Compressor and pumps

The careful selection and design of control valves is important good flow control must be achieved, while keeping the pressure drop as low as possible. The valve must also be sized to avoid the flashing of hot liquids and the supercritical flow of gases and vapors. Control valve sizing is discussed by Chaflin (1974). 

Standards for valves are set by the ASME B16 Standards Committee and can be ordered from the American Society of Mechanical Engineers. General standards are described in ASME B 16.34-2004 (ASME, 2004), while valve dimensions are given in ASME B16.10-2000 (ASME, 2000). Valve design is covered by Pearson (1978). 

Positive displacement pumps, such as reciprocating and diaphragm pumps. 

The single-stage, horizontal, overhung, centrifugal pump is by far the most commonly used type in the chemical process industry. Other types are used where a high head or other special process considerations are specified. Eor example, when small 

Pump selection is made on the flow rate and head required, together with other process considerations, such as corrosion or the presence of solids in the fluid. 

There exist a wide variety of pumps that are designed for various specific applications. However, most of them can be broadly classified into two categories positive displacement and centrifugal. The most significant characteristics of each of these are described below. 

There are many ways to control the flow and pressure of streams discharging from pumps and compressors, but all are not equally efficient. Throttling a valve in the discharge line of a centrifugal pump may be convenient, but it may also be wasteful if long periods of low flow are encountered. And it cannot be done at all with a positive-displacement pump, because pressure ratings would be exceeded. 

The point is, that the type and size of a prime mover dictate the means which are to be used to control it. This is particularly true of compressors which are capable of exhibiting unstable characteristics. 

There are two principal classes of pumps positive-displacement and centrifugal. In positive-displacement pumps, a given volume of fluid is mechanically forced from the suction port to the discharge with every rotation of the shaft. In reciprocating pumps, this is done in a periodic fashion, such that outflow pulsates if multiple cylinders are used, they are phased so as to diminish the amplitude and period of the pulsations, smoothing the flow. Often an air chamber is attached to the discharge line to help absorb these pulsations. 

Shown are two methods for controlling the flow from a gear or vane pump. 

Control of flow from a gear or vane pump may be achieved by manipulating a bypass or by regulating the discharge pressure with a bypass, both of which are shown in Fig. 9.12. 

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In preliminary process design, the primary consideration is contact by inhalation. This happens either through accidental release of toxic material to the atmosphere or the fugitive emissions caused by slow leakage from pipe flanges, valve glands, and pump and compressor seals. Tank filling causes emissions when the rise in liquid level causes vapor in the tank to be released to the atmosphere. 

Material transfer requires pipework, valves, pumps, and compressors. Fugitive emissions occur from pipe flanges, valve glands, and pump and compressor seals. 

W. H. FaragaHah, Hquid Ping Vacuum Pumps and Compressors, Gulf PubUshiag, 1985. 

In a V/f control generally, only the frequency is varied to obtain the required speed control. Based on this frequency, the switching logistics of the inverter control circuit control the inverter s output voltage using the PWM technique to maintain the same ratio of V/f. A W/control is, however, not suitable at lower speeds. Their application is limited to fan, pump and compressor-type loads only, where speed regulation need not be accurate, and their low-spccd performance or transient response is not critical and they are also not required to operate at very low speeds. They arc primarily used for soft starts and to conserve energy... 

There may be many types of the drives in an industry, particularly when it is a process industry. The most common drives are fans, pumps, and compressors etc., employed for the various utilities, storage and process activities of the plant. The plant may be chemical or a petrochemical, water treatment or sewage disposal, paper and pulp unit or even a crane or a hoist application. 

Accumulator vents Blowdown systems Pumps and compressors... 

This chapter examines the overaii performance characteristics of compressors and turbines. This materiai is presented here to famiiiarize the reader with the behavior of these machines, ciassified under the broad term tur-bomaciiinery. Pumps and compressors are used to produce pressure turbines produce power. These machines have some common characteristics. The main eiement is a rotor with biades or vanes, and the path of the fluid in the rotor may be axiai, radiai, or a combination of both. 

Mechanical Drives. Mechanical drive gas turbines are widely used to drive pumps and compressors. Their application is widely used by offshore and petrochemical industrial complexes. These turbines must be operated at various speeds and thus usually have a gasifier section and a power section. These units in most cases are aero-derivative turbines, turbines, which were originally designed for aircraft application. There are some smaller frame type units, which have been converted to mechanical drive units with a gasifier and power turbine. 

API Std 681, Liquid Ring Vacuum Pumps and Compressors, 1st Edition, February 1996. 

Selection between steam, or electricity, or a combination for pumps and compressors. 

Chemical processes involve a strong interaction between mass and energy. Typically, the overall objective of a plant is to convert and process mass. Energy is used to drive reactions, effect separations and drive pumps and compressors. An overview of the main inputs and outputs of a process is shown in Fig. 1.1. The... 

All process plants require both steam and electric power in their operations. Power is cither purchased from local utility companies or generated at the plant site. Even if power is generated by the process plant, arrangements for standby power from the local utility must be made for emergency purposes. Steam is rarely purchased but is generated at the plant for use in the process and as a driving medium for pumps and compressors. 

Kern, R., Flow to Get the Best Process-Plant Layouts for Pumps and Compressors, V. 84, No. 26, 1977,... 

Pumps, Vacuum Pumps and Compressors 87, series of technical articles, published by Dr. Harnisch Verlagsgesellschaft mbH, UBERSEE-POST ORGANISATION, Postf., D-8500 Nurnberg 1/FRG. 

Application. (Very necessary for special motors and desirable for all others especially large motors driving centrifugal and reciprocating pumps and compressors. Advise whether these start under load. If a replacement and previous motor have failed frequently, give all details and reconsideration of electrical specifications as in order)... 

Use of wound-rotor induction motors has been largely in continuous-duty constant-speed supplications where particularly high starting torques and low starting currents are required simultaneously, such as in reciprocating pumps and compressors. These motors are also used where only alternating current is available to drive machines that require speed adjustment, such as types of fans and conveyors. 

Installation requirements for rotary positive-displacement compressors are similar to any rotating machine. Review the installation requirements for centrifugal pumps and compressors for foundation, pressure-relief, and other requirements. As with centrifugal compressors, rotary positive-displacement compressors must be fitted with pressure-relief devices to limit the discharge or inter-stage pressures to a safe maximum for the equipment served. 

Unlike centrifugal pumps and compressors, few criteria can be used directly to determine mixer effectiveness and efficiency. However, product quality and brake horsepower are indices that can be used to indirectly gauge performance. 

Fatigue failure is likely to occur in equipment subject to cyclic loading for example, rotating equipment, such as pumps and compressors, and equipment subjected to pressure cycling. A comprehensive treatment of this subject is given by Harris (1976). 

Dec. 5th) 131. How to get the best process-plant layouts for pumps and compressors. 

Sources Younger, A.H., Ruiter, J.L. Selecting Pumps and Compressors, Chemkd Engineering, June 26, 1961, p. 117. 

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