Capacity optimization configuration method of green ammonia-caustic soda-polyvinyl chloride co-production system driven by green electricity

Abstract

The invention relates to the technical field of new energy and chemical coupling system optimization, in particular to a capacity optimization configuration method of a green ammonia-caustic soda-polyvinyl chloride co-production system driven by green electricity, and aims to solve the problem of collaborative optimization of economical efficiency and low carbon performance of a high-proportion green electricity consumption and multi-product co-production system. Comprising the steps that S1, a green ammonia-caustic soda-polyvinyl chloride co-production system driven by green electricity is built, S2, a system capacity optimization configuration model is built, the model takes the minimum system comprehensive cost as an objective function, and meanwhile the green electricity consumption rate constraint, the production technology constraint of all units and the multi-product yield constraint are met; and S3, calling a CPLEX solver through a YALMIP platform on the basis of the minimum objective function of the comprehensive cost of the system and the constraint conditions, and solving and determining the optimal capacity configuration and corresponding economic and low-carbon indexes of each core unit of the system by means of MATLAB software.

Description

Technical Field

[0001] This invention relates to the field of optimization technology for new energy and chemical engineering coupled systems, specifically a capacity optimization configuration method for a green electricity-driven green ammonia-caustic soda-polyvinyl chloride co-production system. Background Technology

[0002] Green ammonia, caustic soda, and polyvinyl chloride (PVC) are core basic products in the chemical industry. Traditional production methods heavily rely on fossil fuels (such as coal / natural gas ammonia production and coal-fired power generation driving chlor-alkali electrolysis). This not only results in high energy consumption but also significant carbon dioxide emissions, creating a prominent contradiction with the requirements of low-carbon development. Meanwhile, although the installed capacity of renewable energy sources such as wind and solar power has grown rapidly in recent years, the fluctuating and intermittent nature of power output makes it difficult to absorb a high proportion of green electricity. The problem of wind and solar curtailment has not been fully resolved, leading to a waste of green electricity resources and hindering the large-scale application of renewable energy in the chemical industry.

[0003] Currently, research on the coupling of green electricity and chemical product production is gradually underway, but existing technologies have obvious limitations: On the one hand, most coupled systems focus on the production of a single product (such as green electricity to ammonia or green electricity to caustic soda), failing to achieve resource synergy for the joint production of multiple products. For example, hydrogen produced as a byproduct of sodium chloride electrolysis is often directly emitted, and oxygen produced by the air separation unit is not fully utilized, resulting in material waste and low system efficiency. On the other hand, system capacity configuration often focuses on the scale optimization of a single device (such as an electrolyzer), neglecting the matching between renewable energy power generation, energy storage, and various chemical units. This can easily lead to low green electricity consumption rates or large fluctuations in production load, making it difficult to balance economic efficiency and low carbon emissions.

[0004] In addition, the existing optimization models for multi-generation systems often simplify the constraints and do not fully consider the resource utilization of solid waste such as industrial waste salt. The traditional chlor-alkali industry relies on purchasing refined sodium chloride, and the stockpiling of industrial waste salt can easily cause environmental problems. If the waste salt treatment can be coupled with the electrolysis unit, the dual benefits of "solid waste reduction" and "raw material self-sufficiency" can be achieved. However, the existing technology has not yet formed a mature integrated solution.

[0005] In summary, how to construct a green electricity-driven multi-product co-production system, and through scientific capacity optimization, achieve a high proportion of green electricity consumption, multi-material synergistic utilization, and synergistic improvement in system economy and low carbon emissions, has become a key issue that the chemical industry urgently needs to address in its low-carbon transformation. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a capacity optimization configuration method for a green electricity-driven green ammonia-caustic soda-polyvinyl chloride co-production system, in order to solve the problem of synergistic optimization of the economy and low carbon emissions of a high proportion of green electricity consumption and a multi-product co-production system.

[0007] To achieve the above objectives, the specific technical solution is as follows:

[0008] A method for optimizing the capacity configuration of a green electricity-driven green ammonia-caustic soda-polyvinyl chloride co-production system, characterized by comprising the following steps:

[0009] S1: Construct a green electricity-driven green ammonia-caustic soda-polyvinyl chloride co-production system, the system including a renewable energy power generation unit, an air separation unit, a green ammonia synthesis unit, a waste salt treatment unit, an electrolytic sodium chloride unit, an ethylene oxychlorination unit, and a polyvinyl chloride synthesis unit;

