Book - School of Science and Technology

302 Fuels, storage and handlingtank and be fitted with an isolating valve at the terminal end. Although the tanker drivershould purge the fill pipe with air on completion of each delivery, the provision of apermanent drip-tray arrangement is a prudent step.StorageSince the storage of a quantity of oil in or near a building provides the elements of a firehazard, various bodies have drawn up regulations covering the installation of storagetanks and other aspects of oil firing. A number of British Standards has been publishedand reference to the latest (currently BS 5410, Parts 1, 2 and 3) is advisable, alwaysbearing in mind that these publications provide no more than minimum specifications.Local authorities, fire authorities and insurance companies have their own requirementsas far as oil storage is concerned and these too should be noted.At domestic level, a tank capacity of not less than about 3500 litres makes sensibleallowance for the minimum delivery of 2500 litres preferred by oil companies. If a facilityexists whereby a metered `milk round' service is offered, then a tank holding as little as1300 litres may be installed to serve a house built in an area which is fully guaranteed to befrost, ice, snow and strike free.In larger installations, it is frequently necessary to provide two or more storage tanks.This has the advantage that filling and usage may be rotated, thus allowing any sludge orwater to settle out and maintenance to be effected. Table 11.5. gives the consumption ofboiler plants of various sizes based upon a three week operation at full load, 12 hours perday.Tanks used for oil storage are most often of welded steel construction and may be eitherrectangular or cylindrical. A generality might be that vessels mounted in the open air aremore commonly cylindrical, horizontal or vertical, and that tanks housed within abuilding are more commonly rectangular. Construction may be prefabricated completelyor carried out in situ from steel plate or formed sections. The latter method is obviouslynecessary for confined situations. Capacities and sizes, cylindrical and rectangular, aregiven in Table 11.6.Cylindrical vessels for mounting in the open should, where horizontal, be supported onsleeper walls topped by steel cradles. Vertical cylinders should be constructed in a mannerwhich keeps the bottom plate free from overall contact with the supporting base. Rectangulartanks sited in the open should have top plates hipped to reject rainwater and,Table 11.5 Approximate requirements for oil storageBoiler rating(kW)Storage for 3 weeks(litre)Boiler rating(kW)Storage for 3 weeks(litre)20 700 200 6 72040 1 390 300 9 87060 2 080 400 12 88080 2 760 500 15 750100 3 430 750 22 310150 5 090 1 000 28 000Assumptions:1. 21 days 12 hours.2. Boiler efficiency ˆ 75%.3. Oil CV ˆ 41 MJ/kg.4. Error at 1000 kW ˆ 10% and pro rata below.