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Comments on “Experimental investigations on scaled-up methane hydrate production with surfactant promotion: Energy considerations”
Journal of Petroleum Science and Engineering ∎ (∎∎∎∎) ∎∎∎–∎∎∎
Contents lists available at ScienceDirect
Journal of Petroleum Science and Engineering journal homepage: www.elsevier.com/locate/petrol
Comments on “Experimental investigations on scaled-up methane hydrate production with surfactant promotion: Energy considerations” Yasuhiko H. Mori n Department of Mechanical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan
art ic l e i nf o
a b s t r a c t
Article history: Received 2 November 2014 Accepted 17 February 2015
Different opinions are proposed regarding the two major conclusions that Brinchi et al. (2014) described in their recent paper published in this journal [Brinchi et al., J. Petrol. Sci. Eng. 120, 187 193 (2014)]. Although the authors concluded that the gas-compression work is the dominant factor in the total energy consumption required for hydrate production, the gas-compression work should significantly vary depending on the initial pressure of the hydrate-forming gas. The gas-compression work may be insignificant or even eliminated, if a high-pressure natural gas directly supplied from an adjacent gas well is used for the hydrate production. The authors also concluded that the relatively low values of the gas content (the mass fraction of methane contained in each methane-hydrate slurry formed in their study) should be ascribable to the large size (25 L capacity) of their hydrate reactor, suggesting a negative effect of the increasing reactor size on the quality of the available hydrate slurries. It is pointed out that this second conclusion is inconsistent with the related gas content data previously reported by other research groups. & 2015 Elsevier B.V. All rights reserved.
Keywords: gas hydrate methane hydrate surfactant hydrate formation gas content
In their recent paper published in this journal, Brinchi et al. (2014) reported an experimental study of methane hydrate production using a 25-L spray-chamber-type reactor operated in a semi-batch mode, i.e., an operating mode in which methane gas was quasi-periodically supplied to the reactor to maintain the system pressure nearly constant during each hydrate-production run. An aqueous solution of sodium dodecyl sulfate (SDS), an anionic surfactant, was pumped through the reactor and an external recirculation loop such that it was continuously sprayed into the methane-gas phase inside the reactor. Once the reactorþloop system was charged with a specified amount of the solution before the start of the run, it was no longer replenished with the solution till the end of the run. After the run, a hydrate sample was removed from the reactor for measuring its methane content. Besides simply presenting the raw data of such hydrateproduction experiments, the authors reported their thermodynamicsbased estimates of the following classes of work relevant to each hydrate-production run: (a) the work of gas compression to a prescribed pressure to be maintained inside the reactor during the run, (b) the work of gas cooling to the temperature to be maintained inside the reactor, (c) the work of aqueous-solution cooling to this temperature, and (d) the work of pumping the solution to enable its continuous spraying. Based on the experimental data and the work n
Tel./fax: þ81 45 701 2054. E-mail address: [email protected]
estimates outlined above, the authors claimed two major conclusions, which may be briefly itemized as follows: (1) the gas-compression work (a) is dominant over all the others, (b) (d), and (2) the gas content (defined as the mass fraction of methane in each hydrate sample) measured in this study is significantly lower than those reported in the literature based on the experiments using SDS solutions and smaller (less than 1 L capacity) reactors, and this difference is ascribable to a negative reactor-scale effect on the hydrate production. Both of these conclusions may have important implications for the development of hydrate-based technologies, such as natural-gas storage and transport, separation of CO2 and/or H2S from natural gas or industrial flue gases, etc. However, these conclusions are controvertible from engineering viewpoints. In this “Comments” note, I intend to raise a few technical issues about these conclusions.
1. Is gas-compression work generally dominant in total energy consumption accompanying hydrate production? In principle, the magnitude of the work for compressing the feed gas to a pressure suitable for hydrate production is dependent on the initial pressure of the feed gas, i.e., the pressure at which the feed gas is supplied to the hydrate-production facilities, as well as on the chemical species or composition of the feed gas. In the paper by
http://dx.doi.org/10.1016/j.petrol.2015.02.027 0920-4105/& 2015 Elsevier B.V. All rights reserved.
