a spare motor unit should be kept in the stores for all key plant and where drives and power requirements can be standardised for several machines, this should be arranged in order to cut down the number of spares carried Most electrical supply authorities impose a maximum demand tariff on their consumers, and as the dehydrator is involved with a considerable power requirement, and the use of several high powered motors, it is very necessary to install power factor correction equipment in the factory to reduce the start-up load on the meters. It is usually found that the cost of such equipment can be recovered within twelve months of normal operation and this will, of course, depend on the Local authoritys tariff, and to what extent the maximum demand rate is levied on the commercial consumer For a stand-by supply, a 200KVA alternator, driven by a diesel engine or, if a steam supply is available, by a steam turbine, should be adequate to keep the principal preparation plant and the main dryers operational in the event of a mains power failure, and this supply should be arranged so that it can be fed into the mains immediately such a failure occurs. Some factories keep their steam turbine'stand-by' plants continually operating, integrating the supply with that from the mains, and utilising the back pressure steam for process heating in the factory. This is an efficient and economical method of Producing, simultaneously, electricity and low pressure steam at 10-15psi from one power source, ie, the boiler. At the same time the essential plant ca be kept operational in the event of an external power cut or supply failure BOILERS Boiler plant for this scale of operation should be rated at 6500 to 7000kg per hour, at 17.5atm, with a stand-by boiler of similar capacity. This boiler rating is based on the assumption that the whole of the heat requirement fo drying is not expected to be taken from the boilerhouse. This point is considered later in the chapter when fuels for drying operations are re viewe Some dryers incorporate steam batteries and air fans for convection drying and, if this type is used, then the rating of the boiler plant may have to be increased but with the advent of natural gas, and the various forms of Liquid Petroleum Gas, a very much more efficient heat source for drying is now available to the dehydrator, and steam batteries are figuring le prominently in the many modern drying plants The boiler rating stated above, therefore, takes into account the steam requirements for peeling, blanching, scalding, jacketed or coil heated vessels, steam batteries for conditioning bins(see Bin Finishing), steam hosing for sterilisation of plant and equipment, and space heating Dryers relying uponA spaR motor unit should be kept in the stores for all key plant and, where drives and power requirements can be standardised for several machines, this should be arranged in order to cut down the number of spares carried. Most electrical supply authorities impose a maximum demand tariff on their consumers, and as the dehydrator is involved with a considerable power Ilequirement, and the use of several high powered motors, it is very necessary to install power factor comxtion equipment in the factory to reduce the start-up load on the meters. It is usually found that the cost of such equipment can be recovered within twelve months of normal operation and this will, of course, depend on the Local Authority’s tariff, and to what extent the maximum demand rate is levied on the commercial consumer. For a stand-by supply, a 2OOKVA alternator, driven by a diesel engine or, if a steam supply is available, by a steam turbine, should be adequate to keep the principal preparation plant and the main dryers operational in the event of a mains power failure, and this supply should be arranged so that it can be fed into the mains immediately such a failure occurs. Some factories keep their steam turbine ‘stand-by’ plants continually operating, integrating the supply with that from the mains, and utilising the back p~ssure steam for process heating in the factory This is an efficient and economical method of producing, simultaneously, electricity and low pressure steam at IO-15psi from one power source, ie, the boiler. At the same time the essential plant can be kept operational in the event of an external power cut or supply failure. BOILERS Boiler plant for this scale of operation should be rated at GOO to 7000kg per hour, at 17.5atm, with a stand-by boiler of similar capacity This boiler rating is based on the assumption that the whole of the heat requirement for drying is not expected to be taken from the boilerhouse. This point is considered later in the chapter when fuels for drying operations are specifically reviewed. Some dryers incorporate steam batteries and air fans for convection drying and, if this type is used, then the rating of the boiler plant may have to be increased but with the advent of natural gas, and the various forms of Liquid Petroleum Gas, a very much more efficient heat source for drying is now available to the dehydrator, and steam batteries are figuring less prominently in the many modern drying plants. The boiler rating stated above, therefore, takes into account the steam requirements for peeling, blanching, scalding, jacketed or coil heated vessels, steam batteries for conditioning bins (see Bin Finishing), steam hosing for sterilisation of plant and equipment, and space heating. Dryers relying upon 31