Section 9.1.2 - Steam Turbines: Evaluation of Costs

EVALUATION OF COSTS

The economical selection of a turbine considers the initial cost of the turbine and the operating costs. A lower-steam-rate (more efficient) turbine generally has a higher initial cost

TABLE 1  Temperature of dry and saturated steam

To obtain superheat, subtract temperature given above from total initial temperature. Pressure in kPa = 6.895 X lb/in². Temperature in °C = (°F - 32) ÷1.8.

than a turbine with a higher steam rate. The operating costs are the cost of the steam for the number of years upon which the evaluation is to be based:

The cost of installation - foundation, steam piping, and cooling water service (also electric service if required) - is not normally considered unless there are significant differences between the turbines: single-stage versus multistage, direct-connected versus turbine and gear, vertical turbine versus horizontal turbine with a right-angle gear, and so on.

The economical selection of a steam turbine versus an electric motor, diesel engine, gas engine, gas turbine, and so on, must include an evaluation of all installation costs, costs of supporting equipment (starters, switch gear, fuel-supply system, and so on), operating costs, and the initial costs of the various drivers being considered.

FIGURE 10  - Nominal inlet flow capacity. Read inlet nozzle size required to pass maximum flow, based on 150-ft/s (45.7-m/s) steam velocity (lb/in² x 6.895 = kPa;°F_SH x 0.555 = °C_SH)

FIGURE 11  Nominal exhaust flow capacity. Noncondensing exhaust nozzles, based on 200-ft/s (61 m/s) steam velocity

FIGURE 12  High-speed centrifugal pump and single-stage steam turbine mounted on a common shaft. Package is designed for boiler feed in marine, industrial, and process steam plants (Flowserve Corporation).

REFERENCES

1. Church, E. F. Steam Turbines. McGraw-Hill, New York, 1950.
   
2. Single-Stage Steam Turbines for Mechanical Drive Service." NEMA pub. SM22- 1970, 1970.
3. Keenan, J. H., and Keyes, F. G. "Thermodynamic Properties of Steam.' John Wiley & Sons, Inc., New York, 1936.

FURTHER READING

Bergeron, W. L. "Governors and Controls: Each Has Specific Operation.' Sugar J., March 1965.

"Multistage Steam Turbines for Mechanical Drive Service." NEMA pub. SM21-1970, 1970.Skrotzki, B. G. A. "Steam Turbines.' Power special report, 1962.

Steen-Johnsen, H. "Here's What You Should Know Before You Specify Control Systems for Mechanical Drive Steam Turbines.' Power Eng., February-March 1966.

Steen-Johnsen, H. "How to Estimate the Size and Cost of Mechanical Drive Steam Turbines.' Hydrocarbon Processing, October 1967.

Steen-Johnsen, H. "Mechanical Drive Turbines.' Oil Gas Equip., March, April, May, 1967.

Steen-Johnsen, H. "Selecting the Right Steam Turbine for Industrial Use.' Power Eng., Apri 1965.

"Theoretical Steam Rate Tables.' ASME, 1969.

EVALUATION OF COSTS

The economical selection of a turbine considers the initial cost of the turbine and the operating costs. A lower-steam-rate (more efficient) turbine generally has a higher initial cost

TABLE 1  Temperature of dry and saturated steam

To obtain superheat, subtract temperature given above from total initial temperature. Pressure in kPa = 6.895 X lb/in². Temperature in °C = (°F - 32) ÷1.8.

than a turbine with a higher steam rate. The operating costs are the cost of the steam for the number of years upon which the evaluation is to be based:

The cost of installation - foundation, steam piping, and cooling water service (also electric service if required) - is not normally considered unless there are significant differences between the turbines: single-stage versus multistage, direct-connected versus turbine and gear, vertical turbine versus horizontal turbine with a right-angle gear, and so on.

The economical selection of a steam turbine versus an electric motor, diesel engine, gas engine, gas turbine, and so on, must include an evaluation of all installation costs, costs of supporting equipment (starters, switch gear,...