TECHNICAL INFORMATION ABOUT NATURAL GAS TRANSPORT

Transcription

1 TECHNICAL INFORMATION ABOUT NATURAL GAS TRANSPORT I / 7

2 Natural Gas Transport. General principle The most efficient and effective method of natural gas distribution from the place of production to the consumers is transportation via pipelines. Basically, there are three types of transport pipelines: - The gathering system transports raw natural gas from the wellhead to the processing plant. - The transmission line transports natural gas to regional distributors. - The distribution sytem transports natural gas to the consumers. Natural gas is transported via transmission lines to the consumption regions at high pressure. The required pressure is produced by compressor stations distributed along the pipeline. The maximum operation pressure is 200 bar. The subsequent distribution grid supplies the consumers with natural gas. The operation pressure is divided into: - high pressure > bar - middle pressure < bar < 00 mbar - low pressure < 00 mbar.2 Main pipeline components.2. Pipelines Diameters of transmission pipelines usually vary from 6 to 48 inches. Pipes for gathering as well as distribution lines are smaller, often between 2 and 6 inches in diameter. The typical pipe material of gathering and transmisson lines is steel. Raw natural gas may contain high quantities of sulfur and carbon dioxide (sour gas). Sour gas is extremely corrosive, therefore, special pipe material has to be used. Steel pipelines are either covered with a special coating to avoid corrosion or they are protected by cathodic corrosion protection, a technique of running an electric current through the steel pipe to avert corrosion and rusting. As PE pipelines do not corrode, corrosion protection is not necessary. II / 7

3 .2.2 Compressor stations For the transmission of natural gas in transmission pipelines over long distances the gas has to be highly pressurized. Pressure is increased and maintained by compressor stations. The compressor stations are operated by using an electric motor or a gas turbine powered by natural gas from the pipeline. The compressor stations are placed at 50 to 00 km intervals along the pipeline. Compressor stations usually consist of liquid separators, scrubbers and filters to dehydrate the natural gas during the compression process. Natural gas in pipelines is considered dry gas..2.3 Pressure regulation and measuring stations In a pressure regulation and measuring station the gas coming from the production and conditioning is measured (quantity measuring) and regulated to the operation pressure of the subsequent gas network. Pressure regulation stations are mainly placed at the end of transmission lines and also in distribution grids to reduce the transport pressure to the operation pressure of consumption regions. Measuring stations measure the consumption of regional distributors (public utility company). A pressure regulation and measuring station consists of: - input valve - input filter - regulation system with pre-heater - quantity measurement - safety installations - exit valve III / 7

4 FQ 7 FQ Shut-off valve 2 Isolating joint 3 Filter/Separator 4 Pre-heater 5 Safety slam-shut valve 6 Gas pressure regulator 7 Gasmeter 8 Safety relief valve Fig.. - Schematic of a pressure regulation and measuring station Depending on its size the regulation station is arranged in a building or cubicle. Fig..2 - Regulation station in a cubicle IV / 7

5 Fig..3 - Regulation station in a building.3 Distribution The distribution network consists of: - pressure regulation and measuring station - pipelines for supply - house service connections Dimensioning of pipelines is based on the determination of the overall gas consumption of standard and special customers. Customers are connected to the main lines by house service lines and house connections. House connections are provided with a shut-off valve to put down the gas supply in the building. House connection lines are usually between and 3 inches in diameter. V / 7

6 PE pipes are usually used for natural gas distribution, when the pressure is lower than 0 bar. For higher pressure steel pipelines have to be used..4 Planning and construction Special software is applied to calculate the parameters of a pipeline. The design parameters are: - operation pressure - purchased gas quantities - pipeline material - lengths of lines - topography Based on these parameters an arithmetic net plan is generated and the line diameters are defined. Fig..4 - Detail of an arithmetic net plan For further planning the pipe routes are fixed on the basis of maps. Afterwards these routes have still to be agreed with the responsible authorities and property owners (permission procedure, acquisition of title). VI / 7

7 After having performed all preparatory work, construction of the pipeline network, design and installation of control arrangement and installation of house connections have to be carried out by certificated companies. Fig..5 - Construction of a high-pressure pipeline After the construction a pipeline pressure check (tightness test of the system) is carried out. The control arrangement is also checked before commissioning. Afterwards the line system is filled with natural gas and the house connections are put into operation. Following this procedure guarantees the supply of the customers with natural gas. VII / 7