Abstract

A new patented sour gas sweetening process was introduced to the gas processing industry in September 1984. This process consists of bubbling sour gas through a tower filled with a proprietary formulation, an alkaline aqueous solution of an anionic oxidizing agent. The toxic hydrogen sulfide is selectively removed from the sour gas and dissolved sulfides are converted to nonhazardous sulfur by the sweetening solution in the tower. The process is generally operated at ambient temperatures. The spent slurry from this batch process has been classified as a nonhazardous waste by the U.S. Environmental Protection Agency, fourteen state agencies, and the U.K. Department of Energy. The process was initially field tested at various locations in California in cooperation with major gas producers. More than 100 units are now operating in the producers. More than 100 units are now operating in the United States and Canada. The hydrogen sulfide concentrations of sour gases treated with this process range from as low as 10 ppm to more than 20 percent; the operating pressures range between near atmospheric to greater than pressures range between near atmospheric to greater than 1000 psig. The largest unit processes 16 MMscf/d sour gas using one tower at 1035 psig and the smallest unit handles 8 to 10 Mscf/d gas containing greater than 20 percent hydrogen sulfide. This paper presents:

  1. Detailed field data for over 100 operating units

  2. A description of the chemistry of the process

  3. Comparative kinetic data on several hydrogen sulfide scavengers used in other batch processes

  4. Defines factors utilized in the design of improved towers used for this gas sweetening process based on the experience gained in the field.

Introduction

A new patented process for sweetening sour gas offers a number of advantages, including:

  1. Improved economics for hydrogen sulfide removal based on cost performance evaluations

  2. Simplicity of operation

  3. Low capital cost

  4. Adaptability to existing process equipment

  5. The spent slurry generated by the process is classified as a nonhazardous waste by a number of regulatory agencies.

The disposal cost of the nonhazardous waste is 20-25% of the disposal cost for hazardous waste.

CHEMISTRY OF THE NEW PROCESS

The new process absorbs hydrogen sulfide from sour gas into the alkaline solution containing an anionic oxidizing agent, nitrite ion, NO2. The dissolved sulfides are oxidized to sulfur by nitrite ions.

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