Goal and technology path of CO2 mitigation in China's cement industry: from the perspective of co-benefit

Abstract

The concept of co-benefit, a negotiation topic in CO2 mitigation attracts worldwide attention including China in coping with climate change. Energy saving technologies as common measures for CO2 abatement, generally lead to co-benefits of local air pollution (LAP) because most LAP emissions are generated from combustion of carbonic fuels along with CO2. However, in the technological dimension, there are technologies that induce opposite effects on the co-benefit of CO2 and LAP in specific industry sectors. Precalcinating line and shaft kiln, two types of technologies adopted in clinker calcinating procedure in cement industry are examples: the former consume less energy but emit more dust and NOx than the later. As a result, the overall co-benefits of LAP reductions for cement industry are uncertain. This study consequently aims at assessing the overall co-benefit (although it may be a negative co-benefit) of CO2 mitigation policy on dust, NOx, SO2 emissions in China's cement industry aggregately by establishing bottom-up optimization model on the basis of all types of technologies which are called technology system in cement production. CO2 mitigation goal, as represented by reduction rate is regarded as constraint input into the model. In order to investigate the evolution of co-benefits and technology paths with the change of CO2 mitigation goal, hundreds of reduction rates are selected randomly between the range 0.5–10.5%. The lower bound 0.5% reveals CO2 emission reduction that can be reached for cement industry under existing political constraints and without any extra CO2 mitigation goal. The upper bound 10.5% is the greatest reduction rate under which the model could derive feasible solution. According to changes of technology penetration rates as CO2 goal tightens, we could evaluate the more cost-effective technologies from the perspective of co-benefit. They are vertical milling, precalcinating line with the scale of 7000–10,000 ton/day, roll-squeezer belonging to Main Production Technology (MPT), utilization of cement grinding aids, multi-channel coal burner belonging to Affiliated Energy-saving technology (AES), combination of bag-filter and electrostatic precipitator and ultra-low NOx burning technology belonging to Pollution Control Technology (PCT). With respect to the evolution of co-benefits on air pollutions, when the CO2 reduction rate is below 2.3%, co-benefit of dust and SO2 reduction exist while that of NOx does not; and when the rate is above 2.3%, co-benefits of all the three pollutants exist. A practically referable goal of CO2 mitigation rate of short/mid-term is approximately 5.5% in view of the following three considerations: a) co-benefits augment as CO2 reduction rate increases; b) total cost increases as the CO2 abatement goal becomes stricter; and c) the majority of emerging technologies normally cannot penetrate to 100% in cement production within a relatively short time.