CN108800113A - A method of for promoting biomass fuel to stablize burning in fluidized bed combustion - Google Patents

Abstract

In the fluidized combustion of biomass, due to the low ash content of the biomass fuel, the burnt residue is not enough to form the bed material, and a heat storage body needs to be added. The bulk density of the currently used heat storage body is far from that of biomass, which will make the fluidization wind difficult to control and the combustion unstable. It will cause dust sticking and wear of the equipment at the back end of the boiler, or blockage and coking at the tail of the boiler. The invention provides a method for biomass fluidization and full combustion, using high temperature resistant inorganic porous, light natural or artificial materials as heat accumulators, the bulk density of the heat accumulators is 200-1500Kg/m ³ , which is similar to the biomass raw material, is laid flat on the air distribution plate in the furnace, and through the air blower, the fluidized and stable combustion with the biomass can be realized, which can avoid the entrainment of the biomass raw material in the flue gas. Problems such as water flow tube bundles, superheater, economizer, air preheater sticking ash, and local high temperature at the bottom of the boiler caused blockage and coking.

Description

A method for promoting stable combustion of biomass fuel in fluidized bed combustion

technical field

The invention relates to the technical field of energy conversion, in particular to a method for realizing the full combustion of biomass in the process of biomass combustion in a fluidized state.

Background technique

Compared with other combustion technologies, circulating fluidized bed combustion technology has the characteristics of high combustion efficiency, easy control of harmful gas emissions, and large heat capacity. Moreover, it has low requirements for fuel, and some inferior fuels with high water content, low combustible content and low calorific value have good adaptability. Therefore, this combustion technology is currently the preferred technology for large-scale and efficient utilization of biomass waste. In fluidized combustion, the bed material has a high heat capacity, which can provide sufficient preheating and drying for biomass waste, and can still burn stably for biomass with a moisture content of 50%.

At present, because the coal-fired power plant circulating fluidized bed combustion technology is mature and its operation is relatively stable, most of the design, manufacture, and operation parameters of the biomass circulating fluidized bed combustion technology are carried out with reference to coal as fuel. However, due to the wide range of raw biomass fuel sources, large composition changes, low bulk density, low calorific value, and low ash content, the requirements for fluidized bed boilers are completely different from those of coal fuels.

Due to the low ash content of biomass fuel, the burnt residue is not enough to form a bed material. Therefore, referring to the circulating ash in a coal-fired power station, it is necessary to add a heat storage body to ensure the formation of a stable dense-phase zone material layer and achieve fluidization. combustion. The currently added regenerators are generally quartz sand, river sand, alumina, iron oxide, slag, etc.

Although these substances can provide heat for the fuel in the boiler, because their bulk density is far from that of biomass, it will make the fluidization wind difficult to control. Generally, the bulk density of chopped crop straw is 120Kg/m ³ , the bulk density of sawdust is 240Kg/m ³ , and the bulk density of wood chips is 320Kg/m ³ . 1100Kg/m ³ ; the bulk density of quartz, sand and river sand, alumina, iron oxide, etc. is 1800-2100Kg/m ³ , so that the bulk density of the current heat storage body is more than ten times higher than that of biomass under the same particle size times, even after the biomass is granulated, it can reach 2.0 times, so no matter how the partial pressure and the ratio of the primary and secondary partial pressures are adjusted, fluidized and stable combustion cannot be achieved.

When the wind pressure is high, the fluidization of the dense phase area can be guaranteed, but the fuel stays in the furnace for a short time, and it is too late to burn. With the flue gas, it enters the water flow tube bundle, superheater, economizer, air preheater and other equipment at the rear end , resulting in dust sticking, blockage, and wear of related equipment; moreover, the incompletely burned fuel will return to the furnace for combustion through the feeder, and the phenomenon of abnormal return of the feeder is often encountered.

