Author(s)

D. F. Dyer

Abstract

This paper describes a very interesting industrial safety problem and its solutions. Currently, boiler safety controls utilize pressure drop across various boiler elements in an attempt to guarantee adequate combustion air flow, purge air flow, and atomizing media flow. This paper describes various practical situations where these flow measurements are inadequate. Various alternative measures are described to mitigate the problems presented. The paper should serve as a basis for complete re-thinking on these safety controls on both power, industrial, and commercial boilers. Keywords: boiler, safety control, flow measurement. 1 Introduction A typical industrial or steam boiler utilizes approximately 50 different alarms and interlocks to satisfy safety for automatic operation. Some of these interlocks require that flow rate be measured and compared to a minimum requirement. There are two kinds of interlocks that are used in the boiler safety control system: 1. pre-ignition or start-up interlocks and 2. running interlocks. The start-up interlock monitors the pertinent parameter only during start-up and once that parameter is satisfied it allows the boiler to continue in the start-up sequence. Running interlocks are active once the boiler begins firing. These interlocks use a continuously measured signal to shut the boiler down if the pertinent measured parameter does not meet its requirement. A running interlock interrupts boiler operation by causing the closure of two automatic fuel shut off valves. A pre-ignition interlock causes the safety control system to return the boiler to its initial start-up position. Three of these controls are considered in this paper. For each of these controls, the system is described, the problems are

Keywords

boiler, safety control, flow measurement.