Article Perorance and Theroeconoic Analysis o a Biogas Engine Powered Ventilation Syste or Livestock Building Det Darongsak* and Nakorn Tippayawong Departent o Mechanical Engineering, Faculty o Engineering, Chiang Mai University, Chiang Mai 50200, Thailand *E-ail: detddd@gail.co (Corresponding author) Abstract. In this study, a biogas engine powered ventilation an o a sall swine ar was proposed. The research objective was to evaluate perorance o, and apply a theroeconoic analysis to an active ventilation syste powered by a sall biogas engine. Coparison was ade against a gasoline engine and an electric otor. The engine used was a single-cylinder, our-stroke, spark ignited engine with capacity o 118 c 3. The biogas engine was ound to be practically able to drive the ventilation an with acceptable operation over a range o speeds and loads. At null price or biogas, the biogas engine proved to oer the lowest cost per product exergy unit at $0.054/MJ, which was considerably lower than the gasoline engine and electric otor. Keywords: Biogas, exergy costing, gas engine, ventilation. ENGINEERING JOURNAL Volue 18 Issue 3 Received 18 August 2013 Accepted 29 January 2014 Published 10 July 2014 Online at http://www.engj.org/ DOI:10.4186/ej.2014.18.3.1
DOI:10.4186/ej.2014.18.3.1 Noenclature BSFC brake speciic uel consuption (g/kh) btdc beore top dead center (-) C cost rate associated with uel exergy ($/h) c E C w c w cost per exergy unit o uel ($/MJ) exergy rate o uel (MJ/h) cost rate associated with product exergy ($/h) cost per product exergy unit ($/MJ) LHV lower heating value (kj/ 3 ) a engine ass low rate o air (kg/s) P power output ro biogas engine (k) P otor power output ro electric otor (k) v velocity o air (/s) V a voluetric low rate ( 3 /s) exergy rate o product (MJ/h) Z cost rate o the capital investent o the engine ($/h) eng Z an cost rate o a an ($/h) Z o& cost rate o operating and aintenance ($/h) engine theral eiciency (%) 1. Introduction Proper ventilation is o paraount iportance or anial husbandry to aintain the health and coort o ar anials. Norally, natural ventilated building design is not usually able to allow prevailing winds to bring suicient resh air into the buildings. Ventilation requireent o these buildings are oten coproised by the need to avoid livestock stressing ro uncoortable environents. Suicient ventilation rate is required to priarily provide optial theral indoor environent. Ventilation rate is also connected with environental issue in ters o distribution or reoval o airborne containants and gas eissions [1-2]. To provide adequate indoor conditions or ar anials, an understanding o cliate distribution in the building and its relation to the ventilation coniguration and abient outdoor environent is required. Furtherore, recent outbreaks o various diseases like avian and swine lu have induced concern o general public about the way anials are being kept [3], orcing any arers to adopt odern closed aring syste. Prevention o outbreaks aong the ar anials requires the ability to aintain ventilation and theral coort as hoogeneous as possible and within pre-speciied thresholds in occupied zones. This can be achieved by orced ventilation syste. Norally, active ventilation syste has ans ounted at suitable locations to induce resh air and circulate roo air. Proper environental control inside the livestock house relies on the an capacity to supply the required volue o air at the static pressure dierential chosen or the building as well as properly conigured and operated inlets or resh air distribution [4]. In tropical cliate like in Thailand, ar buildings norally operate in tunnel ventilation ode in which air is drawn through evaporative cooling pads at one end o the building and exhausted by large capacity ans at the opposite end. Typically, these ans are powered by electric otors or gasoline engines which account or considerable energy consuption, hence operating cost. Direct on-ar energy usage involves ossil uels and electricity. Faring practices and energy usage have changed in the past decade with increasing concern or uel cost and energy conservation. Iproveent in energy eiciency and renewable energy use can reduce ar operating cost [5]. In Thailand, biogas technology has been a reasonably successul renewable energy technology developed and widely disseinated. Fars norally use biogas or heating, electricity generation and shat work [6-8]. Adoption o biogas engine, in place o gasoline engine or electric otor has great potential to reduce ventilation 2 ENGINEERING JOURNAL Volue 18 Issue 3, ISSN 0125-8281 (http://www.engj.org/)
