3 minute read
Energy efficiency in the industry
enerrgy efficiencgy in the industrgy
Improved industry competitiveness by improving energy efficiency
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The utilization of waste outputs is a theme that underlies the notion of the circular economy. An output stream that could be used to enhance industry effiency is waste heat. The potential amount of energy that could be recovered in this way is large, but effective utilization asks for technological and organizational measures.
The Norwegian industry emits a vast amount of waste heat energy. This heat energy could in principle be utilized, but common challenges are that it is difficult to utilize it close to where the industry is located and that it has a temperature level which is too low to be utilized. It is three main possibilities to valorize this waste energy:
• Produce electricity by implementing a power cycle
• Increase the temperature level by utilization of high temperature heat pumps
• Establish industry clusters where heat demanding industries establish close to the industry having waste heat available.
A further possibility to reduce the amount of waste heat and/or to valorize the temperature level of the heat, is of course to enhance the industry processes in itself.
Technology status and Challenges
Power cycles are being implemented in industries having large amounts (MWs) of high temperature (>400°C) exhaust gas available. For medium to low (250-100°C) temperature waste heat power cycles are implemented to a lesser extent, partly because the existing options have a too low efficiency and partly because the systems are too expensive. Waste heat is often available at temperatures which are not useful for internal use in the industry producing it or by potential users close to the industry. By utilization of high temperature heat pumps the waste heat could be valorized and delivered at a useful temperature level. High temperature heat pumps able to deliver heat at temperature levels in the range 90-250°C is to a small extent available for industry. For larger capacities water (steam) heat pumps are implemented either in open vapor recompression systems or closed vapor compression systems. For medium to large capacities there is a need to develop new technology based on environmentally benign working fluids.
Both power cycles and high temperature heat pumps need to capture heat from the industry sources which often requires specialized heat exchangers often operating in very challenging environments. This raises challenges such as:
• Handling of dirty gases causing particle deposition, scaling etc.
• Heat exchange close to industry processes limiting the working fluids or heat transfer fluids that may be accepted.
• Heat exchangers and working fluids able to accept high temperatures
• Specializes heat exchanger concepts, e.g. to capture heat from cooling of process elements
This raises a need for developing reliable and cost efficient heat exchanger concept that can be implemented for heat recovery in industry
Industry clusters
Waste heat available from one industry may be utilized by one or more industries in an industry cluster. In principle this seems straight forward, but in practice there are several challenges, examples are:
• Coincidence of demand and supply of heat
• Different owners of the different industries that may have different interests
• Risk if one or more of the industries are shut down There exist successful examples of industry clusters, but so far they are more the exemption from the rule. The potential is large and should be explored.
Outlook
The strong competence basis existing in Norway in general, and at NTNU-SINTEF more specifically, related to refrigeration technology and steam power cycles should be utilized to develop cost efficient power cycles for lower temperature waste heat and for high temperature heat pumps. A considerable knowledge also exists in the same competence environments regarding heat exchanger development and heat exchanging issues that can be utilized contribute in this area. The knowledge basis can further be utilized to initiate development of successful industry clusters.
R&D recommendations:
• Develop more cost-efficient power cycles for low to medium temperature heat sources (100-250°C) based on benign working fluids. policy recommendations:
• Develop industry cluster concepts to minimize emissions of waste heat.
