Due to the increase in demand for natural gas during the last decade, energy companies have installed additional pipelines nationwide resulting in more compression required to transport the fuel through the system. Traditionally, compression is achieved through gas-fired reciprocating, or gas turbine driven, centrifugal compressors. The fuel used for compression is calculated through a manufacturer's curve, or a curve developed by the individual company. As power deregulation continues to be adopted across the United States, pipeline companies are beginning to replace gas-fired compression with electric-driven systems and using these systems for their new facilities to address more strict environmental regulations and competitive pricing of electricity. When the natural gas pipelines were using their own gas as a fuel source, little concern was placed on fuel consumption. Natural gas companies generally passed on the fuel cost as a percentage of the gas transported. The addition of power as a fuel source has created a risk management opportunity for companies due to the complexity of utility rate schedules that are replacing more basic fuel bills that were based on energy consumption and a manufacturer's heat rates. In today's highly competitive market all costs are scrutinized. Pricing structures, such as Demand, Commodity and Index-Based charges that are included in the utility rate schedule potentially may add cost to the compression facility even when it is not in use. Ratchet clauses built into some rate schedules also may affect the compression cost depending on the historical use of energy used by a customer. When installing electric-driven compressors, the power supplier's rate schedule should be analyzed to estimate compression costs and profitability. This paper will review the basics of electric pricing structures and suggest ways that natural gas pipelines can reduce operating cost for electric power driven compressor stations. The authors will describe electric driven operating equipment and the relationship between pricing and pipeline operation. Design consideration and strategies for incorporating electric motor driven compression in Pipeline Design & Simulation will also be discussed.
New simple-cycle power plants, combined-cycle power plants using natural gas as a fuel source, and increase in industrial and residential loads have increased the demand for natural gas in the United States. The majority of the compressor stations that are used to transport natural gas use compressors of the 1950-1970 vintage. Most of the compressors are gas-fired reciprocating, or gas-turbine driven centrifugal units. With power deregulation and stricter environmental regulation installing electric-driven compressors should be considered when replacing older units and designing new pipeline facilities. When comparing electric-driven compressors to gas-fired compressors one needs to look at first costs, operating costs, and design issues.
