Methanation reactor heat exchange device and start-up method

Abstract

The application discloses a methanation reactor heat exchange device and a starting method. The device comprises a heat exchange type methanation reactor, a water heat exchange system and an inert gas heat exchange system. The heat exchange medium outlet of the heat exchange type methanation reactor is connected with the rising water inlet of the water heat exchange system through a first pipeline. The falling water outlet of the water heat exchange system is connected with the heat exchange medium inlet of the heat exchange type methanation reactor through a second pipeline. A third pipeline is branched from the first pipeline. The third pipeline is connected with the heat exchange medium inlet of the heat exchange type methanation reactor after passing through the inert gas heat exchange system. The device of the application is a novel methanation heat exchange system with double heat exchange processes and media, and solves the problems of high cost and long time of starting the heat exchange type methanation device.

Description

Technical Field

[0001] This invention relates to a heat exchange device for a methanation reactor and a start-up method thereon. Background Technology

[0002] Currently, both industrial coal gasification and coke oven gas-to-natural gas production employ adiabatic fixed-bed methanation processes. These processes require extensive circulation and steam replenishment to control the adiabatic temperature rise, resulting in very high total investment and water and electricity consumption, leading to poor economic efficiency. This is a major reason why coal gasification technology is difficult to promote on a large scale.

[0003] Heat exchange methanation technology, due to its advantages in equipment investment and operating costs, represents a breakthrough in addressing the poor economic viability of existing coal-to-gas technologies. Over the past decade, domestic companies such as Hangzhou Linda and Nanjing Dunxian have invested significant effort in the development of heat exchange methanation technology, obtaining corresponding intellectual property rights. Other organizations have also actively pursued related technological development. Overall, heat exchange methanation technology is currently still in the research and development and industrial demonstration stage.

[0004] CN103240036A discloses a heat exchange reactor resistant to thermal stress, its combined device and application. The invention adopts a coiled tube fixed bed heat exchange reactor with water or heat transfer oil as the heat exchange medium, and provides a solution to the problem of thermal stress in heat exchange from the structural aspects of the reactor shell and heat exchange components.

[0005] CN104645897A discloses a double-headed controllable water heat transfer reactor, which rationally arranges the heat exchange structure and medium flow direction, and utilizes the phase change heat of water in the heat exchange tubes to convert into steam to remove the reaction heat in the catalyst bed in a timely manner.

[0006] Shanghai Huaxi Company has independently developed a single-stage isothermal methanation technology. This technology employs a tubular fixed-bed reactor, using deoxygenated and demineralized water as the heat transfer medium. The deoxygenated and demineralized water flows through the shell side, while the catalyst is packed inside the tubes. Compared with multi-stage adiabatic methanation technologies from foreign companies such as LURGE, TOPOSE, and Davy, this technology reduces the number of adiabatic reactors by 2-3, steam generation systems by 3-4, and a large circulating compressor by 1, thus saving on investment and patent fees, and significantly reducing operating energy consumption. This technology has been industrialized in Qujing and Etuoke Banner.

[0007] Existing heat exchange methanation technologies all utilize a single heat exchange medium, such as water or heat transfer oil, to remove the heat generated during the methanation reaction and achieve catalyst bed temperature control. Current technologies focus on addressing the thermal stress of the equipment during the reaction process through reactor structural design and rational fluid flow arrangement, without considering the entire lifecycle of the unit, especially the problems encountered during start-up.

[0008] When starting up a methanation unit, the catalyst needs to reach a certain temperature to activate (typically 200-260℃), thus requiring external heat to heat the catalyst bed. For heat exchange methanation reactors, since the reactor is filled with catalyst and the heat exchange tubes or shell are filled with water, more heat is needed to simultaneously heat both the catalyst and the heat exchange medium to activate the catalyst. This increases the cost of the heating medium, and more importantly, extends the start-up time from 1-2 days for an adiabatic fixed-bed reactor to a week or even longer, directly leading to increased start-up and shutdown costs, longer operation times, and greater economic losses due to production delays. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of the prior art and provide a novel methanation heat exchange system with dual heat exchange processes and media, thereby solving the problems of high start-up costs and long start-up times for heat exchange methanation units.

