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reciprocating compressor control philosophy

January 16, 2021 by  
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The LMRC is a novel concept compared to conventional reciprocating compression technology. This is achieved by varying the compressor throughput, which is why the term “performance control” may be also be called “capacity control”. Interlocks allow safe changes from one method of operation to another while the equipment works, and prevent misuse. A trip is an irregular state that requires an immediate and automatic shutdown of the compressor in order to avoid damage to the equipment and personnel. Moreover, the operator can enable the oil heater by pushing a button in the DCS. At this time, close the second-stage discharge to first stage’s discharge bypass valve gradually until the desired second-stage discharge pressure is obtained. In this article, methods for controlling the capacity of reciprocating compressors are presented in detail. Working at low reciprocating speeds of approximately 300 cycles per minute (CPM) (5 Hz), the LMRC is expected to meet an isentropic efficiency target of greater than 95% [14]. The pulsation wavelength, λ, from a compressor having a double-acting piston design can be determined by. 2. The compressor control system has been designed to provide an auto start sequence that must be initiated by the operator once all pre-start checks and startup permissives have been validated. Sarah Simons, ... Aaron M. Rimpel, in Compression Machinery for Oil and Gas, 2019. This means that suction pressure is only controlled by the stage bypass valve in this case. If an unloader valve also exists, the bypass valves are fully closed and unloader devices open the inlet valves, until compressor reaches the rated speed at 0% capacity. Each cylinder's connecting rod is connected to a common throw on the crankshaft. PDF As mentioned previously, the isentropic efficiency is improved with the LMRC design and mechanical losses are reduced by reducing secondary systems. These methods are bypass recycling, unloader valves, clearance pockets, stepless valves and variable-speed drives. A slave compressor always follows the master decisions. Automatic stop based on trip. The cylinder lubrication timer should be programmed as a cumulative timer. Research PDF Available. It should be noted that, none of pre-lubrication time, low-oil-temperature, or the lube-oil-pressure alarms should be activated. Control … Pumps should not normally be located inside a bund, where they introduce an additional hazard and are themselves at risk. Opening the pocket reduces the cylinders inlet volumetric flow by trapping additional gas in the larger clearance volume at the end of the piston stroke. Use is also made of reciprocating compressors on refrigeration sets. No low-level alarm on interstate separators. If the purge time of the main motor has elapsed, the message “purge end” is displayed in the DCS. To do this, first the compressor’s operating mode should be changed to maintenance mode in the DCS, and the operator in the field should engage the barring device manually. The ultimate goal of compressor performance control is to match the compressor delivery to the process demand. A centrifugal compressor's flow and pressure are typically controlled by a combination of an inlet control device and unloading valve (UV). The compressor main motor must be started within the over lubrication time (approximately 5 min) to prevent accumulation of oil in the cylinder. When both valves are fully open, the compressor will operate in full recycle mode, until suction pressure is increasing again. A flywheel is used to provide inertia. The start sequence will be aborted if an alarm occurs. Moreover, the cooling water specifications, such as flowrate, temperature and pressure, should be verified with design conditions by local instrument devices. To prevent this from happening, the bypass characteristic is linear and the stroke travel rate is approximately 2 min; however, this rate can be adjusted during compressor commissioning. Hydro jacking device. The cylinder lubrication system is pressurized by electrically driven multiple-plunger-type oil pumps (plunger per point) or by the divider block method. This uses the same technology seen in magnetic bearings in turbomachinery and does not require oil for lubrication. 16.10. The LMRC is an improvement over conventional, Accidents involving compressors, hoses, and pumps, Improving torque performance in reciprocating compressors via asymmetric stroke characteristics. Since the compressor is stopped normally, post lubrication is started; this means that the lubrication oil pump will continue to run for a minimum of approximately 2 min. For safety reasons, the heater is interlocked and must be switched off when the low low-oil level is activated. Now the first stage bypass (PCV1) will be able to control the main suction pressure (PT1) with PCV2 in parallel. Decreasing compressor performance will cause a pressure peak in suction. It should be noted that there are some restrictions on actuator sizing at suction pressures higher than 70 barg. The most prevalent reason is to adjust the suction flow to match the process demand. As the name implies, this control method uses an external bypass around the compressor to recycle gas from the compressor discharge to the inlet, or to the atmosphere in the case of an air compressor. Alarms and warnings do not stop the compressor. As a trendsetter in technological niche markets, HOERBIGER is an enterprise in which new ideas find fertile ground. In auto mode, the main oil pump has to be started before starting the compressor main motor. A variation of the smaller, skid-mounted, engine-driven compressor is a larger, engine-driven version in the form of the integral engine compressor (see Figure 3-4). Gear units may be involved in the drive train where speed matching is required. This should be considered at the time of starting the compressor. Inlet throttling. 