EXPERIMENTAL INVESTIGATION ON GAS HYDRATE FORMATION IN PRESENCE OF ADDITIVE COMPONENTS

第54卷增刊化工学报VoL 54 SuppL.2003年12月Journal of Chemical Industry and Engineering (China)December 2003EXPERIMENTAL INVESTIGATION ON GASHYDRATE FORMATION IN PRESENCEOF ADDITIVE COMPONENTSSUN Zhigao, FAN Shuanshi and GUO Kaihua?Department of Erruironment Engineering, Yang hou University, Yangzhou 225009, Jiangsu, China;Guangzhou Institute of energy Comversion, The Chinese Academy of Sciences, Guangzhou 510070, Guangdong, China)Abstract Additives were used to increase gas hydrate formation rate and storage capacity. Experimentaltests of methane hydrate formation were carried out in surfactant water solutions in a high-pressure cellSodium dodecyl sulfate (SDS)and alkyl polysaccharide glycoside(APG) were used to increase hydrateformation. The effect of SDS on hydrate formation is more pronounced compared APG. Cyclopentane(CP)also improves hydrate formation rates while it cannot increase methane gas storage capacity.Keywords gas hydrate, additive, storage1 INTRODUCTIONblock further conversion of water to hydrate sothat liquid water is occluded within or under theGas hydrates are crystalline inclusion solid hydrate. Some workers3-6 have studied oncompounds formed by hydrogen-bonding of finding some means for the promotion of hydratewater molecules with helped gas. Gas hydrates formation and reducing occluded water.have drawn much attention these days as not only a Gudmundsen and Borrehaug 7) showed that hydratenew natural energy resource but also a new means technology for transporting natural gas couldor natural gas storage and transport. Gas hydrates reduce cost(24%)compared to liquid natural gashave unique natural gas storage properties(e.g, (LNG ). Khokhar et aL. L5) studied storage180 m gas per m of hydrate). Natural gas hydrate properties of H hydrate with the promoter PVPtechnology is an attractive alternative for storing presence. The hydrate formation for natural gasand transporting natural gas. However, industrial storage and transport purpose has been reportedapplications of hydrate storage processes have beenrecently.2, 6-9hindered by some problems, such as slowfocus of this study is to investigateformation rates, unreacted interstitial water as a experimentally the effect of surfactant and liquidlarge percentage of hydrate mass, the reliability of hydrocarbon on the hydrate formation, particularlyhydrate storage capacity and economy of processto study their ability as hydrate promoter (fornatural gas storage and transport in hydratesHydrate tends to form at vapor-water 2 EXPERIMENTAL APPARATUSnterface, due to the mutual immiscibility of eachAND PROCEDUREphase and the high contents of gas and water inhydrates. Hydrate formation at the interface mayfV凵中国煤化工 p to study naturalgas hyCNMH Gatic diagram of theexperup Is gIven1.ACorresponding author SUN Zhigao. Tel: 86-514-7863852. cylindrical high-pressure reactor is used to produceE-mail:szgyzu@163.comgas hydrate. The reactor is made of stainless steel化工学报December 2003which is designed to operated at pressure up toTable 1 Test fluids used in this work20MPa and temperature in the range of 253--323ComponentPurity of componentK. Its available volume is about 1000 cm. A99.9%water bath was used to provide temperatureSDS≥98%APG98%control of the experiments. There is a interlayeraround the exterior of the reactor. which iscirculated cooling ethylene glycol water solution.The experiments of gas hydrate formationThere are two platinum resistance thermometers were carried out with the presence of additives. Awith an accuracy of +0.01 K. One extends into typical procedure was as follows. The cell wasthe bottom of the cell the other extends into the rinsed with distilled water two times. Air wasgas phase at the top. The pressure was measured evacuated by the vacuum pump. Approximatusing a 10 MPa gauge with an accuracy of +0. 1% 300 g of the surfactant solutions was charged intoof the scale. A constant pressure regulator was the cell for each experiment. The system wasused to maintain constant pressure in the cell cooled to the experimental temperature with aduring the experiments. A model D07-1lM/ZM pressure below hydrate formation pressure. Oncemass gas flowmeter was used to measure gas added the solution in the cell reached the desiredto the cell during hydrate formation. The temperature, the pressure of the cell was raised toflowmeter has a capacity of 0-1000 sccm, at an the experimental pressure by flowing methane intoaccuracy within 2% of full scale and a repeatabilityhe cell. Hydrate formation was followed byof within 0. 2% of flow rate. A data acquisition pressure, temperature, gas mass flows displayedsystem was used to record the pressure andand recorded on the computer.temperature of the cell, gas flow-meter and the 3 RESULTS AND DISCUSSIONtotal gas volume of the consumption gas by theHydrate could form when the experimentalsoftware designed by ourselves in the process oftemperature is lower than hydrate formationhydrate formation as functions of timeequilibrium temperature. In order to reduce theinduction time of hydrate formation, stirring isgaugpressure reg山dhe*usually used during hydrate formationexperiments. By agitation of water, the water-gasinterfacial area is increased and continuallyrenewed to improve hydrate formation rate.Energy costs from stirring increase as slurryhickens. In fact, thickening slurry of a stirredsystem may limit the hydrate mass in the water asFig 1 Schematic diagram of hydratelow as 5% 8. In order to assure hydrate formationat high rate without the disadvantages of a stirredsystem, additives were used in this work. TheThe test fluids used in this work were summed following experiments in this work were carriedin tableSurfactants were weighed on are nf surfactant in theelectronic balance with a readability of +0. 