Liu Junwei 1Remington 1, Liu Jingwei 2Li Zifeng 1, Yang Shuhua1
(1. Institute of Energy Research, Henan Academy of Sciences, Zhengzhou 450008, China; 2. 1 Middle School, Chengguan Town, Fugou County, Henan Province, 461300)
Abstract: The newly designed medium-sized desorption biomass gasifier power supply system was used to study the actual needs of users, especially the relationship between the air supply and the firepower, the relationship between the biomass density and the gasification intensity The relationship and the fastest start-up mode, the best way to seal the fire and other tests, the test results for the gasifier to provide efficient operation and further improve the basis.
Biomass gasification - combustion system uses the first gasification and combustion after the way to use biomass fuels, because the combustion part of the biomass gas is burned, so full combustion does not produce black smoke, does not require dust removal device, and the load adjustment range , Can also be stored and transported, the use of flexible and convenient.Usually use the boiler to directly burn biomass, the fuel thermal efficiency is usually only 15%, the use of biomass gasification 2 combustion, because the biomass can be fully gasified, low residual carbon content in technical ash, Biomass resource utilization efficiency can be increased to about 70%. Down-suction gasifier is a traditional biomass gasification unit that can provide energy for small-scale production, but also suitable for heating the residents, and its characteristics are also compared In line with China's national conditions, there is a good prospect of application, of course, there are still many shortcomings and deficiencies of this device, to be improved and perfected.This paper will design a new gasification based on conventional subsonic gasifier Stove, and put it with the gas device to form a complete combustion system of biomass energy, the gas some of the key operating parameters of the test to explore the measures to achieve the desired effect.
1 system design
1.1 gasification characteristics
The use of gasification under the suction, particulate fuel in the gasifier from top to bottom to form a dry layer, oxide layer, the reduction layer, the ash layer: near the air inlet due to adequate air mainly formed oxide layer; volatile has been precipitated Unburned particles form a reduction layer in the lower part of the pellet fuel through the volatile precipitation, oxidation, reduction and ash and other processes, the final formation of burned white ash. As the reaction progresses, the fuel flows down gradually, the gas produced by Grate delivery to the pipeline, the ash generated by gasification through the rocker periodically discharged into the ash silo .During the operation, the formation of a stable reaction layer is a reliable guarantee gasifier normal gas production.Insulating the furnace not only affects the thermal efficiency of the system, But also played a decisive role in the quick start-up and steady operation of the gasifier[1, 2].
1.2 Structure and parameters
The traditional desiccant gasification adopts the method of evacuation. When the gasifier operates under negative pressure, some acidic substances contained in the high-temperature gas generated by the gasification tend to cause corrosion to the fan, and the content of tar in the gas is high, which may easily cause In order to prevent pipeline blockage, the newly designed gasifier adopts the positive pressure mode to change the ventilation to blower, while the open feeding port is changed to airtight.In order to make the air inlet more evenly distributed, the 4 A mouth to 8 mouth to avoid the oxide layer at the slagging affect the operation of the gasifier. Insulation using three layers, the innermost refractory layer, the middle perlite, furnace body and then coated with insulation paint layer, you can gasification The surface temperature of the furnace is kept below 50 DEG C. The gasification and combustion system is mainly composed of a gasifier, a conveying pipe, a gas burner and a control cabinet. In order to prevent the tar in the gas from precipitating, the conveying pipe is also wrapped with heat preservation material, as shown in FIG. 1 Gasifier related parameters in Table 1.
1.3 device performance and the use of results
The newly designed biomass gasification plant, after the test run, the results show that the performance is good, especially the use of high-temperature gas direct-fired technology and insulation technology, high thermal efficiency, the gasification process is no precipitation of tar clean gas as the heating pot, Stove, boiler fuel is very suitable for the urban environment of the higher urban hotels, guesthouses, bathing and other industries.
(1) High thermal efficiency of biomass fuel utilization The gas produced by the gasification device designed and developed in this paper can be used without direct cooling technology to reduce the waste of thermal energy. The thermal efficiency can reach more than 75% Gasifier higher than 20%, the gas calorific value of more than 30% higher than the average gasifier.
(2) stable operation Gasification plant operating conditions stable, resulting in stable gas composition and calorific value.
(3) start fast, a long time to feed the gasification device start fast, you can start within 3min is completed, plus one can be the longest continuous use of materials 4h.
(4) Convenient Control and Adjustment The quantity of air supply and air supply have a good linear relationship over a wide range. The air volume can be directly controlled by adjusting the supply air volume. The control system is designed to be simple, reliable and reliable.
(5) It is convenient to seal the fire to finish the sealing fire within 1min. As the gasifier strengthens the insulation in the design, less heat loss after the shutdown. The sealing time can last more than 5 days.
(6) Convenient configuration Gasification unit can be separated from the gas unit, and the gas of the gasification unit can be delivered to the gas unit within a distance of 30m by pipelines. According to user needs, a gasifier can also be used Driven by two pipes two combustion equipment.
(7) secondary tar-free pollution, high combustion efficiency As the gasification gas purification without purification, tar burning with the gas, it will not only increase the calorific value of gas production, but also to avoid gas pipeline plug, tar bring The secondary pollution has been solved.
2 Operational Optimization Experimental Analysis
In order to make the system achieve the optimal operation effect and provide a reference for the improvement of the system, the research group used the experimental method to study the relationship between the amount of air supplied by the newly designed and developed gasification unit and the size of the firepower, Gasification strength and the relationship between the gas composition and air equivalence ratio produced by the research and the best way to start and seal the fire were explored.Particle fuel used in the experiment made from corn stalks for the wind by Roots The fan provides the air volume measured by the rotor flowmeter; the fire intensity and the gasification efficiency are measured by a positive balance method, that is, the ratio of the effective utilization of the gasification gas to the input heat of the gasifier.
