CN106225014B

CN106225014B - Round-bottom, flat-bottom vessel heating device with flue gas circulation

Info

Publication number: CN106225014B
Application number: CN201610710040.4A
Authority: CN
Inventors: 黄海涛
Original assignee: Guangdong University of Technology
Current assignee: Guangdong University of Technology
Priority date: 2016-08-23
Filing date: 2016-08-23
Publication date: 2021-07-09
Anticipated expiration: 2036-08-23
Also published as: CN106225014A

Abstract

The invention discloses a round-bottomed and flat-bottomed vessel heating device with flue gas circulation, comprising a furnace and a burner. The heating device is arranged so that the burned flue gas generated by the burner can circulate in the furnace, so The ratio of the bottom volume of the standard round-bottomed pan with the inner volume of the furnace and the caliber of the furnace is greater than 2.5, or the ratio of the volume of the bottom of the standard pan with the inner volume of the furnace and the caliber of the furnace is greater than 2.5. If the ratio is greater than 2, the ratio of the bottom volume of the standard round-bottom pot with the inner volume of the furnace and the caliber of the furnace is preferably greater than 4.5, or, the internal volume of the furnace is compatible with the caliber of the furnace. The ratio of the bottom volume of the pan is preferably greater than 4; the present invention can greatly prolong the residence time of the flue gas, and can strengthen the heating effect for round bottom or flat bottom utensils so as to obtain high thermal efficiency, simple structure, low cost, easy maintenance and New stove heater with long life.

Description

Round bottom and flat bottom vessel heating device with flue gas circulation

Technical Field

The invention relates to the technical field of cooking ranges, in particular to a round bottom and flat bottom vessel heating device with smoke circulation.

Background

Commercial stoves mainly include Chinese food cooking stoves, large pot stoves, soup stoves and the like. Commercial stoves have been low thermal efficiency. The requirements of GB7824-1987 and CJ/T28-1999 on thermal efficiency are not less than 20%. The Chinese meal gas cooking stove CJ/T28-2003 cancels the performance requirement and test method of the thermal efficiency. The energy efficiency limit value of a Chinese food gas cooking stove specified in commercial gas cooking stove energy efficiency limit value and energy efficiency grade GB30531-2014 executed from 1 month in 2015 is 25%.

The reason for the low thermal efficiency of commercial cookers is analyzed as follows: fig. 1 and 2 are schematic structural diagrams of flue-exhausting type and indirect flue-exhausting type stoves in the prior art respectively. Referring to fig. 1, a burner 2 and a round-bottom pot 3 are respectively installed at the bottom and the top of a funnel-shaped hearth 1, and a smoke outlet 4 formed in the wall surface of the hearth 1 leads smoke into a smoke exhaust pipe 5. The residence time of the flue gas generated by the burner 2 in the hearth 1 is very short (for example, the rated heat load of the burner of a Chinese cooking stove of a certain type is 42kW, the caliber of the hearth is 400mm, the depth of the hearth is 270mm, and the residence time of the flue gas in the hearth is only 0.17 s). And because the exhaust pipe 5 has the function of inducing air, flame and smoke are easy to deflect to one side of the exhaust port 4, so that a plurality of smoke can be short-circuited and flows into the exhaust port 4 without contacting the bottom of the pan. The flue gas emissions carry away a large portion of the total heat release from the fuel combustion. In addition, the furnace wall of the furnace 1 also has heat dissipation loss. Therefore, only about 20% of the total heat generated by the combustion of the fuel can be transferred to the round-bottomed boiler 3, and the remaining 80% is wasted by being dissipated to the surrounding environment in the form of heat loss due to smoke discharge, heat loss due to furnace wall, or the like. In the indirect smoke exhaust type kitchen range shown in fig. 2, the round-bottom pot 3 is supported by the pot support 6, and smoke is exhausted into air in a kitchen through an annular gap between the round-bottom pot 3 and the top of the hearth 1 and then is exhausted to the outside through the range hood. The residence time of the flue gases in the furnace 1 is also very short and the flow of the combustion flue gases through the interior space of the kitchen is not conducive to improving the working conditions of the kitchen.

It is noted that the thermal efficiency data of the existing commercial cookers are obtained by laboratory tests according to the specified test method, but the laboratory tests have great differences from the actual use conditions, such as: (1) the temperature of the pot is different: the laboratory test is to boil water, and the temperature is lower than 100 ℃; when the edible oil frying pan is actually used for frying, edible oil (the boiling point of the edible oil is higher than 260 ℃) is arranged in the round bottom pan, and the frying temperature is far higher than the boiling temperature of boiled water. The temperature difference of heat transfer between the smoke and the cookware is small when the temperature of the cookware is high, and the heat efficiency is reduced. (2) The flue gas amount is different: chinese style cooking habits are stir-fried with a strong fire, with a considerable amount of smoke. If the smoke amount is large, the retention time is short, and the thermal efficiency is reduced. (3) The flame conditions are different: in actual use, yellow flame often appears, and incomplete combustion is serious. (4) Round bottom pans are often uncovered during cooking and the entry of ambient cold air into the pan can cause additional convective heat loss. (5) Chinese cooking chefs are used to fry and sometimes cause empty fire and cause additional heat loss. In consideration of the above factors, the thermal efficiency of the prior Chinese cooking range under actual use conditions is generally lower than 20%.

The flue-exhausting and indirect-exhausting cooking ranges, cauldron ranges, soup ranges shown in fig. 1 and 2 have been and are now commonly used in kitchens of various hotels, restaurants, fast food restaurants, collective canteens (including various unit canteens such as factories, enterprises, institutions, schools, troops, social institutions, and groups). According to the statistical data of the catering industry, the total number of Chinese food cooking stoves, large cooking stoves and soup stoves used in China exceeds one hundred million. Cooking fumes are generally considered the third largest source of air pollution behind the exhaust gases of automobiles, industrial waste gases. The cooking fumes contain black carbon particles (PM2.5), nitrogen oxides, carbon monoxide, volatile organics, greenhouse gas carbon dioxide. In addition, a round or flat bottom cooking range heating apparatus similar to that shown in fig. 1 and 2 is widely used in many industries such as food industry, light industry, chinese medicine industry, agricultural and sideline product processing industry, and the like. These large number, wide distribution and low thermal efficiency stove heating devices waste energy and pollute the environment. Therefore, the development of a novel and efficient stove heating device has important practical significance for the country which has a large population, lacks energy resources and faces huge environmental protection pressure.

Disclosure of Invention

The invention aims to solve the problems of short smoke retention time, low heat efficiency and the like of the existing stove heating device, and provides a novel stove heating device which can greatly prolong the smoke retention time, can strengthen the heating effect on a round bottom or a flat bottom vessel so as to obtain high heat efficiency, and has the advantages of simple structure, low cost, easy maintenance and long service life.

The technical scheme of the invention is as follows:

round bottom and flat bottom vessel heating device with flue gas circulation, comprising a hearth and a burner, wherein the heating device is arranged in such a way that burned flue gas generated by the burner can circulate inside the hearth.

