The tanks are about 4 ft. X 10 ft. X 40 ft. and contain approximately 100,000 gallons of chilled, chlorinated water at around 33°F. They can have as many as a few thousand chickens in them at one time, on a continuous basis, for three shifts a day, with one two-hour cleanup period every 24 hours.
The U.S.D.A. requires the plant operators to maintain a 38 ppm total chlorine residual in these tanks to provide adequate sanitation. The plant operators established a maximum residual level of 40 ppm to prevent excessive chlorine "off-gassing," as an employee safety policy. This left only a 2 ppm window of control. To further compound the problem, the U.S.D.A. also required one gallon of fresh, chlorinated water to be added per bird (and a matching volume to drain off to waste), that went through the cooling tanks. This works out to about 200 gpm.
The existing method of chlorine control consisted of two or three employees taking grab-sample tests every hour and comparing results to eliminate human color perception error. The chlorinator then would be manually adjusted up or down based on the readings. On-site testing with an Amperometric Titrator (the most accurate method of chlorine residual testing) showed that the 38 to 40 ppm total chlorine levels provided only 0.5 to 1 ppm free chlorine residuals (the available chlorine in solution for sanitizing). This meant that there was no sanitary action available below 37 ppm total chlorine, so any control system would have to be very accurate and repeatable at high chlorine residual levels, without over- or under-shooting.
Foxcroft Equipment of Glenmoore, Pa., provided a control system consisting of an on-line Amperometric Chlorine Analyzer, PIDA Setpoint Controller, and Chlorine Gas Auto-pacing Valve. The system provided the control the plant operators needed within all the limitations that were against them, and freed the employees doing manual tests to do other necessary work.
Foxcroft Equipment & Service, · Glen Moore, PA
Phone 800-874-0590 · FAX 610-942-2769
