Abstract

The biofiltration process is capable of oxidizing H2S in an air stream to a non-volatile product, sulphate (SO4−2). In order to investigate the effectiveness of this technology in controlling H2S and SO2 emissions from sour gas plants, a suitable production site was chosen, major components in the acid gas stream of that site were identified, and a consortium of microorganisms capable ofoxidizing reduced sulphur compounds was prepared. Laboratory-scale experiments were then used to assess the potential of installing an effective demonstration-scale biofilter on-site.

Introduction

The oil and gas (O & G) industry currently has a variety of sour crude oil and gas wells in production in the province of Alberta. Elemental sulphur recovery units in large plants remove much of the sour component, hydrogen sulphide (H2S). Historically, where recovering the sulphur was not economically feasible and volumes were small enough, it was common practice to flare the sour gas. Now however, regulations require sulphur separation in any processing operations that produce more than one tonne of sulphur per day. This still leaves 50 or more operations where the daily production of sulphur is less than one tonne and the extracted acid gases are flared.

Flares are often inefficient and do not completely oxidize the H2S. Reports from field-testing report efficiencies ranging from 22% to near 100% depending upon the type of flare and prevailing conditions1. There is a growing awareness that conventional flares are not reliable enough to meet present and future needs and as a result, there have been some advances in flare design2. However, both H2S and its oxidation product, sulphur dioxide (SO2, are toxic, and even 100% oxidation of the H2S fails to eliminate the identified health risks associated with flare emissions3. In order to address concerns about odors and health effects, It would be advantageous to provide an alternate, cost-effective technology that could replace flaring and eliminate atmospheric discharge altogether.

Previous studies4–9 have shown that biofiltration is an air pollution control (APC) technology that is capable of treating H2S and has many potential industrial applications. Autotrophic microorganisms colonizing the biofilter matrix are able to utilize the H2S as an energy source to drive CO2 fixation. Most of the sulphur is oxidized to sulfate (SO4−2) which can be rinsed from the biofilter with water. Although in previous studies this technology was shown to have the capability of removing more than 99% of the H2S from a contaminated air stream, testing was limited to concentrations below 300 ppmv. Acid gas streams from target sour gas installations may contain up to 20% or more H2S and the evaluation of this technology under these conditions requires further investigation.

In order to determine the effectiveness of this technology in controlling H2S and SO2 emissions from acid gas streams, access to a suitable natural gas plant was obtained and a study was designed with the following objectives:

  • to identify the major constituents of the acid gas stream,

  • to establish a consortium of microorganisms capable of oxidizing the reduced sulphur compounds in the acid gas stream,

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