Semi-automatic sequencing

In the event of an alarm, an automatic sequence of actions should make the plant safe without the intervention of an operator. The sequence is likely to be simplest for continuous or semi-batch processes typically it may involve no more than stopping the reactant feeds, provided there are no problems with accumulation of reactants. Batch reactors are more difficult, particularly if they contain large amounts of unreacted material and are more likely to require the provision of protective measures such as emergency relief venting, or the provision of dump tanks with drown out facilities. 

The start-up procedure is divided into 12 sequences and is semi-automatic. A list of checks is associated with each sequence a certain number of parameters must be within the correct ranges of values and specific machinery in the right stams, to allow the system to switch to the next sequence. From sequence No. 0 to sequence No. 5 the procedure is manual as the Job Leader, after having all the relevant parameters communicated from the Field Supervisor, presses the start-up button to switch the system to the next sequence. The DCS (Decentralized Control System) does not allow the operation if all parameters are not in the correct range. After sequence No. 5 the procedure becomes completely automatic and it is driven by the DCS. Critical sequences are sequence No. 7, where all the four combustion chambers are ignited, and sequence No. 12, where the mrbine is considered on service. 

Blow molding is a process for converting thermoplastics into hollow objects. Like injection molding, the process is discontinuous or batchwise in nature, involving a sequence of operations that culminates in the production of a molding. This sequence or cycle is repeated automatically or semi-automatically to produce a stream of molded parts. 

The press cycle, or the time taken to perform a series of operations until they are again repeated, varies according to the material being moulded and the requirements, such as the need to load loose cores and metal inserts into the tool. A brief description of the necessary operations on a semi-automatic press (Fig. 9) will now be given to acquaint the reader with the normal sequence of operations for a typical moulding on a compression press. 

These are normally chosen for finer particle substrates which require a greater differential pressure (greater than the 14.7psi maximum differential achieved under full vacuum) in order to achieve a practical rate of filtration, or to minimise cake moisture content and again there are many different designs of filter [26, 27], Several employ a batch process such as the common Plate and Frame Filterpress, but can be semi-continuous as in the Automatic Pressure Filter whereby a continuous filter cloth enables feed, discharge and belt washing to be operated in sequence or fuUy continuous pressure belt filters. 

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