4.2.1
COMPRESSOR PERFORMANCE – GLOSSARY OF TERMS
GLOSSARY OF TERMS FOR ARIEL VER 7.3.1 PERFORMANCE PRINTOUT COMPRESSOR DATA: ELEVATION, m: Elevation is the distance of a compressor above mean sea level. Elevation effects atmospheric pressure and therefore absolute pressure.
BARMTR, MPaa: The site atmospheric pressure based on the elevation of the site above mean sea level.
AMBIENT, C: Ambient temperature is the surrounding temperature at a compressor installation. The range of ambient temperatures is required for the proper application of gas coolers, drivers and auxiliary systems.
TYPE: Just a label. Type of driver such as gas engine or electric motor or fin/fan cooler HP draw.
FRAME: This is the Ariel compressor frame used. Frames with larger crankshaft and piston rod diameters have higher horsepower and rod load ratings.
STROKE, mm: The stroke is the distance the compressor piston moves getting from inner dead center to outer dead center. Higher speed frames have shorter strokes.
ROD DIA, mm: The compressor piston rod has the crosshead at one end and the compressor piston at the other. This is the part that is pulled (tension) or compressed (compression) while the piston moves back and forth due to the gas pressure acting on the piston faces.
MFG: Manufacturer. Just a label. Usually lists driver manufacturer. MAX RL TOT, kgf: Maximum Total Rod Load, kgs. The sum of the maximum tensile
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load placed on the piston rod while it moves inward plus the maximum compressive load placed on the piston rod while it moves outward is used as a frame rating.
MAX RL TENS, kgf: Maximum Rod Load in Tension, kgf. The highest tensile load allowable on the piston rod.
MAX RL COMP, kgf: Maximum Rod Load in Compression, kgf. The highest compressive load allowable on the piston rod
MODEL: The particular driver model is listed here.
RATED RPM: The maximum rotating speed rating for this particular frame. The compressor is designed for full-time operation at this speed.
RATED kW: The maximum power (i.e. horsepower) the frame can pull from a driver without overstressing the compressor frame.
RATED PS, m/s: This is the average speed at which the compressor piston travels. Two times the stroke (in meters) times the Rated RPM.
CALC RPM: This is the RPM used for this performance run.
CALC kW: Compressor power pulled from the driver for this set of pressures, temperatures and RPM. This power plus the fan power (if, say, a fin/fan cooler is being driven from the auxiliary end of the driver) must be less than the available driver power shown as kW.
CALC PS, m/s: This is the average speed at which the compressor piston travels. Two times the stroke (in meters) times the RPM for this particular performance run.
kW:
The site available power available from the driver for continuous operation.
Compressor power plus fan power (typically a percentage of site available kW) must not exceed the site available power listed here. 8
SERVICE STAGE DATA: FLOW REQ'D, E3m3/D: The design flow requested by the customer. This is not the flow that the compressor is moving, rather, it is a label showing what flow was requested. It is also used as a target by the computer when, for a given cylinder selection, a 'load to flow' option is selected.
FLOW CALC, E3m3/D: This is the flow rate the compressor is moving. For the cylinder sizes, pressures, temperatures, and pocket settings shown, the compressor is moving the volume shown here. For example, say 3.0 E3m3/D is shown here. This means 3.0 Thousand Standard Cubic Meters of gas will pass through the compressor in 24 hours.
CYL kW PER STAGE: Cylinder power per stage. The power used by each stage of compression. Does not include frame friction power.
SPECIFIC GRAVITY: The weight of the gas being compressed relative to air e.g., 18.8 MW natural gas/28.97MW air equals a gas gravity of 0.65.
RATIO OF SP HT (N): Ratio of specific heats 'N'. A gas characteristic that indicates how hot the gas will get upon compression. Air has a high N value so it will have a higher discharge temperature for a given amount of compression compared to, say butane. More stages of compression may be needed for high N value gases.
COMP SUCT (Zs): Compressibility Factor, Z, for the gas at suction conditions. Accounts for the fact that a given amount of gas occupies less space at high pressure than the Ideal Gas formulas indicate.