[0010] This invention is achieved through the following technical solution:

[0011] A heat exchange device for a methanation reactor includes: a heat exchange type methanation reactor, a water heat exchange system, and an inert gas heat exchange system. The heat exchange medium outlet of the heat exchange type methanation reactor is connected to the rising water inlet of the water heat exchange system via a first pipe. The falling water outlet of the water heat exchange system is connected to the heat exchange medium inlet of the heat exchange type methanation reactor via a second pipe. A third pipe branches off from the first pipe and is connected to the heat exchange medium inlet of the heat exchange type methanation reactor after passing through the inert gas heat exchange system.

[0012] Furthermore, the heat exchange methanation reactor is a shell-and-tube or plate-and-shell reactor, preferably a shell-and-tube reactor, with a feed gas inlet and a product gas outlet. The area between the feed gas inlet and the product gas outlet is the shell side or tube side, and the area between the heat exchange medium inlet and the heat exchange medium outlet is the tube side or shell side. The feed gas inlet and the product gas outlet are connected to the catalyst in the reactor, and the catalyst is loaded in the shell side or tube side, while the heat exchange medium flows through a tube side or shell side different from the catalyst. The heat exchange medium is an inert gas and water, corresponding to an inert gas heat exchange system and a water heat exchange system, respectively. By switching between the water heat exchange system and the inert gas heat exchange system at different life stages of the device, the catalyst is quickly activated and the heat of reaction is removed.

[0013] Further, the water heat exchange system includes a steam drum. The rising water inlet of the steam drum is connected via a first pipe to the heat exchange medium outlet of the tube side or shell side of the heat exchange methanation reactor (usually located at the top or bottom of the heat exchange methanation reactor). The falling water outlet of the steam drum is connected via a second pipe to the heat exchange medium inlet of the tube side or shell side of the heat exchange methanation reactor (usually located at the bottom or bottom of the heat exchange methanation reactor). A first valve and a second valve are respectively installed on the first and second pipes. The first valve is preferably located between the point where the third pipe branches off from the first pipe and the rising water inlet of the steam drum. The diameter of the steam drum can be, for example, 1200-1600 mm, further 1300-1500 mm, preferably about 1400 mm; the length of the straight pipe section can be, for example, 3500-5000 mm, further 4000-4500 mm, preferably about 4000 mm; the wall thickness can be, for example, 24-30 mm, for example 25-28 mm, preferably about 26 mm; the total volume can be, for example, 6.5-8 m³. 3 Preferably about 7m 3 The total weight of the steel is 7.5-8.5t. The steam drum is equipped with a fresh water inlet connected to the fresh water input pipe and a steam outlet connected to the steam output pipe. The fresh water input pipe is preferably a fresh deoxygenated and desalinated water input pipe.

[0014] Furthermore, the inert gas heat exchange system includes an inert gas buffer tank and a compressor arranged sequentially on a third pipeline along the flow direction of the heat exchange medium, a third valve arranged between the buffer tank and the location where the third pipeline branches off from the first pipeline, and a fourth valve arranged on the third pipeline between the compressor and the heat exchange medium inlet of the methanation reactor of the heat exchanger.

[0015] Furthermore, the third pipeline enters the steam drum after passing through the third valve to preliminarily heat the water in the steam drum, and then exits the steam drum and connects to the inlet of the buffer tank. Preferably, the third pipeline merges with the second pipeline through an inert gas heat exchange system and is then connected to the heat exchange medium inlet of the heat exchange type methanation reactor.

[0016] The present invention further provides a driving method using the above-described device, the method comprising:

[0017] Before starting the machine, all valves in the device of this invention are closed, and the tube side or shell side of the heat exchange methanation reactor is filled with catalyst.

[0018] (1) During the initial start-up phase, hot nitrogen (at room temperature from outside the unit is heated by the start-up furnace built into the methanation unit itself to obtain hot nitrogen, with a flow rate of, for example, 10,000-50,000 m³ / h) is used. 3 / h, preferably 15000-30000m 3 / h, more preferably about 200,000 m 3 / h) The feed gas enters the heat exchange methanation reactor from the feed gas inlet to preheat the catalyst bed to the catalyst activation temperature (catalyst activation temperature, for example, 200-300℃, preferably 260-300℃);