Further, the ratio of the inner volume of the hearth to the pot bottom volume of a standard round-bottom pot with the matched hearth opening diameter is larger than 2.5, or the ratio of the inner volume of the hearth to the pot bottom volume of a standard pan with the matched hearth opening diameter is larger than 2.

Preferably, the ratio of the inner volume of the hearth to the bottom volume of a standard round-bottom pan with a matched hearth opening is preferably greater than 4.5, or the ratio of the inner volume of the hearth to the bottom volume of a standard pan with a matched hearth opening is preferably greater than 4.

Further, the hearth is drum-shaped, waist-drum-shaped, gourd-shaped, cylindrical, horn-shaped, inverted funnel-shaped, cuboid, cube, or polyhedral.

Furthermore, the burner is a blast type burner, the burner is installed at the center of the bottom of the hearth, a smoke exhaust port is further formed in the furnace wall at the lower part of the hearth, or the burner is installed on the furnace wall of the hearth, a smoke exhaust port is further formed in the furnace wall of the hearth, and the smoke exhaust port is located on the furnace wall at the same side as the burner.

Or the burner is an atmospheric burner, the burner is installed at the center of the bottom of the hearth, a plurality of secondary air inlets are formed in the wall surface of the bottom of the hearth around the burner, and a smoke outlet is formed in the wall of the hearth.

Or the burner is composed of a grate for burning solid fuel, the grate is arranged at the central position of the bottom of the hearth, the furnace wall of the hearth is provided with a furnace door, and the furnace wall of the hearth is also provided with a smoke outlet.

Preferably, the blast type burner is a blast type gas burner, and the retention time of burnt flue gas generated by the blast type gas burner under the rated thermal load working condition in the hearth is more than 1 s.

Preferably, the heating device further comprises a smoke exhaust tube, and a smoke exhaust port of the hearth is communicated with the smoke exhaust tube; the heating device also comprises an adjusting valve, and the adjusting valve is arranged on the flue between the smoke outlet and the smoke exhaust tube or on the smoke exhaust tube.

Optionally, the heating device further comprises an annular flue, the annular flue surrounds the furnace, the furnace is uniformly provided with a plurality of smoke outlets along the circumference, the smoke outlets are communicated with the annular flue, and the annular flue is communicated with the smoke exhaust pipe.

The novel heating device is arranged in such a way that the burned flue gas generated by the burner can circularly flow in the hearth, so that the residence time of the burned flue gas in the hearth can be prolonged, and the heating effect on a round bottom or a flat bottom vessel can be enhanced by utilizing the convection heat transfer and radiation heat transfer effects of the circularly flowing burned flue gas. The furnace heating device of the invention has better heating effect and higher thermal efficiency compared with the prior art because the burnt flue gas has longer residence time in the hearth and more sufficiently transfers more burnt flue gas heat to the round bottom or the flat bottom vessel.

Drawings

Fig. 1 is a schematic structural view of a flue-exhausting cooker of the prior art.

Fig. 2 is a schematic structural diagram of an indirect smoke exhaust type cooker in the prior art.

Fig. 3 is a schematic structural view of a range heating apparatus for a blast type burner according to embodiment 1 of the present invention.

Fig. 4 is a schematic structural view of a range heating apparatus for an atmospheric burner according to embodiment 2 of the present invention.

Fig. 5 is a schematic structural view of a solid fuel-fired range heating apparatus according to embodiment 3 of the present invention.

Detailed Description

The present invention will be further described with reference to the following embodiments. Wherein the showings are for the purpose of illustration only and are shown by way of illustration only and not in actual form, and are not to be construed as limiting the present patent; to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of an actual product; it will be understood by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.

The data recited in the present invention are only exemplary data given for better illustrating the embodiments of the present invention and do not constitute any limitation to the claims of the present invention unless otherwise specified.

Example 1

Fig. 3 is a schematic view showing a structure of a range heating apparatus for a blast type burner according to the present invention. Referring to fig. 3, a burner 2 and a round-bottom pan 3 are respectively installed at the bottom and the top of a drum-shaped hearth 1, and a smoke outlet 4 is formed in the wall of one side of the bottom of the hearth 1 for introducing smoke into a smoke exhaust pipe 5. A regulating valve 7 is also arranged on the flue between the smoke outlet 4 and the smoke exhaust 5. In the device, the rated heat load of the combustor is 20kW, the caliber of a hearth is 400mm, the depth of the hearth is 270mm, and the diameter of the hearth with the depth of one half of the hearth is 600 mm. The central axes of the hearth 1, the burner 2 and the round-bottom pan 3 are coincident (hereinafter referred to as the central axes).

When the device is operated, the burner 2 generates flame and high-temperature flue gas jet flow, and the flame and the high-temperature flue gas jet flow of the blast type burner have larger kinetic energy (the speed of the flame sprayed out from the fire hole of the burner is generally more than 10 m/s). Mainly under the drive of flame and high-temperature flue gas jet flow kinetic energy, the burnt flue gas generated by the flame of the burner 2 flows upwards and then flows upwards and outwards along the bottom of the round-bottomed pot 3. The burned flue gas flows downwards again when approaching the wall surface of the hearth 1, and then part of the burned flue gas flows into the smoke outlet 4 and is discharged outwards through the smoke exhaust pipe 5. Meanwhile, when the adjusting valve 7 can provide proper local flow resistance, part of the burned flue gas flows into the negative pressure area at the root of the flame and is mixed with the flame jet flow to flow upwards, and the burned flue gas which does not enter the negative pressure area at the root of the flame also flows upwards under the influence of momentum transfer of the flame jet flow. The above process forms a circular flow of burnt fumes inside the furnace 1 shown in figure 3. The velocity distribution of the burned flue gas circulating flow is axisymmetric with the central axis as the center. The "flame base negative pressure region" refers to a flame base negative pressure region formed by the flame being ejected from the burner 2 at a high speed and being capable of causing ambient gas to flow upward and making the density of the ambient gas around the flame base thin. The negative pressure region can attract surrounding burnt flue gas into the flame jet. As can be seen from the above description, the driving force generated by the circular flow of burned flue gas shown in fig. 3 is the kinetic energy possessed by the flame jet itself.

The inside of furnace 1 of this embodiment contains a large amount of high temperature burnt flue gas and can obviously strengthen the heating effect to round bottom pot 3, this is because:

(1) the burnt flue gas contacts with the bottom of the pan to generate heat convection, and the heat is transferred to the bottom of the pan.

(2) More importantly, the infrared radiation energy emitted by the burnt flue gas in the hearth 1 can transfer heat to the bottom of the boiler. According to the theory of gas radiation heat transfer, the intensity of the flue gas radiation is related to factors such as flue gas components, flue gas temperature, flue gas volume and density.

