Desulfurization using limestone during sludge incineration in a fluidized bed furnace: Increased risk of particulate matter and heavy metal emissions

Abstract

Incineration of sludge can be an effective method to minimise waste whilst producing useful heat. However, incineration can cause secondary pollution issues due to the emission of SO2, therefore a set of experiments of sludge incineration in a bubble bed furnace were conducted with limestone addition to study desulfurization of sludge incineration flue gas. As expected, over 93% emission of SO2 was reduced with limestone addition, and that of CO and NOx were increased and decreased respectively when the fuel feeding rate raised. The distribution of fly ash was also increased by raising the fuel feeding rate due to increasing fragmentation of the ash. However, distributions of PM2.5 and heavy metals in submicron particles have dramatically increased with limestone desulfurization. The mechanism was revealed by SEM and EDS statistical analysis, indicating that the reaction between aluminosilicate and calcium made particles agglomerate and eutectic mixtures form, these larger ash particles were found to divide between collection as cyclone ash and fragmentation into finer particles that bypassed the cyclone. Those fine particles provided more surface area for heavy metal condensation. Furthermore, it was found that the reaction mechanism for semi-volatile metals involved them being released from the sludge and forming PM1 particles due to the vaporization-condensation mechanism, leading to higher emission of PM1 and distribution of heavy metals in PM1. Thus, it should be considered that there may actually be higher emission risks of PM and heavy metal emissions when aiming to desulfurize a flue gas using Ca-based minerals in certain circumstances.

Review of inventory data for the thermal treatment of sewage sludge

“…in various combinations). Several papers consider the behaviour of heavy metals during incineration and flue gas cleaning (Fang et al, 2020;Kasina et al, 2019;Li et al, 2019;Zha et al, 2020;Zha et al, 2018), but only three papers (Cheng et al, 2020;Van de Velden et al, 2008; provide data on the distribution of heavy metals in sewage sludge into both bottom and fly ash. Metals such as Pb, Zn, Cd and Hg are volatile in a chloride-containing high-temperature environment, e.g.…”

Co-Gasification Synergistic Characteristics of Sewage Sludge and High-Sodium Coal

“…Technologies for energy utilization of sewage sludge include combustion, pyrolysis, and gasification. Sewage sludge combustion significantly reduces the sludge volume but produces hazardous gases such as SO 2 and NOx. , Sewage sludge pyrolysis, carried out in an oxygen-free or anoxic high-temperature environment, produces less harmful gases but does not maximize the reduction of sludge volume. , Sewage sludge gasification converts the organic components in sludge into combustible gas, which has the advantages of less harmful gas emission and significant volume reduction effect. − Therefore, sewage sludge gasification is an effective way for the efficient resource utilization of sludge.…”

Dynamic Transformations of Metals in the Burning Solid Matter during Combustion of Heavy Metal-Contaminated Biomass

“…Temperature is a dominant factor for combustion kinetics and also has a significant effect on transformations of metals. , A reducing atmosphere can enhance the conversions of metals to their elemental forms, which often have a high volatility, whereas in an oxidizing atmosphere, metals tend to form their oxide forms with much higher melting points, but sometimes the vaporizations of metals also can be stimulated in an oxygen-rich atmosphere due to a more violent combustion . The presence of chlorine increases the release of metals through the formation of metal chlorides with low melting points, − while silicates can fix metals to generate stable species in the ash. − …”