Performance Assessment Of A Two-Stage Reciprocating Air Compressor

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EJERS, European Journal of Engineering Research and ScienceVol. 4, No. 4, April 2019Performance Assessment of a Two-Stage ReciprocatingAir CompressorIkpobari Amuele Nwakpang, Barinaadaa Thaddeus Lebele-Alawa, and Barinyima Nkoi and the painter’s spray gun. Usually, a compressor is drivenAbstract—This paper presents the performance assessmentof a two-stage reciprocating air compressor operating at an Oiland Gas Terminal in Rivers State, Nigeria. The main focus wasto investigate the effects of control parameters and clogging onthe performance of the compressor. Data were obtained fromthe manufacturer’s manual, field reports and the fieldoperator’s log sheets. Relevant thermodynamic equations wereused to determine and analyse appropriate control parametersof the compressor. Data were also analysed using variousappropriate compressor equations and a thermodynamicanalysis of the compressor was done to evaluate itsperformance. The outcome of all the analyses showed that thecompressor experienced 26% loss or reduction in thevolumetric efficiency, 8% loss in the isothermal efficiency,11.1% loss in volume flow rate and 21% decrease or reductionin the mass flow rate due to clogging when compared with thedesign specifications. The analysis also showed that theperformance of the compressor was affected by several otherfactors including the climatic and environmental conditionssuch as the high operating ambient temperature of the inlet airto the compressor. It revealed that the effects of cloggingcaused a continuous rise in temperature which reduced thedischarge pressure, mass and volume flow rates, isothermaland volumetric efficiencies; thereby reducing its performancein comparison with the design specifications. The resultsfurther revealed that clogging was a major factor that affectedthe performance effectiveness of the reciprocating compressor.Index Terms—Isothermal Efficiency, Compressor ,Compression, Discharge Pressure, Volumetric Efficiency,Intercooler Pressure.I. INTRODUCTIONCompressors are of vital importance in modern-dayindustries. They play tremendous roles in ensuring thatindustrial processes and works are done [1]. Compressorsare mechanical devices that can compress a substance ingaseous state [2]. When air is used as the working fluid in acompressor, it is called an air compressor. This means thatan air compressor is a machine that increases the pressureand temperature of air [3]. During the process of aircompression, the inlet/intake pressure of the air is usuallyraised to a higher exhaust pressure [4].Air compressors have earned a fair amount of popularityin several industries as a result of the various uses ofcompressed air. Some of such uses and applications ofcompressors and compressed air are in the industries and inequipment such as refrigerator, air conditioner, trucks andfor the filling of apparatus used for breathing, bicycle pumpPublished on April 19, 2019.Authors are with I: ria.(e-mail:by a prime mover such as a diesel engine or electric motor[5].In general, air compressors are sometimes classifiedaccording to their working principles or principle ofoperations, according to their actions and according to theirnumber of stages. Furthermore, based on the principle ofoperation, compressors are classified into positivedisplacement compressors and non-positive displacement ssors are also grouped into reciprocating and rotarycompressors. They are also called piston compressors [7].Reciprocating compressors operate on the same principle asthe old, familiar bicycle pump which is by means of a pistonin a cylinder [8].A reciprocating air compressor increases the pressure ofair via the use of piston by ensuring that the volume isreduced in such a way that it takes in successive volumes ofair, confines the air within a space called the cylinder andelevates the air to a higher pressure [9]. The pistoncompressor is considered one of the most widely usedequipment for air and gas services and it embraces the use ofpiston – cylinder arrangement such that the piston is drivenby a crankshaft and that causes a displacement of the pistonin the cylinder thereby resulting in a rise in pressure [10].Some of the key components or parts of a reciprocatingair compressor are cylinder, crankshaft, piston, suction/inletand outlet/delivery valves and connecting rod [11].Reciprocating air compressors may be single or doubleacting, single stage or multi-stage [11], [12]. In a singlestage reciprocating air compressor, compression takes placein one stage while the multi-stage type involves more thanone compression stage for achieving the required highpressure and low temperature by using intercooler [13]. Anexample of the multi-stage compressor is the double or twostage compressor under consideration in this work.Apart from the segmentation of the compression stagesinto different stages to help increase the pressure and reducethe temperature during the compression process for theimprovement of the performance of the compressor, onemajor concern is the problem of compressor clogging whichit experiences - especially in a humid environment. The aircompressor under study is located at an Oil and GasTerminal in Rivers State, Nigeria. The said compressor hadsuffered breakdown in the past due to clogging therebyreducing production because of the period used inmaintenance. The aim of this study, therefore, is to assessthe performance of the compressor with regard to theproblem of clogging. The objectives of this research are toinvestigate the effects of the control parameters (pressure,temperature, mass and volume flow rates) on the74