(a) Smoke components: the carbon dioxide and the water vapor contained in the flue gas have stronger infrared radiation emitting capability. Many types of fuels have a relatively high hydrogen content, so that combustion fumes typically contain a relatively high concentration of water vapor. For example, the water vapor and carbon dioxide concentrations of natural gas combustion flue gases are typically 19% and 9.5% wet flue gas volume, respectively. That is, approximately one-third of the gas components in natural gas flue gas can produce infrared radiation. In addition, black carbon particles generated by yellow flame have strong radiation capability (including a visible light part and an infrared part), so that when the flame generates yellow flame, the radiation intensity of smoke is remarkably increased.

(b) Flue gas temperature: the infrared radiation emitted when the temperature of the burnt flue gas is higher than 1200 ℃ is quite strong; the infrared radiation is still strong at 900 ℃; the infrared radiation is weak below 600 ℃.

(c) Flue gas volume and density: the characteristic of gas radiation is that all radioactive gas molecules emit radiation simultaneously throughout the gas volume, and what is received at the gas volume interface is the sum of the infrared radiation emitted simultaneously throughout the gas volume by all the radioactive gas molecules. Thus, the greater the volume and density of the gas, the higher the intensity of infrared radiation received at the interface of its volume. One parameter used in gas bology to reflect the volumetric radiation power of a gas is the mean path of the rays. A larger mean ray path indicates a greater radiation power. The flue gas radiation is volumetric radiation. In fig. 3, the bottom of the round-bottomed pan 3 is able to receive the infrared radiant energy of the burnt flue gas circulating inside the furnace 1 (including the portion directly received, and the portion reflected to the bottom by the walls of the furnace 1). The larger the internal volume of the hearth 1 is or the higher the density of the flue gas contained in the hearth is, the larger the infrared radiation energy received by the bottom of the boiler is.

Referring to fig. 3, when a large amount of burned flue gas circulates in the furnace 1, as long as the temperature of the burned flue gas is maintained above 800 ℃, the infrared radiation energy emitted by the carbon dioxide and water vapor contained in the burned flue gas can transfer the heat of the burned flue gas to the upper bottom of the boiler. If the burnt flue gas contains black carbon particles generated by yellow flame, the radiation energy of the black carbon particles in the circularly flowing burnt flue gas can also transfer heat to the upper pot bottom. The burned flue gases circulating inside the furnace 1 act as an infrared heater. As long as the flame jet energy generated by the burner 2 is enough to maintain the temperature inside the hearth 1 to be above 800 ℃, and can drive the burned flue gas to generate more remarkable circulating flow, so that the temperature distribution at the upper and lower parts inside the hearth 1 is more uniform, the stove heating device shown in fig. 3 can enhance the heating effect on the round-bottomed pan 3 by utilizing the convection heat transfer and radiation heat transfer effects of the circularly flowing burned flue gas.

To more clearly illustrate the beneficial effects of the present invention, the following compares the prior art fig. 1 and fig. 2 with the embodiment fig. 3: in fig. 1 and 2, the flue gas generated by the burner 2 is inevitably discharged upward rapidly, which is characteristic of high-temperature flue gas, so that the burned flue gas generated by the flame of the burner 2 is only contacted with the bottom of the round-bottomed pan 3 for a short time at one time (actually, in the case that the burner 2 is opened to generate a large amount of flue gas in a large fire range, many of the flue gas in fig. 1 and 2 are discharged upward without contacting the bottom of the pan). Because the heat exchange area of the boiler bottom is small and the flow speed of the flue gas is high, most of the heat of the flue gas can not be transferred to the boiler bottom in time, and the heat is discharged to the atmospheric environment along with the flue gas. Therefore, the heat efficiency of the flue-exhausting type and indirect flue-exhausting type cooking ranges in the prior art shown in the figures 1 and 2 is only about 20 percent.

In contrast, in the embodiment shown in fig. 3, the cooking range heating device is artificially and purposefully arranged such that the burned flue gas generated by the flame of the burner 2 cannot drift upwards and leave the hearth 1 immediately, but can drive the burned flue gas to circulate inside the hearth 1 by means of the kinetic energy of the flame (which requires some specific shape of the hearth 1 and the local flow resistance generated by the regulating valve 7 to match), so that the burned flue gas is contacted with the bottom of the pan for convection heat transfer for a long time and for a plurality of times. More importantly, the embodiment can also utilize the infrared radiation energy of a large amount of circulating flue gas in the hearth 1 to heat the bottom of the pan. Compared with the prior art, the stove heating device of the embodiment has better heating effect and higher thermal efficiency because the burnt flue gas has longer residence time in the hearth 1 and more sufficiently transfers more burnt flue gas heat to the bottom of the pan.

For example, the rated thermal load of the burner of a certain type of flue-exhausting type blast cooking stove in the prior art is 42 kW; the caliber of the funnel-shaped hearth is 400mm, the depth is 270mm, and the diameter of the bottom of the hearth is 120 mm; the geometric volume of the hearth is 0.0157m³The volume occupied by the bottom (depth 110mm) of the standard round bottom pan matched with the caliber of the hearth (namely the volume of the part of the pan lower than the pan ring at the top of the hearth 1, which is referred to as the bottom volume for short) is 0.0076m³(Note: the standard round-bottom pot means a round-bottom pot with a diameter/depth ratio of 0.25 to 0.35; the standard pan means a test pot specified in "energy efficiency limit and energy efficiency grade for domestic gas range" GB 30720-. The internal volume of the hearth is equal to the geometric volume minus the volume of the bottom of the boiler: 0.0157-0.0076 ═ 0.0081m³The ratio of the internal volume of the hearth to the volume of the pot bottom is 0.0081/0.0076 which is 1.07; the internal area of the hearth is 0.4229m²The mean ray path of the flue gas radiation is: 3.6x furnace internal volume/furnace internal area is 0.069 m; rated heat load natural gas consumption 4.378m³Per h, 900 ℃ flue gas amount of 186.47m³The residence time of the flue gas in the hearth is as follows: the volume/smoke gas amount inside the hearth is 0.156 s; flue gas amount of 154.67m at 700 DEG C³The residence time of the flue gas inside the furnace is 0.19 s. Because the smoke retention time is more than zero point one second, the heat efficiency of the air-blast cooking stove can be judged to be lower.

The rated heat load of the combustor is 20kW, the caliber of a drum-shaped hearth is 400mm, the depth of the hearth is 270mm, and the diameter of the bottom of the hearth is 400 mm; the geometric volume of the hearth is 0.044m³The volume occupied by the bottom (the depth is 110mm) of the standard round bottom pot matched with the caliber of the hearth is 0.0076m³The internal volume of the hearth is 0.0364 m³The ratio of the inner volume of the hearth to the volume of the pot bottom is 4.8. It can be seen that the internal volume of the drum-shaped hearth adopted by the embodiment is increased by 0.0364/0.0081 to 4.5 times compared with the internal volume of the funnel-shaped hearth of the blast cooking stove of the certain type under the condition of the same hearth caliber.

The internal area of the hearth of the embodiment is 0.73m²The mean ray path of the flue gas radiation is: the furnace internal volume/furnace internal area is 0.1795m at 3.6 x. The average ray path of the fume radiation of the drum-shaped hearth adopted by the embodiment is increased by 2.6 times (0.1795/0.069) compared with the average ray path of the fume radiation of the funnel-shaped hearth of the blast cooking stove of a certain type.