DOI:10.4186/ej.2014.18.3.1 energy cost. Such strategy would require ull assessent o energy and cost, whether the energy saving would oset the installation cost. There have been a nuber o literatures on biogas ueled spark ignited engine. However, ost studies have been on relatively large engines [9-12]. Reports on sall biogas engine were rather liited. Additionally, exergy and theroeconoic analysis ethods have been used widely in assessents o various energy systes, including engines [13-15]. Theroeconoics cobines the second law o therodynaics and econoics by applying the concept o cost to energy in order to achieve a better production anageent and ore cost eective operation [16]. Exergy is a potential or quality o energy used to evaluate ineiciencies associated with various processes. Exergoeconoic cost is deined as the aount o oney consued to generate an energy low. Theroeconoic analysis is a powerul tool to analyze and iprove the design o energetic systes. There have been a nuber o reports on theroeconoic analysis o coplex energy systes [17-20]. However, there has been relatively odest work in the existing literature reported on sall biogas engine, and no report about its exergy costing analysis. The idea was to use biogas as an alternative energy source or driving the ar ventilation syste. The ain objective o this work was to evaluate biogas engine perorance and copare the exergy cost against existing prie overs used in active ventilation syste or anial husbandry. 2. Perorance Evaluation Experiental evaluation o the perorance o dierent prie overs used to drive a ventilation an was carried out. Biogas engine, electric otor and gasoline engine were tested separately or individual perorance. Aterward, tests were perored or each o the three prie overs coupled to the ventilation an. In this work, biogas was used as alternative uel in place o gasoline. The research engine used in this work was a Honda GX-120. It was a single-cylinder spark ignited engine with overhead valve. Bore and stroke were 60 and 42, respectively. The displaceent volue was 118 c 3. The cobustion chaber is cylindrical in shape with the copression ratio o 7.5:1. The ignition tiing was set at 25 beore TDC. The our-stroke, naturally aspirated, air-cooled, gasoline ueled engine is a widely used engine odel or various applications in Thailand. It was odiied to accoodate the use o biogas. Consequently, its carburetor was replaced with a venture gas-air ixer. The engine copression ratio was adjusted ro 7.5:1 to 10:1. Biogas was supplied through a plastic pipe and ixed with inlet air in the ixer. Change in airlow quantity and velocity causes a change in pressure at the channel contraction which in turn aects a change in biogas low to ix with the ain airlow in the required proportion, prior to intake o the engine cylinder. The odiied engine was coupled to a Fabric TL170 dynaoeter or speed and load control. Sipliied scheatic diagra o the experiental test rig is shown in Fig. 1. It consists o the biogas engine, the ventilation an, a test bed, various sensors or easuring low rates, teperatures, velocity, and a data acquisition syste. Biogas used in the experient was obtained ro a continuously stirred reactor located at the Energy Research and Developent Institute, Chiang Mai University, Chiang Mai, Thailand. It was stored in a closed, collapsible rubber doe ro where it was ed to an engine intake port at a pressure o 64 Pa. The biogas was regularly sapled and analyzed or its properties and coposition. The properties o the biogas used were ound to reain nearly unchanged during the course o experiental run. ith average relative huidity o 80% and ethane content o 59% by volue, lower heating value o the biogas was 17.2 MJ/ 3. Since the heating value and the lae speed o biogas is saller than those o gasoline, proper ignition tiing ust be considered. Consequently, a series o tests were conducted to evaluate biogas engine perorance on stand-alone ode o operation with varying speeds and ignition tiing beore top dead center (btdc). In the test, engine speed was varied between 2000 to 3000 rp. Measureents on engine torque, power output, brake speciic uel consuption (BSFC), and eiciency were perored at ignition tiing o 45, 50, 55, 57, and 59 btdc. The low rate o the biogas was easured by gas eter. Ignition tiing and speed were easured by a SINCRO 105 and a digital tachoeter, respectively. Eiciency o the biogas engine, deined as the ratio o the engine power output to input power ro the biogas, was derived ro the ollowing expression: Pengine (1) VLHV Electric otor used in the experient was a Toshiba DC otor. It was connected to a TERCO DC dynaoeter to evaluate the perorance in ters o torque and current. For a gasoline engine, the original engine o the sae type and odel to that used with biogas was used. The unodiied engine was ENGINEERING JOURNAL Volue 18 Issue 3, ISSN 0125-8281 (http://www.engj.org/) 3