EJERS, European Journal of Engineering Research and ScienceVol. 4, No. 4, April 2019performance of the compressor, to investigate the effects ofclogging on the performance of the compressor and to do athermodynamic analysis of the said compressor to assess orevaluate its performance.In a bid to improving the efficiency of two-stagereciprocating air compressor due to high temperature, anexperimental investigation was performed involving the useof different intercoolants such as air, water, cooling source,radiator coolant and ethylene glycol. Consequently, it wasconcluded that the isothermal work required to compress theair and the power required to drive the reciprocatingcompressor reduced with respect to the intercooling [13].Reference [14] carried out a thermodynamic analysis of areciprocating air compressor. During the thermodynamicanalysis, they found out that the clearance volume is one ofthe parameters on which the performance and efficiency ofthe compressor depend.Reference [15] presented a paper on improving theperformance and development of two stage reciprocating aircompressor with particular focus on the case study of areciprocating air compressor of a locomotive with theassociate problems, diagnosis and solutions highlighted. Itinvolved a simulation model which they did. The simulationmodel can predict volumetric efficiency, free air delivered,indicated power, shaft power, cylinder air pressure, cylinderair temperature, resultant torque and the mass of air drawnin or discharged out per cycle, by varying any operatingparameter like speed, discharge pressure, etc. and physicalparameters like clearance volume, crank radius, connectingrod length and cylinder diameter. Also, compressed air wasproduced without the use of electricity. That was done withthe use of speed breaker setup in roadways. Instead of usingelectric drive, mechanical drive was used to generate thecompressed air. This method of using speed breakers for thegenerating of electricity is of great value especially becauseof the over reliance on electricity for the production ofcompressed air which has been the norm for many yearsnow [16].II. MATERIALS AND METHODSA. MaterialsThe manufacturer’s manual, operational data and fieldreports for the air compressor under investigation were usedfor this study. From these data, values were computed andused for the assessment of the performance of thecompressor. Also, relevant operating parameters such as theinlet and outlet temperatures and pressures of thecompressor were obtained for its thermodynamic analysis.B. MethodsThe analysis and assessment of the compressor were doneto achieve the aim and objectives of this research with theuse of relevant fundamental equations that govern a twostage reciprocating air compressor, relevant models andthermodynamic analysis.1) Analytical ModelA thermodynamic analysis was chosen as a suitableDOI: od for analyzing the compressor under consideration.There are three types of compression processes which arepossible in the reciprocating air compressor. They arepolytropic, isothermal and adiabatic compression processes.Fig. 1. Graph showing different compression processes.The area under Fig. 1 shows the workdone incompressing the air to P2 from P1 and the line with the leastslope (isothermal compression) produces minimum orlowest work. As seen from the graph, isothermalcompression produces minimum work and it is the conditionunder which minimum work can be achieved in acompressor.2) Polytropic CompressionThis process lies between the isothermal and adiabaticprocesses. In Fig. 1, 1-2p is a polytropic process and therelationship between pressure (P) and volume (V) is givenas;PVn C(1)Also, workdone during a polytropic process is given as;n 1 2n P2 2 n W P1V1 1 n 1P 1 (2)where P r p 2 P1 (3)P1 Inlet Pressure (N/m2), P2 Discharge Pressure (N/m2),V1 Inlet Volume (m3), n Index of Compression andr p Pressure Ratio3) Isothermal CompressionIsothermal compression takes place at constanttemperature [14]. Workdone during an isothermalcompression is evaluated as:Wi P1V1 ln rp(4)where P1 Inlet pressure (N/m2), P2 Dischargepressure(N/m2) and rp Pressure Ratio4) Adiabatic CompressionThis type of air compression takes place in the absence ofheat transfer [8]. The workdone during adiabatic75

