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Bio-energy as part of a Clean Growth strategy

12 November 2017

Richard Gueterbock argues for the wider use by the food processing industry of on-site bio-energy production from waste. 

The Scottish Government’s well reported enthusiasm for investment in decentralised, clean energy generation is helping to stimulate interest in generation of bio-energy at food and drink production sites with high energy demand. What is possible is being demonstrated by a number of whisky distilleries that are generating bio-energy from their production residues to reduce energy and operating costs, as well as carbon emissions.  

However, the same technology can also be used by other manufacturers of other alcoholic beverages, to help them limit their environmental footprint. 

Smaller scale Anaerobic Digestion (AD), is particularly suited to use in food and drink manufacturing because the energy can be used where the bio-residues are produced and where it’s needed – an ideal circular economy solution.  

AD is a bio-chemical process, where bacteria break down organic material in the absence of oxygen to produce biogas (predominantly methane (CH4) and carbon dioxide (CO2)).  As well as generating electricity or heat, the gas produced can also be injected into the gas grid or used as vehicle fuel.  

In an energy-intensive industry concerned about its environmental impact, anaerobic digestion of energy-rich residues provides a cost-effective disposal method and a means of accessing their latent energy content.  This should be part of future energy strategy for the development of low carbon manufacture in the UK.
Liquid digestion plants, developed by Clearfleau, are based on a system that breaks the link between liquid retention time (3 to 8 days) to minimise the digester tank size and cost, while extending bio-solids retention (about 50 days) to optimise biogas output.  
Clearfleau has installed a number of digestion plants at larger distillery sites in Scotland, which has offered an attractive return on investment based on a range of benefits:  
Bio-Energy: Cutting fossil fuel use, helps meet energy reduction targets.  
Emissions: Replacing fossil fuel with bio-energy cuts carbon emissions.
Water use: Cleansed water fit for river discharge can be re-used on site.
Land fertility: Residual bio-solids provide nutrients for crops like barley. 
Efficiency: Extracting energy from residues improves resource use.

However, this it is not only the large distilleries that are taking advantage of this technology. Clearfleau’s next distillery project in rural Speyside, will be the smallest digester it has built on a distillery to date. It will be integrated with a biomass boiler, which will also supply heat to the distillery, making it one of Scotland’s most energy-efficient distillery sites. 

This combined bio-energy (biogas and biomass heat) approach has the potential to be deployed widely on many smaller rural and craft distilleries. It should eliminate off-site disposal costs, while reducing reliance on fossil fuels and curbing greenhouse gas emissions. 

The biogas produced can be combusted in a boiler to supply hot water or steam, or used to run a Combined Heat and Power (CHP) engine, generating electricity and heat.  Or, if the gas is upgraded to bio-methane, it can be fed into the gas grid or compressed for use as fuel in commercial vehicles. The range of uses for biogas means that digestion offers a flexible source of on-site renewable energy. 

The current Clearfleau distillery project, due to be completed in Spring 2018, will treat about 130m3 per day of distillery co-products (pot ale and spent lees) which will produce over 2,000m3 per day of biogas.  This will be fed to a CHP engine and will generate about 200kW of power and 230kW of heat for use on site (with about 60% of the power generated used in the distillery).  

There are only two other outputs – residual bio-solids which can be used as fertiliser for farmers growing barley used to produce the raw spirit; and cleansed water that will be discharged to a nearby burn.  

Modular on-site AD offers a more efficient way of treating residues than aerobic treatment, which consumes energy to achieve the same goals.  It will allow distillery sites to benefit from greater energy efficiency and better use of resources. 

Richard Gueterbock is director at Clearfleau. 

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