Hydrogen chloride bonding with calcium hydroxide in combustion and two-stage combustion of fuels from waste

The present study deals with the problem of limiting HCl mobility in processes of combustion of two solid recovered fuels (SRF1 and SRF2) having significant but different contents of chlorine. Large-scale experiments were carried out at a temperature of 1050 °C with the use of a stoker-fired flat grate boiler with the heat output of 1 MW, and with a two-stage combustion system for medical waste incineration (MWI) with the same heat output in which first the process of gasification in the temperature of 650 °C occurs, and subsequently the previously obtained syngas is fired in the temperature of 1000 °C in the reburning chamber of the gas generator. In such a way, two different technologies of combustion have been compared, with regard to HCl capture efficiency using widely available calcium hydroxide sorbent Ca(OH) ₂. In order to simulate the increased concentration of chlorine in SRF1, the fuel was being supplemented with three various additions of poly(vinyl chloride) (PVC) recyclate. Before combustion, SRF1 and SR2 were also blended with Ca(OH) ₂ whose weight amount was being changed: from 0 to 3 wt% with a step equal to 0.5 wt% (combustion) and from 0 to 1.5 wt% with a step equal to 0.5 wt% (two-stage combustion). For both of the methods of SRFs combustion, series of experimental findings have been presented, showing trends in the changes of HCl concentration in flue gas, depending on (i) the amount of PVC recyclate added to SRF1 and amount of Ca(OH) ₂ added to both fuels; and (ii) the molar ratio Ca/Cl ₂. Finally, the ratio of HCl concentrations in flue gas after combustion and two-stage combustion, depending on the amount of added PVC and Ca(OH) ₂ to the fuels was analyzed. The achieved results indicate that in a two-stage process (gasification and recombustion), HCl can be much more effectively bonded than during combustion in stoker-fired boiler.