[0010] The renewable energy power generation unit comprises photovoltaic and wind power generation, coupled with energy storage, to provide green electricity. The air separation unit uses green electricity to drive air pressure swing adsorption separation to obtain oxygen and nitrogen, which provide raw materials for ethylene oxychlorination and green ammonia synthesis, respectively. The green ammonia synthesis unit uses the Haber-Bosch process to synthesize green ammonia from hydrogen produced by sodium chloride electrolysis and nitrogen produced by the air separation unit. The waste salt treatment unit processes industrial waste salt to obtain sodium chloride, which supplies feedstock to the sodium chloride electrolysis unit. The sodium chloride electrolysis unit uses ion-exchange membrane electrolysis technology, utilizing green electricity to electrolyze sodium chloride to generate caustic soda, chlorine, and hydrogen. The chlorine is transported to the ethylene oxychlorination unit, and part of the hydrogen is transported to the green ammonia synthesis unit and part is directly stored. The ethylene oxychlorination unit reacts chlorine, oxygen, and ethylene to produce dichloroethane, which is then cracked to obtain vinyl chloride monomer. The polyvinyl chloride synthesis unit polymerizes the vinyl chloride monomer to produce polyvinyl chloride.

[0011] S2: Establish a system capacity optimization configuration model. The model takes the minimum overall system cost as the objective function and simultaneously satisfies the constraints of green electricity consumption rate, production technology constraints of each unit, and output constraints of multiple products.

[0012] The objective function is shown in the following equation:

[0013]

[0014] In the above formula, C total The total system cost is expressed in yuan; C invt The investment cost for each unit, in yuan, includes the initial investment allocation cost for the renewable energy power generation unit, air separation unit, green ammonia synthesis unit, waste salt treatment unit, electrolytic sodium chloride unit, ethylene oxychlorination unit, and polyvinyl chloride synthesis unit; C oper The annual system operation and maintenance cost is expressed in yuan, including the operation and maintenance costs of each unit; C penl The cost of green electricity curtailment penalties is expressed in yuan; R prod Revenue from the sale of ammonia, caustic soda, and polyvinyl chloride products is expressed in yuan; among which:

[0015]

[0016] In the above formula, I represents the set of system units; k i The unit capacity investment cost for unit i is expressed in yuan / kW or yuan / kg; P i,max R is the rated capacity of unit i, in kW or kg; r is the annual interest rate, in %; n is the system operating cycle, in years.

[0017]

[0018] In the above formula, c oper,i The annual operation and maintenance cost per unit capacity of unit i is expressed in yuan / (kW·year) or yuan / (kg·year);

[0019]

[0020] In the above formula, θ is the curtailment penalty coefficient, with units of yuan / kWh; p penl,t The amount of green electricity abandoned at time t is expressed in kWh.

[0021]

[0022] In the above formula, J represents the product set (ammonia, caustic soda, and polyvinyl chloride); c j M is the selling price of product j, in yuan / kg; j,total Let J be the total annual output of product j, in kg.

[0023] Specifically, the constraint model for constructing the objective function of minimizing the total cost of a green electricity-driven green ammonia-caustic soda-polyvinyl chloride co-production system includes:

[0024] (1) Renewable energy power generation unit

[0025] Wind power output constraints:

[0026]

[0027] In the above formula, P wt,t The wind power output at time t is expressed in kWh; v t The actual wind speed at time t is expressed in m / s; v ci v R and v co These are the fan inlet velocity, rated velocity, and outlet velocity, respectively, in m / s; P wt,max This refers to the rated capacity of the fan, in kW.

[0028] Photovoltaic output constraints:

[0029]

[0030] In the above formula, P pv,tP represents the photovoltaic output at time t, expressed in kWh. pv,max Rated photovoltaic capacity, in kWh; G t and G N These are the actual solar radiation intensity and the rated solar radiation intensity at time t, respectively, in kW / m². 2 ;T t and T N t represents the photovoltaic panel temperature and rated temperature at time t, respectively, in °C; γ is the power temperature coefficient, in / °C.

[0031] Supporting energy storage constraints:

[0032]

[0033] In the above formula, S ess,t The energy storage state of charge at time t is expressed in kWh; σ is the energy storage self-discharge rate, expressed in / h; P ess,in,t P ess,out,t These represent the energy storage charging and discharging power at time t, in kW; η ess,in η ess,out These are the charge and discharge efficiencies, respectively, in 5%;

[0034] Constraints on Supply and Demand Coordination between Wind, Solar and Energy Storage:

[0035]

[0036] In the above formula, P load,t The green load of the system at time t is expressed in kW.

[0037] Green energy consumption constraints:

[0038]

[0039] In the above formula, δ max The maximum allowable curtailment rate is expressed in % (%).

[0040] (2) Spatial separation unit

[0041] Operating power constraints:

[0042]

[0043] In the above formula, P asu,t P represents the operating power of the space distribution unit at time t, in kW. asu,min and P asu,max These are the minimum allowable operating power and rated power of the air separation unit, respectively, in kW;

[0044] Power-nitrogen production constraints:

[0045]

[0046] In the above formula, m N2,t η represents the nitrogen production of the air separation unit at time t, in kg / h. asu The air separation unit operating efficiency is expressed in %; p N2 The power consumption per unit nitrogen production of the air separation unit is expressed in kWh / kg.

