EMERGY SYNTHESIS 6: Theory and Applications of the Emergy Methodology

Transcription

1 EMERGY SYNTHESIS 6: Theory and Applcatons of the Emergy Methodology Proceedngs from the Sxth Bennal Emergy Conference, January 14 16, 2010, Ganesvlle, Florda Edted by Mar T. Brown Unversty of Florda Ganesvlle, Florda Managng Edtor Sharlynn Sweeney Unversty of Florda Ganesvlle, Florda Assocate Edtors Danel E. Campbell US EPA Narragansett, Rhode Island Shu-L Huang Natonal Tape Unversty Tape, Tawan Enrque Ortega State Unversty of Campnas Campnas, Brazl Torbörn Rydberg Centre for Sustanable Agrculture Uppsala, Sweden Davd Tlley Unversty of Maryland College Par, Maryland Sergo Ulgat Parthenope Unversty of Napol Napol, Italy December 2011 The Center for Envronmental Polcy Department of Envronmental Engneerng Scences Unversty of Florda Ganesvlle, FL

2 4 Crtcal Revew of the Usage of Unt Emergy Values n Recent Studes Nana Yaw Amponsah and O. Le Corre ABSTRACT Unt Emergy Values (UEVs) s undoubtedly an mportant concept n emergy studes. UEVs are needed n evaluatng a product or servce s emergy value. Many dfferent UEVs, however, exst for a smlar product or servce accordng to the specfc tme, locaton and technologcal development. The concept of UEV maes emergy unque n that t s path dependent. Two systems start and end at the same state, but the paths they traversed were very dfferent, thus ther UEVs are dfferent even though the output s the same. UEV calculatons can be qute tedous, wth authors or emergy evaluators relyng on publshed UEVs. As such, most UEVs are selected based on the dscrmnaton (predlecton) of the analyst. For example, the UEV for electrc power vares greatly dependng on the type of process used (coal, hydro, wood, wnd, etc), the locaton of the plant (Brazl, Thaland, etc), the year of calculaton, etc. Ths paper presents a comprehensve revew of UEVs (wth focus on transformtes) for several smlar products and servces based on tme (year of calculaton), locaton and technology. The use of UEVs n recent studes wth references to past studes s revewed showng n some specfc cases where UEVs selected by the nvestgator mght be questonable. INTRODUCTION In a world where effcency (not only n the mechancal or thermal sense) s vtal for the economy and well-beng of the world populaton, t s mportant to consder methods to model effcences of processes and systems that are truly global. One of such tools s emergy. By defnton, emergy s the amount of energy of one form (usually solar energy) that s requred, drectly or ndrectly, to provde a gven flow or storage of energy or matter (Odum 1996 [3], Odum 2000[17]). The rato of emergy requred to mae a product to the energy, mass or unts of the respectve materal or energy flow of the product s called the Unt Emergy Value (UEV) [13][2]. Some common UEVs nclude transformty, specfc emergy and Emergy per Unt Money. Solar emergy s expressed n solar emergy oules (called solar emoules or sej) whereas solar transformty s a rato of solar emergy oules per Joule of output flow (sej/j). Materals (specfc emergy) are expressed as emergy per mass (sej/g)[12]. The UEV of solar radaton s assumed equal to 1. UEVs have been calculated for a wde of varety of energes, materals and servces (Odum 1996 [3], Odum 2000[17]); Brown and Ulgat [4]). The am of ths paper s to crtcally consder the use of UEVs especally transformtes, n recent emergy studes. It sees to defne UEVs n a comprehensve form, ponts out some lmts n ts applcaton and dentfes ts mportance n emergy evaluatons. BACKGROUND Transformty Accordng to Odum (1996[3]) emergy accountng uses a thermodynamc bass for all forms of energy, materals and human servces, and converts them nto equvalents of one form of energy (usually solar energy). Emergy accountng s organzed as a top-down approach where frst systems 39

