Abstract: Boiler optimization is included in on-line control of parallel boilers by multiplying the total heat per unit time which must be supplied to all parallel boilers by the percentage of the total heat which should be supplied to each boiler by primary and secondary fuels in order to substantially maximize energy efficiency. The result of such multiplication is the heat per unit time which should be supplied to each boiler by the primary and secondary fuels. The fuel and air supplied to each boiler is controlled so as to supply the thus determined heat per unit time which not only results in maintenance of a desired header pressure but also results in substantially maximizing energy efficiency of the parallel boilers even where multiple fuels are combusted to supply heat.

Abstract: Control of the synthesis loop pressure of an ammonia plant is accomplished by automatically changing the purge rate of the recycle gas to maintain optimum synthesis loop pressure. The control logic of this invention allows compressor speed to be set at a constant value and suction pressure to the first stage of the synthesis loop compressor to be maintained by changing the purge rate of the recycle gas. This allows the synthesis loop pressure to seek the highest possible value at the given feed rates of the synthesis gas and compressor speed assuring optimum compressor loading.If the feed rate of synthesis gas is low, additional control is achieved by using the synthesis loop pressure signal or the concentration of inerts signal to vary the compressor speed.

Abstract: Control of the temperature of an ammonia synthesis reactor is accomplished so as to reduce temperature oscillations throughout the reactor. This allows the ammonia synthesis reactor to be operated close to the lowest stable operating temperature which results in optimal reactor performance. The temperature of the effluent flowing from the ammonia synthesis reactor is monitored to detect the presence of thermal waves. The temperature of the effluent flowing from the synthesis reactor is utilized to generate a correction term which is utilized in temperature control for the ammonia synthesis reactor to stabilize the operation of the ammonia synthesis reactor.

Abstract: An override control system is provided in which the integral mode of the controllers not selected is forced to track the integral mode of the selected controller to prevent windup of the controllers not selected. Selection of the active controller is based only on the proportional mode for proportional-integral controllers. Selection of the active controller is based only on the proportional mode and the derivative mode for proportional-integral-derivative controllers.

Abstract: Control of the inerts concentration level in the synthesis loop of an ammonia synthesis process is accomplished by using process measurements to provide a continuous estimation of the inerts concentration level in the synthesis loop. This estimation is utilized to provide feed forward control of the purge rate. A chromatographic analyzer is utilized to measure the actual inerts concentration level in the synthesis loop. The actual measured inerts concentration level is utilized to correct the estimation of the inerts concentration level at the sample times of the chromatographic analyzer to provide feedback control of the purge rate.

Abstract: A process for the synthesis of ammonia is provided in which the ammonia production is optimized by an automatic control; a predetermined relationship between the equilibrium ammonia-concentration and the outlet ammonia-concentration is controlled; stable operation at a temperature near the temperature of maximum conversion is made possible thereby although the process conditions may vary.