Low-pressure stage

Low-pressure stage casings and interstage circuits on both centrifugal and positive displacement multi-stage compressors are not normally designed for full discharge pressure and must also be provided with overpressure protection. 

Fig. 2.24. Representation of a cooling process in Mollier-h log P diagram(operation with subcooler). Pc, Liquefying pressure P, middle pressure P0, evaporating pressure. 1, Evaporator suctioning condition, stage 1 2.1, compressor pressure gas, low-pressure stage ...

As the fluid flows through the cooler, there is a pressure drop. Typically this pressure drop is about 35 kPa (5 psi), but clearly it is a function of the cooler design. In preliminary design a value of 35 kPa can be used. Note this has a significant effect on the suction pressure to the low pressure stages. 

The penetrometer consists of a capillary column with a sample-holding bulb at one end. The low pressure stage houses the penetrometer in which the sample is placed. It is used to ensure degassing of the material and removal of the air in the celt. The mercury is introduced at a pressure slightly greater than atmospheric pressure it thus flits the cell entirely and surrounds the grains of material. 

In the steam generation system, heat from combustion causes steam to form in the primary steam generation coils (Stultz and Kitto, 1992). The steam vapor rises into the steam drum, where it is accumulated. The steam then successively passes to the convective and radiant superheaters, which use combustion heat to further heat the steam well above its previous temperature. The steam next flows to the turbine, which has both high- and low-pressure stages. 

The main condenser is a three shell type each shell is located at each low-pressure stage turbine exhaust. The tube bundle is perpendicular to turbine axis. 

Tentatively, the turbine will have a double-stage structural arrangement, with a high-pressure and a double-flow low-pressure stage. 

The main advantage of the reheat cycle is that excessive moistime in the low-pressure stages is avoided without emplo5ung a high initial steam temperature. 

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