When the wind pressure is low, the biomass can be fully burned, but the fluidization degree of the dense phase area is low, the heat of the heat storage medium cannot be transferred to the fuel, the tail of the boiler continues to be high temperature, and the heat storage body melts; at the same time, due to the fluidization of the dense phase area Low level and insufficient oxygen supplement will lead to the reduction state of the combustion atmosphere, the pyrolysis and gasification of biomass will dominate, and tar will be precipitated, which will cause coking at the tail of the boiler.

The emergence of the above problems, in addition to reducing the thermal efficiency of the boiler, will affect the main engine and various auxiliary machines of the boiler, increase the maintenance cost of the boiler operation, and if coking, blockage, or coking is serious, the boiler must be shut down for treatment, affecting continuous production.

Contents of the invention

In order to overcome the shortcomings of the prior art above, the present invention provides a method for promoting stable combustion of biomass fuel in fluidized bed combustion. The method provided by the present invention has high stability of biomass fluidized combustion, and by selecting a regenerator that has been mixed and fluidized with biomass fuel, it can solve the problem of the boiler tail (before the slag discharge port and the Coking and blockage between biomass fuel inlets. At the same time, the stable combustion of fluidized state can ensure the full combustion of biomass fuel, avoid dust entrainment, and solve the blockage and wear of water flow tube bundles, superheaters, economizers, air preheaters and other equipment connected to the top of the boiler step by step. question.

The technical scheme adopted by the invention is as follows: a method for promoting the stable combustion of biomass fuel in fluidized bed combustion, the method uses high-temperature-resistant inorganic porous, lightweight natural or artificial materials (including closed-pore materials and open-pore materials) ) as a regenerator, put it into the furnace of the fluidized bed, spread it on the air distribution plate in the furnace, and realize the fluidized combustion with the biomass through the air supply of the blower. The specific heat storage requirements and usage methods are as follows:

1. The regenerator in the invention is composed of inorganic substances, wherein the content of alumina is 0-60%, the content of silicon oxide is 0-60%, the content of calcium oxide is 0-30%, and it may contain other Na, K, Mg , Fe and other elements.

2. The heat accumulator in the invention can withstand high temperature above 850°C, and will not melt or condense when used at high temperature.

3. The thermal accumulator in the invention is made of a porous material, and its pore structure can be either closed or open.

4. The thermal accumulator in the invention has a bulk density of 200-1500Kg/m ³ , preferably 500-1000Kg/m ³ .

5. The regenerator in the invention can be natural minerals or artificial synthetic materials, including ceramsite, pumice, expanded vermiculite, hollow ceramics, perlite, etc., among which ceramsite and pumice are preferred.

6. The thermal accumulator in the invention can be a single material, or can be compounded and mixed with different materials.

7. The heat accumulator in the invention, according to the average particle size of the biomass fuel during use, the maximum particle size used is twice the average particle size of the biomass.

8. The heat accumulator in the invention can provide heat for the fluidized combustion of the original ungranulated biomass fuel, and can also provide heat for the fluidized combustion of the pelletized biomass fuel.

9. The heat accumulator in the invention, before the operation of the boiler, according to the capacity of the biomass boiler, tile a certain thickness on the air distribution plate in the fluidized bed boiler, the bed thickness is generally 10-1000mm, preferably 200mm -600mm.

10. The heat accumulator in the invention should be supplemented according to the actual loss during the operation of the boiler. The supplementary port can share the biomass fuel feed port, or it can enter separately from the side of the boiler.

The heat accumulator described in the present invention can be used not only for the combustion of biomass fluidized bed, but also for the pyrolysis of biomass fluidized bed, the gasification of biomass fluidized bed, etc. In addition, it can be used for the consumption and utilization of chemical materials such as old plastics and waste rubber, office waste such as paper, documents, and newspapers, animal bones, and kitchen waste.

When the present invention is used, before the combustion chamber is ignited, the regenerator is placed on the air distribution plate of the combustion chamber, and the wind entering from the bottom of the combustion chamber and the biomass fuel entering the feed port form a fluidized state, so The bulk density of the fuel and the heat storage body is similar, which can realize stable combustion. During the combustion process of the combustion chamber, if the heat storage body is lost, it can be replenished in an appropriate amount during the combustion process.

