Switching and low-temperature methanol washing driving system and driving method

Abstract

The invention relates to a shift and low-temperature methanol wash start-up system which comprises a start-up system body, an inlet of a main shift converter of the start-up system body is connected with a nitrogen heater through a nitrogen pipeline, the inlet of the main shift converter is further connected with a superheated steam pipeline, and the inlet end of the superheated steam pipeline is externally connected with superheated steam input equipment; when an overtemperature phenomenon occurs in the main conversion furnace, the nitrogen is heated by the nitrogen heater and then is supplemented into the main conversion furnace, so that the overtemperature phenomenon is solved; when the temperature crossing phenomenon occurs in the main conversion furnace, superheated steam is input into the main conversion furnace to supplement heat, and the temperature of a bed layer is maintained; according to the technical scheme, the problems of large fluctuation of raw gas and overtemperature of the conversion furnace caused by simultaneous gas guide of the conversion device and the low-temperature methanol washing device are solved, emptying of process gas is reduced, and the production cost is saved. According to the driving method adopting the system, the driving time is shortened, the consumption in the driving period is reduced, and the problems of large fluctuation, overtemperature and temperature crossing of raw gas are avoided.

Description

Technical Field

[0001] The invention relates to the technical field of natural gas preparation, and in particular to a conversion and low-temperature methanol washing start-up system and a start-up method. Background Art

[0002] The gasification device for natural gas preparation is equipped with 3 frames, each of which is equipped with a start-up flare system. The designed venting volume of the flare is 30655Nm3 / h. The same start-up flare system can only allow the ignition and start-up of one gasifier at the same time. Therefore, each time the device is started, the raw coal gas produced by the gasifier that is normally started is first led to the conversion device and vented through the conversion furnace bypass. In order to meet the start-up requirements of the conversion furnace, the conversion furnace bypass generally maintains a venting volume of 100000Nm3 / h. When the conversion furnace is guided, it is generally vented through the start-up. Bypass the large conversion furnace inlet valve to equalize the pressure of the conversion furnace. After the pressure equalization is completed, continue to open the conversion furnace inlet valve bypass or main line, close the bypass valve, and when the conversion furnace gas conduction is completed, increase the pressure of the conversion device as a whole to normal pressure, and then open the low-temperature methanol wash equalizing valve to pressurize the low-temperature methanol wash high-pressure system. After the pressure is charged, open the large valve of the low-temperature methanol wash boundary area, and then open the low-temperature methanol wash outlet to vent the purified gas, close the conversion device to vent, and conduct gas. After the gas conduction is completed, the purified gas is analyzed and sent to the methanation device if it passes.

[0003] Because the conversion device and the low-temperature methanol washing device have a long process and involve many devices, each time the device is started and restarted, it takes 4 hours for the conversion furnace to prepare for gas conduction and normal operation, 2 hours for low-temperature methanol pressure equalization, 0.5 hours for gas conduction, and 1 hour for qualified purified gas. The entire conversion and low-temperature methanol washing device takes 7.5 hours to start up. The start-up time is long, and the process gas is vented for a long time, resulting in energy waste. If the conversion device and the low-temperature methanol washing device are conducted at the same time, although the start-up time can be greatly shortened, the operation is relatively cumbersome. If it is not done properly, it will cause a large fluctuation in gas volume, causing over-temperature or cross-temperature of the conversion furnace (rapid decrease in bed temperature). Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a conversion and low-temperature methanol washing start-up system and a start-up method to overcome the deficiencies in the above-mentioned prior art.

[0005] The technical solution of the present invention to solve the above technical problems is as follows: a conversion and low-temperature methanol washing start-up system and a start-up method, including a start-up system body, the inlet of the main conversion furnace of the start-up system body is connected to a nitrogen heater through a nitrogen pipeline, the inlet of the nitrogen heater is externally connected to a nitrogen input device, the inlet of the main conversion furnace is also connected to a superheated steam pipeline, and the inlet end of the superheated steam pipeline is externally connected to a superheated steam input device; a valve 23 is provided on the superheated steam pipeline, and a valve 24 is provided on the nitrogen pipeline.

