Coal mine low concentration gas heat accumulation utilization method

Abstract

The application discloses a coal mine low-concentration gas heat accumulation utilization method, and belongs to the technical field of coal mine gas treatment and utilization. The method comprises the following steps: after gas is pretreated by removing mist and dust, the gas enters a heat accumulation oxidation unit; the heat accumulation oxidation unit comprises at least two heat accumulation oxidation chambers, a first heat accumulation layer, a catalytic oxidation layer and a second heat accumulation layer are arranged in each chamber, and the heat accumulation layer is filled with composite heat accumulation bodies; heat internal circulation is realized by controlling the periodic switching of airflow through a reversing valve; when the gas concentration is lower than 1.2%, a heat supplement device is started to maintain the oxidation reaction; high-temperature flue gas generated in the reaction is sequentially subjected to gradient waste heat recovery through a high-temperature section heat exchanger and a low-temperature section heat exchanger; and finally, the flue gas is discharged after being subjected to white smoke removal. The application can suppress concentration fluctuation through the composite phase change heat accumulation material, and realizes efficient and stable oxidation of low-concentration gas and gradient utilization of heat energy by combining wide-concentration self-adaptive control and gradient waste heat recovery, so that the energy recovery efficiency is high, and the operation stability is good.

Description

Technical Field

[0001] This invention relates to the field of coal mine gas treatment and utilization, and in particular to a method for heat storage and utilization of low-concentration coal mine gas. Background Technology

[0002] my country has abundant coal mine gas resources, but the utilization rate of low-concentration gas (volume concentration below 6%) has long been low. The direct release of large amounts of low-concentration gas into the atmosphere not only wastes clean energy but also exacerbates the greenhouse effect.

[0003] Currently, the main technologies for utilizing low-concentration methane include regenerative thermal oxidation (RTO) and regenerative catalytic oxidation (RCO). However, existing technologies still have the following shortcomings in treating coal mine methane: (1) It has poor adaptability to fluctuations in gas concentration and flow rate. When the concentration is below 1%, the oxidation bed is difficult to maintain a self-sustaining reaction and requires a large amount of external heat energy. (2) Traditional regenerative oxidation devices use frequent reversing operations, which leads to large fluctuations in bed temperature. This not only reduces the heat recovery efficiency, but also shortens the service life of the heat storage body and catalyst due to alternating changes in thermal stress. (3) The gas often contains impurities such as dust and water mist, which can easily cause blockage of the heat storage body and poisoning of the catalyst, affecting the long-term stable operation of the unit.

[0004] Based on the above problems, an oxidation treatment and heat recovery method for coal mine extracted gas and ventilation gas with a concentration of 0.3% to 6% is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a method for the heat storage and utilization of low-concentration methane in coal mines, which can achieve stable oxidation of methane over a wide concentration range, improve heat recovery efficiency, and extend the service life of the device.

[0006] To achieve the above objectives, this invention provides a method for the thermal storage and utilization of low-concentration coal mine gas, based on a thermal regenerative oxidation system. The system includes a pretreatment unit, a thermal regenerative oxidation unit, a waste heat recovery unit, and an intelligent control unit arranged sequentially along the gas flow direction, and includes the following steps: S1. Gas Pretreatment: Low-concentration gas extracted from the coal mine first enters the pretreatment unit. After demisting, dust removal, and flame arresting, it enters the buffer tank. The gas concentration and flow rate are monitored online, and the monitoring signals are transmitted to the intelligent control unit. S2. Flow Direction Switching and Heat Storage: The pretreated gas enters the regenerative oxidation unit through the inlet pipe; the regenerative oxidation unit includes at least two regenerative oxidation chambers, each of which is sequentially provided with a first heat storage layer, a catalytic oxidation layer, and a second heat storage layer along the airflow direction; both the first and second heat storage layers are filled with a composite structure heat storage body, which consists of a honeycomb ceramic matrix and phase change heat storage microcapsules loaded on it; the gas flow direction is periodically switched by a reversing valve, so that the gas is preheated in the first heat storage layer and then enters the catalytic oxidation layer to undergo an oxidation reaction, and the generated high-temperature flue gas is discharged after releasing heat through the second heat storage layer; S3, Wide Concentration Adaptive Oxidation: When the gas concentration is below 1.2%, the intelligent control unit activates the heating device to supplement heat to the catalytic oxidation layer; S4. Cascaded waste heat recovery: The high-temperature flue gas discharged from the regenerative oxidation unit is sequentially passed through a high-temperature section heat exchanger and a low-temperature section heat exchanger for cascaded waste heat recovery. S5. Flue gas purification and emission: The low-temperature flue gas after waste heat recovery is discharged through the chimney after being treated to remove white residue.

