Abstract

We introduce a tool for simulation and optimization of gas pipeline networks coupled to power grids by gas-to-power plants. The model under consideration consists of the isentropic Euler equations to describe the gas flow coupled to the AC powerflow equations. A compressor station is installed to control the gas pressure such that certain bounds are satisfied. A numerical case study is presented that showcases effects of fast changes in power demand on gas pipelines and necessary operator actions. Document type: Part of book or chapter of book

Abstract

The United States relies on natural gas for one-quarter of its energy needs. In 2001 alone, the nation consumed 21.5 trillion cubic feet of natural gas. A large portion of natural gas pipeline capacity within the United States is directed from major production areas in Texas and Louisiana, Wyoming, and other states to markets in the western, eastern, and midwestern regions of the country. In the past 10 years, increasing levels of gas from Canada have also been brought into these markets (EIA 2007). The United States has several major natural gas production basins and an extensive natural gas pipeline network, with almost 95% of U.S. natural gas imports coming from Canada. At present, the gas pipeline infrastructure is more developed between Canada and the United States than between Mexico and the United States. Gas flows from Canada to the United States through several major pipelines feeding U.S. markets in the Midwest, Northeast, Pacific Northwest, and California. Some key examples are the Alliance Pipeline, the Northern Border Pipeline, the Maritimes & Northeast Pipeline, the TransCanada Pipeline System, and Westcoast Energy pipelines. Major connections join Texas and northeastern Mexico, with additional connections to Arizona and between California and Baja California, Mexicomore » (INGAA 2007). Of the natural gas consumed in the United States, 85% is produced domestically. Figure 1.1-1 shows the complex North American natural gas network. The pipeline transmission system--the 'interstate highway' for natural gas--consists of 180,000 miles of high-strength steel pipe varying in diameter, normally between 30 and 36 inches in diameter. The primary function of the transmission pipeline company is to move huge amounts of natural gas thousands of miles from producing regions to local natural gas utility delivery points. These delivery points, called 'city gate stations', are usually owned by distribution companies, although some are owned by transmission companies. Compressor stations at required distances boost the pressure that is lost through friction as the gas moves through the steel pipes (EPA 2000). The natural gas system is generally described in terms of production, processing and purification, transmission and storage, and distribution (NaturalGas.org 2004b). Figure 1.1-2 shows a schematic of the system through transmission. This report focuses on the transmission pipeline, compressor stations, and city gates.« le Document type: Report

Abstract

This report identifies potential energy-conservative pipeline innovations that are most energy- and cost-effective and formulates recommendations for the R, D, and D programs needed to exploit those opportunities. From a candidate field of over twenty classes of efficiency improvements, eight systems are recommended for pursuit. Most of these possess two highly important attributes: large potential energy savings and broad applicability outside the pipeline industry. The R, D, and D program for each improvement and the recommended immediate next step are described. The eight technologies recommended for R, D, and D are gas-fired combined cycle compressor station; internally cooled internal combustion engine; methanol-coal slurry pipeline; methanol-coal slurry-fired and coal-fired engines; indirect-fired coal-burning combined-cycle pump station; fuel-cell pump station; drag-reducing additives in liquid pipelines; and internal coatings in pipelines. Document type: Report

Abstract

The U.S. Department of Transportation's Pipeline and Hazardous Materials Safety Administration (PHMSA) is responsible for ensuring the safe, reliable, and environmentally sound operation of the nation's natural gas and hazardous liquid pipelines. Regulations adopted by PHMSA for gas pipelines are provided in 49 CFR 192, and spacing requirements for valves in gas transmission pipelines are presented in 49 CFR 192.179. The present report describes the findings of a scoping study conducted by Oak Ridge National Laboratory (ORNL) to assist PHMSA in assessing the safety impact of system valve spacing. Calculations of the pressures, temperatures, and flow velocities during a set of representative pipe depressurization transients were carried out using a one-dimensional numerical model with either ideal gas or real gas properties for the fluid. With both ideal gas and real gas properties, the high-consequence area radius for any resulting fire as defined by Stevens in GRI-00/0189 was evaluated as one measure of the pipeline safety. In the real gas case, a model for convective heat transfer from the pipe wall is included to assess the potential for shut-off valve failures due to excessively low temperatures resulting from depressurization cooling of the pipe. A discussion is also provided of some additionalmore » factors by which system valve spacing could affect overall pipeline safety. The following conclusions can be drawn from this work: (1) Using an adaptation of the Stephens hazard radius criteria, valve spacing has a negligible influence on natural gas pipeline safety for the pipeline diameter, pressure range, and valve spacings considered in this study. (2) Over the first 30 s of the transient, pipeline pressure has a far greater effect on the hazard radius calculated with the Stephens criteria than any variations in the transient flow decay profile and the average discharge rate. (3) Other factors besides the Stephens criteria, such as the longer burn time for an accidental fire, greater period of danger to emergency personnel, increased unavoidable loss of gas, and possible depressurization cooling of the shut-off valves may also be important when deciding whether a change in the required valve spacing would be beneficial from a safety standpoint. (4) The average normalized discharge rate of {lambda}{sub avg} = 0.33 assumed by Stephens in developing his safety criteria is an excellent conservative value for natural gas discharge at the pressures, valve spacings, and pipe diameter used in this study. This conclusion remains valid even when real rather than ideal gas properties are considered in the analysis. (5) Significant pipe wall cooling effects (T{sub w} " -50 F or 228 K) can extend for a mile or more upstream from the rupture point within 30 s of a break. These conditions are colder than the temperature range specifications for many valve lubricants. The length of the low-temperature zone due to this cooling effect is also essentially independent of the system shut-off valve spacing or the distance between the break and a compressor station. (6) Having more redundant shut-off valves available would reduce the probability that pipe cooling effects could interfere with isolating the broken area following a pipeline rupture accident.« le Document type: Report

Abstract

This quarterly report documents work performed under Tasks 15, 16, and 18 through 23 of the project entitled: ''Technologies to Enhance the Operation of Existing Natural Gas Compression Infrastructure''. The project objective is to develop and substantiate methods for operating integral engine/compressors in gas pipeline service, which reduce fuel consumption, increase capacity, and enhance mechanical integrity. The report first documents a survey site test performed on a TCVC10 engine/compressor installed at Dominion's Groveport Compressor Station. This test completes planned screening efforts designed to guide selection of one or more units for design analysis and testing with emphasis on identification and reduction of compressor losses. The report further presents the validation of the simulation model for the Air Balance tasks and outline of conceptual manifold designs. Document type: Report