EJERS, European Journal of Engineering Research and ScienceVol. 4, No. 4, April 2019compression process is calculated using:2 1 1P1V1 rp 2 1 Wa where Index of compression for air WT 9) Overall Pressure Ratio (rp)The overall pressure ratio of the compressor is given asthe ratio of the discharge pressure of the air to its inletpressure.5) Volumetric Efficiency (ηv) 1 C-C r 1np(6)where C Clearance ratioIsothermal efficiency is given as the ratio of theisothermal work to the actual work.WiWrp P2P1(9)Where P1 Inlet Pressure (N/m2) and P2 DischargePressure (N/m2)10) Intercooler PressureFor minimum work condition with perfect intercooling tobe obtained, the intercooler pressure is evaluated as:6) Isothermal Efficiency ( i ) i (8)(5)This is the ratio of the actual volume of air taken into thecylinder during suction stroke to the pistol displacementvolume (PDV) or swept volume.ηv n 1 2nP1V 1 rp 2 n 1 n 1 (7)7) Multistage CompressorMultistage compression involves more than one stage ofcompression and it is done when high pressures are required[17]. It has the two-stage (low and high pressure stages)compression as its typical example where compression ofthe air is done in two stages with an intercooler incorporatedbetween the two stages [18]. The essence is basically toreduce the discharge temperature and increase the dischargepressure to the required pressure {19]. Achieving lowerwork, better capacity and efficiency while maintainingisothermal condition is very difficult since increasingpressure ratio, rp, causes a decrease in volumetric efficiencyand an increase in delivery temperature, T 2 [20]. Thistherefore requires a multistage compressor (a two-stage typein this case) to solve the problem as shown in Fig. 2.Px P1 P2(10)11) Intercooler TemperatureFor complete or perfect intercooling in a two-stagereciprocating air compressor, the intercooler temperature(also known as the intermediate temperature) is given as; PxTx T1 P 1 Where TxPxP1T1 n 1n (11)Intercooler Temperature, KIntercooler Pressure, N/m2Inlet Pressure, N/m2Inlet Temperature, K12) Heat rejected in the intercoolerThe rate of heat rejected in the intercooler in kg/s is givenasQx Cp (Tx-T1)(12) Where mTxT1Cp Mass flow rate, kg/sIntercooler Temperature, KInlet Temperature, KSpecific heat at constant pressure, KJ/kgkIII. RESULTS AND DISCUSSIONFig. 2. P-V diagram showing 2-stage compressor with intercooler8) Total Work Done (WT)For a 2-stage reciprocating compressor with complete orperfect intercooling, WT is given asDOI: http://dx.doi.org/10.24018/ejers.2019.4.4.1130A. Thermodynamic Performance Assessment of the twostage Reciprocating Air CompressorA thermodynamic analysis of the compressor under studywas done to evaluate its performance behaviour with regardto the problem of clogging with the use of the equationsalready deduced, collected data and the operatingparameters of the compressor.76

EJERS, European Journal of Engineering Research and ScienceVol. 4, No. 4, April 2019B. Reciprocating Compressor AnalysisWith the aid of equations deduced and substitution of theappropriate values of the operating parameters, someparameters were evaluated and tabulated as shown in TableI.Inlet PressureP1 (bar)0.92DischargePressureP2 (bar)6.3TABLE I: CALCULATED VALUES OF CONTROL PARAMETERSVolumetricSuctionIsothermal WorkEfficiencyTemperatureWi (KJ/Kg)ηv (%)T1 (K)66.07287298186.2798Isothermal Efficiencyηi 3303.4189.655390.87462DOI: http://dx.doi.org/10.24018/ejers.2019.4.4.113077