The natural gas consumption of the rated heat load of the embodiment is 2.085m³Per h, 900 ℃ flue gas amount of 88.794m³The residence time of the flue gas in the hearth is as follows: the internal volume/flue gas volume of the furnace is 1.48 s. The smoke residence time of the embodiment is increased by 9.5 times to 1.48/0.156 times compared with that of the air-blast cooking stove of the certain type.

The bottom area of the round bottom pot of the embodiment is 0.1636m²The temperature of flue gas contacting with the bottom of the pan is about 1000 ℃, the temperature of the bottom of the pan is about 300 ℃, the heat transfer temperature difference is 700 ℃, and the convective heat transfer coefficient is about 25W/m²(in FIG. 3, the circular flow of the burned flue gas is driven by the kinetic energy of the flame, the flow velocity is not large, and the convective heat transfer coefficient is 25W/m)²Temperature is reasonable), the convection heat transfer quantity is 2.863kW, the convection heat transfer coefficient x the boiler bottom area x the heat transfer temperature difference.

The average absolute temperature of the burnt flue gas in the drum-shaped hearth is 1173K, and the blackness of the natural gas flue gas is 0.18 according to a Hottel line arithmetic chart when the mean ray path of the flue gas radiation is 0.1795 m. Because the blast type cooking stove has slight yellow flame, the blackness of the burnt smoke is estimated to be 0.3 reasonably. According to the fourth power law of radiation intensity, the radiation heat transfer quantity of the burnt flue gas is 5.273kW which is the fourth power of Stefan-Boltzmann constant x burnt flue gas blackness x boiler bottom area x burnt flue gas average absolute temperature.

The heating power to the bottom of the pan is as follows: the convection heat transfer amount and the radiation heat transfer amount are 2.863+5.273 to 8.136kW, and the thermal efficiency is 40.7% of heating power/rated thermal load of the burner. Therefore, the heating effect on the pot bottom can be enhanced by utilizing the convection heat transfer and radiation heat transfer effects of the circularly flowing burnt flue gas, and the heat efficiency is improved.

The radiant heat transfer capacity is greater than the convective heat transfer capacity. The influencing factors of the convection heat transfer quantity are the convection heat transfer coefficient, the boiler bottom area and the heat transfer temperature difference. The area of the pot bottom is determined by the size and the shape of the pot, the heat transfer temperature difference depends on the temperature of the flue gas, and the convection heat exchange coefficient is mainly influenced by the flow velocity of the flue gas. For a range heating arrangement, these three parameters cannot be greatly improved. The radiant heat transfer is different, and the flue gas radiation is volume radiation. Under the condition that the area of the pot bottom is not changed, only the volume of the flue gas below the pot bottom is increased, and the superposition of the radiant gas in the volume of the flue gas and the heat radiation emitted by the solid particles can greatly increase the intensity of the heat radiation received by the pot bottom, so that the heat transfer quantity of the burnt flue gas to the pot bottom is increased.

The difference between the present invention and the prior art represented by a certain type of air-blast cooking stove is further explained by combining the data: the rated heat load of a certain type of blast cooking stove is 42kW, the retention time of flue gas in the hearth is more than zero one second, and the actual heating power of the blast cooking stove to the bottom of a pot is about 8.4kW (the fire demand of a 400mm round-bottom pot for cooking is 8 kW). When the blast cooking stove is in a middle fire gear (the heat load of a burner is reduced to 20kW), the retention time of the flue gas in the hearth is more than zero for three seconds, the flue gas is still in temporary contact with the pot bottom once and for a moment, the actual heating power of the pot bottom is reduced to about 4.5kW when the middle fire is started, and the fire power requirement of cooking in a 400mm round-bottom pot is not met.

The rated thermal load of the combustor in the embodiment is 20kW, a large amount of combusted flue gas circularly flows below the pot bottom after the drum-shaped hearth is adopted, the combusted flue gas is in contact with the pot bottom for a plurality of times for a long time, and the retention time of the flue gas in the hearth reaches 1.48 seconds. Through the convection heat transfer and radiation heat transfer effects of the circularly flowing combusted flue gas, the heating power of the boiler bottom under the rated heat load of the burner reaches 8.136kW, and the requirement of the fire power of a 400mm round-bottom boiler for cooking can be met. The heating power for the bottom of the boiler is 8.136kW under the condition that the rated thermal load of the burner is 20kW, so that the thermal efficiency reaches 40.7 percent, which is doubled compared with the prior art.

In actual use, round-bottomed pots are often used for cooking, steaming, frying and stewing food in addition to cooking. At this moment, the burner of the embodiment can reduce the firepower to 10kW of heat load, and the reduction of the flue gas quantity when the heat load is reduced can double the retention time of the flue gas in the hearth 1 to reach 3 s. The temperature of the flue gas contacting with the bottom of the pan is still higher, but the flow velocity of the flue gas is reduced, and the convective heat transfer coefficient is about 15W/m²The convective heat transfer capacity is about 1.72 kW. The average absolute temperature of the burnt flue gas in the hearth is reduced to 1073K, and the radiant heat transfer quantity is about 3.69 kW. The heating power to the bottom of the boiler is about 5.41kW, and the thermal efficiency reaches 54.1%. It can be seen that as the burner thermal load decreases, the burned flue gas residence time increases and the thermal efficiency increases.

The formation of the circular flow of the burnt flue gas in the stove heating device shown in fig. 3 and its energy saving effect are related to the shape, volume and internal components of the hearth 1, the type and performance of the burner 2 (especially the flue gas amount and the flue gas kinetic energy), the position and area of the smoke outlet 4, the induced draft of the smoke exhaust pipe 5, and the local flow resistance generated by the regulating valve 7, and the like, which are further described as follows:

(1) shape, volume and internal components of the furnace 1:

(a) shape: the drum-shaped hearth is the best choice, which is not only beneficial to the circular flow of the burnt flue gas, but also can increase the internal volume of the hearth, and is beneficial to the heat radiation reflection of flame and flue gas to the bottom of a boiler by the hearth, and the heat radiation area of the outer surface of the drum-shaped hearth is the minimum when the internal volume of the hearth is the same, and the required hearth manufacturing materials are the minimum. Other hearth shapes such as waist drum shape, gourd shape, cylinder shape, horn shape, inverted funnel shape, cuboid, cube, polyhedron and the like are also beneficial to the formation of the circular flow of the burnt flue gas. However, the funnel-shaped furnace chamber (fig. 1 and 2) commonly used in the prior art is not favorable for forming the circulating flow of the burnt flue gas.

