Hydrates in Production, Processing, and Transportation

The objective of this chapter is provide an overview of how solid masses of hydrates (plugs) form, means of preventing and encouraging plug formation, and means of dissociating plugs once they have formed. 

Unlike the other portions of the book, for example, the thermodynamic calculation methods in Chapters 4 and 5, in this chapter, conceptual pictures indicate how phenomena occur, based upon hydrate research and industrial practice. Particularly emphasized are those that have evolved during the last decade. For those who wish to do prevention calculations, several practical engineering guides are available. The engineering books by Kidnay and Parrish (2006), Carroll (2003), Makogon (1997), and Sloan (2000) prescribe hydrate calculations for the practicing engineer. 

Below are six important points to realize in this chapter  

Hydrate plugs and their dissociation can have major economic and safety impacts on flowline operation. 

While the past methods of preventing hydrate plugs have been to use avoidance with thermodynamic inhibitors such as methanol or glycols, our new understanding of how plugs form, allows us to propose economic risk management (kinetics) to avoid hydrate formation. These concepts differ in type for oil-dominated and gas-dominated systems. 

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Due to the difficulty of quantifying time-dependent phenomena, the present chapter deals with hydrate formation and dissociation in laboratory systems. The principles are extended to hydrate formation/dissociation/inhibition in pipelines in Chapter 8 on hydrates in production, processing, and transportation. Dissociation in porous media, such as the assessment of gas evolution from in situ hydrate reserves using hydrate reservoir models is discussed in Chapter 7 on hydrates in the earth. The present chapter is also restricted mostly to the time-dependent properties of structures I and II due to the limited time-dependent data on structure H. The experimental tools that have been applied to measure hydrate time-dependent phenomena are presented in Chapter 6. 

Some components risually found in natural gas in combination of water can cause hydrate formation. Hydrate formation is one of the problems facing the production, processing and transportation of natural gas [1]. To predict the hydrate formation, it is essential to calculate the pressure-temperature curve for natural gas composition. Table 3 gives the natural gas composition used in Tehran gas network. 

Finally, Chapter 8 considers some common industrial problems (and solutions) concerning hydrates in processing, transportation, and production. The phenomena of how hydrate plugs form and how they are prevented or simulated are illustrated by several industrial case studies. 

Just as engineering is sometimes considered to be an applied science, the concepts of this chapter should provide for applications—to hydrates in the earth (Chapter 7) and to hydrate problems in production, transportation, and processing of oil and natural gas (Chapter 8). As an introduction to the chapter, consider an example of some typical hydrate calculations. 

It should be thermodynamically impossible for one set of Kvst charts to serve both hydrate structures (si and sll), due to different energies of formation. That is, the Kysi at a given temperature for methane in a mixture of si formers cannot be the same as that for methane in a mixture of sll formers because the crystal structures differ dramatically. Different crystal structures result in different xst values that are the denominator of Kvst (= yt/xSi). However, the Katz Kvst charts do not allow for this possibility because they were generated before the two crystal structures were known. The inaccuracy may be lessened because, in addition to the major component methane, most natural gases contain small amounts of components such as ethane, propane, and isobutane, which cause sll to predominate in production/transportation/processing applications. 

Naturally occurring clathrate hydrates are found in marine sediments and in permafrost. Because they contain a large amount of methane, they are thought to have potential as an unconventional energy resource. At the same time, however, clathrate hydrates are a serious problem for the gas and oil industries, because they form easily under suitable conditions at the sites of natural gas production, transportation, and processing. The inhibition and control of hydrates in pipelines adds tremendously to gas production costs. ... 

Coal mine gas (called Coal bed Gas) is a kind of associated gas from the coal seam in coal mine exploitation process in different forms, which is one of the main reasons of the coal mine accident. As the first fatal factor in coal mine, the gas accident not only causes a large number of casualties and huge economic losses, and imperils the safety of coal mine production seriously once it occurs. Gas concerns the major issues of environmental pollution, the greenhouse effect and the future of new energy. It can be used after recovered rapidly if the coal mine gas develops, storages and transports high-efficiently in moderate environment. Meanwhile it will be reduced that the cost, the hidden safety trouble and the gas emission pollution to the environment. Thus it is badly in need of a new type of gas utilization technology to make up for the current technical defects. Hydrate method is an optional way. 

PBSl is obtained by further drying PBS4 to remove its water of hydration in a fluid bed at an inlet air temperature of -180 to 210°C [19]. In practice, lower temperatures may be used. A cooler exhaust temperature of at least 60°C may be used if the relative humidity is kept at -10 to 40% [20]. Since water of hydration is removed from inside the particle, the product has the potential for high attrition. However, all PBSl manufacturers have developed processes that reduce this tendency, and the product in fact has excellent resistance to attrition and can be subjected to pneumatic transport. 

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