A carbon cycle system and its application

Abstract

The present invention discloses a carbon cycle system, including a CO2 generation system, a carbon capture device, a power-to-gas device and a supercritical CO2 power plant, wherein the carbon capture system captures carbon dioxide generated by coal and natural gas to provide a carbon source for the power-to-gas device and the supercritical CO2 system. When the load demand of the power system is low, the minimum output of the coal-fired unit is reduced by the carbon capture system to accommodate more renewable energy; the excess renewable energy power generation will be consumed by the power-to-gas device. The carbon cycle system can be applied to the optimization and scheduling of comprehensive energy systems including new energy.

Description

Technical Field

[0001] The present invention belongs to the field of resource recycling and carbon emission reduction, and in particular relates to a carbon recycling system and its application. Background Art

[0002] In recent years, renewable energy has made great progress in the field of power generation due to its low emissions and sustainability. However, the randomness and volatility of renewable energy also pose great challenges to the safe operation of the power system. The integrated energy system can combine multiple energy sources to promote more renewable energy access to the grid and reduce carbon emissions on the basis of achieving a balance between energy supply and demand for electricity and heat. However, not all renewable energy output can be fully utilized, resulting in waste of resources and large amounts of carbon emissions. It is urgent to recover the CO2 generated by coal and gas to promote energy efficiency and achieve carbon emission reduction.

[0003] Purpose of the Invention

[0004] The purpose of the present invention is to propose a carbon cycle system and application scenario that promotes energy utilization efficiency and carbon emission reduction, so as to solve the defects in the background technology. The present invention applies the carbon cycle system in a comprehensive energy system, which can provide support for improving energy utilization efficiency, the penetration of new energy and low carbon emissions. Summary of the invention

[0005] According to one aspect of the present invention, a carbon cycle system is provided, comprising a CO2 generation subsystem, a carbon capture device, and a power-to-gas device, wherein the CO2 generation subsystem comprises a gas turbine GT using CH4 as fuel, a gas boiler GB, and a combined heat and power CHP and a supercritical CO2 power plant using coal as fuel; the carbon capture device captures the CO2 generated in the CO2 generation subsystem, specifically, separates and captures CO2 from flue gas generated in the gas turbine GT, the gas boiler GB, the combined heat and power CHP and the supercritical CO2 power plant, wherein the supercritical CO2 power plant uses an S-CO2 unit to generate electricity; Part of the captured CO2 enters the supercritical CO2 power plant as a supplementary working fluid, and part enters the power-to-gas device P2G; the carbon cycle system is used in an integrated energy system, which includes a power generation device, a heating device and an energy conversion device, and the power generation device includes a wind power or photovoltaic new energy power generation device, a gas turbine, a gas boiler, a cogeneration and a supercritical CO2 power plant; when the output of the new energy power generation device is high, the power-to-gas device P2G in the carbon cycle system uses excess electricity to reduce part of the CO2 to CH4 and send it to the gas turbine GT or the gas boiler GB as fuel.

[0006] According to another aspect of the present invention, there is provided a method for using the above carbon cycle system for optimizing the scheduling of an integrated energy system, comprising the following steps:

[0007] Step 1: Establish a CO2 generation process model: The source of CO2 generated in the power generation process is designated as natural gas and coal; for the natural gas power generation process, the output of the gas turbine and the gas boiler is represented as shown in formula (1):

[0008]

[0009] Where P and H are the electrical power and thermal power output of the unit, respectively, η is the production efficiency of electricity or heat, Q is the consumption rate of natural gas, and h NG is the calorific value of natural gas. The superscripts GT and GB represent gas turbine and gas boiler, respectively, and the subscripts i and j are the serial numbers of gas turbine and gas boiler, respectively;

[0010] The i-th gas turbine and the jth gas boiler The carbon dioxide emissions are expressed as shown in formula (2):

[0011]

[0012] in, is the density of methane, and are the molecular weights of carbon dioxide and methane, respectively;

[0013] The CO2 produced by the coal combustion process is represented as shown in equation (3) and equation (4):

[0014]

[0015]

[0016] in, and are the carbon emission coefficients of the kth CHP unit, are the carbon emission coefficients of the first S-CO2 unit;

