Prime-movers

Both reciprocating engines and turbines are used as prime movers in production facilities to directly drive pumps, compressors, generators, cranes, etc. Reciprocating engines for oil field applications range in horsepower from 100 to 3,500, while gas turbines range from 1,500 to in excess of 75,000. 

Prime movers are typically fueled by natural gas or diesel. Dual fuel turbine units exist that can run on natural gas and can automatically switch to diesel. So-called dual fuel reciprocating engines run on a mixture of diesel and natural gas. When natural gas is not available, they can automatically switch to 100% diesel. Most prime movers associated with producing facilities are typically natural gas fueled due to the ready availability of fuel. Diesel fueled machines are typically used to provide stand-by power or power for intermittent or emergency users such as cranes, stand-by generators, firewater pumps, etc. 

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Motor nd Drive. The preferred prime mover for a fan is usually an electric motor. Eor fans of low to moderate power, V-belt drives are frequently employed. This permits selection of fans that can be operated over a wide range of speeds rather than being limited to motor synchronous speeds. Furthermore, change of speed is less expensive with V-belt drives. However, fans requiring powerful motors, 37—75 kW (50—100 hp) and higher, are generally directly connected to the motor and driven at synchronous speed. 

Rotary atomisation produces the most uniform atomisation of any of the aforementioned techniques, and produces the smallest maximum particle sise. It is almost always used with electrostatics and at lower rotational speeds the electrostatics assist the atomisation. At higher rotational speeds the atomisation is principally mechanical in nature and does not depend on the electrical properties of the coating material. If the viscosity of a coating material is sufficiendy low that it can be deUvered to a rotary atomiser, the material can generally be atomised. The prime mover is usually an ak-driven turbine and, provided that the turbine has the requked power to accelerate the material to the angular velocity, Hquid-dow rates of up to 1000 cm /min can be atomised using an 8-cm diameter beU. 

G. S. Shareef, D. K. Stone, K. R. Perry, K. L. Johnson, and K. S. Locke "Selective Catalytic Reduction NO Control for Small Natural Gas-Pired Prime Movers," paper 92-136.06, in Ref. 16. 

In I 888 Nikola Tesla (1856-1943) at Columbus, Ohio, USA, invented the first induction motor which has become the basic prime mover to run the wheels of industry today. Below, for simplicity, we first discuss a polyphase and then a single-phase motor. 

On a 3-0 system the frequency variation is normally within limits, which according to lEC 60034-1 is 2% (Figure 1.6). The reason for keeping the frequency variation low is that it is not influenced by any condition outside the generating point, and at the generating point, it is maintained constant through automatic speed regulation of the prime mover (frequency is directly proportional to the speed, equation (1.6a)). The effect of frequency variation, however small, is discussed below ... 

In an industry there may be many drives that may not be required to operate at their optimum capacity at all times. The process requirement may require a varying utilization of the capticity of the drive at different times. In an induction motor, which is a constant speed prime-mover, such a variation is conventionally achieved by throttling the How valves or by employing dampers. 

The system resistance increases and discharge reduces at the same rated speed This condition refers to point B, to which the earlier point A, has now shifted. The system now operates at a higher head f/j2. whereas the actual head has not increased. This condition has occurred due to higher system resistance offered by the throttle. The pump and the prime-mover efficieticy will now reduce to 73 7r from its original 8.3%. 

Cut-in wind speed is the minimum wind speed at which the generator commences the generation of power. At this speed the brakes release and the prime mover (blades) starts rotating. 

Cut-oul wind speed is the maximum w ind speed beyond which the prime mover may overspeed above its permissible limits. As the structure and the blades are designed for a particular maximum speed, a wind speed higher than this may exceed their mechanical endurance and become unsafe. At this speed the brakes apply and the machine is disconnected from the grid. The cut-in and cut-out speeds define the wind speed limits within which the turbine will work safely through the generator. Rated wind speed is the speed at which the prime mover rotates at the rated negative slip and generates the rated power. 

A more economical alternative is found in a submersible pump where the pump, directly coupled with the prime mover, is slid into the tubewell through narrow pipes. Narrow pipes are easy to sink into rocky terrain or very deep water levels. They are less expensive and are easy to install due to the elimination of the need for a pump house. Once the unit is slid into the well it requires little maintenance. (See Figures 7.5-7.7.) Such pumps have a standard centrifugal multistage arrangement, and the motors are required to work under water or any other liquid. These motors have an exclusive application for submersible pumps. 

Soft slarlers, star-delta, wound motor and A/T starters, or when the prime mover is fitted with centrifugal dutches or delayed-action fluid couplings... 

A friction loss of 37.125 m In a total length of 1000 m is quite high and will require a larger motor. Therefore, a 150 mm main pipeline will offer a better and more economical design compared to a 125 mm pipeline such as the reduced cost of the prime mover and lower power consumption during the life of pumping system, in addition to a longer life span of a 150 mm pipe compared to a 125 mm pipe. 

This is the main prime mover (PM) for the generator and may be a gas, petrol or diesel engine, depending upon the availability of fuel. In the discussions below, we emphasize a diesel engine, being used more commonly for captive power generation. 

When a generator is designed for a leading p.f. (in the underexcitation mode) it can operate as both a synchronous motor and a synchronous condenser. The machine is now self-starting and does not require a prime mover. 

The load sharing by the two machines can thus be varied by shifting the drooping curves of the prime movers by altering their power input. 

The load sharing of the tw o generators is therefore dependent on the speed-load (drooping) charaeieristics of the prime movers. 

Active power (kW) sharing By changing the mechanical torque of the prime mover by changing its driving force (fuel supply). 

Figure 16.37 Determining the load sharing between G, and G2 with the help of prime-movers drooping characteristics...

Tail gas expanders are thus an integral part of modern nitrie aeid plants. However, these turboexpanders are also part of a eombined turbomaehinery train eomprised of a prime mover and two or more eompressor easings. 

SELECTING A PRIME MOVER FOR TURBOTRAINS IN NITRIC ACID PLANTS... 

Gas turbines are used as prime movers for pumps, electric generators, and large rotating machinery. Their main economic advantage is driving... 

The gas turbine is the best suited prime mover when the needs at hand such as capital cost, time from planning to completion, maintenance costs, and fuel costs are considered. The gas turbine has the lowest maintenance and capital cost of any major prime mover. It also has the fastest completion time to full operation of any other plant. Its disadvantage was its high heat rate but this has been addressed and the new turbines are among the most efficient types of prime movers. The combination of plant cycles further increases the efficiencies to the low 60s. 

Figure 2-31. Load sharing between prime movers over the entire operating range of a combine cycle power plant.

The petroleum industry is one of the largest users of gas turbines as prime movers for drives of mechanical equipment and also for power generation equipment. Thus the specifications written are well suited for this industry, and the tips of operation and maintenance apply for all industries. This section deals with some of the applicable API and ASME standards for the gas turbine and other various associated pieces. 

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