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SURFACE TENSION MODIFICATION FOR EXHAUST SCRUBBERS

IP.com Disclosure Number: IPCOM000007836D
Original Publication Date: 1996-Aug-01
Included in the Prior Art Database: 2002-Apr-29
Document File: 2 page(s) / 105K

Publishing Venue

Motorola

Related People

Charles D. Howell, P.E.: AUTHOR [+2]

Abstract

The exhaust from the acid exhaust scrubbers at semiconductor plants otlen contains ammonia salts as an emission. These salts are a byproduct of the chemicals used in the manufacture of semiconduc- tors. The salts create a visible emission (plume) Tom the exhaust stack.

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Technical Developments

SURFACE TENSION MODIFICATION FOR EXHAUST SCRUBBERS

by Charles D. Howell, l?E. and Hsi-An Kwong, F?E.

  The exhaust from the acid exhaust scrubbers at semiconductor plants otlen contains ammonia salts as an emission. These salts are a byproduct of the chemicals used in the manufacture of semiconduc- tors. The salts create a visible emission (plume) Tom the exhaust stack.

  Though the salts are soluble in water, and they have been in intimate contact with water in the exhaust scrubber, they still exist as emissions from the scrubber discharge stack. The hypothesis is that this phenomenon occurs because of the way the salts are formed within the scrubber which causes a submicron particle size of the salts. The small, low mass, particles do not contain enough momentum to break the water surface tension barrier.

  The improvement in scrubber efficiency is achieved by the addition of a substance which reduces the surface tension of the recirculating water in the scrubber and allows the submicron ammonia salts to pierce the water drops and dissolve into solution.

  By adding the substance to the scrubber water to reduce the surface tension of the water, an increased amount of the ammonia salts and other submicron particles can break through the surface tension of the scrubber recirculation water droplets and become dissolved in the water, ,thereby reduc- ing the particulate emissions and opacity of the plume from the scrubbers. The ammonia salts will then be in solution and leave the scrubber in the blowdown water and be directed to the industrial waste treat- ment plant.

  This process, which reduces the surface tension of the recirculating liquid in the exhaust scrubber, offers increased efficiency of the pollution abatement equipment and decreased opacity of the emissions.

  Since the water flow rate into (makeup) and out of (blowdown or bleed off) the scrubber is constant, the concentration of the surface active ingredient

(wetting agent) can be controlled with a constant- speed feed pump.

  In one example, the process was put into prac- tice in an acid exhaust scrubber. This scrubber has about 5 CPM blowdown rate, and slightly higher makeup rate. The scrubber has a 500 gallon sump, and a recirculation rate of...