| To achieve the dual-carbon goal of "2030 carbon peak and 2060 carbon neutralization",combined with China’s coal-based energy structure,to avoid the problems of high carbon emissions and high pollution caused by the direct combustion of traditional fossil fuels,it is urgent to gradually increase the proportion of renewable energy represented by solar energy in energy utilization.This paper focuses on the synergistic conversion mechanism and system integration of concentrated solar energy and coal.Thermochemical complementary utilization method of concentrated solar energy and coal is proposed,and the conversion mechanism of fuel chemical energy and the upgrading mechanism of energy level of heat collected by solar energy in the process of thermochemical complementarity are revealed.Thermochemical complementary power generation system,hydrogen production system and hydrogen-electricity cogeneration system based on supercritical water coal gasification are proposed.On this basis,a multi-energy complementary hydrogen production system with near-zero emissions of CO2 is further constructed,and the key process is verified by experiment,achieving the purpose of "improving quality and efficiency" of solar energy and "saving energy at source" of coal.This paper provides a clean,efficient and low-carbon new idea for the multi-energy thermochemical conversion of concentrated solar energy and coal.The main research contents are as follows:To reveal the thermochemical complementary conversion mechanism of concentrated solar energy and coal,a physical model of multi-energy synergistic conversion process is established based on the concepts of energy balance,material balance,exergy balance and energy level.It mainly includes concentrated solar energy conversion process,supercritical water coal gasification process and power output process.A conversion method based on thermochemical complementarity between concentrated solar energy and coal is proposed,and the energy level expression of the thermochemical complementary process is derived.The mechanism of energy level increase of concentrated solar energy driven by energy level decrease of fuel chemical energy in multi-energy thermochemical complementarity is expounded.The one-step method of direct combustion of traditional fossil fuels is transformed into a two-step method in which the fuel chemical energy is first utilized through chemical reactions and then the reaction products are used according to the actual demand.The cascade utilization of fuel chemical energy in the conversion process is realized.Based on the mechanism of multi-energy thermochemical complementary utilization,a new method of supercritical water coal gasification with external heating is proposed,which reduces a large amount of loss of effective components of gasification products in the gasification process with internal heating.Firstly,a power generation system based on chemical recuperative supercritical water coal gasification is proposed,which reasonably couples the gasification island with the power island,and the high-temperature flue gas of the gas turbine provides reaction heat for the supercritical water coal gasification process.The thermodynamic performance of the system and the reasons for the reduction of exergy destruction in the key processes are analyzed,and the mechanism of efficient utilization of fuel chemical energy and thermal energy is revealed.The results show that the net power generation efficiency and exergy efficiency have reached 53.80%and 52.53%,which are 4.89 and 4.78 percentage points higher than that of the conventional coal gasification power generation system,respectively.Secondly,a thermochemical complementary power generation system of concentrated solar energy and coal is proposed,and the coal chemical energy and concentrated solar energy are synergistically converted into high energy level syngas chemical energy through thermochemical complementarity.The comprehensive thermodynamic performance of the complementary system is obtained,the key role of thermochemical complementarity is revealed,and the feasibility of multi-energy thermochemical complementarity is verified.The results show that the syngas chemical energy of the complementary system has increased by 29.70%,and its net power generation efficiency and exergy efficiency have reached 53.06%and 52.24%,which are 6.94 and 6.83 percentage points higher than that of the reference system with separate power generation,respectively.The purpose is to lay the foundation and explore the direction for the further integration of the thermochemical complementary system of concentrated solar energy and supercritical water coal gasification.On the basis of the thermochemical complementary power generation system of concentrated solar energy and coal,it is found that the syngas produced by supercritical water coal gasification process contains a large amount of steam and methane(the ratio is more than 3),which has the potential to further utilize the methane chemical energy.The classification utilization method of fuel chemical energy for supercritical water coal gasification series gasification products reforming is proposed for the first time.Based on this,a thermochemical complementary hydrogen production system of solar coal gasification and reforming is proposed.Concentrated solar energy provides reaction heat for supercritical water gasification process,and high-temperature flue gas produced by combustion process of purge gas from hydrogen production process provides reaction heat for steam methane reforming process.The high purity hydrogen is separated by the pressure swing adsorption after water gas change reaction,realizing the purpose of hydrogen production through the thermochemical complementarity of concentrated solar energy and coal.The results show that the energy efficiency and exergy efficiency of the hydrogen production system reach 50.15%and 50.81%,which are 10.42%and 10.78%higher than that of the reference system with separate hydrogen production,respectively.Increasing the proportion of concentrated solar energy in multi-energy complementarity is essential to reduce fossil fuel consumption and pollutant emissions.Then,a thermochemical complementary hydrogen-electricity cogeneration system of solar coal gasification and reforming is constructed.The reaction heat of supercritical water coal gasification process and steam methane reforming process is provided by concentrated solar energy,which increases the proportion of concentrated solar energy in energy input from 31.27%to 36.15%.More low energy level concentrated solar energy is converted into high energy level hydrogen-rich syngas chemical energy through gasification and reforming two-step reactions,and then high-purity hydrogen is separated by pressure swing adsorption,and the remaining purge gas is compressed and introduced into gas turbine combustion and power generation.The results show that the hydrogen-rich syngas chemical energy produced by the hydrogen-electricity cogeneration system has increased by 49.14%,and its energy efficiency and exergy efficiency have reached 49.37%and 49.84%,which is 11.04%and 11.08%higher than that of the reference system with separate hydrogen production and power generation,respectively.In view of the problem that substantial carbon emission reduction has not been achieved in the process of multi-energy thermochemical complementary hydrogen production,a multi-energy complementary hydrogen production system with near-zero emissions of CO2 is constructed,which focuses on solving the problem of carbon dioxide emissions on the basis of clean and efficient synergistic conversion of concentrated solar energy and coal.Photovoltaic power generation is introduced to drive the solid oxide electrolytic cell to electrolyze water to produce hydrogen,and at the same time,the oxygen produced in the electrolysis process is collected and introduced into the combustion chamber to be mixed with purge gas from hydrogen production process for pure oxygen combustion.The flue gas products produced by pure oxygen combustion process of purge gas are only carbon dioxide and water,which can realize the natural separation and low energy consumption capture of carbon dioxide through condensation,and achieve near zero emission in the process of coal conversion and utilization.The results show that the hydrogen chemical energy produced by the near-zero emission system has increased by 20.87%,and its energy efficiency and exergy efficiency 6.33 and 6.64 percentage points higher than the reference system with separate production,respectively.The experimental platform of 1 kW high-temperature solid oxide electrolysis water for hydrogen production and oxygen production is set up to verify the feasibility of the technical scheme of oxygen collection while electrolyzing water to produce hydrogen,The near-zero emission system provides a clean,efficient and low-carbon coupling new solution for the complementary utilization of photovoltaics,photothermal and coal. |
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