Book - School of Science and Technology

Chapter 11Fuels, storage and handlingExcept where circumstances require that energy cannot be provided by other than eitherelectricity or gas from a public supply, provision must be made on site to accommodatefuel storage. The correct position for the fuel store can be decided only after taking intoaccount a number of determining factors including aesthetics, reasonable proximity to theboiler plant and convenience of access for deliveries. It is a mistake to agree upon aposition, however well suited to the fuel chosen to fire the plant initially, which may theninhibit absolutely any change to an alternative fuel at some time in the future.Storage capacityIt is usual to provide facilities to store fuel in a sufficient quantity to enable the boilerplant to run at full load for a period of three weeks. Except in special cases, such as ahospital unit, the full load figure would not apply to a 24 hour period but to say 12 hoursper day. This rule is one of convenience and is related to an arbitrary estimate of durationfor exceptionally severe weather, for an industrial dispute or some other cause forcessation of supply.For a plant which is quite critical to an industrial process or to, say, a computerbuilding and also in rural situations remote from trunk roads, it may be wise to providestorage for a longer period. In terms of economics, seasonal price differentials may makeit attractive to stock-pile fuel in summer. In the special case of small installations indomestic premises, the fuel supplier may propose a storage capacity suited to his deliveryroutine and offer a reduced unit cost if this be provided.Solid fuelAn explanation is provided in the following chapter of the various types of analysis towhich solid fuel is subjected. A proximate analysis will provide information relevant to thepractical aspects of combustion, the most important items being the proportion of volatilematter, the caking qualities and the properties, etc., of the ash. Volatiles, a grouping of tarsand gases produced as the fuel decomposes in burning, affect not only the rate ofcombustion but also the length of flame produced. After the volatiles have been burntoff, the solid residue (less any ash) is known as the fixed carbon. The cohesive nature ofthe fixed carbon is an indication of the caking and swelling properties which are importantsince they affect the porosity of a fuel bed to air flow. The ash content has an indirectinfluence upon the caking properties and upon the formation of clinker.