[0019] (2) When the catalyst bed temperature meets the catalyst activation conditions, the nitrogen in the process pipeline is gradually switched to process gas (the flow rate can be, for example, 20,000-100,000 Nm³). 3 / h, preferably 50000-80000 Nm 3 / h, more preferably about 30000 Nm 3 The inert gas heat exchange system is activated simultaneously with the following steps: (temperature can be, for example, 200-300℃, preferably 260-300℃). The third valve, fourth valve, and compressor are opened. Inert gas (temperature can be, for example, 20-35℃, preferably room temperature; pressure can be, for example, 0.3-1 MPaG, preferably 0.5-0.8 MPaG; flow rate can be, for example, 5000-10000 m³ / h). 3 / h, preferably 6000-8000m 3 The inert gas enters the heat exchange methanation reactor at a temperature of 20-30°C (preferably ambient temperature) and then returns to the heat exchange methanation reactor via a buffer tank and compressor, thus establishing a reactor-inert gas-steam drum series combination.

[0020] (3) As the unit progresses into operation, when the catalyst bed temperature reaches 200-450℃, preferably 300-350℃, further 305-345℃, further 310-340℃, further 315-335℃ or 320-330℃, and the steam drum water reaches 50-300℃, preferably 100-220℃, preferably 110-210℃, preferably 120-200℃, preferably 130-200℃, preferably 140-190℃, preferably 150-180℃, preferably 160-170℃, gradually close the third and fourth valves, shut down the compressor, and simultaneously gradually open the first and second valves. The amount of hot water in the steam drum that generates saturated steam is generally 92-97% of the total water entering the heat exchange reactor, for example 94-96%, for example about 95%, for example... To generate 16 t / h of steam, the total water entering the reactor is approximately 16 / 0.95 ≈ 17 t / h. This water enters the heat exchange methanation reactor via the second pipe, where it vaporizes in the heat-absorbing section to form rising water that carries away the heat of reaction (the generated saturated steam temperature can be, for example, 200-400℃, preferably 250-350℃, and the pressure can be, for example, 2-5 MPaG, preferably 3-4 MPaG, and most preferably 3.8 MPaG, 297℃ saturated steam). The rising water enters the steam drum via the first pipe for gas-liquid separation. The steam is then discharged from the steam drum via the steam output pipe. Fresh deoxygenated and demineralized water is continuously replenished in the steam drum via the fresh water input pipe. After being heated in the steam drum, the water enters the heat exchange methanation reactor to remove the heat of reaction, gradually switching the inert gas heat exchange system to a water heat exchange system, thus establishing a reactor-steam drum series connection.

[0021] As one of the preferred embodiments of the present invention, the inert gas heat exchange system includes a third valve, a buffer tank, a compressor and a fourth valve arranged sequentially on a third pipeline along the flow direction of the heat exchange medium, and the water heat exchange system includes a steam drum, a first pipeline and a second pipeline connected between the steam drum and the heat exchange methanation reactor, and a first valve and a second valve.

[0022] As one of the preferred embodiments of the present invention, the heat exchange methanation reactor is a shell-and-tube type or a plate-and-shell type heat exchange reactor, preferably a shell-and-tube type reactor.

[0023] As one of the preferred embodiments of the present invention, the heat exchange tubes of the heat exchange type methanation reactor may be filled with a catalyst or circulated with a heat exchange medium, preferably circulated with a heat exchange medium.

[0024] As one of the preferred embodiments of the present invention, the heat exchange medium is a combination of inert gas and water, and different heat exchange media are switched for different operating cycles of the device.

[0025] As one of the preferred embodiments of the present invention, the inert gas heat exchange medium can be a mixture of one or more gases such as nitrogen, carbon dioxide, helium, and argon, preferably nitrogen or / and carbon dioxide, and more preferably nitrogen.

[0026] As one of the preferred embodiments of the present invention, the pressure of the inert gas heat exchange medium is 0.1-6.0 MPaG, preferably 0.1-3.0 MPaG, more preferably 0.1-1.0 MPaG, and most preferably 0.1-0.6 MPaG.

[0027] As one of the preferred embodiments of the present invention, the inert gas heat exchange system (i.e., the third valve, the fourth valve, and the compressor) is turned on during the start-up of the device when the catalyst bed reaches 30-300°C, 50-295°C, 70-290°C, 100-290°C, 110-290°C, 120-290°C, 130-280°C, or 140-270°C, or 150-260°C, or 160-255°C, or 180-250°C, or 190-245°C, or 200-240°C. Preferably, the catalyst bed reaches 150-280°C or 160-270°C. More preferably, the catalyst bed reaches 200-260°C, or 210-260°C, or 220-260°C, or 230-250°C.