[0047] (3) Ammonia synthesis unit

[0048] Hydrogen supply and demand constraints:

[0049]

[0050] In the above formula, m H2,as,t The hydrogen consumption rate for the ammonia synthesis reaction at time t is expressed in kg / h; m H2,NaCl,t S represents the amount of hydrogen produced as a byproduct of the sodium chloride electrolysis unit at time t, in kg / h. H2,t and S H2,t-1 η represents the hydrogen storage capacity of the hydrogen storage tank at time t and t-1, respectively, in kg; H2,in and η H2,out These represent the hydrogen filling and releasing efficiencies of the hydrogen storage tank, expressed in % (%).

[0051] Nitrogen supply and demand constraints:

[0052]

[0053] In the above formula, m N2,as,t m represents the nitrogen consumption rate in the ammonia synthesis reaction at time t, expressed in kg / h. N2,asu,t S represents the nitrogen production of the air separation unit at time t, in kg / h. N2,t and S N2,t-1 These represent the nitrogen storage capacity of the nitrogen storage tank at time t and t-1, respectively, in kg; η N2,in and η N2,out The figures represent the nitrogen storage tank filling and hydrogen release efficiencies, respectively, in percentage (%).

[0054] Hydrogen-nitrogen ratio constraint:

[0055]

[0056] Power-ammonia production constraints:

[0057]

[0058]

[0059] In the above formula, m NH3,t η represents the green ammonia production at time t, in kg / h. as The efficiency of ammonia synthesis reaction is expressed in %; Pas,t P represents the total operating power of the ammonia synthesis unit at time t, in kW. as,base The unit's basic power is expressed in kW; ω NH3 The power consumption per unit yield of ammonia synthesis is expressed in kWh / kg; P as,min and P as,max These are the minimum and maximum operating power of the ammonia synthesis unit, respectively, in kW;

[0060] (4) Waste salt treatment unit

[0061] Supply and demand balance constraints of waste salt raw materials:

[0062]

[0063] In the above formula, m NaCl,pur,t The unit yield of qualified sodium chloride after purification at time t, in kg / h; m salt,in,t η represents the industrial waste salt input at time t, in kg / h. salt,pur Waste salt purification efficiency, expressed in % %.

[0064] Power-salt processing capacity constraints:

[0065]

[0066]

[0067] In the above formula, P salt,t P represents the total operating power of the waste salt treatment unit at time t, in kW. salt,min and P salt,max These represent the minimum and maximum operating power of the waste salt treatment unit, respectively, in kW; η salt,energy Unit energy utilization efficiency, in %; ω salt The unit power consumption for waste salt treatment is expressed in kWh / kg.

[0068] (5) Electrolytic sodium chloride unit

[0069] Green electricity supply and demand balance constraints:

[0070]

[0071] In the above formula, P el,NaCl,t P represents the operating power of the sodium chloride electrolysis unit at time t, in kW. penl,t P represents the amount of green electricity wasted at time t, in kW. dischar,t and P char,t These represent the battery discharge and charge at time t, respectively, in kW;

[0072] Power-product yield constraints:

[0073]

[0074]

[0075]

[0076]

[0077] In the above formula, P el,NaCl,min P represents the minimum allowable operating power of the sodium chloride electrolysis unit at time t, in kW. el,NaCl,max The rated power of the sodium chloride electrolysis unit at time t is expressed in kW; m NaOH m Cl2 and m H2 These represent the yields of caustic soda, chlorine, and byproduct hydrogen at time t, in kg / h; k NaOH k Cl2 and k H2 These are the theoretical production coefficients per unit power for caustic soda, chlorine, and hydrogen in the electrolysis unit, respectively, in kg / (kW·h); η el,NaCl The operating efficiency of the sodium chloride electrolysis unit is expressed in % (%).

[0078] (6) Ethylene oxychlorination unit

[0079] Ethylene supply and demand constraints:

[0080]

[0081] In the above formula, m C2H4,vc,t The ethylene consumption rate of the ethylene oxychlorination unit at time t is expressed in kg / h; m C2H4,sup,t S represents the amount of ethylene purchased at time t, in kg / h; C2H4,t This refers to the storage capacity of the ethylene storage tank, expressed in kg / h.

[0082] Oxygen supply and demand constraints:

[0083]

[0084]

[0085] In the above formula, m O2,vc,t K represents the oxygen consumption of the ethylene oxychlorination unit at time t, in kg / h. O2 / vc The oxygen consumption coefficient for vinyl chloride is expressed in kg / kg; m O2,sup,t S represents the oxygen supply at time t, expressed in kg / h. O2,t This refers to the oxygen storage capacity of the storage tank, expressed in kg / h.

