Energy Efficiency Improvement via waste heat recovery and enhancment of production rate in aluminium industry

The primary object of the project has been to develop and prototype a system for active cooling and waste heat recovery from an electrolysis cell for primary Aluminium, where the heat recovery units are based on Heat Pipe technology. The project team has obtained a unique knowledge about Heat Pipe technology and design off such units for industrial use regarding heat recovery. The development has led to several new Heat Pipe concepts and they have been proven very efficient versus conventional heat exchan gers. The Heat Pipe prototypes have been tested in a special furnace that is simulating the conditions in an electrolysis cell for primary Aluminium. It has been developed a software tools that gives the key parameter of design for Heat Pipes towards new applications. A new concept for mounting of the heat recover unit on the outer sidewall of the cell has been proven to give a high heat transfer together with flexibility. The new compact and flexible design allows the heat recovery units to be installed both on brown and green field cells. The heat recovery units will be a part of an active cooling system that controls the heat balance of the cell. The heat energy that is normally lost to the surroundings is captured and is made available for utilizatio n. In cooperation with a post-doc working under The University of Stavanger, there has been developed a mathematic model for calculation of the ledge (freeze) thickness in the electrolysis cell. The model is used both for simulating different scenarios i n operation of the cell, but also to determine the control philosophy for the active cooling system. The work of the post-doc has been published in important journals for Heat Pipe technology and a presentation are to be held on one of the most important conferences for the Aluminium industry. Goodtech have signed a R&D contract with DUBAL (Dubai Aluminium) to run a pilot project and to develop the technology further.

About 50% of inputenergy in aluminium production is lost as waste heat. This project is targeted to develop a prototype system for waste heat recovery and power generation in the aluminium industry via active cooling based on heat pipe technology. The sys tem will improve energy efficiency by 260 kW per production cell. The production rate will be increased by 20% and operational stability will be extended. The payback period will be between 2 and 3 years. Current heat pipe technology is used in high tech areas (space industry) and in the computer industry as a big volume market. Given the very efficient heat transfer rates compared to established state of the art technologies this technology might be used to recover waste heat of the production process fo r aluminium for significant increase of energy efficiency and the production rate. The project will transfer heat pipe technology to industrial applications, aluminium production as the first targeted industry. It will build up the core know how on indust rial heat pipe technology in Norway. Work to be done in this context lies in the basic heat pipe design (dimension & working fluid) for this novel application. In terms of the heat transfer on the evaporator and condenser end, the heat flux especially wit h focus on the basic heat transfer must be covered. It is the very different thermal expansion rates of the pipe and the surrounding ceramic material for highest possible heat transfer in all operating conditions. Therefore main mechanisms of heat transfe r between the elements must be identified and maximised. Any kind of degradation, aluminium plants operate for about 7 years, must be kept under control. Related to EHS the aspects of relief of over pressure inside the heat pipe, refill and repair will be solved. All other aspect such as selection of material, fluids and other basic aspects of design will be covered also. The work will be done theoretically and experimental and result in a demonstrator.