s speed escapes. In some embodiments, the nozzle is a linear nozzle or a circular nozzle, such as a ring, located above the lower combustion chamber and within the lower half of the upper combustion chamber, and designed to allow the combustion gases to pass directly through the jet area.

Also disclosed is a method of reducing emissions (e.g., particulate emissions, in some cases particles smaller than about 2.5 microns) from a biomass furnace by about 20% to about 90%, comprising: placing gas into the nozzle an inner chamber in which the nozzle is located at or near the flame; increasing the pressure of the gas within the nozzle (e.g. by using a fan or pump to propel the gas inside the nozzle); a plurality of external orifices expelling a quantity of said gas from said nozzle; and directing the injected gas into a flame within a combustion chamber of said biomass furnace, wherein said gas reduces at least The amount of a pollutant. In some embodiments, the volume of gas expelled from the nozzle is between about 10 and 100 standard liters per minute. In some embodiments, the nozzle defines a linear tube or a circular annulus, and an outlet orifice is located in the inner surface of the annulus to help inject gas into the center of the annulus, the outlet orifice having a range between 0.5 and Diameter between 6.0mm. In some embodiments, the outlet orifices are equidistant from the floor of the combustion chamber and the gas is expelled through one or more orifices at a velocity of between 5 and 25 meters per second. In many embodiments, the gas is injected into the flame at an angle between about -10 degrees and about +30 degrees.

Also disclosed herein is a method of reducing particulate matter emissions from a biomass furnace, the method comprising: pumping a gas into a chamber, the gas comprising greater than about 15% _O2 ; directing the gas from the chamber Into a nozzle having an inner surface and an outer surface, the nozzle defines a circular tube having a plurality of outlet orifices on the circular inner surface, wherein the outlet orifices allow gas to flow from the the interior of the tube travels towards the center of the circle; increasing the pressure of the gas within the interior of the nozzle; expelling a quantity of pressurized gas from the nozzle at a velocity between about 5 meters per second and 20 meters per second; and directing the injected gas into the flame in the combustion chamber of the biomass furnace, wherein the gas reduces the amount of at least one pollutant leaving the biomass furnace by a greater amount than the absence of nozzles or the About 25% more furnaces lack pressurized gas in the nozzle. The gas is propelled into the combustion chamber with the help of a pump or blower that also helps draw in the exhaust gas.

detailed description

Described herein are furnaces and furnace accessories that circulate combustion products back to the combustion chamber. In some embodiments, the furnace and furnace accessories may mix the combustion products with fresh air before directing them back into the combustion chamber. In some embodiments, recirculation of exhaust gas into the combustor may provide a strong interaction with non-premixed diffusion-based combustion that occurs between biomass and naturally aspirated incoming air.

While several embodiments of the disclosed circulation devices and systems have been disclosed, other embodiments will become apparent to those skilled in the art from the following detailed description. As will become apparent, modifications can be made in various obvious aspects of the disclosed systems and devices, all without departing from the spirit and scope of the invention. Accordingly, the detailed description is to be regarded as illustrative in nature and not restrictive.

The adverse effect of incomplete biomass burning is damage to the local and global environment. Furthermore, while biomass has been lauded for its potential to provide carbon-neutral energy, they are not climate-neutral because a significant fraction of the carbon contained in fuels is considered as a gas species with global warming potential ( _CH4 and NMHC). discharge again. The cooking stove design described here has the potential to significantly reduce this pollution.

Furthermore, recent studies have shown that black carbon (BC) particulate emissions are the second most important driver of global climate change after _CO2 . Globally, it is estimated that home cooking generates 50% of the total BC emitted to the environment each year, and utilizing technologies such as the cooking stove described herein to substantially reduce global BC emissions has been promoted as the most effective way to combat short-term global warming. One of the strategies of hope.

global fuel savings

It is estimated that biomass stoves are responsible for approximately one-eighth of net deforestation and thus 1.5% of the net anthropogenic _CO2 increase emitted into the atmosphere. More locally, women and children will spend up to 20 hours a week gathering firewood, an activity that prevents their growth and in many cases exposes them to violence (Global Alliance for Clean Cooking Stoves).

There are basically three main analogues of ultra-clean biomass cooking stoves. These analogs are (1) forced-air semi-gasifiers, (2) natural-air semi-gasifiers, and (3) side-fed blast furnaces. Extensive performance data is disclosed herein for various commercially available furnaces, as well as for a novel and surprisingly efficient side-fed blast furnace. Based on Envirofit's extensive market experience, it has been found that:

Forced draft gasifiers that require fuel handling do not meet market expectations regarding price and convenience.

The operational sensitivity of natural gas flow and forced air semi-gasifiers results in high emissions when (1) fuel quality changes, (2) during start-up and shutdown, and (3) the user operates the furnace outside the optimization window possible.

In contrast, side-feed furnaces meet consumer expectations regarding fuel flexibility and ease of use. Furthermore, it allows the furnace to function properly even without operating the fan. While conventional rocket stoves do not meet the 90% emission reduction target, they meet up to 70% emission reduction, thus ensuring reasonable emission reduction even in failure mode.

As side-fed stoves have the greatest potential to meet all aspects of consumer demand, expectations and performance, there is a corresponding need for more efficient side-fed stoves that meet emission reduction targets of 90% or higher. This goal contributes to the previously described benefits of improving the health of rural populations, reducing global environmental impacts, and reducing global biomass use.

While many of the examples described herein use commercially available furnaces such as the Envirofit G3300 furnace as the base biomass combustion unit, the invention can be used with side-fed furnaces and side-fed blast furnaces of various designs. Figure 1 shows several commercially available side-fed stove designs: Stove Tec (top); BioLite (middle); Envirofit (bottom, with and without adapters).

Various forms of exhaust gas recirculation (EGR) have been used in other situations to control flame characteristics. EGR is mainly used in internal combustion engines. The primary purpose of EGR in internal combustion engines is to reduce _NOx formation. It does this by introducing slightly inert exhaust gases into the cylinders, thus reducing the proportion of combustible gases and distributing the thermal energy over a greater mass. This reduces the peak flame temperature, thus reducing the thermal decomposition of _N2 and the consequent formation of _NOx . But because these engines operate near stoichiometric levels, adding exhaust gases can create localized regions of below stoichiometric levels of oxygen. This promotes incomplete combustion and thus generally increases the overall production of particulate matter (partially burned hydrocarbons). However, it has been found that increasing _CO2 concentration can help alleviate the increase in PM production caused by EGR.

Considering the effect of EGR on internal combustion engines, it is counterintuitive to apply EGR to biocooking stoves for three main reasons. First, NOx formation in biomass cooking stoves is not important. This is because the peak combustion temperature in the furnace is low enough that a negligible fraction of the _N2 molecules will thermally decompose. Second, since biomass stoves typically have relatively low peak combustion temperatures compared to engines, technicians would assume that lowering the temperature in cooking stoves by introducing exhaust gases would promote incomplete combustion and increase particulate matter formation. Third, since biomass cooking stoves (particularly rocket-bent stoves) operate with such high excess _O2 values (excess air to stoichiometric air ratio of about 2.3 for the M5000), there is no need to help alleviate The _CO2 concentration in the cooking furnace EGR is likely to be small compared to the minimum concentration of _CO2 in the engine EGR for PM production issues.

Contrary to the expected results described above, applicants have unexpectedly discovered that applying EGR to a biomass cooking stove (1) reduces particulate matter production and (2) increases CO oxidation, as seen in FIGS. 2 and 3 . The current published findings are counter-intuitive compared to EGR combined with a combustion engine. The current literature may provide some hindsight-based theory for this observed emission reduction.

As mentioned earlier, recycling _CO2 into the combustion chamber of a biomass cooking stove is a plausible mechanism for reducing PM production, although this reduction in PM production may be less favorable given the excessive air ratios in rocket-bent stoves. small reduction. The document documents the effect of _CO2 addition on particulate matter emissions in non-premixed flames. These studies focus on soot formation in homogeneous fuels such as propane and ethylene. Earlier literature reported that the addition of carbon dioxide resulted in reduced soot formation in convective diffusion flames through chemical interactions. More recent studies indicate that the reduction in particulate matter caused by the addition of carbon dioxide is due to both a reduction in flame temperature and chemical interactions of the CO ₂ . Figure 4 shows experimental data collected by Oh et al. which clearly demonstrates the soot reduction obtained in the co-flow diffusion flame profile with the addition of carbon dioxide to the oxidant. In the figure, fv represents the volume fraction of soot in the flame, dp is the primary particle size, and Np is the number concentration of primary particles in the flame. According to Oh et al., "in the case of _CO2 instead of _N2 as the diluent, the primary particle size and soot volume fraction decreased dramatically". Again, according to Oh et al., the reduction in soot formation contributes to:

The flame temperature decreases due to the increased heat capacity of _CO2

Dilute the reactive gas species by introducing carbon dioxide

Direct chemical effects of carbon dioxide

These studies confirmed the effect of _CO2 addition on particulate emissions from co-flow non-premixed flames, but none of the currently existing literature reaffirms this effect for solid biomass combustion. Even more surprisingly, applicants have discovered that other other components and spray characteristics (velocity, direction, position, angle, volume) affect PM reduction.

There are other potential mechanisms that could further explain the reduction in PM emissions, such as increasing mixing, increasing _O2 levels, changing the total flow through the furnace and subsequently changing the residence time of combustible components, changing the peak combustion temperature in the furnace, and disrupting circulating PM. These mechanisms are neither fully understood nor easily predicted. There is currently no literature evaluating the effect of these mechanisms on particulate emissions in biomass cooking stoves, especially in relation to the application of EGR in biomass cooking stoves.

