Energy efficiency estimation of a steam powered LNG tanker using normal operating data

Transcription

1 Energy effcency estmaton of a steam powered LG tanker usng normal operatng data Rajendra Prasad Snha 1 1 Department of advanced Marne Engneerngt, Malaysan Martme Academy Kuala Sg Baru Post code 78300, Masjd Tanah, Melaka,Malaysa rajendra@alam.edu.my ph , fax Abstract. A shp s energy effcency performance s generally estmated by conductng specal sea trals of few hours under very controlled envronmental condtons of calm sea, standard draft and optmum trm. Ths ndcator s then used as the benchmark for future reference of the shp s Energy cency Performance (EEP). In practce, however, for greater part of operatng lfe the shp operates n condtons whch are far removed from orgnal sea tral condtons and therefore comparng energy performance wth benchmark performance ndcator s not truly vald. In such stuatons a hgher fuel consumpton readng from the shp fuel meter may not be a true ndcator of poor machnery performance or drty underwater hull. Most lkely, the reasons for hgher fuel consumpton may le n factors other than the condton of hull and machnery, such as head wnd, current, low load operatons or ncorrect trm [1]. Thus a better and more accurate approach to determne energy effcency of the shp attrbutable only to man machnery and underwater hull condton wll be to flter out the nfluence of all spurous and nonstandard operatng condtons from the shp s fuel consumpton [2]. The author n ths paper dentfes parameters of a sutable flter to be used on the daly report data of a typcal LG tanker of shaft power to remove effects of spurous and non-standard shp operatons on ts fuel consumpton. The fltered daly report data has been then used to estmate actual fuel effcency of the shp and compared wth the sea trals benchmark performance. Results obtaned usng data flter show closer agreement wth the benchmark EEP than obtaned from the monthly mn trals. The data flterng method proposed n ths paper has the advantage of usng the actual operatonal data of the shp and thus savng cost of conductng specal sea trals to estmate shp EEP. The agreement between estmated results and specal sea trals EEP s expected to mprove further wth use of better and more accurate flterng technques. Key words: Shp Energy cency, Specfc Fuel Rate, LG, Shaft Power, Hull foulng 1 Introducton It s common practce to conduct specally desgned controlled sea trals to estmate a benchmark shp EEP to be used for future comparson durng shp s actual operaton. Ths benchmark ndex, although more accurate, s less related to the real lfe stuatons n whch the shp actually sals because the operatng envronment s very dfferent [1]. For a meanngful comparson wth benchmark ndex an effectve EEP of the shp should be extracted from the actual operatng parameters whch wll then reflect truly on the condton of ts machnery and hull foulng [2] whch s the man purpose of performance montorng. The fuel effcency of a shp s determned by measurng the quantty of fuel consumed to produce the requred amount of propulson and auxlary power to move the shp at a specfed speed. Lesser the quantty of fuel used the shp s consdered more effcent. Ths effcency has been measured n many dfferent unts but the one most unversally accepted by the Internatonal shppng communty s the Specfc Fuel Rate (). The s expressed n grammes of fuel consumed for every h of power produced by the man propulson machnery plus electrcal generators [3], expressed as: Vessel Fuel Consumed at sea per Dayn grammes Total ( T / G power) h gm h Typcal sample plots of estmates from daly report of January and February 2014 for the shp under nvestgaton are shown n fgure 1. These plots show very nconsstent varatons n the of the shp. It s observed, on a partcular day the shp performs well but then next day the rses very hgh followed by agan a sudden drop ndcatng mprovement n fuel consumpton. Correspondng author: rajendra@alam.edu.my The Authors, publshed by EDP Scences. Ths s an open access artcle dstrbuted under the terms of the Creatve Commons Attrbuton Lcense 4.0 (