[0028] As one of the preferred embodiments of the present invention, during the start-up of the device, the timing for switching from the inert gas heat exchange system to the water heat exchange system is as follows: when the catalyst bed reaches 200-450°C and the steam drum water temperature reaches 50-300°C; preferably when the catalyst bed reaches 250-400°C and the steam drum water temperature reaches 80-260°C; more preferably when the catalyst bed reaches 280-380°C and the steam drum water temperature reaches 100-220°C; more preferably when the catalyst bed reaches 300-350°C and the steam drum water temperature reaches 120-180°C; more preferably when the catalyst bed reaches 310-340°C and the steam drum water temperature reaches 130-170°C; and more preferably when the catalyst bed reaches 320-330°C and the steam drum water temperature reaches 140-160°C.

[0029] As one of the preferred embodiments of the present invention, after the process gas is introduced during start-up, when the bed temperature reaches 450°C or above, but the steam drum temperature has not reached 100°C, the inert gas heat exchange system is switched to a water heat exchange system. This is because the inert gas heat exchange system carries away less heat and is prone to causing the bed temperature to run hot.

[0030] As one of the preferred embodiments of the present invention, during startup, when using hot nitrogen to heat the bed, the inert gas heat exchange system is activated to establish a reactor-inert gas-steam drum series combination, and the steam drum water is preheated; or it can be flexibly activated according to the first startup situation, and the appropriate time to activate the inert gas heat exchange system is found through simulation calculation in advance.

[0031] Compared with the prior art, the present invention has the following characteristics:

[0032] By employing a heat exchange reactor, investment and operating costs for circulating compressors, waste heat boilers, etc., are reduced, catalyst bed temperature is effectively controlled, and the risk of carbon buildup is avoided. More importantly, by providing a novel methanation heat exchange system with dual heat exchange processes and media, the heat required for reactor heating can be significantly reduced during the initial start-up phase, accelerating the start-up process and thus solving the problems of high start-up costs and long start-up times associated with existing heat exchange methanation units. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of a conventional methanation heat exchange system.

[0034] Figure 2 This is a schematic diagram of the methanation heat exchange system of the present invention.

[0035] 1-Heat exchange methanation reactor, 2-Steam drum, 3-Buffer tank, 4-Compressor, A-First valve, B-Second valve, C-Third valve, D-Fourth valve, L1-First pipe, L2-Second pipe, L3-Third pipe, L4-Steam output pipe, L5-Fresh water input pipe. Detailed Implementation

[0036] The embodiments of the present invention are described in detail below. These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments.

[0037] like Figure 2 As shown, a heat exchange device for a methanation reactor includes: a heat exchange type methanation reactor 1, a water heat exchange system, and an inert gas heat exchange system. The heat exchange medium outlet of the heat exchange type methanation reactor 1 is connected to the rising water inlet of the water heat exchange system via a first pipe L1. The falling water outlet of the water heat exchange system is connected to the heat exchange medium inlet of the heat exchange type methanation reactor 1 via a second pipe L2. A third pipe L3 branches off from the first pipe L1 and is connected to the heat exchange medium inlet of the heat exchange type methanation reactor after passing through the inert gas heat exchange system.

[0038] The heat exchange methanation reactor 1 can be a shell-and-tube type or a plate-and-shell type reactor, preferably a shell-and-tube type reactor. It has a feed gas inlet and a product gas outlet, with the feed gas inlet and product gas outlet forming a shell side or tube side. The heat exchange medium inlet and outlet form a tube side or shell side (the feed gas inlet and product gas outlet are connected to the catalyst in the reactor). The catalyst is packed in the shell side or tube side, while the heat exchange medium flows through a tube side or shell side different from the catalyst. The heat exchange medium is an inert gas and water, corresponding to an inert gas heat exchange system and a water heat exchange system, respectively. By switching between the water heat exchange system and the inert gas heat exchange system at different life stages of the device, the catalyst is quickly activated and the heat of reaction is removed.