3 dagrams of processes are drawn to organze evaluatons and account for all nputs and outflows from processes [8]. Tables of the materals, labor and energy flows are constructed from the dagrams. The dfferent flows and ther dmensonal unts are multpled by ther respectve Unt Emergy Values (n whch transformty s one of them) to convert them to ther equvalent solar emergy. Thus transformtes are very mportant n emergy evaluatons. Odum (1996[3]) suggested ten methods for calculatng transformtes. - Evaluatng man energy flows of geobosphere aggregated as necessary coproducts or splts of man flows (methods 1 and 2); - Analyss of subsystems of energy producton and transformaton (3); - From storage development tmes (4); - By combnng other transformtes (5); - From data on energy flows n networs (6); - By means of a computer-solved matrx evaluaton (7), - By source tracng n an energy networ (8), - From herarchcal dstrbuton graphs (9), and turnover tme (10). Transformtes of the man natural flows n the bosphere (wnd, ran, ocean currents, geologcal cycles, etc.) are calculated as the rato of total emergy drvng the entre bosphere to the actual energy of the consdered flow [2]. It may, therefore, be consdered a qualty factor, whch functons as a measure of the ntensty of the bosphere support to the product under study [7]. Transformty as a Unt Emergy Value (UEV) Unt emergy values are calculated based on the emergy requred to produce a product or mantan a servce. There are three man types of Unt Emergy Values n whch Transformty s one of them. The other two are Specfc emergy and Emergy per Unt Money. Specfc emergy s the unt emergy value of matter defned as the emergy per mass, usually expressed as solar emergy per gram (sej/g). Ths s usually from materals (Earth products) and may be best evaluated wth data on emergy per unt mass. Because energy s requred to concentrate materals, the unt emergy value of any substance ncreases wth concentraton. Elements and compounds not abundant n nature, therefore, have hgher emergy/mass ratos when found n concentrated form snce more wor was requred to concentrate them, both spatally and chemcally. Emergy per unt money whch s an UEV s used to convert money payments nto emergy unts. Snce money s pad to people for ther servces and not to the envronment, the contrbuton to a process represented by monetary payments s the emergy that people purchase wth money. How much of a resource that money can buy at any gven tme appears to depend largely on the amount of emergy supportng the economy and the amount of money crculatng and the wllngness to pay or even certan government polces [10]. An average emergy/money rato n solar emoules/unt cost can be calculated by dvdng the total emergy use of a state or naton by ts gross economc product. It vares greatly between natons and has been shown to generally decrease each year [11]. Ths emergy/money rato s useful for evaluatng servce nputs gven n money unts where an average wage rate s approprate. Defnton of Transformty as a Rato A feature of the ratonalst vewpont often assocated wth modernty and scence s to compare qualtatvely dfferent phenomena under transformaton through quanttatve ratos, wth the am of uncoverng any nconsstences n the transformaton change. Ths s defned as the effcency rato of a process. Jorgensen [16] suggests that transformty s also a strong ndcator of the effcency of the system and le the effcency rato; transformty s quanttatvely defned by a smple nput-output rato. The transformty rato, however, s the nverse of the effcency rato n that t nvolves both ndrect and drect energy flows rather than smply drect nput-output energy rato of energy 40

