Steam turbine drives

Right-angle gear drive is preferred for fans over 3 m (10 ft) in diameter, for electric motors over 22.4 kW (30 hp), and with steam-turbine drives. 

The system should have an aeeumulator to maintain suffieient oil pressure while the standby pump aeeelerates from an idle eondition. An aeeumulator beeomes a must if a steam turbine drives the standby pump. Overhead tanks are speeified by many users to assure flow to eritieal maehinery eomponents. The sizing of the tanks varies depending on the applieation. In some gas turbine applieations, the bearings reaeh maximum temperature as long as 20 minutes after shutdown. 

If HjS is continuously present in the flare gas or if the flare seal drum also functions as a sour water disengaging drum, then the effluent seal water must be routed to a sour water stripper, desalter, or other safe means of disposal. Withdrawal from the drum is by pump in place of the normal loop seal arrangement. Two pumps are provided one motor driven for normal use, and the other having a steam turbine drive with low pressure cut-in. The seal drum level is controlled by LIC with high and low alarm lights plus an independent high level alarm. 

The evaluation of steam turbine drives versus electric motor selections for an application is reviewed by Ranade, et al. ... 

The turbine applied to driving mechanical equipment is not operated (very often) with extraction or bleed streams. Here again, this depends upon the plant steam balance, and this is one of the fine features of steam turbine drive. The flexibility of design and application allow it to be set in the proper place for the economic balance of a system. The decision as to condensing or noncondensing should not be... 

Figure 15.37 A single-stage steam turbine driving an alternator...

With commercially available motors and speed reducers, standard speeds are 37, 45, 56, 68, 84, 100, 125, 155, 190, and 320 rpm. Power requirements usually are not great enough to justify the use of continously adjustable steam turbine drives. Two-speed drives may be required when starting torques are high, as with a settled slurry. 

For Steam Turbine Drives. . . Are Dry Cooling Towers Economical Rabb, A. 

The other environmental impact consideration is noise. The air compressor with its tail-gas expander and steam-turbine drive could present a problem. Therefore, this unit should be enclosed in a brick building to contain the noise, with those working inside the building required to wear approved ear protection. 

The first stage of compression uses an axial compressor with steam turbine drive. It has a capacity of 511 m3/min (36 000 kg/h). Using Ref. CE9 (Figure 13.47, p.560), the estimated cost is US 300 000. This figure relates to 1979, when updated to 1986 costs and adjusted for currency differences the final Australian purchase cost is As490 000. 

Separately driven centrifugal compressors are adaptable to low-pressure cryogenic systems because they can be coupled directly to steam turbine drives, are less critical from the standpoint of foundation design criteria, and lend themselves to gas turbine or combined cycle applications. Isentropic efficiencies of 80 to 85% are usually obtained. 

The preceding values apply for motor drives. Multiply indicated velocities bv 0.6 to eive reasonable velocities when steam turbine drives are used. 

Multiple-step variable-speed fan control, type d. is best applied with steam-turbine drives. In aplant with ac auxiliary motor drives, slip-ring motors with damper integration must be used between steps, making the installation expensive. Although dc motor drives would be less costly, few power plants other than marine propulsion plants have direct current available. And since marine units normally operate at full load 90 percent or more of the time, part-load operating economics are unimportant. If steam-turbine drive will be used for the fans, plot the power-input curve LMD, using data from the fan manufacturer. 

Example 5.3 Sizing a Steam-Turbine Drive for a Centrifugal Compressor... 

A steam turbine drives a compressor (Figure PI.2) whose load can change with time. Small variations in the shaft speed of the turbine are controlled through the use of a flyball speed governor. For this system ... 

Kohli, J.P. Design Best Cooling Water System. Hydrocarbon Processing, December 1968, p. 108. Rabb, A. For Steam Turbine Drives—Are Dry Cooling Towers Economical. Hydrocarbon Processing, February 1968, p. 122. 

Secondary circuit water boiling up and abrupt increase of heat removal from the primary coolant occurs to result probably in its freezing. Steam turbine drive of feed water pump and by-pass pipelines connecting steam generator inlet and steam header through orifices are provided in the secondary circuit to decrease consequences of such accidents. 

---