Performance evaluation of two flue gas denitration systems in China using an emergy-based combined approach

Abstract Flue gas denitration systems play an important role in reducing nitrogen oxide emissions. However, their potential resource efficiency, environmental impacts and economic performance should be emphasized. It is necessary to assess their effects from pros and cons so as to reflect their relatively sustainable levels more completely. Since emergy analysis (EmA) considers quality differences among diverse categories of energy, materials and money, as well as the environmental contribution to economic activities, this work put forward an emergy-based combined approach and related indicators, which consider pollution emissions' impacts, for evaluating flue gas denitration systems comprehensively. Next, two flue gas denitration systems in China (the selective catalytic reduction denitration system (SCRDS) and the selective non-catalytic reduction denitration system (SNCRDS)), as study cases, were investigated using the proposed approach and indicators. It is found that (1) purchased nonrenewable input (NP) contributes most to their total emergy input (TE); (2) the emergy loss is main emissions’ impact; (3) the SNCRDS has higher environmental cost but lower economic cost than the SCRDS due to its smaller share of purchased input and lower treatment efficiency; (4) the SCRDS has much higher environmental loading than the SNCRDS due to its higher share of nonrenewable input; (5) the SNCRDS has higher sustainability level than the SCRDS due to its lower dependence on nonrenewable input. Generally the denitration technologies convert lots of purchased nonrenewable resources into the local environmental benefits in an unsustainable way, which could cause the depletion of nonrenewable resources and environmental emissions in other areas in the future. Finally, some suggestions are proposed, including replacing the reducing agent for the SNCRDS, promoting the regeneration of spent denitration catalysts, strengthening energy management, and emphasizing operation training of technical staff.