4 effcency. In other words, t may be defned as the rato of emergy nput to energy output. It was, however, realzed that the term 'energy output' refers to both the useful energy and the non-useful energy outputs. Scubba and Ulgat (2005[1]) argue that the concept of transformty s to capture the emergy nvested per unt product, or useful output. The concept of transformty was then further refned by the same authors as the rato of nput emergy dsspated (avalablty used up) to the unt output exergy. From a practcal pont of vew, Transformty s useful as a convenent way of determnng the emergy of commonly used resources and commodtes. Several studes n lterature rely on the transformtes calculated by Odum and co-worers [17] to calculate the emergy of ther nputs. Accordng to Scubba and Ulgat [1], the total solar emergy (U), drvng a producton process can be expressed as: U TrEx ( ), I = {1.n} (1) Where E x () s the exergy and T r s the solar Transformty of the th nput flow. In another way, the total solar emergy (U) s calculated over all the ndependent nput flows (.e. flows that are not orgnated by the same source). The nputs E x () to a process can be locally renewable (R ), locally non-renewable (N ) or mported from outsde the system (F, feed bacs suppled from outsde to renforce the process). As such, solar emergy (U) can be dfferently defned as: U T R T N T F = {1,,m}; = {1,,m 1 }; = {1,,m 2 } (2) r r r The total solar emergy (U), drvng a process s assgned to the output as a measure of the resource nvestment requred. The UEV of the output flow Tr out s defned as: U Trout (3) Exout Where Ex out s the product exergy. Substtutng (2) n (3) gves: Tr out T r R T r N out T r F (4) Ex RESEARCH QUESTIONS Transformty Values and Current Use To derve the Transformty value of a resource or product, t s necessary to trace bac through all the resource and energy flows that were used for ts producton, and express all the nputs n the amount of emergy that went nto ther own producton process. To avod the emergy calculaton of resources and commodtes every tme a process s evaluated, unt Transformty values establshed earler are commonly used. In a stuaton where more than one process could yeld a smlar product ndependently, can one assume that the Transformty of the product s the same ndependent of the technology or process used? Accordng to the process effcences along a gven pathway, more or less energy mght have been requred to reach the same result. The 2nd law of thermodynamcs dctates that there s a lower lmt below whch a product cannot be made. There s also an upper lmt above whch the process would not be feasble n practce although, n prncple, one could nvest an nfnte amount of fuel n a process and thus have an nfntely hgh Transformty. As such transformtes are not constant nor have they the same value for the same product everywhere, snce many dfferent pathways may be chosen to reach the same end state. As such there s no sngle unt emergy value for most products, but typcally a range: average values are used whenever the exact orgn of a resource or commodty s not nown or not calculated separately. Most emergy analysts commonly use 41

5 Transformty values derved from other studes, by assumng they are stll vald under dfferent condtons of place &/or tme. Ths assumpton may be qute subectve and creates doubts n readers or users mnds. An ncorrect choce of a Transformty value may affect all the other calculatons and the ultmate valdty of the results. What nforms our choces? Few emergy analyses n recent years have recalculated transformty values for ther specfc research. Instead most have used publshed values whch rase some doubts about ther valdty. Usng Mellaud s [5] fundamental thoughts as a bass, some sense of the possble magntude of error may be establshed. Consderng the UEV of electrcty for example, several values can be found from the lterature whch leads to some confuson. Odum [3] publshed several UEV values for electrcty dependng on ts source. Table 1 presents these values. Table 1 presents dfferent values of electrcty transformtes establshed for varous places and types of electrcty producton processes: hydroelectrcty s for example calculated for Sweden and Brazl wth transformtes equal to 8.0E+04 sej/j and 1.65E+05 sej/j, respectvely. It s obvous from Table 2 that for a sngle product (electrcty), there are dfferent transformty values. Authors usng these values, for example, Feng et al (2009[15]) the transformty value selected was from Odum 1996 [3], whle Paol (2008[9]) used the average transformty value of electrcty from Odum (1996[3]). It appears that untl less tedous methods for calculatng transformtes are accepted one should be wary of assumng the publshed transformty values are a vald choce for one s own analyss. At the least, the selecton of transformty values under smlar crcumstances to one s own specfc case would reduce some nconsstences and doubts when evaluatng systems. CONCLUSION UEVs are a very central concept n emergy accountng. Although UEVs calculated by H.T. Odum and hs group are avalable n scentfc lterature for use n current and future studes, t s mportant to revst these values and chec ther qualty before usng them. When a large set of UEVs are avalable, other natural and economc processes can be evaluated by calculatng nput flows, throughput flows, storages wthn the system, and the fnal products n emergy unts. Because the state Table 1: Electrcty UEV values by sources (Odum 1996). Source Value (sej/j) Coal 160, , Thaland, 2 Sweden, 3 Brazl, 4 Texas Hydro 80,246 1,2 165,000 3 Wood 203, ,222 1 Lgnte 151, ,384 4 Table 2: UEV values for electrcty n recent studes and ther respectve authors. Author Value (sej/j) Feng et al, E+05 Paol et al, E+05 Mellaud et al, E+05 Cavalett et al, E+05 Pzzgallo et al, E+05 42

