Process control, automatic cascading systems

The two procedures primarily used for continuous nitration are the semicontinuous method developed by Bofors-Nobel Chematur of Sweden and the continuous method of Hercules Powder Co. in the United States. The latter process, which uses a multiple cascade system for nitration and a continuous wringing operation, increases safety, reduces the personnel involved, provides a substantial reduction in pollutants, and increases the uniformity of the product. The cellulose is automatically and continuously fed into the first of a series of pots at a controlled rate. It falls into the slurry of acid and nitrocellulose and is submerged immediately by a turbine-type agitator. The acid is deflvered to the pots from tanks at a rate controlled by appropriate instmmentation based on the desired acid to cellulose ratio. The slurry flows successively by gravity from the first to the last of the nitration vessels through under- and overflow weirs to ensure adequate retention time during nitration. The overflow from the last pot is fully nitrated cellulose. 

When a cascade system is placed in operation, both controllers are initially set in manual during startup. After the process stabilizes, the secondary controller is placed in automatic and the correct action settings are determined. When the secondary controller operation in automatic is satisfactory, the primary controller is then placed on automatic and its optimum control action settings are determined. 

All solids resulting from processing are loaded (under automatic or remotely operated control) into process bins for transport to Area 400 for decontamination to a 5X condition. Gases released from the operations in this area, with the exception of those from the COINS (which are swept to Area 400 for destruction), are swept into the standard cascade air system utilized to control and condition the plant air in baseline system facilities. 

Forward path The cascaded connection of controller, actuator, and plant or process in an automatic control system. 

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