The benefits of on-site heat and power generation

Sustainability has never been higher on the agenda for food and drink companies than it is now. Not only does operating in an ethical and environmentally responsible way make sense for both planet and pocket, but it’s clear that this is what consumers want too. Research in the UK has revealed that 92% of shoppers think food companies should focus their efforts on securing the future sustainability of food, with many also believing that farmers should be paid more for their produce. So what more could Australia’s food producers be doing to increase their sustainability credentials?

Making the most of waste

In recent years, some of the country’s most forward-thinking food companies have developed a truly circular approach to resource use. Alongside minimising the volume of waste they generate, they are also turning the unavoidable fraction that does occur into renewable energy, for use in their on-site operations. Anaerobic digestion (AD) — in which organic matter is naturally broken down to produce energy and biofertiliser — has taken big strides in Australia over recent years, with more than 240 AD plants now in operation.

While the majority of the country’s AD facilities process landfill, wastewater or agricultural feedstocks, a number are on site at industrial plants. These use waste from red meat processing and rendering, but the potential for the food industry to expand in this area is huge; making use of a variety of process residues, such as vegetable peelings, liquid malt waste and distillery by-products. The benefits for the companies operating these plants are multiple: reduced waste disposal costs; reduced energy costs; security of energy supply, with reduced reliance on fossil fuel-derived power; carbon mitigation; superior green credentials; and creation of a nutrient-rich biofertiliser. Furthermore, the fact that these plants have an on-site use for the power they produce means they are less affected by changes to state and federal legislation on renewable energy.

Take the heat

However, any AD facility that wants to maximise its return on investment also needs to be making use of its full heat output, not just its power output. The AD process generates plenty of surplus heat — most commonly heat produced by biogas combustion in a combined heat and power (CHP) unit, and also via digestate pre-heating, pasteurisation, biogas upgrading to biomethane and in digestate concentration. Ensuring this heat is used either within the AD process itself or within other on-site operations can make a big difference to a plant’s efficiency and therefore profitability.

By using heat exchangers within an AD plant, surplus heat can be taken from one process or place and transferred to another. Two of the most common types supplied to AD plants are plate heat exchangers and tubular heat exchangers; however, there are many different models and refinements and it is advisable to consult a specialist who can explain the benefits of different types and perhaps offer different solutions.

Potential uses for heat in the AD process

When it comes to making full use of the heat, there are a number of options within the AD process itself, including the preheating feedstock; for pasteurising; to reduce the volume of digestate; or to upgrade biogas to biomethane. For on-site plants within the food industry, it can also be used for space heating, cooking, heating liquids, or pasteurising and sterilising foodstuffs. In addition, large sites may have significant office and staff facilities, where there may be the scope to install heating systems.

As the demand on resources increases, there will be a greater need for food companies to demonstrate sustainability across all areas of their business. On-site AD, where full use is made of both the heat and power generated by waste materials, offers an obvious solution.