Apparatus for dry scrubbing a hot gas and start-up process

Abstract

Hot flue gas, such as the flue gas from a fossil fuel furnace or a waste incinerator, to be scrubbed to remove acidic gas, such as sulfur dioxide and hydrogen chloride gas, and particulates, such as fly ash, is passed to a primary drying chamber and contacted therein with a spray of droplets of an absorbent liquid containing particles of an alkali or alkaline reactant. The droplets are partially dried in the primary drying chamber to a tacky condition before reaching a foraminous collecting member extending through a lower portion of the primary drying chamber wherein it collects as a moist, porous mat. As the flue gas continues to flow through the mat depositing on the collecting member, the mat serves as a filter for removing particulates, including fly ash, in the gas and the remaining sulfur oxides in the gas react with unreacted particles of reactant and reactive ingredients of the fly ash collected in the mat. The flue gas leaving the primary drying chamber is passed to a secondary drying chamber wherein it is again passed through the mat which is translated across the secondary drying chamber from the primary drying chamber. As the gas passes through the mat in the secondary chamber, water is evaporated from the mat to dry the particulate material forming the mat thereby facilitating its subsequent removal. During start-up and initial operation, a gas permeable supplemental filter means is selectively positioned across the secondary drying chamber and subsequently withdrawn therefrom in synchronization with the movement of the mat into the secondary drying chamber.