Flexible ammonia synthesis process

Abstract

The flexible ammonia synthesis process comprises the following steps: raw material gas is preheated and heated, then enters a temperature-controlled ammonia synthesis tower and reacts under the action of a catalyst, the reacted gas is subjected to heat energy recovery through an outlet waste heat boiler and then enters an ammonia separation tank after being subjected to multi-stage cooling, and a liquid ammonia product is obtained at the bottom; the top non-condensable gas is pressurized by a circulating compressor and then returns to an inlet of the temperature control ammonia synthesis tower; in the temperature-controlled ammonia synthesis tower, raw material gas enters the tower through a raw material gas inlet and sequentially penetrates through the distribution plate, the catalyst bed I section, the distribution plate and the catalyst bed I section from outside to inside in the radial direction, reaction is carried out while heat exchange is carried out, and reaction gas is led out from a reaction gas outlet in the bottom after being converged in the center. The method is simple in process, easy to control, low in equipment investment and operation cost, energy-saving, consumption-reducing, high in reaction efficiency and loose in reaction condition, temperature runaway or temperature loss of a bed layer is not easily caused under high load, and stable operation of the system can still be kept under 0-120% fluctuation of feed gas flow.

Description

Technical Field

[0001] The invention belongs to the field of renewable energy and clean energy conversion, and specifically relates to a flexible ammonia synthesis process. Background Art

[0002] The CO2 emissions of my country's synthetic ammonia industry reached 219 million tons, and the CO2 emissions of coal-based synthetic ammonia, which accounted for 75%, were 4.2 tons CO2 / ton NH3. By developing new processes, the comprehensive energy consumption of traditional synthetic ammonia units can be reduced, which is conducive to reducing carbon emissions. Using renewable energy to electrolyze water to produce hydrogen, and completing the storage, transportation and conversion of green hydrogen through the green hydrogen-green ammonia process has shown good application prospects.

[0003] At present, my country's wind power, solar energy and other renewable energy sources are developing rapidly, but renewable energy generation is intermittent and volatile, which makes it difficult to integrate renewable electricity into the power grid on a large scale. At the same time, the hydrogen produced by water electrolysis is also volatile. Therefore, in order to achieve stable production of green hydrogen and green ammonia, the synthetic ammonia unit needs to meet the wide load fluctuation situation.

[0004] At present, most of the industrialized synthetic ammonia in China and abroad adopts an ammonia synthesis tower with heat exchange between multiple insulation layers. The catalyst layer is divided into multiple layers, and heat exchangers are installed between the layers. The reactor structure is very complex, the equipment is difficult to inspect and maintain, and the equipment cost is high. At the same time, the reaction pressure of the ammonia synthesis tower is usually between 15MPaG and 20MPaG, and the operating energy consumption is high. In particular, the stacking type is adopted between the beds in the reactor, which makes the connection, sealing, thermal stress, gas transportation, etc. between the beds easily lead to a decrease in the net value of ammonia when the raw gas fluctuates at low load, and even the risk of bed temperature runaway and reaction out of control, which limits its application in green ammonia scenarios.

[0005] Patent CN115893446 discloses a set of multi-bed terminal isothermal ammonia synthesis reactors, which have built-in multi-stage radial catalyst beds and a reactor structure with water temperature control at the end. The equipment height is reduced, but the gas flow on the shell and tube side of the reactor is complex, the bed resistance is large, and the multiple cold air pipes are prone to cause uneven gas mixing, especially during low load fluctuations; at the same time, the steam pressure level of the water heat transfer tube bundle reaches 12MPaG, and the equipment cost is high.

[0006] Patent CN113461027 discloses a low-pressure ammonia synthesis tower and a renewable energy low-pressure ammonia synthesis system. A plurality of catalyst frames are mounted inside the outer sleeve of the reactor, and each catalyst frame is equipped with a catalyst bed. This structure is conducive to efficient heat transfer and preheating of raw gas. However, the reactor is provided with two secondary air inlet pipes, which are complex in structure and prone to overheating.

[0007] Patent CN202410264234.0 discloses a flexible control system and control method for synthesizing green ammonia. A new ammonia cracking device is added. When the ammonia cracking device is operated at low load, it is started to produce raw gas, but this significantly increases the complexity of the device and the operating energy consumption.

[0008] Patent CN202410021111.4 discloses a system for dynamically synthesizing green ammonia from new energy hydrogen production and its operating method, including an ammonia synthesis tower and multiple ammonia synthesis regulating towers. When the new energy fluctuates and the output decreases, causing the load of the ammonia synthesis tower to drop to 10-50%, the ammonia synthesized by the first ammonia synthesis regulating tower is returned to the ammonia synthesis tower to maintain the normal operation of the tower; when the load of the first ammonia synthesis regulating tower drops to 10-50%, the ammonia synthesis tower stops running, and the ammonia synthesized by the second ammonia synthesis regulating tower is returned to the first ammonia synthesis regulating tower to maintain the normal operation of the tower.

[0009] Patent CN201710325686.5 discloses a low-pressure ammonia synthesis process, in which the mixed gas coming out of the first ammonia synthesis tower enters the second ammonia synthesis tower filled with a ruthenium-based catalyst for secondary ammonia synthesis. Two ammonia synthesis reactors are used, and heat exchangers are required to transfer heat externally, which fails to exert the maximum efficiency of the catalyst.

