TABLE OF CONTENTS As stated earlier, hydrates are a significant problem in the natural gas industry. So what can be done when we encounter hydrates in our processes? Or to prevent them from forming in the first place? This chapter outlines some design information for battling hydrates using chemicals.
People who live in colder climates are well aware of methods for combating ice. In the winter, salt is often used to remove ice from roads and sidewalks. A glycol solution is sprayed on airplanes waiting for takeoff to de-ice them. Similar techniques are used for combating hydrates.
Polar solvents, such as alcohol and glycol, and ionic salts, such as common table salt, are known to inhibit the formation of gas hydrates. It is important to note that they do not prevent hydrate formation, they inhibit it. That is, they reduce the temperature or increase the pressure at which a hydrate will form. The mere presence of an inhibitor does not mean that a hydrate will not form. The inhibitor must be present in some minimum concentration to avoid hydrate formation. The calculation of this minimum inhibitor concentration is addressed in detail in this chapter.
In the natural gas industry, alcohols (particularly methanol) and glycols (ethylene glycol or triethylene glycol) are commonly used to inhibit hydrate formation. Figure 5-1 shows the inhibiting effect of methanol on the hydrate of hydrogen sulfide. The curve for pure H 2S is taken from Table 2-6, and the methanol data are from Ng et al. (1985).