Please cite this article as: Mori, Y.H., Comments on “Experimental investigations on scaled-up methane hydrate production with surfactant promotion: Energy considerations”. J. Petrol. Sci. Eng. (2015), http://dx.doi.org/10.1016/j.petrol.2015.02.027i
Y.H. Mori / Journal of Petroleum Science and Engineering ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
Table 1 Summarized data relevant to three studies in which methane-hydrate formation in SDS-containing systems was experimentally investigated. Data source
Reactor Type
Brinchi et al. (2014) Okutani et al. (2008) Pang et al. (2007)
Spray chamber equipped with a liquid circulation loop Vessel containing quiescent gas and liquid phases Vessel containing quiescent gas and liquid phases
Aqueous SDS solution Inside volume
SDS Volume of concentration solution used (ppm)
Hydrate-forming pressure
Gas content in hydrate
Liquid-to-hydrate conversion ratio of watera
(MPa)
(%)
(%)
b
25 L
300
4.0 6.0 L
4.0 8.0
3.0 7.2
21 52
942 cm3
125 4000
300 cm3
3.90 7 0.07
11.3 12.6c
85 97d
10 L
2000
1.0 5.0 L
6.4 6.8
12.0 13.1e
92 100
a The values given in this column were deduced from the corresponding gas content values assuming the hydration number for the methane hydrate to be 6.0 (cf. Circone et al. (2005)). b The system pressure was controlled nearly constant at about a prescribed level (8.0, 7.0, 6.0, 5.0 or 4.0 MPa) during each hydrate-forming operation. No systematic pressure dependence was observed in the obtained gas-content data. c Deduced from the asymptotic value of the cumulative volume (at 101.3 kPa and 0 1C) of methane uptake into the hydrate for each experimental run instead of the value at the end of the effective hydrate-formation time (cf. Fig. 3 in the paper by Okutani et al. (2008)). d These values are slightly higher than those at the end of the effective hydrate-formation time which are shown in Fig. 5 in the paper by Okutani et al. (2008). e Deduced from the asymptotic value of the cumulative methane consumption per unit mass of water for each experimental run (cf. Fig. 3 in the paper by Pang et al. (2007)).
Brinchi et al. (2014), however, the initial methane-gas pressure assumed in evaluating the compression work is not specified. Let me first take up the case of natural-gas hydrate production at a gas-processing site close to a gas field. While the wellhead pressure of natural gas may be significantly different from field to field and/or from well to well, it is typically on the order of 10 MPa (100 bar). Thus, the gas may need pressure reduction, instead of compression, in advance of its supply to hydrate-production facilities. If this is the case, the facilities must be free from any gas-compression work. An alternative scenario of utilizing natural-gas hydrates was planned and tested in Japan during the last decade (Watanabe et al., 2008; Horiguchi et al., 2011). This scenario was to produce hydrate pellets at a location adjacent to an onshore liquefied natural gas (LNG) terminal using the natural gas supplied from a regasification plant installed in the terminal. The produced hydrate pellets are transported by specially-designed trucks to gas consumers at inland districts. In the regasification plant, LNG is pressurized to a prescribed level, typically 3 MP (30 bar), in advance of its regasification such that the produced gas can directly flow into local gas-delivery lines without undergoing an energy-consuming gas-compression process. Thus, the gas-compression work in the hydrate-production facilities is limited to that for boosting the pressure from 3 MP, instead of a near-atmospheric pressure (E0.1 MPa), to a level suitable for the hydrate production. In addition, the two classes of cooling work, (b) and (c), can be eliminated, if the cool energy released in the regasification plant is efficiently recovered and transported to the hydrate-production plant. In contrast to the two cases discussed above, relatively large gascompression work will be inevitable, if one applies the hydrate-based separation technology to the capture of CO2 from low-pressure flue gases. Accordingly, the hydrate-based separation technology has little economic advantage over other rival technologies in this case. In conclusion, the ratio of the gas-compression work to the total energy consumption in the process of hydrate production must be significantly different from case to case, mainly depending on the initial pressure of the available hydrate-forming gas.