[0086] Power-vinyl chloride production constraints:

[0087]

[0088]

[0089] In the above formula, m vcm,t η represents the vinyl chloride production at time t, in kg / h. vcm P represents the vinyl chloride synthesis efficiency, expressed in %; vcm,t P represents the total operating power of the oxychlorination unit at time t, in kW. vcm,min and P vcm,max These are the minimum and maximum operating power of the oxychlorination unit, respectively, in kW;

[0090] (7) Polyvinyl chloride unit

[0091] Power-PVC production constraints:

[0092]

[0093]

[0094] In the above formula, m pvc,t η represents the polyvinyl chloride (PVC) production at time t, in kg / h. pvc The polymerization efficiency of vinyl chloride is expressed in %; k pvc / vcm P is the conversion factor from vinyl chloride to polyvinyl chloride, expressed in kg / kg. pvc,t P represents the total operating power of the oxychlorination unit at time t, in kW. pvc,min and P pvc,max These are the minimum and maximum operating power of the oxychlorination unit, respectively, in kW;

[0095] Preferably, in S2, the wind turbine of the renewable energy power generation unit has a cut-in wind speed of 3~4 m / s, a rated wind speed of 10~12 m / s, and a cut-out wind speed of 20~25 m / s; the rated solar radiation intensity is 1 kW / m². 2 The photovoltaic panel has a rated temperature of 25℃ and a power temperature coefficient of 0.004 to -0.006℃; the battery charging and discharging efficiency is 90% to 98%; and the maximum allowable curtailment rate is 2% to 10%.

[0096] Preferably, in S2, the air separation unit operates at an efficiency of 85%~95%, and the unit energy consumption is 0.12~0.18 kWh / Nm³. 3 The recovery rate of air, green nitrogen, and green oxygen is 50-60%;

[0097] Preferably, in S2, the power consumption of the Haber-Bosch process in the green ammonia synthesis unit is 4.5~5.0 kWh / kg green ammonia, the single-pass conversion rate of ammonia synthesis reaction is 12%~18%, and the hydrogen-nitrogen ratio is 1~3:1;

[0098] Preferably, in S2, the operating efficiency of the sodium chloride electrolysis unit is 85%~95%, and the power consumption per unit of sodium chloride is 2.4~2.8 kWh / kg caustic soda;

[0099] Preferably, in S2, the synthesis efficiency of ethylene oxychlorination unit vinyl chloride is 88%~92%, and the feed gas ratio (molar ratio) is C2H4:HCl:O2 = 1:2.05:0.52;

[0100] Preferably, in S2, the conversion coefficient from vinyl chloride to polyvinyl chloride in the polyvinyl chloride synthesis unit is 0.98~1.0 kg / kg, the polymerization efficiency of vinyl chloride is 95%~98%, and the energy utilization efficiency of the polymerization process is 85%~90%.

[0101] S3: Based on the objective function of minimizing the overall system cost and the aforementioned constraints, the optimal capacity configuration and corresponding economic and low-carbon indicators of each core unit of the system are determined by calling the CPLEX solver through the YALMIP platform and using MATLAB software. This includes the following steps:

[0102] Step 1: Define the core boundary conditions for solving the problem. Take the minimum overall system cost defined above as the core objective function. At the same time, transform the operational constraints of each unit, the green electricity consumption rate constraints, and the multi-product output constraints into mathematical constraints. Use MATLAB software to call the CPLEX solver to solve the objective function under global constraints for the green electricity-driven green ammonia-caustic soda-polyvinyl chloride cogeneration system. Output the initial capacity configuration scheme of each unit (wind power, photovoltaic, energy storage, ion membrane caustic soda electrolyzer, ammonia synthesis unit, chlor-alkali unit, etc.) and the corresponding key parameters such as overall system cost, green electricity consumption rate, and product output.

[0103] Step 2: Construct a multi-dimensional evaluation system, using renewable energy utilization rate (including wind power and photovoltaic absorption rate) as the core indicator, combined with auxiliary indicators such as system comprehensive cost (net value after deducting product sales revenue from investment cost, operation and maintenance cost, and curtailment penalty cost), multi-product output compliance rate (the degree of matching between actual output and required output of green ammonia, caustic soda, and polyvinyl chloride), and carbon emissions (emission reduction based on green electricity replacing fossil energy). Conduct a comprehensive comparative analysis of the multiple capacity configuration schemes output in Step 1; select the scheme with the highest renewable energy utilization rate, the lowest system comprehensive cost, and that meets all production constraints and product output requirements, and determine it as the optimal capacity configuration scheme corresponding to the minimum objective function. Simultaneously, clarify the rated capacity, annual operating cost, product revenue, and green electricity absorption rate of each unit under this scheme, providing a quantitative basis for system engineering applications.