[0010] Patent CN202310675830.3 discloses a green ammonia synthesis system and method, which forms a flexible adjustment link by connecting the synthesis gas compressor to the outlet of the heat exchanger, connecting the heat exchanger to the outlet pipeline of the ammonia synthesis tower, and connecting the water cooler and the cold exchanger to the inlet of the synthesis gas compressor, and provides a set of flexible and adjustable load ammonia synthesis process, but the flexible load adjustment can only be carried out within the range of 10% to 100%.

[0011] Patent CN202310092638.1 discloses a molten salt heat transfer ammonia synthesis process, in which the molten salt is sent into the shell side of the ammonia synthesis tower by a molten salt circulation pump, and the mixed gas enters the tube side from the top of the ammonia synthesis tower. Under the action of the catalyst, the hydrogen and nitrogen in the mixed gas undergo an ammonia synthesis reaction, and the heat released by the reaction is removed by the molten salt in the shell side. However, the reaction pressure still needs to be 10 to 15 MPaG, and it is impossible to perform flexible load adjustment under a large range of load changes. Summary of the invention

[0012] The purpose of the present invention is to solve the above technical problems and to provide a flexible ammonia synthesis process which is simple in process, easy to control, has low equipment investment and operating costs, saves energy and reduces consumption, has high reaction efficiency, has loose reaction conditions, is not prone to temperature rise or loss of temperature under high load, and can fully adapt to fluctuations of 0 to 120% in the raw gas flow rate and can still maintain stable operation of the system.

[0013] The technical scheme of the present invention is as follows: the raw gas is preheated and then enters the temperature-controlled ammonia synthesis tower to react under the action of a catalyst, the gas after the reaction is discharged through the waste boiler to recover heat energy, and then enters the ammonia separation tank after multi-stage cooling, and a liquid ammonia product is obtained at the bottom, and the non-condensable gas at the top is pressurized by a circulating compressor and then returned to the inlet of the temperature-controlled ammonia synthesis tower;

[0014] The top of the temperature-controlled ammonia synthesis tower is a raw gas inlet, and the bottom is a reaction gas outlet. Two radially series-connected catalyst bed sections I and II are arranged in the tower. Distribution plates are arranged at the inlets of the catalyst bed sections I and II. The catalyst bed section I is located in the outer layer, filled with an iron-based ammonia synthesis catalyst, and provided with a plurality of heat exchange tubes. The catalyst bed section II is located in the inner layer, filled with a Ru-based ammonia synthesis catalyst, and provided with a plurality of heat exchange tubes. The raw gas enters the tower through the raw gas inlet, passes through the distribution plate, the catalyst bed section I, the distribution plate and the catalyst bed section II in sequence from the outside to the inside in the radial direction, reacts while exchanging heat, and the reaction gas is led out from the reaction gas outlet at the bottom after merging at the center. The temperature control medium in the heat exchange tube is heat transfer oil or molten salt.

[0015] The center distance of the heat exchange tubes in the catalyst bed section I is 45-60 mm, and the wall distance of the heat exchange tubes in the catalyst bed section II is 50-80 mm.

[0016] The radial thickness of the catalyst bed section I is 2 / 3 to 4 / 5 of the total radial thickness of the catalyst bed, and the radial thickness of the catalyst bed section II is 1 / 5 to 1 / 3 of the total radial thickness of the catalyst bed.

[0017] The inlet temperature of the temperature-controlled ammonia synthesis tower is controlled to be 320-380°C, the outlet temperature of the catalyst bed section I is 300-420°C; the outlet temperature of the catalyst bed section II is 300-400°C, and the reaction pressure is 7.0-13.5MPaG.

[0018] The Ru-based ammonia synthesis catalyst uses a rare earth modified carbon material as a carrier and a Ru-rare earth dual component as an active component.

[0019] The preparation method of the Ru-based ammonia synthesis catalyst is:

[0020] (1) Preparation of rare earth modified carbon material carrier Supp-M: The rare earth precursor is loaded on the carbon material carrier by an impregnation method to obtain a rare earth modified carbon material powder Supp-F, and then the powder Supp-F is placed on the partition in the reactor by a hydrothermal induction method. The reactor is heated to 150-210°C and treated for 8 hours to obtain a powder Supp-S. Supp-S is then treated at 300-350°C for 4 hours under a hydrogen atmosphere to obtain a rare earth modified carbon material carrier Supp-M, wherein the rare earth carrier loading accounts for 0.001-0.010 times the specific surface area of ​​the carbon material carrier, and the rare earth precursor is two or three of lanthanum nitrate, yttrium nitrate, cerium nitrate, and scandium nitrate;

[0021] (2) Preparation of Ru-rare earth dual-active component ammonia synthesis catalyst: Ru and rare earth active component are prepared into a precursor solution, and Ru-rare earth is loaded on a rare earth modified carbon material carrier Supp-M by vacuum ultrasonic impregnation method, followed by calcination to obtain a Ru-rare earth dual-active component ammonia synthesis catalyst, wherein the mass ratio of Ru to the rare earth active component is 0.003:1 to 0.05:1; the mass ratio of Ru to the rare earth modified carbon material carrier Supp-M is 0.001:1 to 0.005:1; the rare earth active component is one of lanthanum nitrate, yttrium nitrate, cerium nitrate, and scandium nitrate.