(b) Volume: the larger the internal volume of the hearth 1 is, the larger the amount of flue gas which can be contained and circularly flows below the pot bottom is, and the better the heating effect on the pot bottom is. Therefore, the invention adopts larger internal volume of the hearth, the ratio of the internal volume of the hearth to the volume of the bottom of the standard round-bottom pan matched with the opening diameter of the hearth is more than 2.5, or the ratio of the internal volume of the hearth to the volume of the bottom of the standard flat pan matched with the opening diameter of the hearth is more than 2. Further, the ratio of the inner volume of the hearth to the bottom volume of a standard round-bottom pan with the matched hearth opening diameter is preferably greater than 4.5, or the ratio of the inner volume of the hearth to the bottom volume of a standard pan with the matched hearth opening diameter is preferably greater than 4. If the ratio of the internal volume of the hearth to the volume of the pot bottom is only about 1, the smoke quantity below the pot bottom is too small, and even if the circular flow of the burnt smoke occurs in the hearth, the effect of improving the heat efficiency is not obvious.

(c) Internal components: the hearth 1 is internally provided with components such as a guide cover, a circular baffle plate, a turned edge or a flue gas flow guider and a Venturi ejector pipe arranged above the combustor 2, so that the circular flow of the combusted flue gas can be enhanced. However, commercial cooking utensils have large heat load and high furnace temperature, and the cost is greatly increased by arranging members in the furnace, and the members in the furnace are easy to be damaged by overheating and difficult to maintain. This embodiment is therefore not provided with furnace internals.

(2) Type and performance of the burner 2 (especially the amount and kinetic energy of the flue gas):

in this embodiment, the fuel used in the stove heating device shown in fig. 3 may be fuel gas (such as natural gas, liquefied petroleum gas, coal gas, etc.), fuel oil (such as diesel oil, heavy oil, alcohol-based fuel, etc.), or other fuel (such as coal powder, coal water slurry, etc.). The greater the kinetic energy of the flue gas generated by the burner 2, the stronger the circulating flow of the burnt flue gas. The present embodiment is preferably selected from burners with high flame injection velocity and large kinetic energy of flue gas. The depth of the drum-like furnace 1 of the present embodiment should be adapted to the flame length of the burner 2. For example, when a blast type fuel burner is adopted, because fuel needs to be atomized, the flame jet flow has a larger length, the depth of the hearth 1 is correspondingly increased, the internal volume of the hearth 1 can be increased, and the heating effect on the bottom of a boiler can be enhanced. Some types of burners require supplemental secondary air in addition to the air supply shown in fig. 3. In this case, the secondary air injection ports can be arranged around the burner 2 at the bottom of the furnace 1, so that the circulating flow of the burnt flue gas can be enhanced.

In actual use, the smoke amount and the smoke kinetic energy are changed along with the fire gear of the burner 2, and the ratio of the maximum smoke amount to the minimum smoke amount can reach 20 to 30 during cooking operation. When the burner 2 is in a middle or large fire gear, the present embodiment can obtain stronger circular flow of the burnt flue gas inside the hearth 1. If the burner 2 is small in fire power (e.g., a heat-insulating fire), the burned flue gas circulating flow driven by the kinetic energy of the flue gas is not significant. In the case of a low burner power of the burner 2, the present embodiment can utilize the temperature difference inside the furnace 1 to generate the circulating flow of the burnt flue gas (i.e. the temperature difference between the fresh high-temperature flue gas generated by the flame of the burner 2 and the old flue gas already existing inside the furnace 1). Specifically, because the flue gas distribution inside the drum-shaped hearth 1 of the present embodiment is always that the flue gas with the highest temperature is located at the position where the flue gas with the highest temperature is in close contact with the bottom of the pan and the flue gas with the lowest temperature is located at the position where the flue gas with the lowest temperature is close to the smoke outlet 4, the fresh high-temperature flue gas generated by the burner 2 will flow upward to reach the bottom of the pan and then fully contact with the bottom of the pan for a long time until most of the heat of the fresh high-temperature flue gas is transferred to the bottom of the pan and the temperature of the fresh high-temperature flue gas is reduced, then the fresh high-temperature flue gas gradually flows downward to. Therefore, under the condition that the firepower of the combustor 2 is very small (heat preservation fire), the high-temperature flue gas in the hearth 1 has very long heat exchange time to fully transfer heat to the bottom of the boiler, so that very high heat efficiency can be obtained.

However, in the currently commonly used indirect smoke exhaust type kitchen range shown in the prior art 2, no matter the amount of smoke, the smoke will rapidly drift upwards through the annular gap between the round-bottom pan 3 and the top of the hearth 1, and the smoke retention time is extremely short. The flue gas residence time in the flue-type stove of prior art fig. 1 increases to some extent but also differs little when the burner 2 fire decreases. Only in the stove heating device of the arrangement mode shown in the figure 3 of the embodiment, the hot flue gas generated by the burner 2 cannot float upwards immediately, the flue gas with higher temperature in the hearth 1 flows upwards, the flue gas with lower temperature flows downwards, so the high-temperature flue gas generated by the burner 2 tends to stay below the pot bottom, is in contact with the pot bottom for a long time, and fully transfers heat to the pot bottom, and the flue gas with reduced temperature tends to be discharged from the smoke outlet 4.

Under the condition that the firepower of the burner 2 is very small, the temperature of the lower part of the hearth 1 can be lower than the dew point temperature of the flue gas, and the water vapor contained in the flue gas is condensed into condensed water, so that the latent heat of condensation of the water vapor of the burnt flue gas can be effectively utilized. It can be seen that the present embodiment can also utilize the higher calorific value of the fuel, including the latent heat of condensation of flue gas steam, with the lower and higher calorific values of natural gas being 34.5 and 38.3MJ/m respectively³The utilization of the latent heat of condensation of the flue gas water vapor can additionally achieve a thermal efficiency increase of about 11%. For the above reasons, the present invention achieves higher thermal efficiencies when used in cooking operations (e.g., boiling, steaming, frying, stewing, boiling, braising, etc.) with a slow fire for longer periods of time.

(3) Position and area of the smoke outlet 4:

the smoke outlet 4 is arranged at the bottom of the hearth 1 in the embodiment, which is favorable for the formation of the circular flow of the burnt smoke. If the smoke outlet 4 is arranged at the upper part of the hearth 1, the smoke outlet 4 and the regulating valve 7 need to have enough local flow resistance to form the circular flow of the burnt smoke in the hearth 1. The area of the smoke outlet 4 is designed according to the maximum smoke discharge.

(4) Induced draft of the chimney 5:

when the blast type burner is used, even if the induced draft of the exhaust pipe 5 is small, the smoke can be discharged smoothly in general. The smaller induced draft force is also beneficial to the formation of the circular flow of the burnt flue gas in the hearth 1 of the embodiment. If the induced draft of chimney 5 is too big, burnt flue gas in furnace 1 can take place the short circuit and flow into exhaust port 4, is unfavorable for forming strong burnt flue gas circulation and flows.

