Improving real-time process data monitoring and benchmarking of energy use can help identify many opportunities to reduce energy demand, from optimising equipment performance, minimising heat gains and losses, optimising the conditions under which equipment operates and shutting down equipment when it is not required.
Some examples of opportunities in this area are outlined below.
To help benchmark current energy use and identify new energy efficiency opportunities, it is recommended that effective energy metering and monitoring capabilities are installed at the process level.
This will help companies to:
- understand how energy is used within different manufacturing processes and major pieces of equipment
- develop accurate modelling of energy and material flows
- identify and evaluate the most cost-effective ways to reduce energy waste
National Foods installed energy-monitoring equipment at its Penrith site at a cost of $14,000. Monitoring the electrical energy use in each processing section led to the reprogramming of chillers to make them more efficient, saving 377MWh (460tCO2e and $30,160) per year. The monitoring equipment paid for itself in 6 months.
Most food and beverage processing plants have energy overheads that lead to heat being lost even when the plant is not processing any product. To address this:
- implement and maintain good ‘control engineering’ to ensure that equipment automatically switches off or shifts to its lowest power mode when not being used. Coca Cola Amatil’s plant in South Australia saves 344GJ per year with sensors to shut down conveyors when not in use
- fix or replace fault-prone equipment so that it can be turned off and on regularly without the risk that it won’t restart properly
- identify and insulate equipment that continues to lose or gain heat when useful services are not being delivered
Food and beverage manufacturing plants have numerous types of equipment operating at different temperatures and pressures. Ensuring this runs at optimal conditions saves significant amounts of energy.
Cooled storerooms are often kept at lower temperatures than required due to concerns about potential equipment failure. However, overcooling a storeroom, as well as wasting energy, raises the probability of equipment failure by increasing the load on the refrigeration plant.
The temperature should always be set to meet product storage requirements.
Operating air compressors at the lowest required pressure settings saves energy.
Other opportunities to explore:
- operate extraction fans only when equipment is in use
- provide make-up air close to the equipment
- ensure that the make-up air inlet is closed when equipment is not in use
Minimising heat gain into refrigerated systems and spaces can reduce the energy to maintain temperatures in these areas.
This can be done by:
- positioning refrigeration units as far away from cooking/boiler equipment as possible
- maintaining cool room efficiency by regularly checking door seals and refrigerant levels of chillers
- ensuring cool rooms are well insulated, with no thermal bridging through metal frames
- insulating pipe work and locating refrigeration heat exchangers away from heat sources, such as radiators and air-conditioning systems, and minimising the temperature of supply air
Heat from boiler systems, cooking equipment and pasteurisers can impact on the energy required to maintain refrigerated areas and increase requirements for air-conditioning cooling loads. Heat loss from boiler systems can be minimised by insulating boiler valves, steam and condensate return pipes and storage units.
Many commercial ovens are either poorly insulated or have metal joints that provide a thermal bridge allowing heat loss. By increasing average insulation around these ovens to an R value of at least 2.5 and reducing thermal bridging, radiated heat can be reduced by up to 75%.
Preventive maintenance programs can detect potentially developing problems, such as heat leaks, leaks in air compressors, seal leaks in chiller rooms and fridges, and bearings running hot.
Allocate a budget and implement a preventive maintenance program to delegate responsibility for specific equipment. For example, assigning responsibility for basic lubrication and identification of leaks in air compressors can prevent unnecessary and costly stoppages.
Redesigning and improving food and beverage manufacturing processes and upgrading equipment can yield the largest energy-efficiency improvements. While this may require significant resources and investment it will often yield significant savings.
This Bakers Delight case study highlights significant savings from applying best practice design, technology and operating practices to a food manufacturing process.
There are many waste heat sources in the food and beverage industry from which useful heat can be recovered and reused, yielding significant onsite savings.
Using steam traps to collect condensed water and return it to the boiler, for example, not only saves water but also lowers boiler heating requirements as the returned condensate is much hotter than feedwater and may not require treatment.
Significant energy-efficiency improvements can be achieved through upgrading or replacing old, equipment. Ensuring correct sizing of equipment for expected loads maximises the benefits.
Using heat to evaporate water involves large amounts of energy. Several methods provide heat for evaporation much more efficiently, such as:
- depressurisation using waste heat
- ambient temperature air or water
- microwave ovens
Where heat is used, efficient heat recovery (including the latent heat of water vapour) is critical.
Heat pump systems can efficiently recover heat for use in other processes, and can even be designed to produce temperatures high enough for steam production.
Pasteurisation is a widely used process applied to food and beverage products to reduce or eliminate microbiological contamination and extend storage life. Energy modelling can estimate the efficiency of heating in pasteurisation, so that losses can be identified and minimised. In theory, using heat for pasteurisation can approach zero net energy if very efficient heat recovery is utilised.
Using high standards of process hygiene and monitoring can avoid or reduce the need for pasteurisation.
Alternatives to pasteurisation also exist, such as:
- microfiltration, which has been used to remove bacteria from beverages, achieving equivalent results to pasteurisation.
- ultraviolet (UV) treatment as a non-heating option for sterilising containers
- ultrasonics, which has a similar effect to irradiation in disrupting the DNA chains of bacteria
These alternative methods are more efficient where products are heat sensitive, or where heat recovery is not practical.
In cooling processes, efficiency declines as the temperature difference over which a chiller operates increases. Staged cooling can improve efficiency by a variety of methods, including the use of:
- residual stored cold product that has to be warmed
- multi-stage chillers rather than single-stage
Solar water heating is well suited to pre-heating boiler feed water for a wide range of food and beverage processing plants. Boiler feed water can be heated in solar panels up to 80ºC before the boiler. Solar cooling systems are also well suited to helping food and beverage companies meet cooling and commercial refrigeration demands.
Most food waste has potential for reuse as an energy or nutrient source. In Australia, such organic waste can be used in horticultural and agricultural sectors as compost and liquid fertiliser, or applied in the generation of renewable energy through anaerobic digesters.
Anaerobic digestion occurs when microorganisms break down organic material in the absence of oxygen, producing biogas (methane) and a rich fertiliser. When this biogas is captured, it can reduce methane emissions from manure decomposition by up to 95%.
Anaerobic digestion and biogas recovery is best suited to large food processing plants with high-strength wastewater, such as dairy processing plants or breweries. Foster’s Australia installed upflow anaerobic sludge blanket (UASB) units as part of the wastewater treatment process at its plant in Brisbane. Biogas is extracted from this process and burnt in boilers, contributing approximately 20% of the energy use on site.
Research is being undertaken into the use of low carbon energy solutions for pest control of food crops post-harvest. A significant percentage of grain production is lost after harvest because of challenges in managing insect infestation of stored grain. For the last 50 years, infestation of Australian stored grain has been controlled by chemical methods as the grain is loaded into grain stores. Environmental concerns and regulations have led to some chemicals, such as methyl bromide, being phased out.