[0007] Preferably, in S2, the method for preparing the composite structure heat storage body is as follows: first, paraffin / silica phase change microcapsules are prepared, then the phase change microcapsules are mixed with honeycomb ceramic powder and binder, and then extruded and sintered at high temperature to distribute the phase change microcapsules in the skeleton pores of the honeycomb ceramic.

[0008] Preferably, the phase change microcapsules have a particle size of 5~50μm, the core material is paraffin wax, the wall material is silicon dioxide, and the core-to-wall mass ratio is 7:3~8:2; the mass fraction of the phase change microcapsules in the composite structure heat storage body is 15%~30%.

[0009] Preferably, the high-temperature sintering is carried out under a nitrogen protective atmosphere, and the sintering temperature is 900~1100℃.

[0010] Preferably, the catalytic oxidation layer is supported on a non-noble metal oxide catalyst, and the active component is MnO. x -CeO2 composite oxide, wherein the molar ratio of Mn to Ce is 3:1 to 5:1, the support is γ-Al2O3, and the catalyst coating amount is 80 to 120 g / L.

[0011] Preferably, in step S2, the gas flow direction switching cycle is 60~180s, and the switching time is adjusted in real time according to the flue gas outlet temperature to keep the temperature distribution of the heat storage layer stable.

[0012] Preferably, the heating device is an electric heating element installed in the catalytic oxidation layer or a pre-embedded gas branch pipe, which supplements heat to the reaction zone to maintain the oxidation reaction temperature at 750℃~850℃; when the gas concentration is higher than 1.2%, the exothermic oxidation reaction can maintain self-sustaining operation.

[0013] Preferably, in step S4, the high-temperature heat exchanger uses molten salt as a heat carrier to reduce the flue gas temperature from 800~850℃ to 400~450℃. After absorbing heat, the molten salt is stored in a high-temperature molten salt tank and used to drive a steam turbine for power generation or to meet the high-temperature hot air requirements for antifreeze in coal mine shafts. The low-temperature heat exchanger uses water or thermal oil as a heat carrier to further reduce the flue gas temperature to 120~150℃, generating hot water or low-pressure steam for heating.

[0014] Preferably, step S1 further includes a gas concentration adjustment step: when the gas concentration is higher than 4%, air is mixed in to dilute the concentration to 1.5%~2.5%.

[0015] Preferably, the regenerative oxidation system includes: The pretreatment unit includes a demister, a filter dust collector, a flame arrester, and a buffer tank connected in sequence. The regenerative oxidation unit includes at least two regenerative oxidation chambers, a reversing valve group and a heat replenishment device. The regenerative oxidation chambers are provided with a first regenerative layer, a catalytic oxidation layer and a second regenerative layer. The waste heat recovery unit includes a high-temperature heat exchanger, a low-temperature heat exchanger, and a molten salt storage tank. The intelligent control unit includes a concentration sensor, a flow sensor, a temperature sensor, and a controller.

[0016] Therefore, the method for utilizing low-concentration methane heat storage in coal mines according to the present invention has the following beneficial effects: (1) By utilizing the heat storage / release characteristics of composite phase change heat storage materials, the temperature change of the bed caused by gas concentration fluctuations is mitigated. Combined with a heat replenishment device, stable oxidation of gas concentrations of 0.3%-6% can be achieved without the need for frequent replenishment of large amounts of fuel.

[0017] (2) By adopting asymmetric reversing control and cascade waste heat recovery, the waste heat recovery efficiency of flue gas can reach more than 90%, and the graded utilization of high, medium and low temperature heat energy can be realized to meet the diverse energy needs of coal mines.

[0018] (3) The composite structure heat storage body combines the high strength and low resistance of honeycomb ceramics with the high heat storage density of phase change materials, which reduces the temperature fluctuation during the switching process and extends the life of the heat storage body and catalyst.

