Waste heat minimisation and recovery are two of the most effective ways to reduce energy costs and greenhouse gas emissions. Reducing heat loss not only lowers energy and maintenance costs, but can also minimise emissions of air pollutants and improve the productivity of furnaces, ovens and boilers.
Investing in waste heat recovery can also provide alternative energy sources and yield significant energy savings in the industrial and commercial building sectors.
Generation technologies that harness waste heat, such as co-generation and waste heat to power (WHP) have the potential to produce electricity below the price charged by the electricity provider. These technologies reduce dependency on external energy inputs.
Companies should be aware of any forecasted increase in costs of fuels, such as natural gas, as this will affect the choice of fuel for new co-generation facilities.
Opportunities to save
There are many opportunities to reduce energy costs through waste heat reduction and recovery strategies, including the following.
Minimise waste heat in existing heat systems
Before implementing waste heat recovery technologies, it is necessary to identify heat losses common to heating equipment and to then optimise the operation of this equipment. This includes reducing heat loss due to flue/exhaust gas releases, air infiltration, wall conduction and radiation in existing furnaces, ovens, and boilers. Ensuring adequate insulation of system pipework and storages is also advisable.
Optimise the operation of existing waste heat recovery systems
Energy savings can be achieved by ensuring good maintenance and monitoring of the performance of heat recovery technologies and systems.
Monitor existing heat recovery systems – Monitor the performance of waste heat recovery technologies to ensure that you are optimising energy and financial savings. Ensure the system is tested under a range of loads and in line with the manufacturer’s instructions.
Ensure regular maintenance of waste heat recovery technologies – To ensure the cost-effectiveness of the heat recovery system, it must run efficiently. This requires a regular maintenance schedule conducted in-house or by the equipment supplier.
Upgrade or invest in new waste heat recovery systems
For many industrial and commercial sectors, heat and power recovery technologies offer the most significant single opportunity to reduce total fossil fuel consumption and improve energy efficiency. Harnessing and repurposing excess heat with recovery technologies is one of the best strategies to achieve significant reductions in energy costs and greenhouse gas emissions.
Future developments in waste heat recovery are outlined below.
Innovations for wider application of waste heat recovery
The US Department of Energy has found that many additional potential waste heat recovery energy savings exist through the latest heat exchange technologies. This is because advances in the construction of heat exchangers have yielded equipment that can be used in environments that were previously too extreme. Such new heat exchanges have been made possible first, because new materials that are resistant to corrosion are used in the construction of heat exchangers.
Second, novel designs and manufacturing techniques have led to heat exchangers that can tolerate higher temperatures and pressures. Because heat exchangers can now be used in these extreme situations, more heat from the process can be captured and utilised, therefore leading to energy savings.
For example, in the manufacture of nitric acid or sodium hydroxide (caustic soda).
Emerging technologies for greater levels of ‘low temperature’ waste heat recovery
Several new technologies are being developed to address opportunities for low temperature waste heat recovery and conversion. One possibility is to convert waste heat into electricity, normally to be consumed onsite. One of the solutions to generate electricity from low temperature heat otherwise dispersed into the environment is the Organic Rankine Cycle (ORC).
With plants available in a wide range of sizes, there are already a number of successful installations of ORC in cement, glass and metal sectors worldwide.
According to the Australian Institute for Refrigeration, Air Conditioning and Heating (AIRAH), the economics of heat pumps in the industrial context have improved due to gas price escalation, technology development and early stage economies of scale.
Waste heat as low as 45°C can easily be recovered by special heat pumps to produce output temperatures in excess of 100°C, suitable for commercial and industrial applications traditionally dependent on gas for heating.
Use of heat pumps may even prove a stepping stone towards complete replacement of boilers and steam systems in the long term. Research is underway to develop systems capable of more than 160°C.
Heat Recovery: A Guide to Key Systems and Applications UK Carbon Trust
Introducing Combined Heat and Power Technology UK Carbon Trust
Waste Heat Recovery: Technology and Opportunities in US Industry US Department of Energy