Energy Sources, Types of Oven and Oven Design

Abstract

The thermal treatment during the baking process is provided by energy derived from the' following sources: wood, brown coal brickettes, fuel oil, natural gas, manufactured gas (town or city gas), anthracite, coke, bituminous coal (hard/mineral or pit-coal); or is applied as electroenergy. The heating effect of the individual energy sources during the baking process can be regarded as being similar, and the choice will depend on availability and cost. Wood, peat or mineral fuels could be the most economic choice in areas remote from industry. The energy is usually transmitted to the dough-piece via an intermediate medium, i.e. air, metal or brickwork. The relative efficiency or exploitation of each energy source varies considerably. Coal heating is about 20%, gas about 50%, and maximal in the case of a directly heated electrical oven, which is 85% efficient. The final choice of the energy source will depend on which resource is naturally available, and economically viable, as well as its relative efficiency and ease of control in the bakery. After taking into consideration all aspects, for example, in many European countries, natural gas has become the final choice for both the tunnel-ovens in industrial bakeries and the various batch-ovens used in the smaller bakeries. Amongst the advantages cited by users of natural gas-fired ovens are: (1) The simplicity in regulation of the gas/air mixture, which is usually automated. (2) Good temperature control and flexibility. (3) Clean and hygienic in operation. However, oven-design is important, and in the case of batch-ovens, the energy saving realized in installing a multi-deck gas-fired hot-air circulation oven, instead of a steam-tube oven with Perkin's tubes, could be 35% or more. In the case of all energy-sources, which produce heat by combustion, the calorific-value is a measure of their heating capacity. It is defined as quantity of heat in kJ or Btu (British thermal unit (FPS-system) = quantity of heat required to raise temperature of lIb water by 1°F, the therm = 10 5 Btu) liberated by burning I kg or lIb of a solid/liquid fuel, I m 3 or I ft3 of gaseous fuel. The heat of combustion, H max , and calorific-value, H c ' are differentiated from one another by the liberated heat of condensation when steam condenses, i.e. Hc = Hmax-2260WA(kJkg-1) 596 C. A. Stear, Handbook of Breadmaking Technology