| The purpose of this study is to determine how to reduce CO and NO emissions from coal-fired boilers by modifying the existing underlying automatic control systems. However, modification of the automatic control system is a low cost method of reducing emissions. Generally, emission control methods require significant and expensive equipment additions or modifications of existing boiler systems. The results of this study may be applicable to other stoker boiler power plants and may easily provide the means to inexpensively reduce emissions in just a few weeks.; Dynamic experiments were conducted on the No.7 boiler system at the Vanderbilt University Power Plant in Nashville, Tennessee to observe the response of CO and NO emissions to changes in the feed air flow rate. First and second order transfer functions with delay time were used to fit the resulting dynamic data. Since the dynamics of the emission data differed with different gas analyzers, the transfer function of the gas analyzer was included separately in the emission transfer function model to generalize the control scheme to apply to any stoker coal-fired boiler system under two mode automatic control. The emission transfer functions developed here were used to estimate the initial controller gain and reset time parameters. Because the system time constants are high and the delay times are long, the system response is slow. This slow system response coupled with the interaction of the reactions producing CO and NO could result in oscillations of the CO and NO emissions and fluctuation of the furnace pressure. To prevent this undesirable action, it is best to control the CO through the underfire air and NO through the overfire air.; The new control system was applied to the No.7 boiler system at the Vanderbilt Power Plant in conjunction with experiments conducted over a four day period. The results showed a positive and significant reduction of CO and NO emissions resulting from the implemented change in gain and reset time control parameters. The new control system proven to be dynamically stable while it controlled the CO and NO emissions, even when the steam flow rate varied. CO emissions were reduced 39% while NO emissions were reduced 16%, both from their respective normal operating levels. The NO emission finally achieved in this study was 0.292 lb per 106 BTU, which is 36.5% lower than the EPA requirement of 0.46 lb of NO per 106 BTU from the coal used. |