[0022] In the preparation method of the catalyst, the calcination conditions of step (2) are: first calcining at 150-300°C using a H2 / Ar mixed gas atmosphere, then calcining at 300-350°C using an O2 / N2 atmosphere, and finally calcining at 350-50°C using an air atmosphere.

[0023] The preheating and temperature raising process of the raw gas includes: the raw gas is preheated and heated in turn through the inlet and outlet heat exchangers and the reaction gas heater and then sent to the temperature-controlled ammonia synthesis tower; the reaction gas leaving the controlled synthesis tower recovers heat energy through the outlet waste boiler and then enters the ammonia separation tank after multi-stage cooling; the multi-stage cooling process includes the reaction gas exchanging heat and cooling with the raw gas through the inlet and outlet heat exchangers, and then further cooling through the water cooler and the cold exchanger, and finally entering the ammonia cryogenic refrigerator for deep cooling.

[0024] The non-condensable gas at the top of the ammonia separation tank is firstly heat exchanged with the reaction gas through a cold exchanger, then pressurized by a circulating compressor, and then mixed with the raw gas, and then preheated by an inlet and outlet heat exchanger and a reaction gas heater before being sent to a temperature-controlled ammonia synthesis tower.

[0025] When the raw gas flow rate is running at a load of 11% to 120%, the temperature control medium exiting the temperature-controlled ammonia synthesis tower is sent to the steam generator to produce high-pressure steam and then returned to the temperature-controlled ammonia synthesis tower via the temperature control medium storage tank; when the raw gas flow rate is running at a load of 0-10%, the temperature control medium exiting the temperature-controlled ammonia synthesis tower enters the temperature control medium storage tank via the bypass of the steam generator and then returned to the temperature-controlled ammonia synthesis tower.

[0026] The control medium leaving the temperature control medium storage tank is divided into two streams. The first stream enters the temperature control ammonia synthesis tower to remove heat, and the second stream enters the reaction gas heater to preheat the raw gas and then returns to the temperature control medium storage tank.

[0027] When the raw gas flow rate is running at 31% to 110% load, the flow rate of the second temperature control medium is 3% to 8% of the total flow rate; when the raw gas flow rate is running at 0 to 30% load, the flow rate of the second temperature control medium is 30% to 40% of the total flow rate.

[0028] When the raw gas flow rate is running at 31% to 120% load, all the reaction gas enters the inlet and outlet waste boilers to produce high-pressure steam; when the raw gas flow rate is running at 0 to 30% load, 70 to 90% of the reaction gas bypasses the outlet waste boiler, and the rest enters the inlet and outlet waste boilers.

[0029] A flow regulating loop is set at the circulating compressor. When the raw gas flow rate is running at a low load of 0-10%, 81-100% of the non-condensable gas is introduced into the flow regulating loop of the circulating compressor for circulation, and the remaining non-condensable gas is introduced into the circulating compressor to maintain low load operation. When the raw gas flow rate is running at a load of 11-20%, all the non-condensable gas is introduced into the circulating compressor.

[0030] When the raw gas flow rate is running at 0-10% load, the temperature control medium storage tank heats the incoming control medium.

[0031] In view of the problems existing in the background technology, the inventor has made the following improvements:

[0032] 1) The arrangement and heat exchange mode of the catalyst bed in the temperature-controlled ammonia synthesis tower are improved: on the one hand, in view of the characteristics of the ammonia synthesis reaction that the nitrogen concentration at the inlet is high and the reaction heat release is large, while the nitrogen concentration at the outlet is low and the heat release is small, two radially connected catalyst bed sections I and II are arranged in series. Compared with the axially arranged heat exchange structure between the insulation layers, the equipment structure is simpler, the manufacturing cost is low, the raw gas is introduced into the catalyst bed from the periphery to the center, the introduction area is larger, the distribution is more uniform, the reaction efficiency is higher, and the reactor heat removal efficiency is higher; on the other hand, the outer catalyst bed section I is filled with a conventional iron-based ammonia synthesis catalyst, such as the pre-reduction catalyst produced by Clariant. This type of catalyst has a low cost and suitable activity, is suitable for raw gas with high nitrogen concentration and large heat release, and can effectively avoid bed temperature runaway with a closer spacing of heat pipes and a temperature control medium; the inner catalyst bed section II is filled with a low-temperature and high-activity Ru-based ammonia synthesis catalyst. This type of catalyst can show good ammonia synthesis performance at a lower temperature and low concentration, and improve the single-pass conversion rate. This radial double-layer catalyst bed structure can minimize costs while increasing single-pass conversion rate and export ammonia net value. In addition, the raw gas does not need an additional side line inlet, but enters the temperature-controlled ammonia synthesis from the top in a single stream, greatly reducing the control difficulty.

