A hot opportunity to cut emissions
Process heat is the steam, hot water or hot gases used in industrial processing, manufacturing and space heating. It is New Zealand's second biggest opportunity to reduce energy-related carbon emissions after transport.
About half of New Zealand's process heat demand comes from burning coal or natural gas.
Businesses can reduce their energy costs and carbon footprint by running boilers and process heat systems efficiently, or switching to innovative new heating technology.
Top ways to save energy costs and reduce carbon
Check the air-fuel ratio
Too little air results in a smoky flame, which means not all the fuel is burned properly. Too much also leads to losses — the excess air has to be heated and adds to the hot flue gas going to the atmosphere.
Check heating patterns to avoid hot and cold spotsIn gas and liquid fuel-fired direct process heating systems, observing the flame pattern can show up blocked jets and the formation of hot spots. Both these inefficiencies can be easily remedied with cleaning or adjustment of the jets.
Check heating equipment conditionPeriodically inspect the elements of processes heated by direct electrical resistance heating. As the elements age, they can gain resistance due to deterioration of the element surface.
Insulate the processThis can be done internally with ceramic and/or externally with a fibre insulation layer, depending on your process. Insulation reduces both convective and radiative losses by reducing the wall temperature.
Minimise conductive losses through support structuresExamples of this might be conveyor frames or piping. Because heat is conducted along metal components, some energy efficiency gains can be achieved by insulating the fixtures immediately around the heated space or by introducing a thermal break where practical.
Minimise air infiltrationA combustion system creates negative pressure within the furnace as the exhaust gases move out through the flue. While this stops combustion gases escaping, ambient air may be able to infiltrate the furnace through leaks and openings. Control this with regular inspection and a pressure control system.
Priorities for efficiency improvements
- Review heat supply options.
- Review insulation and containment.
- Review heat transfer.
- Review options for heat recovery.
- Review controls and material handling.
- Modify the system
New systems and upgrades – opportunities worth investigating
Pre-heat combustion air
Combustion air is low temperature, so can be pre-heated by virtually any waste heat stream. If there's an opportunity to pre-heat combustion air, you can increase your boiler efficiency.
Heat recovery opportunities
Look for hot waste streams exiting your system – it could be flue gas, air, water or even steam. For example, an air compressor may reject a lot of heat into the air that can easily be used to pre-heat water. Outlet air from a tunnel dryer can be partially recirculated and used to pre-heat inlet air through an exchanger before being used in another part of the process.
Assess if it is a significant enough amount, and what temperature it is. Investigate whether it could pre-heat any entering streams. Temperature match is key – you can address timing differences with storage.
Technology would have evolved significantly during the lifetime of your existing process heat asset. For example, some food products historically sterilised with heat can now be processed through high hydraulic pressure systems that are much more energy efficient and powered by New Zealand’s lower carbon electricity.
A wide range of electro-technologies can meet heating requirements, bringing production co-benefits. For example, heating your product directly, rather than heating the air around it is much more energy efficient.
Opportunities with fuel switching
Switching from a coal- or gas-fired process heat system is one of the most impactful ways a business can reduce its carbon footprint. Investigate whether electric or bioenergy options would work for you. Electric heat pump technology has made tremendous progress, making them a valid option for most applications using heat below 100°C.