Natural gas pipeline quality

All gas turbines intended for service as stationary power generators in the U.S. are available with combustors equipped to handle natural gas fuel. A typical range of heating values of gaseous fuels acceptable to gas turbines is 900 to 1100 Btu/scf, which covers the range of pipeline-quality natural gas. Clean liquid fuels are also suitable for use in gas turbines. 

The natural gas feed to the cycle (stream 1) is typical of pipeline quality natural gas within the U.S. containing both sulfur odorants and higher hydrocarbons (C2H6, CsHg, etc.). The odorants... 

To be adjudged pipeline-quality natural gas, the hydrogen sulfide content must be below 25 grains per SCF (standard cubic foot), which calculates out to about 0.0004 mol %. The hydrogen sulfide removed and recovered may be oxidized to the sulfur oxides. 

Permissible carbon dioxide levels in pipeline-quality natural gas are characteristically up to 2-3 mol %. The recovered carbon dioxide is being increasingly touted for enhanced oil recovery operations rather than being vented to the atmosphere. 

As can be seen from the above tables, the process gas chromatograph can be a very accurate and precise technique for analyzing BTU content of pipeline quality natural gas. The analyzer is hnear over a broad range of composition and very repeatable over a wide ambient temperature range. 

To be adjudged pipeline-quality natural gas, the hydrogen sulfide content must be below 25 grains per SCF (standard cubic foot), which calculates out to about 0.0004 mol %. The hydrogen sulfide removed and recovered may be oxidized to the sulfur oxides, to be vented or, preferably, converted, say, in a lime-water wash for disposal as calcium sulfate (gypsum). In sufficient quantities and concentrations, the recovered hydrogen sulfide may be partially oxidized to elemental sulfur via the Claus process or its equivalent. 

Fuel. Coal gasification produces a combustible fuel gas that is principally H2, CO, and sometimes CH4. This fuel is excellent for direct use in combustion turbines and is also an excellent industrial fuel gas. It can easily be processed and converted into pipeline-quality natural gas, or even premium liquid fuels such as methanol or gasoline. These uses of coal gas generally favor oxygen-blown coal gasification processes. Key issues are the supply and price of conventional fuels. Nevertheless, coal gasification sets the maximum price for these conventional fuels and assures an alternative fuel source. 

Sulfur is a common contaminate of fuel. For example, pipeline-quality natural gas may contain 20 ppm of hydrogen sulfide and mercaptains. Clean refinery fuel gas typically has 100 to 200 ppm of total sulfur. Number 2 furnace oil (at least in the United States) will have perhaps 1000 ppm of sulfur. Heavy industrial fuel oil (No. 6 fuel oil or bunker fuel oil) may contain 6 percent (60,000 ppm) sulfur. About 90 percent of the sulfur in these fuels is converted to sulfur dioxide. However, about 10 percent is converted to sulfur trioxide (SO3). 

Sulfur is a common contaminate of fuel. For example, pipeline-quality natural gas may contain 20 ppm of hydrogen sulfide and mercaptains. 

This process uses propylene carbonate as a physical solvent to remove CO2 and H2S. Propylene carbonate also removes C2+ hydrocarbons, COS, SO2, CS2, and H2O from the natural gas stream. Thus, in one step the natural gas can be sweetened and dehydrated to pipeline quality. In general, this process is used for bulk removal of CO2 and is not used to treat to less than 3% CO2, as may be required for pipeline quality gas. The system requires special design features, larger absorbers, and higher circulation rates to obtain pipeline quality and usually is not economically applicable for these outlet requirements. 

Another problem is when the carbon dioxide content of natural gas is too high and must be lowered to produce pipeline-quality gas. Although the current practice is to vent this CO, sequestration of CO, in underground geologic formations is being considered. Already, in the Norwegian sector of the North Sea, CO, has been injected into saline aquifers at a rate of 1 million tons a year to avoid... 

Natural gas (methane) and 40° API crude oil are being pumped through a 6 in. sch 40 pipeline at 80°F. The mixture enters the pipe at 500 psia, a total rate of 6000 lbm/min, and 6% quality. What is the total pressure gradient in the pipe at... 

For WTW analysis, it is a sufficiently accurate assumption, that natural gas mainly consists of methane (CFI4). Compressed natural gas is also referred to as CNG . Natural gas is extracted, processed, transported and distributed via pipeline to the filling stations, where it is compressed to about 25 MPa. Natural gas sources may vary for different countries. Depending on the source (natural gas quality) and the transport distance (e.g., 4000 km or even 7000 km from Russia, depending on the relevant gas fields) the auxiliary energy needs or energy losses, and hence the GHG-relevant emissions can vary. For the calculation of the energy requirement and GHG emissions for the supply of natural gas, a transport distance of 4000 km is assumed. 

The initial biogas recovered is an MHV gas and is often upgraded to high heat value (HHV) gas when used for blending with natural gas supplies. The annual production of HHV gas in 1987, produced by 11 HHV gasification facilities, was 116 x 106 m3 of pipeline-quality gas, ie, 0.004 EJ (121). This is an increase from the 1980 production of 11.3 x 106 m3. Another 38 landfill gas recovery plants produced an estimated 218 x 106 m3 of MHV gas, ie, 0.005 EJ. Additions to production can be expected because of landfill recovery sites that have been identified as suitable for methane recovery. In 1988, there were 51 sites in preliminary evaluation and 42 sites were proposed as potential sites (121). 

High Heat- Value Gas. High heat-value (high Btu) gas (7) has a heating value usually in excess of 33.5 MJ/m3 (900 Btu/ft3). This is the gaseous fuel that is often referred to as substitute or synthetic natural gas (SNG), or pipeline-quality gas. It consists predominantly of methane and is compatible with natural gas insofar as it may be mixed with, or substituted for, natural gas. 

The American Natural Resources Co. had difficulty raising money for the mammoth project which would have produced 125 million cubic feet per day of pipeline quality high-Btu gas. Officials of the company had said that normal debt financing isn t possible because lenders aren t willing to put up the money for what is still an untried process in the United States. Yet outside financing is needed because the partners in the project can only afford to put up 25% of the cost of the plant themselves."... 

---