Horsepower, driver

Once the pump differential pressure is calculated, the required brake horsepower of the pump can be calculated by following equation  

BHP is the required pump horsepower, in hp Q is the pumping rate, in gpm and E is the pump efficiency, in fraction. 

After the required pump Imrsqpower is caloilated, driver horsepower can be estimated based on pump runout flow (maximum expected flow) or using following equation per API 610  

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FIG. 29-61 Horsepower-r/min balance for a lean pump tandem-connected with a power-recovery turbine operating as the sole driver. Horsepower differences are calculated from excess head requirements as typically shown in Fig. 29-60. To convert gallons per minute to cubic meters per hour, multiply by 0.2271 to convert horsepower to kilowatts, multiply by 0.746. 

Preliminary Process Flowsheet. This will show major equipment and lines, preliminary equipment details (vessel diameter, number of trays, pump flow and driver horsepower, etc.), major instrumentation, and, it is hoped, have a material balance at the bottom of each drawing with flows keyed to a numbering system on the diagram. The process flowsheets should cover both the process and utility sides of the plant. 

As suction pressure increases or discharge pressure decreases, the compressor head requirement will decrease and the flow rate will increase. A flare valve will avoid stonewalling or overranging driver horsepower. 

It can be seen from Equation 11-7 that as R is increased, and as clearance is incre ised, volumetric efficiency is reduced. The relationship of volumetric efficiency and clearance is important, because it allows variable clearances (both fixed volume and adjustable volume pockets) to be used to control capacity and obtain the maximum use of available driver horsepower. 

The driver horsepower must be greater than the calculated (or value read from curves) input BHP to the shaft of the pump. The mechanical losses in the coupling, V-belt, gear-box, or other drive plus the losses in the driver must be accounted for in order that the driver rated power output will be sufficient to handle the pump. 

Required fan driver horsepower based on material from Fludson Products Corp., motor shaft horsepower output to fan is ... 

Motor or other driver horsepower recommended and speed... 

Brake horsepower, centrifugal pumps, 200 Driver horsepower, 201 Burst pressure, 405, 456 Cartridge filters, 274-278 Capture mechanism, 279 Edge filler, 278 Filter media, table, 278 Micron ratings, 277 Reusable elements, 281 Sintered metal, 280 Types, 276, 277, 279 Wound vs. pleated, 276, 277 Centrifugal pumps, operating characteristics, 177-180 Calculations, see hydraulic performance Capacity, 180... 

The revolutions per minute (RPM) (or rotational speed) of a fan can be increased by increasing the size of the motor pulley, which is the grooved wheel on the motor shaft. A small increase in the diameter of this pulley will greatly increase airflow through the cooling bundle. But, according to the affinity or fan laws, doubling the diameter of a pulley increases the driver amp load by 800 percent. That is, driver horsepower increases to the cube (third power) of the fan s speed. 

May cause the forced-draft fan to operate out of character, requiring higher driver horsepower. 

A very large percentage of refrigeration systems are not limited by either the compressor driver horsepower, the condenser, or the evaporator. Many refrigeration systems are limited by either ... 

Turning the wheel at the back end of the cylinder counterclockwise, pulls back a large internal plug in the head. Now, when the piston starts to withdraw toward the crank end of the cylinder, there is more gas left inside the cylinder to expand. The greater the volume of gas inside the cylinder when the piston is at bottom dead center, the closer the piston is to top dead center before the intake valve opens. The delay in the opening of the intake valve reduces the amount of gas drawn into the cylinder. This reduces the number of moles of gas compressed by the piston. Compression work also diminishes and the driver horsepower or amp load drops. 

I like to calculate the relative compression efficiency because I do not have to know the flow of process gas. I do not have to know the driver horsepower output, the steam to the turbine, the fuel gas to the gas turbine, or the speed of the compressor. I do not have to know Z (the gas compressibility factor) or K (the ratio of the specific heats). The things I do have to know—the suction and discharge temperature and pressure—I can check with my own hands and my own tools. 

Driver horsepower, HP = BHP/(driver efficiency) = HHP/(pump efficiency)(driver efficiency). 

Compression work (or amp load on the motor driver) is proportional to the volume of gas compressed. Therefore, any increase in the density of gas to the compressor will force the spill-back open, increase the number of moles flowing to the compressor and hence increase the driver horsepower requirement. We might even cause the motor to trip off due to over-amping. 

Specifically, when the viscosity approaches roughly 40 to 60 cs (depending on the size of the pump), a rapid increase in driver horsepower will be required. For most refinery applications, viscosity is in the range of 0.5 to 3.0 cs. 

There are a variety of computer software programs available to optimize the speed, suction throttle valve position, and spill-back valve position to minimize driver horsepower and keep a compressor safely av ay from its surge point while still controlling suction pressure. 

Normally, increasing the flow from a centrifugal pump increases the amperage load on the motor driver, as shown in Fig. 34.11. Driver horsepower is proportional to GPM times feet of head. As shown in Fig. 34.10, as the flow increases, the feet of head developed by the pump decreases. On the flat part of the pump curve, the flow increases rapidly, while the head slips down slowly. Hence the product of GPM times feet of head increase. 

If we cannot open the discharge control valve of a centrifugal pump 100 percent before the FLA point is reached, then we say that the pump is driver-limited. This is a frustrating problem for plant operators, and clearly reflects poor design practice in undersizing the motor driver horsepower. 

This means that an operating change that forces the compressor back up its curve will reduce the driver horsepower. Later in this chapter, you will see how critical this bit of information is. Most constant speed centrifugal compressors are designed to operate on the flat portion of their curves. 

The delay in the opening of the intake valve reduces the amount of gas drawn into the cylinder. This reduces the number of moles of gas compressed by the piston. Compression work is also diminished, and the driver horsepower or motor amp load drops. 

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