Transmission systems, natural gas

San Diego Gas Electric s system was originally installed as a research project. The intent of the research project was to test the hardware in this application, test the feasibility of operating such a system remotely with no local operators, and to prove the economics. Similar systems had been installed within process plants where operators were present to start and stop the system and monitor its operation. However, this was the first system installed on a natural gas transmission system with completely remote operation. 

Natural gas transmission systems operate most efficiently and at lower cost when run continuously at maximum capacity. Therefore, at periods of low demand, gas is pumped to storage reservoirs, preferably located in the consuming regions. 

NOVA, AN ALBERTA CORPORATION owns and operates a natural gas transmission system in the Province of Alberta and handles more than 75 percent of the Canadian gas sold in North America. As of December 31, 1985, NOVA s Alberta Gas Transmission Division recorded receipts of 2.25 trilhon cubic feet with an average of 6.2 billion cubic feet being moved per day. NOVA s system consists of 756 receipt and major delivery metering points connected by 8,559 miles of pipeline. 

Interstate pipelines also use computer simulation programs to calculate pipeline capacity, pressures, horsepower, fuel and other physical characteristics and properties of their systems. Using this information and incorporating variables such as ambient temperatures, facility outages, and changes in market patterns, transmission companies can run daily studies to determine how much natural gas their systems will deliver under expected operating conditions. 

Figure 1 The Snam Rete Gas transmission system consisting of 11 compression plants, 29,600 km of natural gas pipelines with diameters from 25 to 1,200 mm operating at pressures between 0.5 and 75 bar.

Pipelines are a vital part of the energy and chemical transportation infrastructure of modern society. They are generally viewed as a safe and economical means to deliver liquid and gas fuels and chemical raw materials to customers. However, the perception of their safety varies with segments of the population. The most common pipeline with which the average person is familiar is the gas main of the local gas distribution system with service connections to homes and businesses in communities. The overall pipeline infrastructure is much more and includes long-distance transmission pipelines in addition to local distribution system pipelines. Besides natural gas, transmission pipelines transport crude oil, gasoline, petroleum products, and chemical products. 

The depth of cover influences the rupture frequency of a natural gas pipeline. Increased depth of cover results in a decreased chance that the pipeline will be hit during digging activities. Combining for the entire transmission pipeline system, which includes about 12000 kilometer of pipelines, of N.V Nederlandse Gasunie (Dutch natural gas transmission company), the number of incidents in a pipeline depth class with the overall years of experience in a depth class the hit frequency (Eq. 2) could be derived (Jager et al. 2002). 

The National Institute for Pubhc Health and the Environment (RIVM) has estimated the influence of the stamtory one-call system. The derivation of this estimate is described in (Laheij et al. 2008a, Laheij et al. 2008b). In cooperation with N.V Nederlandse Gasunie (a Dutch natural gas transmission company), the old one-call system was reviewed and investigations were made why, despite that an activity was notified, incidents still occurred (Elteren van et al. 2004). 

FIGURE 21.11 Schematic of the off-hne sampling system for monitoring natural gas transmission Unes. 

IGT-Improved Equation. This equation is used widely for natural gas distribution systems. When used for higher-pressure pipelines, the results obtained are conservative. The IGT Equation typically is used for pressure ranges between 1.5 and 100 psig. This equation is not recommended for gas transmission through long... 

Absorber oil units offer the advantage that Hquids can be removed at the expense of only a small (34—69 kPa (4.9—10.0 psi)) pressure loss in the absorption column. If the feed gas is available at pipeline pressure, then Httle if any recompression is required to introduce the processed natural gas into the transmission system. However, the absorption and subsequent absorber-oil regeneration process tends to be complex, favoring the simpler, more efficient expander plants. Separations using soHd desiccants are energy-intensive because of the bed regeneration requirements. This process option is generally considered only in special situations such as hydrocarbon dew point control in remote locations. 

As early as 1966, natural gas was available to all of the lower 48 states in the United States. During the period 1967—1990, the U.S. transmission system grew from 362,700 km to 450,800 km. Over this same time period, the distribution mains increased from 867,800 km to 1,347,000 km. As plastic pipe and reUable joining technology became available, the use of plastic pipe expanded to include the distribution of gas in low pressure systems. By 1990, approximately 24% of the U.S. distribution system was based on plastic pipe (1). 

Natural gas production and transmission systems are complemented by underground storage systems. These systems provide the capabdity to respond to short-term gas demands which exceed the immediate production levels or transmission capabdities. They also provide an opportunity to sustain some production by refilling the storage areas when seasonal temperature variations lead to periods of reduced gas demand. In the United States in 1990, there were 397 storage pools having a combined capacity of 2.2 x 10 (1). 

The more effective deflvery of natural gas is being realized by the use of computerized operation centers that allow rapid responses to the variations ia gas demand. Automated valves, more precise measuting systems, and high speed communication networks make it possible to closely monitor and manage the transmission and deflvery of natural gas. This translates iato improved service and cost effectiveness. 

Some U.S. natural gas pipeline companies are subsidiaries of gas hoi ding companies. The largest U.S. natural gas pipeline companies, in terms of overall length of transmission systems are Northern Natural Gas Company, 26,539 km Tennessee Gas Pipeline Corporation, 23,567 km Columbia Gas Transmission Company, 18,481 km Natural Gas Pipeline Company of America, 17,200 km and Transcontinental Gas Pipe Line Corporation, 17,071 km. For gas moved in 1994, the four largest pipelines were ANR Pipeline Company, 95,278 x 10 m (3,363,275 MMcf), of which 40.8% was gas moved for others Transcontinental Gas Pipe Line Corporation, 87, 050 x 10 m (3,073,801 MMcf), of which 99.7% was moved for others Natural Gas Pipeline Company of America, 83,089 x 10 m (2,933,940 MMcf), of which 87.1% was moved for others and Northern Natural Gas Company, 56, 523 x 10 m ... 

PAFC systems are commercially available from the ONSI Corporation as 200-kW stationary power sources operating on natural gas. The stack cross sec tion is 1 m- (10.8 ft"). It is about 2.5 m (8.2 ft) tall and rated for a 40,000-h life. It is cooled with water/steam in a closed loop with secondary heat exchangers. The photograph of a unit is shown in Fig. 27-66. These systems are intended for on-site power and heat generation for hospitals, hotels, and small businesses. Another apphcation, however, is as dispersed 5- to 10-MW power plants in metropolitan areas. Such units would be located at elec tric utihty distribution centers, bypassing the high-voltage transmission system. The market entiy price of the system is 3000/kW. As production volumes increase, the price is projec ted to dechne to 1000 to 1500/kW. 

See also. Air Conditioning Air Quality, Indoor Appliances Building Design, Residential Coal Consumption of Consumption Edison, Thomas Alva Electric Power Transmission and Distribution Systems Heat and Heating Insulation Lighting Natural Gas, Consumption... 

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