Green ammonia synthesis system adapting to new energy fluctuation and control method thereof

Abstract

The application discloses a green ammonia synthesis system suitable for new energy fluctuation and a control method thereof. The green ammonia synthesis system comprises a raw material gas mixing and compression channel, a reaction gas preheating and temperature control channel, a synthesis reaction channel, a condensation and separation channel and a reaction gas recovery and circulation channel. The control method comprises adopting a multi-steady-state flexible variable load operation strategy and reactor bed temperature control, condensation temperature control, separation tank liquid level and pressure control and the like to realize flexible and stable control of variable load operation of ammonia synthesis. The application is suitable for the new energy fluctuation scene. The current ammonia synthesis process is designed for steady-state operation and does not have an adaptive feasible variable load operation strategy. A green ammonia synthesis system based on the Haber-Bosch method is adopted. On this basis, a feasible variable load operation strategy and control method are designed, so that flexible variable load operation of green ammonia synthesis is realized.

Description

Technical Field

[0001] This invention belongs to the field of green ammonia synthesis technology, and specifically relates to a green ammonia synthesis system and its control method adapted to new energy fluctuations. Background Technology

[0002] Hydrogen energy is a crucial component of the future national energy system. Green hydrogen technology, which utilizes renewable energy sources to produce hydrogen, represents the most advantageous approach for large-scale renewable energy consumption. However, large-scale hydrogen storage remains economically unfeasible, and meeting hydrogen demand still faces significant bottlenecks. Against this backdrop, green ammonia synthesis technology, using green hydrogen as a raw material, not only enables effective localized consumption of renewable energy but also serves as a vital pathway for the green transformation of the chemical industry. Furthermore, the superior chemical properties of ammonia significantly reduce storage and transportation requirements, demonstrating immense potential for large-scale application. Traditional ammonia synthesis technology is designed for stable, long-term, full-capacity, and high-performance chemical operations. However, the instability of renewable energy sources in green ammonia synthesis systems necessitates variable-load operation on the chemical side. The applicant discovered some typical prior art through searches, such as Chinese patent application number 202411126387.5, which proposes a method for controlling the load of synthetic ammonia by using a hydrogen storage tank to reduce system fluctuations; Chinese patent application number 202310140551.7, which proposes a method for supplying nitrogen to a hydrogen storage container to maintain the pressure stability of the hydrogen storage container, thereby ensuring stable production of synthetic ammonia under gaseous hydrogen storage without pressure reduction; Chinese patent application number 202411562603.0, which discloses a process using a Ru-based catalyst and a temperature-controlled synthesis tower to relax reaction conditions and achieve stable system operation under fluctuating feed gas; and Chinese patent application number 202410021111.4, which discloses a process system using multiple ammonia synthesis towers to cope with operation under variable loads.

[0003] To address the intermittent and fluctuating nature of renewable energy in green ammonia synthesis systems, existing technologies have significantly modified the ammonia synthesis process flow, focusing on maintaining stable pressure control. However, this approach lacks effective means for controlling the inlet gas temperature and presents significant design challenges due to substantial differences from existing market applications and system coupling issues. Furthermore, no feasible operational design scheme has yet been proposed for the flexible control of ammonia synthesis systems. Summary of the Invention

[0004] The purpose of this invention is to provide a green ammonia synthesis system and its control method that are adapted to fluctuations in new energy sources. In the context of fluctuating new energy sources, current ammonia synthesis processes are mostly designed for steady-state operation and lack feasible variable load operation strategies. This invention adopts a green ammonia synthesis system based on the Haber-Bosch process, and on this basis, designs feasible variable load operation strategies and control methods to achieve flexible variable load operation of green ammonia synthesis.