1 mg. r中国煤化工experimentaDistilled water was used in all experiments. WaterCNMHGo5 K. sDs surfactantand cyclopentane were weighed on a electronic concentration was maintained at 300ppm, and APGbalance with a readability of +0. oi gat 500ppm. All tests are done in a quiescentVol 54 SuppL.Journal of Chemical Industry and Engineering (China):“m300ppm SD274.05S≥器434ax 3, 92 MPBtime/minFig 2 Capacity and rate of methanehydrate formation in aqueous SDStime/minFig 3 Capacity and rate of methaneAs seen from figure 2, pressure effected thehydrate formation in aqueous APGhydrate formation rate and storage capacity in SDs 4. 34MPat methane system. the higher pressures, theFigure 4 showed the similar results in thequicker hydrate formation rate and the larger system of SDS +CP methane as in figure 3.54( volume gas/volume hydratestorage capacity was achieved within 425 minutes processing pressure of 4.85MPa, 129 V/V storageat a processing pressure of 4.85MPa, 147 Vcapacity at a processing pressure of 3. 80MPa.storage capacity within 460 minutes at a processing Cyclopentane could reduce time costs of hydratepressure of 4. 34MPaformation (the system with SdS presence cost 425igure 3 showed the effect of APG on hydrate minutes and 340 minutes was cost with theformation. The effect of APG on hydrate presence of SDS and CP for hydratte formation at aformation was not the same as the result in theprocessing pressure of 4. 85MPa)system of SDS methane. As observed fromfigure 3, The system, which was in lowerpressures(p=4. 34MPa), had the larger capacityand the higher hydrate formation rate at the firststage of hydrate formation, and the system of300ppm SDShigher pressures had the larger capacity and theT=27405Kquicker hydrate formation rate at the latter stage of=4.85 MPahydrate formation. 112 V/V storage capacity wasachieved within 455 minutes at a processing100200300pressure of 5. 38MPa, 101 V/V storage capacitywithin 370 minutes at a processing pressure ofFig 4 Capacity and rate of methane hydrate4. 96MPa and 80 V/V storage capacity within 285formation in aqueous SDS+CPminutes at a processing pressure of 4. 34MPa. TheFigure 5 showed the comparison of the effectresult also showed that the effect of APG on of SpS and sDS+ CP on hydrate formation. Thehydrate storage capacity is less pronounced中国煤化工 end cyclopentane oncompared to SDS(147 V/V storage capacity with hydraCNMHGmore pronouncedthe presence of SDS, and 80 V/V storage capacity compared to surfactant SDS only, but the gaswith APG presence at a processing pressure of storage capacity in hydrates had a little drop with化December 2003he presence of cyclopentane. The inductionhydrate formation as there was no need of agitationof hydrate formation was reduced withand hydrate formation rate was increased in thipresence of cyclopentane compared to the system work. The effect of APG on hydrate formation iswithout cyclopentane. The explanation for less pronounced compared to SDS. 154 V/Vreducing the induction time of hydrate formation methane storage capacity was achieved at awas that there was a significant shift in hydrate processing pressure of 4. 85MPa with the presformation pressures to lower pressures in the of SDS, 112 V/V methane storage capacity at astem of methane and cyclopentane comparedprocessing pressure of 5. 38MPa with the presencethe system of methaneL9Jof aPG, and 151 V/v methane storage capacity ata processing pressure of 4. 85MPa with SDS andCP presence.Acknowledgements The authors acknowledge the financialsupport by Chinese Natural Science Foundation (50176051)and Chinese Jiangsu Province Education Committee Program(G0109199)4.85MaReferences274.05K1 Rogers R, Yevi G, Swalm M. Hydrates for Storage of Nature300ppm SDS 1 O% CPGas. In: The 2nd International Conference on Nature GasHydrate. Toulouse 1996. 423--4291002003002 Makogon Y F. Hydrates of Hydrocarbons. OklahomaPenn Well Publishing Company, 1997Fig 5 Comparison of effect of SDS andZhong Y, Rogers R E. Surfactant Effects on Gas HydrateSDS+CP on hydrate formationFormation. Chemical Engineering Science, 2000, 55 (19)4 CONCLUSIONS4 Karaaslan U, ParlaktunaPromoters,, Energy &FuelsThe experiment of the effect of additives5 Khokhar AA, Gudmundsson J S, Sloan E D. Gas Storage inStructure H Hydrates. Fluid Phase Equilibria, 1998, 150-(SDS, APG, cyclopentane)on hydrate formation151,383392rate and storage capacity was carried out. Hydrate 6 Guo Y K, Fan SS, Guo K H, Chen Y. Storage Capacity ofMethane in Hydrate Using Calcium Hypochlorite as Additive.formation could be conducted in a quiescent systemIn: The 4th International Conference on gas Hydrates.with the presence of SDs or APG. TheYokohama:2002.1040-1043experimental results showed that surfactant could 7 Gudmundsson J S. Borrehaug A. Frozen Hydrate for Transportmprove the rate of hydrate formation and theof Nature Gas. In: The 2nd International Conference on Natureas Hydrate. Toulouse: 1996. 439-446hydrate storage capacity. Cyclopentane could also 8 Vysniauskas A, Bishnoi P R. A Kinetic Study of Methaneincrease the rates of hydrate formation and reduceHydrate Formation. Chem. Eng. Sci., 1983, 38 (7):hydrate formation induction time, but hydrate1061-1072an SS, Guo K H, Shi L, Wang R Z. Gas Hydratecapacity had a little drop with the presence ofPhase Equilibrium Data of Cyclohexane and Cyclopentane. J.cyclopentane. The results also showed thatChem.Eng.Data,2002,47(2),313-315additives could reduce the processing costs of中国煤化工CNMHG