【047】7BW-100型泥漿泵曲軸箱與液力端特性分析、設(shè)計(jì)

【047】7BW-100型泥漿泵曲軸箱與液力端特性分析、設(shè)計(jì),047,bw,泥漿泵,曲軸,液力端,特性,分析,設(shè)計(jì) 外文原文 畢業(yè)設(shè)計(jì)外文原文 《Standard Handbook of Petroleum & Natural Gas Engineering 》 by Lyons, William C.; Plisga, Gary S. Publication: Burlington, MA Elsevier, 2005 3.3 PUMPS Pumps are a mechanical device that forces a fluid to move from one position to another. Usually a pump refers to the mechanical means to move incompressible (or nearly incompressible) fluid or liquid. Pumps are our earliest machine and are to this day one of our most numerous mechanical devices. Pumps are a very essential part of the oil and gas industry. They are used throughout the industry, from drilling operations through to final delivery to the customer. 3.3.1 Classifications Pumps are classified into two basic classes, displacement and dynamics. The most widely used pumps in the oil and gas industry are reciprocating displacement pumps (in particular piston plunger type), the rotary displacement pump, and the centrifugal dynamic pump. Only these pumps will be discussed in detail. The reciprocating and rotary positive displacement pumps primary characteristic is that they have a nearly direct relationship between the motion of the pumping elements and the quantity of liquid pumped. Thus, in positive displacement pumps liquid displacement (or discharge from the device) is theoretically equal to the swept volume of the pumping element. Figure 3.3.3 shows the typical positive displacement plot of discharge rate Q (ft3/s) versus pressure P (lbs/ft2) [3]. The discharge rate remains the same (assuming a constant rate of rotation for the system) regardless of the pressure in the flow. The pressure in the flow is, of course, the result of resistance in the flow system the pump discharges to. If the resistance increases, rotation can be maintained and more force applied to each stroke of the pump (i.e., power). This is why the reciprocating piston plunger pump is also called a power pump. In practice, pressure does have some influence on the capacity of these pumps. This is because as the pressure increases, there is some leakage of the seals in the system. This leakage is somewhat proportional to the pressure, particularly beyond some characteristic pressure related to the seals. The difference between theoretical flow and the actual flow of a pump is often referred to as slip. This slip is shown in Figure 3.3.3. In the dynamic pump, in particular, the centrifugal pump, the discharge rate Q is determined by the resistance pressure P in the flow system the pump discharges to (assuming some given speed of the pump). This is illustrated in Figure 3.3.4. 3.3.3 Reciprocating Pumps The piston plunger pump is the simplest form of a positive displacement pump. These pumps can be powered by a variety of prime movers, internal combustion engines, and electric motors (and in some cases, powered by a gas turbine motor). In such applications, the separate pump unit is connected to the prime mover by a power transmission. The capacity of a pump is determined by the number of plungers or pistons and the size of these elements (bore and stroke). A reciprocating pump is usually designed for a specific volumetric rate capacity and pressure capability. These factors are set by the application. Once the volumetric rate capacity and pressure capability are known, a designer can determine the plunger piston bore and stroke the rotation speed range and the power of the prime mover needed to complete the system. Reciprocating pumps are fabricated in both horizontal andvertical configurations. 3.3.3.1 Single-Acting Pump A single-acting pump has only one power (and discharge) stroke for its pistons. Such a pump brings fluid into its chamber through the inlet or suction value or the piston is drawn backward to open the chamber. To discharge the fluid, the inlet valve is closed and the outlet valve opened as the piston is forced forward to push the fluid from the chamber into the discharge line. The piston motion is accomplished by a rotating crankshaft that is connected to the piston by a piston rod much like an internal combustion piston engine. The rotating crankshaft of the pump is rotated by the rotational power of the prime mover (through a transmission) [7]. The single-action pump is usually available with three, five and even seven pistons. The odd number of pistons allows the pump to be rotationally balanced, and the use of at least three pistons reduces the discharge pulsation of these single-acting pumps. A three piston pump single-action pump is called a triplex pump. A five piston, or seven piston single -acting pump is called a multiplex pump. 3.3.3.2 Double-Acting Pump Double-acting pumps have two power strokes. As a piston of the pump is pushed forward, the fluid is discharged from the forward chamber into the discharge line (much like a single-action