[0033] 2) The II section is filled with a Ru-based ammonia synthesis catalyst with high activity at low temperature. This type of catalyst is particularly preferably a Ru-rare earth dual-active component ammonia synthesis catalyst, which can be prepared by the above method. It uses a rare earth modified carbon material as a carrier and a Ru-rare earth dual-component as an active component. It has a stable nano-interface structure and surface defect sites. It uses the electron-rich structure of the carbon carrier and the oxygen vacancies of the rare earth element to couple the dual effects of the two, which is conducive to activating N2 molecules and improving the low-temperature activity of the catalyst. It exhibits good ammonia synthesis performance under low pressure (7.0-13.5MPaG) and low temperature (350-380°C) reaction conditions, and the net value of ammonia per pass at the outlet reaches 25-34%. On this basis, the radial thickness of the catalyst bed section I is greater than the radial thickness of the catalyst bed section II, which can adapt to high loads, ensure reaction efficiency, and further reduce catalyst costs.

[0034] 3) In view of the wide load fluctuation (0-120%) of the upstream raw gas in the background technology, in addition to improving the temperature-controlled ammonia synthesis tower, the inventors also set up multiple control means to achieve flexible ammonia synthesis, including:

[0035] The temperature control medium is heat transfer oil or molten salt, and a bypass of the steam generator is set at the same time. When the raw gas flow rate is running at a load of 11% to 120%, the temperature control medium exiting the temperature-controlled ammonia synthesis tower is sent to the steam generator to produce high-pressure steam and then returned to the temperature-controlled ammonia synthesis tower through the temperature-controlled medium storage tank; when the raw gas flow rate is running at a load of 0-10%, the reaction heat is relatively small, and the temperature control medium exiting the temperature-controlled ammonia synthesis tower enters the temperature-controlled medium storage tank through the bypass of the steam generator, does not produce high-pressure steam, and is directly returned to the temperature-controlled ammonia synthesis tower.

[0036] The control medium out of the temperature control medium storage tank is divided into two streams. The first stream enters the temperature control ammonia synthesis tower to remove heat, and the second stream enters the reaction gas heater to preheat the raw gas and then returns to the temperature control medium storage tank. When the reaction load is 31% to 110%, the second stream of temperature control medium maintains 3% to 8% of the total flow. When the reaction gas load increases, the flow of the temperature control medium can be directly increased to better adapt to the fluctuation of the synthetic ammonia working conditions; when the reaction load is 0 to 30%, the flow of the second stream of temperature control medium is 30% to 40% of the total flow to control the preheated reaction gas to reach the reactor inlet temperature, avoid affecting the catalyst performance during low load operation, and increase the service life of the catalyst.

[0037] A bypass is set for the outlet waste boiler. When the load is 0-30%, most of the reaction gas goes through the bypass of the outlet waste boiler to avoid affecting the bed inlet temperature at low load. When the load is 31%-120%, most of the reaction gas inlet and outlet waste boilers produce high-pressure steam.

[0038] A flow regulating loop is set at the circulating compressor. When the raw gas flow is 0-10% low load operation, the circulating compressor maintains low load operation. At the same time, 81-100% of the flow of non-condensable gas is introduced into the flow regulating loop of the circulating compressor for circulation.

[0039] The temperature control medium storage tank is equipped with a heating device. When the raw gas flow is running at 0-10% load, the temperature control medium storage tank heats the incoming temperature control medium. The temperature of the temperature control medium can be flexibly controlled according to the reaction temperature requirements of the temperature control ammonia synthesis tower to adapt to low load operation.

[0040] 4) Introduce the reaction gas into the outlet waste boiler to produce high-pressure steam, introduce the reaction gas into the inlet and outlet heat exchangers to preheat the raw gas, and introduce the reaction gas into the cold exchanger to preheat the non-condensable gas; introduce the temperature control medium out of the reactor into the steam generator to produce high-pressure steam, and introduce part of the temperature control medium into the reaction gas heater to preheat the raw gas. Through multiple multi-stage heat exchanges, sufficient waste heat recovery is achieved, which effectively saves energy and reduces consumption, and reduces operating costs.

[0041] In summary, the process of the present invention is extremely simple, the equipment investment and operating cost are low, and the single-stream feed can fully adapt to the large range fluctuation of 0-120% of the raw gas load. The operation flexibility is extremely large, and the system can maintain the insulation state under 0 load. When starting again, the process gas is directly introduced to the target load, which can greatly simplify the load lifting and lowering operations. The synthetic ammonia reaction pressure can be 7.0-13.5MPaG, the equipment investment can be reduced by more than 30%, the operating cost can be reduced by 15%, the single-pass conversion rate of the reactor is high, and the single-pass ammonia net value of the outlet reaches 25-34%, and the energy-saving and consumption-reducing effect is obvious.

[0042] Instruction Manual

[0043] Figure 1 It is a process flow chart of the present invention.

[0044] Figure 2 This is a schematic diagram of the structure of a temperature-controlled ammonia synthesis tower.

[0045] Among them, R101 is a temperature-controlled ammonia synthesis tower, E101 is an inlet and outlet heat exchanger, E102 is a reaction gas heater, E103 is an outlet waste boiler, E104 is a water cooler, E105 is a cold exchanger, E106 is an ammonia deep cooler, E108 is a bypass cooler, E201 is a steam generator, E301 is an ammonia refrigeration station, V101 is a steam drum, V102 is an ammonia separation tank, and V201 is a temperature-controlled medium storage tank. A is the bypass of the steam generator, B is the bypass of the outlet waste boiler, and C is a flow control loop.