[0039] The water heat exchange system includes a steam drum 2. The rising water inlet of the steam drum 2 is connected to the heat exchange medium outlet of the tube side or shell side of the heat exchange methanation reactor (usually located at the top or bottom of the heat exchange methanation reactor) via a first pipe L1. The falling water outlet of the steam drum 2 is connected to the heat exchange medium inlet of the tube side or shell side of the heat exchange methanation reactor 1 (usually located at the bottom or bottom of the heat exchange methanation reactor) via a second pipe L2. A first valve A and a second valve B are respectively installed on the first pipe L1 and the second pipe L2. The diameter of the steam drum 2 can be, for example, 1200-1600 mm, preferably about 1400 mm; the straight pipe section length can be, for example, 3500-5000 mm, preferably about 4000 mm; the wall thickness can be, for example, 24-30 mm, preferably about 26 mm; and the total volume can be, for example, 6.5-8 m³. 3 Preferably about 7m 3 The total weight of the steel is 7.5-8.5t. The steam drum 2 is equipped with a fresh water inlet connected to the fresh water input pipe L5 and a steam outlet connected to the steam output pipe L4. The fresh water input pipe L5 is preferably a fresh deoxygenated and desalinated water input pipe.

[0040] The inert gas heat exchange system includes an inert gas buffer tank 3 and a compressor 4, which are sequentially arranged on a third pipe L3 along the flow direction of the heat exchange medium. The third pipe L3 branches off from the first pipe L1 and enters the steam drum 2 to preheat the water in the steam drum. After exiting the steam drum 2, it is sequentially connected to the buffer tank 3, the compressor 4, and the heat exchange medium inlet of the heat exchange type methanation reactor. A third valve C is installed between the buffer tank 3 and the location where the third pipe L3 branches off from the first pipe L1. A fourth valve D is installed on the third pipe L3 between the compressor and the heat exchange medium inlet of the heat exchanger methanation reactor.

[0041] Example 1 (Low cost, saves time on startup)

[0042] like Figure 2 As shown, this embodiment processes a gas volume of 30,000 Nm³. 3A simplified flow diagram of a coke oven gas methanation unit with a capacity of / h includes a shell-and-tube fixed-bed heat exchange methanation reactor 1, a steam drum 2, a buffer tank 3, and a compressor 4. In the heat exchange methanation reactor, the tube side carries the heat exchange medium, while the shell side is filled with catalyst. The heat exchange medium is deoxygenated and demineralized water + 0.6 MPaG nitrogen. Before start-up, all valves in the unit are closed.

[0043] During the initial start-up phase, hot nitrogen (obtained from ambient temperature nitrogen outside the unit by heating it in the start-up furnace of the methanation unit itself, at a temperature of approximately 260°C, with a flow rate of approximately 20,000 m³ / s) is used. 3 The catalyst bed is heated by feeding gas into the heat exchanger methanation reactor at a rate of approximately 30,000 Nm³ / h. After about 12 hours, the catalyst bed temperature reaches 240°C, and the process pipeline gradually switches to process gas (flow rate approximately 30,000 Nm³ / h). 3 The process gas, at a temperature of 240℃ and a flow rate of approximately 6000 m³ / h, contains 22% CH₄, 2.61% C₂H₆, 8.26% CO, 2.36% CO₂, 60% H₂, and 4.77% N₂. Simultaneously, compressor 4 is turned on, valves C and D are opened, and the nitrogen heat exchange system is activated. The nitrogen output from the compressor has a pressure of approximately 0.6 MPaG, a temperature of ambient, and a flow rate of approximately 6000 m³ / h. 3 / h, nitrogen enters the heat exchange methanation reactor, carrying away the heat of activation within the reactor. Then, the nitrogen enters the steam drum to heat the ambient temperature water inside. After passing through a buffer tank and compressor, it returns to the heat exchange methanation reactor, establishing a reactor-nitrogen-steam drum series connection. As the unit progresses, approximately 2 hours later, the catalyst bed temperature reaches 300℃, and the steam drum water reaches 160℃. The third valve C and the fourth valve D are gradually closed, compressor 4 is shut off, and the first valve A and the second valve B are opened, switching the nitrogen heat exchange system to a water heat exchange system. The amount of hot water in the steam drum (generally 95% of the total water entering the heat exchange reactor) generates saturated steam. Taking Example 1 as an example, if 16 t / h of steam is generated, then the total amount of water entering the reactor is approximately 16 / 0.95≈17 t / h. The water enters the heat exchange methanation reactor, where the heat absorption part vaporizes to form rising water that carries away the heat of reaction. The rising water enters the steam drum through the first pipe for gas-liquid separation, and then exits the steam drum through the steam output pipe. Fresh deoxygenated and demineralized water is continuously replenished in the steam drum through the fresh water input pipe. After being heated by the steam drum, it enters the heat exchange methanation reactor to remove the heat of reaction. Gradually, the inert gas heat exchange system is switched to a water heat exchange system, establishing a reactor-steam drum series combination. After about 4 hours, the steam drum temperature stabilizes, and approximately 16 t / h of saturated steam at 297℃ and 3.8 MPaG is produced.

