Expansion turbines shaft

The methane warms to 10°C. It then passes through the booster compressors on the expansion turbine shaft, increasing in pressure from 325 psi to 375 psi before being introduced into other gas compressors tliat boost the pressure back up to 600 psi. This is the pressure needed for reintroduction of the natural gas back into the TransCanada pipeline. This 50 psi boost, which makes use of available energy from the expansion turbines, provides a significant savings in electrical power. 

A detailed design for the compressors would be required to determine the inlet and outlet velocities for the steam in the steam turbine, and the tail gas in the tail-gas expander. In this process, tail-gas expansion typically provides about 80% of the required energy with an efficiency of expansion to shaft energy transfer of approximately 36%. The steam turbine provides the remaining 20% of the required energy with an efficiency in the production of shaft energy of less than 25%. 

When combining compressors, expanders, and turbines, the speeds, thermal expansions, and thrust loads on shaft systems exist at different magnitudes and directions. These must be managed and accommodated with skill and experience. 

A modification of the HAT cycle has been proposed by Nakhamkin [11], which is known as the cascaded humid air turbine (CHAT). The higher pressure ratios required in humidified cycles led Nakhamkin to propose reheating between the HP and LP turbines. Splitting the expansion in this way is paralleled by splitting the compression, and enables the HP shaft to be non-generating, as indicated in Fig. 6.15. This implies that the capital cost of the plant can be reduced, but the cycle is still complex. 

A turbine design where the expansion of steam occurs entirely in fixed nozzles. The steam jets from the nozzles are directed into disc-mounted buckets on the rotor forcing the shaft to rotate. 

Step 2. When steam passes through a turbine, it undergoes an isoentropic expansion. The work that the steam does in transferring its momentum to the turbine wheel exactly equals the shaft horsepower developed by the turbine. The entropy of the system is therefore constant. On this basis, extend a line through point A straight down the Mollier diagram. This line represents a constant entropy expansion. 

Turbines utilize the expansion of steam or a gas to deliver power to a rotating shaft. Salient features of such equipment are... 

The air-feed compressor is a dual-stage unit with a calculated duty of 3 MW. Compressor shaft power is provided by tail-gas expansion (80% of required power) and a steam turbine. 

The shaft work given by Eq. (7.27) is the maximum that can be obtained from an adiabatic turbine with given inlet conditions and given discharge pressure. Actual turbines produce less work, because the actual expansion process is irreversible. We therefore define a turbine efficiency as... 

Turbines (Expanders) High-velocity streams from nozzles impinging on blades attached to a rotating shaft form a turbine (or expander) through which vapor or gas flows in a steady-state expansion process which converts internal energy of a high-pressure stream into shaft work. The motive force may be provided by steam (turbine) or by a high-pressure gas (expander). 

Eliminating all surface forces except those that cause expansion or contraction, because a simple system has no gradients or shaft work (i.e., the work of a turbine or a pump) and neglecting Ek and Ep changes by taking the system s center of mass as the frame of reference, the energy balance takes a specific simple form. The energy balance yields... 

Some systems which have mechanical parts that perform work are turbines, mixers, engines, stirred tank reactors, agitators, and many others. The type of work performed by these parts is called shaft work to distinguish it from work due to expansion of the system itself (which is called expansion work). 

Figure 3-2 Examples of work (a) shaft work (wind turbine) (b) PV work for compression/ expansion of a gas in a cylinder (c) PV work associated with volume changes.

In this arrangement the compression heat from the compressor is used to heat up the helium to the desired temperature. The required compressor power was 90 MW with 45 MW generated and regained by the expansion in the gas turbine and 45 MW introduced by the electric drive motor. The selected combination of the turbine and compressor on one shaft resulted in dimensions being comparable with a helium turbine of 300 MW capacity (the reference plant size at the time). 

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