Wesfarmers LPG Plant, Kwinana
In 1985 the State Electricity Commission of WA chose Wesfarmers Ltd to provide a ‘Straddle Plant’ to extract liquefied petroleum gas[1] (LPG) from the gas stream[2] flowing in the Domestic Gas pipeline that brings gas from the North West Shelf Development project, near Dampier, to Perth and further south.
The Kwinana LPG Plant takes the gas stream from the NW Shelf and, using a cryogenic process, removes LPG and small amounts of condensate[3]. The lean[4] natural gas stream is returned to the pipeline and the LPG is stored in refrigerated tanks for export and in pressurised tanks for WA distribution.
Historically, LPG in Australia was a byproduct of crude oil refining and in WA, minor volumes of LPG were produced at the BP Refinery in Kwinana. The development of natural gas production during the sixties and seventies introduced a significant new source which allowed the growth of retail sales as a result of lower costs. In particular, the increasing use of LPG in motor vehicles created a large, new market.
In the early 1980’s, Wesfarmers Kleenheat Gas was increasing LPG market share in WA and dominated the local scene. As Wesfarmers had decided to expand Kleenheat nationally, it was strategically necessary for Wesfarmers to develop a secure, independent source of supply. The timing of this decision coincided with the opportunity to access the residual ‘heavy’ components in the natural gas from the NW Shelf.
Front End Engineering of the LPG project commenced in late 1985, with contractor selected, finance arranged, export market identified and site secured by July, 1986. The decision to proceed was courageous, as Wesfarmers had little previous experience in the construction of high value, high tech projects. Trevor Eastwood (Managing Director), Michael Chaney (Finance Director) and Harry Ramsay (General Manager, Kleenheat Gas) were the key personnel in deciding that Wesfarmers should proceed with the project.
The Kwinana LPG plant was only the second time in Australia that development of a world scale, high technology Oil and Gas processing project was attempted by an Australian company without a major international partner with experience in the required technology. The first such project was the Santos Liquids Project in South Australia, which was completed in the early 1980s.
From a short list of consortia, Wesfarmers awarded a lump sum, design and construct contract to a joint venture between Randall Corporation (USA), O’Connor[5] (South Australia), and Clough Ltd (Western Australia). The cryogenic storage tanks were awarded to a nominated sub contractor, CBI[6] (USA). Randall supplied the process design and process guarantee to the joint venture; O’Connor fabricated the pressure vessels, exchangers and towers; and Clough provided the detailed design and construction.
The process used in the Kwinana LPG Plant involves lowering the gas temperature to condense the heavier components, followed by separation from the gas stream, and then purification of the butane and propane to exacting quality specifications. The low temperatures used in the process require that no water be present in the feed gas to the process unit, so as to avoid water freezing as ice and blocking process equipment. Water removal ("dehydration") is achieved by careful pretreatment. After the LPG fractions have been removed ("stripped"), the lean gas stream is recompressed and returned to the pipeline. Ancillary services at Kwinana include a gas turbine generator which supplies all plant power requirements, and a stand alone fire water system.
The three cryogenic storage tanks each contain approximately 13,000 tonnes of liquid product. Gas ‘boiling off’ each tank is collected, refrigerated until liquified and returned to the tank. The tanks have prestressed concrete secondary containment for protection should there be a failure of the primary tank. Great care was taken to ensure that the tanks were built to the best practice currently available, and they represented approximately one quarter of the project cost.
Export shipping is by specialised, cryogenic tankers. Wesfarmers secured an easement from the plant to the adjacent BHP owned wharf, to carry the product and vapour return pipelines. A mobile ship loading arm was designed ‘in house’ by Wesfarmers; the loading arm is towed into position for each loading event, and is then connected to the product and vapour return lines. After loading, the arm is removed to a secure location and the product and vapour return pipelines are purged.
Construction commenced late in 1986 with commissioning and completion achieved on schedule and within budget in 1988. The plant rapidly reached ‘nameplate’ capacity. Subsequent upgrades have increased capacity and allowed for supply of additional local products.
Author:
Warwick Stone, Wesfarmers LPG Project Manager for the Kwinana LPG Project.
- ↑ Liquefied petroleum gas is propane (C3H8) or butane (C4H10), or a mixture of both. Propane at atmospheric pressure boils at -42oC, and butane at -0.4oC. To remain liquid at normal temperatures these gases must be stored at pressure, hence the familiar LPG cylinder used to fuel domestic barbecues. At the Kwinana LPG plant propane and butane are stored as liquids at atmospheric pressure, so the storage tanks are "cryogenic", in that they must maintain temperatures at or below the boiling temperatures of the stored liquids.
- ↑ The gas stream in the pipeline is a mixture of hydrocarbon gases, predominantly methane, but with small fractions of heavier gases such as ethane, propane, butane, etc.
- ↑ "Condensate" is a general term to cover components of the gas stream which have molecules containing 5 or more carbon atoms, such as pentane (C5H12), hexane (C6H14) etc.
- ↑ "Lean" in this context means that the gas stream is largely methane (CH4) with a small percentage of ethane (C2H6). Heavier fractions of hydrocarbon (propane, butane and condensate) are either not present in the gas or, if they are, they are in minute quantities.
- ↑ T O'Connor and Sons.
- ↑ Originally Chicago Bridge and Iron.