EJERS, European Journal of Engineering Research and ScienceVol. 4, No. 4, April 2019TABLE II: AVERAGE COMPRESSOR OPERATING DATA PER DAY (CLOGGING)Volumetric flow Mass flow rate Discharge TemperatureT2 (K)Discharge PressureP2 .3380.339Daysrate v (m3/s)m 210.280.2530428.83.10.270.23DOI: http://dx.doi.org/10.24018/ejers.2019.4.4.113078

EJERS, European Journal of Engineering Research and ScienceVol. 4, No. 4, April 2019TABLE III: AVERAGE COMPRESSOR OPERATING DATA PER DAY (NORMAL)Volumetric flow Mass flow rate DaysDischarge TemperatureT2 (K)Discharge PressureP2 ageTables II and III represent clogging and normal periodsrespectively, show the various daily average operatingvalues over a 30-day period when the compressor underinvestigation was operating under the influence of cloggingand when it was operating almost normally. In Table II, thevalues are for a period when the compressor experienced theproblem of clogging which negatively affected theperformance of the compressor and thereby caused anincrease in discharge temperature and decrease in dischargepressure, mass and volume flow rates respectively as thedays went by. As observed in Table III, the mean values ofthe control parameters (discharge temperature, dischargepressure, mass and volume flow rates) over another 30-dayperiod referred to as “normal” did not change or fluctuatesignificantly; they only varied around their daily meanvalues thereby making the average values per day over theafore-mentioned period almost constant.C. Off-design Behaviour of the CompressorThe Tables I and II clearly illustrate the trend in terms ofDOI: http://dx.doi.org/10.24018/ejers.2019.4.4.1130rate v (m3/s)m (kg/s)the changes in the operating conditions of thethermodynamic parameters of the compressor. The clarity ofthe effects of these parameters on the performanceassessment of the compressor is therefore simplified viagraphical representations as shown in Figures 3-12.Fig. 3. Effect of Ambient Temperature on Discharge Pressure.79

EJERS, European Journal of Engineering Research and ScienceVol. 4, No. 4, April 2019From Fig. 3, it is observed that the discharge pressure is afunction of the operating ambient temperature of the intakeair such that as the operating ambient temperature of theintake air increases the discharge pressure also increasedcorrespondingly. Also, a decrease in the operating ambienttemperature also led to a drop or decrease in the dischargepressure.The trend in Fig. 6 shows that the change in isothermalwork of the compressor affected the isothermal efficiencysuch that an increase in the isothermal work brought aboutan increase in isothermal efficiency. The reverse is the casewhen the isothermal work decreased as the isothermalefficiency also decreased.Fig. 7. Effect of Clogging on discharge temperature over a period of time.Fig. 4. Effect of Ambient Temperature on Isothermal Work.Fig. 4 illustrates a direct proportionality which shows thatthe isothermal work increased with an increase in theambient temperature. This means that a reduction in theambient temperature also caused a corresponding reductionin the isothermal work of the compressor.Fig. 7 shows what happened to the discharge temperatureduring clogging and normal periods. During the cloggingperiod, the effect of clogging caused a gradual increase inthe discharge temperature of the compressor over time as thedays went by and this is a disturbing trend considering thedanger of continuous rise in temperature on mechanicalsystems which can cause wear and tear, damage andconsequently lead to a complete breakdown of thecompressor if clogging is not minimized. During the normalperiod, the discharge temperature did not experience anysignificant change as the days went by but only the dailyaverage temperature experienced small changes in theirvalues around their mean values per day.Fig. 5. Effect of Discharge Pressure on Volumetric Efficiency.Fig. 5 clearly illustrates the fact that, as the ambienttemperature increased, the volumetric efficiency of thecompressor also increased and verse versa.Fig. 8. Effect of Clogging on discharge Pressure over a period of time.Fig. 8 shows that the discharge pressure continued to dropevery day during the clogging period but this was not thecase when the compressor discharge pressure operated undernormal condition as the discharge pressure did notexperience any significant change as the days went by;rather it only experienced small changes in its values aroundthe mean values per day.Fig. 6. Effect of Isothermal Work on Isothermal Efficiency.DOI: http://dx.doi.org/10.24018/ejers.2019.4.4.113080