[0104] The beneficial effects of this invention are:

[0105] 1. This invention constructs a capacity optimization model under global constraints, with the goal of minimizing the overall system cost. It simultaneously incorporates the operational constraints of the renewable energy power generation unit, the sodium chloride electrolysis unit, the green ammonia synthesis unit, and the ethylene oxychlorination unit. The capacity of the wind, solar and chemical units is co-optimized by calling the CPLEX solver through MATLAB.

[0106] 2. This invention constructs a deep coupling system of "green electricity - multiple chemical products", relying on the differentiated electricity consumption characteristics of multiple units such as green ammonia synthesis, electrolytic sodium chloride, and ethylene oxychlorination to form diversified green electricity consumption scenarios, providing "flexible support" for the fluctuations in wind power and photovoltaic output.

[0107] 3. This invention utilizes waste salt resources and by-product hydrogen for green ammonia synthesis, etc., to reduce dependence on fossil energy and ultimately achieve stable operation of a low-cost, low-emission green electricity-driven hydrogen production and multi-product co-production system. This ensures the lowest possible cost of hydrogen production and significantly reduces carbon emissions through green electricity substitution. Attached Figure Description

[0108] Figure 1 This invention proposes a green electricity-driven green ammonia-caustic soda-polyvinyl chloride co-production system.

[0109] Figure 2 This is a 24-hour light intensity data map of Huanxian County, Qingyang City, Gansu Province, in an embodiment of the present invention.

[0110] Figure 3 This is a 24-hour wind speed data map of Huanxian County, Qingyang City, Gansu Province, as shown in this embodiment of the invention.

[0111] Figure 4 This is a graph showing the 24-hour wind power and photovoltaic output data calculated in an embodiment of the present invention.

[0112] Figure 5 This is a graph showing the 24-hour battery capacity change data calculated in an embodiment of the present invention.

[0113] Figure 6 This is a graph showing the 24-hour battery charge and discharge data calculated in an embodiment of the present invention.

[0114] Figure 7 This is a graph showing the 24-hour green ammonia production data calculated in an embodiment of the present invention.

[0115] Figure 8 This is a graph showing the 24-hour caustic soda production data calculated in an embodiment of the present invention.

[0116] Figure 9 This is a graph showing the 24-hour polyvinyl chloride production data calculated in an embodiment of the present invention. Detailed Implementation

[0117] 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 a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0118] The following embodiments provide a green electric-driven green ammonia-caustic soda-polyvinyl chloride co-production system ( Figure 1 The system includes a renewable energy power generation unit, an air separation unit, a green ammonia synthesis unit, a waste salt treatment unit, an electrolytic sodium chloride unit, an ethylene oxychlorination unit, and a polyvinyl chloride synthesis unit. The output of the renewable energy power generation unit is connected to the input of the air separation unit and the input of the electrolytic sodium chloride unit. The output of the air separation unit is connected to the input of the ethylene oxychlorination unit and the input of the green ammonia synthesis unit. The output of the waste salt treatment unit is connected to the input of the electrolytic sodium chloride unit. The output of the electrolytic sodium chloride unit is connected to the input of the ethylene oxychlorination unit and the input of the green ammonia synthesis unit. The output of the ethylene oxychlorination unit is connected to the input of the polyvinyl chloride synthesis unit.

[0119] This invention selects wind energy and solar energy resource data from Huanxian County, Qingyang City, Gansu Province, my country ( Figure 2 and Figure 3The green electricity-driven green ammonia-caustic soda-polyvinyl chloride co-production system has a green ammonia production of 205 kmol / h, a caustic soda production of 425 kmol / h, and a polyvinyl chloride production of 581 kmol / h. An ion-exchange membrane caustic soda electrolyzer is selected, with an efficiency of 90%. The investment cost of the electrolyzer is 1200 CNY / kW, and its operation and maintenance cost is 60 CNY / kW. The operation and maintenance cost of the wind turbine is 0.028 CNY / kW, with an investment cost of 7400 CNY / kW. The operation and maintenance cost of the photovoltaic field is 0.030 CNY / kW, with an investment cost of 3600 CNY / kW. The operation and maintenance cost of the battery is 0.018 CNY / kW, and the battery's charge / discharge power is 92%.

[0120] Through co-optimization using the CPLEX solver called by MATLAB, the optimal photovoltaic capacity for this green electricity-driven green ammonia-caustic soda-polyvinyl chloride cogeneration system is 180MW. Figure 4 The optimal scale configuration for wind power is 90MW. Figure 4 The optimal energy storage capacity is 20MWh. Figure 5 and Figure 6 The production fluctuations of products chloramine, caustic soda, and polyvinyl chloride are as follows: Figure 7 , Figure 8 and Figure 9 The invention achieves an average 24-hour production rate of 205 kmol / h for green ammonia, 425 kmol / h for caustic soda, and 581 kmol / h for polyvinyl chloride. Compared to single renewable energy-based water electrolysis hydrogen production systems and single chlor-alkali-polyvinyl chloride production systems, this invention reduces the production cost of green ammonia from 4,500 yuan per ton to 2,100 yuan, caustic soda from 1,850 yuan per ton to 1,450 yuan, and polyvinyl chloride from 7,000 yuan per ton to 5,600 yuan.

