Research on low emission MSW gasification and melting system

In order to eliminate secondary pollution caused by municipal solid waste(MSW)incineration,a MSW gasification and melting process is proposed.The process is expected to reduce the emission of pollutants,especially heavy-metals and dioxins.In this paper,the combustible components of MSW and simulated MSW were gasified in a lab-scale fluidized bed at 400°C-700°C when the excess air ratio(ER)was between 0.2 and 0.8.The experimental results indicated that the MSW could be gasified effectively in a fluidized bed at approximately 600°C-700°C when excess air ratio was 0.2-0.4.The melting characteristics of two typical fly ash samples from MSW incinerators were investigated.The results indicated that fly ash of pure MSW incineration could be melted at approximately 1,300°C and that of MSW and coal co-combustion could be melted at approximately 1,400°C.When temperature was over 1,100°C,more than 99.9%of the dioxins could be decomposed and most of the heavy-metals could be solidified in the slag.Based on the above experiments,two feasible MSW gasification and mel-ting processes were proposed for low calorific value MSW:(1)sieved MSW gasification and melting system,which was based on an idea of multi-recycle;(2)gasification and melting scheme of MSW adding coal as assistant fuel.

A steam dried municipal solid waste gasification and melting process

Considering high-moisture municipal solid waste(MSW)of China,a steam dried MSW gasification and melting process was proposed,the feasibility was tested,and the mass and energy balance was analyzed.Preliminary experiments were conducted using a fixed-bed drying apparatus,a 200 kg per day fluidized-bed gasifier,and a swirl melting furnace.Moisture percentage was reduced from 50%to 20%roughly when MSW was dried by slightly superheated steam of 150℃-350℃ within 40 min.When the temperature was less than 250℃,no incondensable gas was produced during the drying process.The gasifier ran at 550℃-700℃with an air equivalence ratio(ER)of 0.2-0.4.The temperature of the swirl melting furnace reached about 1240℃ when the gasification ER was 0.3 and the total ER was 1.1.At these conditions,the fly ash concentration in the flue gas was 1.7 g·(Nm^(3))^(-1),which meant over 95%fly ash was trapped in the furnace and discharged as slag.85%of Ni and Cr were bound in the slag,as well as 60%of Cu.The mass and energy balance analysis indicates that the boiler heat efficiency of an industrial MSW incineration plant reaches 86.97%when MSWis dried by steam of 200℃.The boiler heat efficiency is sensitive to three important parameters,including the temperature of preheated MSW,the moisture percentage of dried MSWand the fly ash percentage in the total ash.