[0019] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of Embodiment 1 of the present invention; Figure 2 This is a flowchart of Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the regenerative oxidation chamber of Embodiment 1 of the present invention; Figure label: 1. Pretreatment unit; 101. Demister; 102. Filter dust collector; 103. Flame arrester; 104. Buffer tank; 2. Regenerative oxidation unit; 201. First regenerative layer; 202. Second regenerative layer; 203. Catalytic oxidation layer; 204. Reversing valve assembly; 3. Waste heat recovery unit; 301. High-temperature section heat exchanger; 302. Low-temperature section heat exchanger; 303. High-temperature molten salt tank; 304. Steam generator; 4. Intelligent control unit. Detailed Implementation

[0021] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0023] The technical principle of this invention is as follows: through the conversion of "chemical energy to thermal energy," combined with two core mechanisms—heat storage and stabilization, and cascade recovery—low-concentration, unstable coal mine gas is transformed into stable, high-grade thermal energy resources. First, catalytic oxidation is used to convert low-concentration gas into thermal energy. Then, a composite phase change thermal storage body and flow direction switching are used to achieve stable heat storage and internal circulation. Finally, cascade recovery converts the heat into electrical and thermal energy, thereby transforming waste coal mine gas into a stable, clean, and high-value energy source.

[0024] Example 1 See Figure 1 A method for utilizing low-concentration methane heat storage in coal mines is based on a system comprising a pretreatment unit 1, a heat storage oxidation unit 2, a waste heat recovery unit 3, and an intelligent control unit 4.

[0025] Combination Figure 2 The process flow diagram shown illustrates that this method specifically includes the following steps: Step 1: Gas pretreatment.

[0026] Pretreatment unit 1 includes a demister 101, a filter dust collector 102, a flame arrester 103, and a buffer tank 104 connected in sequence. Low-concentration methane (concentration 0.8%, flow rate 200 m³ / h) from the coal mine extraction pipeline... 3The gas (methane concentration) first enters the demister 101 to remove liquid water, then enters the filter dust collector 102 to remove dust, and after passing through the flame arrester 103, it enters the buffer tank 104 for pressure buffering. A laser methane sensor and a vortex flow meter are installed on the outlet pipe of the buffer tank 104 to detect the gas concentration and flow rate in real time and transmit the signals to the intelligent control unit 4.

[0027] Step 2: Flow direction switching and regenerative oxidation.

[0028] The regenerative oxidation unit 2 includes two parallel regenerative oxidation chambers and a reversing valve assembly. The structure of each regenerative oxidation chamber is as follows: Figure 3 As shown, a first heat storage layer 201, a second heat storage layer 202, and a catalytic oxidation layer 203 are sequentially arranged along the airflow direction. The first heat storage layer 201 and the second heat storage layer 202 are filled with a composite structure heat storage body. This composite structure heat storage body uses cordierite honeycomb ceramic as a matrix, and phase change heat storage microcapsules are distributed in its pore structure. In this embodiment, the phase change microcapsules are paraffin / silica microcapsules with an average particle size of 20 μm, a core-to-wall mass ratio of 7.5:2.5, a phase change temperature of 650℃, and a latent heat of 120 J / g. The mass fraction of the phase change microcapsules in the composite structure heat storage body is 20%, and it is sintered at 1000℃ under nitrogen protection.

[0029] In the composite thermal regenerator, honeycomb ceramics serve as the framework, providing a large heat exchange area and structural strength, and are responsible for rapid heat transfer (sensible heat exchange). The phase change material (paraffin) encapsulated inside the phase change microcapsules absorbs a large amount of heat when the temperature is above 650℃, melting from a solid to a liquid state (storing "latent heat"), preventing the bed from overheating; when the temperature is below 650℃, the phase change material solidifies, slowly releasing the stored latent heat to replenish the heat and prevent the bed from cooling down too quickly.

[0030] Catalytic oxide layer 203 is supported with MnO x -CeO2 / γ-Al2O3 catalyst, with a Mn to Ce molar ratio of 4:1 and a catalyst coating amount of 100 g / L. When the pretreated gas flows through the catalytic oxidation layer, in the MnO... x - Under the action of non-precious metal catalysts such as CeO2, the activation energy of the reaction between methane and oxygen is significantly reduced. Methane undergoes a flameless oxidation reaction at a temperature of 750℃~850℃ to produce carbon dioxide and water, releasing a large amount of heat.

[0031] The intelligent control unit 4 controls the operating mode based on the real-time gas concentration. Upon initial startup, the electric heating element is first activated to preheat the catalytic oxidation layer 203. When the temperature reaches 600℃, gas is introduced. The gas is preheated to 300-400℃ by the first heat storage layer 201 and then enters the catalytic oxidation layer 203 to undergo an oxidation reaction, maintaining the reaction temperature at approximately 750℃. Since the current gas concentration is only 0.8%, below the self-sustaining oxidation threshold of 1.2%, the intelligent control unit 4 activates the electric heating element to supplement heat and maintain a stable temperature in the reaction zone.

