System and method for further reducing cold temperature of ammonia synthesis ammonia
By adding a third-level ammonia cooler and liquid ammonia heater, the ammonia cooling temperature and liquid ammonia temperature of the ammonia synthesis system are reduced, and the problems of high ammonia cooling temperature, high system pressure and low output in the ammonia synthesis process are solved, achieving the effect of energy saving and increasing production and avoiding the device parking.
Patent Information
- Application Number
- CN202510338302.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-21
- Publication Date
- 2025-06-13
AI Technical Summary
In the existing ammonia synthesis process, the ammonia cooling temperature is high, which leads to an increase in power consumption of the synthesis gas compressor and a decrease in output. The ammonia absorption and refrigeration is insufficient during high loads, and the system pressure is high, which easily leads to the device stopping.
Add a third-level ammonia cooler to reduce the ammonia cooling temperature and add a liquid ammonia heater to reheat the separated low-temperature liquid ammonia to make the product liquid ammonia reach the designed storage temperature, and at the same time recover the cooling capacity to reduce the liquid ammonia temperature entering the first ammonia cooler and diammonia cooler.
Reduce the ammonia content at the inlet of the synthesis tower, reduce the circulation of the synthesis gas compressor, reduce system pressure, improve production capacity, reduce comprehensive energy consumption, solve the problem of long-term low-efficiency operation of the ammonia compressor, and avoid the device stopping.
Smart Images
Figure CN120140982A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of ammonia synthesis, and specifically relates to a system for further reducing the ammonia cooling temperature in ammonia synthesis, and also relates to a method for this system. Background Art
[0002] The existing ammonia synthesis process technology is as follows: The syngas pressurized by the syngas compressor enters the hot gas-gas heat exchanger, exchanges heat with the outlet gas from the boiler feed water preheater, and enters the ammonia synthesis tower in four paths. One path is the main inlet line to the tower, two paths are the catalyst bed temperature adjustment sub-lines, and the other path is the start-up sub-line. After the syngas reacts in the synthesis tower, it comes out from the bottom of the synthesis tower and enters the waste heat boiler, exchanges heat with the demineralized water from the boiler feed water preheater, and simultaneously by-produces steam at 251.8 °C and 4.1 MPa(A). Then it enters the hot gas-gas heat exchanger, exchanges heat with the process gas at the outlet of the syngas compressor, and then successively enters the water cooler and the cold gas-gas heat exchanger for cooling. Then it enters the first ammonia cooler and is cooled to 0 - 20 °C by the liquid ammonia from the ammonia absorption refrigeration device, and then enters the second ammonia cooler, where it is cooled to 0 °C by the liquid ammonia from the ammonia absorption refrigeration device and enters the high-pressure ammonia separator. The separated gas (circulation gas) enters the cold gas-gas heat exchanger for reheating, returns to the recycle section of the syngas compressor for pressurization, and then enters the next cycle of the ammonia synthesis system for continuous reaction. The separated liquid ammonia enters the medium-pressure ammonia separator, and the liquid ammonia coming out of the medium-pressure ammonia separator is sent to the ammonia storage tank at a pressure of 3.65 MPa(G) and a temperature of 2.5 °C. The ammonia absorption refrigeration process has two-stage ammonia cooling, and the designed final cooling temperature is 0 °C. The temperature of the syngas after the second-stage ammonia cooling is 0 °C when entering the ammonia separator. The ammonia content in the gas at the inlet of the synthesis recycle section is 4.36%, and the ammonia content at the inlet of the synthesis tower is 3.3% - 3.5%, which is higher than the ammonia content of 2% in other ammonia synthesis processes. Its disadvantages are as follows: First, the cooling temperature is high. With two-stage ammonia absorption refrigeration, the outlet temperature of the second stage can only be reduced to 0 °C at most. The high ammonia content in the recycle section will inhibit the forward reaction rate of ammonia synthesis, increase the power consumption of the syngas compressor, and the output will also decrease. Second, there is a phenomenon of insufficient cooling capacity in the ammonia absorption refrigeration after high load and high circulating water temperature in summer. Third, this device is also equipped with a turbine-driven centrifugal ammonia compressor, which only provides cooling capacity for the low-temperature methanol washing. The designed margin of the ammonia ice machine is large. At full load, the opening degrees of the two return valves are very large, and the return amounts of the three-way one valve (valve opening degree 45%) and the three-way two valve (valve opening degree 35%) are about the same, resulting in low efficiency. Fourth, at 100% load, the pressure of the synthesis system is close to the control target value of 15.98 Mpa, which limits further production increase, has high comprehensive energy consumption, the ammonia compressor runs inefficiently for a long time, the system pressure is high, and the devices in the system are prone to shutdown. Summary of the Invention
[0003] The object of the present invention is to overcome the above-mentioned drawbacks and provide a system and method for further reducing the ammonia cooling temperature in ammonia synthesis, which includes adding a third-stage ammonia cooler to lower the ammonia cooling temperature, adding a liquid ammonia heater to reheate the low-temperature liquid ammonia after separation, so that the product liquid ammonia reaches the designed storage temperature, while recovering cold energy, reducing the temperature of the liquid ammonia entering the first ammonia cooler and the second ammonia cooler, with high production efficiency, reducing the comprehensive energy consumption, solving the problem of long-term low-efficiency operation of the ammonia compressor, reducing the system pressure, and avoiding the shutdown of the devices in the system.
