CN101319781A - Combustion of ultra-low concentration combustible gas and its thermal energy cascade utilization system - Google Patents

Abstract

The invention relates to an ultra-low-concentration combustible gas combustion and its thermal energy cascade utilization system. The electromagnetic valve and the pipeline form a gas path with periodic changes in the gas flow direction, and are connected to a combustion chamber with a built-in heat storage medium and a heat exchanger; heat is transferred in the gas It is realized between heat storage medium and heat exchanger. When the heat storage medium is loaded with different catalysts, a lower light-off temperature can be achieved; when the amount of heat storage medium is sufficient, a higher gas preheating temperature can be achieved; by changing the number of catalysts and heat storage medium, a higher temperature can be achieved. High working temperature and lower combustion concentration limit, and better gas adaptability and load regulation can be achieved by changing the type of catalyst and the reversing cycle of the solenoid valve. Utilization of high-grade heat energy can be achieved by exchanging heat between the working fluid in the built-in heat exchanger and the high-temperature gas after combustion or using the high-temperature flue gas after system reaction; by reducing the exhaust gas temperature of the final product, the utilization of low-grade heat energy can be realized .

Description

Combustion of ultra-low concentration combustible gas and its thermal energy cascade utilization system

technical field

The invention belongs to the technical field of combustion equipment, and in particular relates to the combustion of coal mine ventilation gas and its thermal energy cascade utilization system.

Background technique

Gas is the biggest safety hazard in coal mining. It is a mixture of various gases based on methane (CH4); among them, gas with a methane concentration of 85% has a calorific value of 34.6MJ/m3. According to statistics, the death rate per million tons of coal in my country was about 3 in 2004, which is more than 100 times that of the United States and more than 10 times that of India. More than 95% of them died in accidents caused by gas explosions, which caused huge losses to the normal production of coal mines.

In the mining of coal mines, in order to prevent gas explosion, the method of ventilation and dilution is usually adopted to control the concentration of gas below 1%. This part of gas is called ventilation gas. Ventilation gas is also a kind of low-grade energy with huge reserves. The ventilation gas with a methane concentration of 1% has a theoretical combustion temperature of 265°C. Although the concentration of gas in ventilation gas is only about 1%, it causes huge waste of energy due to the huge discharge. According to the survey conducted by the US EPA (Environmental Protection Agency), the global VAM (Ventilation Air Methane) emissions in 2000 were 16.6Bm ³ , and China's VAM emissions were 6.5Bm ³ , accounting for 39.2% of the total. It is estimated that CH ₄ emissions will increase to 28 million tons in 2010, of which 70% (90% in China) comes from coal mine ventilation gas with CH ₄ concentration below 1%. According to the national mine gas survey conducted in China in 1996 and 2000, the amount of ventilated gas was 10.6 billion m ³ and 9.6 billion m ³ respectively, ranking first in the world, and the low calorific value of the gas contained was equivalent to 33.7 million tons of standard coal If this part of resources can be developed and utilized as energy, it will play a non-negligible role in ensuring China's energy security.

In addition, a large amount of combustible gas discharged from steel production and petrochemical processes is usually directly emptied or discharged after combustion, and its heat energy is wasted and not fully utilized.

China's "Industrial Safety and Environmental Protection" (2002, 28 (3)) introduced the working principle of the Thermal Flow Reversal Reactor (TFRR). The reactor is divided into three parts: upper, middle and lower, and the middle part is a heat exchanger. The upper and lower parts are heat exchange layers made of quartz sand or ceramic particles that can efficiently store and transmit heat. At the beginning of operation, the electric heating element is used to preheat the heat exchange layer to reach the temperature required for ventilation gas combustion, which is above 1000°C, and then the ventilation gas is introduced, and the ventilation gas flows through the heat exchange layer on one side. It is preheated and reaches the temperature required for combustion to undergo an oxidation reaction, releasing heat and continuing to flow. Part of the heat is released when it flows through the heat exchanger layer, and then reaches another heat exchange layer and releases most of the heat, storing the heat of the combusted gas to maintain the overall temperature in the combustion chamber. As time goes by, the high-temperature section in the reactor will continue to shift to the outlet side, and the temperature of the heat exchange layer on the inlet side will continue to decrease. In order to maintain stable combustion, it is necessary to flow the gas from top to bottom or Switch from bottom to top to ensure that the high temperature section in the reactor fluctuates back and forth in the middle of the reactor. In order to improve the thermal energy utilization efficiency of the reactor, it is necessary to control the switching time of the flow direction within a reasonable range. If the switching time is too short, it means that the heat exchange time of the reactor is too short, and the inlet air temperature cannot be preheated to the combustion temperature; if the switching time is too long , the high temperature section is too far away from the center, most of the heat released by the combustion products will not be absorbed by the heat exchange layer, and the exhaust gas temperature is too high, both of which are likely to cause the reactor to flame out.