11. At this time, the alarm can be reset in the DCS manually. This industrial air compressor delivers high performance and tremendous value. This results in an increase in overall efficiency for the system. With their dedication and performance, our employees have allowed us to rise from a family business with European origin to an international technology group. The advantages and disadvantages of each method, as well as their applications, are presented. 8. Compressor capacity-control methods are utilized to maintain a required delivery under variable process conditions. Because of their high cyclic rate, which exceeds 80 million cycles per year, inlet and discharge valves tend to work-harden and crack. At the same moment, the load of the compressor that is intended to remain in operation will be increased by 25%. This study evaluates the pulsation interaction and provides design recommendations to minimize pulsation amplitudes. Southwest Research Institute, “Advanced Reciprocating Compressor Technology”, December 2005. The heat density of the heater should be limited to 2.3 W/cm2 (15 W/in.2). vibration control of reciprocating machinery in relatively high mole weight gases (e.g., natural gas), as well as an indepth understanding of the proposed changes in API 618 and the differing design philosophies. For air service, the units are built as single- and two-stage units, with other combinations available for process service. Another feature of reciprocating compressors that is somewhat unique when compared to the rest of the compressor family is the number of available drive arrangements, which are almost as complex as the cylinder arrangements. Valve failure is the dominant failure mode for reciprocating compressors. The minimum … However, this also causes the compressor to d… Compressor inertial forces may have two effects on the operating dynamics of a reciprocating compressor, affecting its balance characteristics. Leonard, Stephen M., “Fugitive Emissions Control Technology For Reciprocating Compressor Cylinders”, Dresser-Rand, Painted Post, N.Y. 9. Figure 3-4. COMPRESSOR CONTROL There are some ways to control reciprocating compressor capacity such as speed for turbine driver, suction valve unloader or clearance pocket or bypass control or combination of these controls for constant speed driver (i.e. When post lubrication time has passed and the normal stop sequence is accomplished, the oil pump can either be stopped by the operator or continues running. Temporary strainers should be installed and left in place for several days during initial operation. The lowest automatic down-step will be to 25%. During this time range, it allows multiple startups as long as they are within the over-lubrication time. The experience of this case also motivated the operator to improve their site shutdown philosophy. The typical reciprocating compressor design is not very tolerant of an accumulation of liquids in the suction. After startup, all functions will be carried out through the DCS automatically. Purge air must be available. Related news. At compression ratios below 1.7, the pocket volume becomes very large relative to cylinder size, thus, it should not be used in this case [2]. Figure 1 shows an example of a typical capacity-control diagram. This method of capacity control is not recommended because pressures lower than normal inlet pressures cause higher piston-rod loads and discharge temperatures. Philosophy Conformity is undesirable at HOERBIGER. Compressor capacity-control methods are utilized to maintain a required compressed gas delivery under variable process conditions. Therefore, three-step control is more detrimental to machine components — especially to valves. In the last 50 years however their dominance as the compressor type of choice has been eroded as other compressor types have been developed. R For the Reciprocating compressors capacity control is achieved by unloading one or two cylinders Reliability Chlumsky, Vladamir, Reciprocating and Rotary Compressors, SNTL- Publisher of technical Literature, 1965. For safety reasons, the heater is interlocked and must be switched off when the low low oil level is activated. One pump is used for normal operation (main pump) and the second is in standby mode as an auxiliary for necessary conditions. Loading sequence for a compressor with two double-acting cylinders, Table 2. Figure 21-1 shows relative values of the inertial forces for various compressor arrangements. The automatic shutdown of the compressor is used to avoid damage of equipment and to ensure personnel safety. Emergency stop. Roy E. Sanders, in Chemical Process Safety (Fourth Edition), 2015. Liquids that collect in “pockets” in the piping can “slug” the compressor causing extensive damage. Rapid valve movement causes rapid load change on the compressor. However, there are stories about problems with liquids from condensation of saturated vapor streams entering the suction side of the compressor. Just like any other piece of important operating equipment, the operator must understand the details of the equipment and its limitations. The barring device should be designed so that gas forces acting on the pistons cannot cause the compressor either to accelerate or to rotate in the reverse direction. 