New Treating Techniques Improve Sour - Gas Processing
Authors: Worley M.S. 
Published: December 2007

Introduction

Increased demands for natural gas as a fuel and as a basic raw material for petrochemicals and sulfur products are allowing rapid advances in production and treating methods. Increased world-wide attention to air-, water- and soil-pollution problems is demanding new wellhead production and conditioning schemes. Marginal economics of producing and treating highly acid gas streams are encouraging the development and refinement of new treating processes. Some of the latest techniques and some possible future developments are discussed briefly in the following paragraphs.

Wellhead Conditioning

The discovery and production of extremely sour gas wells have presented numerous problems in recent years. Vented hydrogen-sulfide and sulfur-dioxide gases result in danger and discomfort for people nearby. Domestic animals, vegetation and buildings also are affected adversely by these noxious gases. The sour liquid condensate produced with these gases adds to the air-pollution problem. In some cases the wells are located in remote, cold climates so that transporting the condensate to a central gathering and processing point becomes costly. Wellhead conditioning techniques recently have been developed that allow almost all of the hydrogen sulfide normally vented in wellhead conditioning operations to be kept in the main gas line. This action prevents losses and air pollution. The sour condensate can be dehydrated at high pressure or can be stabilized and sweetened for atmospheric storage. In either event, the hydrogen sulfide and light hydrocarbons are reclaimed. Figs. 1, 2 and 3 illustrate some of the sour-gas conditioning techniques that are receiving increased attention. Many combinations of the basic functions indicated in the flow diagrams are possible, and some of the same principles are also used in sweet-gas conditioning. The operations indicated in Fig. 1 are useful when a considerable quantity of condensate is produced from a sour-gas stream. Provision is made to separate the water, condensate and gas, and to dehydrate the natural gas. The dry gas then is used to strip substantially all of the mechanically entrained and dissolved water from the condensate. The gas then is re-dehydrated before going into the flow line. Also note in Fig. 1 that the water-rich glycol flows into a nearby tower where substantially all of the dissolved acid gases are stripped from the glycol before it is admitted to the atmospheric regenerator. The sour gases reenter the main gas stream prior to final dehydration. This scheme allows remote wellhead dehydration of both the gas and condensate without any significant loss of hydrogen sulfide a toxic gas which otherwise would pollute the atmosphere. After dehydration, the condensate can be transported through a separate line with no hydrate problems, or it can be re-injected into the gas stream to flow into a central collection and processing plant. Dehydrated condensate will not allow a significant amount of water to be re-absorbed by the dry-gas stream if a proper condensate dehydration job is done. The operations indicated in Fig. 2 are useful when it seems desirable to collect or store stable and partially sweetened condensate at the wellhead. In this case, provision also is made to separate water, gas and condensate, and to dehydrate the gas.

JPT

P. 976^