[0005] To achieve the above objectives, the solution of the present invention is:

[0006] A green ammonia synthesis system adapted to fluctuations in new energy sources includes a feed gas mixing and compression path, a reactant gas preheating and temperature control path, a synthesis reaction path, a condensation and separation path, and a reactant gas recovery and circulation path. The feed gas mixing and compression path mixes and compresses the input hydrogen and nitrogen gases before sending them to the reactant gas preheating and temperature control path. The input end of the reactant gas preheating and temperature control path is connected to the output end of both the feed gas mixing and compression path and the reactant gas recovery and circulation path, allowing the mixed compressed gas output from the feed gas mixing and compression path to be fed into the reactant gas recovery and circulation path. The separated gas is subjected to temperature regulation to obtain a temperature-stable circulating gas. The output end of the reaction gas preheating and temperature control path is connected to the synthesis reaction path, and the temperature-stable circulating gas is subjected to a synthesis reaction to obtain a mixed gas after reaction. The input end of the condensation separation path is connected to the mixed gas after heat exchange with the circulating gas, and the mixed gas is cooled to separate unreacted hydrogen and nitrogen. The input end of the reaction gas recovery circulation path is connected to the output end of the condensation separation path, and the unreacted hydrogen and nitrogen are cooled and sent to the reaction gas preheating and temperature control path.

[0007] The raw material gas mixing and compression passage is formed by sequentially connecting a raw material gas mixer, a primary compressor, an interstage cooler for the compressor, and a secondary compressor via a gas pipeline.

[0008] The reaction gas preheating and temperature control pathway is formed by sequentially connecting a circulating gas mixer, a circulating compressor, a cold-side inlet of a heat exchanger, a cold-side outlet of a heat exchanger, and a hot-side inlet of a reaction inlet temperature control heat exchanger via a gas pipeline.

[0009] The synthesis reaction pathway is formed by sequentially connecting the hot-side outlet of the reaction inlet temperature control heat exchanger to the ammonia synthesis reactor via a gas pipeline.

[0010] The condensation separation path is formed by sequentially connecting a primary condenser, a hot-side inlet of a cold exchanger, a hot-side outlet of a cold exchanger, a secondary condenser, an inlet of a separation tank, a liquid-phase outlet of a separation tank, and a flash tank via a gas pipeline.

[0011] The reaction gas recovery circulation path is formed by sequentially connecting the gas phase outlet of the separator, the hot side inlet of the cold exchanger, the hot side outlet of the cold exchanger, and the circulating gas mixer through a gas pipeline.

[0012] The ammonia synthesis reactor is a three-stage intermediate indirect cooling reactor. The catalysts in the three-stage beds are ZA-5 type catalysts, and the three-stage beds are cooled by heat exchangers between the first and second stages and between the second and third stages, respectively.

[0013] A control method for a green ammonia synthesis system adapted to fluctuations in new energy sources includes: adopting a multi-steady-state flexible variable load operation strategy to realize the overall system regulation scheme; and using execution control loops such as reactor bed temperature control, compressor interstage cooling control, condensation temperature control, separator level and pressure control, and flash tank level and pressure control to realize the execution of the variable load strategy.

[0014] The multi-steady-state flexible variable load operation strategy includes designing m steady-state load operation states with n% load as the step size of n1%, n2%, n3%, ..., nm% within the L%-H% load range, and smoothly switching between each steady-state load operation state at a rate of x% / min.

[0015] Each of the m steady-state load operating states is set with m sets of optimal operating parameters under its own load. When the load is switched, the operating parameters are adjusted to the optimal parameters under the corresponding load. During the load switching process, each operating parameter is adjusted according to the planned optimal migration path of the chemical process operating conditions.

[0016] The reactor bed temperature control adopts a feedforward control system with the outlet temperature of each bed as the control target and the inlet temperature of each bed as the intermediate control variable. The optimal operating temperature of each bed is decoupled and rapidly adjusted by controlling the independent cooling flow rate.