[0046] 1 is the raw gas inlet; 2 is the temperature control medium outlet; 3 is the tower wall; 4 is the distribution plate; 5 is the distribution plate; 6 is the catalyst bed section II; 7 is the catalyst bed section I; 8 is the temperature control medium inlet; 9 is the reaction gas outlet and 10 is the heat exchange tube. DETAILED DESCRIPTION

[0047] The process of the present invention is further explained below in conjunction with the accompanying drawings:

[0048] Ru-rare earth dual-active component ammonia synthesis catalyst Example 1:

[0049] (1) Preparation of rare earth modified carbon material carrier Supp-M: The rare earth precursor is loaded on the carbon material carrier by an impregnation method to obtain a rare earth modified carbon material powder Supp-F, and then the powder Supp-F is placed on the partition in the reactor by a hydrothermal induction method. The reactor is heated to 210°C and treated for 8 hours to obtain a powder Supp-S. Supp-S is then treated at 320°C for 4 hours under a hydrogen atmosphere to obtain a rare earth modified carbon material carrier Supp-M (1), wherein the rare earth carrier loading accounts for 0.001 times the specific surface area of ​​the carbon material carrier, and the rare earth precursors are lanthanum nitrate and yttrium nitrate;

[0050] (2) Preparation of Ru-rare earth dual-active component ammonia synthesis catalyst: Ru and rare earth active component are prepared into a precursor solution, and Ru-rare earth is loaded on the rare earth modified carbon material carrier Supp-M by vacuum ultrasonic impregnation method, followed by calcination. The calcination conditions are: first calcination at 150-300°C in H2 / Ar mixed gas atmosphere, then calcination at 300-350°C in O2 / N2 atmosphere, and finally calcination at 350-50°C in air atmosphere to obtain a Ru-rare earth dual-active component ammonia synthesis catalyst, wherein the mass ratio of Ru to the rare earth active component is 0.003:1; the mass ratio of Ru to the rare earth modified carbon material carrier Supp-M is 0.005:1; the rare earth active component is lanthanum nitrate.

[0051] Ru-rare earth dual-active component ammonia synthesis catalyst Example 2:

[0052] (1) Preparation of rare earth modified carbon material carrier Supp-M: The rare earth precursor is loaded on the carbon material carrier by an impregnation method to obtain a rare earth modified carbon material powder Supp-F, and then the powder Supp-F is placed on the partition in the reactor by a hydrothermal induction method. The reactor is heated to 150°C and treated for 8 hours to obtain a powder Supp-S. Supp-S is then treated at 300°C for 4 hours under a hydrogen atmosphere to obtain a rare earth modified carbon material carrier Supp-M, wherein the rare earth carrier loading accounts for 0.010 times the specific surface area of ​​the carbon material carrier, and the rare earth precursor is yttrium nitrate, cerium nitrate, and scandium nitrate;

[0053] (2) Preparation of Ru-rare earth dual-active component ammonia synthesis catalyst: Ru and rare earth active component are prepared into a precursor solution, and Ru-rare earth is loaded on the rare earth modified carbon material carrier Supp-M by vacuum ultrasonic impregnation method, followed by calcination. The calcination conditions are: first calcination at 150-300°C in H2 / Ar mixed gas atmosphere, then calcination at 300-350°C in O2 / N2 atmosphere, and finally calcination at 350-50°C in air atmosphere to obtain a Ru-rare earth dual-active component ammonia synthesis catalyst, wherein the mass ratio of Ru to the rare earth active component is 0.05:1; the mass ratio of Ru to the rare earth modified carbon material carrier Supp-M is 0.002:1; the rare earth active component is one of yttrium nitrates.

[0054] Ru-rare earth dual-active component ammonia synthesis catalyst Example 3:

[0055] (1) Preparation of rare earth modified carbon material carrier Supp-M: The rare earth precursor is loaded on the carbon material carrier by an impregnation method to obtain a rare earth modified carbon material powder Supp-F, and then the powder Supp-F is placed on the partition in the reactor by a hydrothermal induction method. The reactor is heated to 190°C and treated for 8 hours to obtain a powder Supp-S. Supp-S is then treated at 350°C for 4 hours under a hydrogen atmosphere to obtain a rare earth modified carbon material carrier Supp-M, wherein the rare earth carrier loading accounts for 0.0018 times the specific surface area of ​​the carbon material carrier, and the rare earth precursor is yttrium nitrate or cerium nitrate;

[0056] (2) Preparation of Ru-rare earth dual-active component catalyst for ammonia synthesis: Ru and rare earth active component are prepared into a precursor solution, and Ru-rare earth is loaded on a rare earth modified carbon material carrier Supp-M by vacuum ultrasonic impregnation method, followed by calcination. The calcination conditions are: first calcination at 150-300°C in a H2 / Ar mixed gas atmosphere, then calcination at 300-350°C in an O2 / N2 atmosphere, and finally calcination at 350-50°C in an air atmosphere to obtain a Ru-rare earth dual-active component catalyst for ammonia synthesis, wherein the mass ratio of Ru to the rare earth active component is 0.01:1; the mass ratio of Ru to the rare earth modified carbon material carrier Supp-M is 0.005:1; and the rare earth active component is scandium nitrate.

