Help-gas

With the introduction of computerized data systems for data acquisition, reduction, and storage during the 1960s, the efficiency of mass spectrometric analysis grew rapidly and continues to grow to this day. The use of computers for data reduction and analysis helped gas chro-matography/mass spectrometry (GC/MS) become a practical and powerful tool for qualita-... 

About the same time as the initial measurements of sH with methane and adamantane in the Colorado School of Mines (CSM) laboratory by Lederhos et al. (1992), Becke et al. (1992) surmised that they measured the sH equilibrium for methane + methylcyclohexane. Structure H phase equilibria data were reported for binary systems with methane as the help gas (Mehta and Sloan, 1993, 1994, 1996 Thomas and Behar, 1994), with methane and nitrogen as the help gas (Danesh et al., 1994), and binary systems with salt (Hutz and Englezos, 1995). 

A hilfgase or help gas hydrate is composed of small components such as nitrogen or methane that would aid in hydrate formation of a second larger component. 

In a review of the motions of guest molecules in hydrates, Davidson (1971) indicated that all molecules between the sizes of argon (3.8 A) and cyclobutanone (6.5 A) can form si and sll hydrates, if the above restrictions of chemical nature are obeyed. Ripmeester and coworkers note that the largest simple structure II former is tetrahydropyran (THP) (C5H10O) with a van der Waals diameter of 6.95 A (Udachin et al., 2002). Closely following THP are m- and p-dioxane and carbon tetrachloride, each with a molecular diameter of 6.8 A (Udachin et al., 2002). Molecules of size between around 7.1 and 9 A can occupy sH, provided that the below shape restrictions are obeyed and a help gas molecule such as methane is included. 

Hydrate structures containing hydrate former + Xe help gas have been confirmed by 129Xe NMR spectroscopy by Ripmeester and Ratcliffe (1990a). 

Due to shape restrictions, n-butane forms sll (with a small help gas) in the gauche isomer (Davidson et al., 1977b Subramanian and Sloan, 2002)—rather than the trans isomer that is preferred in the gas phase. At most temperatures of interest to the natural gas processor above 100 K, sll guest molecules have only small restrictions to reorientation. 

The specifications for the small help gas molecules that fill the small cages of sH hydrate are less rigorous and all guests that adequately fill the small cages in si and sll hydrate are thought to be suitable sH help gas molecules, for example, Ar, O2, Kr, CO, Xe, CH4, H2S, and then to a lesser extent SO2, CO2, CH3CI, and acetylene. CH4, Xe, H2S, H2 have been confirmed to be small sH help gas molecules by structural tools, such as NMR spectroscopy, x-ray, and neutron diffraction. 

A help gas stabilizes double and mixed hydrates. There is some uncertainty whether these inclusion hydrates are in fact stable without a guest species in the small 512 cages. All the clathrate hydrate structures are known to be stabilized and their melting points raised by including H2S with the guest compounds, which for this reason is called the helpgas [782-786]. Since we know of no experiments where the gas hydrates were prepared in the absence of air or some other gas, this help-gas phenomenon may occur to a more or less degree in all laboratory... 

The s-H hydrates have potential to become a better medium for natural-gas (mixed-gas of CH4 and impurities) storage and transportation . The s-H hydrates helped by CH4 can be generated under lower pressure condition than the pure CH4 hydrate. That is, we can handle the natural-gas hydrate (NGH) under more moderate condition by generating the s-H hydrate. The pressure reduction from pure help-gas hydrate depends largely on the kind of LGS. Some literatures reported that both the molecular size and the molecular shape of LGS have much effect on the equilibrium pressure of s-H hydrate. A lot of phase equilibrium data for the s-H hydrate systems are required to develop the effective storage and transportation system. 

In the present study, CH4 was adopted as help gas from a viewpoint to develop the gas-hydrate technology mentioned above. Ten C6-C8 hydrocarbons, that have various sizes and shapes, were added to CH4+H2O system for phase equilibrium measurement. The objective is to study the relations between the equilibrium conditions and the molecular sizes of LGS. The phase equilibrium relations for CH4+dimethylcyclohexane (DMCH) stereo-isomers, CH4+methylcyclohexane (MCH), CH4+cyclooctane (c-Octane), and CH4+methylcyclopentane (MCP) s-H hydrate systems were measured under four-phase equilibrium condition up to 10 MPa. The four phases were gas, water, liquid LGS, and s-H hydrate phases. In addition, the single-crystals of s-H hydrates were analyzed by Raman spectroscopy in order to obtain Raman spectra about the s-H hydrates. The CH4+1,1-DMCH and CD4+1,1-DMCH s-H hydrate systems were analyzed under four-phase equilibrium conditions up to 30 MPa. 

The program 1 has three advantages. (Dexhaust ventilation methods Due to less external leakage, therefore the mine ventilation is easy to manage. it is no need to set the ventilation structures in the main air routes, so ventilation resistance is small and easy to transport. if the main fan stops for any reason, the airflow pressure will increase in underground, which can inhibit the gas emission and is of help gas management, so the mine is relatively safe. 

I or IT Guests in Groups lie and Ha are not known to form h>drates by themselves but need small help gas molecules (trom Groups la. Ila,. some horn llb) If guest types from la or Ila are present together with guests from Group Pb. Structures I or... 

Ultrasonic degassing also helps gas-evolving processes. 

The discussion on hazardous area standards is concluded with the recommendation that the applicable standard part must be read thoroughly before starting any equipment selection. Since area classification is mainly carried out by mechanical and safety engineers, good coordination is helpful. Gas detection systems for hazardous locations is another area of concern for instmmentation and control engineers so brief discussions on combustible gas detection systems will be dealt with in the next clause. 

Although these measures were helpful, gas defence training remained inadequate. In a report to the Deputy Chief of Staff as late as March 1944, ACofS G 3 (Maj. Gen. Ray E. Porter) stated ... 

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