piston). But during this same stroke, the chamber behind the piston (which contains the connecting rod) is being filled via that chamber’s inlet valve (Figure 3.3.5). When the forward power stroke is complete and the fluid discharged fromthe chamber in front of the piston, the chamber behind the piston is filled. The crankshaft continues to rotate, requiring the piston to begin a rearward stroke. During this stroke the fluid behind the piston is forced from its chamber into the discharge line via the outlet valve and the chamber in front of the piston refills via its inlet valve [7]. Double-acting pumps are usually available with one or twopistons. A one-piston double-action pump is called a double-acting simplex (since there are older single-action steam and pneumatic driven simplex pumps).A two piston double-action pump is called a duplex pump. 3.3.3.3 Flow Characteristics All reciprocating pumps have a pulsating discharge. This is the result of the piston motion as it stops and reverses. At this moment, the flow from that piston theoretically drops to zero. Thus, the discharge curves as a function of time are those illustrated in Figure 3.3.6.By having two or more pistons the pulsation of the discharge from the pump can besmoothed out and the magnitude of the pulsation reduced ifthe pistons motions are timed for proper dynamic balancingof the pump (Figure 3.3.7). For those pumps that have largepulsations, a cushion change (or accumulator) may be used in the discharge line to reduce or eliminate the pulsations (Figure 3.3.8). Single acting mud pump piston? Disclosed is a single acting mud pump piston assembly adapted for use in a mud pump mechanism including a piston and having an end portion with a shoulder reciprocatingly mounted in a cylinder. The assembly includes a circular flange mounted on the end portion in abuttment with the shoulder. A hub is removably mounted on the end portion in abuttment with the flange. A piston cap is mounted about the hub in abuttment with the flange. The assembly is held together by a washer and a nut engaging the end portion. A piston assembly for use in a single acting mud pump including a cylinder and a piston rod reciprocatingly mounted in the cylinder, said piston rod including a cylindrical end portion and a radially outwardly extending shoulder, said piston assembly comprising: a circular planar flange having an outside diameter less than the inside diameter of the cylinder and having a bore through the center thereof, said bore having a diameter substantially equal to the diameter of said cylindrical end portion of said piston rod, said flange being adapted to be carried on said cylindrical end portion in abuttment with said shoulder; means for forming a seal between said flange and said piston rod; a circular planar hub having an outside diameter less than the outside diameter of said flange and having a bore through the center thereof, said bore having a diameter substantially equal to the diameter of said cylindrical end portion of said piston rod, said hub having an axial thickness, said hub being adapted to be carried by said cylindrical end portion of said piston rod in removable abutting relationship with said flange; a circular elastomeric piston cup having a body with an outside diameter substantially equal to the outside diameter of said flange and an outwardly flaring annular lip having an outside diameter greater than the inside diameter of the cylinder, said piston cup having a bore through the center thereof, said bore having a diameter substantially equal to the outside diameter of said hub, said piston cup having a central portion surrounding said bore having an axial thickness at least equal to the axial thickness of said hub, said piston cup being adapted to be removably carried about said hub in removable abutting relationship with said flange; a circular planar washer having an outside diameter greater than the outside diameter of said hub and an inside diameter substantially equal to the diameter of said cylindrical end portion of said piston rod, adapted to be carried by said cylindrical end portion of said piston rod in removable abutting relationship with said hub and the central portion of said piston cup; and a retaining nut adapted to threadably engage said cylindrical end portion of said piston rod to urge said washer into abuttment with said hub and said central portion of said piston cup. A single acting mud pump mechanism which comprises: a cylinder having an inside diameter; a piston rod reciprocatingly mounted in said cylinder, said piston rod including a threaded cylindrical end portion and a radially outwardly extending shoulder; a circular planar flange removably mounted on said end portion in abuttment with said shoulder and having an outside diameter less than the inside diameter of the cylinder and having a bore through the center thereof, said