British Gas

Atlanta Gas Light Co., Atlanta, GA British Gas pic, Loughborough, England Royal Militaiy College of Canada, Kingston, Ontario Sutcliffe Speakman Carbons Ltd, Ashton-in-Makersfield, England... 

Peter C. Eklund, Department of Physics and Astronomy and Center for Applied Energy Research, University of Kentucky, Lexington, Kentucky 40506, USA Philip J. Johnson, Ford Motor Company, Automotive Components Division, Schaefer Court 11, 14555 Rotunda Drive, Dearborn, Michigan 48120, USA Costa Komodromos, Gas Research Centre, British Gas, Ashby Road, Loughborough, Leicestershire LE11 36U, United Kingdom Max L. Lakt, Applied Sciences, Inc. 141 West Xenia Avenue, Cederville, Ohio 45314, USA... 

LPG is a mixture of flammable hydrocarbons which are gas at normal temperature hut liquid under pressure or when cooled below the boiling point at atmospheric pressure. Two mixtures are in common use, commercial propane and commercial butane. Large quantities are stored and handled at British Gas Corporation methane terminal, Shell UK Oil, Mobil Oil Co. Ltd, and Calor t ias LiJ The last also fills and handles large numbers of portable LPG cylinders. 

An example of a process using O2 to oxidize HiS is the Stretford process, which is licensed by the British Gas Corporation. In this process the gas stream is washed with an aqueous solution of sodium carbonate, sodium vanadate, and anthraquinone disulfonic acid. Figure 7-9 shows a simplified process diagram of the process. 

The surface-emissive powers of fireballs depend strongly on fuel quantity and pressure just prior to release. Fay and Lewis (1977) found small surface-emissive powers for 0.1 kg (0.22 pound) of fuel (20 to 60 kW/m 6300 to 19,000 Btu/hr/ ft ). Hardee et al. (1978) measured 120 kW/m (38,000 Btu/hr/ft ). Moorhouse and Pritchard (1982) suggest an average surface-emissive power of 150 kW/m (47,500 Btu/hr/ft ), and a maximum value of 300 kW/m (95,000 Btu/hr/ft ), for industrialsized fireballs of pure vapor. Experiments by British Gas with BLEVEs involving fuel masses of 1000 to 2000 kg of butane or propane revealed surface-emissive powers between 320 and 350 kW/m (100,000-110,000 Btu/hr/ft Johnson et al. 1990). Emissive power, incident flux, and flame height data are summarized by Mudan (1984). 

Harris, R. J. 1983. The investigation and control of gas explosions in buildings and heating plant. British Gas Corporation. 

Table 6.2 presents an overview of surface-emissive powers measured in the British Gas tests, as back-calculated from radiometer readings. Peak values of surface-emissive powers were approximately 100 kW/m higher than these average values, but only for a short duration. Other large-scale tests include those conducted to investigate the performance of fire-protection systems for LPG tanks. 

TABLE 6.2. Average Surface-Emissive Powers Measured in the Tests Performed by British Gas ... 

As previously described, full-scale BLEVE experiments by British Gas (KXX) and 2000 kg of butane and propane released at 0.75 and 1.5 MPa) give average... 

Radiation effects from a fireball of the size calculated above, and assumed to be in contact with the ground, have been calculated by Pietersen (1985). A fireball duration of 22 s was calculated from the formula suggested by Jaggers et al. (1986). An emissive power of 350 kW/m was used for propane, based on large-scale tests by British Gas (Johnson et al. 1990). The view factor proposed in Section 6.2.5. 

As described in Section 6.2.1., British Gas performed full-scale tests with LPG BLEVEs similar to those conducted by BASF. The experimenters measured very low overpressures firom the evaporating liquid, followed by a shock that was probably the so-called second shock, and by the pressure wave from the vapor cloud explosion (see Figure 6.6). The pressure wave firom the vapor cloud explosion probably resulted from experimental procedures involving ignition of the release. The liquid was below the superheat limit temperature at time of burst. 

