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WAD:CE designed and built a plant for the production of a special wax emulsion in the period October 1995 to August 1997. The plant was exported and commissioned for a concrete company in Hong Kong who use the emulsion as an additive for high-strength concrete.
Several interesting innovations were introduced into this plant: (i) A heat pump was used to recover waste heat from the outgoing product which was then used to melt incoming wax, (ii) a novel hydrocyclone was developed to continuously melt wax and (iii) an elegant control scheme involving ratio and cascade control was developed. As a result the plant is highly energy efficient and at the same time suitably compact. At 100 tonnes per day, it has the highest capacity of any such plant in the world. The plant was commissioned in August 1997, with a run of 225 tonnes (see Chemical Engineering in Australia Spring edition 1997).
The St Marys Aquatic Centre is an extensive regional swimming centre based around a large indoor pool and spa. In the the original design there was single supply of hot water for both spa and pool. All of the hot water flowed firstly into the spa and this then overflowed into the main pool. As a result spa and pool temperatures were not simultaneously controllable. The desired spa temperature was 37 to 39 deg C and the pool temperature about 10 deg less than this. In summer the pool temperature tended to climb well into the 30s while in winter the spa tended to be too cold. In addition the heat pump that supplied the hot water was running under stressful conditions that were causing it to fail prematurely.
WAD:CE was asked to design a new system so that both spa and pool temperatures could be independently controlled. Preferably this was to be done without creating a separate water system for the spa as the cost of a complete treatment plant was expected to be excessive.
The solution was to to use a large heat exchanger that took the outflow from the spa and used this to preheat the cooler incoming spa water. A smaller gas-fired heat exchanger added the extra heat to bring the spa up to its temperature set point. WAD:CE did the overall design, the control system and the electric circuits as well as supervising the contractors. The new system has been running since March 2000 and has resulted in reliable control of spa and pool temperatures as well as taking stress from the heat pump that supplies the hot water. The project came in on budget and on time.
The ATWS is a plant for removing volatile organic compounds (VOCs) and other pollutants, both oil and water-soluble, from waste air streams. It is especially suitable for fumes arising from mixed hazardous wastes where the composition and concentration is highly variable.
The ATWS works by contacting waste air with an aqueous scrubbing liquor at below-zero temperatures. This is carried out in a packed column under countercurrent flow. Direct contact of waste air with the ice-cold scrubbing liquor chills the air rapidly causing the VOCs to condense and to form a separate organic phase. Depending on their water-solubility, some VOCs dissolve directly in the aqueous scrubbing liquor while others dissolve in the separate oily phase. Up to 90% of VOCs and other fumes are removed as a liquid which is combined with other liquid wastes for disposal.
The ATWS is ideally placed before activated carbon (AC) absorbers which polish the air released to atmosphere. In this way the majority of VOCs are removed without burdening the expensive AC. Water-soluble fumes that are not absorbed well by AC, are largely removed as well.
ATWS has been in active use in a waste transfer plant in Dunheved NSW since 1995 where it separates out some 10 to 15 litre per day of mixed condensate. The ATWS has been approved by the NSW EPA.