Steam and gas turbines

Turbines are a common feature on process plant, where they provide economical drives for rotating machinery, particularly centrifugal and axial pumps and compressors, as well as electrical generators in power stations. They use the expansion of hot, high-pressure gas or steam to produce mechanical power. 

The gas volumes in the body of the turbine are very small, so that the establishment of flow in the turbine is very fast, with a response time measured in tenths of a second. Since these time constants are an order of magnitude less than the rotor time constant associated with turbine speed, it is permissible to treat the equations of fluid flow as algebraic, simultaneous equations. This simplification receives even greater justification when the model of the turbine and the machine it drives are interfaced with a model of the rest of the process plant, which will be invariably much slower still. It is only when the turbine is being considered in detail on its own, for example in designing a speed-control system, that some of the larger turbine pressure constants, such as those associated with the turbine inlet manifolds, will need to be considered. 

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Now let us take a closer look at the two most commonly used heat engines (steam and gas turbines) to see whether they achieve this efficiency in practice. To make a quantitative assessment of any combined heat and power scheme, the grand composite curve should be used and the heat engine exhaust treated like any other utility. 

Stodola Steam and Gas Turbines, Peter Smith Publishers, p. 312 (Steam Quality). 

Stodola, A., Steam and Gas Turbines, McGraw-Hill Book Co., 1927. 

Reported incidences of fretting have continued to proliferate, in particular in blade/disc fixings in both steam and gas turbines, in PWR and AGR nuclear power plants, between the conductors in overhead power... 

Creep is the gradual extension of a material under a steady tensile stress, over a prolonged period of time. It is usually only important at high temperatures for instance, with steam and gas turbine blades. For a few materials, notably lead, the rate of creep is significant at moderate temperatures. Lead will creep under its own weight at room temperature and lead linings must be supported at frequent intervals. 

Now consider the two most commonly used heat engines (steam and gas turbines) in more detail to see whether... 

The utility system has as typical units steam and gas turbines, electric motors, electric generators, fired or waste heat boilers, steam headers at different pressures and auxiliary units (e.g., vacuum condenser, water treater, deaerator), and provides the required electricity, power, and utilities. 

There are two possible single-shaft configurations, shown in the top and bottom of Figure 2.118. One is to locate the gas turbine and the electric generator at the two ends of the shaft (top), and the other is to locate the steam and gas turbines at the two ends of the shaft (bottom). 

Analysis of Industrial Processes Application to Pressurized Fluidized Bed Combustor with Steam and Gas Turbine Generators," Paper 10, Intern. Conference on Cogeneration, Washington, D.C., Oct. (1981). 

In chemical plants, in steam and gas turbine powered compressor and power stations and pressure control facilities for natural gas, combustible fluids and gases need to be preheated in order to comply with the process parameters,... 

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