The Impact Of Waste Heat Power Generation And Carbon Capture Utilization On The Synergistic Effect Of Environmental Performance And Economic Performance Of Cement Production

The cement industry is both energy intensive and emission intensive.Limestone calcination and fossil fuel combustion in the process of cement production have led to a large amount of carbon dioxide emissions.To achieve the goal of carbon peak by 2030 and carbon neutrality by 2060,the relevant departments of the cement industry have proposed to strengthen the recycling of waste heat and low-grade waste energy from dust-containing waste gas,improve energy efficiency,and develop energy-saving and emission reduction measures such as carbon dioxide separation,recovery and utilization in cement kiln flue gas.However,the upgrading of technology is bound to be accompanied by additional resources and energy consumption.At present,it is not clear whether the implementation of waste heat utilization and carbon capture and utilization measures can promote sustainable development of the industry,which needs to comprehensively assess these measures.Here the comprehensive performance of cement production integrated systems before and after upgrading was investigated by using emergy analysis and improved indicators,combined with carbon emission amounting and economic analysis according to their characteristics.The emergy method is used to calculate the emergy flows at different stages of cement production and related environmental performance through integrating the impact of pollutant emissions into emergy-based indicators.At the same time,the greenhouse gas emission intensity of the system is quantified by carbon emission amounting method,and the economic performance of the system is evaluated by net economic benefit ratio.Finally,the synergistic effect between environmental performance,carbon emissions and economic performance of the system was evaluated by synergistic effect index（SEI）.A cement enterprise in Jilin Province,as a case,was investigated using the proposed approach based on the five scenarios.The main research results are summarized as follows.（1）The results of emergy flow analysis show that,the largest contributor to total input in the five scenarios is limestone,accounting for 56.99%,58.03%,57.47%,58.17%and57.61%of the total emergy input,respectively.This shows that the cement production system is highly dependent on mineral resources.Through comparing the five scenarios,it is found that after the implementation of waste heat power generation and carbon capture and utilization,the total emergy value of the cement production integrated system decreased slightly;therein,Scenario 2 decreases by 1.80%,reaching 6.81E+19sej/yr;Scenario 3 falls by 0.84%,reaching 3.18E+19sej/yr;Scenario 4 declines by 2.03%,arriving at 7.68E+19sej/yr;scenario 5 is reduced by 1.08%,equaling to 4.10E+19sej/yr.Generally,the share of purchased non-renewable resources declines by 3.01%-7.35%after implementation of waste heat power generation and carbon capture and utilization technology.This shows that the implementation of waste heat power generation and carbon capture and utilization technology not only saves resources,but also improves the structure of resource input in the cement production integrated system to varying degrees.（2）Quantitative results of pollutant emissions’impacts show that:the total emergy value of pollutant emissions’impacts from Scenario 1 to Scenario 5 is 1.29E+19 sej/yr,1.21E+19 sej/yr,1.19E+19 sej/yr,1.16E+19 sej/yr and 1.13E+19 sej/yr respectively,mainly from emergy loss（97.89%,97.74%,97.71%,97.65%and 97.60%respectively）;therein,CO₂ contributes the most to the emergy loss.Compared with Scenario 1,the pollutant emissions’impacts of the four simulation scenarios have decreased to different degrees,and the reduction degree of scenario 5 is the largest.In addition,compared with Scenario 1,the dust and CO₂ in Scenario 2 and Scenario 4 have decreased,which is mainly caused by the implementation of waste heat power generation measures;the decrease of SO₂,NO_X and CO₂ in Scenario 3 and Scenario 5 is mainly caused by the implementation of carbon capture and utilization measure.（3）As for the emergy indicators,results of emergy loss percentage（ELP）show that,the ELP of scenario 5 is the lowest,only 0.302%,indicating that the emissions of dust and carbon dioxide decrease after the implementation of waste heat power generation and carbon capture and utilization.The waste recycling benefit ratio（WRBR）of scenario 5 is the largest,indicating that waste heat utilization and carbon capture utilization improve the waste recycling rate of the cement enterprise.From the perspective of improved emergy yield ratio（IEYR）,the values of scenarios 1～5 are 2.3178,2.3758,2.3448,2.3839 and 2.3529,respectively,indicating that scenario 4 has the highest production efficiency.For the improved environmental load rate（IELR）,the values of scenarios 1～5 are 3.3736,3.3230,3.3499,3.3168 and 3.3434,respectively,indicating that the environmental load of Scenario4 is the lowest and that of Scenario 1 is the highest.In terms of the improved emergy sustainability index（IESI）,the values of scenarios 1-5 are 0.6871,0.7150,0.7000,0.7187and 0.7037,respectively,so scenario 4 has the highest level of environmental sustainability.（4）From the carbon emission intensity,it is found that,the total carbon emissions of scenarios 1～5 are 1.242E+06 t CO2-eq,1.195E+06 t CO2-eq,1.146E+06 t CO2-eq,1.189E+06 t CO2-eq,and 1.140E+06 t CO2-eq respectively;among them,the carbon emissions mainly come from carbonate decomposition（57.90%,60.19%,62.79%,60.49%,63.11%for scenarios 1～5,respectively.）.Compared with Scenario 1,the total carbon emissions and the carbon emissions per unit net profit of scenarios 2-4 decrease by 14.47%,18.39%,16.07%,20.00%respectively;therein,Scenario 5 has the lowest carbon emissions per unit net profit in the five scenarios.（5）According to the results of economic analysis:adding waste heat power generation measures in the conventional cement production process can improve the economic benefits of cement enterprises,but the introduction of carbon capture and utilization measure will weaken the economic benefits of cement enterprises.Therein,Scenario 4 has the highest net economic benefit ratio（NEBR,3.22）,showing it has the best economic benefit.（6）According to the synergistic effect,the synergistic effect index（SEI）value of Scenario is 0.640（scenario 1）,and the SEI values of scenarios 2-5 are 1.173,0.958,1.274and 1.035 respectively.Compared with Scenario 1,the index values of Scenario 2-5 change between 49.55%～98.90%.In terms of its comprehensive performance,scenario 4 is the best and should be adopted.To further improve the comprehensive performance of cement production,the following suggestions are put forward,including（1）further promoting the environmental performance of the carbon capture and utilization process,（2）improving the resource structure of cement production,and（3）pushing forward waste heat cascade utilization.