Process system simulation of coupled pyrolysis disposal of domestic waste in coal-fired boiler and pilot study on dioxin emission

Abstract

The disposal of domestic waste has become a critical and costly problem. Incineration for power generation is currently the primary domestic waste treatment method. Due to its small capacity and low parameters, domestic waste incineration is generally uneconomical and associated with significant risks to public health and environmental safety. The coal-fired power plants are generally characterized with huge capacity and high parameters, consequently resulting in much higher power generation efficiency with lower cost emission control. This indicates that co-disposal of domestic waste using existing coal-fired units may significantly reduce its treatment costs associated with the improvement of utilization efficiency and environmental risks. Base on this, a highly-flexible coupling of pyrolysis-pretreated solid waste in pulverized coal furnace is proposed in this paper, and field tests and numerical simulations have been carried out separately according to the process route. The results show that after coupling with pulverized coal boiler, domestic waste pyrolysis pretreatment unit can operate self-sustainably without external energy supply and the process route is feasible. Furthermore, the coupled co-combustion of domestic waste pyrolysis products and pulverized coal was simulated by fluent software. Compared with pure pulverized coal combustion, mixing domestic waste pyrolysis products can promote pulverized coal combustion in the furnace and help the pulverized coal boiler to burn stably at low load. The emission concentrations of NOx at the outlet of the furnace are 530 ppm, 545 ppm and 478 ppm respectively when pulverized coal is burned purely and mixed with 100 t/d and 200 t/d domestic waste. the NOx emissions could be reduced to a certain extent by mixing domestic waste. On the basis of previous research, the field test of coupling disposal of domestic waste by pulverized coal boiler was carried out, and the dioxin concentration in flue gas and fly ash was tested emphatically. The results show that when the amount of waste is less than 4 %, the concentration of dioxin in flue gas is 0.0107 ng TEQ/m3, which meets the latest emission standard of air pollutants in Shanghai coal-fired sludge power plant of 0.02 ng TEQ/m3. Low proportion of domestic waste will not increase the production and emission of dioxins. These studies show that it is feasible and promising to treat municipal solid waste with low coupling ratio by using existing coal-fired units.