Apparatus for removing pollutants from stack effluents

Abstract

Abstract A series of controlled gradient condensers for removing gaseous hydrocarbon pollutants from the stack effluent of an industrial treating plant, such as a veneer dryer. The gaseous effluent stream is conducted from the industrial treating plant to a precooler to bring the effluent temperature to the condensation point of the highest boiling pollutant. Thereafter the effluent stream is passed through a successive series of controlled gradient condenser, each operating in a temperature range lower than that of the immediately preceding condenser. The first several condensers are air cooled and designed to remove the higher boiling pollutants. Each air cooled condenser is wrapped with one or more heater coils, the turns of which are not uniformly wound about the condenser tubes but are more widely spaced toward the outlet or cold end of the condenser. Electric power to each heater coil is controlled by a respective power controller responsive to temperature sensors located inside the condenser for measuring a temperature gradient along the path of flow of the effluent. If any measured temperature gradient exceeds a predetermined maximum allowable limit, the power controller adjusts the electric power through the appropriate heater coil to restore the temperature gradient, and thus the cooling rate, to a value below the maximum limit. As long as the predetermined maximum temperature gradient or cooling rate for each gaseous pollutant is not exceeded the formation of aerosol is avoided and substantially all of the pollutant condenses in collectable liquid form on the walls of the condenser, thereby cleansing the effluent. Each condenser has a reservoir which collects the condensed pollutants by gravity feed, while the uncondensed remaining effluent passes to the next succeeding condenser. The last in the series of condensers is water cooled for condensing those pollutants having the lowest boiling points. The temperature gradient in the water cooled condenser is controlled by temperature sensors, similar to those in the air cooled condensers, which modulate the flow of coolant by controlling the power to the coolant pump. The different temperature ranges at which the respective condensers operate are preferably fixed so that the minimum temperature at the outlet of a respective condenser is greater than the highest melting point of any pollutant condensed within that condenser, so as to prevent solidification of the pollutants and fouling of the condensers. Immersion heaters in the condenser reservoirs further aid in preventing solidification. If solidification of one or more pollutants collected in a particular condenser cannot be avoided, scraper paddles are provided to scrape the solid material off the condenser walls for disposal through a solids removal port. The reservoir of the last in the series of condensers, from which the remaining effluent is vented to the atmosphere, includes a reservoir auxiliary cooling system for the purpose of further reducing effluent temperature if necessary to remove any remaining contaminants.

Inventors

• 👤 E Baum

Bibliographic Details