Industrial furnaces with thermochemical waste-heat recuperation by coal gasification

Abstract

A thermochemical waste-heat recuperation (TCR) system by coal gasification is considered. Two concepts of TCR were analyzed: gasification with steam and gasification with the steam-flue gas mixture. To determine the effectiveness of using TCR systems by coal gasification, a thermodynamic analysis of the gasification process was carried out in the wide ranges of the operation parameters: a temperature range is 200–1200 °C, the steam-to-carbon (S/C) ratio is 0.25–2.0. The thermodynamic analysis has been realized via Aspen HYSYS software. To evaluate the effectiveness of the thermochemical recuperation systems by coal gasification, the heat recuperation degree (HRD) was used as an efficiency criterion of such systems. The algorithm of the calculation of HRD is proposed. It was found in the temperature range up to 700–800 °C HRD increases monotonically and reaches its maximum value at 720 °C for S/C = 1.0, 810 °C at S/C = 0.5 and 930 °C at S/C = 0.25. There is a heat deficit when S/C above 1.0 in the inlet reaction mixture. Thus, two types of HRD were introduced – gross HRD and net HRD. The gross HRD shows the relation between the total recovered heat and heat of exhaust gases. The net HRD shows the relation between the total recovered heat without the enthalpy of residual steam and heat of exhaust gases. The maximum net HRD of 0.97 can be achieved at S/C = 1.0 at a temperature of 800 °C. The heat transformation coefficient (HTC) was analyzed. An increase in the S/C ratio leads to an increase in HTC. With an increase in the S/C ratio above the stoichiometric ratio, HTC increases slightly. When the S/C ratio increases, the specific low heating value of synthesis gas (per 1 kg of syngas) decreases.