Equipment purchase costs motors, electric

When the required shaft horsepower for power input to an item of process equipment is less than 100 Hp, an electric motor is usually the selected drive. For higher horsepower input, consideration is given to combustion gas turbines, steam turbines, and internal combustion gas engines. However, except for remote, mobile, or special situations, steam turbines are the most common alternative to electric motors. Furthermore, steam turbines are considerably more efficient, 50-80%, than gas turbines or engines, which have efficiencies of only 30-40%. Equations for f.o.b. purchase costs of steam and gas turbine drives are included in Table 16.32 as a function of shaft horsepower. 

Even when the time comes to make a purchasing decision, an energy-efficient motor purchase is not a certainty. Sometimes an energy-efficient motor will be the economically efficient choice at other times, not. The capital investment decision is based on the cost in relation to performance, efficiency and reliability. Moreover, the decision depends on the application and the amount of time the motor is in operation. It can be the major component of a product (drill or mixer), or a minor component (computer disk drive) it can be the major component cost of a product (fan), or it can be a minor component cost (stereo tape deck) it can run almost constantly (fan, pump, and machinery), or only a few minutes a day (vacuums and power tools). For example, contractors purchase circular saws almost solely based on performance and reliability. Time is money, and since the saw is operating only a few minutes a day and the contractor is often not responsible for the electricity costs to run the motor, energy efficiency is not a consideration performance and reliability are what matter most. On the other hand, an industrial user, who runs huge electric motors twenty-four hours a day to work pumps, machinery, and ventilation equipment, is very concerned tvitli energy efficiency as well as performance and reliability. 

Depending on the needs and expectations, one should dedde what type and capadty of the injection equipment to purchase. Usually, the initial investment cost of a flow rate-controlled injection equipment is higher than a pressure-controlled equipment. Figure 9.16a shows a flow-rate controlled injection equipment from Radius Engineering Inc. Its major components are (1) a resin cylinder (with a capacity of 2100 cc for this model) with a heater jacket, (2) an electric stepper motor which drives a piston at a desired resin flow rate, (3) a control console to input the process parameters and monitor process variables, (4) communication interfaces to control the equipment through a personal computer instead of the control console if desired and (5) a frame and stand with wheels. 

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