(34g) Troubleshooting Tower Carryover

For most traditional TEG contactors, high capacity structured packing is the ideal mass transfer device due to the low liquid rate in this service. However, structured packing should only be used in a fairly clean system as it is susceptible to plugging. For dirty systems, bubble cap trays have been traditionally applied. There are a few high capacity tray technologies available that can be used to achieve a capacity boost over bubble cap trays albeit with higher glycol carryover. These new high capacity mass transfer devices exceed the capacity of most existing de-entrainment equipment, such as wire mesh and vane packs. The capacity of demisting devices is further reduced with increased entrained liquid loading as the high capacity devices push to higher superficial velocities. Thus, TEG carryover can ultimately dictate the capacity of the TEG contactor if the de-entrainment internals are not specified correctly or not modified during a revamp to handle the additional TEG carryover. High concentrations of H2S and CO2 and even small amounts of contaminants such as heavy hydrocarbon liquids, iron sulfides, salts and other organics in the feed gas can also present operational difficulties. These contaminants can be absorbed in the TEG, accumulate, foul, foam and react to form other byproducts. Therefore, the cleanliness of the system must be considered when selecting internals.

This article summarizes the lessons learned in debottlenecking a “dirty” TEG contactor at our LaBarge Black Canyon Facility in Wyoming US. The facility modifications included replacement of all bubble cap trays with fixed valve trays, modifications to the downcomer inlet sump and seal pan, addition of a new Inlet Vane Diffuser at the gas inlet to the tower, a new full stream carbon filtration system, and optimization of the mist eliminator section at the top of the tower. This work was performed in progressive steps between 2001 and 2004. After completion of this work, the following conclusions can be drawn:

• A clean TEG system will minimize foaming and increase capacity as well as decrease maintenance, operating expense and downtime. As demonstrated, the full stream carbon filtration system reduced TEG liquid carryover by 65-70%.
• Although vendor data was available on demisting cyclones with glycol at elevated pressure and good experience was also available with cyclones in hydrocarbon service at high pressure, this application was outside the data range. The entrained liquid load is also an important parameter that often is ignored or is unknown.
• The combination of the high capacity trays and mist elimination equipment, along with the new solvent filtration system, allowed the gas capacity of the Black Canyon Facility to be almost doubled.