Steam turbines expansion

Steam turbine integration. Figure 6.32 shows a steam turbine expansion on an enthalpy-entropy plot. In an ideal turbine, steam... 

Sodium Chloride. Sodium chloride, a corrodent of many materials, is the archetype contaminant and has been studied more than other salts. The solubiUty of sodium chloride in superheated steam is shown at the conditions of a typical steam turbine expansion in Figure 14. The solubiUties were measured in the region of higher solubiUty (9). As the steam expands, sodium chloride becomes considerably less soluble. The solubiUty, S, in parts per biUion (ppb) can be represented by equation 3 ... 

Silica. Sihca is not actually a corrodent of turbines. However, it can deposit on and cause blocking of turbine passages, thus reducing turbine capacity and efficiency. As Httie as 76 pm (3 mils) of deposit can cause measurable loss in turbine efficiency. Severe deposition can also cause imbalance of the turbine and vibration. The solubihty in steam and water is shown in Figure 15, as is a typical steam turbine expansion. Sihca is not a problem except in low pressure turbines unless the concentrations are extraordinarily high. 

By common usage, the terms turboexpanders and expansion turbines specifically exclude steam turbines and combustion gas turbines, which are covered elsewhere in Sec. 29. 

Turboexpanders are expansion turbines, rotating maehines similar to steam turbines. Commonly, the terms expansion turbines and turboexpanders speeifieally exelude steam turbines and eombustion gas turbines. Turboexpanders (Figure 1-1) ean also be eharaeterized as modern rotating deviees that eonvert the pressure energy of a gas or vapor stream into meehanieal work as the gas or vapor expands through the turbine. If ehilling the gas or vapor stream is the main... 

Smooth starts are possible with steam turbine installations that include an auxiliary boiler because the startup phases of the turbocompressor can be matched to different plant operating conditions. Aside from process-related timing issues, the time elapse or machinery startup duration is generally determined by the temperature gradients admissible on both steam turbine and expander. These factors are influenced by the relative expansion rates of the fixed and rotating components in these machines. 

Dearation can be either vacuum or over pressure dearation. Most systems use vacuum dearation because all the feedwater heating can be done in the feedwater tank and there is no need for additional heat exchangers. The heating steam in the vacuum dearation process is a lower quality steam thus leaving the steam in the steam cycle for expansion work through the steam turbine. This increases the output of the steam turbine and therefore the efficiency of the combined cycle. In the case of the overpressure dearation, the gases can be exhausted directly to the atmosphere independently of the condenser evacuation system. 

TTiere are two main types of expansion turbines axial flow and radial flow. Axial flow expansion turbines are like conventional steam turbines. They may be single-stage or multistage with impulse or reaction blading, or some combination of the two. Turbines of this type are used as power recovery turbines. They are used where flow rates, inlet temperatures, or total energy drops are very high. 

Knowing the turbine efficiency, an approximate condition line for the expansion through the steam turbine can be drawn (to state f at pressure pbO and an estimate made of the steam enthalpy hf. If a fraction of the steam flow is bled at this point then the heat balance for a direct heater raising the water from near the condenser temperature to 7b is approximately... 

Rice [15] made a comprehensive study of the reheated gas turbine eombined plant. He first analysed the higher (gas turbine) plant with reheat, obtaining (t o)h> turbine exit temperature, and power turbine expansion ratio, all as funetions of plant overall pressure ratio and firing temperatures in the main and reheat burners. (The optimum power turbine expansion ratio is little different from the square root of the overall pressure ratio.) He then pre-seleeted the steam eyele eonditions rather than undertaking a full optimisation. 

The basic steam cycle for a steam turbine installation is called a Rankine cycle (named after Scottish engineer and physicist William John Macquorn Rankine). This cycle consists of a compression of liquid water, heating and evaporation in the heat source (a steam boiler or nuclear reactor), expansion of the... 

Low-temperature, high-pressure gases at moderate to low temperatures can be expanded by the use of an expansion turbine (very similar to a steam turbine or even by reciprocating or screw-type compressors) or by the use of a throt-... 

COMMENTS The sole purpose of the reheat cycle is to reduce the moisture content of the steam at the final stages of the turbine expansion process. The more reheating processes, the higher the quality of the steam at the exit of the last-stage turbine. The reheat temperature is often very close or equal to the turbine inlet temperature. The optimum reheat pressure is about one-fourth of the maximum cycle pressure. 

---