Pipeline quality methane

D. Blum Just going a bit further, the liquid-phase methanation process now uses one reactor. You can or you cannot use a polishing reactor as the economics dictate. You can actually go right to pipeline quality gas in one reactor, which is equivalent to about 99.8% conversion of a 20% CO feed gas. We envision at this moment that combined shift-methanation could be done in the same single reactor. It would obviously require lower feed gas rates so you may need two of these reactors. We don t exactly have the numbers yet. I think that s one of the areas that deserves future work. 

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. 

To meet pipeline specifications the product gas requires further processing. It is cleaned and subjected to partial water-gas shift to adjust the H2/CO ratio it is scrubbed to remove acid gases (C02, H2S) finally it is subjected to catalytic methanation to increase the heating value to pipeline quality. 

The number of trim-methanation stages required depends on the final product specifications. Generally, two trim-methanation stages are sufficient to produce a high-methane, pipeline-quality gas. 

Synthetic (substitute) natural gas Pipeline-quality gas that is interchangeable with natural gas (mainly methane). 

A zeolite and carbon molecular sieves (CMS) have been examined for N2/CH4 separation. A process using 4A zeolite for this separation was developed by Habgood (1958), but this process was limited to low temperatures (—79 to 0°C) and a high-methane feed content (>90%). Ackley and Yang (1990) have demonstrated the use of carbon molecular sieve (CMS) for separation of N2/CH4 mixtures in pressure swing adsorption (PSA) processes but have also shown that the potential for CMS to achieve the desired pipeline quality (90% methane) is doubtful. The only two promising sorbents are clinoptilolites and titanosilicates, as discussed below. 

Frankiewicz and DonneUy (1983) showed the promise of a calcium-exchanged clinoptilolite for N2/CH4 separation by a PSA process, but the product was below pipeline quality. This work stimulated a good deal of interest in further investigation. Two Japanese patent applications (61-255,994, in 1986, and 62-132,542 in 1987, see Chao, 1990) disclosed the use of natural clinoptilolite and Ca-exchanged forms for nitrogen removal from methane. Chao (1990) suggested the use of Mg-exchanged clinoptilolite for N2/CH4 separation. 

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. 

In addition to carbon sequestration, technologies that would provide economic benefits include those that enhance oil recovery, produce coalbed methane, and maintain pressures in depleted gas reservoirs to avoid surface subsidence. Currently, companies in the United States sell one billion standard cubic feet of C02 each day, or approximately the C02 output from one conventional coal-fired electric power plant with a power capacity of 2300 MW. This C02 is used economically and with little or no environmental impact for approximately 70 enhanced oil recovery projects and for other industrial applications. Pipeline specifications for C02 quality, pipeline safety issues, and custody of the C02 have a base of industrial experience that goes back to the 1970s. Today, there are operating C02 pipelines of up to 760 mm (30 inches) in diameter and 640 km (400 miles) in length (Fig. 6-6). 

The light fraction always contains methane and nitrogen, sometimes even lighter hydrocarbons. For further use it is either compressed to pipeline pressure or liquefied and used as LNG. Beginning with ethane, the heavy fraction can contain all higher hydrocarbons that may be isolated, if required, by means of fractioning and then be marketed in technically pure quality. 

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