6 of scentfc nowledge s n perpetual flux, calculatons of transformtes are open to revson. We have presented ths paper to revst or rather deepen the dscussons on a crtcal revew of avalable UEVs whch most emergy analysts use n ther studes, snce we beleve the emergy method s stll undergong mprovement and development. One of the man arguments of emergy crtcs s related to bad qualty UEVs used n evaluatons. Ths could reduce the accuracy of fnal ndcators and the effcacy of convncng polcy maers to prortze emergy evaluatons, as they do wth other tradtonal evaluaton methods such as Lfe Cycle Assessments, Materal Flow Accountng etc. Some mportant ssues were rased n ths paper concernng a choce of determned UEV n emergy evaluatons. Avalable UEV calculated from prevous studes should be carefully selected before use n recent evaluatons. If possble, an explanaton about why that UEV was chosen would be useful. REFERENCES Barggl, S., M. Rauge, S. Ulgat Comparson of thermodynamc and envronmental ndexes of natural gas, syngas and hydrogen producton processes. Energy, Volume 29, Issues 12-15, Pages Bastanon, S., D. Campbell, L.Susan, E. Tezz The solar transformty of ol and petroleum natural gas. Ecologcal Modellng, Volume 186, Issue 2, Pages Brown M.T., Buranaarn V Emergy ndces and ratos for sustanable materal cycles and recycle optons, resources conservaton & recyclng, Elsever, vol. 38, pp Brown M.T., Ulgat S Emergy analyss and envronmental accountng. Encyclopeda of Energy, Volume 2. Elsever. Campbell D. E., Mesch E. A Envronmental Accountng Usng Emergy: Evaluaton of the State of West Vrgna, U.S. Envronmental Protecton Agency. Cavalett O., Ferraz J. de Queroz, Ortega E Emergy assessment of ntegrated producton systems of grans, pg and fsh n small farms n the South Brazl, Ecologcal Modellng, Volume 193, Issues 3-4, Pages Feng, X., Wang, L., Mn, S Industral emergy evaluaton for hydrogen producton system from bomass and natural gas. Appled Energy, 86, Hau J. G Integratng Lfe Cycle Assessment, Exergy and Emergy Analyses, A thess submtted to the Oho State Unversty. Jorge L. H., Bash B Promse and problems of emergy analyss, ournal of ecologcal modellng, Ecologcal Modellng, Volume 178, Issues 1-2, Pages Jørgensen, S.E., Nelsen, S.N., Meer, H.F., Emergy, envron, exergy and ecologcal modellng. Ecol. Model. 77, Mellaud F., Gay J.-B Brown M.T., Evaluaton of a buldng usng the emergy method, Solar Energy, Volume 79, Issue 2, Pages Paol C., Vassallo P., Fabano M Solar power: An approach to UEV evaluaton, Ecologcal Engneerng, Volume 34, Issue 3, Pages Pzzgallo A.C.I., Grana C., Borsa S The ont use of LCA and emergy evaluaton for the analyss of two Italan wne farms, Journal of Envronmental Management, Volume 86, Issue 2, Pages Odum H.T Envronmental accountng: emergy and envronmental decson mang, John Wley and Sons, New Yor. Odum H.T., Peterson N Smulaton and Evaluaton wth energy systems blocs, ecologcal modellng, Ecologcal Modellng, Volume 93, Issues 1-3, Pages Odum, H.T., Brown, M.T., Wllams, S.B., Handboo of Emergy Evaluaton: A Compendum of Data for Emergy Computaton Issued n a Seres of Folos. Folo#1 Introducton and Global Budget. Center for Envronmental Polcy, Unversty of Florda, USA. Scubba E., Ulgat S Emergy and exergy analyses: Complementary methods or rreducble deologcal optons? Energy, Volume 30, Issue 10, Pages

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