COMP DISCH (Zd): Compressibility Factor, Z, for the gas at discharge conditions. Accounts for the fact that a given amount of gas occupies less space at high pressure than the Ideal Gas formulas indicate.
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PRES SUCT LINE, MPaa: The pressure you would read on a pressure gage in the gas piping upstream of the compressor cylinder (for the first stage this is at the customer connection at the scrubber inlet connection).
PRES SUCT FLG, MPaa: The pressure gauge reading you would get right at the inlet flange on the compressor cylinder itself.
PRES DISCH FLG, MPaa: The gauge reading you would get right at the discharge flange of the compressor.
PRES DISCH LINE, MPaa: The gauge reading you would get downstream of the cylinder. For the case of the last stage cylinder, this pressure would be measured at the after-cooler outlet (the customer discharge connection).
PRES RATIO F/F: Pressure Ratio Flange-to-Flange. Example, 500kPaa/100 kPaa is a pressure ratio of 5.0. Discharge absolute pressure divided by inlet absolute pressure.
TEMP SUCT, C: The customer’s inlet gas temperature.
TEMP CLR DISCH, C: The requested cooler gas outlet temperature for each stage; usually maximum ambient temperature plus 30 C degrees inter-stage and a 20 C
approach for the after-cooler.
CYLINDER DATA: CYLINDER MODEL: A casting pattern number. Each pattern is available in a couple different bore sizes.
CYLINDER BORE, mm: The bore size of the compressor cylinder. The compressor piston diameter is this size minus several thousandths of an inch for running clearance.
CYL RDP (API), MPag: Compressor Cylinder Rated Discharge Pressure. The pressure not to be exceeded during normal operation. 10
CYLINDER MAWP, MPag: Cylinder Maximum Allowable Working Pressure. The pressure not to be exceeded even by the relief valve setting. The pressure at which the cylinder would be expected to actually burst or fail is several times this number.
CYLINDER DISP, m3/h: Cylinder Displacement, Cubic Meters per Hour. Each sweep of the compressor piston through its stroke displaces a volume equal to the piston area times the stroke. This volume times RPM is the maximum actual cubic meters of gas that particular bore size cylinder could ever move. Clearance volume between the piston and heads and valves reduces the amount of gas that actually moves through the cylinder.
PRES SUCT INTL, MPaa: The gauge pressure you would measure inside the cylinder; after losses in the inlet passages.
TEMP SUCT INTL, C: The temperature of the gas once it has been drawn through the cylinder inlet passages and inlet check valves. This temperature is higher than the suction side outside the cylinder.
SUCT Zsph: The compressibility factor calculated for the gas actually in the compressor cylinder at the pressure and temperature inside the cylinder at the end of the suction stroke.
PRES DISCH INTL, MPaa: The gauge pressure you would measure inside the cylinder; before losses in the discharge passages.
TEMP DISCH INTL, C: The temperature of the gas once it has been compressed prior to its being pushed out through the cylinder discharge passages and discharge check valves. This temperature is higher than the discharge side outside the cylinder.
HE SUCT GAS VEL, m/s: The average speed of the gas passing through the inlet check valves in meters/second.
HE DISCH GAS VEL, m/s: The average speed of the gas passing through the discharge
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check valves in meters/second.
HE SPCRS USED/MAX: A spacer ring underneath a compressor valve adds clearance volume. The number of spacers used and the maximum number that can be installed are shown.
HE VOL PKT AVAIL, %: The amount of clearance that can be added by backing out the Variable Volume Clearance Pocket to full open. Clearance expressed as a percentage is the total clearance volume divided by the swept volume of that end.
HE VOL PKT USED, %: The percentage that the Variable Volume Clearance Pocket is open. It varies from zero to 100%; not to be confused with % Clearance. The Variable Volume Clearance Pockets use a hand wheel screwed plug in the head end that backs out as you turn it thereby adding clearance volume to the head end. Adding clearance volume to a compressor cylinder reduces the flow rate through that cylinder without wasting horsepower. Adding clearance delays opening of the suction check valves. The clearance volume in a cylinder, at the end of the discharge stroke is at discharge pressure. As the piston moves away from the head, this pressure drops until it is slightly below the pressure of the gas in the inlet passage at which time the suction check valves will open due to a small amount of differential pressure across the valve. The valves are not in any way set to open at a certain pressure. Gas enters the compressor only while the suction check valves are open. Added clearance volume is a way to deliberately delay opening the suction valves (the cylinder draws in a smaller amount of gas) to control capacity/throughput.
