Ammonia oxidation DCS control methods: ammonia-to-air ratio adjustment, furnace temperature and ammonia flow rate adjustment. What are the advantages and disadvantages?
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Through research and investigations, it has been found that adjusting the ammonia-to-air ratio offers significant advantages; almost all DCS control systems for ammonia oxidation are designed to take this ratio into account. However, many manufacturers, due to inaccurate air flow meters, experience serious deviations in the ammonia-to-air ratio, and as a result they are forced to abandon this approach and instead adjust the ammonia flow rate directly in order to maintain the temperature of the oxidation furnace. At our company, our air flow meters also exhibit large errors, leading to significant deviations in the ammonia-to-air ratio. Currently, our management has no plans to replace these flow meters. If we were to continue using the method of adjusting the ammonia flow rate to control the furnace temperature, what problems might arise?
Our company’s system can be controlled either by the air-to-ammonia ratio or by flow rate; however, flow rate control is used at the beginning of operation, while air-to-ammonia ratio control is adopted once stability is achieved. Normally, the control is switched back to ammonia flow control only when the air-to-ammonia ratio fluctuates significantly.
There is a roughly direct conversion relationship between the ammonia-to-air ratio and the furnace temperature. The ammonia flow rate can be controlled using the furnace temperature. However, the safety of this method is not as high as that in SIS systems, where both the ammonia-to-air ratio and furnace temperature are used as interlock shutdown conditions!