Total site utility systems optimisation for milk powder production

This study applies the Total Site Heat Integration method, in conjunction with a detailed process and utility model, to investigate three methods to increase the energy efficiency of the utility supply system for milk powder production. Sequentially explored opportunities are: (1) increasing boiler efficiency through condensing economisers, (2) waste heat recovery from the chiller unit, and (3) Combined Heat and Power (CHP) for electricity production. The basis for the analysis is the anticipated future milk powder process design, which incorporates results from recent studies that have focused on improving the process design and integration of the heat treatment and evaporator systems and recovering heat from the spray dryer exhaust, which show a combined specific fuel consumption reduction of 29.6 % and a relatively small increase in electricity use of 4.5 %. To maximise boiler efficiency, the study concludes that a condensing economiser for the flue gas can be indirectly matched with heating fluidised bed air flows through the boiler condensate system, which results in specific fuel use reduction of 227 MJ/tp. Chiller waste heat can be upgraded and integrated as a heat source to replace the equivalent specific fuel use of 101 MJ/tp through integration with the site low temperature hot water loop. By designing the steam system to maximise electricity generation in a new turbine, results show that 51 % of the site’s electricity demand may be satisfied by CHP. The combined effect of implementing these three utility systems opportunities is a specific fuel use of 3,868 MJ/tp, of which 530 MJ/tp result from electricity production, and a specific grid electricity demand of 113.4 kWh/tp.