[0017] By adopting the above scheme, this invention utilizes the coordinated design of a preheating heat exchanger and a reactor inlet temperature control heat exchanger to effectively stabilize and control the inlet temperature of the ammonia synthesis reactor under load fluctuation conditions. With minor modifications to existing commercial systems, it fully adapts to the stable operation requirements under fluctuations in green ammonia synthesis feedstock gas, demonstrating good feasibility. Furthermore, the green ammonia synthesis control method adapted to new energy fluctuations proposed in this invention achieves flexible control of ammonia synthesis under variable load operation through the design of a multi-steady-state flexible variable load operation strategy and execution control loop, providing a feasible synthesis system design and operation scheme for green ammonia production under new energy fluctuation scenarios. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the process flow and main control loop of the green ammonia synthesis system of the present invention;

[0019] Figure 2 This is a schematic diagram of the variable load operation strategy of the present invention.

[0020] The labels in the attached diagram are:

[0021] M101: Feed gas mixer; C101: Primary compressor; C102: Secondary compressor; E101: Compressor interstage cooler; M102: Circulating gas mixer; C103: Circulating compressor; E102: Heat exchanger; E103: Reaction inlet temperature control heat exchanger; RNH3: Ammonia synthesis reactor; R101: First stage bed of reactor; R102: Second stage bed of reactor; R103: Third stage bed of reactor; Interstage heat exchanger (E104); Interstage heat exchanger (E105); E106: Primary condenser; E107: Cold exchanger; E108: Secondary condenser; F101: Separator; F102: Flash tank;

[0022] FC101: Hydrogen inlet flow controller; FC102: Nitrogen inlet flow controller; RC101: Inlet hydrogen-nitrogen ratio controller; FC103: Compressor interstage cooling flow controller; TC103: Compressor interstage cooling temperature controller; FC104: Reactor inlet heat exchanger cold stream flow controller; TC104: Reactor inlet heat exchanger temperature controller; FC105: Reactor first and second stage heat exchanger cold stream flow controller; TC105: Reactor first and second stage heat exchanger temperature controller; FC106: Reactor second and third stage heat exchanger cold stream flow controller; TC106: Reactor second and third stage heat exchanger temperature controller; FC107: First stage condenser cold stream flow controller; TC107: First stage condenser temperature controller; FC108: Second stage condenser cold stream flow controller; TC108: Second stage condenser temperature controller; PC101: Separator pressure controller; LC101: Separator level controller; PC102: Flash tank pressure controller; LC102: Flash tank level controller;

[0023] V101: Hydrogen inlet flow regulating valve; V102: Nitrogen inlet flow regulating valve; V103: Compressor interstage cooling flow regulating valve; V104: Reactor inlet heat exchanger cold stream flow regulating valve; V105: Reactor first and second stage heat exchanger cold stream flow regulating valve; V106: Reactor second and third stage heat exchanger cold stream flow regulating valve; V107: First stage condenser cold stream flow emergency switch valve; V108: First stage condenser cold stream flow regulating valve; V109: Second stage condenser cold stream flow emergency switch valve; V110: Second stage condenser cold stream flow regulating valve; V111: Separator pressure regulating valve; V112: Separator level regulating valve; V113: Flash tank pressure regulating valve; V114: Flash tank level regulating valve. Detailed Implementation

[0024] This invention provides a green ammonia synthesis system adapted to fluctuations in new energy sources. The synthesis system includes a raw material gas mixer M101, a primary compressor C101, a secondary compressor C102, an interstage cooler E101, a circulating gas mixer M102, a circulating compressor C103, a heat exchanger E102, a reaction inlet temperature control heat exchanger E103, an ammonia synthesis reactor RNH3, a primary condenser E106, a cold exchanger E107, a secondary condenser E108, a separation tank F101, and a flash tank F102. The heat exchanger E102 heats the mixed reaction gas to a temperature higher than the reaction temperature, and then the reaction inlet temperature control heat exchanger E103 cools the mixed reaction gas to the reaction temperature. Through the cooperation of these two methods, the reactor inlet temperature is stably controlled even when the inlet fresh gas fluctuates.

[0025] The raw material gas mixer M101, the first-stage compressor C101, the compressor interstage cooler E101, and the second-stage compressor C102 are connected sequentially by a gas pipeline to form a raw material gas mixing and compression path.