(5) The local flow resistance generated by the regulating valve 7:

the main function of the regulating valve 7 is to create a suitable local flow resistance. The opening degree of the regulating valve 7 is regulated according to the firepower of the combustor 2 so as to achieve the required smoke discharge amount. On the premise of achieving the required smoke discharge amount, the opening degree of the adjusting valve 7 needs to generate local flow resistance as large as possible, so that the circular flow of the burnt smoke in the hearth 1 is facilitated. For example, the induced air force of the exhaust pipe 5 is 15Pa, the opening degree of the regulating valve 7 is about 70% to generate a local flow resistance of 10Pa, the local flow resistance of the inlet of the exhaust port 4 is 3Pa, the friction resistance of the exhaust smoke along the way is 1Pa, and the interior of the hearth 1 is slightly negative pressure of 1 Pa. Under the above conditions, if 10Pa local flow resistance generated by about 70% of the opening degree of the regulating valve 7 is lacked, the negative pressure 11Pa is reached in the furnace 1, and then the circulating flow of the burnt flue gas is difficult to form to remarkably prolong the residence time of the burnt flue gas in the furnace 1. It should be noted that instead of the regulating valve 7, other technical means may be used to obtain the appropriate local flow resistance, or that the regulating valve 7 may be replaced by other technical means (for example, by selecting the appropriate exhaust port 4 or flue flow area).

In order to obtain a good effect of circulating the burned flue gas inside the furnace 1, the adjusting valve 7 should be properly adjusted according to the amount of the flue gas. In order to simplify the actual operation, it is preferable that the fire power adjustment mechanism of the burner 2 and the adjustment valve 7 are designed to be linked (for example, a fire power adjustment knob of the burner 2 and a rotary shaft of the adjustment valve 7 are mechanically driven), and the opening degree of the adjustment valve 7 can be automatically changed at the same time when the fire power shift of the burner 2 is adjusted according to the cooking requirement.

The present invention is preferably implemented to fully understand the technical principle of the present invention, and it is more advantageous to obtain a better effect of improving the thermal efficiency by considering the comprehensive arrangement of the above-listed five aspects and properly adjusting the operating conditions. The mere manufacture of the furnace drum and the arrangement of the exhaust port at the bottom of the furnace does not guarantee that a significant circulating flow of the burnt flue gases takes place inside the furnace. The current design specification of the kitchen smoke exhausting facilities of large and medium catering enterprises requires that the wind guiding force of a chimney reaches more than 10 Pa. When the flue type kitchen range is directly connected with a chimney for guiding wind power of 10Pa, but the measure for adjusting the wind power is lacked, the burnt flue gas in the hearth can be drawn away by the wind power guided by the chimney no matter what shape of hearth is, and the obvious circular flow of the burnt flue gas in the hearth is difficult to form.

The present embodiment has other advantageous effects. For example, the recirculated burned flue gas flow may return incomplete combustion products or combustibles contained in the burned flue gas to the flame combustion zone for burnout, thereby reducing pollutant formation and emissions. The circular flow of the burnt flue gas can also make the residual oxygen contained in the burnt flue gas enter the high-temperature combustion area again to participate in the oxidation reaction, thereby fully utilizing the oxidant, reducing the air quantity supplied to the combustor 2 and reducing the heat carried away by the redundant oxygen and nitrogen in the exhausted flue gas. The circular flow of the burnt flue gas can also reduce the temperature of the flame core area and reduce the formation of nitrogen oxides. In addition, the furnace wall of the hearth 1 of the embodiment is arranged to be far away from the flame of the burner 2, so that the requirement on the heat resistance of furnace wall materials can be reduced, the manufacturing and maintenance cost of the stove is reduced, and the service life of the stove is prolonged. This embodiment still has good heat preservation effect: referring to fig. 3, after the cooking is finished and the burner 2 is closed, the hot flue gas can be completely remained in the hearth 1 as long as the regulating valve 7 is closed, and the residual heat of the flue gas can be used for continuously heating and insulating the cookware for a long time. Compared with the prior art, the hot smoke flows upwards completely after cooking in the prior art shown in figure 2, and the heat preservation effect is not achieved; after the cooking in figure 1 is finished, most hot smoke is discharged through the flue, and the heat preservation effect is basically not achieved.

The chamber 1 of the heating device of the cooking range shown in fig. 3 is preferably cast from cast steel or cast iron, but can also be made of refractory material. The outer wall surface of the hearth 1 is provided with an insulating layer (not shown in figure 3).

In this embodiment, the burner 2 may also be another type of burner or heater (e.g., an infrared gas heater) that does not need to supplement secondary air by natural ventilation, and the burner 2 may also be replaced with a heater (e.g., an electric heater). The type of fuel used by the burner 2 may be gas, oil or other.

Although the embodiment is described with reference to a round-bottom pan, the stove heating device shown in fig. 3 can be used to heat other types of dishes.

Example 2

Fig. 4 is a schematic view of a stove heating device for an atmospheric burner according to the invention. Atmospheric burners are burners that use high pressure gas to introduce primary air and rely on natural ventilation to supplement secondary air. The atmospheric burner does not need to be provided with a blower, avoids the power consumption and the operation noise of the blower, and is commonly used as a burner of a kitchen range.

Referring to fig. 4, the bottom and the top of the drum-shaped hearth 1 of the present embodiment are respectively provided with a burner 2 and a pan 8, and a plurality of secondary air inlets are arranged around the burner 2. And a smoke outlet 4 is arranged on the furnace wall at one side of the hearth 1 and used for introducing smoke into a smoke exhaust pipe 5. The side wall of the drum-shaped hearth 1 is provided with a fire observation window (not shown in fig. 4).

Inside the furnace 1, the burner 2 generates a flame and a high temperature flue gas jet, the velocity of the atmospheric burner fuel-air mixture exiting from the burner flame holes being about 1 to 3 m/s. The burnt flue gas generated by the burner 2 flows upwards mainly under the driving of the flame and the jet kinetic energy of the high-temperature flue gas, then flows outwards along the bottom of the pan 8 and then flows upwards along the side wall of the pan. In the flowing process, the heat of the flue gas is transferred to the pot body, and the temperature of the flue gas is reduced. The burned flue gas with lower temperature then flows downwards along the wall surface of the hearth 1, and part of the burned flue gas flows into the smoke outlet 4 and is discharged outwards through the smoke exhaust 5. Meanwhile, when the adjusting valve 7 can provide proper local flow resistance, part of the burned flue gas flows into the negative pressure zone at the root of the flame and flows upwards in a mixed manner with the flame jet. The above process forms a circular flow of burnt fumes inside the furnace 1 as shown in figure 4.

The secondary air supplied to the atmospheric burner 2 is induced by the draft of the exhaust pipe 5. The secondary air intake quantity can be adjusted by changing the opening degree of the adjusting valve 7, and the adjusting method comprises the following steps: when the combustor 2 is in a big fire gear, the regulating valve 7 is fully opened, and when the combustor is in a middle fire gear, the regulating valve 7 is half opened; the fine adjustment is performed based on the above, that is, the opening degree of the adjustment valve 7 is gradually decreased, and the flame combustion condition of the burner 2 is observed. As long as the flame combustion is stable, yellow flame does not appear, and the secondary air inlet does not produce smoke, the opening degree of the regulating valve 7 can be continuously reduced so as to achieve the optimum secondary air intake quantity. If the flame of the burner 2 is obviously deviated to one side of the smoke outlet 4, the opening degree of the regulating valve 7 is also properly reduced.

