Other than Electric Motors

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. 

Drum dryers take a solution or thin slurry and spread it as a thin film over a rotating drum heated internally by condensing steam to produce a flaked product. Typical moisture evaporation rates are 3-6 Ib/hr-ft. One or two drums (side-by-side) may be used. Drum dimensions range from 1 ft in diameter by 1.5 ft long to 5 ft in diameter by 12 ft long. The cost of drum dryers depends on the surface area of the drum. 

Spray dryers produce small porous particles, such as powdered milk and laundry detergent, from a liquid solution by evaporation of the volatile component of the feed, with the purchase cost correlated with the evaporation rate. Size and cost data for other dryers as well as considerations in dryer selection are found in Section 12 of Perry s Chemical Engineers Handbook (1997). 

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For most of the rotary compressors in process service, the driver is an electric motor. Compressors in portable service, however, particularly the helical-lobe compressor, use internal combustion engines. Many of the rotary compressors require the high speed that can be obtained from a direct-connected motor. The dry type helical-lobe compressor is probably the main exception as the smaller units operate above motor speed and require a speed increasing gear which may be either internal or external (see Figure 4-1). The helical-lobe compressor is the most likely candidate for a driver other than the electric motor. Aside from the portables already mentioned, engines are used extensively as drivers for rotaries located in the field in gas-gathering service. Steam turbines, while not common, probably comprise most of process service alternate drive applications. 

Squirrel-Cage Motor. This type of motor finds a broader application and a more extensive and general use than any other type of motor. This is because it is, inherently, the simplest type of electric motor and, also, has excellent characteristics and operates essentially at constant speed. It has greater reliability and low maintenance requirements and thus meets a broad range of applications. 

Electric motors are the most common source of motive power for machine-trains. As a result, more of them are evaluated using microprocessor-based vibration monitoring systems than any other driver. The vibration frequencies of the following parameters are monitored to evaluate operating condition. This information is used to establish a database. 

Harmonic number (h) refers to the individual frequency elements that comprise a composite waveform. For example, h = 5 refers to the fifth harmonic component with a frequency equal to five times the fundamental frequency. If the fundamental frequency is 60 Hz, then the fifth harmonic frequency is 5 x 60, or 300 Hz. The harmonic number 6 is a component with a frequency of 360 Hz. Dealing with harmonic numbers and not with harmonic frequencies is done for two reasons. The fundamental frequency varies among individual countries and applications. The fundamental frequency in the U.S. is 60 Hz, whereas in Europe and many Asian countries it is 50 Hz. Also, some applications use frequencies other than 50 or 60 Hz for example, 400 Hz is a common frequency in the aerospace industry, while some AC systems for electric traction use 25 Hz as the frequency. The inverter part of an AC adjustable speed drive can operate at any frequency between zero and its full rated maximum frequency, and the fundamental frequency then becomes the frequency at which the motor is operating. The use of harmonic numbers allows us to simplify how we express harmonics. The second reason for using harmonic numbers is the simplification realized in performing mathematical operations involving harmonics. 

For the actual systems, compressor work will be higher than for ideal for the isentropic efficiency and other losses. In the case of hermetic or accessible compressors where an electrical motor is cooled by the refrigerant, condenser capacity should be ... 

Automatic valves are part of a control loop, which is shown in Figure 8.6. The loop contains a primary element, which measures the controlled variable, such as temperature, pressure, flow rate, and liquid level. The operation of a control loop is the same regardless of what variable is controlled. In the case of flow-rate control, the controller obtains the flow rate from transmitter a flow meter and compares the measured flow rate with a value that has been preset in the controller. If the flow rate is greater than the preset value, the controller increases air pressure on top or bottom of a diaphragm in the valve. Then, the valve partially closes to reduce the flow rate. On the other hand, if the flow rate is below the preset value, the controller will act to reduce the air pressure on the diaphragm, and hence the valve opens wider. Electric motors can also operate automatic control valves. 

Most of these devices are actually made rather simply, in that there is a particular cable, like a marionette string, that goes directly from the controls to the hands. But, of course, things also have been made using servo motors, so that the connection between the one thing and the other is electrical rather than mechanical. When you turn the levers, they turn a servo motor, and it changes the electrical currents in the wires, which repositions a motor at the other end. 

In analyzing the transition to alternative fuels other than hydrogen— such as ethanol, methanol, CNG, LPG, and electricity—analyses with the TAFV model led to some important conclusions that bear on the proposed hydrogen transition. We find that the transition matters a lot. Furthermore, we can identify some of the most important barriers. For AFVs, the most important barriers seem to be limited fuel availability and vehicle scale economies. For HEVs, incremental vehicle costs are large. As a result, vehicle scale economies matter, but scale cost reductions are more easily attained by the use of widely shared components—such as batteries, motors, and controllers—across multiple vehicle platforms. Similar gains should be possible for FCVs. For HEVs, the dominant transitional factor is the uncertain prospect for LBD. 

Exxon, Arco, Amoco, Mobil, and Ashland also entered the mining of copper and other industrial minerals. For Mobil and Exxon, the latter included uranium. By 1993, however, these units had been spun off. A few firms strayed even further afield. Exxon and Arco undertook the production of computer products and provided computer services. Exxon even went so far as to acquire an innovative electric-motor enterprise. Reliance Electric. As mentioned above, Mobil purchased Montgomery Ward and the Container Corporation of America, while Occidental bought Iowa Beef, the nation s most successful meat packer. By the mid-1990s, however, the petroleum companies had sold off nearly all these acquisitions. By then, nearly all American industrial corporations had learned that such unrelated diversification could rarely remain profitable for more than a decade and defined their strategic boundaries accordingly. 

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