[0006] The beneficial effects of the present invention are as follows: during the gas guiding process, when over-temperature occurs in the main conversion furnace, nitrogen is heated to 300°C by a nitrogen heater and then directly added to the main conversion furnace. Since nitrogen is an inert gas, it can not only increase the air velocity in the reactor and reduce the reaction rate, but also bring out the heat in the main conversion furnace, thereby solving the over-temperature problem. Nitrogen is added after being heated, avoiding the risk of damaging equipment and pipelines due to direct addition due to a large temperature difference. During the gas guiding process, when cross-temperature occurs in the main conversion furnace, superheated steam is input into the main conversion furnace to supplement heat and maintain the bed temperature. The technical solution solves the problem that the raw coal gas fluctuates greatly due to the simultaneous gas guiding of the conversion device and the low-temperature methanol washing device, causing over-temperature of the conversion furnace, reduces the venting of process gas, and saves production costs.

[0007] Based on the above technical solution, the present invention can also be improved as follows.

[0008] Furthermore, a nitrogen heater is arranged between the gas-to-gas heat exchanger and valves 6 and 8 of the start-up system body.

[0009] Furthermore, a flow meter A is provided between valve 1 of the start-up system body and the raw gas scrubber, a flow meter B is provided between the raw gas separator and valve 11, a flow meter C is provided between the raw gas and valve 2, and a flow meter D is provided between the raw material cooler 1 and the raw material cooler 2 and the ammonia pre-washing tower.

[0010] Furthermore, a valve 22 is connected in parallel to the valve 11 of the start-up system body.

[0011] Furthermore, a pressure gauge E is provided at the outlet of the ammonia washing tower of the start-up system body, a pressure gauge F is provided between the raw material cooler 1 and the valve 20 of the start-up system body, and the valve 4 and the valve 21 of the start-up system body are both solenoid valves.

[0012] The present invention also discloses a start-up method for a conversion and low-temperature methanol wash start-up system, which uses the above conversion and low-temperature methanol wash start-up system and includes the following steps:

[0013] Step S01: The main conversion furnace is heated to 300°C. After the heating is completed, valves 1, 2, 3, 4, 5, 6, 7, and 10 are in an open state, and other valves are in a closed state, and the conversion gas is vented to the flare pipeline of the whole plant;

[0014] Step S02: Before the conversion device starts to guide gas, the conversion furnace is first pressure-equalized, and valves 6, 7, and 10 are confirmed to be in an open state, and then valve 22 is slowly opened to pressure-equalize the conversion furnace; at the same time, valve 12 is opened to pressure-equalize the conversion gas pipeline for conversion to low-temperature methanol washing, and after the conversion gas pipeline is pressurized, valve 13 is opened, valve 12 is closed, and then valve 14 is slowly opened to pressure-equalize the low-temperature methanol washing device;

[0015] Step S03: After the conversion device is pressurized, open valve 16, then open valve 11, close valve 2, and guide gas into the main conversion furnace. After valve 11 is fully opened, open valves 17 and 19, slowly open valve 18, and gradually close valve 22 and valve 11. While the main conversion furnace is guiding gas, the low-temperature methanol washing device is pressurized, open valves 15 and 20, close valve 14, and then simultaneously close valve 4 and open valve 21 until valve 4 is completely closed. All process gases are vented to the flare at valve 21, and the conversion and low-temperature methanol washing device gas guiding process is completed.

[0016] Further, step S03 also includes:

[0017] When the main conversion furnace overheats, wait until the bed temperature of the main conversion furnace reaches 420°C, input nitrogen into the nitrogen heater, heat the nitrogen to 300°C through the nitrogen heater, open valve 23, input nitrogen into the main conversion furnace, and when the temperature in the main conversion furnace drops to 380°C, close valve 23 and stop inputting nitrogen;

[0018] When the main conversion furnace crosses the temperature, open valve 24 to input superheated steam into the main conversion furnace. When the bed temperature of the main conversion furnace reaches between 380°C and 400°C, slowly withdraw the input of superheated steam.

[0019] The beneficial effects of the present invention are as follows: the conversion device of the present technical solution and the low-temperature methanol washing device simultaneously perform pressure equalization and gas guiding. Compared with the conversion device in the prior art which first performs pressure equalization and gas guiding, and then performs low-temperature methanol washing and then pressure equalization and gas guiding, the start-up time can be shortened by 3.5 hours, the consumption during start-up is reduced, and the natural gas output is increased. In addition, by setting the heated nitrogen and superheated steam, it is possible to avoid large fluctuations in the raw coal gas when the conversion device and the low-temperature methanol washing device simultaneously guide gas, thereby avoiding the problem of overheating of the conversion furnace. This greatly shortens the start-up time of the coal-to-gas project, reduces the venting of process gas, and saves production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the system structure of the present invention;

[0021] Figure 2 Schematic diagram of the system structure of the prior art. DETAILED DESCRIPTION

[0022] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0023] like Figure 1-2As shown, Example 1, a conversion and low-temperature methanol washing start-up system and a start-up method, include a start-up system body, the inlet of the main conversion furnace of the start-up system body is connected to a nitrogen heater through a nitrogen pipeline, the inlet of the nitrogen heater is externally connected to a nitrogen input device, the inlet of the main conversion furnace is also connected to a superheated steam pipeline, the inlet end of the superheated steam pipeline is externally connected to a superheated steam input device; a valve 23 is provided on the superheated steam pipeline, and a valve 24 is provided on the nitrogen pipeline.

