ESTIMATION METHODS FOR THERMOPHYSICAL PROPERTIES OF CAMELINA SATIVA CRUDE OIL

Transcription

1 U.P.B. Sc. Bull., Seres B, Vol. 78, Iss. 1, 2016 ISSN ESTIMATION METHODS FOR THERMOPHYSICAL PROPERTIES OF CAMELINA SATIVA CRUDE OIL Andreea Crstna PETCU 1, Valentn PLEŞU 2, Cornelu BERBENTE 3 Camelna s one of the most promsng sources of renewable fuels. The crude ol obtaned from ths plant can be chemcally treated and converted nto bo-desel or bo-kerosene. To study straght camelna ol combuston process s very mportant to know as many of ts propertes as possble. In ths artcle, estmaton methods of several thermophyscal propertes, such as: crtcal propertes, densty, thermal conductvty, and specfc heat are presented. Where t was possble, the estmated values have been compared wth expermental measurements, thus valdatng the used method. Keywords: camelna ol, estmaton methods, thermophyscal propertes 1. Introducton Camelna ol s a new, promsng feedstock for second generaton bofuels. The bo-kerosene obtaned from camelna ol meets all the performance and safety requrements so that t can be used n avaton. Blends of classc avaton fuel / bo-kerosene obtaned from camelna ol have been successfully tested on fghtng planes and passenger planes [1]. Accordng to European drectves 2003/30/CE and 2009/28/CE, crude vegetable ols are also consdered bofuels. In the specalzed lterature, there s scarce nformaton regardng the combuston process of crude vegetable ols, n partcular camelna ol. The possblty of usng straght camelna ol as fuel for terrestral applcatons has been taken n consderaton because the process of obtanng the vegetable ol s cheaper and less tme consumng then obtanng bofuels from vegetable ols. To understand better the combuston process of the crude camelna ol, s very mportant to know as many of ts propertes as possble. In ths paper, estmaton methods for several thermophyscal propertes are presented and appled for the partcular case of crude vegetable camelna ol. To valdate the used methods, the estmated values have been compared wth expermental 1 PhD. student, Romanan Research & Development Insttute for Gas Turbnes COMOTI Bucharest, Romana, e-mal: andreea.petcu@comot.ro 2 Prof., Faculty of Appled Chemstry and Materals Scence, Unversty POLITEHNICA of Bucharest, Romana, e-mal: v_plesu@chm.upb.ro 3 Prof., Faculty of Aerospace Engneerng, Unversty POLITEHNICA of Bucharest, Romana, e- mal: berbente@yahoo.com

2 60 Andreea Crstna Petcu, Valentn Pleşu, Cornelu Berbente measurements, where such data were avalable. A detaled presentaton of the expermental procedure used for obtanng the expermental data whch wll be presented n ths paper, can be found n reference [2]. 2. Camelna ol molar weght estmaton The calculatons presented n ths artcle are based on the fatty acds camelna ol chemcal composton, gven n Table 1. The camelna ol fatty acds composton has been analyzed at the Dangerous substances, waste and resdual water testng laboratory from the Natonal Research and Development Insttute for Chemstry and Petrochemstry. Table 1 Camelna ol fatty acds composton Fatty acd Molar fracton Molar weght MW (g/mol) 1 Palmtc acd(c16) Stearc acd (C18) Olec acd (C18:1) Lnolec acd (C18:2) Lnolenc acd (C18:3) Ecosanoc acd (C20:1) Behenc acd (C22) Erucc acd (C22:1) The fatty acds composton of the camelna ol cultvated n Romana, and presented n Table 1, s smlar, but not the same as those reported for ols obtaned from camelna seeds cultvated n Span [3] and n Slovena [4]. The dfferences n the composton may be due to dfferent cultvaton regons and dfferent growng condtons. These fatty acds are found n the camelna ol n the form of trglycerdes. The mathematcal methods presented n ths artcle estmate the termophyscal propertes of these trglycerdes. The camelna ol thermophyscal propertes are calculated startng from these values and consderng that the molar fracton of these trglycerdes s equal wth the molar fracton of the fatty acd n ther composton. The camelna ol molar weght has been calculated usng the followng relaton [5]: MW = 3 x MW ol + (1) where x represents the molar fracton of the fatty acd n the ol's composton, and MW s the molar weght of the respectve fatty acd. Accordng to equaton (1), n order to estmate the molar weght of camelna ol s necessary to calculate frst the weght average molecular weght of all the fatty acds components of the compound, based on ther ndvdual molecular weghts and mole fractons. Ths

