Li Ya Meng 1, 2, Zhou snowflake 1, 2Hu Jianjun 1, 2Zhu Shengnan1, 2, Jingyan brilliant 1, 2Zhang whole country1, 2
(1. College of Mechanical and Electrical Engineering, Henan Agricultural University, Zhengzhou 450002, China; 2. Henan Provincial Center for Biomass Energy Collaborative Innovation, Zhengzhou 450002, China)
Abstract: In view of the current problems of low heat efficiency, insufficient fire intensity, incomplete combustion of air supply, and single function of biomass stoves, based on the demand for clean biomass pellet stoves by centralized feeding and cooking, Combustion of flames for combustion, set cooking, steaming rice, boil water, heating and other functions in one of the biomass particle direct-fired stove.Experimental performance test results show that: the cooking stove thermal efficiency of 42.9%, the overall thermal efficiency of 70.7% , The cooking intensity is 14.1kW, the flue gas emission index is lower than the national standard, and the burning of biomass particles is more adequate. It can provide scientific reference for the design and application of centralized feeding and cooking stove with biomass pellets as fuel.
introduction
Energy is the basis for economic development and social progress, but due to the limited and ever-depleting theoretical reserves of conventional energy, the development and utilization of renewable resources is imminent.As a renewable and environment-friendly energy, biomass energy is widely used Concerned. China has abundant crop straw resources. In 2015, the theoretical amount of crop straw was 1.04 billion tons, the amount of resources collected was 9.0 billion tons, and the utilized amount was 720 million tons, of which the utilization of straw fuel was 100 million tons (equivalent to 0.5 billion tons Standard coal), accounting for 11.4% of the amount of collectable resources [1]Straw biomass has high volatility, high carbon activity, low ash content and low S content. During the whole carbon cycle, CO 2Zero emissions and other advantages, is a kind of high-quality clean fuel.Therefore, straw biomass by direct combustion way, is its most simple and efficient fuel utilization[2- 4].
Due to the looseness and dispersibility of straw, it brings some problems to its storage, transportation and combustion [5], Using physical and chemical methods of sticking the straw, under high temperature and pressure or under the conditions of binder, compressed into granular or lumpy granular fuel with a certain degree of density [6- 8], Easy to transport and storage, high combustion efficiency [9- 10]In order to enable the use of granular fuel for the domestic stove, the government promoted the reform of the fuel-saving stoves, etc. However, through the analysis of the combustion process of the converted stove and the stove, the thermal efficiency was found to be about 20% Of the uneven fuel caused by incomplete combustion and flue gas emissions are not up to standard, at the same time there is a single function, not to achieve a variety of cooking and heating water and heating at the same time [11- 12]The stoves appearing on the market are mainly some small household stoves, which can not meet the demand of some collective catering units for the intensity of cooking and the functions of the stoves.Therefore, this article intends to design a system which can meet the needs of collective feeding, Cooking at the same time, but also to take into account the heating of biomass water supply biomass stove, and its operational performance assessment.
1 design basis
1.1 biomass pellet fuel combustion characteristics
The design of a biomass stove needs to incorporate biomass combustion characteristics.The essence of the biomass particle combustion mechanism belongs to the static osmotic pressure diffusion combustion [13- 14], The combustion process can be divided into dry dehydration, volatile analysis of combustion, coke combustion and burnout four stages[15- 17]:
① biomass particles in the combustion chamber, with the temperature increases, the water gradually evaporated.
② When the temperature of the combustion chamber rises to about 250 ℃, the volatiles will be analyzed. The volatile compounds will combine with oxygen and will burn into the transition zone and diffusion zone.
③ infiltration and diffusion combustion, coke combustion dominate the combustion of carbon monoxide on the surface of the particles, combustion sustained stability, high temperature.
④ burned gray shell continues to thicken, the basic burnout combustible material to form a whole gray shell, gray shell surface can not see the flame, the fuel turns dark red, the combustion process is over [18- 19]The corn straw particle fuel used in the experiment has a particle size of 5-15 mm, a length of 20-30 mm, a density of 800 kg / m 3, Industrial analysis and elemental analysis results shown in Table 1.
1.2 biomass pellet stove design principles
Because most of the centralized feeding requires cooking at cooking time, it can solve the problems of cooking, cooking and using hot water. According to the basic characteristics of burning biomass biomass fuel, the design of the stove should meet the following principles: ① easy to ignite and get angry Fast, stable combustion, complete, fire enough, the air can enter the furnace evenly and smoothly, not black smoke, high energy efficiency. ② complete functions, simple structure, easy to use, low cost, safe and reliable, practical and durable. ③ thermal efficiency High, thermal performance and stability.
2 biomass particles direct-fired stove design
2.1 overall structure
Combining the combustion characteristics of biomass pellet fuel and the needs of cooking, the design of biomass pellet direct-fired furnace structure is shown in Fig. 1, which is mainly composed of evaporator, combustion chamber, primary and secondary air intake fans, Hole, secondary charging carbonization warehouse and other components.