[0024] Since the gas-guiding operation of the converter and the low-temperature methanol washing device is complicated, any improper operation will cause a large fluctuation in gas volume, resulting in over-temperature or cross-temperature of the converter (rapid decrease in bed temperature);

[0025] During the gas guiding process, when the main conversion furnace overheats, the nitrogen is heated to 300℃ by the nitrogen heater and then directly added to the main conversion furnace (during the gas guiding process, the main conversion furnace bed temperature reaches 420℃ and then gradually added, and when the temperature drops to 380℃, the nitrogen addition is gradually withdrawn). As nitrogen is an inert gas, it can not only increase the air velocity in the reactor and reduce the reaction rate, but also take out the heat in the main conversion furnace, thus solving the overheating problem. The nitrogen is heated before being added, avoiding the risk of damaging equipment and pipelines due to direct addition of large temperature difference. During the gas guiding process, when the main conversion furnace overheats, the nitrogen is heated to 300℃ and then directly added to the main conversion furnace (during the gas guiding process, the nitrogen is gradually added when the bed temperature reaches 420℃, and when the temperature drops to 380℃, the nitrogen addition is gradually withdrawn). When the temperature crosses, superheated steam is input into the main conversion furnace to supplement heat (the normal temperature of 4.9MPa superheated steam is 450℃, the upper limit is 480℃, and the lower limit is 440℃. When the temperature of the main conversion furnace is lower than 300℃ during the gas conduction process, superheated steam is added. When the bed temperature of the main conversion furnace reaches between 380 and 400℃, the superheated steam is slowly withdrawn. After withdrawal, the bed temperature is maintained at around 360℃) to maintain the bed temperature. This technical solution solves the problem of large fluctuations in raw coal gas caused by simultaneous gas conduction of the conversion device and the low-temperature methanol washing device, which causes overheating of the conversion furnace, reduces the venting of process gas, and saves production costs.

[0026] Embodiment 2: This embodiment is a further improvement on the basis of embodiment 1, and its details are as follows:

[0027] The nitrogen heater is arranged between the gas-to-gas heat exchanger of the start-up system body and valves 6 and 8. Such arrangement can solve the over-temperature phenomenon of the main conversion furnace, and can also solve the over-temperature phenomenon of the pre-conversion furnace A and the pre-conversion furnace B.

[0028] Embodiment 3, this embodiment is a further improvement on the basis of embodiment 1, and its details are as follows:

[0029] Flowmeter A is set between valve 1 of the start-up system and the crude gas scrubber, flowmeter B is set between the crude gas separator and valve 11, flowmeter C is set between the crude gas and valve 2, and flowmeter D is set between the raw material cooler 1 and raw material cooler 2 and the ammonia pre-washing tower. When the conversion device and the low-temperature methanol washing device are simultaneously conducting gas, in order to prevent a large fluctuation in gas volume, the gas volume entering the conversion furnace and the low-temperature methanol washing volume can be adjusted accordingly by observing the changes in the values ​​of flowmeters A, B, C, and D.

[0030] Embodiment 4: This embodiment is a further improvement on the basis of embodiment 1, and its details are as follows:

[0031] The valve 11 of the start-up system is connected in parallel with the valve 22. Since the diameter of the valve 11 is DN250 and the pipeline diameter is relatively large, the gas volume fluctuates greatly during the gas guide process. Therefore, the valve 22 is connected in parallel with the valve 11, and its diameter is DN100, which can avoid the problem of large gas volume fluctuations during the gas guide process.