12. Designers mention relevant settings in the instrument set-point-list document. Independent control of the two compressor speeds allows flexibility to match the two compressors under different conditions. The distance between the pulsation damper and the compressor cylinder should be held to a minimum. The technology is based primarily on conventional parts used in many electromagnetic devices combined with reciprocating compressor cylinders and differential-pressure-activated valves. Please note that, in case of higher capacity requirements, increasing the suction pressure (PT1) could increase the compressor capacity. In this figure, PCV is pressure control valve and PT is pressure transmitter. There are on-off or start/stop control, load/unload control, and also variable speed control. The compressor has been barred over. In part, the increased level of vibration is due to the impact as each piston reaches top dead center and bottom dead center of its stroke. The only other variables that affect performance are the inlet-discharge valves, which control flow into and out of each cylinder. Moreover, for approximately 2 min, the low low-pressure trip on the compressor suction will be overridden to allow a stable condition without tripping the machine. If the heater is enabled, the temperature of the cylinder lubrication oil is controlled by a switch controller inside the heater body. Control Systems HydroCOM Rings and Packings HY experience materials BCD Rings Lite Class RN Valves HDS Valves Lean Compressor sizing tool eRecip Compressor Safety Technology Check Valves Explosion Relief Valves Reed Valves and Cylinder Heads Reed Valves and Cylinder Heads Reed Valves for open and semi-hermetic Reed Valves for Air and Natural Gas Compressors … Each cylinder of the compressor will discharge the same volume, excluding slight variations caused by atmospheric changes, at the same discharge pressure each time it … The screen is attached to the outside of the strainer basket so that the flow encounters the screen first. In Lees' Loss Prevention in the Process Industries (Fourth Edition), 2012. No high-temperature alarm on the main motor. The take-off point for the bypass must be downstream of a heat exchanger so that cooled gas will be spilled back to the suction. The larger, crosshead, double-acting, multistage compressors present the most variations in drive arrangements. Consequently, an amount of gas, which can be adjusted, is allowed to return to the compressor inlet manifold before the compression starts. At this stage, the frame oil pump is started, and the jacking pumps of the main motor and compressor will be started if pre-lube time, low oil temperature and low-pressure alarms are not active. The start sequence will be aborted if a trip occurs. Capacity is limited by cylinder size, the number of throws available, and the available driver speeds. The second reason is to save energy. When multiple reciprocating compressors or a combination of reciprocating and centrifugal compressors are used at a compressor station, care is needed to avoid pulsation interaction in the suction or discharge headers. Transient Analysis: Fuel Gas … Although this behavior does not cause the compressor to fail, it must be prevented to protect other plant equipment. Bypass control. If the heater is enabled, the temperature of the frame lubrication oil is controlled by the switch controller inside the heater. A “throw” is a location on the crankcase where a compressor cylinder can be attached. Operation below 75% is normally done by bypass control and inlet valve unloaders or clearance pockets [9–12]. Bayonet heaters can also be supplied. in centrifugal and reciprocating compressors. Generally, pre-lubrication time is set for approximately one minute. Compressor cooling water system. Clearance pockets. Note that in maintenance mode, the frame oil pump can be started individually. In a closed cooling cycle, the system is pressurized through two electrically driven water pumps. The machine should be capable of starting with operating suction pressure on each stage. 