Energy-saving reaction control method for green hydrogen synthesis of ammonia based on hydrogen-nitrogen ratio regulation

Abstract

The application discloses a kind of green hydrogen synthesis ammonia energy-saving reaction control methods based on hydrogen nitrogen ratio regulation, belong to synthetic ammonia preparation technical field.The application is realized hydrogen nitrogen ratio dynamic accurate regulation by real-time acquisition of hydrogen nitrogen flow at reactor inlet, using nonlinear predictive control algorithm, and the best stoichiometric ratio is stably maintained;Fusion low-temperature plasma assisted catalysis technology reduces reaction activation energy and reaction temperature;Build hierarchical reaction heat gradient recovery system to improve energy utilization rate;Synchronous coupling green electricity system realizes production load dynamic self-adaptive regulation.This method greatly reduces the energy consumption of synthetic ammonia reaction, adapts renewable energy output characteristics, realizes the low-carbon energy-saving flexible production of green hydrogen synthesis ammonia.

Description

Technical Field

[0001] This invention relates to the field of ammonia synthesis technology, specifically to an energy-saving reaction control method for green hydrogen ammonia synthesis based on hydrogen-nitrogen ratio regulation. Background Technology

[0002] Synthetic ammonia is a fundamental core product of the chemical industry and is widely used in fertilizers, chemicals, energy and other fields. Traditional synthetic ammonia production adopts the Haber-Bosch process, which requires high temperature and high pressure conditions of 400℃-500℃ and 15MPa-25MPa. The reaction process has high energy consumption, and the raw material hydrogen is mostly derived from fossil fuel reforming. The production process has large carbon emissions, which does not meet the industrial development requirements under the "dual carbon" target.

[0003] The synthesis technology of ammonia using green hydrogen coupled with renewable energy can realize the low-carbon transformation of ammonia synthesis production and is a key development direction for the industry.

[0004] However, existing green hydrogen ammonia synthesis technology still faces many technical bottlenecks: First, the hydrogen-nitrogen ratio control mostly adopts conventional PID closed-loop control, which cannot adapt to the strong nonlinearity and large hysteresis characteristics of the ammonia synthesis reaction. The hydrogen-nitrogen ratio control accuracy is low, and it is easy to deviate from the optimal stoichiometric ratio of 3:1, resulting in excessive hydrogen circulation and increased compressor energy consumption. Second, the reaction still requires relatively high temperature and pressure conditions, and the proportion of heat energy and compression energy consumption is high, with limited room for energy saving. Third, the recovery and utilization of the exothermic reaction in ammonia synthesis is singular, and the energy cascade utilization rate is low, resulting in a large amount of energy waste. Fourth, it cannot effectively adapt to the intermittent and fluctuating output characteristics of renewable energy sources such as photovoltaic and wind power, resulting in poor production load adjustment capabilities, easy occurrence of renewable energy curtailment problems, and inability to achieve stable and flexible production. Summary of the Invention

[0005] This invention addresses the technical shortcomings of existing technologies, such as low precision in hydrogen-nitrogen ratio control, high reaction energy consumption, insufficient waste heat utilization, and inability to adapt to fluctuating renewable energy output. It provides an energy-saving reaction control method for green hydrogen ammonia synthesis based on hydrogen-nitrogen ratio regulation, enabling low-energy consumption, high-stability, and flexible production of green hydrogen ammonia.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a green hydrogen ammonia synthesis energy-saving reaction control method based on hydrogen-nitrogen ratio regulation, comprising the following steps: S1. Real-time acquisition of hydrogen and nitrogen input flow data at the inlet of the ammonia synthesis reactor, as well as reaction condition data inside the reactor, and transmission of the acquired data to the nonlinear predictive control module. S2. The nonlinear predictive control module generates control signals for the hydrogen and nitrogen feed regulating valves based on the received data and through preset control logic operations, dynamically adjusting the input ratio of hydrogen and nitrogen to maintain the hydrogen-nitrogen stoichiometric ratio in the reactor at 3:1. S3. Start the low-temperature plasma generator to activate the mixed reaction gas entering the reactor. In conjunction with the Fe-Mo / K catalyst packed in the reactor, regulate the temperature and pressure parameters of the reaction system to start the ammonia synthesis reaction. S4. Construct a reaction heat recovery system to collect the heat energy released during the ammonia synthesis reaction and use it for reaction gas preheating, absorption refrigeration drive and external heating according to the temperature gradient. S5. Real-time acquisition of output power data from the coupled green electricity system, combined with the operating conditions of the reaction system, dynamically adjusts the production load of the ammonia synthesis reaction, and completes flexible production control of green hydrogen ammonia synthesis.

