ABSTRACT

In the present work, we present a case study where a new pipeline system is to be designed according to the supply and delivery contractual conditions. On the supply side, the producer intends to minimize the intake flow variations but, on the other hand, the customer intends to maximize its hourly outtake. These constrictions are considered on the conceptual design, where the advantage of using the transient analysis over the steady state load factor analysis becomes evident. As a conclusion, the results prompt a need for reviewing the current practice where, in the economic evaluation phase, the alternative pipeline configurations are designed using a steady state load factor.

INTRODUCTION

An Energy Consortium intends to convert a power plant cluster from diesel to natural gas. PB Gas, the Shipper Company that takes part in the consortium, is negotiating a Gas Supply Agreement with WellCo, a producer whose facilities are close to the cluster area, and a Gas Transportation Agreement with LINE Gas, a pipeline company which is intended to build a 43.5 mile (70.0 km) line from the gas field to the cluster. The Energy Consortium and PB Gas have signed a Buying and Selling agreement based on the cluster expected load profiles, and now PB Gas wants to make sure that LINE Gas and WellCo will be able to meet the volumes agreed. The focus of this work is to look closely to the pipeline conceptual design phase, when supply and delivery proposed agreements need to be considered.

Buying and Selling Agreement

The gas Buying and Selling Agreement between the Energy Consortium and PB Gas stipulates a 70.6 MMscf (2.00 MMm3) Daily Contracted Quantity (DCQ) and a maximum Hourly Contracted Quantity (HCQ) equivalent to 120% of the hourly DCQ, with a minimum specified delivery pressure of 570 psig (40 kgf/cm2g). The design profile that takes part of the agreement, shown in Figure 2, establishes a one-hour ramp from zero to 84,755 Mscf/d (2.4 MMm3/d), a nineteen-hour flat outtake of 84,755 Mscf/d, a one-hour ramp from 84,755 Mscf/d to zero load and a two-hour zero-load period, totalizing the equivalent 70.6 MMscf DCQ.

Gas Supply Agreement

WellCo. is the only major supplier company for the region and has a significant amount of gas contracted by some other shippers. Without considering gas processing facilities expansion, it will be able to supply a maximum hourly quantity equivalent to 70,630 Mscf/d (2.0 MMm3/d), which results in a flat profile in the present case. By minimizing plant expansion investment, WellCo would be able to raise the maximum hourly quantity equivalent by 10% or a flat 77,690 Mscf/d (2.2 MMm3/d) profile. Naturally, the investment requirement will be reflected in an extra gas cost. Figure 3 shows the 70,630 Mscf/d (blue line) and the 77,690 Mscf/d (red line) profiles.

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