[0121] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for capacity optimization configuration of a green electricity driven green ammonia-caustic soda-polyvinyl chloride co-production system, characterized in that, Comprising the following steps: S1: Constructing a green electricity driven green ammonia-caustic soda-polyvinyl chloride co-production system, said system comprising a renewable energy power generation unit, an air separation unit, a green ammonia synthesis unit, a waste salt treatment unit, an electrolytic sodium chloride unit, an ethylene oxychlorination unit and a polyvinyl chloride synthesis unit; S2: Establishing a system capacity optimization configuration model, said model taking the minimum system comprehensive cost as the objective function, while meeting the green electricity consumption rate constraint, the production technology constraint of each unit and the multi-product yield constraint; S3: Based on the minimum system comprehensive cost objective function and the constraint conditions, through the YALMIP platform calling CPLEX solver, with the help of MATLAB software, the optimal capacity configuration of each core unit of the system and the corresponding economic and low-carbon indicators are determined.

2. The capacity optimization configuration method of the green electricity-driven green ammonia-caustic soda-PVC co-production system according to claim 1, characterized in that: In S1, the renewable energy power generation unit is photovoltaic power generation and wind power generation, and is equipped with energy storage for providing green electricity; the air separation unit separates oxygen and nitrogen by green electricity driven pressure swing adsorption to provide raw materials for ethylene oxychlorination and green ammonia synthesis respectively; the green ammonia synthesis unit synthesizes green ammonia by Haber-Bosch process using hydrogen produced by electrolytic sodium chloride and nitrogen produced by the air separation unit; the waste salt treatment unit is used to treat industrial waste salt to obtain sodium chloride as feed for the electrolytic sodium chloride unit; the electrolytic sodium chloride unit uses ion membrane electrolysis technology to electrolyze sodium chloride with green electricity to generate caustic soda, chlorine and hydrogen, the chlorine is transported to the ethylene oxychlorination unit, and the hydrogen is partly transported to the green ammonia synthesis unit and partly directly stored; the ethylene oxychlorination unit reacts chlorine, oxygen and ethylene to generate dichloroethane, and the dichloroethane is cracked to obtain chloroethylene monomer; the polyvinyl chloride synthesis unit polymerizes chloroethylene monomer to generate polyvinyl chloride.

3. The capacity optimization configuration method of the green electricity-driven green ammonia-caustic soda-PVC co-production system according to claim 2, characterized in that: In S2, the objective function is as follows: ; In the above formula, C total is the system comprehensive cost, with unit of yuan; C invt is the investment cost of each unit, with unit of yuan, including the initial investment allocation cost of renewable energy power generation unit, air separation unit, green ammonia synthesis unit, waste salt treatment unit, electrolytic sodium chloride unit, ethylene oxychlorination unit, and polyvinyl chloride synthesis unit; C oper is the annual operation and maintenance cost of the system, with unit of yuan, including the operation and maintenance cost of each unit; C penl is the green electricity curtailment penalty cost, with unit of yuan; R prod is the sales revenue of green ammonia, caustic soda, and polyvinyl chloride products, with unit of yuan; wherein: ； In the above formula, I is the system unit set; k i is the unit capacity investment cost of unit i, with the unit of yuan / kW or yuan / kg; P i,max is the rated capacity of unit i, with the unit of kW or kg; r is the annual interest rate, with the unit of %; and n is the system operation period, with the unit of years. ； In the above formula, c oper,i The unit capacity annual operation and maintenance cost of unit i is in yuan / (kW·year) or yuan / (kg·year). ； In the above formula, θ is the penalty coefficient of abandoned electricity, with the unit of yuan / kWh; p penl,t is the green electricity abandoned at time t, with the unit of kWh; ； In the above formula, J is the product set (green ammonia, caustic soda and polyvinyl chloride); c j is the sales unit price of product j, in yuan / kg; M j,total is the total annual output of product j, in kg.