Description of drawings

Figure 1 is a schematic diagram of the use of the heat storage body of the present invention.

Detailed ways

The present invention will be further described below by way of examples.

Example 1:

A rated 75t/h steam boiler, rated steam pressure 3.82Mpa, rated steam temperature 450°C, feed water temperature 150°C, primary air preheating temperature 150°C, biomass fuel 50% wheat straw + 50 rice straw, water content 15 %, without granulation, the fuel length is not greater than 10mm. Use ceramsite as heat storage body. After the ceramsite is broken, select particles with a particle size of 0-1.5mm and spread them on the air distribution board in the furnace with a thickness of 500mm. Ignite, control the temperature of the bed material, prevent local overheating, and control the temperature of the air chamber within 800 °C. Start the screw feeder to feed, put in fuel, and feed with the rated load fuel amount of 17t/h. The boiler runs smoothly, the combustion in the dense phase area is stable, the mixed combustion effect of fuel and heat storage body is good, and the thermal efficiency of the boiler is 91%.

Example 2:

One rated 75t/h steam boiler, rated steam pressure 3.82Mpa, rated steam temperature 450°C, feed water temperature 150°C, primary air preheating temperature 150°C, biomass fuel 50% wheat straw + 50 rice straw, water content 10 %, the fuel length is not greater than 10mm. Use ceramsite as heat storage body. The average particle size of ceramsite is 15mm, and the bulk density is 600Kg/m ³ . The regenerator is spread flat on the air distribution plate in the furnace, with a thickness of 600mm. Ignite, control the temperature of the bed material, prevent local overheating, and control the temperature of the air chamber within 800 °C. Start the screw feeder to feed, put in fuel, and feed with the rated load fuel amount of 17t/h. The boiler operates stably, the dense phase zone burns stably, the mixed combustion effect of fuel and heat storage body is good, and the thermal efficiency of the boiler is over 90%.

Example 3:

A rated 75t/h steam boiler, rated steam pressure 3.82Mpa, rated steam temperature 450°C, feed water temperature 150°C, primary air preheating temperature 150°C, biomass fuel is 50% wheat straw + 50 rice straw, granulated, The diameter is 6~12mm, the length is 20~40mm, and the bulk density is 850kg/m ³ . Use ceramsite as heat storage body. The average particle size of ceramsite is not more than 20mm, and the bulk density is the same as that of the fuel, which is 850Kg/m ³ . Ignite, control the temperature of the bed material, prevent local overheating, and control the temperature of the air chamber within 800 °C. Start the screw feeder to feed, put in fuel, and feed with the rated load fuel amount of 17t/h. The boiler runs smoothly, the combustion in the dense phase zone is stable, the mixed combustion effect of the fuel and the heat storage body is good, and the thermal efficiency of the boiler is above 91%.

Example 4:

A rated 75t/h steam boiler, rated steam pressure 3.82Mpa, rated steam temperature 450°C, feed water temperature 150°C, primary air preheating temperature 150°C, biomass fuel is 50% wheat straw + 20 rice straw + 30 rice husk , water content 10%, fuel length not greater than 10mm. Two kinds of ceramsite are selected to be mixed and used as heat accumulator. One type of ceramsite has a maximum particle size of 2mm and a bulk density of 600kg/m ³ , and the other type of ceramsite has a maximum particle size of 20mm and a bulk density of 550Kg/m ³ . Lay flat on the air distribution board in the furnace with a thickness of 500mm. Ignite, control the temperature of the bed material, prevent local overheating, and control the temperature of the air chamber within 800 °C. Start the screw feeder to feed, put in fuel, and feed with the rated load fuel amount of 17t/h. The boiler runs smoothly, the combustion in the dense phase area is stable, the mixed combustion effect of fuel and heat storage body is good, and the thermal efficiency of the boiler is 92%.