The volume of the bottom of the pan (namely the volume of the pan part lower than the pan ring at the top of the hearth 1) is larger. The ratio of the inner volume of the furnace 1 to the volume of the bottom of the pan is about 3 in this embodiment.

Although the present embodiment is described with reference to a pan, the range heating apparatus shown in fig. 4 can be used to heat other types of vessels.

The parts of this embodiment not mentioned are similar to those of embodiment 1, and are not described again here.

Example 3

Fig. 5 is a schematic view showing a structure of a solid fuel-fired range heating apparatus according to the present invention. Referring to fig. 5, a grate 9 is arranged at the bottom of the drum-shaped hearth 1, a smoke outlet 4 is arranged on the furnace wall at one side of the hearth 1, and a furnace door 10 is arranged on the furnace wall at the side opposite to the smoke outlet 4.

The device operates as follows: the door 10 is opened and solid fuel (coal or biomass such as firewood, straw, wheat straw, organic waste, garbage, etc.) is placed in the hearth 1 and stacked on the grate 9. The solid fuel deposited on the grate 9 is ignited by a fire, and the door 10 is closed. The air originally present in the furnace 1 is used for initial combustion of the solid fuel. At the same time, ambient air is passed through the grate 9 into the solid fuel pile (ambient air may be blown in by forced ventilation, such as a blower or artificial bellows, or by natural ventilation). The flame and high-temperature flue gas generated by the combustion of the solid fuel flow upwards to the bottom of the boiler, then flow upwards and outwards and then flow downwards, then part of the burnt flue gas is discharged through a smoke outlet 4 and a smoke exhaust pipe 5, and part of the burnt flue gas flows upwards under the drive of momentum transfer of the flame and the high-temperature flue gas to form circular flow of the burnt flue gas in the hearth 1.

The mechanisms by which the bottom of the pan is heated include convective heat transfer and radiative heat transfer. The components with stronger heat radiation capability in the burnt flue gas generated during the combustion of the solid fuel comprise: (1) carbon dioxide; (2) water vapor (biomass fuel has a large moisture content, and combustion flue gas of the biomass fuel generally has a high water vapor concentration, and sometimes the water vapor concentration is as high as 30 to 50%); (3) black carbon particles generated by yellow flame; (4) flue gas-entrained partially burned or burning solid fuel fragments, fines and coke particles; (5) flue gas entrained solid fuel ash and inorganic particulates. At the combustion temperature, all five of the above components emit strong infrared radiation energy (the latter three also produce visible radiation), with the greatest thermal radiation from the coke particles, second to the black carbon particles. The blackness of solid fuel combustion fumes is generally up to 0.5, which is higher than the thermal radiation intensity of the gas or oil fired flame fumes of examples 1 and 2 above. The embodiment can greatly enhance the heating effect on the bottom of the boiler by utilizing the radiation heat transfer of the burnt flue gas circularly flowing in the drum-shaped hearth 1, and improve the heat efficiency.

The grate 8 of this embodiment may take the form of various grates known in the art. The grate 8 has three functions: (1) supporting a solid fuel stack; (2) combustion air can be introduced into the furnace through the grate; (3) the ash can be discharged through the grate. Depending on the application of the heating means of the stove of the invention, a simple fixed grate (typically consisting of several iron rods of about 5mm diameter and 100mm length arranged at regular intervals, about 5mm apart when coal is the solid fuel to be fired and about 10mm apart when biomass fuel is fired) may be used for small or domestic use. An ash bin, an air duct, etc. may also be installed below the grate 8, as is known in the art. When the invention is used as a commercial stove heating device with larger heat load, a mechanical grate can be selected as the grate 8.

When combustion-supporting air is supplied to the furnace in a natural ventilation mode, the opening of the adjusting valve 7 is changed to adjust the air inflow of the combustion-supporting air flowing into the grate 9, the adjusting method is similar to that of embodiment 2 (the grate 9 and the solid fuel pile of the embodiment are equivalent to the burner 2), when the solid fuel pile is burnt vigorously and the smoke amount is large, the adjusting valve 7 is fully opened, and the adjusting valve is half opened when the smoke amount is medium; the fine adjustment is performed on the basis of the above, namely, the opening degree of the regulating valve 7 is slowly reduced, and the flame combustion condition is observed. As long as the flame combustion is stable, no large-area yellow flame appears, and no smoke is blown down from the grate 9, the opening degree of the regulating valve 7 can be continuously reduced to achieve the optimum air supply amount.

In this embodiment, when forced ventilation is used to supply combustion air to the interior of the furnace 1 through the grate 8, the exhaust port 4 is preferably arranged at the bottom of the furnace 1.

The biomass fuel contains higher volatile components and is mainly combusted in a gas phase. In the embodiment, when the biomass fuel is combusted and the air blower is used for forcibly introducing the combustion air, the further improvement is that the combustion air is divided into two paths: one path is primary air which is introduced through the grate 8; the other path of secondary air is sprayed into the hearth 1 through the furnace wall of the hearth 1. The secondary air injection should be beneficial to the formation of the circular flow of the burned flue gas as shown in fig. 5 (e.g. the secondary air injection inlet is arranged above the smoke exhaust 4).

The parts of this embodiment not mentioned are similar to the above embodiments and are not described again here.

The smoke outlet 4 is arranged on the wall of one side of the hearth 1 in the above three embodiments, which causes asymmetry or non-uniformity of the circulating flow velocity distribution of the burned flue gas in the hearth 1 to a certain extent (although the asymmetry or non-uniformity can be reduced by the local flow resistance of the regulating valve 7). In order to avoid the defects, the invention further improves the method by arranging an annular flue, wherein the annular flue surrounds the hearth 1, a plurality of smoke outlets are uniformly arranged on the wall of the hearth 1 along the circumference, the smoke outlets are communicated with the annular flue, and the annular flue is communicated with the smoke exhaust tube 5.

Above three embodiments combustor 2 all installs in furnace bottom central point puts, makes the pan that is heated can the thermally equivalent, but its shortcoming is when appearing overflowing the pot, take out food from the pan or take off the pan from the kitchen range heating device, and hot water juice, oil droplet, vegetable piece, debris etc. fall 2 fire holes of combustor easily, influence combustor performance, often will clear up and maintain. When the fire holes are seriously polluted, the burner needs to be replaced, which is one of the reasons for short service life of the commercial stove burner. In order to avoid the above-mentioned disadvantages, a further development of the invention consists in mounting the burner 2 on the wall of the furnace 1 (the burner 2 fire hole injection direction is substantially horizontal), and in opening the exhaust port 4 on the same side of the wall as said burner 2, preferably below the burner 2 near the bottom of the furnace 1, also to create a stronger circulating flow of burnt fumes.