bore having a diameter substantially equal to the diameter of said cylindrical end portion of said piston rod; means for forming a seal between said flange and said piston rod; a circular planar hub removably mounted on said end portion in abuttment with said flange and having an outside diameter less than the outside diameter of said flange and having a bore through the center thereof, said bore having a diameter substantially equal to the diameter of said end portion of said piston rod, said hub having an axial thickness; a circular elastomeric piston cup removably mounted about said hub and in abuttment with said flange and having a body with an outside diameter substantially equal to the outside diameter of said flange and an outwardly flaring annular lip having an outside diameter greater than the inside diameter of the cylinder, said piston cup having a bore through the center thereof, said bore having a diameter substantially equal to the outside diameter of said hub, said piston cup having a central portion surrounding said bore having an axial thickness at least equal to the axial thickness of said hub; a circular planar washer removably mounted about said end portion and having an outside diameter greater than the outside diameter of said hub and an inside diameter substantially equal to the diameter of said cylindrical end portion of said piston rod; and a retaining nut threadably engaged with said cylindrical end portion of said piston rod to urge said washer into abuttment with said hub and said central portion of said piston cup.The basic difference between reciprocating motion and circular motion The piston or plunger works within a watertight cylinder. Thebasic difference between a piston and a plunger should be notedA piston is shorter than the stroke of the cylinder;the plunger is longer than the stroke. Another distinguishing featureis that the packing is inlaid on the rim of the piston for a tight seal.When a plunger is used, the packing is moved in a stuffing boxlocated at the end of the cylinder to provide a tight seal. Principles of Operation In general (and with respect to the way that the water is handled), reciprocating pumps may be classified as lift pumps or force pumps, which in turn, are either single-acting or double-acting pumps. Lift Pumps A lift pump is a single-acting pump; it consists of an open cylinder and a discharge or bucket-type valve (see Figure 5-3). An open cylinder and a discharge or bucket-type valve in combination are the basic parts of the lift pump—it lifts the water, rather than forces it. In the lift pump, the bucket valve is built into the piston and moves upward and downward with the piston. A four-stroke cycle is necessary to start the lift pump in operation (see Figure 5-4). The strokes are as follows: _ Air exhaust—The piston descends to the bottom of the cylinder, forcing out the air. _ Water inlet—On this upward stroke, a vacuum is created. Atmospheric pressure causes the water to flow into the cylinder. After the pump has been primed and is in operation, the working cycle is completed in two strokes of the piston—a downward stroke and an upward stroke (see Figure 5-5). The downward stroke of the piston is called the transfer stroke, and the upward stroke is called the intake and discharge stroke, because water enters the cylinder as the preceding charge of water is being discharged. Force Pumps The force pump is actually an extension of a lift pump, in that it both lifts and forces the water against an external pressure. The basic operating principle of the force pump is that it forces water above the atmospheric pressure range, as distinguished from the lift pump, which elevates the water to flow from a spout. 4.4 MUD PUMPS Mud pumps consume more than 60% of all the horsepower used in rotary drilling. Mud pumps are used to circulate drilling fluid through the mud circulation system while drilling. A pump with two fluid cylinders, as shown in Figure 4.4.1, is called a duplex pump. A three-fluid-cylinder pump, as shown in Figure 4.4.2, is called a triplex pump. Duplex pumps are usually double action, and triplex pumps are usually single action. Pumps with six chambers are commercially available as well (Figure 4.4.3). Mud pumps consists of a power input end and a fluid output end. The power input end, shown in Figure 4.4.4 transfers power from the driving engine (usually diesel or electric) to the pump crankshaft. The fluid end does the actual work of pumping the fluid. A cross-section of the fluid end is shown in Figure.4.4.5. 