[0026] The heat exchanger E102 is provided with a cold-side inlet, a cold-side outlet, a hot-side inlet, and a hot-side outlet; the reaction inlet temperature control heat exchanger E103 is provided with a cold-side inlet, a cold-side outlet, a hot-side inlet, and a hot-side outlet; the circulating gas mixer M102, the circulating compressor C103, the cold-side inlet of the heat exchanger E102, the cold-side outlet of the heat exchanger E102, and the hot-side inlet of the reaction inlet temperature control heat exchanger E103 are sequentially connected by a gas pipeline to form a reaction gas preheating and temperature control path.

[0027] The hot-side outlet of the reaction inlet temperature control heat exchanger E103 is sequentially connected to the ammonia synthesis reactor RNH3 via a gas pipeline to form a synthesis reaction pathway with a controllable and stable inlet temperature.

[0028] The separator F101 is provided with an inlet, a gas phase outlet, and a liquid phase outlet; the cold exchanger E107 is provided with a cold side inlet, a cold side outlet, a hot side inlet, and a hot side outlet; the primary condenser E106, the cold exchanger E107 hot side inlet and outlet, the secondary condenser E108, the separator F101 inlet and liquid phase outlet, and the flash tank F102 are sequentially connected by a gas pipeline to form a condensation separation path.

[0029] The gas phase outlet of the separator F101 is connected to the hot side inlet of the cold exchanger E107, the hot side outlet of the cold exchanger E107, and the circulating gas mixer M102 in sequence by a gas pipeline to form a reaction gas recovery circulation path.

[0030] The ammonia synthesis reactor RNH3 is a three-stage intermediate indirect cooling reactor. The catalyst in the three-stage bed is ZA-5 type catalyst, and the three-stage bed is cooled by heat exchangers E104 between the first and second stages and E105 between the second and third stages.

[0031] The present invention also provides a control method for the aforementioned green ammonia synthesis system adapted to new energy fluctuations, including a multi-steady-state flexible variable load operation strategy and an execution control loop.

[0032] The multi-steady-state flexible variable load operation strategy designs n1%, n2%, n3%...... nm% steady-state load operation states with n% load as the step size within the L%-H% load range, and smoothly switches between each load steady-state operation state at a rate of x% / min.

[0033] The execution control loop includes reactor bed temperature control, compressor interstage cooling control, condensation temperature control, separator level and pressure control, and flash tank level and pressure control.

[0034] Each of the m steady-state load operating states is configured with m sets of optimal operating parameters under its own load. Each set of operating parameters includes the inlet temperature of the secondary compressor C102, the cold side outlet temperature of the heat exchanger E102, the hot side outlet temperature of the reaction inlet temperature control heat exchanger E103, the hot side outlet temperature of the inter-stage heat exchanger E104, the hot side outlet temperature of the inter-stage heat exchanger E105, the hot side outlet temperature of the primary condenser E106, and the hot side outlet temperature of the secondary condenser E108. When the load changes, the operating parameters are adjusted to the optimal parameters under the corresponding load. During the load change process, each operating parameter is adjusted according to the planned optimal migration path of the chemical process operating conditions.

[0035] The reactor bed temperature control is a feedforward control system with the outlet temperature of each bed as the control target and the inlet temperature of each bed as the intermediate control variable. The optimal operating temperature of each bed is decoupled and rapidly adjusted by controlling the independent cooling flow rate.

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] The process flow and main control loop of the green ammonia synthesis system proposed in this invention are as follows: Figure 1 As shown.