In addition to the potential benefit of EGR on particulate matter formation, experimental and literature data indicate that carbon monoxide may be reduced using EGR through mechanisms such as increased mixing and water in the exhaust stream that catalyzes CO oxidation.

In some embodiments, the furnace and furnace accessories can include means for actively moving air, and the means can be powered by a power source. In some embodiments, the air moving device may be a fan or blower. The power source may be a battery, which may include an adapter and/or charging circuit. Figure 5 shows several possible embodiments. In one embodiment, the power source includes an AC/DC adapter with a battery and charging circuitry. This embodiment may be desirable in certain markets, such as India, where over 70% of the target market has access to electrical energy at least some of the time of day. Another embodiment may include a hand-operated generator (or dynamometer). A hand-operated generator can be combined with the charging circuit and battery described above. With an expected fan power draw of about 1-3 watts, manual charging wouldn't be too taxing. Figure 5 also shows a thermoelectric generator (TEG) power supply system that can use heat from the furnace to generate electricity. In many cases, TEGs can generate over 1-3 watts, which also allows charging of batteries and/or other electronic devices (lamps, light sources, mobile phones, computers, etc.). The potential to generate excess electrical energy is attractive. Other options will be apparent to those skilled in the art and are fully consistent with the invention described herein.

6-9 depict several embodiments of the disclosed furnace and furnace accessories. The example shown in Figure 6 includes a commercially available furnace, the Envirofit G3300. This example was used to test many aspects of the claimed furnace and furnace accessories. For example, the emissions data shown in Figures 2 and 3 were generated using this embodiment.

Figure 7 shows a second embodiment of the disclosed oven and oven accessories. This embodiment of an EGR-enabled furnace is used to analyze several variables, such as those that can affect the emissions performance of the furnace, such as gas injection location, nozzle geometry, gas path temperature, flow rate, and TEG location. The example of Figure 7 also includes a commercially available furnace, the Envirofit M5000. Figure 7 does not show the conduits leading the gas from the EGR outlet to the side feed openings in the furnace. Catheters not shown in FIG. 7 are shown in the embodiment depicted in both FIGS. 8 and 9 . These ducts direct the gas from the EGR outlet to side feed openings in the furnace. A pulse width modulator and power supply may be included in the disclosed apparatus to help control the speed of the fan/blower motor. Furthermore, the TEG incorporated into the EGR path of the embodiment of FIG. 7 helps characterize the energy generation/recovery of the cycled exhaust.

Figure 10 depicts another embodiment of an EGR permitting furnace. This example illustrates how an EGR furnace accessory can be added to a furnace as an accessory, for example an EGR device can be added to a rocket bent tube furnace. In this embodiment, exhaust gases are drawn through a grid of manholes, which may be located at or near the furnace roof, as depicted herein. The exhaust gas flows through ducts that may be placed around the perimeter of the pot rim. Exhaust gases within this duct then flow through one or more additional ducts at or near the front of the pan skirt and are injected back into the mouth of the combustion chamber. A fan or blower injecting air may be located between the inlet hole and the injection hole. In some embodiments, as depicted in Figure 10, the fan is located at the rear side of the pan skirt. The power supply can be located near the fan.

As discussed above, the air-jetting blower may be supplied with electrical energy provided by a power source such as a thermoelectric generator, solar battery, hand powered generator (crank charger) or house electricity. Power supply selection can be based on cost assessment and comparison with market requirements. The materials selected for the furnace and furnace accessories can vary depending on the thermal, chemical and mechanical environments to which the material is exposed. In many embodiments, the components within the device may vary and need not be the same or similar to those utilized in the Envirofit G3300 or M5000 furnaces discussed above. In many embodiments, the EGR device may allow the furnace to function properly and efficiently when the EGR system is shut down and/or fails.

For most embodiments of the disclosed EGR system, the furnace may include an air/fuel inlet (or mouth) that feeds wood fuel or similar biomass into the mouth of the furnace, and air is drawn into the mouth by convection. Ministry. In these embodiments, combustion typically occurs within a combustion chamber. The geometry and materials of the combustion chamber can be optimized to properly burn the biomass and minimize heat transfer to the furnace body. In many embodiments, exhaust from biomass combustion may be drawn up through the upper combustion chamber and into one or more exhaust inlet orifices. In some embodiments, the exhaust gas inlet aperture is defined in an annulus structure located at or near the top of the upper combustion chamber. This ring structure may be referred to as an "EGR inlet skirt" and its interior may define an exhaust collection chamber. Figure 7 depicts an embodiment of an "EGR inlet skirt". A pump/blower arrangement can be integrated into the furnace to help draw exhaust gases into the EGR inlet skirt. The exhaust gas travels through the duct and through the pump/blower arrangement into one or more injection ducts until it is injected into the combustion chamber of the furnace.

In many embodiments, exhaust may enter an intake port, which may be located at or near the top of the combustion chamber. The orifice may be in fluid communication with the interior of an exhaust collection chamber, which may be in fluid communication with one or more exhaust conduits that contain exhaust and direct the exhaust to a pump or blower in fluid communication with the exhaust conduit. A pump or blower assists in actively moving exhaust gas from the exhaust conduit into one or more injection conduits which direct the exhaust gas into one or more injection nozzles. The injection nozzle has a plurality of orifices that allow exhaust gas to escape inside the injection nozzle.

Testing of the disclosed devices and systems indicated that injection location, nozzle geometry and flow rate affect the discharge performance of the furnace. Therefore, for various combinations of spray positions and nozzle geometries, an optimal flow rate was determined. Next, various combinations were compared to minimize PM emissions to determine the optimal design of the test furnace. The disclosed tests identified some preferred combined embodiments for injection location and nozzle geometry, although not fully optimized. Some exemplary combinations are described below.

Exemplary Furnace Nozzle Design

There are several locations in the combustion chamber where injection nozzles can be placed. Likewise, the injection orifice defined in the plane of the nozzle may have several geometries and configurations. Various designs were tested and a preferred injection location and nozzle configuration for PM abatement was found for one embodiment of the disclosed furnace. Figures 11 and 12 depict such a preferred embodiment of spray location and nozzle geometry. In this embodiment, the injection nozzle location is at or near the top of the combustion chamber.

In this embodiment, two injection nozzles are located at or near the sides of the combustion chamber. Other embodiments may include more than two nozzles or one nozzle. In this embodiment, the nozzles are placed parallel and perpendicular to the direction of gas flow of combustion products through the upper combustion chamber of the furnace. In some embodiments, the nozzles may not be parallel or perpendicular to the gas flow. In this embodiment, 6 injection orifices are defined within the nozzle face. In this embodiment, the injection orifices are spaced 9/16 inch center-to-center apart, and each orifice has a diameter of about 3/16 inch. In many embodiments, such as those in which the nozzle defines a substantially linear tube structure, such as those shown in FIGS. About 1/2 inch from the mouth. In other embodiments, the nozzle may define a ring structure that may be located at or near the wall of the upper chamber (or chimney).

The injection nozzle may define an injection orifice confined in a horizontal section of the combustion chamber. In many embodiments, the horizontal section is less than about 20 cm, 19 cm, 18 cm, 17 cm, 16 cm, 15 cm, 14 cm, 13 cm, 12 cm, 11 cm, 10 cm, 9 cm, 8 cm, 7 cm, 6 cm, 5 cm, 4 cm, 3 cm, 2 cm, or 1 cm , and greater than 0.5 cm, 1 cm, 2 cm, 3 cm, 4 cm, 5 cm, 6 cm, 7 cm, 8 cm, 9 cm, 10 cm, 11 cm, 12 cm, 13 cm, 14 cm, 15 cm, 16 cm, 17 cm, 18 cm, or 19 cm. In some embodiments, such as those shown in Figures 16, 26, and 29, the orifices are located substantially planarly within the combustion chamber and parallel to the floor of the combustion chamber. When the outlet orifices are in the same plane as the bottom surface, the center of each outlet orifice is positioned at the same distance (or a change in distance of less than about 0.5 cm) from the bottom surface of the combustion chamber. In some embodiments, the distance from the bottom surface to each aperture varies by less than 0.5 cm, 1 cm, 2 cm, 3 cm, 4 cm, 5 cm, 6 cm, 7 cm, 8 cm, 9 cm, 10 cm, 11 cm, 12 cm, 13 cm, 14 cm, 15 cm , 16cm, 17cm, 18cm or 19cm (when the variation is less than about 0.5cm, the orifice can be said to be planar). When the nozzle defines a ring structure, orifices may be located throughout the ring and designed to direct gas into the center of the ring.