2. Is the low gas content in hydrates formed in this study ascribable to a negative reactor-scale effect? The gas content (i.e., the mass fraction of methane) in each hydrate sample that Brinchi et al. (2014) obtained with a 300-ppm
SDS solution was, according to Table 1 in their paper, 3.0% at the lowest and 7.2% at the highest. It should be noted here that what they called a “hydrate sample” must have been a mixture of hydrate crystals and the residual liquid, which was left inside the reactor at the end of each hydrate-forming experiment. For the clarity of the discussion which follows, basic literature data concerning the methane-hydrate formation in SDS-containing systems are summarized in Table 1. The data obtained in the study by Brinchi et al. (2014) are compared to those obtained in the previous two studies by Pang et al. (2007) and Okutani et al. (2008). Obviously, the gas-content values obtained by Brinchi et al. (2014) are significantly lower than those that Pang et al. (2007) and Okutani et al. (2008) obtained with smaller reactors. Is this difference in the obtained gas content mainly ascribable, as Brinchi et al. (2014) indicated, to the differences in the scale of the reactors used in the three studies? Despite the over 10fold difference in the reactor scale between the studies by Pang et al. (2007) and Okutani et al. (2008), the gas-content values obtained in these studies are only slightly different from each other. Thus, we cannot consistently interpret the gas-content values obtained in the three studies by simply assuming such a negative scale effect that Brinchi et al. (2014) suggested. Instead, we should pay attention to the structural designs, rather than the scales, of the reactors. Stable operation of a spray-chamber-type reactor, such as the one that Brinchi et al. (2014) used, is possible on the condition that the mixture of the formed hydrate crystals and the residual liquid still has a sufficient fluidity and can be pumped through the external circulation loop attached to the main body of the reactor. The gascontent range from 3.0% to 7.2% corresponds to a 2152% conversion of the water substance contained in the reactor from the liquid phase to the hydrate phase (see Table 1). This fact means that, at the end of each experimental run, the inside space of the reactor used by Brinchi et al. (2014) was occupied by a pool of a dense hydrate slurry (i.e., a dense aqueous-liquid-based suspension of hydrate crystals) and a methane-gas phase. Further operation of the reactor would cause plugging of the circulation-loopþspray-nozzles assembly due to the lack of a sufficient fluidity of the hydrate slurry and the resultant agglomeration of hydrate crystals. In contrast, the reactors used by Pang et al. (2007) and Okutani et al. (2008) were free from any moving or flow-driving mechanism. Hence, these reactors could be safely operated until the aqueous liquid having remained in the interstices of hydrate agglomerates almost disappeared. As discussed above, it does not seem plausible to ascribe the low gas-content values obtained in the study by Brinchi et al. (2014) to the large scale of the used reactor. In addition, it may be
Please cite this article as: Mori, Y.H., Comments on “Experimental investigations on scaled-up methane hydrate production with surfactant promotion: Energy considerations”. J. Petrol. Sci. Eng. (2015), http://dx.doi.org/10.1016/j.petrol.2015.02.027i
Y.H. Mori / Journal of Petroleum Science and Engineering ∎ (∎∎∎∎) ∎∎∎–∎∎∎
worthy to note that an excessive increase in the gas content causing the overly depletion of the liquid in the formed hydrate slurry may be unfavorable for its subsequent use. For example, engineers at the Mitsui Engineering & Shipbuilding Co. found that natural-gas-hydrate slurries containing liquid water up to 40 70% (mass basis) were suitable for use in their hydrate-pellet production machines (Takahashi et al., 2008; Murayama et al., 2011). The gas-content values in such hydrate slurries are estimated to be 4 9%. References Brinchi, L., Castellani, B., Rossi, F., Cotana, F., Morini, E., Nicolini, A., Filipponi, M., 2014. Experimental investigations on scaled-up methane hydrate production with surfactant promotion: energy considerations. J. Pet. Sci. Eng. 120, 187–193. Circone, S., Kirby, S.H., Stern, L.A., 2005. Direct measurement of methane hydrate composition along the hydrate equilibrium boundary. Chem. Eng. Sci. 109, 9468–9475.