EJERS, European Journal of Engineering Research and ScienceVol. 4, No. 4, April 2019Fig. 9. Effect of Clogging on Volume flow rate over a period of time.Fig. 12. Effect of Temperature during clogging on discharge pressure overa period of timeFig. 9 shows that the volumetric flow rate of the air keptdecreasing as the number of days increased therebynegatively affecting the flow capacity of the air compressorand lowering its performance. The case was different andbetter when the compressor operated under normalcondition.Fig. 12 shows that the effect of clogging (during theclogging period) caused a gradual temperature increase thatresulted in a gradual decrease in the discharge pressure overtime as the days went by.IV. CONCLUSIONFig. 10. Effect of Clogging on Mass flow rate over a period of timeFig. 10 also illustrates the fact that as the days went by,the mass flow rate reduced continuously. This gradualdecrease in the mass flow rate continued until after the 26thday when a sharp decrease began.Fig. 11. Effect of Temperature during clogging on Volume flow and Massflow ratesFig. 11 shows that during the clogging period, everyincrease in temperature caused decrease in the mass andvolume flow rates. The negative effect of clogging on theperformance of the compressor was such that, as thetemperature increased daily, the volume flow rate and themass flow rate of the discharged air decreased.DOI: http://dx.doi.org/10.24018/ejers.2019.4.4.1130The performance of the two-stage reciprocating aircompressor located and operating at an Oil and GasTerminal in Rivers State, Nigeria was assessed and analysedvia the application of some relevant thermodynamicequations. From the analysis of the performance of thecompressor, it was evident that the performance of thereciprocating air compressor depended significantly on theeffects of clogging on the compressor.From the thermodynamic analysis done, it was evidentthat the compressor experienced 26% loss in the volumetricefficiency of the compressor, 8% reduction or decrease inthe isothermal efficiency, 11.1% loss in the volume of airdischarged every second and 21% loss or reduction in themass flow rate when compared with the designspecifications. These low efficiencies could be as a result ofclogging which may have taken place to cause the reductionin the performance of the compressor to such a level.Table II and Figures 7 to 12 show that clogging hadnegative effects on the performance of the compressorwhich caused increase in discharge temperature, decrease indischarge pressure, mass and volume flow rates. Therefore,it may be justifiable to say that minimising clogging in thecompressor would likely cause improved performance thatmay meet the required design performance. This worktherefore shows an effective thermodynamic performanceevaluation of the compressor at an Oil and Gas Terminal inRivers State, Nigeria; hence, the objectives of this researchwork have been achieved. This study also contributes to theunderstanding that thermodynamic analysis is a veritabletool that can be used in analysing and accessing the effectsof clogging in two-stage reciprocating air compressors.In order to solve or minimize the menacing problem ofclogging for an improved performance of the aircompressor, the double-filter installation method should beapplied to limit the degree and amount of unwantedelements gaining entrance into the compressor. Periodic andtimely change of the desiccants inside the compressor’s airdryer is also recommended to minimise clogging and toprevent moist air from being discharged; thereby ensuring81