Since the TFRR uses quartz sand or ceramic particles, the pressure drop is relatively large when the gas flows through it, and sometimes special pressurization equipment is required to overcome the pressure drop along the way, which increases the complexity and investment cost of the system. At the same time, due to the poor heat transfer performance of quartz sand or ceramic particles, it takes a long time for the airflow to change direction, which results in a small processing capacity. In addition, because TFRR only utilizes the heat energy released by the high-temperature reaction gas, and does not recover the low-grade heat energy in the exhaust smoke, the energy utilization efficiency is not maximized.

The Catalytic Flow Reversal Reactor (CFRR) developed by the Canadian Center for Mineral and Energy Technology Research (CANMET) has basically the same structural design and operation mode as TFRR, and uses catalysts to reduce the ignition temperature of ventilated gas. However, the shortcomings of CFRR, such as the addition of special booster equipment, small processing capacity, and not maximized energy utilization efficiency, still exist due to the use of quartz sand and ceramic particles. In addition, since the CFRR adopts the design method of separating the catalyst and the heat storage medium, it is difficult to replace the catalyst and the gas adaptability is poor.

The two-way countercurrent coil reactor invented by Hu Pengfei of the University of Science and Technology of China uses the heat exchange between the reacted gas and the pre-reacted gas to achieve the purpose of preheating the intake air and reducing the exhaust gas temperature. Although the structure is simple and the cost is low, it is There are disadvantages such as poor adaptability to gas types and concentrations, complicated modification, and high cost. And this invention is only a kind of combustion reactor, does not propose the comprehensive utilization plan of thermal energy.

The reciprocating porous medium combustion high-temperature air generation system invented by Cen Kefa of Zhejiang University and others can also achieve the purpose of enhanced combustion and low pollutant emissions. But it is characterized in that the burner and the heat storage medium are divided into two independent parts, and the heat storage medium only plays the role of storing part of the heat energy of the high-temperature flue gas. The combination of porous media combustion and heat storage to generate high-temperature air is realized by gas circulating and switching between the heat storage medium on both sides and the burner. However, this design method will increase the control complexity of the system, and has higher requirements on the thermal insulation and construction of the system, and has not realized the cascade utilization of heat energy.

Deng Yangbo and Xie Maozhao invented the porous medium superadiabatic combustion device under reciprocating flow, although it can also realize the self-sustaining combustion of rarefied gas. But its principle is that it is only suitable for combustible gas with relatively high concentration. After being ignited by the igniter, the self-sustaining combustion of rare gas can be realized by gradually reducing the gas flow. It is not suitable for ultra-low concentration combustible gases that cannot be ignited and burned.

Chen Yiliang and others invented the methane oxidation device for coal mine exhaust air, although its structure is similar to the present invention, but its principle is based on traditional oxidation reaction, which is different from the present invention based on catalytic reaction. And it doesn't say whether it can only be applied to coal mine exhaust air or any low-concentration combustible gas.

Contents of the invention

The invention provides an ultra-low-concentration combustible gas combustion and its heat energy cascade utilization system, which can not only burn the ultra-low-concentration combustible gas, but also utilize the heat energy generated by it in cascades.

Technical scheme of the present invention is realized like this:

The fan is connected to the flow control valve through the pipeline; the flow control valve and another flow control valve are connected to the concentration monitoring meter; the concentration monitoring meter is connected to the first solenoid valve and the second solenoid valve; the first solenoid valve is connected to the second solenoid valve The third solenoid valve is connected with the fourth solenoid valve; the time relay is connected to control the first solenoid valve and the third solenoid valve; the time relay is connected to control the second solenoid valve and the fourth solenoid valve; the first solenoid valve, the second solenoid valve, The third solenoid valve and the fourth solenoid valve are connected to the reactor; the reactor has a built-in electric heating element and another electric heating element, a honeycomb porous heat storage medium with a catalyst, a temperature measuring thermocouple bundle, a heat exchanger; a preheating recovery device It is connected with the heat exchanger, the third solenoid valve and the fourth solenoid valve.