3
Horiguchi, K., Watanabe, S., Moriya, H., Nakai, S., Yoshimitsu, A., Taoda, A., 2011. Completion of natural gas hydrate (NGH) overland transportation demonstration project. In: Proceedings of the 7th International Conference on Gas Hydrates. July 17 21, Edinburgh, Scotland, UK, Paper ID: 371. Murayama, T., Iwabuchi, W., Ito, M., Takahashi, M., 2011. Effect of guest gas on pelletizing performance of natural gas hydrate (NGH) pellets. In: Proceedings of the 7th International Conference on Gas Hydrates. July 17 21, Edinburgh, Scotland, UK, Paper ID: 543. Okutani, K., Kuwabara, Y., Mori, Y.H., 2008. Surfactant effects on hydrate formation in an unstirred gas/liquid system: an experimental study using methane and sodium alkyl sulfates. Chem. Eng. Sci. 63, 183–194. Pang, W.X., Chen, G.J., Dandekar, A., Sun, C.Y., Zhang, C.L., 2007. Experimental study on the scale-up of gas storage in the form of hydrate in a quiescent reactor. Chem. Eng. Sci. 62, 2198–2208. Takahashi, M., Moriya, H., Katoh, Y., Iwasaki, T., 2008. Development of natural gas hydrate (NGH) pellet production system by bench scale unit for transportation and storage of NGH pellet. In: Proceedings of the 6th International Conference on Gas Hydrates. July 6 10, Vancouver, BC, Canada, Paper no. P-166. Watanabe, S., Takahashi, S., Mizubayashi, H., Murata, S., Murakami, H., 2008. A demonstration project of NGH land transportation system. In: Proceedings of the 6th International Conference on Gas Hydrates. July 6 10, Vancouver, BC, Canada, Paper no. 5442.
Please cite this article as: Mori, Y.H., Comments on “Experimental investigations on scaled-up methane hydrate production with surfactant promotion: Energy considerations”. J. Petrol. Sci. Eng. (2015), http://dx.doi.org/10.1016/j.petrol.2015.02.027i
Contents lists available at ScienceDirect
Journal of Petroleum Science and Engineering journal homepage: www.elsevier.com/locate/petrol
Comments on “Experimental investigations on scaled-up methane hydrate production with surfactant promotion: Energy considerations” Yasuhiko H. Mori n Department of Mechanical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan
art ic l e i nf o
a b s t r a c t
Article history: Received 2 November 2014 Accepted 17 February 2015
Different opinions are proposed regarding the two major conclusions that Brinchi et al. (2014) described in their recent paper published in this journal [Brinchi et al., J. Petrol. Sci. Eng. 120, 187 193 (2014)]. Although the authors concluded that the gas-compression work is the dominant factor in the total energy consumption required for hydrate production, the gas-compression work should significantly vary depending on the initial pressure of the hydrate-forming gas. The gas-compression work may be insignificant or even eliminated, if a high-pressure natural gas directly supplied from an adjacent gas well is used for the hydrate production. The authors also concluded that the relatively low values of the gas content (the mass fraction of methane contained in each methane-hydrate slurry formed in their study) should be ascribable to the large size (25 L capacity) of their hydrate reactor, suggesting a negative effect of the increasing reactor size on the quality of the available hydrate slurries. It is pointed out that this second conclusion is inconsistent with the related gas content data previously reported by other research groups. & 2015 Elsevier B.V. All rights reserved.