EJERS, European Journal of Engineering Research and ScienceVol. 4, No. 4, April 2019that discharged air are always dry. Periodic cleaning of thecylinders of the reciprocating air compressor helps tominimize clogging caused by accumulation of deposits andunwanted build-ups due to corrosive effects on the internalsurface of the cylinders. Further research could be carriedout to detect the presence of clogging and the exact quantityof clog in reciprocating compressors without opening thecompressor during maintenance.[6][7][8][9][10]ACKNOWLEDGMENT[11]The authors would like to profoundly appreciate thedepartment of Mechanical Engineering, Rivers StateUniversity, Port Harcourt, Nigeria for the technical supportsgiven during the process of this research work.[12][13][14]REFERENCES[1][2][3][4][5]Raj, N.D., Shujathullah, M., Dinesh, M., & Reddy; P.V. (2016).Thermodynamic Analysis of Gas Compressor. International. Journalof Mechanical and Production Engineering, 4, (10), 110-113.Sathyaraj, A., (2015). Analysis and Performance Enhancement ofIntercooler in Two Stage Reciprocating Air Compressor Using CFD.International Journal on Applications in Mechanical and ProductionEngineering, 1(2), 1-5.Wadbudhe, R.C., Diware, A., & Kale, P. (2017). A Research Paper onImproving Performance and Development of Two StageReciprocating Air Compressor. International Journal of Research inScience & Engineering, 3(2), 272-279.Sasmal, J.K., Suhane, A., & Agnihotri, G. (2013). ConditionMonitoring and Maintenance Program of Two Stage ReciprocatingAir Compressor. Internal Journal of Science and Research (IJSR),4(6), 2596-2602.Bagade, A.S., & Kadam, G.A. (2017). Design and Analysis ofReciprocating Double Acting Two Stage Air Compressor Crankshaft.International Journal of Research Publications in Engineering andTechnology (IJRPET), 3(9), 80-83.DOI: [16][17][18][19][20]Khan, A.R.A. (2014). Applied Thermodynamics: ReciprocatingCompressor, 1-30. -free.htmlLin, P., & Avelar, V. (2017). The Different Types of CoolingCompressors. A Journal of Different Technologies for Cooling DataCentres, 254, catingCompressors-pdfBloc, H. P., & Hoefner, J. J. (1993). Reciprocating Compressors &Operation Maintenance. Houston TX: Gulf Professional Publishing.Balu, S. (2010). Parts of an Air Compressor, 1-5. fan-air-compressorWillingham, R.A. (2009). Testing and Modelling of Compressors forLow Lift Cooling Applications, 1-138.Mishra, P. (2018). Air Compressor and its Types, -compressor-andits-types.htmlBalu, S. (2010). Effects of a Multi-stage Air Compressor, ets-of-a-multistage-air-compressorPipalia, V.F., Shukla, D.D., & Mehta, N.C. (2015). Investigation onReciprocating Air Compressor-A Review. International Journal ofRecent Scientific Research, 6(12), 7735-7739.Wadbudhe, R.C., Lodhe, A., & Shelke, A. (2017). A Research Paperon Improving Performance and Development of Two StageReciprocating Air Compressor. International Journal of Research inScience & Engineering, 3(2), 285-288.Kumar, V. D., Gokulnath, A., Kumar P.N., & Kumar S.V. (2017).Working Of Air Compressor with Aid of Speed Braker. InternationalJournal of Advanced Research, Ideas and Innovations in Technology3(2), 477- 481.Rogers, G., & Mayhew Y. (1992). Engineering Thermodynamics:Work & Heat Transfer (2nd ed.). India: Dorling Kindersley (India)Pvt. Ltd.Çengel, Y. A., & Boles, M. A. (2006). Thermodynamics: AnEngineering Approach (5th ed.). New York: McGraw-Hill.Dunn, D. J. (2007). Engineering Thermodynamics: Reciprocating AirCompressors, 1-23.Eastop, T. D., & McConkey, A. (1993). Applied Thermodynamics forEngineering Technologists. India: Dorling Kindersley (India) Pvt. Ltd.82

acting, single stage or multi-stage [11], [12]. In a single stage reciprocating air compressor, compression takes place in one stage while the multi-stage type involves more than one compression stage for achieving the required high pressure and low temperature by using intercooler [13]. An example of the multi-stage compressor is the double or .

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