Glycol contacting units provide the bulk of dehydration operations in gas processing and NGL recovery plants. This covers both on-shore and off-shore gas treating and NGL unit operations. In gas treating plants, glycol dehydration is the only dehydration operation required. For NGL liquids recovery, glycol dehydration is followed by further (mole sieve) drying to meet ultra-low-dew-point specifications.
Modern developments in glycol contacting technology cover both process design of the glycol contactor and regenerator system and the mechanical design of the mass-transfer equipment. Key issues include ultra-low-dew-point operation of the glycol contactor, mass-transfer equipment efficiency, mass-transfer equipment capacity, and internal distributor design. Design criteria and methods are given for these areas.
Two case studies are shown. The first covers new design techniques applied to a grass-roots off-shore dehydration unit. Major concerns in this case center on keeping equipment size to a minimum to reduce off-shore structure investment. The second case centers on ultra-low-dew-point design for an expansion of an NGL recovery plant from 12,500 kNCMD (500 MMSCFD) to 15,625 kNCMD (625 MMSCFD). This revamp directly expanded the glycol contactor and regenerator capacities and used a modified process scheme for the dehydrator to lower the outlet dew point. The reduced water load in the dehydrator outlet permitted the mole sieve driers (downstream of the dehydrator) to be switched from series to parallel operation. The parallel mole sieve drier operation increased the drier capacity and reduced the pressure drop through the NGL plant. Consequently, many modifications were avoided.
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