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Because of extensive heat shortage and serious air pollution, industrial excess heat (IEH) has attracted much attention in the district heating (DH) markets of Northern China, as it has great potential for recycling and satisfying the large demand. Most of the available IEH is released at low temperature by steel plants, chemical plants, etc., which are located far away from the heat users. The energy consumption and pipe investment for heat transportation should be optimized to improve the comprehensive efficiency. This study will use systematic models to make optimization to primary-network temperatures and corresponding connecting forms. Several suggestions will be proposed to help improving the energy efficiency. Furthermore, based on a real case study, two new schemes are proposed and compared with the existing scheme. The connecting form of the optimized scheme is different to conventional heat pump systems using sources such as sewage and ambient water. The rated COP is estimated to be 6.16, and the annual electricity consumption is 40.78 kWh/GJ. The system has significant advantages in terms of energy savings and reductions in pollution emissions in comparison to conventional source systems, implying that it can be worth exploiting IEH even at low temperatures and long distances.

In China, district heating systems are facing a dilemma between rapid growth in demand owing to urbanization and environmental problems related to coal-fired boilers. The utilization of industrial surplus heat has great potential on improving the power of heating systems and reducing coal consumption of boilers. However, few industrial systems are constructed under the consideration of district heating. Some features of the surplus heat, such as the position, grade, and production schedule, are significantly different to traditional heat sources. To recover the surplus heat, retrofits of district heating systems are necessary. In this paper, according to the current situations and the future developments, a scheme is proposed to integrate the surplus heat of two steel plants into a large-scale district heating network. Three sources of surplus heat are involved: slag-flushing water, cooling water, and low-pressure steam. The scheme has been partly applied in a corresponding demonstration project. The actual performance proves the feasibility of the integrated system and implies significant benefits in terms of economic cost, CO 2 emission and pollutant emissions. Furthermore, the potential to extend the scheme in Northern China is also evaluated.

Large quantities of low grade waste heat are discharged into the environment, mostly via water evaporation, during industrial processes. Putting this industrial waste heat to productive use can reduce fossil fuel usage as well as CO2 emissions and water dissipation. The purpose of this paper is to propose a holistic approach to the integrated and efficient utilization of low-grade industrial waste heat. Recovering industrial waste heat for use in district heating (DH) can increase the efficiency of the industrial sector and the DH system, in a cost-efficient way defined by the index of investment vs. carbon reduction (ICR). Furthermore, low temperature DH network greatly benefits the recovery rate of industrial waste heat. Based on data analysis and in-situ investigations, this paper discusses the potential for the implementation of such an approach in northern China, where conventional heat sources for DH are insufficient. The universal design approach to industrial-waste-heat based DH is proposed. Through a demonstration project, this approach is introduced in detail. This study finds three advantages to this approach: (1) improvement of the thermal energy efficiency of industrial factories; (2) more cost-efficient than the traditional heating mode; and (3) CO2 and pollutant emission reduction as well as water conservation.