[0057] Temperature controlled ammonia synthesis tower structure:

[0058] See also Figure 2 The top of the temperature-controlled ammonia synthesis tower is a raw gas inlet 1, and the bottom is a reaction gas outlet 9. Two radially connected catalyst beds I and II are arranged in series in the tower. Distribution plates 4 and 5 are arranged at the inlets of the catalyst beds I and II, and holes of φ2 to φ5 mm are evenly distributed on the distribution plates. The catalyst bed I is located in the outer layer, filled with an iron-based ammonia synthesis catalyst, and provided with a plurality of heat exchange tubes 10 with a tube center distance of 45 to 60 mm. The catalyst bed II is located in the inner layer, filled with a Ru-based ammonia synthesis catalyst, and provided with a plurality of heat exchange tubes 10 with a tube center distance of 50 to 80 mm. The raw gas enters the tower through the raw gas inlet 1, passes through the distribution plate 4, the catalyst bed I, the distribution plate 5 and the catalyst bed II from the outside to the inside in sequence in the radial direction, and reacts while exchanging heat. The reaction gas is led out from the reaction gas outlet 9 at the bottom after merging at the center. The temperature control medium in the heat exchange tube is heat transfer oil or molten salt. The lower end of the heat exchange tube is connected to the temperature control medium inlet 8, and the upper end is connected to the temperature control medium outlet 2.

[0059] The radial thickness of the catalyst bed section I is 2 / 3 to 4 / 5 of the total radial thickness of the catalyst bed, and the radial thickness of the catalyst bed section II is 1 / 5 to 1 / 3 of the total radial thickness of the catalyst bed.

[0060] Process Example:

[0061] See also Figure 1 and Figure 2 The raw gas (composed of 75% hydrogen and 25% nitrogen by volume) from the upstream process is preheated and heated in turn through the inlet and outlet heat exchangers E101 and the reaction gas heater E102, and then sent to the temperature-controlled ammonia synthesis tower R101; in the temperature-controlled ammonia synthesis tower R101, the raw gas enters the tower through the raw gas inlet 1, flows downward along the outer peripheral tower wall, and passes through the distribution plate 4, the catalyst bed I section 7, the distribution plate 5 and the catalyst bed II section 6 from the outside to the inside, while reacting and transferring heat synchronously through the heat exchange tube, and the reaction gas is led out from the reaction gas outlet 9 at the bottom after merging at the center, and the temperature control medium in the heat exchange tube is heat transfer oil. The inlet temperature of the temperature-controlled ammonia synthesis tower E101 is controlled to be 320-380°C, the outlet temperature of the catalyst bed I section is 300-420°C; the outlet temperature of the catalyst bed II section is 300-400°C, and the reaction pressure is 7.0-13.5MPaG.

[0062] The reaction gas from the controlled synthesis tower R101 is recovered through the outlet waste boiler E103 to produce by-product steam after heat energy is recovered, and is cooled by heat exchange with the raw gas through the inlet and outlet heat exchangers E101, and then is further cooled by the water cooler E104 and the cold exchanger E105, and then enters the ammonia deep freezer E106 for deep cooling, and finally enters the ammonia separation tank V102 for gas-liquid separation, and liquid ammonia product is obtained at the bottom. The non-condensable gas at the top is firstly heat exchanged with the reaction gas through the cold exchanger E105, and then is pressurized by the circulating compressor C201, and then mixed with the raw gas, and then preheated and heated by the inlet and outlet heat exchangers E101 and the reaction gas heater E102, and then sent to the temperature-controlled ammonia synthesis tower R101.

[0063] Considering the change of raw gas load in the upstream process between 0-120%, the specific flexible control measures are as follows:

[0064] When the raw gas flow rate is running at a load of 11% to 120%, the temperature control medium exiting the temperature-controlled ammonia synthesis tower R101 is sent to the steam generator E201 to produce high-pressure steam and then returned to the temperature-controlled ammonia synthesis tower R101 via the temperature-controlled medium storage tank V201; when the raw gas flow rate is running at a load of 0-10%, the temperature control medium exiting the temperature-controlled ammonia synthesis tower R101 enters the temperature-controlled medium storage tank V201 via the bypass A of the steam generator and then returned to the temperature-controlled ammonia synthesis tower R101.

[0065] The control medium out of the temperature control medium storage tank V201 is divided into two streams, the first stream enters the temperature control ammonia synthesis tower R101 for heat removal, and the second stream enters the reaction gas heater E102 for preheating the raw gas and then returns to the temperature control medium storage tank V201. The specific control means are: when the raw gas flow is running at 31% to 110% load, the flow of the second temperature control medium is 3% to 8% of the total flow (total flow of the temperature control medium); when the raw gas flow is running at 0 to 30% load, the flow of the second temperature control medium is 30% to 40% of the total flow.

[0066] When the raw gas flow rate is running at 31% to 120% load, all the reaction gas enters the inlet and outlet waste boiler E103 to produce high-pressure steam; when the raw gas flow rate is running at 0 to 30% load, 70 to 90% of the reaction gas flows through the bypass B of the outlet waste boiler, and the rest enters the inlet and outlet waste boiler E103.