[0007] Optionally, in step S1, a Coriolis mass flow meter is used to collect the input flow rate data of hydrogen and nitrogen, and the collection frequency is set to 5Hz-50Hz; the collected reactor internal reaction condition data includes reactor bed temperature, reaction pressure, reactor outlet ammonia concentration, and circulating gas hydrogen-nitrogen ratio data; all collected data are transmitted to the nonlinear predictive control module via industrial Ethernet. In step S2, the control logic of the nonlinear predictive control module includes three stages: mechanism prediction model construction, rolling time-domain optimization, and feedback correction. The mechanism prediction model is constructed based on the nonlinear kinetic equation and material balance equation of the ammonia synthesis reaction. It uses hydrogen flow rate and nitrogen flow rate as control inputs and the hydrogen-nitrogen ratio in the reactor and the outlet ammonia concentration as control outputs to predict the trend of hydrogen-nitrogen ratio changes within a preset time domain. The rolling time-domain optimization aims to minimize the deviation of the hydrogen-nitrogen ratio from the 3:1 set value and the hydrogen circulation flow rate. It uses the adjustment amplitude of the regulating valve and the rated operating parameters of the equipment as constraints to solve a finite-time open-loop optimization problem in each control cycle and generate the regulating valve control signal for the current control cycle. After each control cycle, the feedback correction stage uses the actual collected hydrogen-nitrogen ratio and ammonia concentration data to correct the output error of the mechanism prediction model and updates the initial prediction value for the next control cycle.

[0008] Optionally, in step S3, the low-temperature plasma generator adopts a dielectric barrier discharge structure and is located between the inlet preheating section and the catalyst bed of the ammonia synthesis reactor. The mixed reaction gas is directly introduced into the catalyst bed after activation treatment. The Fe-Mo / K catalyst uses γ-Al2O3 as a support, and the active components include 10%-20% Fe, 3%-8% Mo, and 1%-5% K by mass fraction. It is prepared by an equal-volume impregnation method. The temperature control range of the reaction system is 300℃-350℃, and the pressure control range is 8MPa-12MPa. The discharge power of the low-temperature plasma generator is synchronously adjusted with the production load and inlet flow rate of the reaction system. The discharge power adjustment range is 50W-500W, and the discharge frequency adjustment range is 5kHz-20kHz.

[0009] Optionally, in step S4, the reaction heat cascade recovery system includes a primary gas-to-gas heat exchanger, a secondary waste heat boiler, and a tertiary circulating water heat exchange unit. The high-temperature reaction gas from the outlet of the ammonia synthesis reactor first enters the primary gas-to-gas heat exchanger to exchange heat with the ambient temperature inlet gas at the reactor inlet, thus preheating the reaction inlet gas. The reaction gas after the primary heat exchange enters the secondary waste heat boiler, and the saturated steam generated by the heat exchange is used to drive the absorption chiller unit. The reaction gas after the secondary heat exchange enters the tertiary circulating water heat exchange unit, and the circulating hot water after the heat exchange is used for industrial or domestic external heating. The reaction gas after the heat exchange is completed enters the ammonia separation unit, and the separated unreacted circulating gas is returned to the reactor inlet to mix with the fresh feed gas.

[0010] Optionally, in step S5, the coupled green power system includes a photovoltaic power generation system, a wind power power generation system, and an energy storage subsystem; the real-time collected green power system data includes real-time photovoltaic output, real-time wind power output, energy storage SOC value, and grid interaction power data; the dynamic adjustment process of the production load is as follows: based on the collected green power output data, the range of available green power in the next 15-60 minutes is predicted, and a load adjustment command is generated in combination with the minimum stable operating load and rated operating load of the reaction system; during the load adjustment process, the total feed flow of hydrogen and nitrogen is adjusted synchronously, and the nonlinear predictive control module synchronously adjusts the control parameters of the hydrogen-nitrogen ratio to maintain a stable hydrogen-nitrogen ratio; the load adjustment range is 20%-100% of the rated load, and the load adjustment rate does not exceed 10% of the rated load per minute.

[0011] Optionally, the system can collect real-time data on the hydrogen-nitrogen ratio, bed temperature, and reaction pressure within the reactor, and set up a tiered safety interlock control logic. When the hydrogen-nitrogen ratio deviates from the set value of 3:1 by more than ±10%, a first-level early warning interlock is triggered, the system issues an audible and visual warning signal, and the nonlinear predictive control module increases the adjustment range of the regulating valve. When the bed temperature exceeds 380℃ or the reaction pressure exceeds 13MPa, a second-level regulation interlock is triggered, the system reduces the total feed flow and production load, and adjusts the discharge power of the low-temperature plasma generator. When the hydrogen-nitrogen ratio deviates from the set value by more than ±20%, the bed temperature exceeds 400℃, or the reaction pressure exceeds 14MPa, a third-level emergency shutdown interlock is triggered, the system closes the hydrogen and nitrogen feed regulating valves, cuts off the power supply to the low-temperature plasma generator, and opens the system's emergency vent valve.

[0012] Optionally, the nonlinear predictive control module performs self-optimization training on the mechanism prediction model every 24-72 hours based on the collected historical operating data; The self-optimization training process is as follows: Valid sample data with a hydrogen-nitrogen ratio deviation of less than ±2% and stable system operation in historical operation were selected to construct a training sample set. The training objective was to minimize the mean square error between the model prediction value and the actual operating value. The gradient descent method was used to correct the kinetic parameters of the mechanism prediction model. During the parameter correction process, the theoretical parameter range of the ammonia synthesis reaction kinetics was used as the constraint boundary. The training convergence condition was that the mean square error decreased by less than 0.05% for 10 consecutive iterations, and the model parameters were updated.