[0044] The entire driving process took approximately 20 hours.

[0045] Example 2

[0046] like Figure 2 As shown, this embodiment processes a gas volume of 30,000 Nm³. 3 A simplified flow diagram of a coke oven gas methanation unit with a capacity of / h includes a shell-and-tube fixed-bed heat exchange methanation reactor 1, a steam drum 2, a buffer tank 3, and a compressor 4. The reactor tubes are filled with catalyst, while the shell side carries the heat exchange medium, which is deoxygenated and demineralized water + 0.6 MPaG nitrogen. Before start-up, all valves in the unit are closed.

[0047] During the initial start-up phase, hot nitrogen (temperature 270℃, flow rate 25000 L / min) is introduced into the heat exchanger methanation reactor from the feed gas inlet to raise the catalyst bed temperature. After approximately 12 hours, when the catalyst bed temperature reaches 270℃, the process pipeline gradually switches to process gas (flow rate 30000 Nm³). 3 At a speed of 270℃, the process gas consists of 22% CH4, 2.61% C2H6, 8.26% CO, 2.36% CO2, 60% H2, and 4.77% N2. Simultaneously, compressor 4 is turned on, valves C and D are opened, and the nitrogen heat exchange system is activated. The nitrogen output from the compressor is at a pressure of 0.6 MPaG, a temperature of ambient temperature, and a flow rate of 7000 m³ / h. 3 At a rate of / h, nitrogen enters the heat exchange methanation reactor, carrying away the heat of activation within the reactor. Then, the nitrogen enters the steam drum to heat the ambient temperature water inside, before returning to the heat exchange methanation reactor via a buffer tank and compressor, establishing a reactor-nitrogen-steam drum series connection. As the unit progresses into operation, approximately 2 hours later, the catalyst bed temperature reaches 300℃, and the steam drum water reaches 160℃. At this point, valves C and D are gradually closed, compressor 4 is shut off, and valves A and B are opened to exchange the nitrogen. The thermal system is switched to a water heat exchange system. Hot water (flow rate of 17 t / h) in the steam drum enters the heat exchange methanation reactor, where the heat-absorbing portion vaporizes to form rising water that carries away the heat of reaction. The rising water enters the steam drum through the first pipe for gas-liquid separation. The saturated steam is then discharged from the steam drum through the steam output pipe. Fresh deoxygenated and demineralized water is continuously replenished into the steam drum through the fresh water input pipe. After being heated in the steam drum, the water enters the heat exchange methanation reactor to remove the heat of reaction. Gradually, the inert gas heat exchange system is switched to a water heat exchange system, establishing a reactor-steam drum series combination. After about 3 hours, the steam drum temperature stabilizes, producing approximately 16 t / h of saturated steam at 297℃ and 3.8 MPaG.

[0048] The entire driving process took approximately 20 hours.

[0049] Example 3

[0050] The process is basically the same as in Example 1, except that after about 10 hours, the catalyst bed temperature reaches 200°C and the process pipeline is gradually switched to process gas; when the catalyst bed temperature reaches 350°C and the steam drum water reaches 170°C, the third valve C and the fourth valve D are gradually closed, the compressor 4 is turned off, and the first valve A and the second valve B are opened.

[0051] Comparative Example 1 (High cost, time-consuming driving)

[0052] like Figure 1 As shown, the comparative example is a gas processing capacity of 30,000 Nm³. 3 A simplified flow diagram of a coke oven gas methanation unit with a capacity of [number] h includes a shell-and-tube fixed-bed heat exchange methanation reactor 1 and a steam drum 2. The heat exchange medium flows through the tubes of the reactor, while the catalyst is loaded in the shell side. The heat exchange medium is deoxygenated and demineralized water.