[0032] The reversing valve assembly 204 switches the airflow direction every 120 seconds. Taking the first half-cycle as an example: when the reversing valve puts the first regenerative oxidation chamber in the air intake state, the second regenerative oxidation chamber is in the flue gas exhaust state; at this time, in the first regenerative oxidation chamber, the cold gas flows through the first regenerative layer 201, which has been heated in the previous cycle, and is preheated to the reaction temperature, and then enters the catalytic oxidation layer 203 to undergo an oxidation reaction. The generated high-temperature flue gas flows through the second regenerative layer 202, and its heat is transferred to the second regenerative layer 202 for storage. The cooled flue gas is discharged from the outlet of the first regenerative oxidation chamber; at the same time, the second regenerative oxidation chamber acts as a flue gas passage. The high-temperature flue gas discharged from the first regenerative oxidation chamber flows in the opposite direction through the second regenerative oxidation chamber, and exchanges heat with the heat storage body inside it. After further recovering the waste heat of the flue gas, it enters the waste heat recovery unit 3.

[0033] When switching to the second half-cycle, the functions of the two chambers are interchanged. The second regenerative oxidation chamber becomes the air intake state, and the first regenerative oxidation chamber becomes the flue gas exhaust state, thereby realizing the internal circulation and continuous treatment of heat.

[0034] Step 3: cascade waste heat recovery.

[0035] Waste heat recovery unit 3 includes a high-temperature heat exchanger 301 and a low-temperature heat exchanger 302. The high-temperature heat exchanger 301 uses molten salt (ternary nitrate, melting point 142℃) as the heat carrier to cool the flue gas to 420℃. After absorbing heat, the molten salt is stored in a high-temperature molten salt tank 303. The molten salt in the high-temperature molten salt tank 303 is pumped to a steam generator 304 to produce medium-pressure steam at 2.5MPa and 400℃, which drives a back-pressure turbine to generate electricity with a power output of approximately 500kW. The low-temperature heat exchanger 302 uses water as the heat carrier to further cool the flue gas to 130℃, producing 90℃ hot water for heating the mine area.

[0036] Step 4: Flue gas purification and emission.

[0037] The flue gas is finally treated by a de-whitening device before being discharged. Tests show that the methane concentration in the discharged flue gas is less than 0.01%.

[0038] Comparative Example 1 Conventional honeycomb ceramic heat storage medium (without phase change microcapsules) was used, and other conditions were the same as in Example 1. During operation, it was found that when the gas concentration fluctuated to 0.6%, the temperature in the reaction zone dropped below 650°C, requiring frequent activation of the heat replenishment device. Furthermore, the outlet flue gas temperature fluctuated by ±80°C during the reversal process, leading to instability in subsequent waste heat recovery parameters.

[0039] Example 2 The difference between this embodiment and Embodiment 1 is that the pretreatment unit 1 also includes a gas concentration adjustment device. When the incoming gas concentration is higher than 4% (5.2% in this embodiment), the intelligent control unit 4 controls the concentration adjustment device to mix in some air, diluting the gas concentration to 2.5% before it enters the regenerative oxidation unit, thus preventing the reaction zone from overheating. The remaining steps are the same as in Embodiment 1, and the operation is stable without any overheating.

[0040] Example 3 The difference between this embodiment and Embodiment 1 is that the supplementary heating device uses a pre-embedded gas branch pipe instead of an electric heating element. When the gas concentration is below 1.0%, a small amount of high-concentration gas (from a gas source around the mine) is introduced into the catalytic oxidation layer as supplementary combustion fuel to maintain the reaction temperature. This method has lower operating costs than electric heating and is suitable for mines with a stable high-concentration gas source.

