4/25/2016 Understanding Gas Hydrates and its Utility for Energy Solutions Rajnish Kumar 4/25/2016 1 Gas hydrates are ice like crystalline material and they shares some of the unique properties of water Cooper, A.I., J. Mater. Chem ., 2000, 10 , 207-234 • Density of solid water (ice) is lower than liquid water and this y ( ) q is one reason why life exist of earth. • Water molecules have very different boiling point compared to other molecule of similar molecular weight. • Within the solid ice phase, 13 known phases of ice has been identified 4/25/2016 2 1
4/25/2016 Molecular structure of water in different phases Photographs are from Janda Lab 4/25/2016 Dr. Rajnish Kumar, NCL ‐ Pune 3 Gas hydrates are ice like crystalline material Gas hydrates are crystalline non- • stoichiometric compounds consisting p g of water and natural gas (CO 2 , CH 4 etc.) physically resembling ice. Hydrogen bonded water molecules • (host) create a cage that encloses a guest molecule (typically small molecules like H 2 , CO 2 , CH 4 , neo-hexane) I In nature gas hydrates are frequently h d f l • encountered under sub sea environment (due to native high pressure and low temperature environment) 4/25/2016 4 2
4/25/2016 Different guest size results in different hydrate structure r ≈ 5.71A r ≈ 4.33A r ≈ 3.91 A r ≈ 4.06A r ≈ 3.95A 5 12 (S) 5 12 6 2 (L) 5 12 (S) 4 3 5 6 6 3 (M) 5 12 6 8 (L) Structure I (sI) � 2S.6L.46H 2 O Structure H (sH) � 3S.2M.1L.34H 2 O r ≈ 4.73A r ≈ 3.91A 5 12 (S) 5 12 6 4 (L) Structure II (sII) � 16S.8L.136H 2 O Semi-clathrate � 2S.XXX.38H 2 O 4/25/2016 5 Importance of Natural Gas for Energy Solutions Coal Coal 27 27 kg of C ned ned per GJ of energy obtain per GJ of energy obtain 21 21 kg of C Oil Natural 14 kg 14 kg of C gas Wood, muscles H 2 power 0* 0* 1960 2005 20xx 1800 (Post industrial revolution) 4/25/2016 Dr. Rajnish Kumar, NCL ‐ Pune 6 3
4/25/2016 Clathrate Hydrates in Nature Natural gas is a mixture of mainly methane (90-99%), ethane (0-10%), • propane (0-6%) & CO 2 (0-5%) etc. Both pure methane and natural gas hydrates exist in the natural world (not • only on earth but also on other planets) Large quantity of methane hydrate exist on earth either in permafrost or • under the sea bed along continental margin Gas hydrates are a good energy resource but it can also be a potential geo y g gy p g • hazard. Methane is 21 times more potent green house gas than CO 2 and due to rise • in global warming, methane in natural hydrates can decompose and create runaway effect 4/25/2016 Dr. Rajnish Kumar, NCL ‐ Pune 7 Why Study Clathrate Hydrate • Understanding the hydrate at molecular level and at what is the Flow Assurance right temperature and pressure zone where these hydrates can exist. right temperature and pressure zone where these hydrates can exist. Gas Hydrate • Understanding the mechanism of hydrate formation and As a source of methane As a means to develop /natural gas technology decomposition Permafrost-associated Deepwater marine natural Desalination Refrigeration Gas storage Gas separation natural gas hydrate gas hydrate • Potentially a sustainable energy source while still being a potential Methane separation Hydrogen storage Natural gas production geo hazard and role in global warming CH 4 + CO 2 /H 2 S Natural gas storage & CO 2 separation (CCS) CO separation (CCS) transportation CH 4 + O 2 /N 2 • Safety in deep oil drilling operations CO 2 + H 2 CH 4 + C 2 H 6 + C 3 H 8 • Other technological applications and energy solutions like gas N 2 + CO 2 separation, methane storage and transportation 4/25/2016 Dr. Rajnish Kumar, NCL ‐ Pune 8 4
4/25/2016 Gas hydrates are found below permafrost or the ocean floor A hydrate glacier sits on the sea floor, 850 m below the surface* Methane hydrate samples http:/ / communications uvic ca/ releases/ mr020909ph html http:/ / communications.uvic.ca/ releases/ mr020909ph.html Total Conventional NG: 300 300 – – 370 TCM (around the world) 370 TCM (around the world) • NGH estimates worldwide: ~ 20,000 TCM 20,000 TCM (mean estimate) • NGH estimates in India: ~2000 TCM (NGHP estimate) • Even if 10 % is recoverable � 200 TCM 200 TCM – World consumption of Natural Gas per year = 2.4 TCM 2.4 TCM – 9 4/25/2016 Proposed GH exploitation techniques (adapted from Collett, 2002). (a) thermal injection, (b) depressurization, (c) inhibitor or other additive 4/25/2016 10 5