Example 5:

A rated 35t/h steam boiler, rated steam pressure 5.29Mpa, rated steam temperature 485°C, feed water temperature 150°C, primary air preheating temperature 150°C, biomass fuel is 50% wheat straw + 50 rice straw, granulated, The diameter is 6~12mm, the length is 20~40mm, and the bulk density is 850kg/m ³ . Use ceramsite as heat storage body. The average particle size of ceramsite is not more than 20mm, and the bulk density is the same as that of fuel, which is 850Kg/m ³ . Ignite, control the temperature of the bed material, prevent local overheating, and control the temperature of the air chamber within 800 °C. Start the screw feeder to feed, put in fuel, and feed with the rated load fuel amount of 10t/h. The boiler runs smoothly, the combustion in the dense phase area is stable, the mixed combustion effect of fuel and heat storage body is good, and the thermal efficiency of the boiler is 90%.

Example 5:

A rated 35t/h steam boiler, rated steam pressure 5.29Mpa, rated steam temperature 485°C, feed water temperature 150°C, primary air preheating temperature 150°C, biomass fuel is 50% wheat straw + 50 rice straw, granulated, The diameter is 6~12mm, the length is 20~40mm, and the bulk density is 850kg/m ³ . Use loss vermiculite as heat storage body. The average particle size of the vermiculite is not more than 25mm, and the bulk density is 650Kg/m ³ . The heat accumulator is spread on the air distribution plate in the furnace with a thickness of 400mm. Ignite, control the temperature of the bed material, prevent local overheating, and control the temperature of the air chamber within 800 °C. Start the screw feeder to feed, put in fuel, and feed with the rated load fuel amount of 10t/h. The boiler runs smoothly, the combustion in the dense phase area is stable, the mixed combustion effect of fuel and heat storage body is good, and the thermal efficiency of the boiler is 90%.

Claims (12)

1. a kind of for promoting biomass fuel to stablize the method for burning in fluidized bed combustion, this method is with heat safe inorganic more Hole, lightweight natural or artificial material as heat storage, throwing is placed in the stove of recirculating fluidized bed, is layered on air distribution plate in stove On, by the air-supply of air blower, realize the fluidized combustion with biomass.

2. according to the method described in claim 1, it is characterized in that the heat storage, is made of inorganic matter, wherein aluminium oxide contains Amount is 0-60%, silica content 0-60%, calcium oxide content 0-30%, while can contain the members such as other Na, K, Mg, Fe Element.

3. according to the method described in claim 1, it is characterized in that the heat storage, is resistant to 850 DEG C or more of high temperature, high temperature makes Used time does not melt, non-condensing.

4. according to the method described in claim 1, it is characterized in that the heat storage is constituted for porous material, pore structure is to close Hole or trepanning.

5. according to the method for claim 1, it is characterised in that the bulk density of the heat storage is in 200-15000Kg/m³,.

6. according to the method for claim 1, it is characterised in that the heat storage is natural minerals, haydite, float stone, expansion leech Stone, hollow ceramic, perlite.

7. according to the method for claim 1, it is characterised in that the heat storage is for homogenous material or by different materials Compounding is used in mixed way.

8. according to the method described in claim 1, it is characterized in that the heat storage, according to the flat of biomass fuel when use Equal grain size, the maximum particle diameter used are 2 times of biomass average grain diameter.

9. according to the method described in claim 1, it is characterized in that the heat storage, is the primary biomass fuel not being granulated The burning of stream state provides heat, or provides heat with the biomass fuel fluidized combustion after granulation.

10. according to the method described in claim 1, it is characterized in that the heat storage, before boiler running process, according to life The capacity of substance boiler capacity, tiling certain thickness is on air distribution plate, thickness of bed layer is generally 10- in fluidized-bed combustion boiler 1000mm。

11. according to the method described in claim 1, it is characterized in that the heat storage should basis in boiler running process Active loss is supplemented, and supply port is to share biomass fuel feedstock mouth, or individually laterally individually entered in boiler.

12. according to the method described in claim 1, it is characterized in that the heat storage be used for biomass fluid bed burning, Or for it is biomass fluid bed be pyrolyzed, biomass fluid bed gasification, reaction raw materials include traditional biomass, old plastics, Scrap rubber, paper, file, newspaper waste material, Animal Bone skin, kitchen garbage.