The stove adopts intermittent feeding, the fuel is fed from the charging port of the poly-fire mouth and the auxiliary silo, the auxiliary silo is designed to ensure that the cooking needs the fuel. When the fuel of the silo can not meet the needs of cooking, Of the feed inlet, the fuel will gradually slide into the furnace combustion. At the same time the combustion chamber can fuel the auxiliary silo drying and gasification, improve energy efficiency; using the ignition mode, the particles from top to bottom combustion; gray room In the lower part of the hearth, the grate is mounted on the ash tray of the drawer type. In front of the hearth, there is a No. 1 fan (12W) which can adjust the size of the primary air and the secondary air by adjusting the control knob on the fan Than in the fire outlet is set above the fire hole to observe the adequacy of the supply of air in the combustion process, and equipped with No.2 fan (12W) to achieve three times for the wind; set in the top of the furnace and the bottom of the pot in close contact with the stent Annular evaporator, the use of flame and flue gas on the evaporator heating, water from the inlet into the evaporator below, the evaporator and the stove outside the water level gauge connected to ensure that the amount of water intake, burning In the high-temperature steam generated from the evaporator outlet, high-temperature steam used to steam rice, porridge and hot water to achieve the cooking and steaming at the same time, shorten the cooking time, the steam outlet with steam Pressure valve, when the pressure exceeds the safety value, the pressure relief device automatically relief pressure. All parts of the device using die to complete the stamping, stretching, automatic cutting of materials, automatic round welding, furnace assembly using modular and assembly line assembly process , To ensure the unity of product quality and appearance.
2.2 Furnace design
The combustion characteristics of the biomass pellet fuel are required to ensure the uniformity of the supply air so that the upper and lower parts of the hearth are designed to be tapered.The size of the hearth is determined by the volumetric heat load of the hearth and the volumetric heat load of the hearth is too large, On the contrary, the furnace volume heat load is too small, the furnace volume is too large, burning decentralized, firepower is not concentrated because the stove is to meet the needs of centralized feeding, so the fuel consumption to take 9kg / h , The thermal efficiency of the stove take 0.65, the capacity of the stove heat load is generally 250 ~ 400W / m 3The design capacity of heat load take 380kW / m3[20].
Furnace volume is
2.3 into the wind sleeve design
For most biomass particle furnace insufficiency and inhomogeneity problem, designed a height of 19cm, the radius of 25cm circle on the non-structural mesh cone inlet sleeve, shown in Figure 2.
In the same level, with the same distance from the same size with the inlet hole, a time into the wind and the secondary air inlet are provided at the inlet cone set, so that the wind through the air inlet into the rotation of the furnace body to achieve Each air inlet ventilation uniformity, so as to ensure uniform fuel combustion. Primary air and secondary air supply is controlled by the 12W fan, the ratio between them through the fan on the control knob to control.
2.4 hanging fire height and poly crater design
Hanging height refers to the vertical distance between the bottom of the pot and the grate to burn the flame of the high temperature zone is up to the bottom of the pot is appropriate, according to biomass combustion characteristics of pellet fuel, generally small biomass furnace hanging height of 28 ~ 30cm [21], While the size of the pot will have a impact on the height of the fire, the design of the furnace height to take 40cm. Due to the choice of combustion of fuel layer combustion, will produce flammable volatile gases, the stove specially designed flare poly fire mouth (Φ14cm) , Is conducive to gathering flame, pulling up the height of the flame.
2.5 chimney cross-sectional area calculation
3 biomass particles of direct-fired stove performance test
3.1 test basis
According to the reference '22 ', the cooking efficiency of the cooking stove was tested, and the flue gas emission test of the stove was calculated by the method of reference 23. The overall test data was measured by on-line and on-site measurement.
3.2 test system
The main test equipment used is the test system of the main body of the furnace (including furnace, evaporator, flue, air duct, etc.), temperature test system (including thermometer and thermocouple), flue gas analyzer,
3.3 test and test equipment
2 buckets, each with a capacity of 0.01m 3XK3190A12E electronic floor scale, accuracy 10g; clock 1, the difference is less than 1min; anemometer, measuring range 0 ~ 10m / s, accuracy of 0.5m / s; nickel-chromium-nickel Silicon K type thermocouple, temperature range - 200 ~ 1200 ℃, KMQuintox 9106 flue gas analyzer.
3.4 Test conditions and methods
The test is carried out indoors, the ambient temperature is about 25 ℃, the relative humidity is less than 85%, the indoor wind speed is less than 1.0m / s, the test medium is normal temperature water, the test stove is far away from other heat sources, the fuel is corn straw molding fuel, For the dry cotton stalks, each test is carried out 3 times, find the average value.
3.5 Results and Analysis
The performance test data of the biomass particle stove are shown in Table 2.
Table 3 shows the test results of the thermal performance and flue gas discharge of the stove. The thermal efficiency of cooking of the biomass direct-fired stove reached 42.9%, higher than the efficiency of the ordinary household-use grain-fired stove [24- 25]The design of the annular evaporator effectively utilizes the heat carried by the external flame and the flue gas to improve the overall thermal efficiency of the cooker to 70.7% and the cooking fire intensity of 14.1kW, which meets the thermal efficiency (≥35%) of the national standard biomass cooking stove. , Cooking fire intensity (≥ 10kW) [26]The requirements of smoke SO 2The average mass concentration of 13.45mg / m 3, The average volume fraction of CO was 0.087%, the average concentration of NO was 103.27mg / m 3, NO 2The average mass concentration of 4.11mg / m 3, Greenman blackness is less than 1. Design of direct combustion particulate stove exhaust flue gas indicators are in line with relevant state regulations [23, 26], With good social and environmental benefits.
4 Conclusion
(1) The thermal efficiency of biomass burning stoves is 42.9%, the overall thermal efficiency is 70.7%, and the fire intensity of cooking is 14.1kW, which meets the requirements of biomass cooking stoves and can meet the needs of centralized food supply.
(2) The average mass concentration of NO in the exhaust of biomass particles direct-fired stoves was 103.27mg / m 3, NO 2The average mass concentration of 4.11mg / m 3, The average volume fraction of CO is 0.087%, SO 2The average mass concentration of 13.45mg / m 3, Flue gas Greenman blackness less than 1, are in line with the relevant provisions of the stove, to achieve clean combustion.
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