[0004] The object of the present invention and the solution to its main technical problems are achieved by the following technical solutions: A system for further reducing the ammonia cooling temperature in ammonia synthesis according to the present invention includes a liquid ammonia heater, a first ammonia cooler, a second ammonia cooler, a third ammonia cooler, a high-pressure ammonia separator, a medium-pressure ammonia separator, a cold gas heat exchanger, a water cooler, a hot gas heat exchanger, a boiler feed water preheater, a waste heat boiler, and an ammonia synthesis tower. The waste heat boiler is connected to the boiler feed water preheater through a pipeline, the boiler feed water preheater is connected to the hot gas heat exchanger through a pipeline, the hot gas heat exchanger is respectively connected to the water cooler and the ammonia synthesis tower through pipelines, the water cooler is connected to the cold gas heat exchanger through a pipeline, the cold gas heat exchanger is respectively connected to the first ammonia cooler and the high-pressure ammonia separator through pipelines, the first ammonia cooler is connected to the second ammonia cooler through a pipeline, wherein the liquid ammonia heater is respectively connected to the first ammonia cooler, the third ammonia cooler, and the medium-pressure ammonia separator through pipelines, the third ammonia cooler is respectively connected to the second ammonia cooler and the high-pressure ammonia separator through pipelines, and the high-pressure ammonia separator is connected to the medium-pressure ammonia separator through a pipeline.
[0005] A method for further reducing the ammonia cooling temperature in ammonia synthesis, characterized in that: the syngas after being pressurized by the syngas compressor enters the hot gas heat exchanger, exchanges heat with the outlet gas from the boiler feed water preheater, and enters the ammonia synthesis tower in four paths. One path is the main inlet line to the tower, two paths are the catalyst bed temperature adjustment auxiliary lines, and the other path is the start-up auxiliary line. After the syngas reacts in the ammonia synthesis tower, it comes out from the bottom of the ammonia synthesis tower, enters the waste heat boiler, exchanges heat with the demineralized water from the boiler feed water preheater, and at the same time by-produces steam at 251.8 °C and 4.1 MPa(A). Then it enters the hot gas heat exchanger, exchanges heat with the process gas at the outlet of the syngas compressor, and then successively enters the water cooler and the cold gas heat exchanger for cooling; then it enters the first ammonia cooler and is cooled to 12 °C by the liquid ammonia from the ammonia absorption refrigeration device, then enters the second ammonia cooler and is cooled to 0 °C by the liquid ammonia from the ammonia absorption refrigeration device, then enters the third ammonia cooler and is cooled to -10 to -15 °C, and then enters the high-pressure ammonia separator. The separated recycle gas enters the cold gas heat exchanger for reheating, returns to the recycle section of the syngas compressor to be pressurized, and then enters the next cycle of the ammonia synthesis system for continuous reaction; the separated liquid ammonia enters the medium-pressure ammonia separator. The liquid ammonia coming out of the medium-pressure ammonia separator exchanges heat with the liquid ammonia from the absorption refrigeration through the liquid ammonia heater, and then the liquid ammonia with a pressure of 3.65 MPa and a temperature of 2.5 °C is sent to the ammonia storage tank for storage. The liquid ammonia on the shell side of the third ammonia cooler comes from the existing ammonia compressor work-saving device, with a pressure of 0.4 MPa and a flow rate of 12 t / h. The liquid ammonia on the shell side of the third ammonia cooler evaporates under the conditions of -15.1 °C and 0.13 MPa, reducing the temperature of the syngas on the tube side to -10 to -15 °C; the gaseous ammonia evaporated on the shell side is depressurized to 70 - 75 kPaA and sent to the separator at the inlet of the first stage of the ammonia compressor for separation.