[0053] During the initial start-up phase, hot nitrogen (temperature 260℃, flow rate 20000 L / min) was used to heat the catalyst bed and drum water through process piping. After approximately 4 days, the catalyst bed temperature reached 240℃, and the drum water temperature reached 220℃. The process piping was then gradually switched to process gas (flow rate 30000 Nm³). 3 / h, temperature 240℃); as the unit started up, the catalyst bed temperature reached 300℃ after about 2 hours. After about 4 hours, the steam drum temperature stabilized, producing 3.8 MPaG saturated steam. The total start-up process took about 4.5 days.

[0054] Compared with Example 1, this device reduces the investment in inert gas compressor and buffer tank by about 150,000 yuan, but consumes 500,000 yuan more heating medium during start-up, increases other start-up costs by about 1 million yuan, consumes about 3 more days, produces about 600 tons less LNG, reduces revenue by about 3 million yuan, and reduces profits by about 1.5 million yuan.

[0055] Comparative Example 2 (High Equipment Wear and Tear)

[0056] like Figure 1 As shown, the comparative example is a gas processing capacity of 30,000 Nm³. 3 A simplified flow diagram of a coke oven gas methanation unit with a capacity of [number] h includes a shell-and-tube fixed-bed heat exchange methanation reactor 1 and a steam drum 2. The heat exchange medium flows through the tubes of the reactor, while the catalyst is loaded in the shell side. The heat exchange medium is deoxygenated and demineralized water.

[0057] During the initial startup phase, use 20,000 m³ of hot nitrogen gas at 260-300℃. 3 The catalyst bed is heated via process piping at a rate of / h. After approximately 12 hours, the catalyst bed temperature reaches 240℃, and the process piping is gradually switched to process gas (flow rate 30000 Nm³). 3 / h, 260℃); at this point, the water heat exchange system is switched on, establishing a reactor-steam drum series combination. The steam drum water is at room temperature. Due to the large temperature difference between the catalyst bed and the heat exchange medium, the equipment is prone to stress damage from cold shock, and the catalyst is easily broken by thermal shock, increasing bed resistance and reducing the lifespan of both the catalyst and the equipment. As the unit progresses, the catalyst bed temperature reaches 300℃ after approximately 6 hours. The steam drum temperature stabilizes after approximately 6 hours, producing 3.8 MPaG saturated steam. The total start-up time is approximately 24 hours.

[0058] Compared to Example 1, this device reduces the investment in the inert gas compressor and buffer tank by approximately 150,000 yuan. However, due to the quenching, the lifespan of the equipment and catalyst is shortened. The catalyst lifespan is reduced from 3 years to 2.5 years, resulting in a catalyst cost loss of approximately 100w / 3*0.5 = 166,000 yuan; the equipment lifespan is shortened from 30 years to 20 years, resulting in an equipment cost loss of approximately 100w / 30*10 = 333,000 yuan.

[0059] The preferred embodiments of the present invention have been described above. However, it should be understood that the above description is for illustrative purposes only and does not constitute any limitation on the present invention. Many modifications or equivalent substitutions can be made to the present invention without departing from its spirit and scope, and all such modifications and equivalent substitutions should be included within the protection scope of the present invention.

Claims

1. A heat exchange device for a methanation reactor, characterized in that, It comprises a heat exchange methanation reactor, a water heat exchange system, and an inert gas heat exchange system. The heat exchange medium outlet of the heat exchange methanation reactor is connected to the rising water inlet of the water heat exchange system via a first pipe. The falling water outlet of the water heat exchange system is connected to the heat exchange medium inlet of the heat exchange methanation reactor via a second pipe. A third pipe branches off from the first pipe and connects to the heat exchange medium inlet of the heat exchange methanation reactor after passing through the inert gas heat exchange system. The water heat exchange system includes a steam drum. The rising water inlet of the steam drum is connected to the heat exchange medium outlet of the tube side or shell side of the heat exchange methanation reactor via a first pipe. The falling water outlet of the steam drum is connected to the heat exchange medium inlet of the tube side or shell side of the heat exchange methanation reactor via a second pipe. A first valve and a second valve are respectively installed on the first pipe and the second pipe. The inert gas heat exchange system includes an inert gas buffer tank and a compressor arranged sequentially on a third pipeline along the flow direction of the heat exchange medium. A third valve is installed between the buffer tank and the location where the third pipeline branches off from the first pipeline. A fourth valve is installed on the third pipeline between the compressor and the heat exchange medium inlet of the methanation reactor of the heat exchanger. The third pipeline enters the steam drum after passing through the third valve, and then exits the steam drum and connects to the inlet of the buffer tank.