[0067] A flow regulating loop C is set at the circulating compressor. When the raw gas flow rate is running at a low load of 0-10%, 81-100% of the non-condensable gas is introduced into the flow regulating loop C of the circulating compressor for circulation, and the remaining non-condensable gas is introduced into the circulating machine compressor C201 to maintain low load operation. When the raw gas flow rate is running at a load of 11-120%, all the non-condensable gas is introduced into the circulating compressor C201.

[0068] When the raw gas flow rate is running at 0-10% load, the temperature control medium storage tank V201 (with a heating device) heats the incoming control medium to meet the temperature control requirements in the temperature control ammonia synthesis tower R101. When the raw gas flow rate is running at 11-120% load, the heating is stopped.

[0069] The boiler feed water of the waste boiler E103 at the reactor outlet is dynamically adjusted. When the load is 0-30%, the boiler feed water of the waste boiler E103 at the outlet is reduced, and the amount of by-product steam is reduced to avoid affecting the bed inlet temperature at low load. When the load is 31%-120%, the boiler feed water valve of the waste boiler E103 at the outlet is opened wide, and the amount of by-product steam is increased to reasonably utilize the heat released by the reaction.

[0070] In process examples 1-3 using the above process example, the catalyst bed section I is filled with an iron-based ammonia synthesis catalyst (a pre-reduction catalyst produced by Clariant), and the catalyst bed section II is replaced with corresponding three catalysts in the three examples, respectively. The reaction conditions and results are specifically shown in Table 1. Comparative Examples 1 and 2 are the same as Process Example 1, and the specific differences are shown in Table 1.

[0071] Table 1

[0072]

[0073] It can be seen from process examples 1 to 3 that by using a temperature-controlled ammonia synthesis tower and the catalysts of examples 1 to 3, under corresponding reaction conditions, the net ammonia value can reach 23.8%, and the high value can reach 32.2%. When the load peak operation is 0 to 120%, the temperature of the entire bed is relatively stable.

[0074] In comparative example 1, the outlet temperature of the ammonia tower reaches 430°C and the pressure is as high as 15 MPaG, while the net value of outlet ammonia is only 19.5%, which is significantly lower than that of process example 1. The equipment investment and moving equipment energy consumption are relatively high. When operating at a low load of 10%, the bed is prone to cross-temperature.

[0075] In Comparative Example 2, if the bed layer II is loaded with the same catalyst as the catalyst bed layer I, under the same reaction conditions as in Process Example 1, the net value of outlet ammonia is only 18.3%, which is lower than that in Process Example 1, and the low-temperature temperature control effect of the temperature-controlled ammonia synthesis tower cannot be effectively exerted.

Claims

1. A flexible ammonia synthesis process, characterized in that: The raw gas is preheated and then enters the temperature-controlled ammonia synthesis tower, where it reacts under the action of the catalyst. After the reaction, the gas is discharged through the outlet waste boiler to recover heat energy, and then enters the ammonia separation tank after multi-stage cooling. Liquid ammonia products are obtained at the bottom, and the non-condensable gas at the top is pressurized by the circulating compressor and returned to the inlet of the temperature-controlled ammonia synthesis tower. The top of the temperature-controlled ammonia synthesis tower is a raw gas inlet, and the bottom is a reaction gas outlet. Two radially series-connected catalyst bed sections I and II are arranged in the tower. Distribution plates are arranged at the inlets of the catalyst bed sections I and II. The catalyst bed section I is located in the outer layer, filled with an iron-based ammonia synthesis catalyst, and provided with a plurality of heat exchange tubes. The catalyst bed section II is located in the inner layer, filled with a Ru-based ammonia synthesis catalyst, and provided with a plurality of heat exchange tubes. The raw gas enters the tower through the raw gas inlet, passes through the distribution plate, the catalyst bed section I, the distribution plate and the catalyst bed section II in sequence from the outside to the inside in the radial direction, reacts while exchanging heat, and the reaction gas is led out from the reaction gas outlet at the bottom after merging at the center. The temperature control medium in the heat exchange tube is heat transfer oil or molten salt.

2. The flexible ammonia synthesis process according to claim 1, characterized in that: The center distance of the heat exchange tubes in the catalyst bed section I is 45-60 mm, and the wall distance of the heat exchange tubes in the catalyst bed section II is 50-80 mm.

3. The flexible ammonia synthesis process according to claim 1, characterized in that: The radial thickness of the catalyst bed section I is 2 / 3 to 4 / 5 of the total radial thickness of the catalyst bed, and the radial thickness of the catalyst bed section II is 1 / 5 to 1 / 3 of the total radial thickness of the catalyst bed.

4. The flexible ammonia synthesis process according to claim 3, characterized in that: The inlet temperature of the temperature-controlled ammonia synthesis tower is controlled to be 320-380°C, the outlet temperature of the catalyst bed section I is 300-420°C; the outlet temperature of the catalyst bed section II is 300-400°C, and the reaction pressure is 7.0-13.5MPaG.

5. The flexible ammonia synthesis process according to claim 1, characterized in that: The Ru-based ammonia synthesis catalyst uses a rare earth modified carbon material as a carrier and a Ru-rare earth dual component as an active component.