2 (x) Relatve wnd speed n knots and drecton wth respect to shp s headng, degree Daly report entres also nclude summary of energy performance estmates, propeller slp and total power produced by the man engne and generators for the daly voyage. Fuel consumed durng maneuverng and n port stay are entered separately. Typcal daly report sample s shown n table 1. 3 Energy cency Estmaton The shpboard performance montorng system estmates shp EE by measurng the total fuel consumed by the shp n 24 hours (converted n grammes), Equaton (1) and then dvdng t by the klo-watts average over the same perod as n Equaton (2). Algebracally, EE s expressed as n Equaton 3. Total fuel consumed durng 24 hour voyage, Fgure 1. Sample from Daly report Obvously ths knd of random varatons n shps fuel effcency cannot be attrbuted to hull condton or machnery. Most lkely the cause of hgh fluctuaton could be some external factor such as the sea envronment or operatng procedures. Hence, to acheve accurate estmates, the adverse effect of these factors on the fuel consumpton needs to be fltered out. The author n ths paper ams to answer ths queston by proposng a sutable data flter. 2 Data Acquston and Management An automatc data montorng system s nstalled n the shp to record 24 hourly average value of followng operatonal parameters whch s then sent to the man offce as daly report [3,4]. () Shp speed n knots () Duraton of operaton at specfc speed n hours () for duraton of specfc speed (v) Shaft rpm for duraton of specfc speed (v) Lqud fuel consumpton for the duraton of specfc speed, s (v) Gas fuel consumpton for the duraton of specfc speed, s (v) Total equvalent fuel consumpton for the duraton of specfc speed, s (v) Dstance covered by the shp at specfc speed by shp s Log, nautcal mles (x) Dstance covered by the shp at specfc speed by GPS, nautcal mles average = q Q = 1 (1) 1 P t t 1 Shp = average (2) Q (3) The shp n voyage leg method s calculated usng equaton 4 &5. q () =, P t E() = ( ) t 1 (4) Shp daly energy effcency performance, Shp = E 1 ( ) (5) P = (Shaft power + Generator power) for specfc voyage leg, t = Voyage leg duraton, hour q = Voyage leg fuel consumpton, grams =umber of voyage legs n a 24 hour sea passage 4 Shp Energy cency Analyss [2,4,5] The daly report data of the shp from January-December 2014 has been consdered for analyss. The benchmark of 300 g/h from the orgnal sea acceptance tral 2

3 report conducted by the shpbulder has been used for comparson of shp energy effcency n ths analyss. system recorded s for both months n fg 1 are above benchmark acceptable level. For nstance, on days 11,17 n January and 12, 22 n February the s over 500 g/h whle on many days durng ths ntervals the s very close to the benchmark of 300 g/h. But the physcal nature of the machnery and hull agng process should show a gradual change n the wth tme. Therefore, ths knd of abrupt varaton n readngs cannot be used to predct actual condton of the machnery or growth n underwater hull foulng whch s the chef objectve of shp energy effcency montorng. 5 Voyage Analyss To determne actual of the shp from daly report data, voyage leg analyss method has been used whch works as follows. A day s voyage of 24 hours s generally made of a number of short voyage legs of few hours each wth shp salng at dfferent speeds and shaft power. Also each voyage leg of a partcular day s salng s entered separately n the daly report wth correspondng fuel consumpton data. Therefore, by usng Equaton 3, t s possble to determne the of an ndvdual voyage leg of a 24 hours voyage together wth ts actual contrbuton to the day s overall. A voyage leg wth small or nsgnfcant contrbuton to the overall day s may be then treated as spurous operatng nose source whch s not truly related to shp energy system performance and hence can be gnored wthout causng serous error to the day s overall estmate. The voyage leg analyss can be thus used as flter to remove all spurous and non-standard operatng condtons whch wll then gve more steady and accurate estmate of a 24 hours day s voyage. Ths estmaton method has been used by the author to determne true of the shp. Table 1 shows detals of sample voyage legs, duratons, shaft power and correspondng fuel consumpton on four dfferent days n January 2014 when recorded s are hgh (shp s energy performance s low). average of 8290 amounts to 1.85 s extra fuel consumpton by the shp. Table 1 Vessel Data January 2014 Voyage Day 11 Day 17 s,, Ton avg Table 1 Vessel Data January 2014 Voyage Day 27 Day 25 s, avg Results and Dscussons [2,3,5] Result of analyss usng voyage leg method to estmate actual effectve of 24 hour voyage for January and February 2014 n fgure 1 s dscussed n ths secton. Day 11 n January had three dstnct voyage legs wth correspondng and ther mpact on the effectve as shown n fgure 2. The mpact of voyage leg 1 on the overall effectve s very small whch s ndcatve of a non-standard shp operaton that does not really relate to actual machnery or hull condton. Therefore, the true shp effectve for 11 January 2014 voyage may be qute accurately estmated from the sum of only voyage legs 2 and 3 s.e g/h as compared to the of 528 g/h recorded by the energy performance montorng system. Ths gves estmaton error of 97.2 g/h whch for an Fgure 2 Recorded versus estmated 3