In many embodiments, there may be a preferred flow rate for the exhaust gas flow into the combustor, which may help reduce PM emissions from a furnace equipped with the disclosed system. In many embodiments, the preferred flow rate may be about 20 to 70 standard liters per minute (SLPM). For the nozzle configurations described above and shown in Figures 11 and 12, the preferred flow rates for PM abatement vary between 50 and 70 standard liters per minute. In most embodiments, the flow rate can be increased with increasing firepower to minimize PM emissions. For example, at a power of 2.4 kW, the preferred flow rate may be about 50 SLPM, and at powers greater than 2.6 kW, the preferred flow rate may be increased to 70 SLPM to minimize PM emissions. In some cases, with firepower less than about 2.4 kW, the flow rate may need to be adjusted below 50 SLPM to avoid blowing out the flame, such as less than about 40 SLPM, 30 SLPM, 20 SLPM, 10 SLPM, or 5 SLPM. In many embodiments, the gas flow rate is related to the fire power of the furnace. For example, a flow rate of about 40 SLPM may be required to obtain the desired PM reduction in a 2.5 kW furnace, while a flow rate of about 60 SLPM is required for a 20 kW furnace (such as a chimney draft furnace) for the same level of PM reduction. In some embodiments, the flow rate may be less than about 110 SLPM, 100 SLPM, 90 SLPM, 85 SLPM, 80 SLPM, 75 SLPM, 70 SLPM, 65 SLPM, 60 SLPM, 55 SLPM, 50 SLPM, 45 SLPM, 40 SLPM, 35 SLPM, 30 SLPM, 25 SLPM, or 20 SLPM, and greater than about 10 SLPM, 20 SLPM , 25SLPM, 30SLPM, 35SLPM, 40SLPM, 45SLPM, 50SLPM, 55SLPM, 60SLPM, 65SLPM, 70SLPM, 75SLPM, 80SLPM, 85SLPM, 90SLPM, 100SLPM, or 110SLPM.

For the cold start water boil test, the embodiment of the EGR permitting furnace depicted in Figures 11 and 12 is capable of emitting PM ₁₀ from 275 mg/MJd (PM per megajoule of energy delivered to water) for a base M5000 furnace with pot skirt ₁₀ mg) was reduced to 125 mg/MJd for the same furnace with optimized EGR flow rate.

To better understand the variables affecting PM emission reduction for the embodiments depicted in Figures 11 and 12, some of the underlying variables can be analyzed experimentally. These experiments revealed that one mechanism for reducing PM mass emissions is an increase in the size of the oxidation zone due to elevated _O concentration in the flame, which in turn increases the proximity of the fuel to the oxidizer. The oxidizing zone is the area of the flame where oxygen is dispersed in concentrations sufficient to support combustion. Furthermore, these tests showed that _O2 was more effective in reducing particulate matter mass emissions when injected closer to the beginning of the oxidation zone (closer to the nadir of the flame front). In contrast, injection directed at the charcoal substrate or directly into or onto the fuel was found to result in higher PM mass emissions.

The embodiment depicted in Figures 11 and 12 uses a nozzle location (near the top of the combustion chamber) that allows the gas to be injected near the bottom of the oxidation zone, but sufficiently above the fuel to prevent smoldering or blowing out of the flame and This results in higher emissions.

These studies also identified other variables that can affect PM emissions. For example, increased residence time of particles in the oxidation zone (such as via recirculation) helps reduce PM emissions, as does the forced mixing of combustion gases. In many cases, however, manipulating these two variables appears to be less effective than increasing the _O2 concentration in the oxidizing region of the flame. In addition, it was determined that the sequestering effect of the _CO cycle had less impact on PM emissions _than increasing O concentrations. In some cases, increased fuel consumption rates were observed in some embodiments of the disclosed EGR enabled furnaces, which alone may lead to increased PM emissions. However, when these effects are combined, as they are present in many disclosed EGR permitting systems, a net reduction in PM mass emissions is observed.

Since tests showed elevated _O2 concentration in the flame oxidation zone as a mechanism for PM mass reduction, the same nozzle configuration and injection location were tested with fresh air (non-EGR) injection that should also provide higher _O2 concentration. With full fresh air injection, the cold start water boil test PM ₁₀ emission was reduced to 91 mg/MJd. This shows that EGR embodiments with this nozzle geometry and injection location can provide PM emission reductions greater than or equal to those utilizing exhaust gas.

As described below, the disclosed EGR systems and devices may be modified in various ways to reduce emissions from biomass combustion furnaces. For example, fresh air injection, nozzle position and nozzle geometry can be modified. Other modifications, changes and permutations to the disclosed systems and methods may be included to further reduce PM mass and are included within the scope of the present invention.

All references disclosed herein, whether patent or non-patent, are hereby incorporated by reference as if each citation was incorporated herein in its entirety. In the event of a conflict between a reference and the specification, the present specification, including any definitions, will control.

Although the present invention has been described with a certain degree of particularity, it should be understood that the invention has been made by way of example and that changes in detail or structure may be made without departing from the spirit of the invention as defined in the appended claims. .

Example II-EGR—PM emission reduction analysis

The embodiment of Figure 7 was used to perform initial tests of exhaust gas recirculation. Specifically, particulate matter (PM _2.5 ) was measured during these tests to test for effective emission reductions. The test analyzes several variables such as: temperature of the recirculated exhaust gas, exhaust gas composition, exhaust gas injection location and nozzle configuration, and exhaust gas flow rate.

Circulating Gas Composition

To ensure that the amount of ambient air being drawn into the EGR pot surround is minimized, two sets of Water Boiling Tests (WBT) were run with identical EGR flow rates, injection locations, and nozzle configurations but with different inlet configurations: one set using the above The ring configuration described was performed, and a second set of data was collected using a duct that draws exhaust directly from the center of the combustor outlet. This second configuration ensures that all or nearly all of the gas drawn into the system comprises exhaust gas. The concentration of molecular oxygen was sampled throughout the test using a gas analyzer (TESTO) located in the path of the EGR system. By comparing the oxygen concentration, it can be determined whether ambient air (fresh or non-exhaust) is entering the system at a high flow rate.

The temperature of the circulating gas

The temperature of the recirculated exhaust gas was tested by incorporating a heating strip with a proportional-integral-derivative (PID) temperature controller into the test platform. A photograph of this test system can be seen in Figure 13.

10 cold start water boil tests were performed in which the test variables were held constant except for the temperature of the circulating gas. The average cycle gas temperature varies between about 20°C and 100°C. The lower limit of the test temperature replicates the effect of exhaust gas that has been completely cooled to ambient temperature. The upper bound of the test temperature represents a situation where the temperature of the exhaust gas at the lower edge of the pot remains nearly constant throughout the system from exhaust gas entry to injection into the combustion chamber. The gas temperature is lowered by cooling it with an ice bath, and resistive heating bands are used to raise the gas temperature. Thermocouples along the EGR path are used to measure gas temperature in one-second intervals.

Nozzle and flow rate optimization process

These studies were also used to compare the minimum PM _2.5 emissions of various nozzle configurations. A unique nozzle and flow rate optimization process was developed to roughly estimate the minimum PM _2.5 emissions for a specific nozzle configuration. Two assumptions were made in these tests discussed further below. In general, the progression of the test process includes Step 1 - Design and manufacture the nozzle, Step 2 - Determine the flow rate for the starting fire phase, Step 3 - Determine the optimized flow rate for the steady state fire phase, and Step 4 - Run the cold start water boil test at the optimized flow rate .

In the EGR experimental optimization portion of this study, three iterations of this procedure were done. The details of each step in the sample iterations of the process are discussed below. Step 1: Design and manufacture the nozzle. The nozzle is designed using a combination of fluid mechanics and combustion concepts and previous experimental results. Step 2: In Step 2, the optimal flow rate for PM _2.5 emission reduction in the start-up phase is determined. For each data point, a standard cold start water boil test procedure followed and ended at a water temperature of 30°C. A water temperature of 30°C was selected as the cutoff value for these tests. When the water temperature reaches 30°C, the firepower is no longer in a transient state and has entered a steady state. Flow rates were varied in intervals of 10 to 20 SLPM, and 1 to 2 data points were collected for each flow rate. The flow rate-optimized sampling structure for the start-up phase can be seen in the diagram of FIG. 14 . This graph shows that the optimized start-up flow rate for this exemplary data set is about 40 SLPM.

In step 3, the optimal flow rate for PM _2.5 emission reduction during the steady-state firepower phase is determined. The steady state optimal flow rate was determined using the quasi-simmer test method. First, bring the stove body, pot and water to boiling temperature. Once it reaches a steady-state boiling temperature, remove the charcoal and burning fuel while leaving the pot and water in place. A known weight of fuel is then ignited in the combustion chamber using a propane torch. Propane torches were used to ignite the fuel since the steady state fire stage (3-3/4" x 3/4" x 12" pine branches) fuel dosing method was used from the beginning of each sampling. Prior to beginning sampling PM _2.5 Allow the fire to burn for one minute. This one-minute delay prevents PM _2.5 sampling from taking place while the tree branches are lit. PM _2.5 emissions are then sampled for ten minutes, or until the branches are nearly exhausted while the fire remains at a constant level. Upon completion of the PM _2.5 sampling cycle, The remaining fuel and charcoal were removed and weighed. The re-ignition process and subsequent ten-minute sampling period was then repeated at various flow rates. The water and pot remained in place and at boiling temperature throughout the duration of this test. Additionally, The time between sampling cycles is less than 3 minutes, which prevents significant cooling of the furnace and/or pan. This test procedure allows a rough estimate of the relationship between PM emissions and flow rate for a particular nozzle setting during the steady state fire phase. PM emissions are determined by the unit The mass of PM _2.5 emitted by the mass of fuel consumed (referred to as the emission factor (EF)) is plotted. In calculating EF, the mass of fuel consumed is corrected for moisture content and sampling time. The steady state fire phase can be seen in Figure 15 Exemplary Results of Flow Rate Optimization. It can be seen that an exemplary optimized steady state phase flow rate is about 80 SLPM.

