AIR EMISSION FROM SLUDGE FLUID BED INCINERATION SYSTEM

Fluid bed incineration has been gaining more attention over the last few years as municipalities and industries focus on reducing sludge volumes and producing class A type sludge. A concern surrounding incineration has to do with emissions from the combustion process. In general, these concerns can be divided into 3 areas: heavy metal emissions, particulate emissions, and gaseous emissions (nitrogen oxides, hydrocarbons, carbon monoxide). In this paper air emissions recorded at several Infilco Degremont sludge incineration plants are presented. The ultimate goal of this paper is to create a database of recorded emissions for all air pollutants from a sludge bed incineration plant. The database will be a useful tool for engineers and regulators when establishing air requirements and designing air pollution control systems. Heavy Metal Emission Analysis of the data shows that out of ten metals, mercury and selenium had the lowest removal efficiencies. Mercury and selenium also had lower boiling point temperatures compared to other metals (arsenic, cadmium, chromium, copper, nickel, lead, zinc, and beryllium). On average, removal efficiencies for arsenic, cadmium, chromium, copper, nickel, lead, zinc, and beryllium were in excess of 98%. Furthermore, a linear relationship was observed between metal emission and total particulate removal for cadmium, zinc, copper and lead. However, a similar relationship could not be established between the two parameters for arsenic, chromium, nickel, selenium, beryllium and mercury. When metal removal efficiency was compared to concentration of the metal in the inlet sludge, results indicated that the removal efficiency decreased significantly with decreasing inlet concentrations for selenium and mercury. Removal efficiencies were also slightly lower for cadmium, chromium, copper, nickel, lead, and zinc at lower inlet concentrations. Particulate Emission When total particulate emission levels of thirteen plants were compared to US EPA requirement (1.3 lb/dry ton), all thirteen plants had emission levels within the requirement. Total particulate emissions varied between 0.01 and 1 lb per dry ton with an average of 0.25 lb per dry ton. Overall, particulate emissions were substantially lower at plants having Wet electrostatic precipitator or hydrosonic venturi scrubber. For instance, Bayshore fluid bed incineration plant had a total particulate emission level of 0.013 lb/dry ton, which was significantly lower than the emission level reported by N W Bergen Plant No. 1 (0.35 lb/dry ton). The large difference between the emission levels of two plants was due to the Wet electrostatic precipitator installed after venturi scrubber at Bayshore plant Gaseous Emissions When carbon monoxide (CO) emission levels of twelve plants were compared to US EPA requirement (100 ppmv), all twelve plants had significantly lower emission levels ranging from a minimum of 0.4 ppmv to a maximum of 22.5 ppmv corrected to 7% O2. The average emission was 7.5 ppmv, which was well within the US EPA requirement of 100 ppmv. When total hydrocarbon as CH4 emission levels of eight fluid bed plants were compared to US EPA requirement (100 ppmv), all eight plants had significantly lower emissions. The average hydrocarbon emission was 1.8 ppmv, which was significantly lower than 100 ppmv required by US EPA. The lowest and highest hydrocarbon emissions were 0.5 and 5.45 ppmv respectively. The average nitrogen dioxide (NO2) emission levels of nine plants was 33.1 ppmv, ranging from a minimum of 0.97 ppmv to a maximum of 69.36 ppmv corrected to 7% O2. Although, regulatory emission requirements for nitrogen oxide vary by location in the US, the incineration plants, which provided the data for this study, comply with the emission requirements within their localities.