[0041] Therefore, this invention provides a method for heat storage and utilization of low-concentration coal mine gas. By employing a composite structure of "honeycomb ceramic + phase change heat storage microcapsule" heat storage body, the latent heat storage / release characteristics of phase change materials are utilized to effectively mitigate drastic temperature changes in the bed caused by fluctuations in gas concentration. Combined with the adaptive heat replenishment strategy of the intelligent control unit, the system can operate stably within a wide concentration range of 0.3% to 6%, significantly improving the utilization rate of coal mine gas. Simultaneously, through a tiered waste heat recovery scheme combining high-temperature molten salt heat exchange and low-temperature water / heat transfer oil heat exchange, highly efficient tiered energy utilization is achieved, with a comprehensive waste heat recovery efficiency of over 90%, demonstrating significant economic, safety, and environmental benefits.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for utilizing low-concentration coal mine gas through heat storage, based on a heat storage oxidation system, the system comprising a pretreatment unit, a heat storage oxidation unit, a waste heat recovery unit, and an intelligent control unit arranged sequentially along the gas flow direction, characterized in that, Includes the following steps: S1. Gas Pretreatment: Low-concentration gas extracted from the coal mine first enters the pretreatment unit, and after demisting, dust removal and flame arresting, it enters the buffer tank, and the gas concentration and flow rate are monitored online. S2. Flow Direction Switching and Heat Storage: The pretreated gas enters the regenerative oxidation unit through the inlet pipe; the regenerative oxidation unit includes at least two regenerative oxidation chambers, each of which is sequentially provided with a first heat storage layer, a catalytic oxidation layer, and a second heat storage layer along the airflow direction; both the first and second heat storage layers are filled with a composite structure heat storage body, which is composed of a honeycomb ceramic matrix and phase change heat storage microcapsules loaded on it; the gas flow direction is periodically switched by a reversing valve, so that the gas is preheated in the first heat storage layer and then enters the catalytic oxidation layer to undergo an oxidation reaction, and the generated high-temperature flue gas is discharged after releasing heat through the second heat storage layer; S3, Wide Concentration Adaptive Oxidation: When the gas concentration is below 1.2%, the intelligent control unit activates the heating device to supplement heat to the catalytic oxidation layer; S4. Cascaded waste heat recovery: The high-temperature flue gas discharged from the regenerative oxidation unit is sequentially passed through a high-temperature section heat exchanger and a low-temperature section heat exchanger for cascaded waste heat recovery. S5. Flue gas purification and emission: The low-temperature flue gas after waste heat recovery is discharged through the chimney after being treated to remove white residue.

2. The method for low-concentration methane heat storage and utilization in coal mines according to claim 1, characterized in that, In S2, the method for preparing the composite structure heat storage body is as follows: first, paraffin / silica phase change microcapsules are prepared, then the phase change microcapsules are mixed with honeycomb ceramic powder and binder, and then extruded and sintered at high temperature to distribute the phase change microcapsules in the skeleton pores of the honeycomb ceramic.

3. The method for low-concentration methane heat storage and utilization in coal mines according to claim 2, characterized in that: The phase change microcapsules have a particle size of 5-50 μm and a core-to-wall mass ratio of 7:3-8:2; the mass fraction of the phase change microcapsules in the composite heat storage body is 15%-30%.

4. The method for low-concentration methane heat storage and utilization in coal mines according to claim 2, characterized in that: The high-temperature sintering is carried out under a nitrogen protective atmosphere at a temperature of 900~1100℃.

5. The method for low-concentration methane heat storage and utilization in coal mines according to claim 1, characterized in that: The catalytic oxidation layer is supported on a non-noble metal oxide catalyst, with MnO as the active component. x -CeO2 composite oxide, wherein the molar ratio of Mn to Ce is 3:1 to 5:1, the support is γ-Al2O3, and the catalyst coating amount is 80 to 120 g / L.

6. The method for low-concentration methane heat storage and utilization in coal mines according to claim 1, characterized in that: In S2, the gas flow direction switching cycle is 60~180s, and the switching time is adjusted in real time according to the flue gas outlet temperature.

7. A method for utilizing low-concentration methane heat storage in coal mines according to claim 1, characterized in that: The heating device is an electric heating element installed in the catalytic oxidation layer or a pre-embedded gas branch pipe.

8. The method for low-concentration methane heat storage and utilization in coal mines according to claim 1, characterized in that: In S4, the high-temperature section heat exchanger uses molten salt as the heat carrier. After absorbing heat, the molten salt is stored in a high-temperature molten salt tank for power generation or high-temperature heating. The low-temperature section heat exchanger uses water or heat transfer oil as the heat carrier to generate hot water or low-pressure steam for heating.

9. A method for heat storage and utilization of low-concentration coal mine gas according to claim 1, characterized in that: S1 also includes a gas concentration adjustment step: when the gas concentration is higher than 4%, air is mixed in to dilute the concentration to 1.5%~2.5%.

10. A method for heat storage and utilization of low-concentration methane gas in coal mines according to claim 1, characterized in that, The regenerative oxidation system includes: The pretreatment unit includes a demister, a filter dust collector, a flame arrester, and a buffer tank connected in sequence. The regenerative oxidation unit includes at least two regenerative oxidation chambers, a reversing valve group and a heat replenishment device. The regenerative oxidation chambers are provided with a first regenerative layer, a catalytic oxidation layer and a second regenerative layer. The waste heat recovery unit includes a high-temperature heat exchanger, a low-temperature heat exchanger, and a molten salt storage tank. The intelligent control unit includes a concentration sensor, a flow sensor, a temperature sensor, and a controller.

Images