In step 4, the minimum PM emission for a particular nozzle is determined. Using the optimized flow rates determined in steps 2 and 3, complete the cold start water boiling experiment. The optimized flow rate determined in step 2 will be used until a water temperature of about 30°C, and the optimized flow rate determined in step 3 will be used for the remainder of the cold start. The PM emissions resulting from step 4 were used in the design of the next nozzle together with the supplementary conclusions drawn from steps 2 and 3.

Several assumptions were made during these experiments. Specifically, during these tests, the cold start water boil test was divided into two phases, a start-up phase and a steady state phase. The test concluded that emissions during the start-up phase (where more transient and generally lower firepower is present) are different than emissions during the steady state firepower phase (where steady and generally higher firepower is present). Therefore, it is assumed that different firepower will require different forced air flow rates to achieve maximum PM emission reduction. Therefore, cold start water boil test emissions can be minimized if the flow rate tracks real-time firepower. In order for the flow rate to continuously follow the real-time fire power, a function of fire power and flow rate can be developed. This function allows determining the optimal flow rate for many fires, as well as the control system for continuous monitoring of the fires. Alternatively, the controller can act on a time-based function (stepped, block or continuous).

To save time, only the optimized flow rates for the two distinct fire stages were determined, and the flow rates during the cold start test followed a step function pattern. Inherent in the method is the assumption that the measured PM _2.5 emissions from a cold start test utilizing a two-fire staged model will be similar to emissions from a cold start test in which the flow rate continues to follow real-time fire.

The gas injection flow rate can be changed according to the power output. In some embodiments, a fan located in the exhaust path can help regulate flow rate based on firepower. In other embodiments, the flow rate may remain constant during fan operation. In further embodiments, the fan may operate at multi-stepped speeds, where there are two or more operating speeds. In many embodiments, the controller can be programmed with various fan speed functions based on firepower (which can be measured) the controller or time of use.

In some cases, the use of the flow rates determined by the steady state flow rate optimization process relies on the assumption that the gas flow rate does not significantly affect the thermal efficiency of the furnace during the steady state firing phase. The reason for this assumption is that it is impractical in these tests to obtain accurate measurements of the energy transferred to the water during the test.

Nozzles tested

Finally, for the EGR furnace, three iterations of this optimization process are performed. Three different nozzle configurations that were tested can be seen in FIG. 16 . These settings occupy two main injection positions. The estimated injection locations are listed below in the cross-sectional view at the lower right of FIG. 16 . Diffusion nozzles are designed to inject gas below the fuel bed and are positioned below the fuel. Air curtain nozzles are designed to inject gas at or near the mouth or inlet and at the top of the combustion chamber. Side injection nozzles are also designed to inject gases at or near the top of the combustion chamber. The air curtain embodiment shown in FIG. 16 has a gap approximately 4" x 1/4" wide and sprays gas downward at an angle of approximately 45 degrees relative to horizontal. The side injection nozzle shown in the embodiment of Figure 16 has a 4.9 mm diameter hole that injects air perpendicular to the furnace's natural gas flow. The diffuser nozzle embodiment of Figure 16 has two 3/4' diameter tubes shown flattened and directing the gas beneath a perforated metal grate.

Cycle Gas Composition - Results/Discussion

The composition of the cycle gas can significantly affect the concentrations of nitrogen, oxygen, carbon dioxide and carbon monoxide in the combustor. As discussed above, ambient air (fresh or non-exhaust) can be drawn into the EGR pot skirt inlet at high EGR flow rates, affecting test results. In the following, Table 1 shows the average oxygen concentration with the two inlet configurations described above.

Table 1. Circulation exhaust gas composition

The results in Table 1 demonstrate that the average oxygen concentration in the recirculated exhaust gas seems to increase slightly when a modified EGR inlet is installed which takes the exhaust gas directly from the center of the combustion chamber outlet. However, if ambient air is drawn into the standard EGR pan inlet, the oxygen concentration in the recirculated exhaust gas is expected to be higher than if the modified EGR inlet were installed. This effect was not observed, indicating that little or no ambient air was drawn into the standard EGR inlet at high EGR flow rates. The fact that the opposite relationship was observed may instead indicate that when a modified EGR inlet is installed, gases are drawn in before the available _O2 combustion is complete.

The temperature of the circulating gas

The effect of the temperature of the cycle gas was tested by a set of eight cold start WBTs. Four different gas path set point temperatures were tested with two replicates for each temperature. Figure 17 depicts the results of these tests. The temperature values plotted on the x-axis represent the average measured temperature of the gas measured throughout the WBT immediately before being injected into the combustion chamber. It should be noted that for all tests, an air curtain nozzle was used and the EGR flow rate was consistently maintained at about 70 SLPM.

The results of these experiments shown in Figure 17 did not identify a strong correlation between gas temperature and PM emissions. While some embodiments may include isolation structures in the gas paths, many embodiments may not include isolated gas paths. For subsequent testing described below, no isolation structures along the EGR path were incorporated.

Nozzle and flow rate optimization

Figures 18, 19 and 20 present the results of initial flow rate optimization for air curtain nozzles, diffuser nozzles and side jet nozzles, respectively. Table 2 summarizes the main results of flow rate optimization. By selecting an approximate minimum location on the plot of FIG. 18, a value for the optimal flow rate was determined. The values of PM _2.5 in Table 2 represent stage-specific emissions at optimized EGR flow rates.

Table 2. EGR nozzle flow rate optimization

Using the optimized flow rates seen in Table 2, a cold start WBT was done for each nozzle configuration. The results of these tests can be seen in Table 3-1. The PM _2.5 emissions for these tests represent the minimum amount of PM _2.5 emissions for each nozzle configuration. As can be seen in Table 3, side injection nozzles injecting near the top of the combustion chamber caused the greatest reduction in PM _2.5 emissions from the base M5000 PM _2.5 emissions (see Table 3-2 for M5000 base values; PM; 461mg base vs 248mg for side injection nozzles ; specific energy PM 280 mg/MJd base vs 150 mg/MJd for side jet nozzles) reduced by 44%. The use of the side jet nozzle also appears to increase the firepower compared to the usual base firepower and the firepower of the other two nozzle configurations.

Table 3-1. Minimized PM _2.5 emissions for various nozzles utilizing EGR

Table 3-2. Basic M5000 performance

Using the emission factors found in Table 2, and knowing the total amount of fuel consumed in the WBT, the total weight of PM emitted can be estimated. A comparison between predicted PM and measured PM allows a determination of whether the measurements in the flow rate test can provide a relatively accurate representation of emissions from a completely cold start WBT. A comparison between projected and measured PM emissions can be seen in Table 4.

Table 4. Projected vs Measured PM _2.5 Emissions

The error values seen in Table 4 indicate that a shorter test for flow rate optimization can be used to accurately predict total optimized cold start emissions. Furthermore, this indicates that the constant efficiency assumption in step 3 of the nozzle optimization process does not introduce significant inaccuracies.

Finally, the results of this section indicate that emission reductions can be achieved by applying an EGR system to an existing furnace such as the Envirofit M5000 furnace. Testing also provides support for generating and testing new nozzle configurations using the four-step process described above.

Example III - Analyzing the Variables Involved in EGR Emission Reduction

In the tests described in the previous section, it was shown that emission reductions could be achieved by applying EGR. This section utilizes similar testing to identify, isolate, and measure the various mechanisms that affect emissions reductions observed when EGR passes through side-injection nozzles.

testing platform

The M5000 was again used for these tests; however, the EGR furnace test platform was modified from that described above. First, route the conduit so that gas can be injected from the compressed gas cylinder into the M5000. The flow rate of the injection gas is regulated by a high-performance Alicat mass flow controller.

Test Methods

It is hypothesized that the reduction in PM emissions from EGR cooking stoves can be the net result of a combination of the following mechanisms:

Increased particle residence time;

O ₂ /CO ₂ chemistry;

mix;

dilution;

temperature; and

firepower.

This test was performed in order to isolate and determine, as far as possible, the relative importance of each of these mechanisms relative to the EGR side injection nozzle configuration.

Increased particle residence time

The effect of increased residence time of particulate material in the flame was determined by injecting particulate-free replicated EGR gas into the furnace. The EGR replica gas consisted of 15% _O2 , 5% _CO2 and 80% _N2 , similar to the composition measured above. The replication gas was injected at a mass flow rate equal to the optimized mass flow rate for the side injection nozzle. In the experiments described above, it was determined that the optimum flow rates for the side-injection nozzles were 50 to 70 SLPM for the start-up and steady-state fire phases, respectively. However, temperature measurements at the blower wheel indicated an average temperature at the fan of about 333K throughout the cold WBT at the optimized EGR flow rate for the side jet nozzle. To match the mass flow rate of EGR gas to the replicated EGR gas, a temperature correction was applied and a flow rate of 44.7 to 62.6 SLPM was used (where SLPM was according to Alicat mass flow controller specifications, 298K and 14.7 psi). In all, three cold start WBT replications were done using EGR replication gas.

Chemistry of the CO ₂ /O ₂ Cycle

To replicate/isolate the _O2 chemistry, pure molecular _O2 was injected into a furnace configured with a side injection nozzle. Two important considerations must be made in order to estimate the _O2 chemistry seen in the previously described EGR furnace tests. First, the mass flow rate of injected pure _O2 should be similar to the mass flow rate of injected _O2 in the optimized EGR furnace test. Considering that the EGR gas comprises approximately 15% _O2 , a flow rate equal to 15% of the temperature corrected optimal flow rate should be used. This resulted in pure _O2 injection flow rates of 6.7 and 9.4 SLPM for the start-up and steady state fire phases, respectively. Second, the velocity of the injected _O2 should be similar to the velocity of the injected EGR gas in order to simulate the injection depth of the gas into the combustion chamber. To match the velocity between tests, the diameter of the hole in the side jet nozzle through which the gas escapes was modified such that the new hole area was reduced to 15% of the original hole area. Three cold-start WBT replicates were completed, in which pure _O2 was sparged into the furnace.

