Inter national J our nal of P o wer Electr onics and Dri v e Systems (IJPEDS) V ol. 9, No. 1, March 2018, pp. 73 79 ISSN: 2088-8694 73 The Dimensioning of A Compr essed Air Motor Dedicated to A Compr essed Air Storage System Ilham Rais 1 and Hassane Mahmoudi 2 1 Mohamadia Engineering School Mohammed V uni v ersity Rabat, Morocco 2 Po wer Electronic and Control T eam (EPCT), Department of Electrical Engineering Article Inf o Article history: Recei v ed Oct 31, 2017 Re vised Jan 10, 2018 Accepted Feb 3, 2018 K eyw ord: CAES Rene w able ener gy Compressed Air Motor Compressor storage ABSTRA CT Storage represents the k e y to the penetration of rene w able ener gies especially wind and solar ener gy on the netw ork electric. It a v oids unloading in the e v ent of o v erpro- duction, ensuring real-time The production-consumption balance and also impro v e the rob ustness of the electricity grid. CAES (Compressed Air Ener gy Storage) is a mature technology that allo ws to store long or short duration an amount of ener gy suf ficient to support the number of c ycles requested. The E-PV -CA ES system will be presented and the modeling of the compressed air engine will also be treated in more detail in this article. Copyright c 2018 Insitute of Advanced Engineeering and Science . All rights r eserved. Corresponding A uthor: Ilham Rais Af filiation:Po wer Electronic and Control T eam (EPCT), Department of Electrical Engineering Mohamadia Engineering School Mohammed V uni v ersity Rabat, Morocco Email:ilhamrais@research.emi.ac.ma 1. INTR ODUCTION Storage in general in v olv es a number of technologies, both old and ne w , which are based on a c ycle of storage - daily destocking and which can e xtend to a seasonal storage of ener gy . These technologies co v er a wide range of applications: Applications for impro ving the quality of the current and which generally ha v e a v ery short response time (less than one second) and operating time of a fe w minutes, Such as flywheel, supercapacitors, superconductors and storage in electrochemical batteries, - Applications which impro v e the profitability of the production system and which ha v e a slightly longer response time (a fe w tens of seconds to a fe w minutes) and an operating time of a fe w hours, such as pumping w ater and compression air . The latter is based on the storage of compressed air in ca v es. Rene w able electricity or electricity produced during periods of lo w ener gy demand is used by compressors and st ored in con v entional tanks and produced in case of need by means of a compressed air engine. Using the po wer of compressed air has man y adv antages. First, as a po wer source, the compressed air is both clean and safe. Second, it can also be used for v ar ious tasks such as actuating tools and pistons in order to mo v e or cool materials [1][2][10][11]. 2. PRESENT A TION OF THE SYSTEM PR OPOSED In con v entional g as turbines widely used in the generation of electrical ener gy (especially in the e v ent of peak demand), there are tw o phases: A first where the air is compressed before an e xpansion phase where, after injection of comb ustible Then the hot g ases thus obtained pass through a turbine, supplying mechanical ener gy which can then be transformed into electrical ener gy [3][14]. The CAES operates in the same w ay by decoupling these tw o phases. Thus, the ener gy to be stored is used to compress the air by a compressor and to store it, often in a natural ca vity ,The e xpansion of the air will then mak e it possible to produce electrical ener gy by the same process as a g as turbine. Compressed air ener gy storage can store lar ge quantities of ener gy for long periods of time, making it an alt ernati v e to h ydro-electric storage. In addition, installation costs are lo wer J ournal Homepage: http://iaescom.com/journals/inde x.php/IJPEDS DOI:  10.11591/ijpeds.v9.i1.pp73-79 Evaluation Warning : The document was created with Spire.PDF for Python.
74 ISSN: 2088-8694 than those of the latter technology , although safety tests often require significant mea ns and, lik e h ydroelectric storage, CAES generally requires a particular geographic en vironment (ca vities Groundw ater , aquifers, etc.) to store compressed air (although storage methods abo v e ground are increasingly e xtended to lar ge-scale storage) [1][4][15][16]. Figure 1. Schema of the principal of function of a compressed air storage system 3. TYPES OF COMPRESSED AIR MO T OR The compressed air motor (CAM) transforms compressed air from Electricity via an alternator associ- ated with its pneumatic part . It performs the re v erse function of a compressor . Dif ferent types of CAM can be distinguished as motors with pallets as sho wn in Figure 2, a piston engines , geared motors or turbine engines [2][6][15]. Figure 2. Schema of compressed air motor with piston (right)and compressed air motor with (left) The characteristics of the CAM are sho wn in torque-speed (C-N) and po wer -speed (P-N) curv es as sho wn in Figure 3. The pressure on the pistons, pallets or teeth bei ng proportional to the pressure, and the pressure v arying as a function of the pressure drops in the machine, which are proportional to the square of the air v elocity (that is to say the Square of the rotation speed), it follo ws that the torque-speed curv e (C - N) theoretically has a parabolic shape. This curv e al w ays has a ne g ati v e slope: the torque decreases as the speed increases, to cancel out at the speed of runa w ay . The useful po wer being the product of the torque by the speed, it therefore increases to pass through a maximum and v anishes for the Speed of runa w ay [7][2][8]. IJPEDS V ol. 9, No. 1, March 2018: 73 79 Evaluation Warning : The document was created with Spire.PDF for Python.