3 Estmaton methods for thermophyscal propertes of camelna satva crude ol 61 s multpled by 3 to take nto account the 3 dentcal fatty acd chans found n the fatty acd correspondng trglycerde. In addton, one also needs to take nto account the glycerol part of the trglycerde, whch s composed of 3 carbon atoms and 5 hydrogen atoms (-CH 2- CH-CH 2 -), as well as the dfference of 3 hydrogen atoms between the fatty acds and the fatty acd chans n the composton of the trglycerde. The sum of these contrbutons, calculated usng equaton (2) [5], leads to the obtanng of the second term on the rght-hand sde of equaton (1): 3 MWCarbon + 5 MWHdrogen 3 MWHdrogen = (2) By applyng equaton (1) the molar weght of the camelna ol has been estmated to g/mol. 3. Crtcal propertes estmaton methods To determne the thermophyscal propertes of a substance, estmaton methods use as nput data the characterstc constants of the respectve compound, defned n the followng: normal bolng pont, crtcal temperature, crtcal pressure, crtcal volume and acentrc factor. To determne expermentally these constants s very dffcult, because the majorty of substances chemcally decompose before reachng the crtcal pont. The crtcal temperature represents the temperature value above whch the substance can no longer be lquefed, no matter how much pressure s appled. The crtcal pressure s the pressure of the substance's vapor pressure at the crtcal temperature. The crtcal volume s the volume occuped by 1 mole of substance at ts crtcal temperature and pressure. The normal bolng pont represents the temperature value at whch the compound's vapor pressure s equal to the atmospherc pressure [6]. The acentrc factor s a measure of the sphercty of the molecule [7]. The used estmaton methods are presented n Table 2. Table 2 Crtcal propertes estmaton methods Method Equaton Joback [7] T b [ K] = 198+ x ΔT b (3) 2 1 Tc [ K] = T b x ΔTc ( x ΔTc) (4) P [ bar] ( n x P ) 2 c = + A Δ c (5) 3 Vc [ cm / mol] = xδvc (6) Constantnou & Gan [8] T b [ K ] = ln( x Δ T b1 + y ΔT b2 ) (7) T c[ K ] = ln( x Δ T c 1 + x Δ T c2 ) (8)

4 62 Andreea Crstna Petcu, Valentn Pleşu, Cornelu Berbente 2 Pc [ bar] = ( x Δ P c 1 + y Δ P c ) (9) V 3 c[ cm / ] = ( x Δ V c 1 + y Δ V c2 ) (10) Fedor [6,9] Tc [ K] = 535 log 10 ( x ΔTc) (11) 3 Vc [ cm / mol] = x ΔV c (12) Marrero & Gan [10] T b [ ] ln( x T b1 y b2 ) (13) Tc [ K] = ln( x Δ T c 1 + x ΔT c2 ) (14) 2 Pc [ bar] = ( x Δ P c 1 + y Δ P c ) (15) 3 Vc [ cm / mol] = ( x Δ V c 1 + y ΔV c2 ) (16) Nannoolal [11] x ΔT T [ ] b b K = n (17) Banks [12] log 10 T b [ ] = / M (18) Burnop [12] log 10 T b [ ] x b M 8 / M (19) The results obtaned usng the above estmaton methods are summarzed n Tables 3-6. Table 3 Estmaton of normal bolng pont T b Constantnou Gan & T b [K] Joback Nannoolal Banks Burnop & Gan Marrero Trpalmtn 1, Trstearn 1, Trolen 1, , Trlnolen 1, , Trlnolenn 1, , Trecosanon 1, Trbehenn 1, , Trerucn 1, , Camelna ol 1,710,95 828,65 852,33 1, Table 4 Estmaton of crtcal temperature T c [K] Joback Constantnou & Gan Gan & Marrero Fedor Trpalmtn 3, , , Trstearn 4, , , Trolen 4, , , Trlnolen 3, , , Trlnolenn 3, , , Trecosanon 8, , ,062.49

