Energy Efficiency Improvements to Huletts Sugar Refinery

The central Tongaat-Hulett Sugar Refinery in Rossburgh generates steam and part of its electrical power requirement from burning coal, with the balance of electricity being purchased from the Durban Corporation grid. Energy is one of the Refinery's major cost components. The efficient use of this commodity is therefore important to its financial viability. Outside consultants examined the energy balance and applied, among others, the principles of pinch technology. On the basis of their report, the following changes were made: The single effect evaporator was converted to a double effect, by adding a plate evaporator as first stage and a plate heat exchanger as pre-heater. Flash from the condensate, mainly from the pan calandrias, is drawn into the Vapour 2 line of the evaporator instead of venting into the atmosphere. Vapour 3 from the syrup flash is used for pre-heating the boiler feed water make-up, using a plate heat exchanger. longer season, compared with white-end refineries attached to individual sugar mills, it has the disadvantage that, energywise, it cannot be integrated with any raw sugar mills. All heat energy has to be produced by burning coal, which is an important factor in the economics of running the refinery. Most of the energy is required for evaporation, be it for preconcentrating the sugar liquor or for evaporative crystallisation in batch pans. The pan steam requirement could be reduced by utilising the vapour from the pans to heat a second stage of pans operating at lower pressures, as is sometimes practised in the beet sugar industry, but this would require major capital expenditure. Thus most of the attention in recent times has been on reducing the steam required by the existing evaporator. Other cost components under consideration were: the treatment cost for boiler feed water make-up, which could be reduced by increasing the amount of recovered condensate andlor reducing the amount of HP steam required. High pressure (HP) steam is no longer let down directly the cost of bought-in electricity from the power utility, into the 510 kPa(a) process vapour line, but through a which could be reduced by being more self sufficient in thermo-compressor, which draws 220 kPa(a) exhaust vapown power production. our from the back-pressure turbo-alternator, enabling this machine to generate additional in-house electrical power. Plant set-up prior to modifications The use of plate evaporators on a factory scale and of thermocompressors is fairly new to the South African sugar industry, and these have thus far performed without any problems. Among the advantages arising from this project are: Reduced overall steam consumption, resulting in coal cost savings. Lower purchased electricity cost. Increased availability of condensate for boiler feed water, with correspondingly reduced need for expensive treated raw water for make-up.