IJPEDS ISSN: 2088-8694 75 Figure 3. Schema of The performance curv e for an air motor operating at a constant air pressure 4. AD V ANT A GES AND LIMITS OF THE COMPRESSED AIR MO T OR The adv antage of this system is that it produces locally no polluting emissi ons, whether particulat es, oxides of nitrogen or CO2. Ho we v er the compressed air does not e xist naturally . Therefore it must be produced, which requires ener gy and raises the same problems as the production of h ydrogen: The non-rene w able nature of sources of ener gy , the production of pollution, greenhouse g as or radioacti v e w aste by po wer plants, ener gy losses during the con v ersion in pneumatic ener gy , etc. Besides, if the compressed air engine is v ery used on certain sector (pneumatic drill, dentist’ s drill ...), its appli- cation in autonomous v ehicles is still at the stage of de v elopment. Indeed, the compressed air contains not much ener gy and, e v en with a reserv oir of 300 liters at 300 bars, the autonomy of such a v ehicle is v ery small. There- fore, these are the w ays of the h ybridization electric/compressed-air and bi-fuel engines oil-fuel/compressed-air which are currently being e xplored [3][2]. 5. THE PO WER SELECTED COMPRESSED AIR MO T OR The po wer of the compressed air motor is 8kW . Indeed, this po wer has been selected to feed The isolated site with 5kW and the rest (3kW) tak es Considering the mechanical and ener gy losses between the MA C and its alternator on the one hand And serv es, on the one hand, to heat heating resistors placed after each stage of The compressed-air engine to heat the air after the e xpansion and F ormation of frost on the air circuit and damage to the latter . 6. THE MODELING OF COMPRESSED AIR MO T OR TYPE PIST ON In order to analyze and si mulate the pneumatic ener gy con v ersion process, it is essential to determi ne the model of the compressed air motor (CAM) used. The ideal model should tak e into account all the ph ysical phenomena in v olv ed in the con v ersion of ener gy . The compressed air motor chosen for this study is of the ”piston” type Because i t is the most mature, reliable, cheaper and allo ws full use of the polytropic e xpansion of compressed air in the c ylinder especially if the relaxation of the air is done in se v eral stages [2][6][13]. 6.1. Operating mode The compressed air reserv oir has suf ficient pressure, its ener gy Potential can be con v erted into me- chanical ener gy on the motor shaft and into electrical ener gy On the alternator shaft. The c ycle of the pneumatic motor is carried out in three stages: load Cylinder , e xpansion and e xhaust. The foll o wing figure sho ws, the ba- sic function CAM with piston and the P-V diagram idealized for the c ycle of air injected into the engine [5] [12]. The c ycle of compressed air injected into a compressed air motor of the type ”piston” Comprises the follo wing three steps: Cylinder load: The load v alv e is open from point 1 to point 3 (figure 5) The Dimensioning of A Compr essed Air Motor Dedicated to A Compr essed ... (Ilham Rais) Evaluation Warning : The document was created with Spire.PDF for Python.
76 ISSN: 2088-8694 Figure 4. Schema of the basic function CAM with piston Figure 5. Schema ofthe P-V diagram idealized for the c ycle of air injected into the CAM From point 1 to point 2, air from the tank is e xpanded in the c ylinder . From point 2 to point 3, the e xpansion continues at constant pressure and equal to the pressure Of the tank (Assuming that the v olume of the reserv oir is much higher than the v olume Of the c ylinder). The w ork of the pneumatic motor c ycle can v ary continuously in Adapting the closing angle of the load v alv e (Figure, lines dotted). Relaxation: The load v alv e is closed from point 3 to point 4 (Figure 5): the Load air relax es. The total relaxation strok e (step 2 to step 4) produce the w ork Of the c ycle. In order to achie v e a complete relaxation of the air char ge, the angle of Closing of the load v alv e must be optimized in such a w ay as to superimpose the Points 4 and 5. Exhaust: The e xhaust v alv e opens at point 4 (Figure 5). Point 4 at point 5, the c ylinder air e xpands in the e xhaust (open to atmosphere Or other lo w-pressure storage tank) and the potential ener gy of the air At point 4 is lost. From point 5 to point 1, the e xhaust strok e Mass of residual air in the e xhaust duct at atmospheric pressure Or to the pressure of another lo w-pressure storage tank. IJPEDS V ol. 9, No. 1, March 2018: 73 79 Evaluation Warning : The document was created with Spire.PDF for Python.