[0038] Hydrogen from the new energy hydrogen production system and nitrogen from the air separation nitrogen production system are thoroughly mixed in the feed gas mixer (M101). The flow rates of both gases are regulated by hydrogen inlet flow control valves V101 and V102, respectively. The hydrogen-nitrogen ratio is distributed by the inlet hydrogen-nitrogen ratio controller RC101 to maintain the hydrogen-nitrogen ratio at 2.8-3.0 after mixing. The mixed fresh gas is pressurized to 40-45 bar by the first-stage compressor C101. After being cooled to 35-40°C by the compressor interstage cooler E101, the fresh gas enters the second-stage compressor C102. The gas is first pressurized to 80-85 bar; the pressurized fresh gas is then mixed with the hydrogen and nitrogen separated by refrigeration in the recirculation gas mixer M102, and then pressurized to 115-120 bar in the recirculation compressor C103; after the recirculation gas is heated to 345-355℃ in the heat exchanger E102, it enters the reaction inlet temperature control heat exchanger E103 for temperature regulation, and the two work together to stabilize the recirculation gas temperature at 320-330℃; the temperature-stabilized recirculation gas first enters the first bed R101 of the ammonia synthesis reactor RNH3 for the synthesis reaction, and the mixed gas after the reaction is heated. The mixture, initially at 480-490℃, is cooled to 330-340℃ by the first-to-second stage heat exchanger E104 before entering the second stage bed R102 of the reactor. After reaction in the second stage bed, the temperature rises to 430-440℃. It is then cooled to 360-370℃ by the second-to-third stage heat exchanger E105 before entering the third stage bed R103 of the reactor. The mixture exiting the reactor at 410-420℃ first enters the heat exchanger E102 to heat the circulating gas from the recirculating compressor, where its temperature is cooled to 130-140℃. After initial cooling in the heat exchanger, the mixture then enters... After being cooled to 35-40℃ by the first-stage condenser E106, the gas enters the cold exchanger E107 to recover some of the cold energy and is cooled to 25-30℃. Then it enters the second-stage condenser E108 to be further cooled to -10℃. The liquid ammonia separated from the condensed gas-liquid mixture in the separator F101 enters the flash tank F102 for temperature and pressure regulation. Unreacted hydrogen and nitrogen are separated and sent back to the cold exchanger E107 to cool the mixer after the reaction and recover some of the cold energy. Then it is mixed with the fresh gas from the second-stage compressor C102 in the circulating gas mixer M102 and enters the above-mentioned circulating reaction loop.

[0039] During system operation, the hydrogen and nitrogen inlet flow controllers FC101 and FC102 respectively regulate the flow rates of fresh gas (hydrogen and nitrogen) and RC101, respectively, to maintain a relatively stable hydrogen-nitrogen ratio in the fresh gas. The compressor interstage cooling temperature controller TC103 regulates the temperature of the fresh gas between the compressor stages. The cold stream flow controller FC104 regulates the flow rate of the cold stream in the reactor inlet heat exchanger, and the circulating gas temperature is adjusted by the reactor inlet heat exchanger temperature controller TC104. The cascade control system formed by these two controls constitutes a reactor temperature feedforward control system with the bed outlet temperature as the control target and the bed inlet temperature as the intermediate control variable. Similarly, the temperature control systems of each section of the reactor adopt similar feedforward control systems to quickly and stably control the temperature of each section to the set value.

[0040] The schematic diagram of the multi-steady-state flexible variable load operation strategy proposed in this invention is shown below. Figure 2 As shown.

[0041] Within the load range of 30%-110%, 17 steady-state load operating states are designed with 5% load increments, ranging from 30% to 40%, and so on. These steady-state load operating states are smoothly switched at a rate of 0.5% / min. Each of the 17 steady-state load operating states has 17 sets of optimal operating parameters for its respective load. During load switching, the operating parameters are adjusted to the optimal parameters for the corresponding load. Each set of operating parameters includes the inlet temperature of the secondary compressor C102, the cold-side outlet temperature of the heat exchanger E102, the hot-side outlet temperature of the reaction inlet temperature control heat exchanger E103, the hot-side outlet temperature of the inter-stage heat exchanger E104, the hot-side outlet temperature of the inter-stage heat exchanger E105, the hot-side outlet temperature of the primary condenser E106, and the hot-side outlet temperature of the secondary condenser E108. During load switching, each operating parameter is adjusted according to the planned optimal migration path of the chemical process operating conditions.

[0042] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media containing computer-usable program code.

