Microwave pre-heating epoxy resin saves $865,000 per year

Article by John Bows, Unilever Research Colworth, UK

During 2001, a major multinational chemical company in the Midwest (US) doubled production rates and made many processing savings in their resin heating line by using a 915 MHz cylindrical microwave heating system to pre-heat the resin.

The challenge was to pre-heat epoxy resin from 50 to 180°C prior to extrusion while maintaining a final product specification within acceptable quality ranges. Difficulties of conventional heating through a tubular heat exchanger include low volume throughput, high volumes of catalyst and wide ranging variation in final product quality. Also, frequent shut down of the production line due to solidification of the epoxy in the heat exchanger resulting from the lack of temperature control was a problem, as well as high maintenance costs resulting from the need to clean 61m of heat exchanger.

The solution was provided by Industrial Microwave Systems (IMS), who took 9 months from original R & D trials to the supply of commercial equipment. Installation and commissioning took less than 30 days. Operator training in use of the generator and control system was accomplished in less than one week.

The installation comprises a 100 kW, 915 MHz Cylindrical Heating System. The 130°C change in temperature was achieved in less than two seconds through a microwave exposure region of less than one metre resulting in an ideal consistent final product quality.

The system uses a two stage elliptical heating applicator. Each applicator has a heating length of 30 cm, overall height of 61 cm and a diameter of 25 x 41 cm in the elliptical dimension. With interconnecting pipe work and wave guides, the overall height was 3 metres. The unit it replaced was a 61 m long, 5 dm diameter tubular heat exchanger with a steam heating jacket.

Process benefits were a doubling of throughput volumes, a four-fold reduction of production line shut-downs, and a ten-fold reduction in maintenance costs. The line achieved a 98% absorption efficiency of the microwave energy generated and a total system efficiency of 83%. Uniform, volumetric microwave heating also eliminated clogging and the associated shut downs and maintenance.

The total annual value of the microwave heater is $865,000, based on the following value proposition:

1. Value of Throughput Increases. Additional capacity of 230 kg/hour generated 1360 tonnes additional product per year, worth $750,000 of Incremental Contribution Margin generated by the microwave heater alone.
2. Value of Catalyst Reduction. Normal operating mode catalyst consumption was 0.8 kg/hour. Catalyst consumption when employing the microwave heater was reduced to 0.6 kg/hour. Annual savings at 100% production capacity, at a catalyst cost of $11 / kg., are $57,600. As the microwave heater doubled production throughput, the annual saving doubled to $115,200.

The microwave power required to heat 550 kg/hour of resign is 42 kW of absorbed power. Allowing for microwave conversion and absorption efficiencies, the actual power required for this duty was 53 kW. Operating 24 hours/day for 50 weeks, 7 days a week and at an electricity cost of 4.5 cents/kWh, the total power cost is $20,034. The maintenance cost is $1 per kWhr per magnetron or $8,400 so the total operating cost is $28,434.

Even if the steam heated tubular unit heating cost was $10,000 per year, the annual downtime, loss of production due to change out of the exchanged and labour and materials involved in jack hammering the tubes plugged with solid resin cost at least $100,000. Add to that the savings in catalyst, and the increased production as stated earlier, then the savings become even more significant.

The installed and commissioned capital cost of the microwave heating and control system was around US$ 250,000. As a comparison, the shell and tube unit without steam boilers, installed steam train and control system was about $100,000. So the payback on the capital investment was less than 3 months.

A company spokesman said of the installation: "After the microwave heater replaced the steam heated tubular unit, production rate doubled, downtime due to fouling was virtually eliminated and there were savings resulting from less use of catalyst in our formulation."

IMS's approach on successful applications of microwave heating is to focus on applications where the customer has a clear economic advantage in changing to microwave technology, and only invest efforts where the unique benefits of IMS's ability to create a uniform field of microwave energy are of benefit to the customer.

About IMS
IMS, founded in 1997 and located in Morrisville, North Carolina, develops and markets microwave-based heating and drying systems for continuous flow manufacturing processes. These systems are significantly more energy efficient, are less expensive to install, operate and maintain, provide dramatic increases in processing speeds and deliver substantially more consistent and higher quality product resulting in overall production cost reductions.