To replicate and isolate the _CO2 chemistry, pure _CO2 is sparged into the furnace. Since _CO2 comprises approximately 5% of the EGR gas, a flow rate equal to 5% of the temperature-corrected optimal flow rate should be used. This resulted in pure _CO2 injection flow rates of 2.2 and 3.1 SLPM for the start-up and steady state fire phases, respectively. Since these flow rates are significantly lower than the total air flow through the furnace, it is difficult to match the spray depth to the side spray nozzles. To reconcile this problem, use the diffuse spray setting. This ensures that the furnace's natural gas flow carries the _CO2 into the combustion chamber at the center of the flame. Three WBT replicates were done.

Since the _CO2 flow rate was extremely low to simulate EGR gas including 5% _CO2 , additional tests were run with higher _CO2 flow rates to make any chemical/physical effects more apparent. The same procedure was followed as used in the pure _O2 injection test, instead replicating the chemistry of _CO2 in the EGR gas including 15% _CO2 . Three WBT replicates were done.

Mixing, dilution and temperature reduction caused by circulating nitrogen

To complete this study, argon was injected through a side injection nozzle at an optimized EGR flow rate. In summary, three cold start WBTs were performed.

Initially, an attempt was made to run these tests with pure nitrogen, replicating exactly the mixing, dilution and temperature-lowering effects of circulating nitrogen. However, the heat capacity of nitrogen makes it impossible to sustain a flame. Therefore, argon was chosen for these tests because it has half the heat capacity of nitrogen. The low heat capacity of argon allows a better understanding of the effect of flame cooling without having to cool the flame so much that combustion cannot be sustained.

Furthermore, its inert nature allows the isolation of mixing, dilution and cooling effects by removing the intrinsic chemical effects from the equation.

firepower

To isolate the effect of increased firing power observed in Section 4.4.3 with the EGR test, the expected PM emissions at the measured firing power in the EGR furnace were compared to the base M5000 emissions using the same fuel feed method.

In addition, using the relationship between firepower and PM emissions in the base furnace described above, all tests done in this section were compared to expected base emissions based on measured firepower. This allows more accurate isolation of the effect of each tested mechanism.

Results/Discussion

All tests were done using the side jet nozzle configuration and quoted the optimum flow rate of 50 to 70 SLPM as determined above. Therefore, the importance of each mechanism's effect on PM emissions should be compared to the observed PM emission reductions (as seen in Table 3-1) in EGR tests utilizing side-injection nozzles. As a reminder to the reader, the average cold start water boil test PM emissions achieved with this optimized EGR configuration was 150 mg/MJd.

Increased particle residence time

In an EGR furnace, a portion of the particulate matter is circulated through the flame. This would result in a reduction in the net PM _2.5 mass emitted, assuming oxidation is the net dominating mechanism along the particle path. As indicated above, the rates of formation and oxidation start to antagonize at temperatures around 800°C. Fortunately, the temperature distribution measured in the flame bend exceeds 800°C in most of the combustion chamber. This means that oxidation can outpace formation rates and particle circulation through the flame can play a large role in PM _2.5 reduction.

The effect of cycling PM _2.5 and thus increasing its oxidation time was isolated by performing a set of cold start WBTs using particle-free EGR replicating gas (consisting of 80% _N2 , 15% _O2 and 5% _CO2 ). The results of these tests can be seen in Table 5 below.

Table 5. EGR replica gas test results

In the tests described above, it was determined that firepower played a large role in PM emissions, and a model was presented for base M5000 PM _2.5 emissions. To better isolate the role of particle circulation, the tests detailed in Figure 5 are compared to expected base M5000 emissions based on the measured firepower of these tests. This allows comparing the emissions produced by the tests in Table 5 with the base emissions at the same firepower, so that firepower is no longer a factor and allows more accurate experimental isolation of the mechanism of interest. This comparison is detailed in Table 6.

Table 6. EGR Replication Test Results Compared to Firepower Corrected Base

Average PM _2.5 (mg/MJd) for EGR replica gas test 180 Average measurement FP(kW) 3.4 Estimated basal PM _2.5 (mg/MJd) at measured FP 440

As can be seen in Table 6, a reduction from 440 (mg/MJd) to 180 (mg/MJd) was achieved with particle-free EGR replica gas. This indicates that most of the PM _2.5 emission reductions observed in EGR furnaces are not caused by particle recycling, but by chemical and physical interactions of the gas components of the recycled exhaust gas products. However, the resulting emissions for the particulate-free EGR replica gas test were slightly higher than the optimized EGR furnace emissions of 150 (mg/MJd). This could mean that particle circulation is responsible for some of the emission reduction from 180 (mg/MJd) to 150 (mg/MJd).

Chemistry of the CO ₂ /O ₂ Cycle

Previous measurements of the cycle gas indicated that it consisted on average of about 15% _O2 , 5% _CO2 and 80% _N2 during the optimized EGR furnace cold start WBT. Other gas components may include carbon monoxide and argon, but their concentrations are low enough that their contribution is considered negligible. Considering that _N2 is used as a relatively inert gas due to the relatively low combustion temperature experienced during biomass combustion in the rocket bending furnace, it can be assumed that the dominant chemical effect is the result of the _O2 / _CO2 cycle.

The test results for isolating the chemical effects of _O2 and _CO2 can be seen in Table 7. Note that the "pure _O2 injection at 15% of the optimized flow rate" and "pure _CO2 injection at 5% of the optimized flow rate" tests directly replicate their respective chemistry in an EGR gas consisting of 15% _O2 and 5% _CO2 effect. A 15% sparged pure _CO2 test at an optimized flow rate was done so that any potential chemical effects of the _CO2 would be more apparent. Considering that the recycle gas must always be 80% _N2 , a 15% _CO2 composition would indicate that the furnace is close to the total gas flow Operating at the stoichiometric level of .Since rocket bent-tube furnaces typically operate at fairly low fuel concentrations, replicating the 15% _CO2 composition can be considered an estimate of the absolute maximum potential chemical contribution of _CO2 .

Table 7. Test results for the effect of _CO2 and _O2

Based on the measured firepower from these tests, the test results detailed in Table 7 are compared in Table 8 with expected base M5000 emissions. This allows more accurate isolation of the chemical effect of interest by making the firepower variation no longer a factor.

Table 8. Test results for the effect of _CO2 and _O2 compared to a firepower-corrected basis

As can be seen in Table 8, the injection of pure _O2 caused a drastic reduction in the emitted PM mass. The visually observed mixing effects throughout these tests _were negligible, and it can be assumed that the O concentration near the fuel was not affected. However, _O2 was visually observed to be injected into the flame near the top of the lower combustor, causing the injected _O2 streams on either side of the combustor to converge as they entered the M5000's stack. Therefore, it can be concluded that a significant reduction in the mass of PM _2.5 occurs and is mainly caused by the chemical action caused by increasing the _O concentration in the flame zone above the fuel.

The chemistry of _CO sequestration does not appear to cause any significant effect on the mass of emitted PM _2.5 . This indicates that _CO2 chemistry across the potential concentration range has a significant effect on PM emissions.

Mixing, dilution and temperature reduction

To better understand the various effects of circulating nitrogen through side injection nozzles, argon was injected at an optimized EGR furnace flow rate. Three cold start WBTs were performed with argon sparging at an optimized flow rate, the results of which are seen in Table 9 below.

Table 9. Test Results for Mixing, Dilution and Temperature Lowering Effects

The test results detailed in Table 9 are compared in Table 10 with expected base M5000 emissions based on the measured firepower of these tests, as described in the previous section. This allows for more accurate isolation of the mechanism of interest by making changes in firepower no longer a factor.

Table 10. Test results for mixing, dilution and temperature reduction effects compared to fire corrected base

As can be seen in Table 10, the effect of sparging argon causes a small increase in PM _2.5 emissions. This small increase in emissions is the net result of a combination of increased mixing, dilution of the reacting components, and lower temperature.

To better understand the respective roles of these three mechanisms, mixing will first be considered. For this test set, the EGR furnace mass flow rate was optimized to match the argon. Each cycled exhaust molecule is replaced by an argon molecule injected at the same velocity. Consider that mixing is a function of particle momentum, and that argon has a molecular weight of 40 (kg/kmol), while recycle offgas has a molecular weight of about 29 (kg/kmol). Due to the greater molecular weight of argon, its momentum and mixing will be approximately 38% greater.

The effect of enhanced mixing during the combustion of solid biomass has been shown to reduce carbonaceous particulate emissions. Emissions of soot and soot precursors are exacerbated by insufficient mixing, wherein small batches of unburned vapors and particles can leave the combustion zone. Therefore, it is hypothesized that the sequestering effect of argon-induced mixing reduces PM _2.5 emissions.