[0006] Compared with the prior art, the present invention has obvious beneficial effects. From the above technical solutions, it can be seen that the liquid ammonia heater (1) is respectively connected to the first ammonia cooler, the third ammonia cooler, and the medium-pressure ammonia separator through pipelines. The third ammonia cooler is respectively connected to the second ammonia cooler and the high-pressure ammonia separator through pipelines. The high-pressure ammonia separator is connected to the medium-pressure ammonia separator through a pipeline. A third-stage ammonia cooler is added after the second-stage ammonia cooler in the synthesis system to reduce the ammonia cooling temperature, so as to reduce the ammonia content in the recycled gas entering the synthesis tower, increase the ammonia net value, reduce the recycled gas volume, reduce the load of the synthesis gas compressor, and finally achieve the purpose of energy conservation and output increase. The liquid ammonia required for refrigeration is supplied by the ammonia ice machine, and the gaseous ammonia generated by refrigeration flashing is incorporated into the inlet of the ammonia ice machine. A liquid ammonia heater is added after the medium-pressure ammonia separator in the synthesis system to reheat the low-temperature liquid ammonia after separation, so that the product liquid ammonia reaches the designed storage temperature, and at the same time, the cold energy is recovered, and the temperature of the liquid ammonia entering the first ammonia cooler and the second ammonia cooler is reduced. Comparison before and after the transformation; the average data of three days of operation before and after the transformation. It can be seen from the table that after the transformation, while increasing the liquid ammonia production by 528.7 t in three days and the average hourly liquid ammonia production by 7.4 t, the ammonia content at the inlet of the synthesis tower drops to 1.83%, a decrease of 1.91%, the pressure of the ammonia synthesis system drops by 0.25 MPa, the recycled gas volume increases by 10611 Nm3 / h, the rotational speed drops by 113 rpm, and the steam consumption of the 9.8 MPa steam of the synthesis gas compressor per hour decreases by 8 t under the condition of increasing the production by 7.4 t per hour. The energy conservation, output increase and consumption reduction of the synthesis system are released, and the reflux of the ammonia compressor is completely closed, improving the efficiency of the ammonia compressor. According to statistics, the annual efficiency can be increased by more than 30 million yuan, achieving the expected goal of output increase, energy conservation and consumption reduction.
[0007] Technical effects: reduce the ammonia content at the inlet of the synthesis tower, reduce the recycle volume of the syngas compressor, lower the pressure of the synthesis system, which is beneficial to improving the production capacity of the syngas compressor and the synthesis system and reducing the comprehensive energy consumption; reduce the steam consumption of the syngas compressor and the absorption refrigeration section, playing a role in energy conservation and carbon reduction; reasonably utilize the surplus cooling capacity of the ammonia compressor to solve the problem of long-term low-efficiency operation of the ammonia compressor; break through the production capacity limit and increase the liquid ammonia output; lower the system pressure and also reduce the risks of equipment and pipeline leakage and overpressure; when there are problems in the absorption refrigeration system and the first and second ammonia coolers cannot operate normally, the newly added third ammonia cooler can maintain the system operation and avoid plant shutdown. Among them, the third ammonia cooler is a newly purchased equipment with a structural type of NKU and a manufacturer of Lanzhou LS Heavy Equipment Co., Ltd.; the liquid ammonia heater is a newly purchased equipment with a structural type of BEM and a manufacturer of Lanzhou LS Heavy Equipment Co., Ltd. In short, the present invention adds a third-stage ammonia cooler to lower the ammonia cooling temperature, adds a liquid ammonia heater to reheat the low-temperature liquid ammonia after separation, enables the product liquid ammonia to reach the designed storage temperature, simultaneously recovers the cooling capacity, reduces the liquid ammonia temperature entering the first and second ammonia coolers, has high production efficiency, reduces the comprehensive energy consumption, solves the problem of long-term low-efficiency operation of the ammonia compressor, lowers the system pressure, and avoids plant shutdown within the system. Brief Description of the Drawings
[0008] Figure 1 is a schematic structural diagram of the present invention.