The present invention does not involve any complex, precise, expensive and high-tech parts of the plant, nor advanced combustion technology. The novel stove heating device provided by the invention aims at solving the practical problems in the actual situation, and is simple in structure and feasible. The invention is characterized in that the stove heating device is arranged in a way that a large amount of burnt flue gas can circularly flow under the bottom of a pan. The invention may be embodied in a wide variety of ways depending on the type of fuel, burner type and parameters, shape, size and use of the vessel to be heated, direct or indirect fume extraction, kitchen conditions, and many other factors. The novel stove heating device has larger hearth volume, and the stove wall is far away from flame, so the requirement on the heat resistance of the stove wall material can be reduced. But the heat radiation area of the outer wall of the hearth is correspondingly increased, and the requirement on the heat insulation performance of the heat insulation layer is higher. In addition, the regulating valve 7 also has certain requirements for heat resistance. The adjusting valve 7 can be arranged at a position (arranged in a flue or a smoke exhaust tube) which is far away from the smoke outlet 4, has lower smoke temperature and is more convenient to adjust.

Generally, the invention has the advantages of high thermal efficiency, simple structure, low cost, easy maintenance and long service life.

In the above three embodiments, the adjustment is mainly performed by observing the combustion condition of the flame, which is time-consuming, labor-consuming and not accurate enough. The further improvement of the invention is to configure a PLC automatic control device, which is described as follows (taking the device shown in figure 3 as an example of adopting a blast type gas burner): a carbon monoxide sensor and an oxygen sensor are installed in a flue, a pressure sensor is installed on the flue between an adjusting valve 7 and an exhaust port 4, a variable frequency speed regulator is installed on a blower of a combustor 2, the adjusting valve 7 adopts an electromagnetic valve with an opening changed by electric control, and a gas valve opening sensor is installed (the opening of the gas valve is adjusted by a user according to the cooking firepower requirement). The sensor is connected with the input end of the PLC, and the output end of the PLC is connected with the variable frequency speed regulator of the air blower and the electromagnetic valve of the regulating valve 7. The PLC control step is to rapidly change the rotating speed of the blower and adjust the opening of the valve 7 according to the opening signal of the gas valve, and then to finely adjust on the basis: if the carbon monoxide does not reach the standard, increasing the rotating speed of the blower; after the carbon monoxide reaches the standard, if the oxygen concentration is high, the rotating speed of the blower is reduced; the opening degree of the regulating valve 7 is finely adjusted according to the range of keeping the flue pressure between the regulating valve 7 and the smoke outlet 4 at the negative pressure of 1-4 Pa.

The above embodiments show the specific implementation of the present invention when applied to common burners and common round-bottom pots and pans. These examples are given for the purpose of clearly illustrating the invention and are not intended to limit the embodiments of the invention. Due to the variety of burners used by people and the diversified use and form of pots, there are many kitchen facilities of different types and different scales in different areas, and the installation and use conditions of the stove heating device are greatly different. It is not possible to give specific embodiments of the invention one for each specific case, and it is neither necessary nor possible to exhaustively enumerate all embodiments of the invention.

It will be apparent to those skilled in the art that other variations and modifications can be made in the above-described embodiments depending on the specific circumstances. For example, buildings used by large catering establishments typically have a chimney that is specially designed to have a height of 5 to 10 meters or more. In this case, the smoke outlets 4 of several sets of the inventive stove heating device can be connected to one and the same chimney. Conversely, many small food and beverage establishments (e.g., fast food restaurants, pasta stores) use buildings without specialized chimneys. In this case, the novel range heating device of the present invention can be simplified. For example, in fig. 4, the smoke exhaust 5 can be eliminated, the smoke exhaust 4 is changed to be arranged at the top of the hearth 1 (beside the pan 8), the smoke exhaust 4 is provided with a regulating valve 7, and smoke of the stove heating device is directly exhausted into air in a kitchen through the smoke exhaust 4. Similar changes or modifications as will be apparent to those skilled in the art may be made depending on the particular situation.

Any modification, simplification, replacement, addition, combination, modification, equivalence replacement and improvement made within the spirit and principle of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. Round bottom and flat bottom vessel heating device with flue gas circulation, which is characterized in that: the heating device is arranged to enhance the superposition effect of infrared radiation of the burnt flue gas so as to increase the intensity of heat radiation received by the round-bottom and flat-bottom vessels to enhance the heating effect on the round-bottom and flat-bottom vessels, and the heating device is arranged so that the burnt flue gas in the hearth cannot drift upwards to leave the hearth;

the ratio of the internal volume of the hearth to the pot bottom volume of a standard round-bottom pot matched with the hearth opening diameter is more than 2.5, or the ratio of the internal volume of the hearth to the pot bottom volume of a standard pan matched with the hearth opening diameter is more than 2;

the hearth is drum-shaped, gourd-shaped, cylindrical, horn-shaped, inverted funnel-shaped or polyhedral.

2. The round bottom, flat bottom vessel heating apparatus with flue gas recirculation of claim 1, wherein: the ratio of the internal volume of the hearth to the pot bottom volume of the standard round-bottom pot matched with the hearth opening diameter is more than 4.5, or the ratio of the internal volume of the hearth to the pot bottom volume of the standard pan matched with the hearth opening diameter is more than 4.

3. The round bottom, flat bottom vessel heating apparatus with flue gas recirculation of claim 1, wherein: the burner is a blast type burner, the burner is installed at the center of the bottom of the hearth, a smoke exhaust port is further formed in the furnace wall of the lower portion of the hearth, or the burner is installed on the furnace wall of the hearth, a smoke exhaust port is further formed in the furnace wall of the hearth, and the smoke exhaust port is located in the furnace wall on the same side as the burner.

4. The round bottom, flat bottom vessel heating apparatus with flue gas recirculation of claim 1, wherein: the burner is an atmospheric burner, the burner is installed at the center of the bottom of the hearth, a plurality of secondary air inlets are formed in the wall surface of the bottom of the hearth around the burner, and a smoke outlet is formed in the wall of the hearth.

5. The round bottom, flat bottom vessel heating apparatus with flue gas recirculation of claim 1, wherein: the burner is composed of a grate for burning solid fuel, the grate is installed at the center of the bottom of the hearth, a furnace door is arranged on the wall of the hearth, and a smoke outlet is further formed in the wall of the hearth.

6. The round bottom, flat bottom vessel heating apparatus with flue gas recirculation of claim 3, wherein: the blast type burner is a blast type gas burner, and the retention time of burnt flue gas generated by the blast type gas burner under the rated thermal load working condition in the hearth is more than 1 s.

7. The round bottom, flat bottom vessel heating apparatus with flue gas recirculation of claim 1, wherein: the heating device also comprises a smoke exhaust tube, and a smoke exhaust port of the hearth is communicated with the smoke exhaust tube; the heating device also comprises an adjusting valve, and the adjusting valve is arranged on the flue between the smoke outlet and the smoke exhaust tube or on the smoke exhaust tube.

8. The round bottom, flat bottom vessel heating apparatus with flue gas recirculation of claim 7, wherein: the heating device further comprises an annular flue, the annular flue surrounds the hearth, a plurality of smoke outlets are uniformly formed in the hearth along the circumference, the smoke outlets are communicated with the annular flue, and the annular flue is communicated with the smoke exhaust tube.