Renewable Energy from Waste Material

Dr Stuart Wagland, Lecturer in Renewable Energy from Waste in the Department of Environmental Science and Technology at Cranfield University, talks AZoCleantech about collecting renewable energy from waste material.

Cranfield University have developed a new approach to estimate the amount of renewable energy that can be collected from waste material. Can you provide a summary on this novel approach?

This approach is based on very simple principles. For the initial image analysis, the sample image is captured over a known area (we used 1x1 metre); however, this would be dependent on the conveyor belt dimensions in a facility. The images are then analysed using specialised software to correct and normalise the image prior to a ‘dot-grid’ step where the number of dots covering specific waste components are quantified.

The method needs to be calibrated first in order to convert the number of dots into a composition metric; this helps to minimise the limitations in using a 2D tool to analyse 3D samples. To do this, we carefully calculated a kg per dot for every component and used this in the calibration of the method. The number of dots is then converted into a total mass within the sample, and therefore a percentage composition.

The microwave analysis works on absorption, and so a transmitter and receiver unit is placed either side of the sample (i.e., over and below the conveyor belt) and the variances in absorption in the material can be converted into percentage moisture content.  

The two outputs can then be used to calculate the net calorific values (using a database of characteristics, such as gross calorific values, for the waste components), the biogenic fraction (again, a database), and finally the net energy from the biogenic fraction.

What are the current issues with the energy and waste industry when considering renewable resources?

The main issue is with cost. To understand the renewable energy yield from mixed waste materials there are several methods.  These include manual sorting, which is disruptive and time consuming; selective dissolution - a chemical analysis method which is often carried out off-site and has a number of limitations.  Finally, the renewable energy can be calculated by capturing samples of the flue gas and submitting these for carbon dating (14C) analysis.  This analysis is relatively expensive and needs to be done by a specialised laboratory.

The carbon dating approach is widely accepted as the most accurate method for determining the renewable energy yield from mixed waste materials.  

How does this new approach to calculating potential renewable energy compare to current methods and how does this challenge the current issues with managing waste material?

This method uses data from carbon dating; however, it allows an operator to calculate the renewable energy potential of the sample prior to thermal conversion.  This is particularly useful in the production of refuse-derived fuels [RDF] or solid recovered fuels [SRF] where end-user confidence is important.  In essence, if the net calorific value and the net calorific value of the renewable fraction is known, then the end-user knows exactly what they are getting.  

What tools have been used to apply this new method?

The tools used during development have included the microwave technology from the National Physical Laboratory [NPL], and specialised image analysis software for the processing of digital images of the samples.

Are there any particular disadvantages with this new method for calculating potential renewable energy and is this method affected by any confounding factors?

The main disadvantage of the image analysis method is that the dot-grid analysis is a manual technique, requiring someone to process the images. This typically takes less than 5 minutes per image, and the number of images required for a representative sample will vary depending on the quantity of waste processed.  

However, whilst the manual input is not ideal at the current stage, this is off-set by the advantages this tool has over existing techniques.

Another limitation is that as it is database-linked, some margins of error are possible.  These are, however, reduced when a more comprehensive database is used (such as the one compiled by Cranfield).

What type of waste material does this new method focussed on? Are there any particular waste materials that challenge the accuracy of this new method?

This method is focused on residual wastes, such as those collected from households and commercial and industrial premises. The method can be applied to shredded wastes, such as RDF/SRF; however, the sample sized would need to be reduced.  So instead of using a 1x1 metre image, it may be necessary to do a number of 10x10 cm samples.

How valid is this new method?

The accuracy of the method is really quite good.  There is a very strong correlation between the actual and determined percentage composition, and the renewable energy calculated by the image analysis tool is within 5% of the actual value.

What does this new analysis method mean for energy suppliers and the waste industry on a local and global scale?

There are two clear applications for this: one is to determine the renewable energy of the material prior to thermal processing, and the other is to determine the renewable energy potential of a waste-derived fuel.  These are two different markets, with one being a fuel user and the other being a waste processing fuel producer.

How does your research team plan on developing the tools and testing this on a diverse range of waste handling facilities?

We are currently looking to automate the system and to improve the accuracy and decrease the reliance on database properties. To do this we will be looking at other ways of calculating the desired parameters. There is also a need to undertake some long-term trials of the tool in a waste handling environment, with a view to developing the system further towards the point of commercialisation.

How can you see this new analysis method shaping how waste material is handled?

This system allows the user to manage the blending and processing of their waste, particularly if they are aiming to produce fuels of higher net calorific value and/or higher biogenic content. The technique still needs further development, and there is a lot of very exciting potential for research in this area.

About Dr. Stuart Wagland

Dr Stuart Wagland joined Cranfield University in 2009 and is currently a Lecturer in Renewable Energy from Waste. He has a degree in Chemistry, which was followed up with a PhD from Cranfield University in Environmental Chemistry. Stuart is a Chartered Chemist [CChem], a member of the Royal Society of Chemistry [RSC] and currently sits on the committee of the Environmental Chemistry Group [ECG] within the RSC.

Stuart has interests in the properties of solid waste materials, such as the composition, recovery of resources and the energy potential of UK waste streams.

He is the Course Director of the MSc Renewable Energy Technology course, and is directly involved with the management of various taught modules and delivering lectures across a number of MSc courses, along with the supervision of research students across a range of industry-relevant topics. Stuart’s current work involves the understanding of physical and chemical properties of organic materials for the recovery of energy from waste, and the energy from the biogenic fraction of wastes.