The honeycomb porous heat storage medium with catalyst is selected from single components or mixed materials including high alumina bricks, silica bricks, composite silicon carbide, magnesia bricks, corundum, kaolin, cordierite or andalusite, which can withstand a temperature of 1000°C ~1800°C heat storage material, and there are uniform through holes of any shape to facilitate the flow of gas.

The electric heating element is a built-in electric heating rod or an electric heating belt that uniformly heats the honeycomb porous heat storage medium loaded with catalyst.

Because the present invention adopts the honeycomb heat storage medium with catalyst, on the one hand, due to the existence of honeycomb through holes, the pressure loss during gas flow is reduced, and the system can be directly installed at the ventilation shaft of the mine or in the iron and steel chemical industry. Exhaust outlet, no need for special booster equipment. On the other hand, due to the use of porous honeycomb heat storage medium, the heat transfer efficiency between gas and solid is greatly improved, which improves the processing capacity of the system.

Because the catalyst is loaded on the inner wall of the through hole of the honeycomb heat storage medium in the present invention, the specific surface area is increased due to the presence of pores on the inner wall, the loaded amount of the catalyst can be increased, and the catalytic combustion efficiency can be further improved. At the same time, due to the adoption of the overall supported catalysis, the adaptability to the type and concentration of the gas is greatly improved. If the type of gas changes, only the heat storage medium with the catalyst needs to be replaced, which saves the transformation time and cost.

Since the present invention adopts the honeycomb heat storage medium loaded with catalyst, if it is desired to achieve a higher working temperature and further reduce the concentration limit of combustion, it only needs to increase the amount of heat storage medium; at the same time, it can also be achieved by changing the type of catalyst The purpose of reducing the concentration limit of combustion.

Because the invention can not only utilize the high-grade heat energy in the middle of the reactor, but also recover the low-grade heat energy of the flue gas at the tail to preheat the working medium of the built-in heat exchanger or provide hot water, thereby realizing the purpose of cascaded utilization of heat energy.

The honeycomb catalytic heat storage medium and heat energy utilization scheme adopted by the system of the present invention can not only achieve the purpose of achieving higher working temperature and lowering the concentration limit of combustion, but also achieve cascaded utilization of heat energy. The system of the invention has good adaptability to gas types and concentrations, low modification cost, and convenient and quick modification means. The system of the invention is suitable for ultra-low concentration combustible gases including coal mine ventilation gas, natural gas, marsh gas, oil layer gas, blast furnace gas and combustible waste gas in steel and petrochemical production.

Description of drawings

Figure 1 is a schematic structural view of the present invention with a heat exchanger in the middle of the reactor and a waste heat recovery device at the tail.

Fig. 2 is a structural schematic diagram of extracting part of the high-temperature flue gas in the middle of the reactor for work and installing a waste heat recovery device at the tail of the present invention.

The present invention will be further described in detail below in conjunction with the accompanying drawings.

Detailed ways

As shown in Figure 1, its system mainly includes:

The fan 1 is connected to the flow control valve 2 via a pipeline; the flow control valve 2 and another flow control valve 3 are connected to the concentration monitoring meter 4; the concentration monitoring meter 4 is connected to the first electromagnetic valve 5 and the second electromagnetic valve 6; the first The solenoid valve 5 is connected to the second solenoid valve 6; the third solenoid valve 11 is connected to the fourth solenoid valve 12; the time relay 13 is connected to control the first solenoid valve 5 and the third solenoid valve 11; the time relay 14 is connected to control the second solenoid valve 6 and the fourth solenoid valve 12; the first solenoid valve 5, the second solenoid valve 6, the third solenoid valve 11, and the fourth solenoid valve 12 are connected to the reactor 15; the reactor 15 has a built-in electric heating element 7 and another electric heating element Component 8, honeycomb porous heat storage medium 9 loaded with catalyst, temperature measuring thermocouple bundle 10, heat exchanger 16;

The electric heating elements 7 and 8 adopt built-in silicon carbide rods. The heat exchange wall 16 adopts a water-cooled wall on the inner wall in the middle of the reactor, the waste heat recovery device adopts a shell-and-tube heat exchanger, and the honeycomb porous heat storage medium is extruded with andalusite. The through-hole size is 2mm×2mm, and the wall thickness is 1mm. Honeycomb heat storage medium, the catalyst is Ce-Zr-Mn-O solid solution catalyst prepared by sol-gel method, and it is loaded on the inner wall of the through hole of the heat storage medium by impregnation-roasting method.

