Trace Organic Pollutants Emission From Large-Scale Circulating Fluidized Bed Incinerators of Co-Firing Chinese MSW and Coal

Complex components, high moisture and low caloric value of raw Chinese MSW (Municipal Solid Waste) lead to the difficulties of keeping stable burning and low pollutant emission. Differential Density Circulated Fluidized Bed (DDCFB) incinerator was first developed by Zhejiang University to overcome such difficulties. The research of organic pollutants, especially dioxins and polycyclic aromatic hydrocarbons emission and control from MSW incinerators has been carried out in ITPE since 1998. The aim of this paper is to provide the scheme of a new co-firing CFB incineration technology, and useful data for environmental evaluation of trace organic pollutants emission from incinerators. The art of co-firing CFB is presented briefly in the first part of this paper. The dioxin content in original Chinese MSW is estimated to be 10 pg I-TEQ/g based on the data from Abad et al. Several test runs are conducted in a real-scale (150ton/day) incinerator co-firing MSW and coal to investigate dioxins and polycyclic aromatic hydrocarbons emission to ambient air. Test results show that dioxins input into the incinerator is estimated around 300∼600 mg I-TEQ/y, dioxins output is estimated 3∼100 mg I-TEQ/y, and dioxins emitted to ambient air is around 0.1∼15mg I-TEQ/y. It seemed that most of dioxins in original waste are decomposed by incineration process. For seventeen priority PAHs, its emission to ambient air is around 200∼4160g/y for co-firing runs, which is much more than 80g/y for coal combustion only. This suggests that PAHs emission to ambient air needed to be more concerned than dioxins. That is to say, PAHs emission regulatory should be proposed as soon as possible to restrict all incinerators. Several new incinerators (200 tons/day per unit and 300 tons/day per unit) were built by using new Co-firing CFB technology in past few years. From the environmental evaluation report, dioxins emission in stack gas is in range of 0.0025∼0.06 ng I-TEQ/Nm³, which seemed far below the European limit. The annual dioxin emission to air for 200ton/day or 300 t/d units is around 3∼6 mg I-TEQ. It shows that co-firing CFB incinerator is capable of reducing dioxin emission effectively. Based on industrial demonstration experience of new co-firing CFB incineration technology, it has been proven environmental friendly method for thermal treatment of MSW in developing countries. Some reasons for low dioxin emission of co-firing processes are discussed in this paper.