However, the total effect of the argon sparge actually leads to increased PM _2.5 emissions. Therefore, the combined effect of dilution and temperature reduction of argon actually causes an increase in PM _2.5 emissions. To better understand the effect of cooling on the flame, the cooling capacity of circulating nitrogen was compared with that of sparged argon in an optimized EGR furnace. Argon has a heat capacity of 0.52 (kJ/(kg-K)), and N2 has a heat capacity of 1.04 (kJ/(kg-K)). Furthermore, the calculated mass flow during the steady state phase was 114 g/min for argon and 83 g/min for circulating N2. Considering that the initial injection temperatures of the two gases are still close to the ambient, it can be concluded that the cooling effect of circulating _N2 (which is estimated by multiplying the mass flow rate by the heat capacities of the two gases) is approximately 45% greater than that of Argon %. This indicates that circulating N2 in the EGR furnace has a greater effect on emissions. Finally, the literature indicates that the effect of cooling the flame in small biomass combustion applications will increase the mass emission of particulates. This can be explained by the expansion of the cooler region below about 800°C, where particle formation tends to be greater than particle oxidation.

The segregation effect of dilute reaction components in solid biomass combustion is not readily apparent from the test data. Furthermore, this effect is not well documented in the literature. Therefore, the combined effects of dilution and temperature reduction were combined as one emission mechanism that was observed to cause the increase in PM _2.5 emissions.

firepower

In tests utilizing EGR at an optimized flow rate through a side-injection nozzle, an unexpected increase in firepower was observed. This is due to the forcing of oxidants near the biomass surface. To isolate the effect of the increased firing observed with the optimized EGR test, the expected PM emissions at the measured firing in the EGR furnace were compared to base M5000 emissions using the same fuel feed method.

Table 11. Effect of firepower increase due to application of EGR

The results seen in the table indicate that the isolated effect of the increased firepower caused by the application of EGR resulted in a slight increase in PM emissions.

General Conclusions for Understanding EGR Emission Reduction Mechanisms

Experimental optimization of the EGR furnace resulted in a reduction in PM _2.5 mass emissions. The optimized configuration reduces the emission from the base value of 280mg/MJd to the optimized value of 150mg/MJd. The optimized furnace employs side injection nozzles that inject the recirculated exhaust gases into the oxidation zone of the flame with forced mixing and an increase in the rate of fuel consumption. To better understand the driving forces behind net emission reductions, underlying mechanisms that could affect PM _2.5 mass were identified and their effects were experimentally isolated.

Mechanisms identified for reducing PM _2.5 mass emissions include chemical interaction resulting from injection of optimized O concentration _over fuel within the flame, increased residence time of particles in the flame via recirculation, and enhanced mixing. Among the mechanisms for reducing _PM2.5 emissions, the chemical role of injection-optimized _O2 concentrations was shown to be the most prominent. The sequestering effect of the _CO cycle was determined to have no significant effect on PM _2.5 emissions. Furthermore, the combined effect of temperature reduction and dilution caused by circulating nitrogen and the sequestering effect of increased fuel consumption rate caused by the application of EGR is likely to lead to increased PM _2.5 emissions. However, when the effects of these mechanisms were combined, a net reduction in the mass of emitted PM _2.5 was observed.

Example IV - EGR vs. Air Injection

It has been found that one of the first mechanisms for emission reduction in EGR furnaces is the chemical action of _O2 when injected into the oxidizing zone of the flame. These results indicate that furnaces employing air injection in a similar manner to the EGR furnace side injection nozzle configuration may result in similar or greater emissions reductions. Studies were conducted to confirm this assumption and to understand the relative influence between two fundamentally different forced air systems.

Test Methods

The M5000 was used for these tests. For forced air injection systems, compressed air regulated by Alicat mass flow controllers is routed through side injection nozzles. The side injection nozzles were the same as those used above, with 12 holes of 4.9 mm diameter injecting air perpendicular to the flow of furnace gas at the top of the combustion chamber.

For a fair comparison of EGR and air injection, the minimum PM emissions for each forced air system were determined for the side injection nozzle configuration. The minimum emissions for this configuration utilizing EGR were previously determined above. To determine the minimum discharge with air injection, follow the same procedure as outlined in Section 4.4.3. Once the minimum emissions for each forced air system are determined, compare them.

Results/Discussion

The results of the air flow rate optimization test can be seen below in FIG. 19 . The optimal flow rates with air injection were determined to be 40 and 80 SLPM for the start-up and steady state phases, compared to the optimal EGR flow rates of 50 and 70 SLPM. The results of the three cold start WBTs using the optimized air flow rate and the previously defined results of the optimized EGR flow rate test can be seen in Table 12 below.

Table 12. Comparison of air and EGR

The results in Table 12 indicate that the air injection furnace outperformed the EGR furnace with an overall emission reduction of 70% (compared to 44%). As shown above, increasing the _O2 concentration in the flame oxidation zone is the main factor contributing to the emission reduction. Air-injection furnaces force _O2 concentration up without the need to dilute or cool the flame like EGR furnaces do, where the recirculating exhaust gas is partially made up of _CO2 , thus increasing the overall _O2 chemistry.

These results demonstrate that air jets may be a viable option for forced air systems in rocket elbow cooking ovens. Therefore, the remainder of this study focuses on further optimization of the air injection method.

In some embodiments, different nozzle configurations may be better suited for EGR rather than air injection, or vice versa.

Example V - Optimizing Air Injection Nozzle Diameter for Side Injection Nozzles

After finding that the performance of the forced air system would be better than or equal to the performance of the EGR system in the case of the small rocket bent tube furnace, it was decided that research would continue to further optimize the nozzle using air injection. In Section 7, the effect of varying the hole diameter of the side jet nozzle while utilizing a fixed jet position and a fixed number of holes is explored.

Test Methods

The M5000 was used for these tests. For forced air injection systems, compressed air regulated by Alicat flow controllers is routed through side injection nozzles. The side injection nozzles are located at the top of the combustion chamber, in parallel orientation, 6 holes per nozzle.

Four different diameters were tested, including 2.3, 3.2, 4.9 and 5.7mm. For each diameter, flow rate optimization as described above was done. Three cold start WBTs were then performed at optimized flow rates for each diameter.

Results/Discussion

Nozzle diameter and optimized flow rate

The main results of the flow rate optimization for each diameter can be seen in Table 13. Detailed results of the flow rate sweep test can be found at Figures 30-36.

Table 13. Nozzle Diameter Optimization Results for Side Jet Nozzles

PM _2.5 emission reductions relative to base M5000 PM _2.5 emission data are presented for comparison. It can be seen that for each nozzle diameter tested, significant PM _2.5 emission reductions of approximately 70% relative to base were achieved (p=0.03, 0.02, 0.02 and 0.02 for diameters of 5.7, 4.9, 3.2 and 2.3 mm, respectively) .

It can be seen that the optimized flow rates are quite different between the start-up phase and the steady-state phase. This indicates that, as shown above, flow rate can be correlated with viability.

It should also be noted that the optimized steady-state flow rate tends to decrease slightly with decreasing diameter. This can be explained by the observed increased tendency of the flue gases to burst out of the front of the combustion chamber at higher forced air velocities. This action limits the flow rate through the small diameter high velocity nozzle.

Nozzle diameter and PM emission

Figure 20 presents optimized PM _2.5 emissions as a function of nozzle diameter. Error bars represent 80% confidence intervals for each set of tests.

It can be seen that the optimized PM _2.5 emissions are similar across the range of diameters tested, indicating that the various diameters will yield similar emission reductions if the optimized flow rates are used.

Figure 21 shows the velocity of air injected at a steady state flow rate for each diameter. Again, error bars represent 80% confidence intervals for each set of tests. Data points from left to right represent 5.7, 4.9, 3.2 and 2.3 mm diameters. The diameter of the orifice in the spray nozzle can be greater than about 0.5 mm and less than about 3.5 mm. In many embodiments, the diameter of the orifice in the spray nozzle may be less than about 9.0mm, 8.0mm, 7.0mm, 6.0mm, 5.0mm, 4.5mm, 4.0mm, 3.5mm, 3.0mm, 2.9mm, 2.8mm, 2.7 mm, 2.6mm, 2.5mm, 2.4mm, 2.3mm, 2.2mm, 2.1mm, 2.0mm, 1.9mm, 1.8mm, 1.7mm, 1.6mm, 1.5mm, 1.4mm, 1.3mm, 1.2mm, 1.0mm, 0.9mm, 0.8mm, 0.7mm, 0.6mm, or 0.5mm, and greater than about 0.4mm, 0.5mm, 0.6mm, 0.7mm, 0.8mm, 0.9mm, 1.0mm, 1.1mm, 1.2mm, 1.3mm, 1.4mm , 1.5mm, 1.6mm, 1.7mm, 1.8mm, 1.9mm, 2.0mm, 2.1mm, 2.2mm, 2.3mm, 2.4mm, 2.4mm, 2.5mm, 2.6mm, 2.7mm, 2.8mm, 2.9mm, 3.0 mm, 3.5mm, 4.0mm, 5.0mm, 6.0mm, 7.0mm, 8.0mm or 9.0mm.

In Fig. 21, it can be seen that the velocity of the injection air increases significantly with the decrease of the hole diameter of the side injection nozzle, but the optimized PM emission remains relatively constant. This implies that the velocity can be varied if an optimized flow rate is used for the diameter range tested. In many embodiments, the velocity of the gas exiting the injection nozzle may be from about 5 m/s to 20 m/s. In some embodiments, the velocity of the gas may be greater than about 1 m/s, 2 m/s, 3 m/s, 4 m/s, 5 m/s, 6 m/s, 7 m/s, 8 m/s, 9 m/s, 10 m/s s, 11m/s, 12m/s, 13m/s, 14m/s, 15m/s, 16m/s, 17m/s, 18m/s, 19m/s, 20m/s or 25m/s, and less than about 30m /s, 25m/s, 20m/s, 19m/s, 18m/s, 17m/s, 16m/s, 15m/s, 14m/s, 13m/s, 12m/s, 11m/s, 10m/s , 9m/s, 8m/s, 7m/s, 6m/s, 5m/s, 4m/s, 3m/s or 2m/s. When the velocity is too low (due to too large a jet orifice and/or too little gas volume delivered), the gas may not be able to traverse the flame, bringing additional oxidant to the center of the flame.