[0017] Therefore, the CO2 emissions generated by the entire combustion process can be expressed as shown in formula (5):

[0018]

[0019] Step 2: Construct a carbon dioxide capture process model: The power consumption of the carbon capture device is expressed as shown in formula (6):

[0020]

[0021] Wherein, α is the energy consumption rate of the carbon capture device; the amount of CO2 discharged into the atmosphere after carbon capture is expressed as shown in formula (7):

[0022]

[0023] Among them, η CCS The operating efficiency of the carbon capture device;

[0024] Step 3: directly utilize or store the captured CO2, which is expressed as and The relationship between them is expressed as shown in formula (8):

[0025]

[0026] Where g is the ratio between CO2 utilization and storage;

[0027] Part of the utilized CO2 is used to generate natural gas CH4 through the power-to-gas device P2G, and the other part enters the supercritical CO2 power plant as a supplementary working fluid, wherein the supercritical CO2 power plant is an S-CO2 device; the process of generating natural gas CH4 through the power-to-gas device P2G includes two stages, namely, the electrolysis process and the methanogenic reaction process, wherein the flow rate of hydrogen generated by the electrolysis of water is Power consumption of the P2G device Satisfies the relationship shown in formula (9):

[0028]

[0029] Where β is the rate of hydrogen production by water electrolysis;

[0030] During the methanation reaction, the amount of CO2 consumed by the power-to-gas device P2G and the amount of CH4 produced The quantity satisfies the relationship shown in formula (10):

[0031]

[0032] Heat energy is released during the methanogenesis process and is used for heating. Assume that the proportion of the released heat energy used for heating is η P2G2H , then the total thermal power of the power-to-gas device P2G It is expressed as shown in formula (11):

[0033]

[0034] Among them, γ is the heat released by the methanogenic reaction to produce a unit of methane;

[0035] During the operation of the first supercritical CO2 unit, the flow rate of the supplementary working fluid The output power of the first supercritical CO2 unit Satisfies the relationship shown in formula (12):

[0036]

[0037] Among them, δ is the supplementary working fluid flow rate required for the unit electrical power of the supercritical CO2 unit;

[0038] The CO2 sources of the power-to-gas device P2G and the supercritical CO2 power generation device are partly provided by the carbon capture device, and the other part is purchased from the outside, which is expressed as shown in formula (13):

[0039]

[0040] In the formula, is the mass flow rate of CO2 purchased from outside, The mass flow rate of CO2 provided to the carbon capture device.

[0041] Step 4: Calculate the operating cost of the integrated energy system: The operating cost of the integrated energy system is defined as the fuel purchase consumption of coal-fired and gas-fired units. For the i-th gas turbine and the j-th gas boiler, the consumption during operation is represented as shown in formula (14) and formula (15), respectively:

[0042]

[0043]

[0044] in, and Represent the gas consumption of the i-th gas turbine and the j-th gas boiler, is the purchase price of methane;

[0045] When calculating the cost of purchasing methane, some of the methane produced by P2G is removed. The consumption of the methane produced by P2G is expressed as shown in equation (16):

[0046]

[0047] For the first supercritical CO2 unit, the operating cost and the output power of the unit satisfy the relationship shown in formula (17):

[0048]

[0049] Among them, a, b and c are operating cost coefficients;

[0050] The fuel consumption of the cogeneration unit is expressed as shown in formula (18):

[0051]

[0052] Other costs during operation also include the cost of purchasing CO2, which is expressed as shown in formula (19):

[0053]

[0054] The total operating cost of the integrated energy system is expressed as shown in formula (20):

[0055]

[0056] Where T is the entire scheduling time, N T 、N B 、N C 、N S They are the number of gas turbines, gas boilers, cogeneration and supercritical CO2 units respectively.

