| China is the largest cement manufacturer in the world,accounting for about 57%of global cement production,yet cement production is an energy-intensive and high-emission process.The production process of cement clinker not only generates a large amount of medium and low temperature exhaust gases,but also has the second highest carbon emissions after the power industry.At present,the waste heat power generation technology of domestic cement plants has been widely used.In the context of "double carbon" target requirements,flue gas carbon capture in cement production process is an important initiative to achieve low carbon and clean production in cement industry.Considering the characteristics of low-temperature exhaust waste heat in cement production process which is difficult to be used efficiently and the flue gas carbon capture process which requires low-temperature heat source for heat supply,this paper proposes a carbon capture system for waste heat power generation using flash steam for heat supply(new system 1)and a carbon capture system for waste heat power generation using steam turbine exhaust for heat supply(new system 2)based on the cement kiln flash waste heat power generation system and MEA method carbon capture unit.The new system 1 uses the saturated steam from the primary flash steam as the heat source for the carbon capture unit,and the saturated steam is exothermic to saturated water and then the low-pressure saturated steam from the secondary flash steam enters the turbine as a make-up steam to do work.The new system 2 uses the exhaust steam from the high-pressure section of the multi-stage turbine to supply heat to the carbon capture unit.The exothermic exhaust steam is mixed with the work water shunted from the PH furnace economizer and then enters the flash evaporator together,and the resulting saturated steam enters the low-pressure section of the turbine to do work.Based on the principle of "temperature matching and gradient utilization",the new system can realize the graded utilization of heat through the efficient thermal integration of flash waste heat power generation system and carbon capture unit,and realize the carbon capture while satisfying the waste heat power generation of exhaust gas.In this paper,Aspen Plus software is used to simulate the carbon capture unit and EBSILON software to simulate the flash waste heat power system respectively.From the perspective of energy and exergy,a comprehensive thermodynamic analysis of the new system can be carried out.The results show that the power generation capacity of the original cement kiln flash waste heat power generation system can reach 10.871 MW,while the power generation capacity of the new system coupled with the carbon capture unit is reduced to 7.452 MW and 6.341 MW respectively.The net power generation efficiency is reduced from 23.03%to 18.76%and 15.12%,respectively,and the net power generation exergic efficiency is reduced from 36.8%to 20.2%and 16.3%.The new system has a reduced power generation capacity but also brings the environmental benefits of carbon reduction.With 10%of the flue gas volume and process improvement of the carbon capture unit,the annual carbon capture capacity of the new system can reach 110,000 tons.In addition,the thermal performance of the new systems 1 is better than that of the new system 2 in terms of power generation,net thermal efficiency of power generation,net exergic efficiency of power generation and total system power loss.The above two new systems are proposed to provide a new technical route and method for the modification of waste gas carbon capture in cement plants with flash waste heat generation systems. |
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