Comparison of the performance of a single and two-stage variable-throat venturi scrubber

Abstract

The efficient removal of fine particulate matter from a gas stream by a venturi scrubber is achieved usually at the expense of a high gas-phase pressure drop with a coincident high fan running cost. It is desirable, therefore, to investigate ways of reducing venturi pressure loss for a given overall collection efficiency. This paper is principally a theoretical investigation of the effects of two-stage venturi operation. The theoretical predictions are borne out qualitatively by experimental work. The paper shows that above a certain pressure drop, which is dependent upon particle size, collection efficiencies can be increased significantly (and hence the pressure loss reduced) by using a two-stage design. The value of the main parameters in the collection efficiency—pressure drop relationship for single-stage operation determines to what extent two-stage scrubbing is an advantage. The improvement in performance becomes greater as both the particle size and system pressure drop increase. The lower efficiencies obtained with single-stage venturi operation are shown to be the result of a “diminishing returns” inherent in the scrubbing process at higher Stokes' Numbers.