DOI:10.4186/ej.2014.18.3.1 coupled to a Fabric TL170 dynaoeter to investigate the engine perorance in ters o engine power output, torque, BSFC, and brake theral eiciency. This was conducted to investigate i the gasoline engine could run at optiu speed and give the required torque or driving the ventilation an. The otor and gasoline engine perorances were used to copare with those obtained ro biogas engine testing. Air Filter Fig. 1. Biogas Gas low eter Venturi ixer Scheatic o a ventilation an driven by biogas engine. Biogas engine 3. Exergy Costing Analysis This section is concerned with the potential o each prie over to generate energy to drive the ventilation an in the swine ar. Thereore, exergy costing analysis on each o the prie overs was conducted. Coparison was ade between the energy cost obtained ro biogas with those ro gasoline and electricity. In the analysis o exergy costing, each cost was associated with each rate o exergy strea [21-22]. Thus, the cost rates related to the entering and exiting exergy strea can be written as C c E (2) C c (3) where c and c denote the cost per exergy unit o uel and generated power, respectively, while E and denote the exergy transer rates o uel and work, respectively. Exergy rate o electric otor is given by Eq. (4), while exergy rates o gasoline and biogas engines are given by Eq. (5). Exergy rates o ventilation an driven by electric otor, gasoline engine, and biogas engine are coputed using Eq. (6). E P (4) E, otor otor V LHV (5), engine 2 v ai ai i (6) 2 where subscripts i = 1, 2, 3 which denote otor, gasoline engine, and biogas engine, respectively. c c E Prie over Z an Fig. 2. Exergy strea o the syste. Z eng, Z o& Exergy costing involves the balance o cost expressed or each coponent separately. A cost balance applied to a coponent, shown in Fig. 2, was expressed as the equal su between the su o cost rates associated with all exiting exergy streas ( C ) and the su o cost rates o all entering exergy streas ( C ) 4 ENGINEERING JOURNAL Volue 18 Issue 3, ISSN 0125-8281 (http://www.engj.org/)
DOI:10.4186/ej.2014.18.3.1 plus the appropriate cost rates due to the capital investent o the engine ( Z eng ), an ( Z an ), and operating and aintenance expense ( Z o& ). For a particular syste considered, the cost rate associated with the inlet air induced into the engine, lue gas loss, and heat reoved ro the engine were neglected. Thus, the cost rate balance can be generally written as C C Z Z Z (7) eng an o& Substituting the cost rates o Eqs. (2) and (3) into (7) yielded c c E Z Z Z (8) eng an o& Thus, the cost per exergy unit o the generated power was obtained as ollows: c E Zeng Z an Zo& c (9) To investigate and copare the energy costs between biogas, gasoline, and electricity, all variables ust be obtained. Table 1 presents required data o cost per product exergy unit and exergy rate associated with each o the prie overs. Table 2 shows cost rates due to the capital investent o the prie overs, an, and operating and aintenance. Table 1. Table 2. Cost per product exergy unit and exergy rate associated with prie overs. Prie Mover c E (MJ/h) ($/MJ) (MJ/h) Motor 0.029 2.83 0.602 Gasoline engine 0.027 21.76 0.916 Biogas engine 0 36.35 0.676 Cost rates associated with prie overs. Z eng Z an Prie Mover Z o& ($/h) ($/h) ($/h) Motor 0.00453 0.00457 0.000168 Gasoline engine 0.00557 0.00457 0.012 Biogas engine 0.01960 0.00457 0.012 4. Results and Discussion 4.1. Biogas Engine Perorance The experiental evaluation o the biogas engine, taken at a ean abient teperature o 30 C, provides the perorance curves in ters o torque, power, BSFC and eiciency with respect to the engine speed and ignition tiing between 45 and 55 btdc against the gasoline engine, shown in Figs. 3 to 6. For all cases o biogas engine considered, the engine torque, power output, and eiciency were ound to initially increase with speed until they reached their axiu, and decline as the speed approached 3000 rp. On the other hand, the BSFC was ound to initially decrease with speed until it reached the iniu, and then increased with increasing engine speed. It was clear that the gasoline engine gave better perorance than the biogas engine or the range o engine speed considered. The biogas engine was