Partially spent caustic solutions from natural gas liquids (NGL) sweetening processes can be used as reagent for sulfur dioxide (SO2) scrubbing facilities, reducing the costs for purchasing scrubber reagent and eliminating the costs and liabilities associated with waste disposal.

This paper discusses: 1) the characteristics of typical spent NGL sweetening solutions, 2) State and Federal regulations governing the disposal of these solutions as wastes, 3) the operational variables affecting reuse of these solutions in SO2 scrubbers, 4) field and laboratory analytical data from a pilot project conducted to evaluate the reuse of a partially spent NGL sweetening solution as SO2 scrubber reagent, and 5) economic data from the pilot project.

For the pilot project, a partially spent caustic NGL sweetening solution was used in place of soda ash solution as reagent in a SO2 scrubber serving two steam generators burning sour gas. Emissions testing of the scrubber demonstrated that the solution provided effective removal of oxides of sulfur (SOx) in both gaseous and particulate phases to meet permitted limits. Data from the pilot project is used in the paper to: 1) quantify SO2 scrubber performance with partially spent caustic solutions in terms of SOx removal efficiency, 2) identify the necessary modifications in scrubber operation (reagent feed rate, scrubber liquor pH and specific gravity, blowdown rate) to achieve acceptable performance using partially spent caustic solutions, and 3) describe the effect that the use of partially spent caustic solutions has on physical and chemical properties of scrubber liquor.

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