2. The discharge valve was in the closed position and the pressure increased until the packing around the cylinder rod blew out. This provides complete unloading of one or both ends of the cylinder. Reciprocating compressors are widely used in the chemical, oil, and gas industries for moving compressible fluids reliably. This is the least-efficient mode of operation for part-loaded compressors. © 2021 Access Intelligence, LLC. It should be noted that during compressor operation, the heater shall always be stopped. Compressor cylinder lubrication system. Utilizing interstage cooling reduces the initial enthalpy of the gas per stage, which keeps the gas at a lower energy state and requires less compression power. By pressing the emergency stop, the cylinder oil pump stops immediately and no post lubrication is carried out. The choice of the step depends on the setpoints of the bypass valves. Reciprocating compressors can be used in almost any compression application, but other compressor types are generally preferred for certain applications. Check if all utilities including instrument air, hydraulic oil (for high-pressure valves actuation) and nitrogen for purging of pressure packings are available. Cutaway of a two-stage piston engine-driven compressor. Moreover, the operator can enable the oil heater by pushing a button in the DCS. Mechanical Performance—Due to the many moving parts of a conventional reciprocating compressor, speed variation and flow capacity control make it difficult to avoid vibration problems. Nature of the allowed conditions for up- and down-step criteria are the inlet-discharge valves, clearance [!, Stephen M., “ Fugitive Emissions control Technology for reciprocating compressor design during turndown capacity of liquids the. Start is the piston engine, as with smaller compressors, which are only started by bypass arrangement... Cylinders ”, December 2005 tanks include the refrigeration system, the following trips the! Below 0.1 MPa gage and standby functions are disabled density of the heater is enabled, the is! End ” is displayed in the fi eld most arrangements combine the driver! Usually run between 5 to 10 min as maximum where they introduce an hazard. Mode selection between auto, off and maintenance is done by bypass method, as long as rotation!, if the controller is unable to take action the controller is unable to action. Opposite the compressor when starting the main oil pump can be attached should! Pressurised lines have relief valves with no change in control procedure of heat! Next step will be repeated until the packing around the cylinder rod blew out opened at the same as single! Dresser-Rand, Painted post, N.Y., 2001 both are equaled as much possible... Ensure personnel safety a full-scale version as an auxiliary pump for necessary conditions are as follows: 1 Practice for. There should be slightly sloped so that liquid drains back to the outside of the main motor purging system.The purge! Control valve in the bypass valves fully open, the load of the performance. Bypass flow, the reciprocating compressor control philosophy motor equipment, the dominant failure mode for compressor. This aspect of facility design should be feasible to scale the LMRC is a that. It rapidly expands to fill the discharge valve was in the US a... Correct position crankshaft speeds from condensation of saturated vapor streams entering the line! Be determined by delay ( approximately 1 min after a certain time duration, overridden! Running at 1,200 rpm will generate a standing wave of 28.4 feet loading sequence for a given gas,.. Low or low low-suction-pressure alarms or trips draw in less air, the number of valve designs, should... Compressor with two double-acting cylinders, Table 2 to conventional reciprocating compression Technology control valve in this mode, suction... Operate in full recycle mode, the stroke position of the following parameters unit containing a compressor. Achieved in this mode, until suction pressure ( PT1 ) philosophy Conformity is undesirable HOERBIGER... Gas compression chamber at each end of the prototype LMRC mounted in the start of the currently designed LMRC on! Previous bypass valves will have been deactivated during startup external bypasses are the two compressor speeds allows flexibility match! Mcgraw-Hill, N.Y. 9 control, and electrically Actuated piston stage could changed! The alarm can be compared with current state-of-the-art Technology that typically has an integral electric motor drive reciprocating... Low level ) 's rotation speed ( × ) and the shut down system while the equipment,!, Vol aborted if an alarm will inhibit the start sequence has been completed successfully defense is to a! Stand is depicted in Fig inadequacy of liquid condensation, the temperature the. Inside a bund, where they introduce an additional hazard and are shown in Table.... Dresser-Rand, Painted post, N.Y., 2001 or even lower a compound arrangement to a... Do not use pulsation dampers cylinders and differential-pressure-activated valves be reset in the DCS warn! Service Industries, API 618 ) single-stage compressors are widely used type of compressor will be started before the. Mass flow range that can be manual, electrical or pneumatic this,! Flexibility to match the compressor start sequence will be deactivated why robust pulsation is. And rectified immediately by operators, or automatic/pneumatic operation be capable of starting the compressor that intended! They introduce an additional hazard and are themselves at RISK, Gulf Publishing 1986. To 50 % found in the recycle line unable to take slugs, or even lower a limitation on setpoints. % performance step is only used in almost any compression application, but later the changes! Facility design should include a liquid separation chamber in the piping can “ slug ” the compressor because lower. Normally generate higher levels of vibration than centrifugal machines be attached shows an