HE MIN CLR, %: The Head end clearance volume (expressed as a percentage of swept volume which is piston area times the stroke) due to piston-to-head clearance and valves with no added clearance volume.
HE TOT CLR, %: The Head end fixed clearance plus whatever clearance has been added by opening the Variable Volume Clearance Pocket and/or adding spacer rings.
CE SUCT GAS VEL, m/s: The average speed of the gas passing through the inlet check
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valves in meters/second.
CE DCH GAS VEL, m/s: The average speed of the gas passing through the discharge check valves in meters/second.
CE SPACRS USED/MAX: A spacer ring underneath a compressor valve adds clearance volume. The number of spacers used and the maximum number that can be installed are shown.
CE MIN CLR, %: The crank end clearance volume (expressed as a percentage of swept volume, which is piston area times the stroke) due to piston head clearance and valves with no added clearance volume.
CE TOT CLR, %: The crank end clearance volume (expressed as a percentage of swept volume, which is piston area times the stroke) due to piston head clearance and valves and any spacer rings that have been added.
SUCT VOL EFF HE/CE, %: Head end Volumetric Efficiency. The suction check valves open once the pressure in the cylinder falls slightly below the inlet passage pressure. The suction valves, therefore are not open for the full stroke, but only some percentage of the stroke. The volumetric efficiency is the percent of the compressor stroke for which the suction valves are open. It is not an energy efficiency value and it is not an indication of wasted horsepower. High clearance volume and high pressure ratio lowers the volumetric efficiency. It is an indicator of how large a cylinder bore size is needed to move the required volume of gas.
DISCH EVENT HE/CE, ms: Crank end Volumetric Efficiency. The suction check valves open once the pressure in the cylinder falls slightly below the inlet passage pressure. The suction valves, therefore are not open for the full stroke, but only some percentage of the stroke. The volumetric efficiency is the percent of the compressor stroke for which the suction valves are open. It is not an energy efficiency nor is it an indicator of wasted horsepower. High clearance volume and high pressure ratio lowers the volumetric efficiency. It is an indicator of how large a cylinder bore size is needed to move the required volume of gas. 13
SUCT PSEUDO-Q HE/CE, %: A number that signals if standard valving is suitable. For example, high mole weight gases or very low volumetric efficiencies will cause this number to be out of range. Hoerbiger Valve Co. requires that Pseudo Q% be less than 15%.
It is the ratio of pressure drop across the valves to pressure drop across the whole cylinder. It is valve pressure drop divided by the sum of valve passage pressure drop plus valve pressure drop plus pressure drop across the piston face. Heavy gases, 0.8 and higher, propane (1.5 SG), and carbon dioxide (1.5 SG) often exceed 15%. To get back below 15%, run performance at reduced speed.
GAS ROD LD COMP, kgf: The compressive load on the rod, which occurs as the piston moves away from the compressor frame.
GAS ROD LD TENS, kgf: The tensile load on the rod, which occurs as the piston moves towards the compressor frame.
GAS ROD LD TOT, kgf: The sum of the out and in rod load. XHD PIN DEG/% RVRSL: Gas Rod Load Reversal. The load on the piston rod must reverse from compression to tension so the cross head pin can maintain lubrication.
FLOW CALC, E3m3/D: This is the flow rate the compressor is moving. For the cylinder sizes, pressures, temperatures, and pocket settings shown, the compressor is moving the volume shown here. For example, say 3.0 E3m3/D is shown here. This means 3.0 Thousand Standard Cubic Meters of gas will pass through the compressor in 24 hours.
CYLINDER kW: The power each cylinder pulls from the compressor frame.
4.3.0
COMPRESSOR - GENERAL DESCRIPTION
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