The polyester plant has five coal-fired boilers(58600MJ).In order to cut down NOx in the exhaust fumes up to the standard , installing a denitration device before the fuel gas emission was proposed and the se-lective non-catalytic reduction (SNCR) method was applied to the denitration process , in which, S7-300 PLC answers for the control and taking WinCC as SCADA software .The attentions were directed at the analog input and conversion , configuration and program code of PID control loop and the ammonia flow accumulation process.%聚酯生产装置共有5台58600MJ的燃煤锅炉，为了使锅炉烟气中的NOx 达标排放，在烟气排放前增加了脱硝装置，脱硝工艺采用选择性非催化还原法，以S7-300 PLC作为其控制核心，采用WinCC设计操作站的监控和数据采集系统，重点给出了模拟量的输入与转换、PID控制回路和氨水流量累积过程的组态和程序代码。
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