Key points
Challenges facing the industry
The food and drink sector is currently facing enormous pressures. Supply chain issues, inflation, difficulty sourcing ingredients, managing production with COVID, in addition to climate change and sustainability issues around energy, water and packaging which have to be managed to meet consumer expectation, are creating a perfect storm. As a result, any new technology developments that can help alleviate the current situation are very welcome.
Thermal processing is a common method used by manufacturers to preserve and extend the shelf-life of many food and drink products. The process faces challenges regarding sustainability, as many manufacturers are using gas boilers for steam production for their thermal processing applications.
The use of gas boilers can be energy intensive and the large carbon footprint associated with burning oil and gas for steam production severely reduces any credibility around depletion of natural resources.
With many governments setting net zero emissions targets, the food and drink industry needs to re-evaluate its processing methods for optimisation to meet the sector’s own decarbonisation strategies and commitments.
This article explores some options available now and future possibilities.
Process optimisation
The first area for manufacturers to focus on is optimising current processes. Many manufacturers in the retort or continuous product processing sectors often over process their products because they may not be considering the accumulated lethality during the heating phase or the additional lethality acquired during cooling.
While additional safety margins should be included in the product, in many cases products can see a substantially greater level of lethality. This could be minimised to enable manufacturers to improve processing times, product quality, reduce fouling (which reduces waste), as well as save energy and increase profitability. Campden BRI is currently running a project which is focused on optimising continuous processing to explore the true benefits which can be made in this area (1)
Hydrogen
Another aspect which is being explored is reducing reliance on natural gas. UK studies have focused on boilers and houses with a raised percentage of hydrogen in the grid, to assess the functionality and safety of introducing this (2). There are also some industry trials exploring the impacts this may have on industrial processes, to ensure there are no unintended side effects from the introduction of hydrogen. Hydrogen is one option which will allow manufacturers to benefit from a reduced carbon method for steam production.
Electric technologies
In addition to considering gas alternatives, equipment manufacturers have been developing technology solutions to allow companies to pasteurise products through electrification of processes. By locking in deals with energy providers for green energy or having owned renewable energy sources onsite, manufacturers can benefit from electrified technologies knowing the source of their generation is the most economical they can obtain.
There are some non-thermal technologies such as high pressure processing, pulsed electric fields or low energy electron beam, as well as some rapid thermal processing methods, which are all powered via electricity that manufacturers could benefit from for preserving their food and drink product.
Emerging technologies
Some technologies have been around for a long time but have not had widespread adoption. However, these technologies will emerge and find more applications as the need for manufacturers to decarbonise their processes and push to electric supply gathers pace. Other technologies have been developed more recently.
Ohmic
An example of a technology that has been around for a while is ohmic heating. This consists of applying electricity to a product as it passes through two electrodes. The resistance of the product to the current causes it to heat up. It is also known as resistive heating.
This process can be very energy efficient with more than 95% of the applied electrical power being converted to useful heat. This technology is particularly beneficial for large food pieces in a liquid which need to be heated together in a continuous flow such as peach slices in a liquor.
In a scraped surface heat exchanger there is an overprocessing of the liquid component to get the temperature in the particulates. Ohmic heating can heat particulates in liquid at the same rate, reducing overprocessing of the liquid part of the product.
It is important that the conductivities of the product and different components are understood and controlled as this could lead to differential heating if they are too different. This may be an advantage in a small number of cases but it may limit some products being suitable for ohmic heating.
Radio frequency and microwave
More recently there have been developments in continuous technology for liquids in Radio Frequency (RF)/ Microwave (MW) technologies. While new applications are in continuous liquids, these technologies are already being used for blanching, thawing, tempering, drying and pasteurising applications commercially (3).
Liquid products and in particular those with particulates, can also benefit from RF and MW technologies. The heating mechanism uses dielectric heating albeit at different electromagnetic frequencies. The technologies have permitted frequency bands they can operate in.
RF uses 13.56 MHz, 27.12 MHz, and 40.68 MHz frequencies and MW uses 2450 MHz which operates worldwide except for countries which use 2375 MHz. Another common industrial MW band is 915 MHz.
Components in food which are electric dipoles (a partial positive and negative charge at opposite ends, like water for example), will try to align with the electric fields generated with RF or MW, which causes oscillation and rotation. The electromagnetic energy absorbed by these molecules causes them to collide with other molecules, dispersing energy and leading to temperature increases in a food or liquid.
Delivery to a continuous product with particulates means there are no hot surfaces heating the product, which can reduce fouling. The penetration of the electromagnetic energy into the product can also allow volumetric heating of liquids and particulates, which can also reduce overprocessing. A challenge with the technology is maintaining uniformity of heating but ensuring correct mixing can help limit this in continuous liquid applications.
The two technologies are more influenced by the dielectric properties of the product compared to ohmic which is influenced by conductivity, so could unlock heating for products not suitable for ohmic processes.
Typically, the energy efficiency of MW and RF systems (input energy vs delivered energy) is roughly 60%. Recent developments in solid state electronic components, means there is now potentially more scope to shift frequencies within a permitted band to move the standing wave patterns around to optimise heating uniformity (4). These systems, when processing in a cavity, can have feedback loops to control energy inputs, as well as the potential to have multiple entry points to reduce heating uniformity.
Programmable algorithms have the potential to heat products more uniformly. Shorter run times and energy savings are a possibility if a product can heat more evenly. In traditional magnetron systems, the process runs until the cold spot achieves the target temperature. If there are large hot and cold spot variations there will be overprocessing for some parts of the product, impacting the product quality and the time it takes to heat.
Induction heating
Another emerging technology with some great benefits for manufacturers is induction heating for liquid products (5). In a domestic setting, an induction coil is powered and conducts heat to the pan on the hob.
For an industrial processing system, the induction coil can be placed around a pipe and can heat a mixing element inside the pipe to generate middle out heating. The mixing element also accommodates more surface area to transfer heat.
All heating is electrical which means the technology offers faster start-up times and responsive changes to temperature fluctuations. Having a larger heating surface means faster heating rates with a more compact heating zone (5 m vs 45 m for a tube in tube heat exchangers). The reduction in the heating zone reduces the volume of product in the tube and hence waste if there is a line stoppage.
This technology would not currently compete with particles in liquids like the Ohmic, RF and MW. Energy efficiencies are improved with this technology compared to a gas boiler generating steam used in a tube or plate pack heat exchanger.
Trials have shown induction heating to have a 92% heat transfer efficiency, compared to 18% – 35% typically seen across gas boilers and traditional heat exchangers. Being able to replace a boiler steam system and heat the liquids directly for product using kettle heating, in pipe pasteurisation or sterilisation or cleaning chemicals for a clean-in-place scenario, allows manufacturers to decarbonise whilst receiving all the benefits described.
If you are a manufacturer exploring how to future proof your processes and operations in response to environmental changes and external pressures, then as you can see, there are a range of options available in the thermal processing space for you to consider.
References
- www.campdenbri.co.uk
- www.hydeploy.co.uk
- 3.) Chandrasekaran, S., Ramanathan, S. and Basak, T. (2013) Microwave food processing—A review. Food research international, 52(1).
- Tang, Z., Zhang, S., Hong, T., Zhu, H., and Huang, K. (2020). Frequency‐selected microwave heating: Its mathematical physics basis and characteristics. International Journal of RF and Microwave Computer-Aided Engineering, 30(4).
- www.inductionfoodsystems.com