4/25/2016 Pressure reduction, thermal stimulation or additive addition disturbs the three phase equilibria of natural gas hydrate Hydrate Hydrate Hydrate Hydrate (solid) (solid) Pressure Methane (gas) + Water Methane (gas) + Water (g (g ) ) (liquid) (liquid) Temperature 4/25/2016 11 Sustainable production of methane by molecular replacement � Thermodynamic feasibility � Kinetics of replacement � Structure stability & Thermodynamic stability 4/25/2016 12 6
4/25/2016 Schematic of the experimental setup The current setup has been designed and built with a design pressure of 15 MPa, and temperature range between -15 and 60°C. This setup can study methane hydrate dissociation in a wide range of conditions; like water depth of up to 1500 meters, and typical soil overburdens with different methane hydrate saturations overburdens with different methane hydrate saturations. Thermocouples PC DAQ GC PR PCR V4 vent cv V6 SPV vent V5 V3 CR Crystallizer R R Reservoir R i V1 CV Control Valve V2 PC PC & Controller DAQ Data Acquisition System PCR & PR Pressure Transmitter ER External Refrigerator ER GC Gas Chromatography SPV Safety Pressure Valve CR R G a s 4/25/2016 13 A set of mass flow meter and pressure controllers simultaneously simulates the marine environment in lab scale setup 4/25/2016 14 7
4/25/2016 Temperature and pressure controlled high pressure setup for gas hydrate studies 4/25/2016 15 Bench Scale High Pressure Continuous Setup for Studying Methane Decomposition Kinetics at sub-Sea Environment in Presence of Identified Additives 4/25/2016 16 8
4/25/2016 Hydrate formation is exothermic Hydrate formation is a crystallization process Typical gas uptake curve for hydrate formation Temperature = 273.7 K, P = 10.0 MPa 0.14 275.0 G s pt k Gas uptake 0.12 274.5 Temperature Gas uptake [mol] Temperature [K] 0.10 274.0 0.08 273.5 0.06 273.0 0.04 0.04 G T 272.5 0.02 (induction time = 19.0 min) 0.00 272.0 0 20 40 60 80 100 120 Time [min] Chemical Engineering Science, 62, 4268-4276 , 2007 17 Hydrate formation kinetics shows multiple nucleation event drate conversion (mol%) 50 100 % saturation 75 % saturation 50% saturation 40 30 20 Water to hyd 10 0 0 3 6 9 12 15 18 Time (h) 0.010 100 % saturation 75 % saturation er/hr) 0.008 50% saturation tion T 2 T-2 (mol of gas/mol of wate Rate of hydrate format T-3 T-1 0.006 0.004 Cooling / Heating Coil 0.002 0.000 4/25/2016 0 3 6 9 12 15 18 18 Time (hr) 9
4/25/2016 Conclusion from lab scale measurements � Methane recovery through thermal stimulation alone is possible � Kinetics of hydrate decomposition is lumped kinetics � Decomposition of methane hydrate and its recovery by depressurization alone (without any thermal stimulation) does not self sustain. � In absence of thermal stimulation partial recovery of methane is obtained at slower kinetics � CH 4 recovery by CO 2 replacement is technically feasible, however focus should not only be on the kinetics of methane replacement but also on overall methane recovery methane recovery � Still the question remains, what is the mechanism for such replacement? And what drives the replacement ? 4/25/2016 19 Understanding gas hydrate & methane recovery at molecular level • Understanding the structure and cage dynamics of gas hydrates through state of the art analytical tools h d t th h t t f th t l ti l t l • Understanding molecular level replacement kinetics through molecular dynamics simulation of hydrate formation and decomposition. 4/25/2016 20 10
4/25/2016 Understanding gas hydrate at molecular level through state of the art analytical tools: measurement on solid hydrate phase Solid state NMR Solid state NMR T min = -120 o C P max = ~ few MPa Quantitative technique for Cage occupancy X-ray Diffraction T min = -150 o C P max ~ few MPa (rare) Structure Raman Spectroscopy Raman Spectroscopy determination determination T min = -190 o C P max ~ few GPa Qualitative technique for Cage occupancy 21 Different guest size results in different hydrate structure r ≈ 5.71A r ≈ 4.33A r ≈ 3.91 A r ≈ 4.06A r ≈ 3.95A 5 12 (S) 5 12 6 2 (L) 5 12 (S) 4 3 5 6 6 3 (M) 5 12 6 8 (L) Structure I (sI) � 2S.6L.46H 2 O Structure H (sH) � 3S.2M.1L.34H 2 O r ≈ 4.73A r ≈ 3.91A N 2 C 3 H 8 5 12 (S) 5 12 6 4 (L) Structure II (sII) � 16S.8L.136H 2 O 4/25/2016 22 11
4/25/2016 Large to small cage ratio in SI is 3:1, and in SII is 1:2 -1 2906 cm Intensity (a.u.) Methane with a sII -1 former 2917 cm 2940 2930 2920 2910 2900 2890 2880 -1 ) Wavenumber (cm -1 2915 cm a.u.) Intensity (a -1 2904 cm 2960 2940 2920 2900 2880 2860 2840 4/25/2016 23 Methane hydrate in sI -1 ) Wavenumber (cm Distribution of natural gas in the hydrate phase AIChE J. 54,2132-2144, 2008. 12
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