Hydrates, in natural gas

The object of this chapter is to provide an overview of the experimental methods, the phase equilibria data, and the thermal property data available on hydrates since Hammerschmidt (1934) on hydrates in natural gas systems. The tabulations and figures illustrate that more data are needed, particularly for phase equilibria mixtures of noncombustible components, structure H components, and for thermal property data. 

Kent, R.P., Coolen, M.E., Hydrates in Natural Gas Lines, Mobil Internal Report (1992). 

Kvenvolden K. K. and Lorenson T. D. (2001) The global occurrence of natural gas hydrate. In Natural Gas Hydra-tes.Occurrence, Distribution and Detection, Geophysical Monograph 124 (eds. C. K. Pauli and W. D. Dillon). American Geophysical Union, Washington, DC. 

Hammerschmidt, E.G, 1934. Formation of gas hydrates in natural gas transmission lines. Industrial and Engineering Chemistry, 26 851 pp. 

Haq B. U. (20(X)) Climate impact of natural gas hydrate. In Natural Gas Hydrate in Oceanic and Permafrost Environments (ed. M. D. Max), pp. 137-148. Kluwer Academic Publishers, Dordrecht. 

If produced gas contains water vapour it may have to be dried (dehydrated). Water condensation in the process facilities can lead to hydrate formation and may cause corrosion (pipelines are particularly vulnerable) in the presence of carbon dioxide and hydrogen sulphide. Hydrates are formed by physical bonding between water and the lighter components in natural gas. They can plug pipes and process equipment. Charts such as the one below are available to predict when hydrate formation may become a problem. 

Although there are no new methane VPO competitive processes, current technology may be usehil for the production of impure methanol in remote areas for use as a hydrate inhibitor in natural gas pipelines (119,120). 

Methanol is frequently used to inhibit hydrate formation in natural gas so we have included information on the effects of methanol on liquid phase equilibria. Shariat, Moshfeghian, and Erbar have used a relatively new equation of state and extensive caleulations to produce interesting results on the effeet of methanol. Their starting assumptions are the gas composition in Table 2, the pipeline pressure/temperature profile in Table 3 and methanol concentrations sufficient to produce a 24°F hydrate-formation-temperature depression. Resulting phase concentrations are shown in Tables 4, 5, and 6. Methanol effects on CO2 and hydrocarbon solubility in liquid water are shown in Figures 3 and 4. 

Doctor et al. (2000) point out the technical problems in the transport infrastructure that could arise from impurities in the C02. Any transport system requires the C02 to be dried to prevent the formation of C02 hydrates. Considerable problems with the formation of iron sulphide in natural gas pipelines indicate that C02 also has to be cleaned of hydrogen sulphide content. 

Kvenvolden KA (1995) A review of the geochemistry of methane in natural gas hydrate. Org... 

Desiccants - [DESICCANTS] (Vol 7) - [ALUMENUMCOMPOUNDS - ALUMINIUMOXIDE(ALUMINA) - HYDRATED] (Vol 2) -arsenic compounds as [ARSENIC COMPOUNDS] (Vol 3) -use of bromides [BROMINE COMPOUNDS] (Vol 4) -use in natural gas processing [GAS, NATURAL] (Vol 12)... 

Holder et al. Phase Behavior in Systems Containing Clathrate Hydrates Rev. Chem. Eng. 1990 Katz and Lee Gas Hydrates and Their Prevention in Natural Gas Engineering ... 

Kvenvolden, K.A. A Review of the Geochemistry of Methane in Natural Gas Hydrate... 

In the mid-1930s Hammerschmidt studied the 1927 hydrate review of Schroeder (D.L. Katz, Personal Communication, November 14, 1983) to determine that natural gas hydrates were blocking gas transmission lines, frequently at temperatures above the ice point. This discovery was pivotal in causing a more pragmatic interest in gas hydrates and shortly thereafter led to the regulation of the water content in natural gas pipelines. 

Makogon, Y.F., Hydrates of Natural Gas, Moscow, Nedra, Izadatelstro, 208 (1974 in Russian). Translated by WJ. Cieslesicz, Penn Well Books, Tulsa, Oklahoma, 237 (1981 in English). 

Figure 2.4 Hydrogen bonding (hydrogen bonds are crosshatched) (a) between two molecules (Reproduced and modified from Makogon, Y.F., Hydrates of Natural Gas, Moscow, Nedra, Izadatelstro, p. 208 (1974 in Russian) Translated by W.J. Cieslesicz, PennWell Books, Tulsa, Oklahoma, p. 237 (1981 in English). With permission), and (b) between four molecules. (Reproduced from Franks, F., Reid, D.S., in Water A Comprehensive Treatise (Franks, F., ed.) Plenum Press, New York, 2, Chap. 5 (1973). With permission.)... 

For si and sll, Davidson et al. (1977a, 1981) performed NMR spectroscopy and dielectric relaxation measurements where applicable, in order to estimate the barriers to molecular reorientation for simple hydrates of natural gas components, except carbon dioxide. Substantial barriers to rotation should also affect such properties as hydrate heat capacity. 

Section 5.2 shows the prediction method of phase diagrams of the major components of natural gas, namely methane, ethane, and propane hydrates and their mixtures at the common deep-ocean temperature of 277 K. Many of the commonly observed phenomena in natural gas systems are illustrated, while the power of the method is shown to go beyond that of Chapter 4, to illustrate future needs. 

In addition to the three known natural gas hydrates, several other hydrate structures exist. Dyadin et al. (1991) found four hydrate structures and Jeffrey (1984) proposed five additional hydrate structures. These structures have yet to be confirmed in natural gas systems, although new hydrate structures have been identified using x-ray diffraction such as a tetragonal structure for bromine (Udachin et al., 1997b), a trigonal structure for dimethyl ether (Udachin et al., 2001a),... 

Lapin, A., Cinnamon, S.J., Problem of Hydrate Formation in Natural Gas Systems, in Proc. Liquid Natural Gas Its Production, Handling, and Use, London, p. 198, 3/25-28 (1969). 

The hydrates-in-nature paradigm is currently changing. The above tables and quantity estimates indicate that much of the natural gas containing hydrates is in the ocean bottom, and while production of gas from such deep-lying hydrates is now too expensive, it is likely that in the near future mankind will need to... 

FIGURE 7.9 (See color insert following page 390.) Qualitative relationships between fluid fluxes and geologic-biologic response. Each picture has a field of view 3 1 m across. (From Roberts, H.H., in Natural Gas Hydrates Occurrence, Distribution and Detection, (Pauli, C.K., Dillon, W.P., eds.) p. 145. American Geophysical Union, Washington, DC (2001). With permission.)... 

---