ound to peror best at ignition tiing o 55 btdc. An increase in advanced ignition tiing appeared to iprove the overall perorance o the biogas engine. However, liited tests at 57 and 59 btdc showed slight drop in torque, BSFC and eiciency. At ignition tiing o 55 btdc, torque was higher than the required torque used to drive the ventilation an over a range o speeds. The electric otor used in the experient was eployed to drive the ventilation an. The current was easured to be 4.33 A during the operation o the an at 1450 rp. The corresponding torque required to drive the an was ound to be 1.95 N. The biogas engine torque was initially ound to be 2.6 N at 2024 rp and increase with engine speed, reach its axiu o 4.5 N at 2415 rp, and decline to 3.0 N as the speed approached 3000 rp. For a ixed ignition tiing, siilar characteristics were observed or the engine eiciency and the power output. The eiciency o the engine was 6.3% at 2024 rp and reached its axiu o 11.5% at 2415 rp and ENGINEERING JOURNAL Volue 18 Issue 3, ISSN 0125-8281 (http://www.engj.org/) 5
Power output (k) Torque (N) DOI:10.4186/ej.2014.18.3.1 declined to 9.3% as the speed approached 3000 rp. hile the power output was 0.55 k at 2024 rp and reached its axiu power output o 1.15 k at 2617 rp, and declined to 0.95 k as the speed approached 3000 rp. BSFC was estiated ro the power output and the easured volue low rate o biogas. The highest BSFC was 4000 g/kh at 2024 rp, while the lowest BSFC o 2190 g/kh was observed at 2415 rp. 8.0 gasoline engine 7.0 6.0 5.0 biogas engine 4.0 3.0 2.0 55 o btdc 50 o btdc 45 o btdc 1.0 0.0 2000 2200 2400 2600 2800 3000 engine speed (rp) Fig. 3. Variation o torque with engine speed or biogas and gasoline engines. 2.0 gasoline engine 1.5 biogas engine 1.0 0.5 55 o btdc 50 o btdc 45 o btdc 0.0 2000 2200 2400 2600 2800 3000 engine speed (rp) Fig. 4. Variation o power output with engine speed or biogas and gasoline engines. 6 ENGINEERING JOURNAL Volue 18 Issue 3, ISSN 0125-8281 (http://www.engj.org/)
Eiciency (%) BSFC (g/kh) DOI:10.4186/ej.2014.18.3.1 10000 8000 6000 4000 2000 400 200 0 biogas engine gasoline engine 2000 2200 2400 2600 2800 3000 engine speed (rp) 45 o btdc 50 o btdc 55 o btdc Fig. 5. Variation o BSFC with engine speed or biogas and gasoline engines. 25.0 gasoline engine 20.0 15.0 biogas engine 10.0 5.0 55 o btdc 50 o btdc 45 o btdc 0.0 2000 2200 2400 2600 2800 3000 engine speed (rp) Fig. 6. Variation o theral eiciency with engine speed or biogas and gasoline engines. 4.2. Exergy Costing 4.2.1. Choice o prie overs In this work, three dierent types o prie overs were used to drive a ventilation an. Electric otor, gasoline engine, and biogas engine were run at 1450, 1850, and 2440 rp, respectively. hen the an was driven by the electric otor, a product strea o the syste was the power generated by a an driven by the otor. Exergy entered the otor at a rate o 2.83 MJ/h with a unit cost c 1 = $0.029/MJ. Exergy rate o work generated by a an was 0.602 MJ/h. In addition, the capital and other expenses or the syste were shown in Table 2. The capital or the otor and an were $0.00453/h and $0.00457/h, respectively. The operating and aintenance cost o the syste was $0.000168/h. Thereore, the cost per exergy unit o the syste was $0.152/MJ. hen the prie over was changed to a gasoline engine, exergy entered the gasoline engine at a rate o 21.76 MJ/h with a unit cost c 2 = $0.027/MJ. Exergy rate o work generated by a an was 0.916 MJ/h. Table 2 provides all other expenses related to the syste. The capital or the gasoline engine and an were ENGINEERING JOURNAL Volue 18 Issue 3, ISSN 0125-8281 (http://www.engj.org/) 7
Fuel cost rate ($/h) DOI:10.4186/ej.2014.18.3.1 $0.00557/h and $0.00457/h, respectively. The operating and aintenance cost o the syste was $0.012/h. The cost per exergy unit o the syste using a gasoline engine as a prie over was $0.668/MJ. For a biogas engine, the exergy entered at a rate o 36.35 MJ/h with a unit cost c 3 = $0/MJ. Exergy rate o work generated by a an was 0.676 MJ/h. The capital or the biogas engine and an were $0.0196/h and $0.00457/h, respectively. The operating and aintenance cost o the syste was $0.012/h. The cost per exergy unit o the syste was $0.054/MJ. 4.2.2. Assessent o cost rate The results o cost rates associated with all exergy strea plus cost rates due to the engine capital investent and operating and aintenance are discussed. The cost rate associated with the entering exergy strea, C, can be coputed using Eq. (2) with the data given in Table 1. As a result, uel cost rates associated with otor, gasoline