Equipment design surge controls

Some consideration of surge characteristics should be made, and unless your own plant design includes antisurge controls, it should definitely be mentioned in the specification. Possibly, the vendor can quote antisurge equipment with his offering. At a later date, the specification will serve as a good reminder to both the vendor and purchaser if some mention of compressor control is made. The details may be worked out at any convenient point, such as at the bid review or possibly later in a coordination meeting. 

An extrusion trial was performed at the processor s plant using a 38.1 mm diameter production extruder, a proprietary screw design, and resin that had previously exhibited flow surging and reduced rate. The extruder was equipped with three barrel zone heaters with control thermocouples (labeled Tl, T2, and T3) and two pressure sensors. One pressure sensor was located in the midsection (zone 2) of the barrel (P2) and the other at the end of the barrel near the tip of the screw (P3). Both transducers were positioned over the top of the screw such that a pressure variation due to screw rotation would be observed. 

Scrubbing is a continuous operation and needs comparatively little plot area compared with a conventional AC system. It also has the advantages common to continuous plants in the way of control and the steady requirement of utilities. It lacks, however, the reserve of capacity inherent in an AC bed which, even when close to breakthrough, can absorb large amounts of solvent if a surge of solvent in air reaches it. This is likely to happen from time to time if a batch drier is upstream of the air cleaning equipment, which must be designed to cope with such a peak. 

Screw feeders are normally subjected to flood feed of a bulk material over the exposed inlet section of the screw. The volume of material moved by the feeder is then dependent upon the speed of rotation of the screw. In a wider sense the term screw feeder applies to screw conveyors that normally operate with their feed rate controlled by prior equipment, but act as feeders by controlling the rate of discharge when material in the supply channel completely covers the screw at the inlet point. These circumstances apply in hoppers subjected to surge loads, batch fills, or products accumulated in the supply hopper if the screw is stationary for a short period. Such applications are here termed coUectmg screw feeders , and screw conveyor feeders , but considerations relative to screw feeders of all types bear strongly upon the design of such equipment and their feed channels. 

The Class 1 electrical equipment, identified in Table 2.5.2-1 of Reference 4.4, has electrical surge withstand capability and can withstand electromagnetic interference, radio frequency interference and electrostatic discharge conditions that would exist before, during and after a Design Basis accident without loss of safety function for the time required to perform the safety function. SSCs required to perform the plant safety functions (reactivity control, core heat removal control, exposure to radioactive material, release of radioactive material) that could be vulnerable to these effects are classified as Class 1. 

As mentioned previously, a large centrifugal compressor with a gas turbine as a driver is typically a multi-million dollar investment. A dedicated computer control system is usually employed to monitor multiple operating parameters, and that is specifically designed for the purpose. Such a control system is shown in Figure 7.27. The control of a centrifugal compressor involves the control of capacity, the prevention of surge and the protection of equipment. 

---