[0043] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0044] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A green ammonia synthesis system adapted to fluctuations in new energy sources, characterized in that: The system includes a feed gas mixing and compression path, a reactant gas preheating and temperature control path, a synthesis reaction path, a condensation and separation path, and a reactant gas recovery and circulation path. The feed gas mixing and compression path mixes and compresses the input hydrogen and nitrogen gases before sending them to the reactant gas preheating and temperature control path. The input of the reactant gas preheating and temperature control path is connected to the output of both the feed gas mixing and compression path and the reactant gas recovery and circulation path. The mixed compressed gas output from the feed gas mixing and compression path and the separated gas output from the reactant gas recovery and circulation path are temperature-regulated to obtain a temperature-stable circulating gas. The output of the reactant gas preheating and temperature control path is connected to the synthesis reaction path, where the temperature-stable circulating gas undergoes a synthesis reaction to obtain a reacted mixed gas. The input of the condensation and separation path is connected to the mixed gas after heat exchange with the circulating gas. The mixed gas is cooled and separated to obtain unreacted hydrogen and nitrogen. The input of the reactant gas recovery and circulation path is connected to the output of the condensation and separation path, where the unreacted hydrogen and nitrogen are cooled before being sent to the reactant gas preheating and temperature control path.

2. The system as described in claim 1, characterized in that: The raw material gas mixing and compression passage is formed by sequentially connecting the raw material gas mixer, the first-stage compressor, the compressor interstage cooler, and the second-stage compressor via gas pipelines.

3. The system as described in claim 1, characterized in that: The reaction gas preheating and temperature control pathway is formed by sequentially connecting the circulating gas mixer, circulating compressor, cold side inlet of heat exchanger, cold side outlet of heat exchanger, and hot side inlet of reaction inlet temperature control heat exchanger via gas pipeline.

4. The system as described in claim 1, characterized in that: The synthesis reaction pathway is formed by sequentially connecting the hot-side outlet of the reaction inlet temperature control heat exchanger to the ammonia synthesis reactor via a gas pipeline.

5. The system as described in claim 1, characterized in that: The condensation separation path is formed by sequentially connecting a primary condenser, a hot-side inlet of a cold exchanger, a hot-side outlet of a cold exchanger, a secondary condenser, an inlet of a separation tank, a liquid-phase outlet of a separation tank, and a flash tank via a gas pipeline.

6. The system as described in claim 1, characterized in that: The reaction gas recovery circulation path is formed by sequentially connecting the gas phase outlet of the separator, the hot side inlet of the cold exchanger, the hot side outlet of the cold exchanger, and the circulating gas mixer via gas pipelines.

7. The system as described in claim 1, characterized in that: The ammonia synthesis reactor is a three-stage intermediate indirect cooling reactor. The catalysts in the three-stage beds are ZA-5 type catalysts, and the three-stage beds are cooled and cooled by heat exchangers between the first and second stages and between the second and third stages, respectively.

8. A control method for a green ammonia synthesis system adapted to new energy fluctuations, characterized in that: This includes adopting a multi-steady-state flexible variable load operation strategy to achieve the overall system control scheme, and using reactor bed temperature control, compressor interstage cooling control, condensation temperature control, separator tank level and pressure control, and flash tank level and pressure control to implement the variable load strategy.

9. The control method as described in claim 8, characterized in that: The multi-steady-state flexible variable load operation strategy includes designing m steady-state load operation states with n% load as the step size of n1%, n2%, n3%, ..., nm% within the L%-H% load range, and smoothly switching between each steady-state load operation state at a rate of x% / min.

10. The control method as described in claim 8, characterized in that: Each of the m steady-state load operating states has m sets of optimal operating parameters under its own load. When the load is switched, the operating parameters are adjusted to the optimal parameters under the corresponding load. During the load switching process, each operating parameter is adjusted according to the planned optimal migration path of the chemical process operating conditions.

11. The control method as described in claim 8, characterized in that: The reactor bed temperature control adopts a feedforward control system with the outlet temperature of each bed as the control target and the inlet temperature of each bed as the intermediate control variable. The optimal operating temperature of each bed is decoupled and rapidly regulated by controlling the independent cooling flow rate.

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