[0057] Step 5: Calculate the cost of pollutant control: The pollutants in the coal and gas combustion process are limited to SO2 and NO produced by the CHP and S-CO2 units of the cogeneration. x , their processing costs are expressed as shown in formula (21) and formula (22):

[0058]

[0059]

[0060] in, and are the pollutant treatment costs of CHP and S-CO2 units for combined heat and power generation, respectively;

[0061] The total pollutant treatment cost of the integrated energy system is expressed as shown in formula (23):

[0062]

[0063] Step 6: Calculate the penalty cost for abandoning wind and solar power: The penalty for abandoning electricity is expressed as shown in formula (24):

[0064]

[0065] Where N WT With N PV are the number of wind power and photovoltaic units, respectively, WT With K PV is the penalty coefficient for wind power and photovoltaic power abandonment, and They are the predicted and actual power of wind power, and They are the predicted and actual power of photovoltaics;

[0066] Step 7: Solution for integrated energy system scheduling: The solution for scheduling is to minimize the total cost of the integrated energy system by configuring the output of each unit and the integrated energy system under the constraints. The total cost of the integrated energy system is expressed as the sum of the operating cost, the pollutant control cost and the penalty cost for wind and solar power abandonment, as shown in formula (25):

[0067] C=C D +C P +C R (25);

[0068] The supply and demand balance between the power output and the load during the operation of the integrated energy system is expressed as shown in equations (26) and (27):

[0069]

[0070]

[0071] In the formula, P is the electrical power generated or consumed by each system, and H is the thermal power generated or consumed by each system; and are the electricity and heat load demands, respectively; TES and EB represent the heat storage system and electric boiler, respectively;

[0072] According to the dispatch results, the wind curtailment rate υ, which represents the access rate of new energy, is obtained WT and the light abandonment rate PV , as shown in equations (28) and (29):

[0073]

[0074]

[0075] The energy utilization efficiency of the integrated energy system is defined as the ratio between the energy connected to the power grid and the heat network and the total input energy, as shown in formula (30):

[0076]

[0077] Among them, σ and p coal are the calorific value and unit price of coal, and are the energy efficiency of wind power and photovoltaic power respectively;

[0078] Compare the actual CO2 emitted into the atmosphere with the net CO2 emissions They are expressed as shown in formula (31) and (32) respectively:

[0079]

[0080] BRIEF DESCRIPTION OF THE DRAWINGS

[0081] Figure 1 This is a flow chart of the carbon cycle system of the present invention;

[0082] Figure 2 is a wind power prediction power diagram in an embodiment of the present invention;

[0083] Figure 3 is a photovoltaic prediction power diagram in an embodiment of the present invention;

[0084] Figure 4 Grid-connected wind power power diagrams in different scenarios according to the embodiments of the present invention;

[0085] Figure 5 Grid-connected photovoltaic power diagrams in different scenarios according to the embodiments of the present invention; DETAILED DESCRIPTION

[0086] The following description is used to disclose the present invention so that those skilled in the art can implement the present invention. The preferred embodiments described below are only examples, and those skilled in the art may think of other obvious variations.

[0087] Figure 1 is a flow chart of the carbon cycle system of the present invention, such as Figure 1 As shown, the carbon cycle system includes a CO2 generation subsystem, a carbon capture device, and a power-to-gas device, wherein the CO2 generation subsystem includes a gas turbine GT using CH4 as fuel, a gas boiler GB, and a cogeneration CHP and a supercritical CO2 power plant using coal as fuel; the carbon capture device captures the CO2 generated in the CO2 generation subsystem, specifically, separates and captures CO2 from the flue gas generated by the gas turbine GT, the gas boiler GB, the cogeneration CHP and the supercritical CO2 power plant, and the supercritical CO2 power plant uses an S-CO2 unit to generate electricity; part of the captured CO2 enters the supercritical CO2 power plant as a supplementary working fluid, and part enters the power-to-gas device P2G. The carbon cycle system is used in an integrated energy system, which includes a power generation device, a heating device and an energy conversion device. The power generation device includes a new energy power generation device of wind power or photovoltaic power, a gas turbine, a gas boiler, a cogeneration and a supercritical CO2 power plant; when the output of the new energy power generation device is high, the power-to-gas device P2G in the carbon cycle system uses excess electricity to reduce a portion of CO2 to CH4 and send it to the gas turbine GT or the gas boiler GB as fuel.