[0013] Optionally, the circulating gas flow rate and hydrogen-nitrogen ratio data at the outlet of the ammonia separation unit are collected in real time, and the circulating gas data is input into the nonlinear predictive control module. When generating control signals for the hydrogen and nitrogen feed regulating valves, the nonlinear predictive control module simultaneously superimposes the circulating gas hydrogen-nitrogen ratio and flow rate data to correct the hydrogen and nitrogen ratio of the fresh feed and eliminate the impact of circulating gas hydrogen-nitrogen ratio fluctuations on the total hydrogen-nitrogen ratio in the reactor. The circulating gas circulation ratio is adjusted synchronously with the production load, and the circulation ratio adjustment range is 3-8.

[0014] This invention provides an energy-saving reaction control method for green hydrogen ammonia synthesis based on hydrogen-nitrogen ratio regulation, which has the following beneficial effects: Dynamic and precise control of the hydrogen-nitrogen ratio is achieved through a nonlinear predictive control algorithm. The predictive control logic is constructed based on the nonlinear mechanism model of the ammonia synthesis reaction. It can adapt to the strong nonlinearity and large lag conditions of the reaction process, effectively reduce the deviation between the hydrogen-nitrogen ratio and the optimal stoichiometric ratio, reduce the compressor energy consumption caused by excessive hydrogen circulation from the source, and solve the problems of insufficient accuracy and poor adaptability of traditional PID control.

[0015] This invention integrates low-temperature plasma-assisted catalysis technology with an Fe-Mo / K composite catalyst, effectively reducing the activation energy of the ammonia synthesis reaction and significantly lowering the reaction temperature and pressure. This reduces the heat input and gas compression energy consumption during the reaction process, overcoming the high energy consumption bottleneck of the traditional Haber process. Furthermore, this invention utilizes a staged reaction heat recovery system to utilize the reaction exothermics in multiple scenarios according to the temperature gradient, sequentially completing inlet gas preheating, refrigeration drive, and external heating, significantly improving the utilization rate of reaction waste heat and reducing the system's external energy input.

[0016] This invention is deeply integrated with photovoltaic and wind power green electricity systems. It dynamically adjusts production load based on renewable energy output, while simultaneously maintaining a stable hydrogen-nitrogen ratio during load adjustment. This effectively adapts to the intermittent and fluctuating output characteristics of renewable energy, reduces renewable energy curtailment rates, and achieves flexible production through the synergy of "source-load-storage-production." Overall, this invention realizes low-carbon and energy-saving production of green hydrogen for ammonia synthesis, effectively promoting the transformation of the ammonia synthesis industry towards a green electricity-driven low-carbon model. Attached Figure Description

[0017] Figure 1This is a schematic diagram of the invention process. Detailed implementation mode

[0018] The following combines the control method logic, supporting system structure and embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art without creative efforts based on the embodiments of the present invention belong to the scope of protection of the present invention. Embodiment 1

[0019] I. The structure and function of the green hydrogen synthesis ammonia reaction system supporting this embodiment are as follows: 1. The raw material feeding and flow rate regulation subsystem includes a hydrogen storage tank output by the green hydrogen preparation unit and a nitrogen storage tank output by the air separation unit, a hydrogen feeding pipeline and a nitrogen feeding pipeline; a Coriolis mass flowmeter, an electric proportional regulating valve, and a check valve are arranged in sequence along the gas flow direction on each pipeline; a pipeline type static mixer is arranged after the hydrogen and nitrogen feeding pipelines converge, and the outlet of the mixer is connected to the ammonia synthesis reactor through an intake main pipe; 2. The ammonia synthesis reactor subsystem uses an axial adiabatic fixed bed reactor. The reactor cavity is sequentially provided with an intake preheating section, a low-temperature plasma generating device, a catalyst bed, and an outlet section from top to bottom; the low-temperature plasma generating device adopts a coaxial cylindrical dielectric barrier discharge structure, including a high-voltage stainless steel electrode, a grounding electrode, and a quartz glass dielectric barrier layer, and the high-voltage electrode is equipped with a frequency-adjustable high-voltage power supply; the catalyst bed is filled with an Fe-Mo / K composite catalyst. The catalyst uses γ-Al2O3 as a spherical carrier, and the active components include 15% Fe, 5% Mo, and 3% K by mass fraction, and is prepared by the equal-volume impregnation method; 5 groups of armored thermocouples are arranged along the axial direction of the catalyst bed on the outer wall of the reactor, a high-precision pressure transmitter is arranged at the top of the reactor cavity, and a laser Raman gas analyzer is arranged at the outlet of the reactor; Among them, the low-temperature plasma generating device is used to perform non-thermal plasma activation on the mixed reaction gas, break the N≡N triple bond at normal temperature and pressure, generate highly active nitrogen free radicals, greatly reduce the activation energy of the ammonia synthesis reaction, and cooperate with the catalyst to realize the ammonia synthesis reaction at low temperature and low pressure. It is the core hardware of the present invention to reduce the reaction energy consumption; the thermocouple is used to collect the axial temperature distribution data of the catalyst bed in real time, the pressure transmitter is used to collect the real-time reaction pressure inside the reactor, and the laser Raman gas analyzer is used to detect the ammonia concentration at the outlet of the reactor and the hydrogen-nitrogen ratio data of the unreacted gas in real time, providing core data support for reaction condition regulation, hydrogen-nitrogen ratio closed-loop control, and safety interlock; 3. The reaction heat recovery subsystem is configured in series according to the heat energy grade, from high to low, consisting of a first-stage shell-and-tube gas-to-gas heat exchanger, a second-stage waste heat boiler, and a third-stage shell-and-tube circulating water heat exchanger. The shell-side inlet of the first-stage gas-to-gas heat exchanger is connected to the reactor outlet, the tube-side inlet is connected to the static mixer outlet of the raw material feed subsystem, and the tube-side outlet is connected to the reactor inlet preheating section. The shell-side inlet of the second-stage waste heat boiler is connected to the shell-side outlet of the first-stage gas-to-gas heat exchanger, and the boiler steam outlet is connected to the lithium bromide absorption chiller unit. The shell-side inlet of the third-stage circulating water heat exchanger is connected to the shell-side outlet of the second-stage waste heat boiler, the tube-side is connected to the circulating water supply / return water network, and the circulating water return is connected to the industrial / civilian heating network. The shell-side outlet of the third-stage circulating water heat exchanger is connected to the ammonia separation unit. 4. Ammonia separation and circulating gas subsystem, including an ammonia condenser, an ammonia liquid separator, and a circulating compressor; the ammonia condenser inlet is connected to the shell-side outlet of the three-stage circulating water heat exchanger, and the refrigerant inlet of the ammonia condenser is connected to the absorption chiller unit driven by the two-stage waste heat boiler; the liquid phase outlet of the ammonia liquid separator is connected to the liquid ammonia storage tank, and the gas phase outlet is connected to the circulating compressor through a circulating pipeline; the outlet of the circulating compressor is connected to the main gas inlet pipe of the reactor inlet; a Coriolis mass flow meter and a laser gas analyzer are installed on the circulating pipeline; 5. The nonlinear predictive control and safety interlocking subsystem adopts a Siemens S7-400 industrial PLC controller, equipped with an industrial touch screen, audible and visual alarm, and emergency vent valve. The PLC controller has a built-in nonlinear predictive control module, which is divided into a data acquisition unit, a mechanism prediction unit, a rolling time domain optimization unit, a feedback correction unit, and a hierarchical interlocking control unit. All flow meters, sensors, and analyzers communicate with the data acquisition unit via industrial Ethernet. All electric regulating valves, plasma high-voltage power supplies, and emergency vent valves are electrically connected to the output module of the PLC controller. 6. Green electricity coupled power supply system, including a 10MW photovoltaic power generation system, a 2MWh lithium battery energy storage subsystem, a grid-connected inverter, and an energy management system (EMS); the energy management system collects real-time photovoltaic output, energy storage SOC value, and grid interaction power data, and communicates with the nonlinear predictive control module in real time via the Modbus protocol.

