INNOVATIVE OXY-COAL COMBUSTION PROCESS SUITABLE FOR FUTURE AND MORE EFFICIENT ZERO EMISSION POWER PLANTS

摘要

The problem with CO_2 capture from a flue gas stream is related to its low concentration, which makes the process of separation very energy-intensive, complex and, as a result, expensive. The CO_2 separation process can be optimized by increasing the concentration of CO_2 and reducing nitrogen concentration in the stream as it happens in the oxy-fuel combustion process. In such a case, the oxidant flow is typically a mixture of oxygen, steam and carbon dioxide, with a very low concentration of nitrogen. Since the oxy-combustion process lead to very high temperatures, flue gases must be circulated through the chemical reactor to keep the combustion adiabatic temperature below acceptable values, due to the limits imposed by material resistance. This paper focuses on an innovative oxy-coal combustion process, based on a flameless combustion technique, which is mentioned in recent literature also as "Mild" combustion. The combustion process take place within a pressurized and refractory-lined furnace, approaching temperatures close to 2000 K. The chemical reactor is fed with a gaseous oxidant mixture and a coal slurry spray. The process has been experienced at pressurized conditions up to 4 bar on a 5 MW pilot plant for thousands of hours. In this paper, starting from a detailed description of the process, results obtained by the preliminary experimental tests are presented and discussed. Then, a development and demonstration program to assess the suitability of this technology for zero emission power generation at large scale is presented .