5 Estmaton methods for thermophyscal propertes of camelna satva crude ol 63 Trbehenn 94, , , , Trerucn 23, , , , Camelna ol 4, , , Table 5 Estmaton of crtcal pressure P c [bar] Joback Constantnou & Gan Gan & Marrero Trpalmtn Trstearn Trolen Trlnolen Trlnolenn Trecosanon Trbehenn Trerucn Camelna ol Table 6 Estmaton of crtcal volume V c [cm 3 Constantnou & Gan & /mol] Joback Gan Marrero Fedor Trpalmtn 2, , , , Trstearn 3, , , , Trolen 3, , , , Trlnolen 3, , , , Trlnolenn 3, , , , Trecosanon 3, , , , Trbehenn 3, , , , Trerucn 3, , , , Camelna ol 3, , , , There are no expermental data or nformaton n the specalzed lterature regardng these propertes for the camelna ol. In Table 7, values of the crtcal propertes of smlar vegetable ols and of trglycerdes found n the composton of the camelna ol, avalable n the specalzed lterature, are presented. Table 7 Crtcal propertes values found n the lterature Substance T b [K] T c [K] P c [bar] V c [cm3/mol] Rapeseed ol 584 [13] 765 [13] - - Jatropha ol [14] [14] - - Trpalmtn [15] 675 [16] Trolen [15] 953 [17] 977 [18] [17] 3.34 [18] 3090 [17] 3250 [18] Trstearn 682 [14] - - -

6 64 Andreea Crstna Petcu, Valentn Pleşu, Cornelu Berbente Comparng the lterature data wth the calculated data, t has been concluded that the best result for the normal bolng pont has been obtaned usng the Banks method [12], whle for the crtcal propertes the best results have been obtaned usng the Constantnou & Gan method [8]. A method to verfy the consstency of the crtcal propertes values s to calculate the crtc compressblty factor, gven by the relaton (20) [6]: Pc Vc Zc = (20) R Tc Ths factor s value should be smaller than [7]. In our case ths factor has the value of Another mportant materal constant whch s used as nput data n other estmaton methods s the acentrc factor. Ths factor s calculated usng the relaton (21) [7]: Zc = ω (21) For the camelna ol, the value of 1.96 has been obtaned. 4. Densty estmaton methods To estmate the densty of camelna ol, two methods have been used: the Ihmels method [5] and the Zong method [5]. The calculaton formula proposed by the Ihmels method s: MW MW ρ = = (22) V nδν where MW represents the molar weght and V the molar volume. The molar volume s calculated by summng up the volume group contrbutons Δν multpled by the number of group's appearances n the compound, n. Δν s calculated usng the followng temperature dependng polynomal functon [5]: 2 Δ ν = A + BT + CT (23) The values of the structural group specfc coeffcents A, B and C are presented n reference [5]. The calculaton formula proposed by the Zong method s [5]: MW MW ρ = = (24) V N frag, A VA( T) where N frag. A represents the number of fragment A present n the compound, and VA ( T) represents the molar volume of the respectve fragment. VA ( T ) s gven by the followng relaton [5]:

