The falling cloud heat exchanger commercial pilot plant operation

Abstract

Tests on the falling cloud commercial pilot plant have demonstrated that a high proportion of heat from hot exhaust gases flowing up the chimney can be recovered. In fact, overall thermal efficiencies of up to 55% were obtained from heat recovery tests on the commercial pilot plant. Thermal efficiencies greater than this can be achieved by optimising the plant in general. The maximum gas-to-particle heat transfer coefficients in the main column were found to compare extremely well with those obtained from the experimental rig at the University of Aston in Birmingham [3]. However, a general drop in the heat transfer rates was noted at extremes of particle flow conditions. This was mainly attributed to the particle flow at the dispersion nozzle, restricted cooling water supply and lack of uniform fluidisation in the heat exchanger. It was found that the heat recovery rate from the commercial pilot plant was up to 27% greater than that obtained from the Aston University experimental rig operating under similar conditions. This finding is of extreme commercial value to the falling cloud heat exchanger applications. It is hoped that the high levels of heat recovery can be maintained or impr through-out the entire operating range of the plant. On the whole, the pilot plant operated extremely smoothly and brought the concept of the falling cloud heat exchanger industrial application closer to reality. We are now assessing the viability of the plant in a client's works for industrial applications and commercial exploitation. Major advantages of the falling cloud heat exchanger can be summarised as: (1) The overall thermal recovery rate and efficiency are high. (2) Heat is recovered from contaminated waste exhaust gases. (3) There is no fouling of heat exchanger surfaces, therefore, no cleaning or washing down is required. (4) The gas leaving the plant is at a lower temperature, and therefore requires smaller gas cleaning units, thereby cutting down the gas cleaning and fan power costs. (5) No gas bypass ducting system is required and no back-pressure problems as associated with conventional heat exchangers.