Biomass handling in the food and drinks sector

Across Europe food and drink manufacturers have been piling into the bioenergy sector for some time, turning waste and production by-products into energy. Some are successfully producing sufficient energy – both heat and power – for their own needs, with surplus energy feeding back to the grid.

AD processes producing biogas from liquefied waste tend to dominate, but in some sectors dried production residues are also being used to fuel combustion plants, including fluidised bed boilers and gasification solutions.

Food waste is a valuable resource that should never end up in landfill

In the UK, we throw away some 14.8 million tonnes of food every year throughout the supply chain. This accounts for over 20 million tonnes of greenhouse gas emissions and 6.2 billion litres of water.

Around 40% of this food waste ends up in landfill where it produces harmful methane that has a Global Warming Potential (GWP) 21 times greater than carbon dioxide.

A significant change in the waste industry over the past few years has been the shift in mindset from waste to resource. Central to this shift is the waste hierarchy and landfill tax, which push waste materials higher up the value chain by increasing the cost of landfill and placing a greater importance on the principles of reduce, re-use, recycle and recover.

This is what the UK could look like in 2020 if we achieve zero food waste to landfill

• Over 1.1 terawatt-hours of energy produced
• Greenhouse gas emissions reduced by 27 million tonnes
• £3.7 billion potential savings in the public sector
• £12 billion saved by UK householders
• £2 billion saved by UK PLC (retailers, manufacturers and caterers)

Coffee & Grain by-products are a perfect biofuel with a high calorific content

Coffee, or more correctly spent coffee grounds, are produced in vast quantities as a by-product of instant coffee manufacture. All those coffee pods and capsules that have brought new convenience to that morning coffee, once destined for landfill, is a perfect biofuel with a high calorific content.

Distillers Dried Spent Grain (DDSG) is another. It too is produced in huge quantities by an industry that produces millions of litres of spirits each year in the UK alone and is finding new uses as a biofuel in the drive for energy self-sufficiency. 

Resolving Sticky & cohesive material handling and storage problems

But these and other food and agricultural residues, such as palm kernels, make up a group of biomass products all with similar characteristics. The material is sticky, cohesive and non-free flowing with a tendency to compact and bridge.

For energy plant operators and developers, these properties can easily disrupt storage and conveying systems if plant design is defective, resulting in poor or erratic material flow, and periods of prolonged outage.  Excessive manual intervention and troubleshooting may be required especially at transfer points to remove blockages. This can be hugely costly and some plants may never reach their full potential.

Saxlund’s experience is ideally suited to resolving these material handling and storage problems. While the majority of bioenergy fuel handling projects we work on involve waste wood as the fuel – we are currently involved in 13 projects in the UK – we are also seeing an increase in projects within the food and drink sectors.

The ability to work with variations in the material composition

At one site in the UK for a major distillery business, a new fuel handling solution to feed Distillers Dried Spent Grain into an adjacent bio-energy plant is completing trials and testing. The system is based on the principles of activated and wiped surfaces, removing the opportunity for material to stick and build up in the system and restrict the flow.

The design involves a series of transport screws and elevating chain conveyors to transfer biomass cake 40 metres up and into an adjacent combustion plant. The standalone design ensures reliable 24/7 operation during production phases and is rated up to 30 tonnes per hour while ensuring additional handling system capacity for future expansion.

For this project Saxlund provided detailed consultancy with a number of design options, including live site trials for a section of the main elevating chain conveyor, to deliver proof of concept and project confidence.  The ability to work with variations in the material composition, including changes in moisture content, was a further design requirement.

Experienced solutions for the coffee drinks sector

Saxlund also has experience of handling coffee grain discharge solutions at a number of international coffee processing facilities. In the UK, for example, we recently completed the design and installation of a 150m³ capacity storage and discharge solution for handling spent coffee grounds used to fuel a fluidized-bed boiler.

Incorporating a welded stainless steel flat bottom silo, in place of conventional conical designs, with Saxlund Sliding Frame technology [click for more information here] at its base, the solution has been designed to provide an efficient and reliable storage and discharge system, with capacity to handle peaks in supply from freeze and spray dried production processes.

Measuring 12 metres high and four metres in diameter the silo sits on a base frame to allow vehicle access beneath the structure.  Pressed coffee grounds are pneumatically transferred to the top of the silo via separate blow lines while the reciprocating action of the Sliding Frame at the base of the silo continuously sweeps the material into a central trough which incorporates two separate screw conveyors to achieve the desired discharge option.

Unlike conical silos which rely entirely on gravity, the reciprocating action of the Saxlund sliding frame creates a ‘live base’ of material at the bottom of the silo to provide an entirely reliable and consistent discharge solution.

With both these projects, a full understanding of the flow characteristics of the material involved becomes important with a direct bearing on the engineering solution and long-term plant reliability. Particle size, mass flow properties, density variations, moisture content and compressibility are all important considerations. The composition of the biomass (or its source) may also change over time, and this needs to be factored into the system design to ensure a robust, enduring solution which can deliver an uninterrupted and consistent flow of material to ensure plant reliability.

As well as activated and wiped surfaces, Saxlund solutions also favour ‘first in, first out’ design principles, important where the calorific value of the material can degrade and for products that are likely to compact.

For more information on how we can help you optimise your existing biomass handling and storage systems or for turnkey engineering solutions, contact us.