Life cycle assessment of transformation from a sub-critical power plant into a polygeneration plant

Abstract

Coal-fired power plants retirement is a worldwide problem due to the universal desire to control temperature increase less than 2 °C. Chinese government has also made clear plans to develop renewable electricity gradually in place of coal-fired electricity. The first to be affected are the small power units, which suffer from decreased operation hours and environmental protection problems simultaneously. The two possible fates of these small power plants are to be decommissioned or to be retrofitted into more advanced energy systems. Recently, we transformed a sub-critical power plant into a polygeneration plant using the dual fluidized bed pyrolysis technology and proposed two transformation methods, including the partial and complete transformation. A life cycle assessment (LCA) of the three scenarios, including two transformation scenarios and the original power plant scenario, is also performed to assess the transformation effect. The life cycle results are also compared with that of the ultra-supercritical (USC) unit and the integrated coal gasification combined cycle (IGCC) unit. As a result, 3600 MJ of energy output is adopted as the function unit. The LCA analysis indicates that the complete transformation for polygeneration is the best of all the five scenarios in view of almost all impact categories (CML 2001) and energy utilization performance. Compared with the original sub-critical power plant, the complete transformation can reduce greenhouse gas emissions by 36.5 percent. Besides, the complete transformation can also reduce acidification potential by up to 50.1 percent relative to IGCC. Moreover, the net energy efficiency of the complete transformation scenario is 3.65 percent higher than that of USC technology. Therefore, the current study may demonstrate the feasibility of transformation from the existing power plants to the polygeneration plants to achieve the goal of cleaner production, which may also provide a new idea for the upgrading of small power plants.