[0088] Example

[0089] The comprehensive energy system in this embodiment includes power generation, heat supply and various forms of energy conversion devices. For power generation and heat supply devices, the installed capacities of wind power, photovoltaics, gas turbines, gas boilers, cogeneration and supercritical CO2 are 750MW, 400MW, 500MW, 50MW, 200MW and 300MW respectively. The proportion of renewable energy power generation reaches 52.3%. For coal-fired and gas-fired units, the minimum output power is 50% of the maximum output power. For energy conversion devices, the maximum power of power-to-gas and electric boilers is 100MW and 50MW respectively. The maximum energy capacity and power of the heat storage device are 120MWh and 50MW respectively. The efficiencies of gas turbines, gas boilers, carbon capture, power-to-gas heating, electric boilers, wind power and photovoltaics are 34%, 82%, 90%, 82%, 32% and 12% respectively.

[0090] First, calculate the operating cost of the comprehensive energy system. The purchase price of methane is 2.65 yuan / m 3 , density is 0.0007174t / m 3 The purchase cost of CO2 is 300 yuan / t, and the operating cost coefficient of the S-CO2 unit is 0.02585 yuan·MW. -2 , 103.57 yuan / MW, and 10,210.56 yuan. The operating cost coefficients of CHP units are 0.2415 yuan / MW respectively. -2 , 101.5 yuan / MW, 2650 yuan, 0.21 yuan·MW -2 , 29.4 yuan / MW, and 0.217 yuan. Step 2 is to calculate the cost of pollutant treatment. Among them, the pollutant treatment cost coefficients of the S-CO2 unit are 0.00238 yuan·MW -2 , 9.55 yuan / MW, 941.07 yuan. The operating cost coefficients of CHP units are 0.02226 yuan / MW respectively. -2 , 9.35 yuan / MW, 244.24 yuan, 0.019 yuan·MW -2 , 2.71 yuan / MW, 0.02 yuan. Step three is to calculate the penalty cost for abandoning wind and solar power. Among them, the penalty coefficient for abandoning wind power and photovoltaic power is 150 yuan / MW.

[0091] The predicted power of wind power and photovoltaic power in this embodiment is as follows: Figure 2 and Figure 3 According to the parameter settings in the above embodiment, the grid-connected power of wind power and photovoltaic power before and after the carbon cycle system is added can be obtained, as shown in Figure 4 and 5According to the calculation in step 4 of the invention content, the wind abandonment rate before and after the addition of the carbon cycle system is 3.1% and 0 respectively, and the solar abandonment rate is 10.8% and 0 respectively.

[0092] When calculating the energy efficiency, the calorific value and unit price of coal were taken as 25330 kJ / kg and 500 yuan / t respectively. The calculation shows that before and after the addition of the carbon cycle system, the energy efficiency of the comprehensive energy system was 34.5% and 35.5% respectively, an increase of 1%.

[0093] When calculating the actual CO2 discharged into the atmosphere and the net CO2 emissions, the energy consumption rate of the carbon capture device is 0.15MWh / t, the ratio between carbon utilization and storage is 0.075g, the rate of hydrogen production by water electrolysis is 0.025t / MWh, the heat released by the methanation reaction per unit of methane is 2.865MWh / t, the supplementary working fluid flow rate required per unit of electrical power of the supercritical CO2 unit is 0.393t / MWh, and the carbon emission coefficient of the supercritical CO2 unit is 0.0001 yuan·MW. -2 , 0.4278 yuan / MW, 42.17 yuan. The carbon emission coefficients of CHP units are 0.001 yuan / MW -2 , 0.4192 yuan / MW, 10.95 yuan, 0.00087 yuan·MW -2 , 0.1214 yuan / MW, 0.0009 yuan. The scheduling results show that at each moment, the actual CO2 discharged into the atmosphere and the net CO2 emissions before and after the addition of the carbon cycle system are shown in the following table:

[0094]

[0095]

[0096] From the results in the above table, it can be calculated that the actual carbon emissions and net carbon emissions of the system before joining the carbon cycle are equal, both of which are 12392t. The carbon emissions and net carbon emissions after joining the carbon cycle are 1309t and -155.6t respectively.

