Control efficiency of submicron particles by an efficient venturi scrubber system

Abstract

An efficient venturi scrubber system combining a particle growth device and a traditional venturi scrubber was designed and tested in the laboratory. Before the venturi scrubber, saturated steam at 100 degrees C was mixed with normal temperature waste stream to achieve supersaturation conditions allowing submicron particles to grow into micron sizes. Hence the control efficiency of submicron particles was greatly enhanced at a reasonably low pressure drop as compared to that found in the literature. At a flow rate of 250 L/min and a liquid to gas ratio of 2.5 L/m(3), the control efficiency of the present venturi scrubber system for NaCl particles greater than 100 nm is greater than 90%, and pressure drop is only about 44 cmH(2)O (4.3 kPa). In comparison, to remove only 50% of 0.6 mu m particles at the same liquid to gas ratio, the pressure drop needed will be greater than 200 cmH(2)O (or 19.6 kPa). Theoretical calculation has also been conducted to simulate particle growth process and the control efficiency of the venturi scrubber considering the effects of mixing ratio (ratio of steam to waste stream by mass flow rate) and particle diameter. Theoretical results using Calvert's theory (1970) were found to agree well with the experimental data for NaCl particles greater than 50 nm, and for SiO2 particles greater than 150 nm.