The influence of membrane-cryogenic technology of oxygen separation from air on the efficiency of supercritical coal units with the CCS installation

摘要

In this paper, a 600-MW power plant with the oxy-type coal-fired pulverized bed boiler, integrated with a membrane-cryogenic oxygen separator and carbon capture and storage installation, was analyzed. The proposed air separation plant can reduce the energy requirement for the oxygen production in comparison with the cryogenic technology, what influences the net efficiency of electricity production of the power plant. The hybrid, membrane-cryogenic oxygen separator consists of a membrane module and a double cryogenic distillation column, and enables to obtain oxygen of a purity of 95%. The auxiliary power of such a hybrid oxygen production installation was calculated. Several methods of energy consumption reduction were presented, that is, by using two section vacuum pump, by reducing the cooling temperature between sections of this machine to 20 degrees C, by assuming lower flow resistance in the membrane module and by using membranes with improved separation properties towards oxygen and nitrogen. The auxiliary power rate of each technological installation of the power plant was calculated. The net efficiency of the oxy-type coal unit as a function of the selectivity parameter of the membrane was determined. Different options for improving the net efficiency of the coal unit were analyzed. In this paper, the economic analysis was also performed. The break-even price of electricity for the coal unit with oxygen membrane separator of different selectivity coefficients was calculated. The potential of electricity price reduction as a function of operating conditions in the membrane module of the hybrid separator was also presented.