LTX units

The next chapter discusses the use of LTX units to melt the hydrates as they form, and the use of indirect fired heaters to keep the gas temperature above the hydrate formation temperature. Chapter 8 describes processes and equipment to dehydrate the gas and keep free water from forming. 

Low-temperature exchange (LTX) units use the high flowing temperature of the well stream to melt the hydrates after they are formed. Since they operate at low temperatures, they also stabilize the condensate and recover more of the intermediate hydrocarbon components than would be recovered in a straight multistage flash separation process. 

These units are designed to allow hydrates to form and to melt them with the heat of the incoming gas stream before they can plug down stream equipment. In addition, the low-temperature separation that occurs in an LTX unit results in stabilizing the liquids as discussed in Chapter 6. This results in an increase in liquids recovered and a corresponding decrease in the heating value of the gas over what would be the case with separation at normal temperatures. 

It should be clear from the description of LTX units in Chapter 5 that the lower pressure separator in an LTX unit is a simple form of cold-feed condensate stabilizer. In the cold, upper portion of the separator some of the intermediate hydrocarbon components condense. In the hot, lower portion some of the lighter components flash. 

An LTX unit is not a very efficient stabilizer because the absence of trays or packing keeps the two phases from approaching equilibrium at the various temperatures that exist in the vessel. In addition, it is difficult to control the process. Typically, for a 100-psi to 200-psi operating pressure, a 300°F to 400°F bottoms temperature is required to stabilize completely the condensate. The heating coil in an LTX separator is more Uke-... 

There may be some additional recovery from an LTX unit than would be realized from a straight two-stage flash sep" " — r"— increment is normally small and may not justify the increased equipment cost and operating complexity associated with an LTX unit. 

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