[0020] II. Specific implementation steps of the control method based on the above system are as follows: Step S1: Real-time acquisition and transmission of operating data. Fresh hydrogen and nitrogen input flow rate data are acquired in real time via Coriolis mass flow meters on the hydrogen and nitrogen feed pipelines, with the acquisition frequency set to 20Hz. Catalyst bed temperature and internal reactor reaction pressure data are acquired in real time via thermocouples and pressure transmitters on the reactor. Ammonia concentration data at the reactor outlet is acquired in real time via a laser Raman gas analyzer. Circulation gas flow rate and hydrogen-to-nitrogen ratio data are acquired in real time via flow meters and analyzers on the circulation pipeline. All acquired data is transmitted in real time via industrial Ethernet to the data acquisition unit of the nonlinear predictive control module for data filtering and preprocessing, providing accurate basic data for subsequent control logic operations.

[0021] Step S2: Dynamic and precise control of the hydrogen-nitrogen ratio based on nonlinear predictive control. The nonlinear predictive control module performs calculations based on the received real-time data and through preset control logic, generating control signals for the hydrogen and nitrogen feed regulating valves. This dynamically adjusts the input ratio of hydrogen and nitrogen to maintain a stable hydrogen-nitrogen stoichiometric ratio of 3:1 within the reactor. The specific control logic consists of three core components: (1) Based on the nonlinear kinetic equation of the ammonia synthesis reaction and the material balance equation of the whole system, a mechanism prediction model is constructed. The fresh hydrogen feed flow rate and the fresh nitrogen feed flow rate are used as control inputs, and the hydrogen-nitrogen ratio in the reactor and the ammonia concentration at the reactor outlet are used as control outputs. The prediction time domain is set to 10 control cycles and the control cycle is set to 2s. The trend of hydrogen-nitrogen ratio change in the next 20s can be predicted. (2) With “minimum deviation of hydrogen-nitrogen ratio from 3:1 set value and minimum hydrogen circulation flow” as the dual optimization objectives, and with the maximum adjustment range of the regulating valve and the rated operating parameters of the equipment as constraints, the finite time domain open-loop optimization problem is solved in each 2s control cycle to generate the hydrogen and nitrogen feed regulating valve opening control signal for the current control cycle and output it to the field regulating valve. (3) After each control cycle, the actual collected data of hydrogen-nitrogen ratio and ammonia concentration at the reactor outlet are used to calculate and correct the output error of the mechanism prediction model, update the prediction initial value for the next control cycle, and eliminate prediction deviations caused by model mismatch and external interference. Simultaneously, the flow rate and hydrogen-nitrogen ratio data of the circulating gas are collected in real time and input into the nonlinear predictive control module. When generating the control signal of the fresh feed regulating valve, the hydrogen-nitrogen ratio and flow rate data of the circulating gas are simultaneously superimposed to correct the hydrogen and nitrogen ratio of the fresh feed and eliminate the influence of the fluctuation of the hydrogen-nitrogen ratio of the circulating gas on the total hydrogen-nitrogen ratio in the reactor. The circulation ratio of the circulating gas is adjusted synchronously with the production load. In this embodiment, the circulation ratio is stably controlled at 3-5.

