Heat recovery from a spray dryer using a glass tube heat exchanger

Abstract

This project at ABM Chemicals demonstrates the use of a glass tube heat exchanger to recover heat directly from a spray dryer exhaust to pre-heat the inlet air. It was originally envisaged that this would reduce the energy consumption of the dryer by around 20%.

Funding was granted by the Energy Efficiency Office of the Department of Energy under the Energy Efficiency Demonstration Scheme for both a feasibility study and the installation and monitoring of the project. The heat recovery was installed in June 1983 and an initial monitoring exercise carried out. Technical problems have prevented further monitoring and this interim report discusses the background to the project and the results to date.

Because of the corrosive and fouling nature of the exhaust and the arrangement of the ductwork, the most cost-effective option for this particular installation, was a glass tube air-to-air heat exchanger. Depending upon the production outputs, the expected savings were in the range 3.6–5.5 TJ/yr. These savings are worth £10,700 to £16,300/yr from reduced gas consumption and give a simple payback against the £27,000 installation cost, of between 1.7 and 2.5 yr. In other situations it might also be possible to reduce installation costs, which would also lead to a payback of less than two years.

Measurement of the performance of the heat exchanger showed that the amount of heat being recovered, 3.0 TJ/yr, was less than anticipated. Under these conditions the savings would give a 3 yr payback. This reduced performance is believed to be due to a higher-than-anticipated level of fines in the exhaust. This has led to fouling of the heat transfer surfaces, and eventually to the failure of a number of the glass tubes. Measures are currently in hand to reduce the carryover and further monitoring of the replacement exchanger is planned.

This project is one of a package of demonstrations for heat recovery in spray dryers. A similar project at Clayton Aniline uses a run-around coil heat exchanger to recover energy from the dryer exhaust, and a project at BIP Chemicals demonstrates the use of a separate heat source to pre-heat the dryer inlet air.

Within the U.K., widespread adoption of heat recovery on spray dryers would lead to energy savings of 100,000 tonnes of coal equivalent/yr (tce/yr). It is estimated that within the next 5 yr around 20% of