Utilisation of waste heat from food factories. Executive summary prepared for DEFRA

Abstract:

<p>This executive summary describes work on the project AFM248Br, which involved CCFRA and Bristol University as a research consortium and the collaboration of Shipston Mill, Kerry Aptunion, Kraft Europe, Kellogg's UK, Warburtons, Unilever, RHM Culinary Brands, Greencore, Weetabix and Glaxo Smith Kline Nutritionals.</p> <p>AFM248Br was a one year Bridge-LINK project that finished in October 2007. The project identified sources of waste thermal energy from food processes that could be recovered to produce mechanical power using Stirling engine technology. In the context of the project 'waste thermal energy' implied any source of heat released from a process that was rejected to the environment. Flue gases from combustion processes, hot air from baking ovens, steam or steam condensate from cooking operations were a few examples found in the food industry.</p> <p>The project proposed the assessment of Stirling engine technology to achieve this purpose. Stirling engines are external combustion heat engines, with several advantages that make them suitable for waste heat streams (no contact between heat source and moving parts, scalable to application, low maintenance). They have high theoretical efficiencies and have been developed for several applications (micro CHP systems, biomass and solar powered), although they have not reached yet full commercial development except for very specific niche applications.</p> <p>Ten different food factories were visited to gather information on waste energy streams released from processing operations. The nature of manufacturing operations studied was varied because the companies chosen for collaboration in the study belonged to different food sub-sectors. These included bread and cereal manufacturing, wheat processing, fruit processing, production of coffee, elaborated and prepared foods and soft drinks. </p> <p>The project showed that although a significant amount of energy was lost through food manufacturing operations, the range of temperatures at which it was released (typically in the range between 30 and 200&deg;C maximum) did not allow for an efficient and cost effective transformation into mechanical power. It concluded that exploitation of this potential was constrained by the lack of suitable technology. Attractive alternatives to the Stirling are now emerging: for example rotary scroll compressors for refrigeration and automotive air-conditioning. Together with new methods of manufacturing compact heat exchangers and reactors (direct laser deposition, DLD), these could form the basis of a new rotary heat engine using a recuperated rotary Ericsson cycle. This "scroll" engine will have the same theoretical efficiency as the Stirling, but will achieve a higher proportion of it in practice, at commercially acceptable costs. A research proposal on this concept was submitted to Defra following the finalisation of this project.</p> <p>However, another potential application for heat engines within food processing facilities was identified. This comprised the concept of utilising high grade primary energy (from gas burning) to run a Stirling engine and produce electricity, and then use the remaining thermal energy to run the food process (e.g. baking oven).</p>

Author(s):

CCFRA