4.4.1 Pump Installation 4.4.1.1 Suction Manifold The hydraulic horsepower produced by mud pumps depends mainly on the geometric and mechanical arrangement of the suction piping. If suction-charging centrifugal pumps (e.g., auxiliary pumps that help move the mud to the mud pump) are not used, the pump cylinders have to be filled by the hydrostatic head. Incomplete filling of the cylinders can result in hammering, which produces destructive pressure peaks and shortens the pump life. Filling problems become more important with higher piston velocities. The suction pressure loss through the suction valve and seat is from 5 to 10 psi. Approximately 1.5 psi of pressure is required for each foot of suction lift. Since the maximum available atmospheric pressure is 14.7 psi (sea level), suction pits placed below the pump should be eliminated. Instead, suction tanks placed level with or higher than the pump should be used to ensure a positive suction head. Figure 4.4.6 shows an ideal suction arrangement with the least amount of friction and low inertia. A poorly designed suction entrance to the pump can produce friction equivalent to 30 ft of pipe. Factors contributing to excessive suction pipe friction are an intake connection with sharp ends, a suction strainer, suction pipe with a small diameter, long runs of suction pipe, and numerous fittings along the suction pipe. Minimizing the effect of inertia requires a reduction of the suction velocity and mud weight. It is generally practical to use a short suction pipe with a large diameter. When a desirable suction condition cannot be attained, a charging pump becomes necessary. This is a common solution used on many modern rigs. 4.4.1.2 Cooling Mud Mud temperatures of 150? can present critical suction problems. Under low pressure or vacuum existing in the cylinder on the suction stroke, the mud can boil, hence decreasing the suction effectiveness. Furthermore, hot mud accelerates the deterioration of rubber parts, particularly when oil is present. Large mud tanks with cooling surfaces usually solve the problem. 4.4.1.3 Gas and Air Separation Entrained gas and air expands under the reduced pressure of the suction stroke, lowering the suction efficiency. Gas in water-base mud may also deteriorate the natural rubber parts used. Gases are usually separated with baffles or by changing mud composition. 4.4.1.4 Settling Pits The normally good lubricating qualities of mud can be lost if cuttings, particularly fine sand, are not effectively separated from the mud. Adequate settling pits and shale shakers usually eliminate this trouble. Desanders are used occasionally. 4.4.1.5 Discharge Manifold A poorly designed discharge manifold can cause shock waves and excessive pressure peaks. This manifold should be as short and direct as possible, avoiding any sharps turns. The conventional small atmospheric air chamber, often furnished with pumps, supplies only a moderate cushioning effect. For best results, this air chamber should be supplemented by a large atmospheric air chamber or by a precharged pulsation dampener. 4.4.2 Pump Operation 4.4.2.1 Priming A few strokes of the piston in a dry liner may ruin the liner. When the pump does not fill by gravity or when the cylinders have been emptied by standing too long or by replacement of the piston and liner, it is essential to prime the pump through the suction valve cap openings. 4.4.2.2 Cleaning the Suction Manifold Suction lines are often partly filled by settled sand and by debris from the pits, causing the pump to hammer at abnormally low speeds. Frequent inspection and cleaning of the suction manifold is required. The suction strainer can also be a liability if it is not cleaned frequently. 4.4.2.3 Cleaning the Discharge Strainer The discharge strainer often becomes clogged with pieces of piston and valve rubber. This may increase the pump pressure that is not shown by the pressure gauge beyond the strainer. The strainer should be inspected and cleaned frequently to prevent a pressure buildup. 4.4.2.4 Lost Circulation Materials Usually special solids, such as nut shells, limestone, expanded perlite, etc., are added to the drilling muds to fill or clog rock fractures in the open hold of a well. Most of these lost circulation materials can shorten the life of pump parts. They are especially hard on valves and seats when they accumulate on the seats or between the valve body and the valve disc. 4.4.2.5 Parts Storage Pump parts for high-pressure service are made of precisely manufactured materials and should be treated accordingly. In storage at the rig, metal parts should be protected from rusting and physical damage, and rubber parts should be protected from distortion and from exposure to heat, light, and oil. In general, parts should remain in their original packages where they are usually protected with rust-inhibiting coatings and wrappings and are properly supported to avoid damage. Careless stacking of pistons may distort or cut the sealing lips and result in early failures. Hanging lip-type or O-ring packings on a hook or throwing them carelessly into a bin may ruin them. Metal parts temporarily removed from pumps should be thoroughly cleaned, greased, and stored like new parts.