[0032] Embodiment 5, this embodiment is a further improvement on the basis of embodiment 1, and its details are as follows:

[0033] A pressure gauge E is provided at the outlet of the ammonia washing tower of the start-up system, and a pressure gauge F is provided between the raw material cooler 1 and the valve 20 of the start-up system. The valves 4 and 21 of the start-up system are both solenoid valves. During the gas guiding process, the valves 4 and 21 can automatically control the opening according to the pressure gauges E and F respectively, and can always keep the pressure and flow stable during the gas guiding process;

[0034] In specific implementation, when the conversion and low-temperature methanol are guided at the same time, the control is mainly based on valve 21. When the air intake of the main conversion furnace increases, or the main conversion furnace overheats and requires a large amount of air intake, in order to prevent the low-temperature methanol washing inlet air volume from suddenly increasing, in order to control the low-temperature methanol flow, the opening of valve 21 is controlled according to the flow. At this time, the increased gas volume of the low-temperature methanol flow is much smaller than the gas intake volume of the main conversion furnace, and the system pressure will rise. The pressure gauge E will transmit the signal to valve 4 through the transmitter, and valve 4 will open automatically. This not only increases the conversion gas volume, but also controls the low-temperature methanol gas volume. Then, according to the low-temperature methanol washing working conditions, valve 21 can continue to be opened until valve 4 is completely closed.

[0035] Embodiment 6, a method for starting up a conversion and low-temperature methanol washing system, using the conversion and low-temperature methanol washing system of any one of embodiments 1 to 5, comprising the following steps:

[0036] Step S01: The main conversion furnace is heated to 300°C. After the heating is completed, valves 1, 2, 3, 4, 5, 6, 7, and 10 are in an open state, and other valves are in a closed state. At this time, the bypass gas volume of the conversion furnace is not less than 100,000 Nm3 / h, the pressure is 2 MPa, and the conversion gas is vented to the flare pipeline of the whole plant;

[0037] Step S02: Before the conversion device starts to guide gas, the conversion furnace is first pressure-equalized, and valves 6, 7, and 10 are confirmed to be in an open state, and then valve 22 is slowly opened to pressure-equalize the conversion furnace; at the same time, valve 12 is opened to pressure-equalize the conversion gas pipeline for conversion to low-temperature methanol washing, and after the conversion gas pipeline is pressurized, valve 13 is opened, valve 12 is closed, and then valve 14 is slowly opened to pressure-equalize the low-temperature methanol washing device;

[0038] Step S03: After the conversion device is pressurized, open valve 16, then open valve 11, close valve 2, and guide gas into the main conversion furnace. After valve 11 is fully opened, open valves 17 and 19, slowly open valve 18, and gradually close valve 22 and valve 11. While the main conversion furnace is guiding gas, the low-temperature methanol washing device is pressurized, open valves 15 and 20, close valve 14, and then simultaneously close valve 4 and open valve 21 until valve 4 is completely closed. All process gases are vented to the flare at valve 21, and the conversion and low-temperature methanol washing device gas guiding process is completed.

[0039] Step S03 also includes:

[0040] When the main conversion furnace overheats, wait until the bed temperature of the main conversion furnace reaches 420°C, input nitrogen into the nitrogen heater, heat the nitrogen to 300°C through the nitrogen heater, open valve 23, input nitrogen into the main conversion furnace, and when the temperature in the main conversion furnace drops to 380°C, close valve 23 and stop inputting nitrogen;

[0041] When the main conversion furnace crosses the temperature phenomenon (i.e. the conversion furnace temperature is lower than 300°C), open valve 24 to input superheated steam into the main conversion furnace. When the main conversion furnace bed temperature reaches between 380°C and 400°C, slowly withdraw the input of superheated steam.

[0042] During the gas guiding process, when the main conversion furnace overheats, the nitrogen is heated to 300℃ by the nitrogen heater and then directly added to the main conversion furnace (during the gas guiding process, the main conversion furnace bed temperature reaches 420℃ and is gradually added, and when the temperature drops to 380℃, the nitrogen addition is gradually stopped). As nitrogen is an inert gas, it can not only increase the air velocity in the reactor and reduce the reaction rate, but also take out the heat in the main conversion furnace, thus solving the overheating problem. The nitrogen is heated before being added, avoiding direct addition due to large temperature difference. There is a risk of damaging equipment and pipelines by the introduction of superheated steam; during the gas conduction process, when cross-temperature phenomenon occurs in the main conversion furnace, superheated steam is input into the main conversion furnace to supplement heat (the normal temperature of 4.9MPa superheated steam is 450℃, the upper limit is 480℃, and the lower limit is 440℃. During the gas conduction process, when the temperature of the main conversion furnace is lower than 300℃, superheated steam is added. When the bed temperature of the main conversion furnace reaches between 380 and 400℃, the superheated steam is slowly withdrawn, and the bed temperature is maintained at about 360℃ after withdrawal) to maintain the bed temperature.