When in use, first start the electric heating elements 7, 8 to heat the honeycomb porous heat storage medium 9 above the catalytic light-off temperature of the combustible gas, and keep it for a certain period of time according to the temperature data measured by the temperature measuring thermocouple bundle 10 to ensure that the entire The temperature in the reactor was uniform and constant, after which the electric heating element was turned off. If the temperature in the reactor is lower than the catalytic light-off temperature during the working process of the reaction system, the electric heating element can be used again for thermal compensation.

The combustible gas enters the gas supply pipeline through the flow valve 3, and the concentration is controlled by the concentration monitoring meter 4. When the amount of air contained in the combustible gas is insufficient, the combustible gas can be burned to the required amount by controlling the air flow in the fan 1. Make up the amount of air (the amount of supplemented air varies with the difference of the combustion air required by the combustible gas) to ensure the stable operation of the entire reaction system.

Taking the flow direction of combustible gas from top to bottom as an example, at this time, the solenoid valves 5 and 12 are opened, and the solenoid valves 6 and 11 are closed. The gas flows into the reactor 15 through the electromagnetic valve 5. At this time, the gas temperature is lower than the temperature of the honeycomb porous heat storage medium 9. As the gas flows downward, the upper honeycomb porous heat storage medium 9 is gradually cooled, and the gas temperature continues to rise. When it rises to the catalytic light-off temperature, the gas undergoes a catalytic combustion reaction and releases heat. At this time, part of the heat is absorbed by the water-cooled wall in the middle, and the preheated working fluid in the water-cooled wall is heated and passed to the generator set to generate electricity. The gas continuously flows downward and releases heat. At this time, the gas is continuously cooled, and the lower honeycomb porous heat storage medium 9 is continuously heated until it flows to the solenoid valve 12 through the outlet. Because the exhaust gas temperature still has some low-grade heat energy at this time, a waste heat recovery device 17 heat exchanger can be added at the end to preheat the working fluid entering the water-cooled wall in the middle of the reactor to recover this part of heat energy. Finally, the exhaust gas is evacuated through a shell-and-tube heat exchanger.

As the reaction continues, the temperature of the honeycomb porous heat storage medium 9 at the entrance will continue to decrease, the temperature of the honeycomb porous heat storage medium 9 at the exit will continue to rise, and the high temperature zone of the reaction will shift from the middle to the exit. After the offset reaches a certain level, it is possible that the incoming gas cannot be preheated to the catalytic light-off temperature or the heat released by the gas cannot be absorbed by most of the lower honeycomb porous heat storage medium 9, resulting in the flameout of the entire reaction system. Therefore, it is necessary to switch the flow direction of the gas through the time relay controllers 13 and 14 to ensure that the high temperature zone of the reaction is periodically shifted in a certain area in the middle of the reactor 15 .

Similarly, when the gas flows from bottom to top, the solenoid valves 6 and 11 are opened and the solenoid valves 5 and 12 are closed, and the working process of the system is the same as above.

When stopping work, first cut off the air supply, and then use the fan to blow the entire system for 5 minutes.

The system shown in Figure 2 mainly includes:

Combustible gas supply pipeline, fan 1, flow control valve 2, 3, concentration monitoring meter 4, first, second, third, fourth solenoid valve 5, 6, 11, 12, time relay controller 13, 14 , electric heating elements 7, 8, honeycomb porous heat storage medium 9 loaded with catalyst, temperature measuring thermocouple bundle 10, reactor 15, waste heat recovery device 17, gas turbine 18.

