Assessment Method And Study Of Life-cycle Assessment Of Fossil Fuel Driven Chemical Looping Combustion Energy System

Chemical looping combustion(CLC)has been identified as the most promising"second generation" carbon capture technology,which has been evolved from the"proof of concept" to 3 MWth demonstration plant.Researches on CLC reactors,oxygen carriers and system integration have become an importantly international hotpoint.China is a maj or carbon emitter and a major member of the Paris Agreement.It will serve as the main role for carbon mitigation within the following years.At the national level,it is of great significance to explore efficient new carbon capture technologies.This thesis has focused on the fossil fuel driven CLC system integration mechanism and study of system assessment method within four main subparts,including CLC reaction mechanism,CLC thermo-economic assessment method,CLC life-cycle carbon emissions assessment and coal-driven CLC for combined cooling,heating and power distributed energy system.At present,the mechanism of CLC reaction mechanism studies emphasizes on exploring the chemical energy cascade utilization within CLC,and on the other hand analyzing the adsorption mechanism of molecular structure from the perspective of micro-oxygen carrier materials.With the combination of CLC and solar thermal chemistry,especially the development of mid-temperature solar thermochemical fuels,the study of mid-temperature heat-driven CLC has received abundant attentions from international scholars.In this study,the adsorption energy,bond energy and bond length of CHx molecules on the surface of NiO crystals are studied from the microscopic reaction pathway,and the most stable adsorption sites of CHx molecules on the surface of NiO crystals are sought.On this basis,the dehydrogenation mechanism and the transition state energy barrier of CHx molecules on the surface of NiO crystal are further analyzed.The results show that the transition energy barrier required for CH3=CH2+H elemental reaction is the highest(2.06 eV).By changing the reaction pathway of this reaction,reducing the energy barrier is an important method to achieve the combustion of the mid-temperature CLC.Although fossil fuel driven CLC technology has been developed for nearly 30 years,the system integration principles for CLC power system and its related assessment methods still need to be solved.In light of fuel chemical energy and physical energy cascade utilization principle,this paper analyzes the changing law of irreversible loss of CLC process based on the physical properties of oxygen carrier,the thermal energy level of CLC reactions and the fossil fuel energy level.On this basis,the relationship between irreversible loss of CLC power system and cost of electricity is further derived and given.Taking the current natural gas-based and coal-based CLC power system as an example,the assessment method of CLC power system is studied,and the technical roadmap for the sustainable development of CLC power system is given.Using the above relationship,the effects of fuel grade(Ar),reduction reaction endothermic coefficient(?re),and thermodynamic cycle initial temperature(ATTT)on economic performance are analyzed.The results indicate that the role between the fuel energy level,the energy level change within CLC reactions,and the change in the thermal cycle energy level is an important factor in determining the economics of CLC power system.In order to explore the low carbon,clean-utilization and high-efficiency fossil fuel driven CLC technology,the life cycle assessment of CLC power system is studied,i.e.assessment of carbon emission throughout its life cycle.The results show that for the natural gas driven CLC power system,the oxygen carrier lifetime and oxygen carrier loading in the CLC process are the main factors affecting the life-cycle carbon emissions,and the influence of power efficiency is weak.When the oxygen carrier lifetime reaches 4000 hours,increasing the thermal performance of the system can further reduce the life-cycle carbon emissions,but the effect is small.When the oxygen carrier lifetime is between 1000 hours and 4000 hours,the oxygen carrier lifetime is a major factor in determining carbon emissions throughout its lifetime.Based on the above theoretical analysis,the coal-based CLC process was explored by simultaneously producing cooling,heating and power.The effects of parameters such as steam-carbon ratio,oxygen-carbon ratio and CLC reaction pressure on energy efficiency,cold-power ratio(C/P),heat-power ratio(H/P)and energy saving ratio are analyzed.The coal syngas yield with the optimum energy saving ratio is given,and the steam-carbon ratio and oxygen-carbon ratio corresponding to the optimal yield are given.