Incorporating ash removal unit in local rice parboiling industries for flue gas cleaning and heat recovery

Abstract

South Asia is considered the home of parboiled rice as it produces and consumes over 90 percent of the world's parboiled rice. Bangladesh, one of the world's top rice-consuming countries, has a large number of rice parboiling industries. However, the local rice parboiling industries of Bangladesh are burdened with heavy emissions. One of the existing issues in local rice parboiling industries is the severe particulate matter (e.g. fly ash, carbon soot, and other particulates) emission from the exhaust. The alarming level of emitting fly ash or particulates depositing to the nearby aquatic system hampers ecological sustainability; meanwhile, heavy particulates emission also poses a severe health threat to the locality. Despite recent modifications in the rice-parboiling boiler, the amount of stack emission (especially particulate matter) from the local rice parboiling industry is still considerably high to jeopardize public health and environmental sustainability. Currently, there is no provision of flue gas cleaning in the local rice parboiling industries since flue gas cleaning often requires significant investment, complicated installation, and heavy maintenance that local industries may not afford. Therefore, a suitable flue gas cleaning system for local rice parboiling industries was sought under this study. After considering the affability of available flue gas cleaning technologies, a modified flue gas cleaning system, namely Ash removal unit (ARU), was designed for simultaneously and synergistically removing particulate matter (PM), SO2, NOx, CO2, and heat from flue gas of local rice parboiling industries. The designed ash removal unit (ARU) was incorporated in a local rice parboiling industry for evaluating the co-removal efficiency of ARU. Installation of ARU eliminated particulate matter (PM) from flue gas by 91.8%, which ultimately brought down the particulate matter emission level below the prescribed IFC standard. Meanwhile, the installed ash removal unit successfully removed 78.5% SO2, 78.3% NOx, and 23.9% CO2, respectively, from the emitting stack. Other than flue gas cleaning, the installed ash removal unit (ARU) also facilitated heat exchange between flue gas and boiler feed water. Hence, flue gas temperature dropped by 42.1%, while boiler feed water temperature rose by 36% in 30 minutes. Moreover, adopting ash removal unit (ARU) also improved the ambient air quality surrounding the industrial area since it reduced SO2, NOx, SPM, PM2.5, and PM10 levels in ambient air by 81.7%, 78.2%, 21.1%, 22.9%, and 43.1%, respectively