Advantages of a steam pulp drier and the production cost of such drying

On the basis of mass and enthalpy balances of a pulp drier utilizing superheated steam, the corresponding exergy balances were computed. The way of carrying out this computation by using the diagrams of Baloh is indicated and discussed. Exergy balances give a complete picture of the energy economy, as well as of the thermodynamic efficiency of the processes and the installations: they unveil the thermodynamic losses resulting from the entropy increase or the exergy decrease, the losses during burning or heat transfer, during throttling, expansion, steam cooling etc. Ail of these losses are not indicated in the enthalpy balances. The advantage of an exergy balance is that the losses found can be converted directly into kWh which could be gained if those losses were avoided. The coefficient of exergy efficiency, which is computed from the ratio of the exergy obtained to the exergy expended, characterizes thermodynamic transformations better than does the enthalpy efficiency coefficient. On the basis of the exergy balance of a pulp drier utilizing superheated steam, the cost of production of dried pulp by this method is better compared with the cost of the usual system of drying the pulp by hot gases derived from fuel burning. A share of the fuel used in the boiler house of the sugar factory is proposed to be apportioned to the pulp drying with superheated steam. The technical and technological problems of installing a new pulp drier utilizing superheated steam in existing sugar factories are discussed. The introduction of a pulp drier utilizing superheated steam is furthermore an incentive to improving the whole energy economy of the factory. A study of every individual case is needed.