[0022] In the ammonia synthesis reaction, there is a pure time lag of 10–15 seconds between the activation of the fresh feed regulating valve and the detection of a change in the hydrogen-nitrogen ratio at the reactor outlet. Furthermore, the reaction rate exhibits a strongly nonlinear variation with temperature, pressure, and hydrogen-nitrogen ratio. Traditional PID control relies solely on feedback adjustment based on the current deviation, lacking predictive capability and failing to adapt to conditions with large time lags and strong nonlinearity. This leads to overshoot and oscillations, with the maximum hydrogen-nitrogen ratio deviation of conventional PID control in the industry reaching ±10%.

[0023] The nonlinear predictive control employed in this invention predicts the hydrogen-nitrogen ratio change trend in advance for the next 20 seconds through a mechanistic model, updates the control signal every 2 seconds, achieves advance adjustment through rolling optimization, and eliminates model errors in real time through feedback correction, forming a fully closed-loop control.

[0024] The shaft power of the circulating compressor satisfies the following formula: in For compressor shaft power, For circulating gas volume, To reduce the pressure difference between the inlet and outlet.

[0025] In this embodiment, the hydrogen-nitrogen ratio deviation is ≤±2%, the hydrogen excess is ≤3%, and the circulation ratio is stably controlled at 3~5; while the traditional process (Comparative Example 1) has a hydrogen-nitrogen ratio deviation of ±10%, a hydrogen excess of about 15%, and a circulation ratio of 6~10. The comparison shows that the circulating gas volume of this invention is reduced by about 40%, corresponding to a 40% reduction in the energy consumption of the circulating compressor, thus reducing the ineffective energy consumption caused by excessive hydrogen circulation at the source.

[0026] Step S3: Control of the ammonia synthesis reaction assisted by low-temperature plasma. The high-voltage power supply of the low-temperature plasma generator is started, with a discharge power of 200W and a discharge frequency of 10kHz. The mixed reaction gas, after preheating in the inlet preheating section, enters the plasma generator for activation. The activated highly reactive gas directly enters the catalyst bed. The catalyst bed temperature is stabilized at 320℃ through the reactor's heating and cooling tracing system, and the internal pressure of the reactor is stabilized at 10MPa through the system back pressure valve, thus initiating the ammonia synthesis reaction. During subsequent production load adjustment, the discharge power of the low-temperature plasma generator is synchronously and linearly adjusted with the production load and inlet flow rate of the reaction system to ensure stable gas activation under different loads.

[0027] This invention employs a low-temperature plasma-assisted catalytic pathway, using non-thermal plasma to break the N≡N triple bond and generate highly reactive nitrogen free radicals, reducing the apparent activation energy of the ammonia synthesis reaction to 80 kJ / mol, which is only 50% of that of traditional thermal catalysis. Therefore, a stable ammonia synthesis reaction can be achieved under mild conditions of 320℃ and 10 MPa, with the reaction temperature reduced by 130℃ and the reaction pressure reduced by 10 MPa compared to the traditional process.

[0028] The theoretical isentropic power consumption of a fresh gas compressor satisfies the following formula: in The adiabatic index of the gas. The gas constant is... Intake air temperature, Intake pressure, This refers to the exhaust pressure.

[0029] Step S4: Graded and stepped recovery and utilization of reaction heat. A three-stage series reaction heat recovery system is used to collect the reaction heat released during ammonia synthesis and utilize it according to the temperature gradient. (1) The high-temperature reaction gas at about 320°C at the reactor outlet first enters the shell side of the first-stage gas-to-gas heat exchanger and exchanges heat with the room-temperature fresh feed gas in the tube side to preheat the feed gas to above 280°C, thus completing the preheating of the reaction gas. No additional electric heating furnace or gas heating furnace is required. (2) The reaction gas, which is cooled to about 180°C after the first heat exchange, enters the second waste heat boiler and generates 0.6MPa saturated steam for heat exchange, which is used to drive the lithium bromide absorption chiller unit to provide -5°C cooling capacity for the ammonia separation unit, replacing the traditional electric drive compression chiller unit. (3) The reaction gas, which is cooled to about 100°C after the secondary heat exchange, enters the tertiary circulating water heat exchange unit to heat the circulating water from 40°C to 85°C. The circulating hot water after heat exchange is used for heating in the surrounding residential areas. After the heat exchange is completed, the reaction gas enters the ammonia separation unit. After the liquid ammonia is separated, the unreacted circulating gas returns to the reactor inlet, mixes with the fresh feed gas, and participates in the reaction again.

[0030] The ammonia synthesis reaction is a strongly exothermic reaction. For every 1 mol of liquid ammonia produced, about 46 kJ of heat of reaction is released. Traditional processes only use a single-stage heat exchanger to preheat the inlet gas, which can only recover about 30% of the high-grade heat of reaction. The remaining 70% of the medium and low-grade waste heat is lost to the environment through circulating water cooling, resulting in extremely low waste heat utilization. At the same time, additional electrical energy is required to provide cooling capacity for the ammonia separation unit.