Keywords: gas hydrate methane hydrate surfactant hydrate formation gas content
In their recent paper published in this journal, Brinchi et al. (2014) reported an experimental study of methane hydrate production using a 25-L spray-chamber-type reactor operated in a semi-batch mode, i.e., an operating mode in which methane gas was quasi-periodically supplied to the reactor to maintain the system pressure nearly constant during each hydrate-production run. An aqueous solution of sodium dodecyl sulfate (SDS), an anionic surfactant, was pumped through the reactor and an external recirculation loop such that it was continuously sprayed into the methane-gas phase inside the reactor. Once the reactorþloop system was charged with a specified amount of the solution before the start of the run, it was no longer replenished with the solution till the end of the run. After the run, a hydrate sample was removed from the reactor for measuring its methane content. Besides simply presenting the raw data of such hydrateproduction experiments, the authors reported their thermodynamicsbased estimates of the following classes of work relevant to each hydrate-production run: (a) the work of gas compression to a prescribed pressure to be maintained inside the reactor during the run, (b) the work of gas cooling to the temperature to be maintained inside the reactor, (c) the work of aqueous-solution cooling to this temperature, and (d) the work of pumping the solution to enable its continuous spraying. Based on the experimental data and the work n
Tel./fax: þ81 45 701 2054. E-mail address: [email protected]
estimates outlined above, the authors claimed two major conclusions, which may be briefly itemized as follows: (1) the gas-compression work (a) is dominant over all the others, (b) (d), and (2) the gas content (defined as the mass fraction of methane in each hydrate sample) measured in this study is significantly lower than those reported in the literature based on the experiments using SDS solutions and smaller (less than 1 L capacity) reactors, and this difference is ascribable to a negative reactor-scale effect on the hydrate production. Both of these conclusions may have important implications for the development of hydrate-based technologies, such as natural-gas storage and transport, separation of CO2 and/or H2S from natural gas or industrial flue gases, etc. However, these conclusions are controvertible from engineering viewpoints. In this “Comments” note, I intend to raise a few technical issues about these conclusions.
1. Is gas-compression work generally dominant in total energy consumption accompanying hydrate production? In principle, the magnitude of the work for compressing the feed gas to a pressure suitable for hydrate production is dependent on the initial pressure of the feed gas, i.e., the pressure at which the feed gas is supplied to the hydrate-production facilities, as well as on the chemical species or composition of the feed gas. In the paper by
http://dx.doi.org/10.1016/j.petrol.2015.02.027 0920-4105/& 2015 Elsevier B.V. All rights reserved.
Please cite this article as: Mori, Y.H., Comments on “Experimental investigations on scaled-up methane hydrate production with surfactant promotion: Energy considerations”. J. Petrol. Sci. Eng. (2015), http://dx.doi.org/10.1016/j.petrol.2015.02.027i
Y.H. Mori / Journal of Petroleum Science and Engineering ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
Table 1 Summarized data relevant to three studies in which methane-hydrate formation in SDS-containing systems was experimentally investigated. Data source
Reactor Type
Brinchi et al. (2014) Okutani et al. (2008) Pang et al. (2007)
Spray chamber equipped with a liquid circulation loop Vessel containing quiescent gas and liquid phases Vessel containing quiescent gas and liquid phases
Aqueous SDS solution Inside volume
SDS Volume of concentration solution used (ppm)
Hydrate-forming pressure
Gas content in hydrate
Liquid-to-hydrate conversion ratio of watera
(MPa)
(%)
(%)
b
25 L
300
4.0 6.0 L
4.0 8.0
3.0 7.2
21 52
942 cm3
125 4000
300 cm3
3.90 7 0.07
11.3 12.6c
85 97d
10 L
2000
1.0 5.0 L
6.4 6.8
12.0 13.1e
92 100
a The values given in this column were deduced from the corresponding gas content values assuming the hydration number for the methane hydrate to be 6.0 (cf. Circone et al. (2005)). b The system pressure was controlled nearly constant at about a prescribed level (8.0, 7.0, 6.0, 5.0 or 4.0 MPa) during each hydrate-forming operation. No systematic pressure dependence was observed in the obtained gas-content data. c Deduced from the asymptotic value of the cumulative volume (at 101.3 kPa and 0 1C) of methane uptake into the hydrate for each experimental run instead of the value at the end of the effective hydrate-formation time (cf. Fig. 3 in the paper by Okutani et al. (2008)). d These values are slightly higher than those at the end of the effective hydrate-formation time which are shown in Fig. 5 in the paper by Okutani et al. (2008). e Deduced from the asymptotic value of the cumulative methane consumption per unit mass of water for each experimental run (cf. Fig. 3 in the paper by Pang et al. (2007)).
