Integrated Air Separation Facilities For Hydrocarbon And Sulphur Recovery
Authors: Metzler Kurt J. , Hvizdos Leonard J. , Hegarty W. Patrick 
Published: March 2010

The concept of using an air separation plant to generate nitrogen jar enhanced hydrocarbon recovery and oxygen for sulphur production is reviewed. Nitrogen generation (for injection) and nitrogen rejection processes are discussed and cost curves are presented. Conventional oxygen enrichment and the COPE ™ (Claus Oxygen-based Process Expansion) sulphur recovery processes are compared. Locations where an air separation facility can be designed to produce both nitrogen jar injection and oxygen jar sulphur recovery are identified. Having identified potential sites for integration, oxygen and nitrogen economics are presented.

Introduction

North America contains vast reserves of conventional crude oil, heavy oil, oil sands, and natural gas containing sulphur (as hydrogen sulphide). In order to produce these reserves economically, industry is constantly investigating the application of new methods to enhance production. Some of these methods use industrial gases such as nitrogen (in secondary and tertiary hydrocarbon recovery projects) and oxygen (in situ combustion for heavy oil recovery and to displace air in sulphur recovery units). These gases are co-produced in cryogenic air separation facilities. However, to date, the application of air separation technology has been very site/project specific and designed to recover only one industrial gas. Many air separation facilities have been installed to deliver nitrogen for enhanced hydrocarbon recovery (EHR). At these locations the low-purity oxygen by-product is vented to the atmosphere even though it could be used as an efficient source of oxygen for combustion processes, such as sulphur recovery from a Claus unit.

Hydrocarbon Recovery- Nitrogen Injection/Rejection

The use of cryogenically produced nitrogen from an air separation unit (ASU) was initiated in the late seventies as a cost-effective alternative to natural gas injection(I.2). Its use for EHR has grown dramatically and has been applied primarily in the "lower 48" United States. In their June 1985 paper, Clancy et al.(2) provide a list of 33 reservoirs which have used nitrogen injection technology. Figure 1 locates the sites (illustrated by triangles) from this list which have used cryogenic air separation facilities to produce nitrogen. Sites where a nitrogen rejection unit (NRU) is installed as well are located by a darkened triangle in Figure 1. One of the eight sites where both nitrogen injection and rejection and are practiced is Dome's Willesden Green Field in Alberta(4). Exxon operates an integrated injection/ rejection project at Jay-Little Escambia Creek Field near the Florida/Alabama border(5). The remaining six sites are located at University Block 31 (Texas), Anschutz Ranch East Field (Wyoming), Andector-Ellenberger Field (Oklahoma), Fordoche Field (Louisiana), and two at the Painter Field (one triangle shown in Wyoming).

Sulphur Recovery

The primary method of producing elemental sulphur from natural gas is with the use of the Claus process. A typical modified Claus sulphur recovery unit (SRU) with two catalytic conversion stages and a modem reheat scheme uses air as the course of oxygen to recover 93% to 96% of the sulphur from a relativelyrich acid gas feed.