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FROM SINGLE TO DUAL STATE
A single stage version of the system was installed last year in Aladdins Laundry at Parramatta (see “Gas Topics”, June 1991). When the Unitech team first discussed the possibilities of an installation at ACF Wetherill Park, they were talking about the biggest system they had yet proposed in Australia. They did so for two reasons. ACF operated on a much larger and more complex scale than Aladdins Laundry, and the system’s concept itself had progressed considerably since the early installations.
What the Unitech team suggested to ACF was a dual stage system. The waste heat escaping up the boiler flue would still be trapped and put to use – but at two levels.
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In the first, it would preheat the feed water entering a natural gas fired boiler. In the second, it would itself produce 80,000 litres of hot water per hour – a task for which a second boiler is used.
ACF’s engineering heads were impressed. They agreed. Unitech proceeded to install their dual-stage economizer over a three-month period. Production was not affected, because the actual process of linking the system to the existing plant took only a single weekend.
And in May this year, the whole installation came into action.
WHAT IT DOES
The system captures no less than 80% of the heat that previously discharged straight from the boiler flues into the atmosphere. The natural gas boiler that received feed water heated by the recycled energy in stage 1 produces steam. This is used for a variety of purposes, but mainly for specialised heat exchangers engaged in the pasteurising of milk and longlife shelf products.
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The hot water produced by the captured heat in the second stage is used for washing tanks and machinery.
With so many of their heat extracted, the temperature of the discharge gases from the boiler flue has plunged from 180oC to around 65oC to 70oC. This information is provided by temperature monitors and flow computers, which are important components of the system.
GREATER EFFICIENCY
Before the installation, the Wetherill Park plant operated two natural gas Maxitherm boilers – one rated at 3MW and the other at 3.5MW. Now, because the system produces some of its own hot water, often only one boiler is needed to meet the plant’s requirements. In addition, further savings come from the greatly reduced need to use steam to preheat the water in storage and feed water tanks.
The system’s efficiency is also enhanced by a fan on its discharge side. Controlled by a variable speed drive inverter, this keeps the boiler temperature at a constant level. |
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