[0031] This invention employs a three-stage cascade recovery system, matching the application scenarios according to the grade of heat energy, to achieve full recovery of reaction heat: High-grade heat energy above 300℃ is used for intake preheating, recovering about 50% of the total heat of reaction; Medium-grade thermal energy at 150-300℃ is used to generate steam in a waste heat boiler to drive absorption refrigeration, recovering approximately 30% of the total heat of reaction. Low-grade heat energy at 80-150℃ is used to heat the circulating water externally, recovering about 15% of the total reaction heat. According to the actual measurement in this embodiment, the total waste heat recovery rate is ≥95%.

[0032] By using a two-stage waste heat recovery system to drive absorption refrigeration, the refrigeration power consumption of the ammonia separation unit is reduced by about 80% compared to traditional electric refrigeration units. The low-grade waste heat can be used for external heating, which can replace coal-fired boilers for heating. The corresponding reduction in carbon emissions and energy consumption further enhances the energy-saving and low-carbon benefits of this invention.

[0033] Step S5: Dynamic adaptive adjustment of the production load of the coupled green power system. The energy management system collects real-time photovoltaic output, energy storage SOC value and grid interaction power data of the coupled green power system in real time. Based on the collected historical output data and meteorological data, the range of green power available in the next 30 minutes is predicted. Combined with the minimum stable operating load and rated operating load of the reaction system, a load adjustment command is generated. During load adjustment, the total feed flow rate of hydrogen and nitrogen is adjusted proportionally, and the nonlinear predictive control module adjusts the control parameters of the hydrogen-nitrogen ratio simultaneously. During the wide range of load adjustment, the hydrogen-nitrogen ratio in the reactor is always kept stable at 3:1. In this embodiment, the load adjustment range is 30%-100% of the rated load, and the load adjustment rate is controlled at 8% of the rated load per minute to avoid instability of the reaction conditions caused by rapid load fluctuations. This invention breaks the strong dependence of the reaction on self-heating equilibrium through low-temperature plasma-assisted catalysis, and can still maintain a stable ammonia synthesis reaction under 20% low load conditions. At the same time, by predicting the output of green electricity in the short term and combining it with nonlinear predictive control, the hydrogen-nitrogen ratio is kept stable during the load adjustment process, avoiding the instability of the operating conditions caused by load fluctuations. The load adjustment range is widened to 20%-100% of the rated load, and the production load can be dynamically adjusted in complete accordance with the output of renewable energy. Example 2

[0034] This embodiment employs the energy-saving reaction control method for green hydrogen ammonia synthesis based on hydrogen-nitrogen ratio regulation described in this invention, and applies it to a multi-series green hydrogen ammonia synthesis production system coupled with a wind power-photovoltaic complementary green power system. The specific implementation process is as follows: 1. The system is configured as two independent ammonia synthesis reaction series. Each series is equipped with an independent raw material feed and flow control unit, nonlinear predictive control branch, low-temperature plasma generator, catalyst bed and reaction heat cascade recovery unit. The two series share a set of ammonia separation unit, green electricity management system and total control system. The hydrogen and nitrogen feed flow acquisition frequency of each series is set to 50Hz, and the operating data of each series is uploaded to the total control system.

[0035] 2. Each series adopts an independent nonlinear predictive control module for closed-loop control of the hydrogen-nitrogen ratio, and the control logic is completely consistent with that in Example 1. The discharge power of the low-temperature plasma generator of each series is adjusted synchronously with the production load of the corresponding series. The discharge power adjustment range is 100W-400W, the reaction temperature control range is 300℃-340℃, and the pressure control range is 8MPa-12MPa.

[0036] 3. The reaction heat recovery systems of each series operate in parallel, and the recovered heat energy is used uniformly for the intake preheating, refrigeration drive and external industrial heating of the entire system; the main control system is based on the real-time output data of the wind power-photovoltaic complementary green power system to uniformly allocate the production load of each series. When a single series fails, the other series can maintain normal operation, and the load adjustment range is 20%-100% of the rated load.

[0037] 4. The nonlinear predictive control module completes model self-optimization training based on historical operating data of each series every 72 hours. Each series is equipped with independent three-level safety interlock control logic. The interlock action of a single series does not affect the normal operation of other series.

[0038] This embodiment adopts a multi-series distributed control architecture. The load regulation and fault interlocking of a single series do not affect the normal operation of other series, and the system availability is improved by more than 40% compared with a single-series system. At the same time, through the wind power-photovoltaic complementary green power system, the daytime and nighttime fluctuations of renewable energy output are smoothed out. Combined with the wide-range load regulation capability of this invention, uninterrupted green hydrogen ammonia synthesis and low-carbon production throughout the year is achieved, with an annual renewable energy consumption rate of more than 98%, and the comprehensive carbon emissions per ton of ammonia are reduced by more than 99% compared with traditional coal-based ammonia synthesis.

[0039] Comparative Example 1 This comparative example uses the traditional Haber process for ammonia synthesis control, applied to a single-series ammonia synthesis system with the same capacity as Example 1. The specific process is as follows: The system employs conventional PID closed-loop control to regulate the hydrogen and nitrogen feed ratio. It lacks a low-temperature plasma-assisted catalytic device and uses a traditional molten iron catalyst. The reaction temperature is controlled at 450℃ and the reaction pressure at 20MPa. Waste heat from the reaction is only preheated by a single-stage heat exchanger, without a graded recovery system. The system is not coupled to a green energy system and operates under a grid power supply and fixed rated load mode, lacking flexible production adjustment capabilities.

