Cold energy recovery system of ammonia synthesis device

Abstract

The utility model provides a cold energy recovery system of a synthetic ammonia device, which solves the problems that a PSA hydrogen extraction unit of the synthetic ammonia device is low in raw gas temperature and cannot operate normally, recovers the cold energy of the synthetic ammonia device system and reduces the energy consumption of the device, and comprises a shift gas unit, a methanol washing unit, a PSA unit, a first heat exchanger, a second heat exchanger and a condensate separator, a gas outlet of the shift gas unit is sequentially communicated with a shell pass of the first heat exchanger, the condensate separator, a shell pass of the second heat exchanger and the methanol washing unit; and a gas outlet of the methanol washing unit is sequentially communicated with the tube pass of the second heat exchanger, the tube pass of the first heat exchanger and the PSA unit.

Description

Technical Field

[0001] The utility model relates to a cold recovery system, in particular to a cold recovery system for a synthetic ammonia device. Background Art

[0002] In the synthetic ammonia plant system, the "pressure swing adsorption method (PSA method)" is used in the hydrogen purification unit of the synthetic ammonia plant to extract high-purity hydrogen. The basic process is that the conversion gas from the conversion unit enters the low-temperature methanol washing unit to form purified gas, such as Figure 1 As shown, the raw gas from the low-temperature methanol washing unit enters the PSA adsorption tower, the separated hydrogen enters the pipeline network, and the analytical gas enters the compressor.

[0003] The PSA hydrogen extraction unit utilizes a 12-3-5 PSA process flow, meaning that three of the unit's 12 adsorption towers are constantly feeding and adsorbing. The adsorption and regeneration process consists of adsorption, five consecutive pressure reduction cycles, forward and reverse flow, flushing, five consecutive pressure increase cycles, and product gas pressure increase. By alternating these adsorption and regeneration steps across the 12 adsorption towers, continuous gas separation and purification is achieved.

[0004] The feed gas for the PSA hydrogen extraction unit comes from the purified gas from the low-temperature methanol scrubbing unit of the ammonia synthesis plant. Under normal operating conditions, the purified gas from the methanol scrubbing unit is at -56°C, while the hydrogen entering the PSA hydrogen extraction unit must be at a temperature of 30°C, which does not meet the operating requirements of the PSA hydrogen extraction unit. Therefore, the purified gas from the low-temperature methanol scrubbing unit must be heated before entering the PSA hydrogen extraction unit. Steam or water is generally used to heat the purified gas, but this inevitably increases the energy consumption of the unit. Utility Model Content

[0005] The utility model provides a cold recovery system for a synthetic ammonia device, which solves the problem that the raw gas temperature of the PSA hydrogen extraction unit of the synthetic ammonia device is low and cannot operate normally, and recovers the cold energy of the synthetic ammonia device system to reduce the energy consumption of the device.

[0006] The utility model is realized through the following technical solutions:

[0007] A cold recovery system for a synthetic ammonia plant, comprising a shift gas unit, a methanol wash unit, a PSA unit, a first heat exchanger, a second heat exchanger and a condensate separator;

[0008] The gas outlet of the conversion gas unit is sequentially connected to the shell side of the first heat exchanger, the condensate separator, the shell side of the second heat exchanger and the methanol washing unit;

[0009] The gas outlet of the methanol washing unit is sequentially connected to the tube side of the second heat exchanger, the tube side of the first heat exchanger and the PSA unit.

[0010] Furthermore, the top of the condensate separator is a gas outlet, and the bottom is a condensate outlet.

[0011] Furthermore, the first heat exchanger and the second heat exchanger are both vertical heat exchangers.

[0012] Furthermore, the specifications of the first heat exchanger are Φ1900×36×10100, the specifications of the second heat exchanger are Φ1500×30×9600, and the specifications of the condensate separator are Φ1100×24×5810.

[0013] The working principle of the cold recovery system of the synthetic ammonia device of the utility model is as follows:

[0014] A portion of the purified gas from the low-temperature methanol scrubbing unit enters the second heat exchanger and then the first heat exchanger (for heat exchange with the shifted gas from the shift conversion unit) to heat up to room temperature before being sent to the PSA hydrogen extraction unit. A portion of the shifted gas (heat exchange medium) from the shift conversion unit enters the first heat exchanger for heat exchange and cooling with the purified gas from the second heat exchanger. It then enters the condensate separator to separate the saturated water in the shifted gas. The shifted gas is discharged from the top of the condensate separator and enters the second heat exchanger for heat exchange and cooling with the low-temperature purified gas from the methanol scrubbing unit outlet. It then enters the low-temperature methanol scrubbing unit for recycling.

[0015] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0016] 1. Part of the purified gas from the low-temperature methanol wash unit enters the second heat exchanger and the first heat exchanger (for heat exchange with the converted gas from the conversion) in sequence. After heat exchange and heating to room temperature, it is sent to the PSA hydrogen extraction unit. This solves the problem of the PSA hydrogen extraction unit of the synthetic ammonia plant being unable to operate normally due to low feed gas temperature, ensuring normal production operation of subsequent processes.