Thus, the BLEVE theory predicts that, when the temperature of a superheated liquid is below T, liquid flashing cannot give rise to a blast wave. This theory is based on the solid foundations of kinetic gas theory and experimental observations of homogeneous nucleation boiling. It is also supported by the experiments of BASF and British Gas. However, because no systematic study has been conducted, there is no proof that the process described actually governs the type of flashing that causes strong blast waves. Furthermore, rapid vaporization of a superheated liquid below its superheat limit temperature can also produce a blast wave, albeit a weak... 

The surface-emissive power E, the radiation per unit time emitted per unit area of fireball surface, can be assumed to be equal to the emissive powers measured in full-scale BLEVE experiments by British Gas (Johnson et al. 1990). These entailed the release of 1000 and 2(XK) kg of butane and propane at 7.5 and IS bar. Test results revealed average surface-emissive powers of 320 to 370 kW/m see Table 6.2. A value of 350 kW/m seems to be a reasonable value to assume for BLEVEs for most hydrocarbons involving a vapor mass of 1000 kg or more. 

This design procedure is detailed in the British Gas publication Flues for Commercial and Industrial Gas Fired Boilers and Air Heaters (lM/11). This publication addresses itself to ... 

Additional guidance in the design of flues for condensing systems is given in the British Gas publication Installation Guide for High Efficiency (Condensing) Boilers — Industrial and Commercial Applications (lM/22). 

It is additionally recommended in the British Gas publication Guidance Notes on the Installation of Gas Pipework, Boosters and Compressors in Customers Premises (lM/16) that for buildings containing plant over 2 MW total heat input and being supplied with gas at pressures above 1 bar, a remotely operable valve shall be fitted in the gas supply to the building. In the case of large boiler houses, provision for remote operation of the valves shall be provided both inside and outside the building. 

In the particular case of oxygen, valves shall be resistant to exposure for up to 12 h at all pressures up to 2 bar at 20° C. Requirements for non-return valves for oxygen are also discussed in the British Gas publication Guidance Notes on the Use of Oxygen in Industrial Gas Fired Plant and Working Flame Burners (lM/1). 

Gas burners should comply with the relevant Codes of Practice, depending on whether the plant is low or high temperature. Low-temperature plant is defined as that having a normal working temperature insufficient to ignite the fuel, that is, below 750°C at the working temperature walls. The British Gas Codes of Practice are ... 

The amount of process plant that can be defined accurately as automatic is relatively small, and manual intervention is often involved at some stage. The relevant design criteria are therefore often IM/12 or IM/18. In practice, fully automatic burner controllers tested and certified by British Gas are available that comply with the requirements of BS 5885. Although these have features which may not be applicable to non-automatic plant, it may be more appropriate to use such a controller, particularly as its safety is well proven. It may also be less expensive than buying and installing separate timers, relays, etc. For some processes (for example, those that do not need and cannot tolerate a long purge) such controllers may not be appropriate. 

If an automatic isolation valve is specified, the selection of the valve and its operating system must be carefully considered, particularly with respect to the design and methods of restoring the gas supply in those cases where appliances do not incorporate automatic flame safeguards. Where possible, valves should be to BS 5963 and systems in compliance with the British Gas publication Weep By-Pass Pressure Proving Systems (lM/20). 

After testing for soundness it will be necessary to safely introduce gas into the pipework displacing the air or inert gas that is in it. Similarly, if pipework is decommissioned for any reason fuel gas must be displaced by air or inert gas. This is a requirement of the Gas Safety (Installation and Use) Regulations, Regulation 21. Guidance on recommended procedures is given in the British Gas publication Purging Procedures for Non-Domestic Gas Installations (IM/2). 

For polyethylene pipe, compression couplings may be used provided they comply with British Gas Specification PS/PL3. 

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