[0043] The conversion device and the low-temperature methanol washing device of the technical solution simultaneously perform pressure equalization and gas guiding. Compared with the conversion device in the prior art which first performs pressure equalization and gas guiding, and then performs low-temperature methanol washing and then pressure equalization and gas guiding, the start-up time can be shortened by 3.5 hours, the consumption during start-up is reduced, and the natural gas output is increased. In addition, by setting the heated nitrogen and superheated steam, it is possible to avoid large fluctuations in the raw coal gas when the conversion device and the low-temperature methanol washing device simultaneously guide gas, thereby avoiding the problem of overheating of the conversion furnace. This greatly shortens the start-up time of the coal-to-gas project, reduces the venting of process gas, and saves production costs.

[0044] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A conversion and low temperature methanol wash-out system, characterized in that: The system comprises a start-up system body, wherein the inlet of the main conversion furnace of the start-up system body is connected to a nitrogen heater via a nitrogen pipeline, the inlet of the nitrogen heater is externally connected to a nitrogen input device, the inlet of the main conversion furnace is also connected to a superheated steam pipeline, the inlet end of the superheated steam pipeline is externally connected to a superheated steam input device; a valve 23 is provided on the superheated steam pipeline, and a valve 24 is provided on the nitrogen pipeline.

2. A conversion and low temperature methanol wash-out system according to claim 1, characterized in that: The nitrogen heater is arranged between the gas-to-gas heat exchanger and valves 6 and 8 of the start-up system body.

3. A conversion and low temperature methanol wash-out system according to claim 1, characterized in that: A flow meter A is arranged between valve 1 of the start-up system body and the crude gas scrubber, a flow meter B is arranged between the crude gas separator and valve 11, a flow meter C is arranged between the crude gas and valve 2, and a flow meter D is arranged between the raw material cooler 1 and the raw material cooler 2 and the ammonia pre-washing tower.

4. A conversion and low temperature methanol wash-out system according to claim 1, characterized in that: The valve 11 of the start-up system body is connected in parallel with a valve 22 .

5. A conversion and low temperature methanol wash-out system according to claim 1, characterized in that: A pressure gauge E is provided at the outlet of the ammonia washing tower of the start-up system body, a pressure gauge F is provided between the raw material cooler 1 and the valve 20 of the start-up system body, and both the valve 4 and the valve 21 of the start-up system body are solenoid valves.

6. A start-up method for a conversion and low-temperature methanol wash start-up system, characterized in that: The conversion and low-temperature methanol wash-out system according to any one of claims 1 to 5 comprises the following steps: Step S01: The main conversion furnace is heated to 300°C. After the heating is completed, valves 1, 2, 3, 4, 5, 6, 7, and 10 are in an open state, and other valves are in a closed state, and the conversion gas is vented to the flare pipeline of the whole plant; Step S02: Before the conversion device starts to guide gas, the conversion furnace is first pressure-equalized, and valves 6, 7, and 10 are confirmed to be in an open state, and then valve 22 is slowly opened to pressure-equalize the conversion furnace; at the same time, valve 12 is opened to pressure-equalize the conversion gas pipeline for conversion to low-temperature methanol washing, and after the conversion gas pipeline is pressurized, valve 13 is opened, valve 12 is closed, and then valve 14 is slowly opened to pressure-equalize the low-temperature methanol washing device; Step S03: After the conversion device is pressurized, open valve 16, then open valve 11, close valve 2, and guide gas into the main conversion furnace. After valve 11 is fully opened, open valves 17 and 19, slowly open valve 18, and gradually close valve 22 and valve 11. While the main conversion furnace is guiding gas, the low-temperature methanol washing device is pressurized, open valves 15 and 20, close valve 14, and then simultaneously close valve 4 and open valve 21 until valve 4 is completely closed. All process gases are vented to the flare at valve 21, and the conversion and low-temperature methanol washing device gas guiding process is completed.

7. The start-up method of the conversion and low-temperature methanol wash start-up system according to claim 6, wherein the step S03 further comprises: When the main conversion furnace overheats, wait until the bed temperature of the main conversion furnace reaches 420°C, input nitrogen into the nitrogen heater, heat the nitrogen to 300°C through the nitrogen heater, open valve 23, input nitrogen into the main conversion furnace, and when the temperature in the main conversion furnace drops to 380°C, close valve 23 and stop inputting nitrogen; When the main conversion furnace crosses the temperature, open valve 24 to input superheated steam into the main conversion furnace. When the bed temperature of the main conversion furnace reaches between 380°C and 400°C, slowly withdraw the input of superheated steam.

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