Brinchi et al. (2014), however, the initial methane-gas pressure assumed in evaluating the compression work is not specified. Let me first take up the case of natural-gas hydrate production at a gas-processing site close to a gas field. While the wellhead pressure of natural gas may be significantly different from field to field and/or from well to well, it is typically on the order of 10 MPa (100 bar). Thus, the gas may need pressure reduction, instead of compression, in advance of its supply to hydrate-production facilities. If this is the case, the facilities must be free from any gas-compression work. An alternative scenario of utilizing natural-gas hydrates was planned and tested in Japan during the last decade (Watanabe et al., 2008; Horiguchi et al., 2011). This scenario was to produce hydrate pellets at a location adjacent to an onshore liquefied natural gas (LNG) terminal using the natural gas supplied from a regasification plant installed in the terminal. The produced hydrate pellets are transported by specially-designed trucks to gas consumers at inland districts. In the regasification plant, LNG is pressurized to a prescribed level, typically 3 MP (30 bar), in advance of its regasification such that the produced gas can directly flow into local gas-delivery lines without undergoing an energy-consuming gas-compression process. Thus, the gas-compression work in the hydrate-production facilities is limited to that for boosting the pressure from 3 MP, instead of a near-atmospheric pressure (E0.1 MPa), to a level suitable for the hydrate production. In addition, the two classes of cooling work, (b) and (c), can be eliminated, if the cool energy released in the regasification plant is efficiently recovered and transported to the hydrate-production plant. In contrast to the two cases discussed above, relatively large gascompression work will be inevitable, if one applies the hydrate-based separation technology to the capture of CO2 from low-pressure flue gases. Accordingly, the hydrate-based separation technology has little economic advantage over other rival technologies in this case. In conclusion, the ratio of the gas-compression work to the total energy consumption in the process of hydrate production must be significantly different from case to case, mainly depending on the initial pressure of the available hydrate-forming gas.
2. Is the low gas content in hydrates formed in this study ascribable to a negative reactor-scale effect? The gas content (i.e., the mass fraction of methane) in each hydrate sample that Brinchi et al. (2014) obtained with a 300-ppm
SDS solution was, according to Table 1 in their paper, 3.0% at the lowest and 7.2% at the highest. It should be noted here that what they called a “hydrate sample” must have been a mixture of hydrate crystals and the residual liquid, which was left inside the reactor at the end of each hydrate-forming experiment. For the clarity of the discussion which follows, basic literature data concerning the methane-hydrate formation in SDS-containing systems are summarized in Table 1. The data obtained in the study by Brinchi et al. (2014) are compared to those obtained in the previous two studies by Pang et al. (2007) and Okutani et al. (2008). Obviously, the gas-content values obtained by Brinchi et al. (2014) are significantly lower than those that Pang et al. (2007) and Okutani et al. (2008) obtained with smaller reactors. Is this difference in the obtained gas content mainly ascribable, as Brinchi et al. (2014) indicated, to the differences in the scale of the reactors used in the three studies? Despite the over 10fold difference in the reactor scale between the studies by Pang et al. (2007) and Okutani et al. (2008), the gas-content values obtained in these studies are only slightly different from each other. Thus, we cannot consistently interpret the gas-content values obtained in the three studies by simply assuming such a negative scale effect that Brinchi et al. (2014) suggested. Instead, we should pay attention to the structural designs, rather than the scales, of the reactors. Stable operation of a spray-chamber-type reactor, such as the one that Brinchi et al. (2014) used, is possible on the condition that the mixture of the formed hydrate crystals and the residual liquid