[0009] Reference Signs in the Drawings 1. Liquid ammonia heater; 2. First ammonia cooler; 3. Second ammonia cooler; 4. Third ammonia cooler; 5. High-pressure ammonia separator; 6. Medium-pressure ammonia separator; 7. Cold gas heat exchanger; 8. Water cooler; 9. Hot gas heat exchanger; 10. Boiler feed water preheater; 11. Waste heat boiler; 12. Ammonia synthesis tower. Detailed Embodiments
[0010] The following will describe in detail the specific embodiments, structures, features and functions of the present invention in conjunction with the accompanying drawings and preferred embodiments.
[0011] A system for further reducing the ammonia cooling temperature in ammonia synthesis, comprising a liquid ammonia heater 1, a first ammonia cooler 2, a second ammonia cooler 3, a third ammonia cooler 4, a high-pressure ammonia separator 5, a medium-pressure ammonia separator 6, a cold gas heat exchanger 7, a water cooler 8, a hot gas heat exchanger 9, a boiler feed water preheater 10, a waste heat boiler 11, and an ammonia synthesis tower 12. The waste heat boiler 11 is connected to the boiler feed water preheater 10 through a pipeline. The boiler feed water preheater 10 is connected to the hot gas heat exchanger 9 through a pipeline. The hot gas heat exchanger 9 is respectively connected to the water cooler 8 and the ammonia synthesis tower 12 through pipelines. The water cooler 8 is connected to the cold gas heat exchanger 7 through a pipeline. The cold gas heat exchanger 7 is respectively connected to the first ammonia cooler 2 and the high-pressure ammonia separator 5 through pipelines. The first ammonia cooler 2 is connected to the second ammonia cooler 3 through a pipeline. It is characterized in that the liquid ammonia heater 1 is respectively connected to the first ammonia cooler 2, the third ammonia cooler 4, and the medium-pressure ammonia separator 6 through pipelines. The third ammonia cooler 4 is respectively connected to the second ammonia cooler 3 and the high-pressure ammonia separator 5 through pipelines. The high-pressure ammonia separator 5 is connected to the medium-pressure ammonia separator 6 through a pipeline.
[0012] A method for further reducing the ammonia cooling temperature in ammonia synthesis, which is characterized in that the syngas pressurized by a syngas compressor enters the hot gas heat exchanger 9, exchanges heat with the off-tower gas from the boiler feed water preheater 10, and enters the ammonia synthesis tower 12 in four paths. One path is the main in-tower line, two paths are the catalyst bed temperature adjustment sub-lines, and the other path is the start-up sub-line. After the syngas reacts in the ammonia synthesis tower 12, it comes out from the bottom of the ammonia synthesis tower 12 and enters the waste heat boiler 11, exchanges heat with the desalted water from the boiler feed water preheater 10, and simultaneously by-produces steam at 251.8 °C and 4.1 MPa(A). Then it enters the hot gas heat exchanger 9, exchanges heat with the process gas at the outlet of the syngas compressor, and then successively enters the water cooler 8 and the cold gas heat exchanger 7 for cooling; then it enters the first ammonia cooler 2 and is cooled to 12 °C by the liquid ammonia from the ammonia absorption refrigeration device, then enters the second ammonia cooler 3 and is cooled to 0 °C by the liquid ammonia from the ammonia absorption refrigeration device, then enters the third ammonia cooler 4 and is cooled to -10 to -15 °C, and then enters the high-pressure ammonia separator 5. The separated recycle gas enters the cold gas heat exchanger 7 to be reheated, returns to the recycle section of the syngas compressor to be pressurized, and then enters the next cycle of the ammonia synthesis system to continue the reaction; the separated liquid ammonia enters the medium-pressure ammonia separator 6. The liquid ammonia coming out of the medium-pressure ammonia separator 6 exchanges heat with the liquid ammonia from the absorption refrigeration through the liquid ammonia heater 1, and then the liquid ammonia with a pressure of 3.65 MPa and a temperature of 2.5 °C is sent to the ammonia storage tank for storage. The liquid ammonia on the shell side of the third ammonia cooler 4 comes from the existing ammonia compressor work-saving device, with a pressure of 0.4 MPa and a flow rate of 12 t / h. The liquid ammonia on the shell side of the third ammonia cooler 4 evaporates under the conditions of -15.1 °C and 0.13 MPa, reducing the temperature of the syngas on the tube side to -10 to -15 °C; the evaporated ammonia gas on the shell side is depressurized to 70 - 75 kPaA and sent to the separator at the inlet of the first stage of the ammonia compressor for separation.