[0040] Comparative Example 2 This comparative example uses a conventional green hydrogen ammonia synthesis control method, applied to the same ammonia synthesis system coupled with photovoltaic power generation as in Example 1. The specific process is as follows: The system only uses conventional PID closed-loop control to adjust the hydrogen-nitrogen ratio, without a nonlinear predictive control module; it lacks a low-temperature plasma-assisted catalytic device, uses a traditional iron-based catalyst, and controls the reaction temperature at 400℃ and the reaction pressure at 15MPa; the waste heat from the reaction is only recovered through a single-stage heat exchange, without any graded or cascaded utilization; the system only adjusts the production load based on the green electricity output, without synchronous hydrogen-nitrogen ratio coordinated control during the load adjustment process, and without model self-optimization and graded safety interlocking functions.

[0041] Comparison of performance parameters between the examples and the comparative examples Table 1 Comparison of core performance parameters between the embodiments and comparative examples. Performance Comparison Conclusion The reaction temperatures and pressures of Examples 1 and 2 were significantly lower than those of Comparative Examples 1 and 2, which effectively reduced the heat input and gas compression energy consumption during the reaction process. The hydrogen-nitrogen ratio control deviation range of the examples was smaller, and the hydrogen circulation rate was lower, which could significantly reduce the operating energy consumption of the circulating gas compressor.

[0042] The embodiment adopts a staged reaction heat recovery system, which can realize the utilization of reaction heat in multiple scenarios throughout the entire process. The waste heat utilization rate is significantly higher than that of Comparative Example 1 and Comparative Example 2, which only use single-stage heat exchange, and reduces the external energy input of the system.

[0043] The embodiment can achieve a wide range of production load adjustment based on green electricity output, effectively adapting to the fluctuating output of renewable energy, and there is no power curtailment; Comparative Example 1 has no load adjustment capability, and Comparative Example 2 has a narrow load adjustment range, and the hydrogen-nitrogen ratio control stability is poor during the adjustment process, which easily leads to renewable energy curtailment.

[0044] Example 2 employs multi-series distributed control, where a single series failure does not affect the normal operation of the remaining series, and the system's continuous operation stability is significantly better than that of Comparative Example 2; the three-level safety interlock control logic of Example 2 can effectively ensure the safety of the system under all operating conditions.

[0045] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for controlling the energy-saving reaction of green hydrogen ammonia synthesis based on hydrogen-nitrogen ratio regulation, characterized in that, Includes the following steps: S1. Real-time acquisition of hydrogen and nitrogen input flow data at the inlet of the ammonia synthesis reactor, as well as reaction condition data inside the reactor, and transmission of the acquired data to the nonlinear predictive control module. S2. Based on the received data, the nonlinear predictive control module generates control signals for the hydrogen and nitrogen feed regulating valves through preset control logic operations, dynamically adjusts the input ratio of hydrogen and nitrogen, and maintains the hydrogen-nitrogen stoichiometric ratio in the reactor at 3:

1. S3. Start the low-temperature plasma generator to activate the mixed reaction gas entering the reactor. In conjunction with the Fe-Mo / K catalyst packed in the reactor, regulate the temperature and pressure parameters of the reaction system to start the ammonia synthesis reaction. S4. Construct a reaction heat recovery system to collect the heat energy released during the ammonia synthesis reaction and use it for reaction gas preheating, absorption refrigeration drive and external heating according to the temperature gradient. S5. Real-time acquisition of output power data from the coupled green electricity system, combined with the operating conditions of the reaction system, dynamically adjusts the production load of the ammonia synthesis reaction, and completes flexible production control of green hydrogen ammonia synthesis.

2. The energy-saving reaction control method for green hydrogen ammonia synthesis based on hydrogen-nitrogen ratio regulation according to claim 1, characterized in that, In step S1, a Coriolis mass flow meter is used to collect the input flow rate data of hydrogen and nitrogen; the collected reactor internal reaction condition data include reactor bed temperature, reaction pressure, reactor outlet ammonia concentration, and circulating gas hydrogen-nitrogen ratio data. The control logic of the nonlinear predictive control module in step S2 includes three stages: mechanism prediction model construction, rolling time-domain optimization, and feedback correction. The mechanism prediction model is constructed based on the nonlinear kinetic equation and material balance equation of the ammonia synthesis reaction. It uses hydrogen flow rate and nitrogen flow rate as control inputs and the hydrogen-nitrogen ratio in the reactor and the outlet ammonia concentration as control outputs to predict the trend of hydrogen-nitrogen ratio change within a preset time domain. The rolling time-domain optimization aims to minimize the deviation of the hydrogen-nitrogen ratio from the 3:1 set value and the hydrogen circulation flow rate. It uses the adjustment amplitude of the regulating valve and the rated operating parameters of the equipment as constraints to solve a finite-time open-loop optimization problem in each control cycle and generate the regulating valve control signal for the current control cycle. After each control cycle, the feedback correction stage uses the actual collected hydrogen-nitrogen ratio and ammonia concentration data to correct the output error of the mechanism prediction model and updates the prediction initial value for the next control cycle.