4. The capacity optimization configuration method of the green electricity-driven green ammonia-caustic soda-PVC co-production system according to claim 3, wherein: In S2, the constraint model of the minimum total cost of the green electricity driven green ammonia-caustic soda-polyvinyl chloride co-production system includes: (1) Renewable energy power generation unit Wind power output constraint: ； In the above formula, P wt,t is the wind power output at time t, with units of kWh; v t is the actual wind speed at time t, with units of m / s; v ci , v R , and v co are the cut-in wind speed, rated wind speed, and cut-out wind speed, respectively, with units of m / s; P wt,max is the rated capacity of the wind turbine, with units of kW; Photovoltaic output constraint: ； In the above formula, P pv,t is the photovoltaic output at time t, with units of kWh; P pv,max is the photovoltaic rated capacity, with units of kWh; G t and G N are the actual solar radiation intensity and the rated radiation intensity, respectively, at time t, with units of kW / m 2 ; T t and T N are the photovoltaic panel temperature and the rated temperature, respectively, at time t, with units of °C; and γ is the power temperature coefficient, with units of / °C. Supporting energy storage constraint: ； In the above formula, S ess,t is the energy storage state of charge at time t, with units of kWh; σ is the energy storage self-discharge rate, with units of / h; P ess,in,t , P ess,out,t are the energy storage charge and discharge powers at time t, with units of kW; η ess,in , η ess,out are the charge and discharge efficiencies, with units of 5%. Wind-solar-energy storage supply and demand coordination constraint: ； In the above formula, P load,t is the green electricity load of the system at time t, in kW; Green electricity consumption constraint: ； In the above formula, δ max is the maximum allowable rate of power loss, in %; (2) Air separation unit Operating power constraint: ； In the above formula, P asu,t is the operating power of the air separation unit at time t, in kW; P asu,min and P asu,max are the minimum allowable operating power and the rated power of the air separation unit, respectively, in kW; Power-nitrogen yield constraint: ； In the above formula, m N2,t is the nitrogen production of the air separation unit at time t, in kg / h; η asu is the operating efficiency of the air separation unit, in %; p N2 is the power consumption per unit of nitrogen production of the air separation unit, in kWh / kg; (3) Ammonia synthesis unit Hydrogen supply and demand constraint: ； In the above formula, m H2,as,t is the hydrogen consumption of the ammonia synthesis reaction at time t, in kg / h; m H2,NaCl,t is the amount of hydrogen by-produced by the electrolysis of sodium chloride at time t, in kg / h; S H2,t and S H2,t-1 are the hydrogen storage amounts of the hydrogen storage tank at time t and time t-1, respectively, in kg; η H2,in and η H2,out are the hydrogen charging and discharging efficiencies of the hydrogen storage tank, respectively, in %. Nitrogen supply and demand constraint: ； In the above formula, m N2,as,t is the nitrogen consumption of the ammonia synthesis reaction at time t, in kg / h; m N2,asu,t is the nitrogen production of the air separation unit at time t, in kg / h; S N2,t and S N2,t-1 are the nitrogen storage amounts of the nitrogen storage tank at time t and time t-1, respectively, in kg; η N2,in and η N2,out are the hydrogen charging and discharging efficiencies of the nitrogen storage tank, respectively, in %. Hydrogen-nitrogen ratio constraint: ； Power-ammonia yield constraint: ； ； In the above formula, m NH3,t is the green ammonia production at time t, in kg / h; η as is the ammonia synthesis reaction efficiency, in %; P as,t is the total operating power of the ammonia synthesis unit at time t, in kW; P as,base is the unit base power, in kW; ω NH3 is the ammonia synthesis unit power consumption per unit of production, in kWh / kg; P as,min and P as,max are the minimum and maximum operating powers of the ammonia synthesis unit, respectively, in kW; (4) Waste salt treatment unit Waste salt raw material supply and demand balance constraint: ； In the above formula, m NaCl,pur,t is the qualified sodium chloride production after unit purification at time t, in kg / h; m salt,in,t is the industrial waste salt input at time t, in kg / h; η salt,pur is the waste salt purification efficiency, in %. Power-salt treatment amount constraint: ； ； In the above formula, P salt,t is the total operating power of the waste salt treatment unit at time t, with units of kW; P salt,min and P salt,max are the minimum and maximum operating powers of the waste salt treatment unit, respectively, with units of kW; η salt,energy is the energy utilization efficiency of the unit, with units of %; ω salt is the unit treatment power consumption of the waste salt, with units of kWh / kg; (5) Electrolytic sodium chloride unit Green electricity supply and demand balance constraint: ； In the above formula, P el,NaCl,t is the operating power of the electrolytic sodium chloride unit at time t, in units of kW; P penl,t is the green electricity abandoned at time t, in units of kW; P dischar,t and P char,t are the discharging and charging amounts of the battery at time t, in units of kW; Power-product yield constraint: ； ； ； ； In the above formula, P el,NaCl,min is the minimum allowable operating power of the sodium chloride electrolysis unit at time t, with units of kW; P el,NaCl,max is the rated power of the sodium chloride electrolysis unit at time t, with units of kW; m NaOH , m Cl2 , and m H2 are the caustic soda, chlorine, and byproduct hydrogen production at time t, respectively, with units of kg / h; k NaOH , k Cl2 , and k H2 are the unit power theoretical production coefficients of the caustic soda, chlorine, and hydrogen of the electrolysis unit, respectively, with units of kg / (kW·h); η el,NaCl is the operating efficiency of the sodium chloride electrolysis unit, with units of %. (6) Ethylene oxychlorination unit Ethylene supply and demand constraint: ； In the above formula, m C2H4,vc,t is the ethylene consumption amount of the ethylene oxychlorination unit at time t, in kg / h; m C2H4,sup,t is the ethylene outsourcing amount at time t, in kg / h; S C2H4,t is the ethylene storage amount of the ethylene storage tank, in kg / h; Oxygen supply and demand constraint: ； ； In the above formula, m O2,vc,t is the oxygen consumption of the ethylene oxide chlorination unit at time t, in kg / h; k O2 / vc is the unit chlorine ethylene oxygen consumption coefficient, in kg / kg; m O2,sup,t is the oxygen supply amount at time t, in kg / h; S O2,t is the oxygen storage amount of the oxygen storage tank, in kg / h; Power-chloroethylene yield constraint: ； ； In the above formula, m vcm,t is the vinyl chloride production at time t, in kg / h; η vcm is the vinyl chloride synthesis efficiency, in %; P vcm,t is the total operating power of the oxychlorination unit at time t, in kW; P vcm,min and P vcm,max are the minimum and maximum operating power of the oxychlorination unit, respectively, in kW; (7) Polyvinyl chloride unit Power-polyvinyl chloride yield constraint: ； ； In the above formula, m pvc,t is the PVC production at time t, in kg / h; η pvc is the vinyl chloride polymerization efficiency, in %; k pvc / vcm is the conversion coefficient of vinyl chloride to PVC, in kg / kg; P pvc,t is the total operating power of the oxychlorination unit at time t, in kW; P pvc,min and P pvc,max are the minimum and maximum operating power of the oxychlorination unit, respectively, in kW.

