Research On The Key Issues Of Low-grade Industrial Waste Heat Utilization For District Heating

To increase the energy efficiency of manufacturing industry and to reduce the fossil energy consumption in district heating have become the key tasks of energy saving, emission reduction and air pollution controlling. Although low-grade waste heat discharged from manufacturing industry is unlikely to be fully reused within the factories where waste heat is generated, it can fill up the shortfalls in district heating systems without consuming extra fossil energy. Many projects involving industrial waste heat utilization for heating have emerged in recent years. Yet most of them have so many drawbacks in designing and operation, due to the lack of systematic theoretical guidance. Based on the theory of entransy analysis, this paper illustrates the essence of heating process using low-grade industrial waste heat, and focuses on the key issues and solutions within the system. The results of the research might be used to guide the design, optimizing and operation of the system.For the issue of collecting information of low-grade industrial waste heat, three levels of targets and corresponding approaches are proposed. The macro-data-based approach is used for macro policy making; the approach combining both field research and questionnaire inquiry is suitable for energy planning or heating planning; the approach of thorough and careful field research is necessary for the purpose of setting up a new heating project using industrial waste heat.For the issue of integrating multiple sources of industrial waste heat, taking T-Q chart as the main research tool, a complete theory is established of how to integrate low-grade industrial waste heat. The theory explains the inner mechanism, effect, and application occasion of various methods or techniques that could be used in the integration of waste heat, such as modified pinch technology, discarding part of the waste heat, absorption heat pump, and electrically driven heat pump, etc. The theory might guide the design and optimizing of the waste heat collecting process.For the issue of long-distance delivery of low-grade industrial waste heat, quantitative indexes have been put forward to evaluate th e influence of return water temperature on the primary side of the heating network. The indexes reveal the significance of lowering the return water temperature. Several kinds of techniques which could effectively reduce the return water temperature on the primary side are listed. The effect of each technique, on either the delivery process or the heat transfer process, is analyzed in a qualitative manner.For the issue of regulation and peak-shaving of the system, low-grade industrial waste heat has inherent deficiencies within it of both safety and regulatory performance. Therefore, low-grade industrial waste heat should only provide the base load for the district heating system, while the fossil-fuel heat acts as the peak shaver.To combine theoretical research with project practice, the first-ever demonstration project using low-grade industrial waste heat from a copper smelter for district heating is built in Chifeng city. By in-situ tests and data from the monitoring system, the performance and the remarkable benefits in social, economic, and environmental respects are displayed. It has also been verified that the key issues are essential to the practice of district heating using low-grade industrial waste heat, and that corresponding solutions to these issues are feasible and thus playing important roles.