3. The energy-saving reaction control method for green hydrogen ammonia synthesis based on hydrogen-nitrogen ratio regulation according to claim 1, characterized in that, In step S3, the low-temperature plasma generator adopts a dielectric barrier discharge structure and is located between the gas inlet preheating section and the catalyst bed of the ammonia synthesis reactor. The mixed reaction gas is directly introduced into the catalyst bed after activation treatment. The Fe-Mo / K catalyst uses γ-Al2O3 as a support, and the active components include 10%-20% Fe, 3%-8% Mo, and 1%-5% K by mass fraction. It is prepared by equal volume impregnation method. The discharge power of the low-temperature plasma generator is synchronously adjusted with the production load and gas inlet flow rate of the reaction system.

4. The energy-saving reaction control method for green hydrogen ammonia synthesis based on hydrogen-nitrogen ratio regulation according to claim 1, characterized in that, In step S4, the reaction heat cascade recovery system includes a primary gas-to-gas heat exchanger, a secondary waste heat boiler, and a tertiary circulating water heat exchange unit. The high-temperature reaction gas from the outlet of the ammonia synthesis reactor first enters the primary gas-to-gas heat exchanger to exchange heat with the ambient temperature inlet gas at the reactor inlet, thus preheating the reaction gas. The reaction gas after the primary heat exchange enters the secondary waste heat boiler, where the saturated steam generated is used to drive the absorption chiller unit. The reaction gas after the secondary heat exchange enters the tertiary circulating water heat exchange unit, where the circulating hot water is used for industrial or domestic external heating. After the heat exchange is completed, the reaction gas enters the ammonia separation unit, where the separated unreacted circulating gas is returned to the reactor inlet and mixed with the fresh feed gas.

5. The energy-saving reaction control method for green hydrogen ammonia synthesis based on hydrogen-nitrogen ratio regulation according to claim 1, characterized in that, In step S5, the coupled green power system includes a photovoltaic power generation system, a wind power power generation system, and an energy storage subsystem; the real-time collected green power system data includes real-time photovoltaic output, real-time wind power output, energy storage SOC value, and grid interaction power data; The dynamic adjustment process of production load is as follows: Based on the collected green electricity output data, the range of green electricity available in the next 15-60 minutes is predicted. Combined with the minimum stable operating load and rated operating load of the reaction system, a load adjustment command is generated. During the load adjustment process, the total feed flow of hydrogen and nitrogen is adjusted simultaneously, and the nonlinear predictive control module adjusts the control parameters of the hydrogen-nitrogen ratio to maintain a stable hydrogen-nitrogen ratio.

6. The energy-saving reaction control method for green hydrogen ammonia synthesis based on hydrogen-nitrogen ratio regulation according to claim 1, characterized in that, The system collects real-time data on the hydrogen-to-nitrogen ratio, bed temperature, and reaction pressure within the reactor and sets up a tiered safety interlock control logic. When the hydrogen-to-nitrogen ratio deviates from the set value of 3:1 by more than ±10%, a first-level early warning interlock is triggered, and the system issues an audible and visual warning signal. Simultaneously, the nonlinear predictive control module increases the adjustment range of the regulating valve. When the bed temperature exceeds 380℃ or the reaction pressure exceeds 13MPa, a second-level regulating interlock is triggered, and the system reduces the total feed flow and production load while adjusting the discharge power of the low-temperature plasma generator. When the hydrogen-to-nitrogen ratio deviates from the set value by more than ±20%, the bed temperature exceeds 400℃, or the reaction pressure exceeds 14MPa, a third-level emergency shutdown interlock is triggered, and the system closes the hydrogen and nitrogen feed regulating valves, cuts off the power supply to the low-temperature plasma generator, and simultaneously opens the system's emergency vent valve.

7. The energy-saving reaction control method for green hydrogen ammonia synthesis based on hydrogen-nitrogen ratio regulation according to claim 2, characterized in that, The nonlinear predictive control module performs self-optimization training on the mechanism prediction model every 24-72 hours based on the collected historical operating data. The self-optimization training process is as follows: select effective sample data from historical operations where the hydrogen-nitrogen ratio deviation is less than ±2% and the system is operating stably to construct a training sample set; use the minimum mean square error between the model prediction value and the actual operating value as the training objective, and use the gradient descent method to correct the kinetic parameters of the mechanism prediction model; during the parameter correction process, the theoretical parameter range of the ammonia synthesis reaction kinetics is used as the constraint boundary, and the training convergence condition is that the mean square error decreases by less than 0.05% for 10 consecutive iterations, thus completing the update of the model parameters.

8. The energy-saving reaction control method for green hydrogen ammonia synthesis based on hydrogen-nitrogen ratio regulation according to claim 1, characterized in that, Real-time data acquisition of circulating gas flow rate and hydrogen-nitrogen ratio at the outlet of the ammonia separation unit, and input of circulating gas data into the nonlinear predictive control module; When generating control signals for hydrogen and nitrogen feed regulating valves, the nonlinear predictive control module simultaneously superimposes the hydrogen-nitrogen ratio and flow rate data of the circulating gas to correct the hydrogen-nitrogen ratio of the fresh feed. The circulation rate of the circulating gas is adjusted synchronously with the production load.

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