steam heating may require a further 5000kg per hour of steam at 17.5atm Steam usage is related to evaporation of water from the product, and it requires 1. 9kg steam per kg of evaporation. HEAT RAISING PLANT Heating systems used in air drying are either direct or indirect Direct System Here the fuel is burned in the air stream and has direct impact on the product. This system calls for a high degree of purity and nontoxic constituents in the fuel. The development of natural gas propane and butane for commercial applications has provided the dehydrator with an ideal and economical fuel for vegetable drying and, in the authors opinion, is to be preferred against all other fuels, wheever the dryer lends itself to direct firing LPG in the form of propane is particularly suitable on account of its cry low sulphur content(0. 02 percent), its consistency of composition and freedom from unsaturated compounds. It is clean and easily controlled adjustableto special requirements and, moreover, it is relatively competitivPropane combustion chamber showing burner arrangement and air control damper developed by Aeromatic Ltd. steam heating may require a further 5000kg per hour of steam at 17.5atm. Steam usage is related to evaporation of water from the product, and it requires 1.9kgsteam per kg of evaporation. HEAT RAISING PLANT Heating systems used in air drying are either direct or indirect. Direct System Here the fuel is burned in the air stream and has direct impact on the product. This system calls for a high degree of purity and non toxic constituents in the fuel. The developmentof natural gas propane and butane for commercial applications has provided the dehydrator with an ideal and economical fuel for vegetable drying and, in the author’s opinion, is to be against all other fuels, wheever the dryer lends itself to direct preferred firing. LPG in the form of propane is particularly suitable on account of its very low sulphur content (0.02 percent), its consistencyof composition and freedom from unsaturated compounds. It is clean and easily controlled, adjustable to special requirements and, moreover, it is relatively competitive