Another conclusion that can be drawn from Figure 21 is that the spread of optimal emissions can increase with increasing velocity. As mentioned before, this can be explained by the observed increased tendency of the flue gases to burst out of the front of the combustion chamber at higher forced air velocities.

Behavior of local peak emissions

During flow rate testing, interesting localized peak emission behavior was observed in several instances. An example of this localized peak behavior can be seen below at 30SLPM in Figure 22 and 40SLPM in Figure 23, where Figure 22 shows the results for a range of forced air flow rates for a 3.2 mm diameter nozzle during start-up and Figure 23 shows Results for a range of forced air flow rates for a 5.7 mm diameter nozzle in the steady state phase.

Visual observations of flame and fluid flow properties help to justify these localized peaks in emissions. Figure 24 depicts the observed flow patterns.

The flow profile drawn on the right is a rough depiction of the flow through the combustion chamber, and the side injection nozzles supplement the flow at black arrows for curves 1 to 3.

Point 0 represents undisturbed natural gas flow through the combustor without forced airflow. At point 1 (which is at about 20 SLPM in Figure 23), the oxidizing region of the flame is supplemented, thus reducing PM emissions, but no mixing occurs below the side injection nozzle. At point 2 (which is at about 40 SLPM in FIG. 23 ), the forced airflow is strong and focused enough to extinguish the oxidizing region of the flame at the nozzle level, but not strong enough to induce mixing below the nozzle. Oxygenated areas that extinguish flames cause localized increases in PM emissions. At point 3 (which corresponds to flow rates of 60 SLPM and above in Figure 23), the forced air flow is strong enough to overcome the furnace's natural gas flow and induce mixing throughout the combustion chamber. This distributes the forced air flow more evenly, allows for a better forced air flow rate without thereby extinguishing the flame, and ultimately results in a significant reduction in PM emissions.

This effect was not observed in all flow rate ranges. The likely premise is that this effect would be observed across all flow ranges if a finer resolution of the flow range was used.

EXAMPLE VI - OPTIMIZATION OF AIR INJECTION POSITION

To further investigate the air injection method, the injection location was evaluated. In this section, explore various injection locations in the G3300.

Test Methods

Comparison of PM emission performance of G3300 and M5000

The G3300 used in these tests is similar in design to the M5000, with some differences. The G3300 is insulated around the combustion chamber, while the M5000 uses aluminum radiation shielding construction. Compared to the M5000, the G3300 has a slightly larger combustion chamber with a wider opening. Finally, the G3300 ceramic base is smaller than the M5000 ceramic base. In other respects, both furnaces have similar chimney dimensions. These differences were found to cause differences in the underlying PM _2.5 emissions between the two furnaces. However, an additional comparison was made between the performance of the furnaces when forced air flow was applied. This second comparison was done to ensure that the forced airflow knowledge gained from previous work on the M5000 was extendable to work on the G3300.

The comparison between the minimum PM _2.5 emission and the optimized flow rate for each furnace was done using a 2.3mm diameter side jet nozzle. Determine minimum PM _2.5 emissions and optimal flow rates for each furnace using the same process outlined above.

spray position

The comparison between the minimum PM _2.5 emission and the optimized flow rate was tested for 4 injection locations, including the top of the combustion chamber and the bottom, middle and top of the stack section. Figure 25 presents a cross-sectional view of the bent-tube design of the G3300 rocket, marking the general injection location. The distance from the top of the ceramic substrate (bottom) is indicated in centimeters.

To test the top of the combustion chamber injection location, a side injection nozzle is used. To test the injection location within the chimney section, a "chimney ring" nozzle was fabricated. Figure 26 shows a chimney ring nozzle for the lowermost part of the chimney. The chimney ring nozzle shown in Figure 26 injects gas horizontally towards the vertical axis of the chimney.

For all nozzles in this section, 12 holes with a diameter of 1.5mm are used. 1.5mm was chosen because preliminary studies indicated that a chimney ring nozzle with a larger diameter could reduce the flame at a slow flow rate. In some cases, this can cause smoke and flames to be vented out of the front of the combustion chamber. The 1.5 mm diameter reduces this effect and allows higher forced air flow rates to be used. Further discussion of the 1.5 mm diameter for the injection location study is provided below. Finally, 12 holes were used to help distribute the forced air flow across the flame and to maintain consistency with previous work. In some embodiments, the number of injection orifices (holes) may be greater than twelve or less than twelve. In some embodiments, the injection orifices may or may not be evenly spaced within the nozzle to aid in the delivery of oxygen to the interior of the flame.

Results/Discussion

Comparison of PM emission performance of G3300 and M5000

Table 14 presents the main results of a comparison of optimized PM _2.5 emissions between the G3300 and M5000 when utilizing side jet nozzles with a diameter of 2.3 mm. Means represent the average of 3 tests.

Table 14. Comparison of PM emission performance of G3300 and M5000 and optimized flow rates with similar configurations

It can be seen that the optimized flow rates are similar for both furnaces. This indicates that geometrical differences between the two combustion chambers do not result in significant differences or limitations to the optimized forced air flow rate. This also implies that the optimized forced air flow rates for the two furnaces and other nozzle configurations will be similar.

Furthermore, it can be seen that the PM _2.5 emissions are similar for both furnaces (p=0.82). This indicates that the optimized PM _2.5 emission performance measured in previous work with the M5000 is comparable to that with the G3300 and that the difference between the two furnace performances is less pronounced when the optimized flow rate is applied _.

spray position

Table 15 presents the main results of the injection location study. More detailed results of the flow rate range tests can be found in Figures 30-36.

Table 15. Injection position optimization results

It can be seen that the optimized flow rates across the bottom three injection locations are similar. However, at the top injection position, the optimal flow rate drops to 10 SLPM. Figure 27 is composed of images taken for the top injection position during a range of flow rates.

The disclosed devices, methods and systems can help reduce pollutants from biomass furnaces. As demonstrated by the examples above and below, the present invention can help reduce particulate mass emissions, such as PM _2.5 emissions, from biomass furnaces relative to gases that are not actively injected into the flame (i.e., fans or blowers turned off, or not For the same furnace with injection system installed). In some cases, the present invention provides reductions in PM _2.5 emissions of between about 20% and about 95%. In many embodiments, the PM _2.5 reduction is between about 25% and 85%. In some embodiments, the reduction in PM _2.5 emissions is greater than about 20%, 25%, 30, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 90%, and less than about 100%, 95%, 90%, 85%, 80%, 75%, 70%, 65%, 60%, 55%, 50%, 45%, 40%, 35% , 30% and 25%.

At a flow rate of 0 SLPM, the flame from the top of the chimney is tall and slender. At a flow rate of 10 SLPM, the flame was shorter and more concentrated. When using a flow rate of 20 SLPM, the flame top was completely extinguished at the injection location. This causes the airflow through the furnace to be significantly reduced and causes a lot of smoke and flames to leave the front of the furnace. Ultimately, this limits the optimal flow rate at the top of the stack injection location to 10 SLPM and limits the PM _2.5 emission reduction potential of this configuration. But this phenomenon is less important for embodiments where the ring nozzle is located lower in the combustion chamber because the flame is stronger at the lower position and is less susceptible to the effects seen in FIG. 27 . Instead, at lower levels, gas is injected into the oxidizing region of the flame (rather than extinguishing it) to deliver oxygen and promote additional oxidation and PM reduction.

Comparing the optimized PM emissions from the bottom three injection locations leads to the conclusion that the bottom of the chimney is the optimal injection location. However, injecting at the top of the combustion chamber also results in good performance. These locations can be assumed to result in the greatest reduction because they are injected where the flame is strongest and supplement the oxidation of the particles without causing the flame to cool or extinguish.

Another important observation is the role of boil time and firepower at each jet location. The bottom of the chimney jet location seems to result in a significant increase in firepower as well as a greatly reduced boil time, both features that are quite valuable to the consumer.

Finally, it may be desirable to inject forced air at the bottom of the chimney. This placement can help reduce emissions relative to base (p=0.001) and can provide a relatively unobtrusive design compared to side injection nozzles, which intrude into the combustion chamber. In many embodiments, the placement of the injection nozzles facilitates injection of gas above the level of solid biomass in the combustor. In most embodiments, the gas is injected between 0.5 and 30.0 cm above the solid fuel (such as firewood as seen in Figure 26). In most embodiments, the gas is injected into the flame at a height greater than about 0.5 cm, 1.0 cm, 1.5 cm, 2.0 cm, 2.5 cm, 3.0 cm, 3.5 cm, 4.0 cm, 4.5 cm, 5.0 cm , 5.5cm, 6.0cm, 6.5cm, 7.0cm, 7.5cm, 8.0cm, 8.5cm, 9.0cm, 9.5cm, 10cm, 11cm, 12cm, 13cm, 14cm, 15cm, 16cm, 17cm, 18cm, 19cm, 20cm or 25cm, and less than about 30cm, 25cm, 20cm, 19cm, 18cm, 17cm, 16cm, 15cm, 14cm, 13cm, 12cm, 11cm, 10cm, 9.5cm, 9.0cm, 8.5cm, 8.0cm, 7.5cm, 7.0cm, 6.5 cm, 6.0cm, 5.5cm, 5.0cm, 4.5cm, 4.0cm, 3.5cm, 3.0cm, 2.5cm, 2.0cm, 1.5cm or 1.0cm.