7 Estmaton methods for thermophyscal propertes of camelna satva crude ol 65 V ( T) A 1+ B T 2, A = (25) B1, A The values of coeffcents B 1,A and B 2,A are presented n reference [5]. The results obtaned by usng the estmaton methods presented above are summarzed n Table 8. Table 8 Camelna ol densty ρ [kg/m 3 ] T[K] Expermental data Ihmels method Error Zong method Error % % % % % % % % % % % % % % % % % % % % Both methods have a good accuracy n estmatng the camelna ol's densty, as t can been observed from the data presented n Table 8. Comparng the two methods, the values obtaned wth the Zong method are n a very good agreement to the expermental data, havng an error under 1%. By extrapolatng the obtaned data on a larger temperature range than the one for whch expermental data are avalable, t can be observed n Fg. 1 that the results obtaned wth the Zong method are very closed to the those obtaned by extrapolatng the expermental data, whle the results obtaned usng the Ihmels method tend to dverge, startng from the temperature of 450 K. Fg. 1 Camelna ol densty ρ (kg/m 3 )

8 66 Andreea Crstna Petcu, Valentn Pleşu, Cornelu Berbente 5. Specfc heat estmaton methods To estmate the camelna ol specfc heat at constant pressure two methods have been used: the Ceran method [5] and the Zong method [5]. The calculaton formula proposed by the Ceran method s: Cp = Nk ( Ak + Bk T) (26) where N k represents the number of structural groups k present n the substance, and A k and B k are the method s coeffcents specfc to each structural group. The values of parameters A k and B k used n the calculatons are presented n [5]. The calculaton formula proposed by the Zong method s: Cp = N frag. A CpA, ( T) (27) where N frag. A represents the number of fragment A present n the substance, and CpA, ( T ) represents the specfc heat of fragment A. CpA, ( T) s calculated usng the lnear equaton below: CpA, ( T) = A1, A+ A2, A( T) (28) The values of parameters A 1,A and A 2,A, specfc to each fragment, used n the calculatons are presented n [5]. The results obtaned by usng the estmaton methods presented above are summarzed n Table 9. Table 9 Camelna ol specfc heat c p [J/(kg K)] T[K] Expermental data Ceran method Error Zong method Error 293 2,053 1, % 2, % 294 2,043 1, % 2, % 295 2,056 1, % 2, % 296 2,070 1, % 2, % 297 2,059 1, % 2, % 298 2,072 1, % 2, % 299 2,062 1, % 2, % 300 2,075 1, % 2, % 301 2,089 1, % 2, % 302 2,078 1, % 2, % 303 2,092 1, % 2, % From the results presented above, t can be observed that, for the temperature range for whch expermental data are avalable, the values obtaned usng both estmaton methods are comparable. Comparng them wth the expermental data, the error n the case of the Ceran method s around 7%, whle n the case of the Zong method the error s smaller, beng around 2%.

9 Estmaton methods for thermophyscal propertes of camelna satva crude ol 67 Extrapolatng the results on a larger temperature nterval, t can be observed from Fg. 2 that the results obtaned usng the Ceran method follow the trend of the expermental data, whle the results obtaned usng the Zong method get farther away wth the ncrease of the temperature. Fg. 2 Specfc heat of camelna ol [J/(kmol K)] 6. Thermal conductvty estmaton methods To estmate camelna ol thermal conductvty, two methods have been used: the Sastr-Rao method [6] and the Baroncn method [6]. The calculaton formula proposed by the Sastr-Rao method s: k = k b α β (29) kb = nδk (30) where: γ 1 T r β = 1 (31) 1 T br where n represents the number of group n the compound, Δk s the coeffcent specfc to each group, T r s the reduced temperature and Tbr represents the rato of the normal bolng pont and the crtcal temperature. The constants α and γ have the followng values: 0.16, respectvely 0.2. The values of the Δk coeffcents used n the calculatons are gven n reference [6]. The calculaton formula proposed by the Baroncn method s: 0.38 α β γ (1 Tr ) b c 1/6 Tr k = A T M T (32)