6. The flexible ammonia synthesis process according to claim 5, characterized in that: The preparation method of the Ru-based ammonia synthesis catalyst is: (1) Preparation of rare earth modified carbon material carrier Supp-M: The rare earth precursor is loaded on the carbon material carrier by an impregnation method to obtain a rare earth modified carbon material powder Supp-F, and then the powder Supp-F is placed on a baffle in a reactor and treated again by a hydrothermal induction method. The reactor is heated to 150-210°C and treated for 8 hours to obtain a powder Supp-S. Supp-S is then treated at 300-350°C for 4 hours under a hydrogen atmosphere to obtain a rare earth modified carbon material carrier Supp-M, wherein the rare earth carrier loading accounts for 0.001-0.010 times the specific surface area of ​​the carbon material carrier, and the rare earth precursor is two or three of lanthanum nitrate, yttrium nitrate, cerium nitrate, and scandium nitrate; (2) Preparation of Ru-rare earth dual-active component ammonia synthesis catalyst: Ru and rare earth active component are prepared into a precursor solution, and Ru-rare earth is loaded on a rare earth modified carbon material carrier Supp-M by vacuum ultrasonic impregnation method, followed by programmed temperature calcination to obtain a Ru-rare earth dual-active component ammonia synthesis catalyst, wherein the mass ratio of Ru to the rare earth active component is 0.003:1 to 0.05:1; the mass ratio of Ru to the rare earth modified carbon material carrier Supp-M is 0.001:1 to 0.005:1; the rare earth active component is one of lanthanum nitrate, yttrium nitrate, cerium nitrate, and scandium nitrate.

7. The flexible ammonia synthesis process according to claim 6, characterized in that: In the preparation method of the catalyst, the programmed temperature calcination conditions of step (2) are: first calcining at 150-300°C in a H2 / Ar mixed gas atmosphere, then calcining at 300-350°C in an O2 / N2 atmosphere, and finally calcining at 350-50°C in an air atmosphere.

8. The flexible ammonia synthesis process according to any one of claims 1 to 6, characterized in that: The preheating and temperature raising process of the raw gas includes: the raw gas is preheated and heated in turn through the inlet and outlet heat exchangers and the reaction gas heater and then sent to the temperature-controlled ammonia synthesis tower; the reaction gas leaving the controlled synthesis tower recovers heat energy through the outlet waste boiler and then enters the ammonia separation tank after multi-stage cooling; the multi-stage cooling process includes the reaction gas exchanging heat and cooling with the raw gas through the inlet and outlet heat exchangers, and then further cooling through the water cooler and the cold exchanger, and finally entering the ammonia cryogenic refrigerator for deep cooling.

9. The flexible ammonia synthesis process according to claim 8, characterized in that: The non-condensable gas at the top of the ammonia separation tank is firstly heat exchanged with the reaction gas through a cold exchanger, then pressurized by a circulating compressor, and then mixed with the raw gas, and then preheated by an inlet and outlet heat exchanger and a reaction gas heater before being sent to a temperature-controlled ammonia synthesis tower.

10. The flexible ammonia synthesis process according to claim 8, characterized in that: When the raw gas flow rate is running at a load of 11% to 120%, the temperature control medium exiting the temperature-controlled ammonia synthesis tower is sent to the steam generator to produce high-pressure steam and then returned to the temperature-controlled ammonia synthesis tower via the temperature control medium storage tank; when the raw gas flow rate is running at a load of 0-10%, the temperature control medium exiting the temperature-controlled ammonia synthesis tower enters the temperature control medium storage tank via the bypass of the steam generator and then returned to the temperature-controlled ammonia synthesis tower.

11. The flexible ammonia synthesis process according to claim 10, characterized in that: The control medium leaving the temperature control medium storage tank is divided into two streams. The first stream enters the temperature control ammonia synthesis tower to remove heat, and the second stream enters the reaction gas heater to preheat the raw gas and then returns to the temperature control medium storage tank.

12. The flexible ammonia synthesis process according to claim 11, characterized in that: When the raw gas flow rate is running at 31% to 120% load, the flow rate of the second temperature control medium is 3% to 8% of the total flow rate; when the raw gas flow rate is running at 0 to 30% load, the flow rate of the second temperature control medium is 30% to 40% of the total flow rate.

13. The flexible ammonia synthesis process according to claim 1, characterized in that: When the raw gas flow rate is running at 31% to 120% load, all the reaction gas enters the inlet and outlet waste boilers to produce high-pressure steam; when the raw gas flow rate is running at 0 to 30% load, 70 to 90% of the reaction gas flow rate bypasses the outlet waste boiler, and the rest enters the inlet and outlet waste boilers.

14. The flexible ammonia synthesis process according to claim 1, characterized in that: A flow regulating loop is set at the circulating compressor. When the raw gas flow is running at a low load of 0-10%, 81-100% of the non-condensable gas is introduced into the flow regulating loop of the circulating compressor for circulation, and the remaining non-condensable gas is introduced into the circulating compressor to maintain low load operation; when the raw gas flow is running at a load of 11-120%, all the non-condensable gas is introduced into the circulating compressor.

15. The flexible ammonia synthesis process according to claim 10, characterized in that: When the raw gas flow rate is running at 0-10% load, the temperature control medium storage tank heats the incoming control medium.

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