still has a sufficient fluidity and can be pumped through the external circulation loop attached to the main body of the reactor. The gascontent range from 3.0% to 7.2% corresponds to a 2152% conversion of the water substance contained in the reactor from the liquid phase to the hydrate phase (see Table 1). This fact means that, at the end of each experimental run, the inside space of the reactor used by Brinchi et al. (2014) was occupied by a pool of a dense hydrate slurry (i.e., a dense aqueous-liquid-based suspension of hydrate crystals) and a methane-gas phase. Further operation of the reactor would cause plugging of the circulation-loopþspray-nozzles assembly due to the lack of a sufficient fluidity of the hydrate slurry and the resultant agglomeration of hydrate crystals. In contrast, the reactors used by Pang et al. (2007) and Okutani et al. (2008) were free from any moving or flow-driving mechanism. Hence, these reactors could be safely operated until the aqueous liquid having remained in the interstices of hydrate agglomerates almost disappeared. As discussed above, it does not seem plausible to ascribe the low gas-content values obtained in the study by Brinchi et al. (2014) to the large scale of the used reactor. In addition, it may be
Please cite this article as: Mori, Y.H., Comments on “Experimental investigations on scaled-up methane hydrate production with surfactant promotion: Energy considerations”. J. Petrol. Sci. Eng. (2015), http://dx.doi.org/10.1016/j.petrol.2015.02.027i
Y.H. Mori / Journal of Petroleum Science and Engineering ∎ (∎∎∎∎) ∎∎∎–∎∎∎
worthy to note that an excessive increase in the gas content causing the overly depletion of the liquid in the formed hydrate slurry may be unfavorable for its subsequent use. For example, engineers at the Mitsui Engineering & Shipbuilding Co. found that natural-gas-hydrate slurries containing liquid water up to 40 70% (mass basis) were suitable for use in their hydrate-pellet production machines (Takahashi et al., 2008; Murayama et al., 2011). The gas-content values in such hydrate slurries are estimated to be 4 9%. References Brinchi, L., Castellani, B., Rossi, F., Cotana, F., Morini, E., Nicolini, A., Filipponi, M., 2014. Experimental investigations on scaled-up methane hydrate production with surfactant promotion: energy considerations. J. Pet. Sci. Eng. 120, 187–193. Circone, S., Kirby, S.H., Stern, L.A., 2005. Direct measurement of methane hydrate composition along the hydrate equilibrium boundary. Chem. Eng. Sci. 109, 9468–9475.
3
Horiguchi, K., Watanabe, S., Moriya, H., Nakai, S., Yoshimitsu, A., Taoda, A., 2011. Completion of natural gas hydrate (NGH) overland transportation demonstration project. In: Proceedings of the 7th International Conference on Gas Hydrates. July 17 21, Edinburgh, Scotland, UK, Paper ID: 371. Murayama, T., Iwabuchi, W., Ito, M., Takahashi, M., 2011. Effect of guest gas on pelletizing performance of natural gas hydrate (NGH) pellets. In: Proceedings of the 7th International Conference on Gas Hydrates. July 17 21, Edinburgh, Scotland, UK, Paper ID: 543. Okutani, K., Kuwabara, Y., Mori, Y.H., 2008. Surfactant effects on hydrate formation in an unstirred gas/liquid system: an experimental study using methane and sodium alkyl sulfates. Chem. Eng. Sci. 63, 183–194. Pang, W.X., Chen, G.J., Dandekar, A., Sun, C.Y., Zhang, C.L., 2007. Experimental study on the scale-up of gas storage in the form of hydrate in a quiescent reactor. Chem. Eng. Sci. 62, 2198–2208. Takahashi, M., Moriya, H., Katoh, Y., Iwasaki, T., 2008. Development of natural gas hydrate (NGH) pellet production system by bench scale unit for transportation and storage of NGH pellet. In: Proceedings of the 6th International Conference on Gas Hydrates. July 6 10, Vancouver, BC, Canada, Paper no. P-166. Watanabe, S., Takahashi, S., Mizubayashi, H., Murata, S., Murakami, H., 2008. A demonstration project of NGH land transportation system. In: Proceedings of the 6th International Conference on Gas Hydrates. July 6 10, Vancouver, BC, Canada, Paper no. 5442.
Please cite this article as: Mori, Y.H., Comments on “Experimental investigations on scaled-up methane hydrate production with surfactant promotion: Energy considerations”. J. Petrol. Sci. Eng. (2015), http://dx.doi.org/10.1016/j.petrol.2015.02.027i