engine, and biogas engine were coputed using Eq. (10). C c E (10) i i i where subscripts i = 1, 2, 3 which stand or otor, gasoline engine, and biogas engine, respectively. The results are shown in Fig. 7. It was noticeable that there was no cost rate associated with energy ro biogas engine since the biogas was reely available in the ar, while the other two sources o energy, electricity and gasoline uel, the energy ust be paid or. It was coprehensible that the cost rate o $0.590/h associated with gasoline was the highest aong all energy sources due to a recent high oil price. The cost rate associated with electric otor was $0.082/h, approxiately seven ties saller than that associated with gasoline engine. Aong the three types o prie overs, the biogas engine was ound to provide the lowest cost rate. However, i the biogas cannot be suiciently produced to run the biogas engine, the electric otor ay teporary be used to drive the an. The capital investent on the electric otor, gasoline engine, and biogas engine were $0.00453/h, $0.00557/h, and $0.01960/h, respectively. It was obvious that the capital investent on biogas engine was the highest aong the three prie overs. This was due to the high cost o the engine and its odiication requireent. However, the biogas engine oered no payent on uel. This provides a great opportunity in a long ter operation to any swine ars that are capable o producing the biogas to utilize it as a uel. On a contrary, the electric otor and gasoline engine oered a low capital investent, but the energy costs can be expensive. 0.70 0.60 0.590 0.50 0.40 0.30 0.20 0.10 0.00 0.082 0.000 Motor Gasoline engine Biogas engine Fig. 7. Fuel cost rates associated with dierent prie overs. 8 ENGINEERING JOURNAL Volue 18 Issue 3, ISSN 0125-8281 (http://www.engj.org/)
Cost per product exergy unit ($/MJ) DOI:10.4186/ej.2014.18.3.1 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.00 0.668 0.152 0.054 Motor Gasoline engine Biogas engine Fig. 8. Cost per product exergy unit over dierent prie overs. Figure 8 shows the results o cost per product exergy unit obtained ro the analyses o the active ventilation syste. Aong the three cases, the cost per product exergy unit o gasoline engine was highest, with the price o $0.668/MJ. This was due directly to the very high oil price in the arket. The electric otor was ound to have the cost per product exergy unit o $0.152/MJ, while the biogas engine showed the lowest cost per product exergy unit o $0.054/MJ, since the biogas was available or ree in the ar. 5. Conclusions Analysis o a ventilation syste driven by three dierent prie overs, i.e. electric otor, gasoline engine, and biogas engine was carried out or their perorances. Investigation o the cost-eective syste was also carried out in ters o cost per exergy unit and cost rate associated with all exergy streas. Results showed that the biogas engine can provide the lowest cost per product exergy unit o $0.054/MJ, which was estiated to be three and twelve ties lower than those ro the otor and gasoline engine, respectively. Regarding the uel cost rate, biogas oered no cost rate, while electricity and gasoline would cost about $0.082/h and $0.590/h, respectively. The biogas engine can be practically eployed as a prie over or driving the ventilation an in a sall swine ar. Acknowledgeents Technical assistance ro the Energy Research and Developent Institute, Chiang Mai University is grateully acknowledged. Reerences [1] V. Blanes, S. Pedersen, Ventilation low in pig houses easured and calculated by carbon dioxide, oisture, and heat balance equations, Biosystes Engineering, vol. 92, pp. 483-493, 2005. [2] K. Y. Ki, H. J. Ko, H. T. Ki, Y. S. Ki, Y. M. Roh, and C. N. Ki, Eect o ventilation rate on gradient o aerial containants in the conineent pig building, Environental Research, vol. 103, pp. 352-357, 2007. [3] J. P. T. M. Noordhuizen and J. H. M. Metz, Quality control on dairy ars with ephasis on public health, ood saety, anial health and welare, Livestock Production Science, vol. 94, pp. 51-59, 2005. [4] K. D. Casey, R. S. Gates, E. F. heeler, H. Xin, Y. Liang, A. J. Pescatore, and M. J. Ford, On-ar ventilation an perorance evaluations and iplications, Journal o Applied Poultry Research, vol. 17, pp. 283-295, 2008. [5] J. A. Bailey, R. Gordon, D. Burton, and E. K. Yiridoe, Factors which inluence Nova Scotia arers in ipleenting energy eiciency and renewable energy easures, Energy, vol. 33, pp. 1369-1377, 2008. ENGINEERING JOURNAL Volue 18 Issue 3, ISSN 0125-8281 (http://www.engj.org/) 9
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