Steam production is an essential auxiliary process in meal manufacture because of the steam requirements of the main machines, cookers, presses, steam dryers and evaporators. Principally, two different arrangements for steam supply are utilized: the oil-fired steam boiler (the most widely used; at variable loads it delivers steam at constant pressure, and is automatically controlled) and the supply of steam together with electrical power. The joint generation of electricity and heat is advantageous in regions with unsteady, inadequate and expensive electric power. The principle of this arrangement is to let steam at a pressure of about 40 kg/cm2, expand in a turbine to about 10 kg/cm2. The work of expansion is converted by a dynamo into electric power while the low pressure steam is applied as required for heating processes in the factory. Back pressure turbines capable of generating 15 to 60 MW electricity are available. In regions where the electricity supply is ample and regular, the combined production of steam and electricity is normally not advisable due to difficulties in balancing the consumption and supply of the two.
For large steam boilers the economic advantages of installing refinements such as economizers, combustion air pre-heating, blow-down heat recovery, and so on, should be considered. Furthermore, the use of alternative fuels such as coal, wood or natural gas may, in several places, prove more economical.