4 For a voyage duraton of 2.3 hours ths s a sgnfcant estmaton error n the energy effcency montorng system. The voyage leg, effectve voyage (E), effectve and recorded for day 11 n fgure 2 clearly ndcate that the actual effectve estmate from voyage leg analyss s more accurate than the recorded by EE montorng system. Smlar analyss results of the daly report data for day 17 January s shown n fgure 3(a,b). As expected, the day s effectve estmate s lower than the recorded. The reason why voyage leg analyss method gves lower values s obvous because t flters out fuel consumpton of non-standard operatons from the day s total fuel consumpton and mprove EE estmates. s expected to reveal underlyng physcs of mproved flterng. Table 2 shows daly report data whch are used for estmatng effectve for those days. Though, flterng spurous and non-standard operatons by usng voyage leg analyss method gve lower and more accurate effectve estmates as shown n fgures 2&3 but stll n absolute terms the values on most days n January/February are above the sea tral benchmark of 300 g/h. Ths ndcates that removal of spurous and non-standard operatng condtons from the daly report data n fgures 2&3 has not been fully acheved and further flterng of daly report data s stll necessary to obtan shp actual whch truly reflects the hull and machnery condtons. Fgure 4 recorded versus estmated Fgure 3 recorded versus estmated To mprove data flterng method further, daly reports of 22,23,24 and 30 January 2014 have been analyzed. As the s recorded on those days closely agree wth the sea trals benchmark of 300 g/h, ths analyss Fgure 5 recorded versus estmated On day 22, fgure 4, voyage legs 3 and 7 have neglgble contrbuton to the overall day s and hence can be 4

5 safely gnored. The actual for that day may be the sum of the remanng voyage legs whch adds to 297 g/h as aganst the recorded of 321 g/h. Contrarly, on day 23, all four voyage legs make sgnfcant contrbuton, fgure 5 whch ndcates absence of any spurous or non-standard operaton. The effectve s thus the total sum of all voyage legs. Table 2 Vessel Data January 2014 Voyage Day 22 Day 23 s,, avg Table 3 Estmated versus Voyage Day 11 January 2014 (E) avg 8290 Table 3, Estmated versus Voyage Day 17 January 2014 (E) avg 6602 Table 4, Estmated versus Voyage Day 22 January 2014 (E) avg Table 4, Estmated versus Voyage Day 23 January 2014 (E) avg The summary of voyage leg analyss for days 11,17, 22 and 23 January 2014 are shown n tables 3&4. The voyage leg analyss reveals, when average s much lower than the sea trals condton.e of h then the day effectve s much hgher than the sea trals benchmark of 300 g/h. But as the value of average ncreases and reach closer to the sea trals condton the day s effectve also mproves and moves close to the benchmark value of 300 g/h, as shown n tables 3&4. Therefore apart from voyage duraton, strong wnd and optmum trm the average s another crtcal parameter of the flter to estmaton of accurate from the daly report data. The dfference n effectve estmates from voyage leg analyss and EE montorng system records arses manly due to ncluson of non-standard operatng condtons n the montorng system whch are fltered out n the voyage leg analyss method. The selected flter parameters are shown n table 5. 5