10 68 Andreea Crstna Petcu, Valentn Pleşu, Cornelu Berbente where M represents the molar mass (g/mol), T b s the normal bolng pont, T c s the crtcal temperature, T r s the reduced temperature, and A, α, β andγ are constants specfc to the method. In the case of esters, these constants have the followng values: A=0.0415, α=1.2, β=1 andγ =0.167 [6]. In the case of camelna ol thermal conductvty, expermental data are avalable only for the temperature of 298 K. Comparng ths value wth the ones obtaned by applyng the estmaton methods the followng errors have resulted. Table 10 Thermal conductvty of camelna ol k [W/(m K)] T[K] Expermental data Sastr-Rao Error Baroncn Error method method % % From the results presented above, t can be concluded that the Sastr-Rao method s better suted for estmatng the thermal conductvty of camelna ol at the temperature of 298 K. Snce no expermental data are avalable for other temperatures, the accuracy of the method cannot be assessed for other temperature values. 7. Conclusons Fg. 3 Thermal conductvty of camelna ol [W/(m K)] In ths paper thermophyscal propertes estmaton methods for the partcular case of camelna crude ol have been presented. The lterature data regardng these propertes for the camelna ol s very scarce. Some of the camelna ols propertes have been determned expermentally, but not on a very large temperature nterval. Beng mportant to know as many as possble

11 Estmaton methods for thermophyscal propertes of camelna satva crude ol 69 propertes of camelna ol to better understand ts combuston process, mathematcal methods have been employed to estmate some of these propertes. In the case of the crtcal propertes of the camelna ol, t has been concluded that the normal bolng pont s estmated wth the best accuracy by the Banks method, whle the crtcal temperature, pressure and volume are estmated wth the best accuracy by the Constantnou & Gan method. In the case of densty, although on the temperature nterval for whch expermental data s avalable both presented methods have good accuracy, on a larger temperature range the Zong method s the most accurate. In the case of the specfc heat at constant pressure, on the temperature range for whch expermental data s avalable both methods have comparable errors: the Zong method 12-13%, and the Ceran method 17-18%. Extrapolatng on a larger temperature nterval, the results obtaned wth the Ceran method follow the trend gven by the expermental data, whle the results obtaned usng the Zong method become dvergent above a certan temperature. In the case of the thermal conductvty, data for only one temperature value, 298 K, s avalable. Two methods have been used to estmate the thermal conductvty correspondng to ths temperature value. The best result has been obtaned by the Sastr-Rao method, wth an error under 2%. Other expermental data not beng avalable, t cannot be sad f the results obtaned wth ths estmaton method on larger temperature ntervals wll have the same good accuracy. The values of the camelna ol thermophyscal propertes presented n ths artcle are very smlar wth those of varous vegetable ols [13, 19, 20], ols from whch bofuels can be obtaned. Thus, for the future t s consdered to carry out straght camelna ol combuston tests on a heatng plant s burner. R E F E R E N C E S [1]. D.R. Shonnard, L. Wllams, T.N. Kalnes, Camelna-Derved Jet Fuel and Desel: Sustanable Advanced Bofuels, Envronmental Progress & Sustanable Energy, vol. 29, no. 3, p , 2010 [2]. A.C. Petcu, R. Carlanescu, C. Berbente, Straght and Blended Camelna Ol Propertes, Recent Advances n Mechancal Engneerng Seres, vol. 11, p , 2014 [3]. C. Cubota-Rose, J.R. Ruz, M.J. Ramos, A. Perez, Bodesel from Camelna satva: A comprehensve charactersaton, Fuel, vol. 105, p , 2013 [4]. H. Abramovc, V. Abram, Physco-Chemcal Propertes, Composton and Oxdatve Stablty of Camelna satva Ol, Food Technology and Botechnology, vol. 43, p.63-70, 2005 [5]. Y.C. Su, Y.A. Lu, "Selecton of predcton methods for thermophyscal propertes for process modelng and product desgn of bodesel manufacturng", Journal of Industral and Engneerng Chemstry Research, vol. 50, p , 2011 [6]. D.W. Green, R.H. Perry, "Perry s Chemcal Engneers Handbook", 8 th edton, McGraw Hll, 2008

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