[0013] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.
Claims
1. A system for further reducing the ammonia cooling temperature of ammonia synthesis, comprising a liquid ammonia heater (1), a first ammonia cooler (2), a second ammonia cooler (3), a third ammonia cooler (4), a high-pressure ammonia separator (5), a medium-pressure ammonia separator (6), a cold air heat exchanger (7), a water cooler (8), a hot air heat exchanger (9), a boiler feed water preheater (10), a waste heat boiler (11), and an ammonia synthesis tower (12), wherein the waste heat boiler (11) is connected to the boiler feed water preheater (10) via a pipeline, the boiler feed water preheater (10) is connected to the hot air heat exchanger (9) via a pipeline, the hot air heat exchanger (9) is connected to the water cooler (8) and the ammonia synthesis tower (12) via pipelines, the water cooler (8) is connected to the cold air heat exchanger (7) via pipelines, the cold air heat exchanger (7) is connected to the first ammonia cooler (2) and the high-pressure ammonia separator (5) via pipelines, and the first ammonia cooler (2) is connected to the second ammonia cooler (3) via a pipeline, characterized in that; The liquid ammonia heater (1) is connected to the first ammonia cooler (2), the third ammonia cooler (4), and the medium-pressure ammonia separator (6) through pipelines, the third ammonia cooler (4) is connected to the second ammonia cooler (3) and the high-pressure ammonia separator (5) through pipelines, and the high-pressure ammonia separator (5) is connected to the medium-pressure ammonia separator (6) through a pipeline.
2. A method for further reducing the cooling temperature of ammonia synthesis, characterized in that: The synthesis gas after being pressurized by the synthesis gas compressor enters the hot gas heat exchanger (9) to exchange heat with the outlet gas from the boiler feed water preheater (10), and enters the ammonia synthesis tower (12) in four ways, one of which is the main line for entering the tower, two are auxiliary lines for adjusting the temperature of the catalyst bed, and the other is the auxiliary line for starting up. After the synthesis gas reacts in the ammonia synthesis tower (12), it comes out from the bottom of the ammonia synthesis tower (12) and enters the waste heat boiler (11) to exchange heat with the desalted water from the boiler feed water preheater (10), and at the same time produces 251.8 by-products. ℃, 4.1MPa(A) steam, then enters the hot gas heat exchanger (9), exchanges heat with the process gas from the outlet of the synthesis gas compressor, and then enters the water cooler (8) and the cold gas heat exchanger (7) for cooling; then enters the first ammonia cooler (2), is cooled to 12℃ by the liquid ammonia from the ammonia absorption refrigeration device, then enters the second ammonia cooler (3), is cooled to 0℃ by the liquid ammonia from the ammonia absorption refrigeration device, then enters the third ammonia cooler (4) to be cooled to -10 to -15℃, then enters the high-pressure ammonia separator (5), the separated circulating gas enters the cold gas heat exchanger (7) to be reheated, returns to the circulation section of the synthesis gas compressor to increase the pressure, and then enters the next circulation section of the ammonia synthesis system. The reaction continues in a cycle; the separated liquid ammonia enters the medium-pressure ammonia separator (6); the liquid ammonia coming out of the medium-pressure ammonia separator (6) exchanges heat with the liquid ammonia coming out of the absorption refrigeration through the liquid ammonia heater (1); the liquid ammonia coming out is sent to the ammonia storage at a pressure of 3.65 MPa and 2.5°C; the liquid ammonia on the shell side of the third ammonia cooler (4) comes from the existing ammonia compressor economizer, with a pressure of 0.4 MPa and a flow rate of 12 t / h; the liquid ammonia on the shell side of the third ammonia cooler (4) evaporates at -15.1°C and 0.13 MPa, and the temperature of the synthesis gas on the tube side is reduced to -10 to -15°C; the evaporated gaseous ammonia on the shell side is depressurized to 70-75 kPaA and sent to the separator at the inlet of the first stage of the ammonia compressor for separation.