Maintaining Low Oxygen (O2) in Coal Fueled Utility Boilers Using CO Instrumentation

Abstract

Following evaluation of various CO monitors and close attention to the boiler operating conditions, Southwestern Public Service Company has been successful in reducing the operating level of oxygen in Unit #1 at Tolk Station. This paper will present the experience to this point indicating the value of the increased efficiency and the annual fuel savings possible from this O2 reduction. Unit til 1.8 a pulverized coal fired, 565 MW, CE boiler system placed in service July 27, 1982. Complete and safe combustion in this boiler is maintained by continuously monitoring O2 and CO in the boiler exhaust. The addition of CO monitors has enabled SPS to begin the process of establishing exhaust O2 levels at each firing rate. The CO signal is recorded and monitored, but it has not been used as an active element in closed loop control. The target CO level of 100-200 ppm produces an average O2 level of between 2.0% and 2.5%. Transient peaks of 1000 to 1200 ppm of CO are not unusual because CO production is affected by many process variables. SPS's selection of a multi-parameter CO/CO2/H2O instrument provide the ability to measure CO2 and CO and to validate accuracy of these components on-line by introduction of standard gases at stack temperature and pressure. Crosschecking the O2 monitor and the calculated O2 reading from the CO monitor, also, provides on-fine confirmation of each instrument. Experience also validates the relationship between CO, excess air and NOx production.