5. The capacity optimization configuration method of the green electricity driven green ammonia-caustic soda-polyvinyl chloride co-production system according to claim 4, characterized in that: In the renewable energy power generation unit, the fan cut-in wind speed is 3-4 m / s, the rated wind speed is 10-12 m / s, and the cut-out wind speed is 20-25 m / s; the solar rated radiation intensity is 1 kW / m 2 , the rated temperature of the photovoltaic panel is 25℃, the power temperature coefficient is 0.004-0.006 / ℃; the charging and discharging efficiency of the battery is 90%-98%; and the maximum allowable power abandonment rate is 2%-10%. In the air separation unit, the operation efficiency is 85%~95%, and the unit energy consumption is 0.12~0.18 kWh / Nm 3 The recovery rate of air, green nitrogen and green oxygen is 50~60%. In the green ammonia synthesis unit, the Haber-Bosch process power consumption is 4.5-5.0 kWh / kg green ammonia, the one-way conversion rate of ammonia synthesis reaction is 12%-18%, and the hydrogen-nitrogen ratio is 1-3:

1. In the electrolytic sodium chloride unit, the operation efficiency is 85%-95%, and the unit sodium chloride power consumption is 2.4-2.8 kWh / kg caustic soda; In the ethylene oxychlorination unit, the chloroethylene synthesis efficiency is 88%-92%, and the raw material gas ratio is C2H4:HCl:O2 = 1:2.05:0.52; In the polyvinyl chloride synthesis unit, the conversion coefficient of chloroethylene to polyvinyl chloride is 0.98-1.0 kg / kg, the chloroethylene polymerization efficiency is 95%-98%, and the energy utilization efficiency of the polymerization process is 85%-90%.

6. The capacity optimization configuration method of the green electricity-driven green ammonia-caustic soda-PVC co-production system according to claim 4, wherein: In S3, the following steps are specifically included: Step 1: Clearly define the core boundary conditions, take the minimum system comprehensive cost defined above as the core objective function, and convert the operation constraints of each unit, green electricity consumption rate constraints, and multi-product yield constraints into mathematical solving constraints. Through MATLAB software calling CPLEX solver, the objective function of green electricity driven green ammonia-caustic soda-polyvinyl chloride cogeneration system is solved under the constraints of the whole domain, and the initial scheme of capacity configuration of each unit and the corresponding key parameters of system comprehensive cost, green electricity consumption rate and product yield are outputted; Step 2: Build a multi-dimensional evaluation system, taking renewable energy utilization rate as the core index, combining system comprehensive cost, multi-product yield standard rate and carbon emission as auxiliary indexes, and comprehensively comparing and analyzing the multiple capacity configuration schemes outputted in step 1; Select the scheme with the highest renewable energy utilization rate, the lowest system comprehensive cost and meeting all production constraints and product yield requirements to determine the optimal capacity configuration scheme corresponding to the minimum value of the objective function, and clearly define the rated capacity, annual operation cost, product income and green electricity consumption rate of each unit under this scheme, providing quantitative basis for system engineering application.

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