6 Table 5 Data flter Parameters [2,6] S.o Parameter Flter lmt 1 Voyage Duraton <0.5 hour 2 average > Trm < 0.5 m 4 Wnd speed <15 knots 5 Beaufort Sea State <3 7 Conclusons estmate obtaned from energy effcency montorng system s based on total fuel consumed durng normal and also non-standard short operatonal voyages. Because of that t does not represent true performance of the man machnery and underwater hull condton. In contrast the effectve estmate from voyage leg method s lower than values recorded by the system because t has been obtaned by usng a data flter to elmnate the contrbutons of spurous and non-standard operatons of the shp. The Data flter parameters, table 5, have been selected after analysng contrbutons of each voyage leg to the shp for a 24 hour passage and those relatng to non-standard operatng condtons have been gnored or fltered out. Ths procedure therefore gves effectve of the shp comng from only standard operatng condtons. The effectve can be then used for comparson wth the shp benchmark performance ndex to assess actual condton of shp s underwater hull and machnery. Fgure 6 Shp estmate versus Comparson of energy effcency.e effectve of the shp based on voyage leg analyss and those recorded from the montorng system for January 2014 n fgure 6 ndcates voyage leg analyss gves a lower and more accurate estmates. Glossary: EE LG (E). References Energy cency Shaft power, Lquefed atural Gas Specfc Fuel Rate calculated by the Energy Performance montorng system Specfc Fuel Rate of a Voyage et contrbuton of ndvdual voyage leg on over all of the day Estmate of actual after flterng contrbuton of nonstandard voyages [1] Tadeusz Borkowsk,Lech Kasyk, Przmyslaw Kawalak, Assessment of Shp Engne effectve Power Fuel Consumpton and emssons usng the vessel speed, Journal of Kones Powertran and Transport, Vol 18, o2, [2] Kevn P Logan, Usng Shp Propeller for Hull Condton Montorng, Presented at ASE Intellgent Shp Symposum IX, 25 May 2011, Phladelpha, PA,USA [3] Jonas Kallman, Shp Power Estmaton for Marne Vessels Based on System Identfcaton, Thess, Department of electrcal Engneerng LIKOPIGS Unversty, SF Lnkopng, Sweden. [4] Snha R P, Fuel cent Shp Operaton An Optmzaton Approach, 6 th Internatonal Engneerng Conference (ECO 2013) 1-4 July 2013, Kuchng, Malaysa [5] Thomas Hellstrom, Optmum Ptch, Speed and Fuel Control at Sea, Journal of Marne Scences and Technology, Vol 12, o2 pp 71-77(2004) [6] Stefan Petursson, Predctng Optmal Trm Confguraton of Marne Vessels wth respect to fuel usage, Master Thess, School of Engneerng and atural Scences, Unversty of Iceland, Reykjavk 2009 [7] Rashad A, Mahy A. EL, Energy and Exergy Analyss of Steam Power Plant n Egypt, Internatonal Conference on Aerospace Scences & Avaton Technology, ASAT-13, May , asat@mtc.edu.eg [8] Snha R P, Wan M orsan Wan k, Energy Analyss of Steam Power Plant of a Medum Sze LG Tanker, Internatonal Conference on Martme Technology, Kuala Terengganu, [9] Zab Bazar, Tore Longva, Assessment of IMO Mandated Energy cency measures for Internatonal Shppng, L:\LED\IF\PRESS\2011\EEDI Study Presentaton\Report. 6