IJPEDS ISSN: 2088-8694 77 7. THE W ORK OF THE COMPRESSED AIR MO T OR The w ork of the pneumatic motor c ycle is the sum of the w ork during all Phases of the c ycle sho wn in figure 5 . W = W 1 2 + W 2 3 + W 3 4 + W 4 5 + W 5 1 (1) By definition, the w ork e xchanged between the c ylinder g ases and the piston is defined by: W = Z P dv (2) As a result, the w ork of an isochore (constant v olume) transformation is zero and Therefore : W 1 2 = W 4 5 = 0 (3) T ransformations 4-5 and 1-2 sho wn in the P-V diagram (Figure5) As being isochorous are in f act adiabatic transformations representati v e of the e xpansion and compression which the air under goes respecti v ely at the end of the e xpansion after opening of the e xhaust soup and at the end of e xhaust at the moment Of the opening of the intak e v alv e. 7.1. W ork during the admission The intak e (2-3) is an isobaric transformation which tak es place at a constant pressure ( P = P 2 = P 3 ) . The w ork of the piston during this phase is calculated as follo ws: W 2 3 = Z 3 2 P 2 dV = P 2 Z 3 2 dV = P 2 ( V 3 V 2 ) = P 2 V 2 (1 V 3 V 3 ) (4) By replacing the ratio of v olumes by its e xpression, = V 3 V 2 W ork of the isobaric admission then becomes: W 2 3 = P 2 V 2 ( 1) (5) 7.2. W orking during r elaxation Relaxation is a polytropic transformation characterized by Laplace’ s la w Allo ws to write: P V = P 3 V 3 = P 4 V 4 (6) P = P 3 V 3 V (7) Then: P = P V 4 V 3 V (8) By replacing the ratio of the v olumes by its e xpression = V 4 V 3 , the e xchanged w ork Between the air and the piston during the e xpansion is then calculated from the follo wing formula: W 3 4 = Z 4 3 P dV = Z 4 3 P 3 V 3 V dV = 1 1 ( P 4 V 4 P 3 V 3 ) = P 3 V 3 1 ( 1 1) (9) 7.3. W ork during exhaust During the phase of the e xhaust isobaric ( P = P 5 = P 1 ) , air is pushed out Of the c ylinder during the rising of the piston. The w ork of the piston e xchanged during this phase Calculated from the follo wing relation: W 5 1 = Z 1 5 P dV = P 5 Z 1 5 dV = P 1 V 1 (1 V 5 V 1 ) = P 1 V 1 (1 " ) (10) C y is the total c ylinder capacity of the engine, V m is the c ylinder dead v olume and " V olumetric compression ratio defined by: The Dimensioning of A Compr essed Air Motor Dedicated to A Compr essed ... (Ilham Rais) Evaluation Warning : The document was created with Spire.PDF for Python.
78 ISSN: 2088-8694 " = V 5 V 1 = V 1 + C y V 1 = V m + C y V m (11) The w ork of the thermodynamic c ycle of a CAM with piston is the sum of the w ork admission, relaxation and e xhaust, where: W = P 2 V 2 ( 1) + P 3 V 3 1 ( 1 1) P 1 V 1 (1 " ) (12) kno wing that : V 1 = V 2 = V m , P 2 = P 3 = P r , P 1 = P a , V 3 = V m ,W can be writ as : W = V m (( P r ( ( 1 ) + ( 1) 1 ) + P a ( " 1)) (13) 166 168 170 172 174 176 4.7 4.75 4.8 4.85 4.9 4.95 5 5.05 x 10 4 Maximal pressur of storage (bar ) the work devolopped by the motor (KJ)     C=200 C=300 C=400 C=500 C=600 Figure 6. Schema of W ork de v eloped by CAM with piston according to the admission pressure and c ylinder capacity Cy The figure sho ws the v ariations of the w ork De v eloped by a single-c ylinder CAM as a function of the air pressure at the inlet of the CAM (storage tank pressure) and Engine. It is simple to note that the w ork of the CAM v aries linearly with tank pressure. This is because the v olumetric compression ratio, " , of the motor is fix ed at a constant v alue equal to (10). The rotational speed of the compressed air motor is set at 1200 rpm. From this figure it can be concluded that the higher the pressure in the Reserv oir decreases, plus the w ork de v eloped by the CAM. This leads to the conclusion that the po wer supplied by the CAM will ne v er be constant with a continuous withdra w al of the compressed air from the storage tank and consequently the CAM will no longer be able to supply an isolated site By the required electrical po wer (8 kW). F or this reason, obtaining po wer Constant, it is necessary to v ary the flo w of compressed air injected into the CAM as a function of the V ariation of the pressure in the reserv oir . 8. CONCLUSION in this paper a short presentation of the system proposed W ind-photo v oltaic- compressed air storage has been motioned and the dif ferent types of the compres sed air motor and their adv antage and limits ,then the modeling of the compressed air engine based on special ener gy criteria is studied , Since it is considered as a main agent in the principle of operation of the system presented . The h ybrid system wind-photo v oltaic-compressed air represents An interesting solution to en viron- mental and resource related to the problems of ener gy supply to isolated sites It allo ws: T o incre ase the pene- tration rate of wind and solar ener gy by taking adv antage of all the a v ailable ener gy and by storing the e xcess ener gy in the form of compressed air instead of shedding it through compressors and Compressed air motor and significantly reduce fuel consumption and GHG emissions. IJPEDS V ol. 9, No. 1, March 2018: 73 79 Evaluation Warning : The document was created with Spire.PDF for Python.
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