[0097] From the above calculation results, it can be seen that after adding the carbon cycle system, the wind power and photovoltaic power abandonment rates of the integrated energy system were reduced by 3.1% and 10.8% respectively, the system energy utilization efficiency was increased by 1%, and the actual carbon emissions and net carbon emissions reached 1309t and -155.6t, respectively, a decrease of 89.4% and 101.3%.

[0098] In summary, the present invention provides a structure of a carbon cycle system and an application method thereof in an integrated energy system, which promotes the access rate of new energy, energy utilization efficiency and carbon emission reduction.

[0099] The above specific embodiments show and describe the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions only describe the principles of the present invention. The present invention may be subject to various changes and improvements without departing from the spirit and scope of the present invention. These changes and improvements fall within the scope of the present invention to be protected. The scope of protection claimed by the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for optimizing the scheduling of an integrated energy system, characterized in that: The following steps are involved: Step 1: Establish a CO2 generation process model: The source of CO2 generated in the power generation process is designated as natural gas and coal; for the natural gas power generation process, the output of the gas turbine and the gas boiler is represented as shown in formula (1): Where P and H are the electrical power and thermal power output of the unit, respectively, η is the production efficiency of electricity or heat, Q is the consumption rate of natural gas, and h NG is the calorific value of natural gas; the superscripts GT and GB represent gas turbine and gas boiler, respectively, and the subscripts i and j represent the serial numbers of gas turbine and gas boiler, respectively; The i-th gas turbine and the jth gas boiler The carbon dioxide emissions are expressed as shown in formula (2): in, is the density of methane, and are the molecular weights of carbon dioxide and methane, respectively; The CO2 produced by the coal combustion process is represented as shown in equation (3) and equation (4): in, and are the carbon emission coefficients of the kth CHP unit, are the carbon emission coefficients of the first S-CO2 unit; Therefore, the CO2 emissions generated by the entire combustion process can be expressed as shown in formula (5): Step 2: Construct a carbon dioxide capture process model: The power consumption of the carbon capture device is expressed as shown in formula (6): Where α is the energy consumption rate of the carbon capture system; the amount of CO2 discharged into the atmosphere after carbon capture is expressed as shown in formula (7): Among them, η CCS The operating efficiency of the carbon capture device; Step 3: directly utilize or store the captured CO2, which is expressed as and The relationship between them is expressed as shown in formula (8): Where g is the ratio between CO2 utilization and storage; Part of the utilized CO2 is used to generate natural gas CH4 through the power-to-gas device P2G, and the other part enters the supercritical CO2 power plant as a supplementary working fluid, wherein the supercritical CO2 power plant is an S-CO2 device; the process of generating natural gas CH4 through the power-to-gas device P2G includes two stages, namely, the electrolysis process and the methanogenic reaction process, wherein the flow rate of hydrogen generated by the electrolysis of water is The power consumption P of the power-to-gas device P2G t P2G Satisfies the relationship shown in formula (9): Where β is the rate of hydrogen production by water electrolysis; During the methanation reaction, the amount of CO2 consumed by the power-to-gas device P2G and the amount of CH4 produced The quantity satisfies the relationship shown in formula (10): Heat energy is released during the methanogenesis process and is used for heating. Assume that the proportion of the released heat energy used for heating is η P2G2H , then the total thermal power of the power-to-gas device P2G It is expressed as shown in formula (11): Among them, γ is the heat released by the methanogenic reaction to produce a unit of methane; During the operation of the first supercritical CO2 unit, the flow rate of the supplementary working fluid The output power of the first supercritical CO2 unit Satisfies the relationship shown in formula (12): Among them, δ is the supplementary working fluid flow rate required for the unit electrical power of the supercritical CO2 unit; The CO2 sources of the power-to-gas device P2G and the supercritical CO2 power generation device are partly provided by the carbon capture device, and the other part is purchased from the outside, which is expressed as shown in formula (13): In the formula, is the mass flow rate of CO2 purchased from outside, The mass flow rate of CO2 provided to the carbon capture device; Step 4: Calculate the operating cost of the integrated energy system: The operating cost of the integrated energy system is defined as the fuel purchase consumption of coal-fired and gas-fired units. For the i-th gas turbine and the j-th gas boiler, the consumption during operation is represented as shown in formula (14) and formula (15), respectively: in, and Represent the gas consumption of the i-th gas turbine and the j-th gas boiler, is the purchase price of methane; When calculating the cost of purchasing methane, some of the methane produced by P2G is removed. The consumption of the methane produced by P2G is expressed as shown in equation (16): For the first supercritical CO2 unit, the operating cost and the output power of the unit satisfy the relationship shown in formula (17): Among them, a, b and c are operating cost coefficients; The fuel consumption of the cogeneration unit is expressed as shown in formula (18): Other costs during operation also include the cost of purchasing CO2, which is expressed as shown in formula (19): The total operating cost of the integrated energy system is expressed as shown in formula (20): Where T is the entire scheduling time, N T 、N B 、N C 、N S are the number of gas turbines, gas boilers, cogeneration, and supercritical CO2 units, respectively; Step 5: Calculate the cost of pollutant control: The pollutants in the coal and gas combustion process are limited to SO2 and NO produced by the CHP and S-CO2 units of the cogeneration. x , their processing costs are expressed as shown in formula (21) and formula (22): in, and are the pollutant treatment costs of CHP and S-CO2 units for combined heat and power generation, respectively; The total pollutant treatment cost of the integrated energy system is expressed as shown in formula (23): Step 6: Calculate the penalty cost for abandoning wind and solar power: The penalty for abandoning electricity is expressed as shown in formula (24): Where N WT With N PV are the number of wind power and photovoltaic units, respectively, WT With K PV is the penalty coefficient for wind power and photovoltaic power abandonment, and They are the predicted and actual power of wind power, and They are the predicted and actual power of photovoltaics; Step 7: Solution for integrated energy system scheduling: The solution for scheduling is to minimize the total cost of the integrated energy system by configuring the output of each unit and the integrated energy system under the constraints. The total cost of the integrated energy system is expressed as the sum of the operating cost, the pollutant control cost and the penalty cost for wind and solar power abandonment, as shown in formula (25): C=C D +C P +C R (25); The supply and demand balance between the power output and the load during the operation of the integrated energy system is expressed as shown in equations (26) and (27): Where P is the electrical power generated or consumed by each system, and H is the thermal power generated or consumed by each system; P t D and are the electricity and heat load demands, respectively; TES and EB represent the heat storage system and electric boiler, respectively; According to the dispatch results, the wind curtailment rate υ, which represents the access rate of new energy, is obtained WT and the light abandonment rate PV , as shown in equations (28) and (29): The energy utilization efficiency of the integrated energy system is defined as the ratio between the energy connected to the power grid and the heat network and the total input energy, as shown in formula (30): Among them, σ and p coal are the calorific value and unit price of coal, and are the energy efficiency of wind power and photovoltaic power respectively; Compare the actual CO2 emitted into the atmosphere with the net CO2 emissions They are expressed as shown in formula (31) and (32) respectively:

