From time to time Tenneco Gas receives requests from various customers to increase the minimum contractual pressure at which the customer can receive gas. This paper reviews one such request. In this case the customer has indicated that they need a minimum of 700 psig from Tenneco to meet their certain downstream requirements. However, Tenneco is obligated to deliver gas to them at substantially lower pressures. The ultimate solution to this problem is the installation of compression on the customers pipeline near the interconnect with Tenneco. The goal of this analysis is to determine operational solutions which Tenneco could employ on a best efforts basis to meet this customers pressure needs during periods of simultaneous high demand on both pipelines. Following an examination of the extent of the problem, three operational methods of meeting the pressure requirement are considered, and the general cost-benefit implications of these solutions are examined.
High throughput of the Tenneco pipeline in this area is approximately 1,500 MMcfd with a suction pressure of 487 psig and a discharge pressure of 734 psig at Station C. Gas is delivered to Customer X near the discharge of Station C. The pressure drop between Station C discharge and the Customer X delivery point is approximately seven psi during periods of high throughput.
According to customer X his compressor station is capable of moving 140 MMcfd operating at suction and discharge pressures of 700 and 855 psig, respectively. The station is equipped with two turbines totaling 2,280 horsepower. The Maximum Daily Quantity (MDQ) (the maximum obligation to deliver) for Customer X is 125 MMcf. Customer X desires a minimum delivery pressure of 700 psig when high flow rates are needed. Given a seven psi pressure drop between Station C discharge and the Customer X meter, this minimum would require Station C to discharge at 707 psig. Although the design pressure at Station C is 734 psig and Customer X's requested pressure is 707 psig, problems arise when the Tenneco system is operating at peak flow requiring lower than design line pack and thus a lower discharge pressure at Station C. Also, Station C may be operating at lower discharge pressureswhen flow is less than peak requiring a transition in flow and pressure conditions when Customer X demands higher pressure. The operating solutions to follow are relevant to this latter case also.
To determine the extent of the customers potential problem, historical throughput and pressure data were examined.
The mean discharge pressure at Station C during the past two winter seasons has generally been below 707 psig. The mean discharge pressure at Station C was less than 707 psig a total of 73 days during the 1989-90 winter season (defined here as November 1 through March 31). During the 1990-91 winter season, the mean discharge pressure fell below 707 psig a total of 76 days.