Optimization Method for Minimum Carbon Emission Operation of Comprehensive Energy Park Based on Dynamic Carbon Emission Factor

: With the grand goals of "carbon peaking" and "carbon neutrality" being put forward, establishing an efficient comprehensive energy system and promoting the allocation and consumption of clean energy have become the challenges faced by many industrial parks in energy conservation and carbon reduction. Because the comprehensive energy park has various energy forms such as cold, heat, electricity, and gas, the energy structure is complex, and the renewable energy and load are highly volatile. Aiming at this problem, this paper builds a low-carbon operation model of comprehensive energy parks based on dynamic carbon emission factors, which can significantly improve the accuracy of the total carbon emission consumption in the park, and provide strong support for guiding the operation of equipment in the park and the charging and discharging of energy storage equipment.


Preface
China has clearly put forward the grand goals of "carbon peaking" and "carbon neutrality". This goal has promoted the adjustment of industrial structure and energy structure, and transformed into a green and low-carbon energy supply and consumption model while taking into account economic development [1] . The goal also puts forward higher requirements for power grid companies to accelerate the promotion of diversified and clean energy supply, low carbonization, and efficient energy consumption [2] . At the same time, more than 70% of my country's industrial energy consumption is concentrated in industrial parks, which consume a large amount of electricity, and users' energy consumption methods are diversified and accompanied by a large amount of cooling and heating demand [3] . Therefore, how to strengthen the multi-energy collaborative supply, energy cascade utilization and low-carbon efficient operation of this part of the comprehensive energy park has become a new focus and research focus [4] .
Under the condition that cold, heat, electricity and gas are all integrated into the system, ensuring the economical and efficient operation of the integrated energy system is a key factor in promoting the sustainable development of the industrial park [5] . Under the national dual carbon goal, the comprehensive energy system of the park has great potential to achieve carbon emission reduction, so how to make the low-carbon economic operation of the comprehensive energy park become the focus of research. In the existing comprehensive energy park operation optimization methods, the goal is often to optimize the economy, and the model considering carbon emissions only directly substitutes the regional power carbon emission factor, or converts the carbon price into the economic goal, and does not consider the new energy high-speed Dynamic characteristics of carbon emission factors under development [6] .
In view of the above problems, this paper proposes a dynamic power carbon emission factor calculation method, aiming at the lowest carbon emission, considering equipment operation constraints and energy balance constraints, and using the dynamic carbon emission factor to optimize the equipment operation mode of the comprehensive energy park , to obtain the unit operation mode combination with the lowest carbon emission. This method can more accurately describe the total carbon emission consumption of the comprehensive energy park, provide an optimization plan for low-carbon operation, and give suggestions on the operation mode of each equipment, so as to effectively guide the park to improve system energy efficiency, improve the utilization rate of key equipment and reduce Operating costs [7] .

Calculation method of dynamic carbon emission factor of the park
The provincial dynamic carbon emission factor calculation takes the province as the calculation unit. First, the carbon emissions of the coal-fired units, gas-fired units and external incoming electricity are counted in the province, and then the total on-grid electricity of the provincially-regulated units is counted, including but not limited to coal-fired units. Power generation, gas power generation, hydropower generation, photovoltaic power generation, wind power generation and nuclear power generation, and finally calculate the province's dynamic power carbon emission factor. The specific calculation process is shown in Figure 1.

Figure1. Calculation method of carbon emission factor on the power supply side
The dynamic model of the carbon emission factor on the power supply side is: In the formula: f is the carbon emission factor of the provincial power supply side, the unit is tCO2/kWh; i is the energy type of the provincial power supply side unified regulation unit, including coal-fired power generation, gas power generation, hydropower generation, photovoltaic power generation, wind power generation and nuclear power etc.; w is the area of incoming electricity; c is the coal-fired unit type; g is the gas-fired unit type; G is the power generation, the unit is kWh, and the value is the cumulative value measured at the gate for 15 minutes; EF is the carbon emission factor of a certain type of unit, the unit It is tCO2/kWh. Coal-fired power generation and gasfired power generation are selected according to the aforementioned research. Different types of units correspond to different carbon emission factors. EFw is the average carbon emission factor in the area of foreign electricity, which needs to be analyzed according to the type of foreign electricity; t represents time.
After further obtaining the provincial dynamic carbon emission factor, we can continue to refine the carbon flow of each prefecture and city according to the province's power topology map, and obtain the dynamic carbon emission factor of the city to which the comprehensive energy park belongs, which can be substituted into subsequent calculations.

Low-carbon operation objective function
The low-carbon goal is to consume as little primary and secondary energy as possible on the premise of meeting the needs of multiple loads such as cooling, heating, and electricity, including coal, gas, and grid power purchases. Use more electricity when clean energy is booming, and use less electricity when the proportion of coal-fired power is high. The specific meaning of the objective function is as follows: In the formula: Elec Emis W represents IES purchases electricity from the grid, CO 2 emission factor per unit of electricity,which changes dynamically over time,the unit is tCO 2 /kWh; FromGrid P represents electricity purchased from the grid,the unit is kWh; number.Among them, the emission coefficient of each device is the property of the device itself, which is specific.

Relevant constraints
Constraints include energy balance constraints and operating constraints of various equipment in the integrated energy park. Further, the energy balance constraints include electrical balance, heat balance and cold balance constraints, and the equipment operation constraints include capacity constraints, start-stop constraints, and input and output constraints. The basic equipment of the comprehensive energy park includes transformers, photovoltaics, fans, energy storage batteries, cold storage equipment, heat storage equipment, coalfired units, gas-fired units, electric boilers, heat pumps, absorption chillers, chillers, etc.

Energy balance constraints
The electricity balance constraint is described as the total electricity load in the park equal to the difference between the electricity purchased in the park and the electricity ongrid in the park plus the difference between the output power and the input power of the related equipment, using the formula: In the formula: load P represents the total electrical load in the park; The thermal balance constraint is described as the total thermal load of the park is equal to the difference between the output power and the input power of the thermal energy-related equipment, using the formula: In the formula: Load

Equipment Operation Constraints
The equipment operation constraints are related to the energy consumption type of each equipment and its own equipment attributes, mainly considering the conversion relationship between the input and output power and efficiency of the equipment and the start-stop status of the equipment. The following takes the chiller as an example to analyze the equipment operation constraints , using the formula: EnforceRun OperatState(t) 1-EnforceOutage   (8) In the formula: install j C represents the installation capacity of the chiller equipment; EnforceRun represents whether the device is forced to run, a 0-1 variable; EnforceOutage represents the equipment is overhauled, out of service, or in standby is a 0-1 variable; OperatState represents the running state of the equipment, where 1 means running, and 0 means out of service.

Conclusion
Aiming at the operation optimization problem of comprehensive energy parks including electricity, heat, gas and other energy forms, this paper constructs a lowcarbon operation model of comprehensive energy parks based on dynamic carbon emission factors [8][9] . By accurately depicting the total carbon emission of the comprehensive energy park and the phenomenon of low power carbon emission factor when the photovoltaic and other new energy generating units have high power generation, it can more accurately guide the equipment operation of the comprehensive energy park and the charging and discharging of the energy storage equipment, which can significantly improve the The park's comprehensive energy system operation efficiency helps save energy and reduce carbon emissions [10] .