2. A carbon cycle system using the method for optimizing the scheduling of an integrated energy system according to claim 1, comprising a CO2 generation subsystem, a carbon capture device, and a power-to-gas device, characterized in that: in, The CO2 generation subsystem includes a gas turbine GT and a gas boiler GB using CH4 as fuel, and a cogeneration CHP and a supercritical CO2 power plant using coal as fuel; the carbon capture device captures the CO2 generated in the CO2 generation subsystem, specifically, separates and captures CO2 from the flue gas generated by the gas turbine GT, the gas boiler GB, the cogeneration CHP and the supercritical CO2 power plant, and the supercritical CO2 power plant uses an S-CO2 unit to generate electricity; part of the captured CO2 enters the supercritical CO2 power plant as a supplementary working fluid, and part enters the power-to-gas device P2G; the carbon cycle system is used in an integrated energy system, which includes a power generation device, a heating device and an energy conversion device, and the power generation device includes a new energy power generation device of wind power or photovoltaic power, a gas turbine, a gas boiler, a cogeneration and a supercritical CO2 power plant; when the output of the new energy power generation device is high, the power-to-gas device P2G in the carbon cycle system uses excess electricity to reduce part of the CO2 into CH4 and send it to the gas turbine GT or the gas boiler GB as fuel.

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