Built plants designed by SN2

Dr. Wayne Davies designed and headed a team that 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 used the emulsion as an additive for high-strength concrete.

The plant was built in Sydney, exported and commissioned for a concrete company in Hong Kong who used the emulsion as an additive for high-strength concrete. Its capacity was 100 tonnes per day. SN2 managed the entire project from primary research, costing, study of alternatives, P and IDs, equipment specification both mechanical and electrical, scaled piping plan, control scheme, handover and commissioning.

Research focused on the only major unknown, which was the rate of melting of wax pieces under defined conditions of agitation and temperature. This work showed that particle surface area and temperature difference were the important parameters.

Several innovations were introduced into this plant:

• Because cooling water was too warm in Hong Kong to resolidify the wax droplets, a heat pump was used to recover waste heat from the outgoing product. The reject heat was then used to melt incoming wax
• A hydrocyclone was developed to continuously melt incoming wax particles. This allowed solids to remain away from the discharge pipe so that only liquid wax would enter while keeping particles well suspended
• A control scheme involving ratio and "inverted" cascade control was developed to meter the liquid streams: water, liquid wax and emulsifier into a high-pressure homogeniser. Head pressure on a "balance tank" feeding the homogeniser was used to set the flowrate of incoming water, the value of which was proportioned and sent as set points to the other control loops for wax and emulsifier. The controller used for commissioning was a multiloop three-term control package written in-house that ran on a Macintosh computer using ADAM© modules.

The plant was highly energy efficient and suitably compact. At 100 tonnes per day, it had the highest capacity of any such plant in the world. The plant was commissioned with a run of 225 tonnes (see Chemical Engineering in Australia Spring edition 1997).

Plan drawing showing vortex bearing in place

This plant was designed for research into commercial applications of supercritical extractions and reactions. The plant was designed in May 2003 and was commissioned with its first run in October that year. The plant features pressures to 250 bar at 4 litres/hour and temperatures to 400 deg C. Operation is under computer control and there is extensive data logging of key parameters.

The plant is currently being used to examine a number of reaction schemes in development: (i) a special process for converting a wastesteam to a useful product, (ii) transesterification and esterification reactions used to make biodiesel and (iii) methanolysis of organics such as lignite and plastics wastes, (iv) dechlorination of organochlorines such as dichloroethane and vinyl chloride monomer. The dechlorination processes being studied remove chlorines in a totally aqueous system that is completely sealed.

The St Marys Aquatic Centre is an extensive regional swimming centre based around a large indoor pool and spa. In 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 too frequently.

Dr Wayne Davies was asked to design a new system so that both spa and pool temperatures could beindependently controlled. Preferably this was to be done without creating a separate watersystem for the spa as the cost of a complete treatment plant was expected to be excessive.

To do this a large heat exchanger took the outflow from the spa and used this stream's heat 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. Dr Wayne Davies 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.