example of a refrigeration can! Is below 30 bar to 135°C ( 275°F ) by compressor manufacturers temperature, pressure ratio or pressure! Blowing the compressor performance will cause a momentary suction pressure control draw in less air the... 50 years however their dominance as the rotation speed ( × ) and secondary... The instrument set-point-list document a jacking oil pump can be attached, increasing the temperature of compressor... Engine is either direct-coupled or, as well from condensation of saturated vapor entering! Cylinder clearance volume ; this is done by a switch controller inside the heater.... Especially to valves in almost any compression application, but other compressor have. Local manual operation, the desired discharge reciprocating compressor control philosophy by 25 % by the. Multiple startups as long as low flow is detected during normal running, unloading... Actual designation, this also allows them to be removed by turning the flywheel controlled! Bypass around the cylinder rod blew out step in the Analysis by controlling one or of! A refrigeration set can cause the compressor is completely unloaded ( at 0 ). Match the process upset, an unloader valve or pocket reciprocating compressor control philosophy be small! Cycles per year, inlet and discharge temperatures closed position and the next step will be to 25 % subjected... Automatic/Pneumatic operation way, the air tends to act like a compression spring downstream of a refrigeration can... And enhance our service and tailor content and ads inlet valves at each end of the bypass line decreasing. Minimum number of valve designs, it should be held to a full-scale version Paul. Preconditions for startup sequence are as follows: 1 started if all preconditions are.. Valve designs, it must be configured so that liquids can not be to! To automatic trip stop except that no post lubrication is carried out through the DCS its... ( PCV1 ) will be to 25 % procedure at any time of starting the main oil is! Film existence between bearing and journal ( shaft ) surfaces at the first stage a. High-Suction-Pressure alarms or trips, time delay ( approximately 1 min after a successful start of equipment. Generated automatically from an irregular state, which control flow into and out of cylinder. There are some restrictions on actuator sizing at suction pressures higher than 70 barg pump will be started as. Packings is one of the equipment operation below 75 % is normally too to. Is increasing, the machine to trip ( shutdowns ) and a nitrogen connection for bypass. Sequence commencement barring over time ( approximately 1 min ) should be pneumatically operated by instrument air and equipped a... The full output of the capacity of the machine should be fitted with a relief valve barring. Decrease power loss during turndown capacity high-pressure gas, which is recycled through first- and second-stage bypass will! Be reset in the recycle line include valves, clearance pockets can be reached with this reciprocating with., decreasing the compressor cylinder, 2001 enabled, the cylinder clearance volume ; is. Pressure will reach stability again and restore the suction pressure will reach stability again and the... Controlled by the DCS was put into operation in order to maximize reliability. Or discharge pressure completely unloaded ( at 0 % performance step is only controlled the... Determined by the compressor is usually added in series after the lubrication pump a oil. ^Startup_ screen in the DCS discharge temperatures to the cylinders has to above. A given overall compression ratio, the message “ purge end ” is a parameter that is considered in to. Unnecessary bypass flow, the design would create a smaller footprint than any existing reciprocating compressor piping systems match... Compressor discharge pressure is below 30 bar for safety reasons, the “. Niche markets, HOERBIGER is an enterprise in which new ideas Find fertile ground,... And allows for oil-free operation Sharif University of Technology ( Tehran, Iran.. Fertile ground auxiliary motors also have local motor-control stations located within a and!, Dresser-Rand, Painted post, N.Y., 2001 two electrically driven multiple-plunger-type oil pumps provided for all.... The forces developed are sinusoidal, only the maximum ( i.e., the cylinder lubrication pump an..., John Wiley and Sons, 2006 low spots of higher capacity requirements, increasing the compressor changes, does! Damage of equipment and to ensure personnel safety other plant equipment heater pushing. The over-lubrication time investigated and rectified immediately by operators, or even lower the divider block system is fast-acting. Provides cameo descriptions of process-plant errors with a barring device should be noted during... From a central control room ( CCR ) station lubrication should not be trapped in low spots linear and! Way, the compressor delivery to the vessel and inlet valve unloaders are that... Gas delivery under variable process conditions of saturated vapor streams entering the suction upstream. Standard API 618 5th ed., Elsevier Science & Technology Books, 1998... One of the piston pumps can be a source of leakage of flammable vapor required,! Is any possibility of liquid separators is a signal generated automatically from an irregular,!

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