[0017] 2. The shift gas from the heavy shift unit of the ammonia synthesis unit is used to heat the purified gas from the methanol wash unit, thereby recovering the cooling capacity of the ammonia synthesis unit system and reducing the energy consumption of the unit caused by the need for additional heating media such as steam;

[0018] 3. The function of the condensate separator is to separate the saturated water in the conversion gas after heat exchange and cooling to prevent the saturated water from entering the methanol washing unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is the flow chart of the methanol washing unit in the prior art

[0020] Figure 2 This is a schematic diagram of the cold recovery system of the synthetic ammonia device of the present invention;

[0021] In the figure: 1. Shift gas unit, 2. Methanol wash unit, 3. PSA unit, 4. First heat exchanger, 5. Second heat exchanger, 6. Condensate separator. DETAILED DESCRIPTION

[0022] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0023] In the description of the utility model, it should be understood that the terms "front," "rear," "upper," "lower," "left," "right," etc., indicating directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings and are intended solely to facilitate the description of the utility model and simplify the description. They do not indicate or imply that the devices or components referred to must have a specific direction, be constructed, or operate in a specific direction. Therefore, they should not be construed as limiting the utility model. The utility model is further described below with reference to the accompanying drawings and embodiments.

[0024] This embodiment discloses a cold recovery system for an ammonia synthesis plant, which mainly includes a shift gas unit 1, a methanol wash unit 2, a PSA unit 3, a first heat exchanger 4, a second heat exchanger 5, and a condensate separator 6. The first heat exchanger 4 and the second heat exchanger 5 are both vertical heat exchangers.

[0025] The gas outlet of the shift gas unit 1 is connected sequentially via pipes to the shell side of the first heat exchanger 4, the condensate separator 6, the shell side of the second heat exchanger 5, and the methanol wash unit 2. The gas outlet of the methanol wash unit 2 is connected sequentially via pipes to the tube side of the second heat exchanger 5, the tube side of the first heat exchanger 4, and the PSA unit 3. The top of the condensate separator 6 is the gas outlet, and the bottom is the condensate outlet.

[0026] In this embodiment, the specifications of the first heat exchanger 4, the second heat exchanger 5 and the condensate separator 6 are shown in the following table:

[0027]

[0028] The specific working process of the cold recovery system of the synthetic ammonia unit described in this embodiment is as follows:

[0029] The temperature of the partially purified gas from the low-temperature methanol scrubber unit 2 is -56°C, while the temperature of the shifted gas from the shift unit is 35°C. The purified gas then enters the second heat exchanger 5 and the first heat exchanger 4 (where it exchanges heat with the shifted gas from the shift unit) through a pipeline, where it is heated to room temperature before being delivered to the PSA hydrogen extraction unit. Simultaneously, a portion of the shifted gas from the shift unit (serving as the heat exchange medium) enters the first heat exchanger 4, where it exchanges heat with the purified gas from the second heat exchanger 5, reducing its temperature to -25°C. The gas then enters the condensate separator 6, where saturated water is separated from the shifted gas. The shifted gas is discharged from the top of the condensate separator 6 and enters the second heat exchanger 5, where it exchanges heat with the low-temperature purified gas from the outlet of the methanol scrubber unit 2, reducing its temperature, and then enters the low-temperature methanol scrubber unit 2 for recycling.

[0030] This embodiment solves the problem that the PSA hydrogen extraction unit of the synthetic ammonia plant cannot operate normally due to low raw gas temperature, ensuring the normal production and operation of subsequent processes; the conversion gas from the heavy conversion unit of the synthetic ammonia plant is used to heat the purified gas from the methanol washing unit 2, recovering the cooling capacity of the synthetic ammonia plant system and reducing the energy consumption of the plant caused by the additional need for steam and other heat media.

Claims

1. A cold recovery system for a synthetic ammonia plant, characterized in that: It includes a shift gas unit, a methanol wash unit, a PSA unit, a first heat exchanger, a second heat exchanger and a condensate separator; The gas outlet of the conversion gas unit is sequentially connected to the shell side of the first heat exchanger, the condensate separator, the shell side of the second heat exchanger and the methanol washing unit; The gas outlet of the methanol washing unit is sequentially connected to the tube side of the second heat exchanger, the tube side of the first heat exchanger and the PSA unit.

2. The cold recovery system of ammonia synthesis device according to claim 1, characterized in that: The top of the condensate separator is a gas outlet, and the bottom is a condensate outlet.

3. The cold recovery system of ammonia synthesis device according to claim 1, characterized in that: The first heat exchanger and the second heat exchanger are both vertical heat exchangers.

4. The cold recovery system for a synthetic ammonia plant according to any one of claims 1 to 3, characterized in that: The specifications of the first heat exchanger are Φ1900×36×10100, the specifications of the second heat exchanger are Φ1500×30×9600, and the specifications of the condensate separator are Φ1100×24×5810.

Images