The gas combustion process is the same as that of the system shown in Figure 1, the difference is that in the high-temperature reaction zone in the middle of the reactor 15, 50% to 70% of the high-temperature flue gas is extracted to the gas turbine 18 for power generation, and the remaining gas is used for The lower part of the honeycomb porous heat storage medium 9 is heated, and the exhaust gas heat energy is recovered through the shell-and-tube heat exchanger arranged at the tail to provide domestic hot water. The air extraction ratio in this system cannot be too large or too small. If the air extraction ratio is too large, the honeycomb porous heat storage medium 9 at the outlet cannot get enough heat compensation, which is not enough to heat the next intake air to the catalytic light-off temperature, causing the reaction system Turn off the flame; the air extraction volume is too small, the exhaust gas temperature is too high, and the waste heat recovery device at the tail is not enough to absorb all the heat, resulting in waste of heat.

When stopping work, first cut off the air supply, and then use the fan to blow the entire system for 5 minutes.

Because the composition of some gases will fluctuate to a certain extent, the required combustion air may be supplemented, so when the required air volume is insufficient, it may threaten the safe operation of the system, so it needs to be monitored through the concentration detection table 4 Data to control the air flow of fan 1 to ensure the stable operation of the whole system.

Since the present invention adopts the honeycomb porous heat storage medium 9 loaded with catalyst, it not only has strong heat storage capacity and high heat transfer efficiency, but also has good thermal shock resistance and long service life. Because the catalyst is attached to the inner wall of the through hole of the heat storage medium, there are a large number of capillary pores on the inner wall of the medium, which increases the specific surface area and improves the loading capacity of the catalyst. Catalysts for different gases can also be loaded at the same time, which enhances the adaptability of gas types. In addition, the maintenance and replacement of the system is also simple and easy. It only needs to change the type of heat storage medium or change the cycle of flow direction change, and the cost is low and the construction period is short.

In addition, the system of the present invention also utilizes the low-grade heat energy in the exhaust smoke, and also improves the overall heat energy utilization efficiency.

The system of the invention is designed for the current situation that the average concentration of methane in coal mine ventilation gas is between 0.1% and 1%. The recycling of this part of ventilation gas can not only realize the effective utilization of low-grade energy, but also receive great economic and environmental benefits through emission reduction in exchange for carbon sinks.

The system of the present invention is also applicable to any combustible gas that can catalyze the combustion system. These gases will not change the thermal properties of the intake airflow as fuel. Different combustible gases only have different ignition temperatures and calorific values. When the gas is not ventilated gas, only It is only necessary to change the type of the supported catalyst and change the preheating temperature of the heat storage medium, and the transformation cost is low and easy to implement.

Claims (3)

1. the burning of a super low concentration combustible gas and thermal energy step thereof utilize system, and this system comprises:

Blower fan (1) links to each other with flow control valve (2) via pipeline; Flow control valve (2) links to each other with concentration monitor table (4) with another flow control valve (3); Concentration monitor table (4) is connected with second magnetic valve (6) with first magnetic valve (5); It is characterized in that first magnetic valve (5) links to each other with second magnetic valve (6); The 3rd magnetic valve (11) links to each other with the 4th magnetic valve (12); The time relay (13) connects control first magnetic valve (5) and the 3rd magnetic valve (11); The time relay (14) connects control second magnetic valve (6) and the 4th magnetic valve (12); First magnetic valve (5), second magnetic valve (6), the 3rd magnetic valve (11), the 4th magnetic valve (12) link to each other with reactor (15); The honeycomb porous regenerator medium (9) of reactor (15) in-built electrical heating element heater (7) and another electrical heating elements (8), appendix catalyst, temperature thermocouple bundle (10), heat exchanger (16); Pre-heat reclamation device (17) links to each other with heat exchanger (16), the 3rd magnetic valve (11), the 4th magnetic valve (12).

2. the burning of super low concentration combustible gas according to claim 1 and thermal energy step thereof utilize system, it is characterized in that, the honeycomb porous regenerator medium (9) of appendix catalyst but select the one-component that comprises high-alumina brick, silica brick, complex silicon carbide, magnesia brick, corundum, kaolin, cordierite or andalusite for use or the heat-storing material of 1000 ℃～1800 ℃ of heatproofs that multiple material mixes, and exist uniform arbitrary shape through hole to make things convenient for gas to flow through.

3. the burning of super low concentration combustible gas according to claim 1 and thermal energy step thereof utilize system, it is characterized in that electrical heating elements (7,8) is built-in electrically heated rod or the heat tape that evenly heats the honeycomb porous regenerator medium (9) of appendix catalyst.

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