2.1 air equivalence ratio and firepower, gasification efficiency of the relationship between
Gasification device is running, the gasification intensity of the furnace unit is the unit of cross-sectional area of gas produced, the size and the amount of air supply is closely related to the operation to master the appropriate amount of air supply is very important if the air supply is too small, The gasification rate of biomass fuel will be too slow, resulting in the furnace firepower is not strong, gasifier gasification efficiency will be very low; if the air supply is too large, the biomass fuel gasification will be too strong, leading to gas Although the internal heat of the furnace is intensely gathered or even slagging, the fire power in the furnace is not necessarily strengthened correspondingly although the fuel consumption is greatly increased, and the gasification efficiency of the gasifier is not necessarily high. The air supply is adjusted to the suitable fire intensity and the maximum thermal efficiency Also higher [3]Adjusting the different operating conditions and measuring the fire intensity, the results in Figure 2 and Figure 3 are obtained.
As can be seen from Figure 2, when the air supply is less than 14m3 / h (converted to air equivalence ratio less than 0.23), the fire intensity increases with the increase of air supply, but after exceeding 14m3 / h, For the large amount of wind, fire intensity growth slowed down, the curve tends to be straight.As can be seen from Figure 3, when the air equivalence ratio is 0.22 near the highest gasification efficiency, indicating that the energy of biomass feedstock has been the largest in the furnace Limited to the export of gas.
2.2 The relationship between biomass density and gasification strength
Unformed biomass fuels have low bulk energy density and are not easily transportable and stored over long distances and are therefore generally compressed into pellets, lumps, or rods to fit large-scale applications [4]Due to the compression process or for other reasons, there will be differences in the density of the formed fuel, and this difference will also affect the gasification effect.Three kinds of forms with different densities of the pellets and the lump fuel are used in the experiment. 4 is the fire intensity that can be achieved in the same gasifier with various biomass-forming fuels; Figure 5 shows the continuous operating time that can be achieved for each fuel, the length of time reflecting the stability of the gasifier operation .
It can be seen from the figure that the gasification intensity of the pellet fuel used as the raw material gasification unit is higher than that of the lump and the continuous running time is longer than that of the lump. This is because the lump fuel has the advantages of large volume, large porosity and density The same shape of the molding fuel, the gasification effect is the density of the density is better than the density of Practice shows that the use of qualified particulate fuel, the newly developed gasifier can start running continuously. This is because the compact particles have good fluidity. As the reaction progresses, the pellet fuel layer can move down slowly by its own gravity, and the following oxide layer and reduction layer are added to ensure gasification stability.
2.3 start-up mode
In addition to operating characteristics, rapid start-up of gasifiers is also one of the key technologies for gasification systems because the cold start performance of the gasification plant affects the environmental pollution at startup and ease of use. Incomplete heating value can not be burned, only venting, polluting the surrounding air environment, so the gasification device startup time is as short as possible; short start-time gasification device can quickly reach a stable state of gas production, also Easy to use gasifier. Gasifier in the cold start, the general should first use wood and other combustible material oven, oven temperature and time directly affect the start-up effect .Figure 6 is the oven time and the starting gas Time of the test results, the trial to stop each time after the oven to add wood, enter the start state to join the particulate material and start timing, start the initial gas is not flammable, until the gas is completely combustible start to end into normal operation .
As can be seen from the figure, the longer the oven time, the shorter the start-up time. Therefore, in practice, in order to shorten the startup time and reduce the emission of exhaust gas, warm-up should be sufficiently heated before starting.
2.4 fire way
The sealing performance also affects the usability of the gasifier. Similar to a coal-fired stove, a small amount of air needs to be injected into the biomass gasifier to maintain the temperature in the furnace. Natural air drawn into the air, and add the valve to adjust the amount of air into the furnace.The main factors affecting the sealing performance is the introduction of air and raw materials in the furnace, the effect of insulation also indirectly affect the sealing performance.
The test found that the gasifier in the furnace during the sealing of raw materials if too much, a large number of raw materials in the precipitation of water will make the gasifier within the condensation of water, leading to the next furnace can not be started normally; However, raw materials If not enough, it can not provide enough heat for the gasifier during the sealing period.The results show that for the gasifier with the inner diameter of 400mm, the best raw material allowance in the furnace is 5 ~ 7kg if it is sealed for 10h. The amount of air introduced into the furnace during the fire sealing also has a great effect on the sealing effect.If the amount of air is too large, the raw material will burn out in advance and lead to flameout. If the amount of air is too small, the heat generated in the furnace will not be enough to maintain the furnace temperature, The system adopts DN20 venting valve when the fire is sealed, and the test results show that the opening degree is between 70% and 80%.
3 Conclusion
In this paper, the design and development of medium desorption biomass particle positive pressure gasifier, using a positive pressure operation, the gas does not need cooling to purify the direct combustion, while strengthening the insulation, so the thermal efficiency, no secondary pollution.Through testing to explore the gasification Optimization of furnace operation, the results show that:
(1) Adopting the method of high temperature and direct combustion of gasification gas has greater superiority, the tar does not precipitate, and the secondary pollution is solved;
(2) When the air equivalence ratio is between 0.22 and 0.23, the fire intensity is larger and the gasification efficiency is the highest at this time;
(3) The gasification intensity is the highest when dense granular fuel is used and the operation of gasifier is the most stable. Because of its large porosity and poor fluidity, low-density formed fuel, scrap or large-scale shaped fuel are not suitable for use.
(4) With the correct method of operation, this gasification power supply system can be quickly started, and can achieve the seal fire.
references:
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