regulate the throat opening. The problem is in the nature of the control instrument operation that over reacts in order to correct a rapid and large deviation in the process condition being monitored causing cycling. A control cycling, a pattern of zigzag path of the monitored process indicator, is known by most process engineers for this kind of control behavior. Control cycling, however, is not acceptable for this service not only due to the stringent emission discharge standard but also because the control over reaction can cause the upstream economizer to buildup pressure beyond its pressure rating and to slow down the engine speed. The task was to develop an automated Venturi scrubber that can handle rapid and large flow changes and to design a control scheme for the exhaust gas system that can maintain the system pressure stable without affecting the operation of the upstream Diesel engine system operation.

    At the onset of this project, Advanced Industrial Technology Corp. (AIT) had already developed two prototype automated Venturi throats (see Fig. 2 for the arrangements), one with a plunger type adjustment mchanism and the other with a damper type arrangement. These automated Venturi throats use a mechanical dynamic control and do not rely on any instrumentation for their operation. Both models have performed well in variable flow conditions in pilot testings. Additional pilot tests were then made to evaluate which of these two models has the faster