A Fast, Highly Accurate Means of Modeling Transient Flow in Gas Pipeline Systems by Variational Methods

Abstract

Abstract The cost-effective design of real pipeline systems must consider thetransient response induced by equipment failure and sales rate changes. Hereare described methods developed over the past decade for simulating slowtransient response; these are followed by a presentation of a new variationalmethod. The latter is formulated to treat fast as well as slow transients, andgives results in excellent agreement with data for diverse cases. The computer resources required are small enough that a 1,000-pipe networkcan be simulated in core on widely available computing facilities (CDC 6600).On the average, 1 hour of 1,000-pipe system operation can be simulated in 100seconds of CDC 6600 central processor time. Introduction To design and operate a gas transmission system cost-effectively requiresaccounting for its response under unsteady or transient conditions. Even thoughcare is given to the optimum design of a system to support steady loads, suchloads represent only a theoretical condition. Actua1 operations invariablyencounter transient states. The loss of a compressor, the addition or loss ofsupply or sale points, replacement of equipment, and customers who demandvariable sale rates are a few of the causes of line transients. The design for cost-effective operation of a system should be completed beforeany capital is spent. For pipeline systems this should begin with optimizingthe required facilities to meet the projected sales rates. But engineering isnecessary beyond that to provide the pipe and compression for steady deliveryof gas. If some of the projected sales are time varying, a quantitative studyshould be made of the fraction of the varying demand that can be met by linepack and the fraction that must be satisfied by local peaking facilities. Onlyby approaching the cost optimum among feasible pipe sizes, compression levels, and peaking facility capabilities can cost-effective use be made of availablecapital. Other facets of cost-effective design for operation are the sizing and locationof standby equipment, its relationship to the capacity of the transmissionsystems, and the cost of failure of the system to meet commitments. Anymechanical system is subject to failure. The allowable time for bringingstandby equipment on line so as to meet all commitments depends upon thecapacity of the standby equipment, the capacity and response rate of thetransmission system, and the amount and location of excess compression or othercapacities elsewhere in the system.