TABLE OF CONTENTS Powered chemical processing equipment includes pumps, compressors, agitators and mixers, crushers and grinders, and conveyors. Drivers are electric motors, steam or gas turbines, and internal combustion engines. For loads under 150 HP or so electric motors are almost invariably the choice. Several criteria are applicable. For example, when a pump and a spare are provided, for flexibility one of them may be driven by motor and the other by turbine. Centrifugal and axial blowers and compressors are advantageously driven by turbines because the high operating speeds of 4000 10,000 rpm are readily attainable whereas electric motors must operate through a speed increasing gear at extra expense. When fuel is relatively cheap or accessible, as in the field, gas turbines and internal combustion engines are preferred drivers. Turbines, internal combustion engines, and direct current motors are capable of continuous speed adjustment over a wide range. Energy efficiencies vary widely with the size and type of driver as shown in this table.
Driver
Efficiency (%)
10 kW
100 kW
1000 kW
10,000 kW
Gas turbine and internal combustion engine
28
34
38
Steam turbine
42
63
78
Motor
85
92
96
97
Since the unit energy costs are correspondingly different, the economics of the several drive modes often are more nearly comparable.
Although each has several subclasses, the three main classes of motors are induction, synchronous, and direct current. Higher voltages are more efficient, but only in the larger sizes is the housing ample enough to accomodate the...
