Do you have waste heat and don’t know what to do with it?
Energy costs are hurting business. Yet often there are concentrated sources of energy going to waste in manufacturing environments. Recovering waste heat back into processes can save substantial amounts of energy cost, and increase the spare heating capacity of existing systems.
Data matters
Doing heat recovery well requires good data and a good understanding of the existing systems, combined with a methodical approach to determining the optimum solution. Especially where there are multiple heat sources and heat sinks.
A Pinch Analysis is the gold standardAccreditation scheme for voluntary carbon offset and renewable energy projects. The tradable instruments are Verified Emission Reductions (VERs). The Gold Standard label can also be applied to CERs and I-RECs where the project meets the Gold Standard requirements around sustainable development and project additionality. More for optimising heat recovery in your plant, but discrete feasibility studies are also very useful.
How can waste heat be recovered and used?
Waste heat can be available from a range of sources, including exhaust air from gas burners, de-superheating a refrigerant prior to latent heat rejection, oil coolant systems on air compressor and refrigeration compressors, wastewater discharge, furnace exhaust, refrigeration condensers, and many other sources.
Direct heat exchange using a tube or plate heat exchanger is a simple method for heat recovery, however, there are other methods. For example, a waste heat source at a relatively low temperature can be used to heat a process flow to a higher temperature using a heat pump. Indirect heat exchange can be achieved using a hot oil circuit where the heat source is too hot for direct heat exchange with the heat sink.
Waste heat can also be used in many ways:
- re-heat combustion air for a furnace or oven
- Use directly in a dryer
- Heat water in pasteurisers
- Generate electricity using an Organic Rankine Cycle or Steam turbine to drive a generator
- Generate hot water up to 100°C or steam at up to 160oC by extracting heat from a lower temperature waste heat source..
Optimising waste heat recovery
Where a site has numerous heat sources and sinks, a “Pinch” analysis can be used to determine the optimum combination of heat recovery alternatives for that site. PinCH analysis attempts to identify similar heat loads nearest to available heat sources and minimise the use of artificial heating (e.g. from natural gas or electricity). The optimum combination from a heat recovery perspective is not always practical in a retrofit though, so the key is to determine how to get as close to the optimum as possible in a practical and cost-effective way.
Implementing waste heat recovery
Implementation should take into account a number of factors:
- The operating characteristics of the process, to ensure the implementation doesn’t impact on output, product quality, process reliability or productivity.
- Staging of projects if possible, to minimise process disruption and spread capital spend.
- Heat quality available (temperature and rate of supply) and proximity to heating loads
- Measurement, monitoring, and verification so that energy savingsElectricity or gas savings or both. More can be measured over time, and energy-saving or carbon abatement certificates can be created
- Future plans for expansion or plant upgrades
Make informed and smart decisions about heat recovery.
Northmore Gordon is passionate about helping large industrial and commercial customers increase energy productivity. We have done a number of pre-feasibility studies and business cases specifically investigating waste heat recovery options. We can help you identify and quantify your heat sinks and sources, determine the optimum solution for your situation, and develop an investment-grade business case.
For more specific details on heat recovery contact Andrew at a.clarke@northmoregordon.com