Example VII - Optimizing the Air Injection Nozzle Diameter for a Chimney Ring Nozzle

In the above, it was found that the nozzle diameter is not a strong determinant for minimizing PM emissions when the injection location is at the top of the combustion chamber with side injection nozzles. However, for other injection locations and nozzle configurations, minimized PM emissions may not be a weak function of diameter. Therefore, in this section, the effect of diameter on discharge for a chimney ring nozzle located at the bottom of the chimney is explored.

Test Methods

The effect of spray diameter on emissions was tested in G3300 for a chimney ring nozzle located at the bottom of the chimney. Hole diameters of 1.5 and 3.0 mm were tested. For each diameter, flow rate optimization was done as described above. Then, three cold start WBTs were performed at optimized flow rates for each diameter. The resulting optimized discharge and flow rates are then compared.

Results/Discussion

The diameter optimization results for chimney ring nozzles are shown in Table 16 below.

Table 16. Diameter optimization results for the injection position at the bottom of the chimney

It can be seen that the 1.5mm diameter nozzle has a larger optimized steady-state flow rate. This is because the 3.0mm diameter nozzle caused the flame to extinguish at a flow rate greater than 20 SLPM, causing smoke and flame to be expelled from the front of the combustion chamber. It can also be seen that PM _2.5 emissions optimized for the 1.5 mm diameter are significantly lower compared to the 3.0 mm diameter (p=0.04). Extinguishment of the flame limits the forced air flow rate, which in turn limits the amount of PM _2.5 emission reduction.

This data indicates that for chimney ring nozzles, the diameter may be less than about 3 mm.

Example VIII - Optimizing the Air Injection Angle of a Chimney Ring Nozzle

In the above, injection location was investigated in addition to diameter. Here, the effect of varying the spray angle on the spray position and diameter is explored.

Test Methods

To understand the effect of spray angle, compare the minimum emissions for the two configurations. The injection location used for these tests was at the bottom of the chimney, the optimum injection location was found in Section 8. The spray angle tested was horizontal or 30° above horizontal. Figure 28 shows the location of the two nozzles used in this study. Furthermore, the two nozzles used in this study had 12 holes with a diameter of 1.5 mm. Figure 28 shows the spray angles tested at the bottom of the chimney. Figure 29 shows a chimney ring nozzle spraying at a 30° angle relative to horizontal.

Results/Discussion

Table 17 shows the results of the injection angle study. More detailed results of the flow rate range tests can be found in Figures 30-36.

Table 17. Jet Angle Test Results

It can be seen that for a spray angle of 30°, the optimum flow rate is limited to 10 SLPM. Furthermore, the emission reduction achieved with the horizontal injection angle was greater than that achieved with the 30° injection angle (p=0.02).

Angled jets achieve less emissions reduction because the angle of the forced airflow promotes high total airflow through the furnace. Increasing the total airflow through the furnace can significantly cool the flame, especially if high levels of mixing are not present. Cooling the flame increases the volume of the particle generation zone and reduces the particle oxidation zone.

Although a horizontal injection angle is preferred, the injection angle can range from about -50° (0° relative to horizontal, i.e., down from the nozzle toward the fuel) to about +50° (0° relative to horizontal, i.e., toward the upper burner top of the chamber upwards), preferably from about -30° to about +30°. In many embodiments, the spray angle may be greater than about -55°, -45°, -40°, -45°, -30°, -25°, -20°, -15°, -10°, -9° , -8°, -7°, -6°, -5°, -4°, -3°, -2°, -1°, 0°(horizontal), 1°, 2°, 3°, 4° , 5°, 6°, 7°, 8°, 9°, 10°, 11°, 12°, 13°, 14°, 15°, 16°, 17°, 18°, 19°, 20°, 25 °, 30°, 35°, 40°, 45°, or 50°, and less than 55°, 50°, 45°, 40°, 35°, 30°, 25°, 20°, 19°, 18°, 17 °, 16°, 15°, 14°, 13°, 12°, 11°, 10°, 9°, 8°, 7°, 6°, 5°, 4°, 3°, 2°, 1°, 0°, -1°, -2°, -3°, -4°, -5°, -6°, -7°, -8°, -9°, -10°, -11°, -12° , -13°, -14°, -15°, -16°, -17°, -18°, -19°, -20°, -25°, -30°, -35°, -40°, - 45°, -50° or -55°.

Claims (20)

1. a kind of device for being used to reduce the emission of biomass stove, described device includes：

Fluid intake aperture；

Entry conductor with outer surface and inner surface, the inner surface limits inlet, and the inlet is via the entrance Aperture and the appearance fluid communication, interior chamber are used to direct fluid；

In the inlet and positioned at the fan of the entrance aperture distal end, the fan is used to fluid being aspirated through The entrance aperture is simultaneously drawn into the room, and enter；

Delivery channel, the delivery channel has the inner surface for limiting downstream chamber, and the downstream chamber connects with inlet's fluid It is logical；

One or more nozzles with the inside being in fluid communication with the downstream chamber, the nozzle is used to direct fluid to life In the combustion chamber of material stove；And

Multiple exit apertures on the surface of the nozzle are limited at, the exit aperture is designed to allow that fluid leaves institute State the inside of nozzle.

2. device as claimed in claim 1, wherein, the nozzle is located at or near the top of lower combustion chamber.

3. the device as described in any one in claims 1 to 3, wherein, the exit aperture have 0.5 and 3.5mm it Between average diameter.

4. the device as described in any one in claims 1 to 3, wherein, the exit aperture limits circular, square, three Angular or ellipse, the average diameter is measured by the center of the circular, square, triangle or ellipse.

5. the device as described in any one in Claims 1-4, wherein, from one or more of nozzle escaping gas Volume be greater than about 10 Standard Liters per Minutes and less than about 100 Standard Liters per Minutes.

6. the device as described in any one in claim 1 to 5, wherein, gas is escaped from one or more of nozzles Speed is greater than about 5 metre per second (m/s)s and less than about 20 metre per second (m/s)s.

7. the device as described in any one in claim 1 to 6, wherein, the nozzle is selected from linear nozzle or round nozzle.

8. device as claimed in claim 7, wherein, the nozzle is annulus, its be located above the lower combustion chamber and In the lower half of top combustion chamber, and it is designed to allow burning gases directly through jeting area.

9. device as claimed in any of claims 1 to 8 in one of claims, wherein, the fluid is gas, and it includes greater than about 15% O₂, oxygen.

10. a kind of method for the emission for reducing biomass stove, methods described includes：

Gas is placed into the interior chamber of nozzle, the nozzle is located at or near flame；

Increase the pressure of the gas in the nozzle；

The multiple outer apertures limited by the outer surface by the nozzle discharge a certain amount of gas from the nozzle；And

The gas sprayed is guided into the flame in the combustion chamber of the biomass stove, wherein, the gas is reduced and left The amount of at least one pollutant of the biomass stove.

11. method as claimed in claim 10, wherein, the amount of gas is in about 10 Standard Liters per Minutes and 100 standard liters per minutes Between clock.

12. the method as described in any one in claim 10 to 11, wherein, the nozzle limits ring, and exit aperture In the inner surface of the ring, to help gas injection to the center of the ring.

13. the method as described in any one in claim 10 to 12, wherein, the exit aperture is limited to 0.5 and 6.0mm Between diameter.

14. the method as described in any one in claim 10 to 13, wherein, the exit aperture and the bottom of the combustion chamber Face is an equal distance away.

15. the method as described in any one in claim 10 to 14, wherein, by electric fan or air blower by the gas Body is advanced in the nozzle.

16. the method as described in any one in claim 10 to 15, wherein, by one or more apertures with 5 and 25 Speed between metre per second (m/s) discharges the gas.

17. the method as described in any one in claim 10 to 16, wherein, the emission of reduction is less than about 2.5 microns Particulate matter.

18. the method as described in any one in claim 10 to 17, wherein, from being less than that the fire grate is put during burning The amount fewer than the amount discharged when the gas pressure in the nozzle does not increase about 25% and 90% of about 2.5 microns of particulate matter it Between.

19. the method as described in any one in claim 10 to 18, wherein, with about -10 degree to the angle between about+30 degree Degree is by the gas injection into flame.

20. a kind of method for the granular material discharged thing for reducing biomass stove, methods described includes：

Gas is drawn into room, the gas includes greater than about 15% O₂；

The gas is directed into the nozzle with inner surface and outer surface from the room, the nozzle limits round tube, institute Stating round tube has multiple exit apertures on round inner surface, wherein, the exit aperture allows gas from the pipe Advance at the internal center towards circle；

Increase the pressure of the gas in the inside of the nozzle；

A certain amount of gas-pressurized is discharged from the nozzle with the speed between about 5 metre per second (m/s)s and 20 metre per second (m/s)s；And

The gas sprayed is guided into the flame in the combustion chamber of the biomass stove, wherein, with lacking nozzle or described The stove for lacking gas-pressurized in nozzle is compared, and the gas reduces the amount at least one pollutant for leaving the biomass stove More than about 25%.