2. The heat exchange device for the methanation reactor according to claim 1, characterized in that, The heat exchange methanation reactor is a shell-and-tube reactor with a feed gas inlet and a product gas outlet. The area between the feed gas inlet and the product gas outlet is either the shell side or the tube side. The area between the heat exchange medium inlet and the heat exchange medium outlet is either the tube side or the shell side. The feed gas inlet and the product gas outlet are connected to the catalyst in the reactor. The catalyst is loaded in the shell side or the tube side, while the heat exchange medium flows through a tube side or the shell side that is different from the catalyst.

3. A method for starting up a methanation reactor heat exchanger as described in claim 1 or 2, the method comprising: (1) During the initial start-up phase, hot nitrogen gas enters the heat exchange methanation reactor from the feed gas inlet to preheat the catalyst bed to the catalyst activation temperature. (2) When the catalyst bed temperature meets the catalyst activation conditions, the nitrogen in the process pipeline is gradually switched to process gas. At the same time, the inert gas heat exchange system is activated, the third valve, the fourth valve and the compressor are opened, and the inert gas enters the heat exchange methanation reactor. The inert gas carries away the activation reaction heat in the heat exchange methanation reactor. Then the inert gas enters the steam drum to heat the water in the steam drum, and then returns to the heat exchange methanation reactor through the buffer tank and the compressor, establishing a reactor-inert gas-steam drum series combination. (3) As the unit is started up, the temperature of the catalyst bed rises. The third and fourth valves are gradually closed, the compressor is turned off, and the first and second valves are gradually opened. The hot water in the steam drum enters the heat exchange methanation reactor, the heat absorption part is vaporized to form rising water that carries away the heat of reaction. The rising water enters the steam drum through the first pipe for gas-liquid separation. The saturated steam is then discharged from the steam drum through the steam output pipe. Fresh deoxygenated and demineralized water is continuously replenished in the steam drum through the fresh deoxygenated and demineralized water input pipe. After being heated by the steam drum, it enters the heat exchange methanation reactor to remove the heat of reaction. The inert gas heat exchange system is gradually switched to the water heat exchange system, and a reactor-steam drum series combination is established.

4. The method according to claim 3, wherein, The inert gas is a mixture of one or more gases selected from nitrogen, carbon dioxide, helium, and argon.

5. The method according to claim 4, wherein, The inert gas is nitrogen and / or carbon dioxide.

6. The method according to claim 3, characterized in that, The timing for starting the inert gas heat exchange system in step (2) is when the catalyst bed reaches 30-300℃.

7. The method according to claim 6, characterized in that, The timing for starting the inert gas heat exchange system in step (2) is when the catalyst bed reaches 150-280℃.

8. The method according to claim 7, characterized in that, The timing for starting the inert gas heat exchange system in step (2) is when the catalyst bed reaches 200-260℃.

9. The method according to claim 8, characterized in that, The timing for starting the inert gas heat exchange system in step (2) is when the catalyst bed reaches 200-240℃.

10. The method according to any one of claims 3-9, characterized in that, In step (3), the timing for switching from the inert gas heat exchange system to the water heat exchange system is when the catalyst bed temperature reaches 200-450℃ and the steam drum water reaches 50-300℃.

11. The method according to claim 10, characterized in that, In step (3), the timing for switching from the inert gas heat exchange system to the water heat exchange system is when the catalyst bed temperature reaches 250-400℃ and the steam drum water reaches 80-260℃.

12. The method according to claim 11, characterized in that, In step (3), the timing for switching from the inert gas heat exchange system to the water heat exchange system is when the catalyst bed temperature reaches 280-380℃ and the steam drum water reaches 100-220℃.

13. The method according to claim 12, characterized in that, In step (3), the timing for switching from the inert gas heat exchange system to the water heat exchange system is when the catalyst bed temperature reaches 300-350℃ and the steam drum water reaches 120-180℃.

14. The method according to claim 13, characterized in that, In step (3), the timing for switching from the inert gas heat exchange system to the water heat exchange system is when the catalyst bed temperature reaches 310-340℃ and the steam drum water reaches 130-170℃.

15. The method according to claim 14, characterized in that, In step (3), the timing for switching from the inert gas heat exchange system to the water heat exchange system is when the catalyst bed temperature reaches 320-330℃ and the steam drum water reaches 140-160℃.

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