Waste processing reaches new levels

The number of multi-million pound waste treatment facilities being designed, developed and commissioned within the UK, has risen significantly over the past year or so - as has the level and sophistication of the design and process technologies being applied at these plants.

Many of these projects are focused on generating energy from waste. An estimated 200 million tonnes of waste produced each year in England alone could be converted to energy with the potential to supply up to 4% of the country’s energy needs.

This is driving a clear expansion in areas such as anaerobic digestion (AD), which is growing by 30% a year, according to data from the Anaerobic Digestion and Biogas Association.

A more important marker for the energy-from-waste (EfW) industry, though, is the scale and sophistication of projects coming on stream

There are now 104 AD plants outside the water sector in the UK, compared to 69 in late 2011 These figures were helped by a recent re-classification of previously designated on-farm and off-farm facilities.

All plants are now categorised as either industrial, agricultural or community, meaning that previously unclassified plants are now clearly identifiable.

Stuart Reynolds, chair of the Chartered Institution of Wastes Management (CIWM), welcomes the inclusion of these plants. This, he said, now gives “a more complete picture of the situation for biogas output from anaerobic digestion in the UK.”

Perhaps a more important marker for the energy-from-waste (EfW) industry, though, is the scale and sophistication of projects coming on stream, with many facilities now highly automated.

Automation systems can play a significant role in managing EfW plants: helping to maximise incineration capacity, and keeping combustion and steam production stable. This also allows high availability of the production processes.

These potential benefits are, for example, evidenced by CNIM’s selection of a Metso automation system to maximise efficiency in a greenfield waste-to-energy plant in Great Blakenham, Suffolk.

The new plant is owned by the Suffolk County Council and will be operated by Sita Suffolk Ltd. It will have an electric output of 20MWe and is designed to handle 269 kilotonnes/year of residual waste. The plant is planned to go on line by the end of 2014.

CNIM will install an extensive Metso DNA automation system and safety system to the new plant - similar ones for EfW plants in North Hykeham, Lincolnshire, and Four Ashes, Stafford.

The system will cover all plant processes from boilers to turbines, and is designed to ensure high levels of reliability through an integrated TÛV-certified safety system.

Meanwhile, in developing new biogas projects, plant designers must ensure the facilities meet an increasing range of regulatory and technical requirements - a demand that is attracting the attention of plant design
software companies, among others.

Some experts point out that newly built and commissioned treatment facilities are now being found to have serious issues with under-capacity, over-capacity or procurement of inadequate or inappropriate equipment.

In response, engineering consultancy Wardell Armstrong has developed what it claims is the first ever process modelling tool to represent complex dynamic treatment processes in the waste industry.

The model uses a CAD layout overlaid with a process map to visualise each element of the process in the context of its built environment, with bespoke icons for each individual item of equipment. The process map spans all operational activities and resources from input to output.

This starts with waste delivery vehicles entering the site, transferring to the reception area, unloading and leaving the site via a weighbridge.

It shows waste accumulating in a stock-pile, being transferred via loading shovel to a pre-shredder, and then recyclates and the residual fraction destined for use as a fuel being separated into their individual material streams by various sorting technologies and manual picking stations.

The modelling software allows operational data to be added to each individual activity. This data can include process or task times, resources such as plant and labour, capacity constraints, input and output behaviour such as batching, or joining material streams, time schedules, and costs.

Operational scenarios can be simulated in compressed time, 50 minutes of actual processing can be condensed into less than two minutes, enabling users to observe, test and explore process efficiency and operational dynamics in a completely unique way.

Process parameters can be changed to simulate operational scenarios, such as reducing operating costs without reducing capacity, or if inputs increase by 20%.

The waste management industry is also generating interest within the research community, where, for example, Cranfield University is now developing a new approach for calculating the potential renewable energy derived from waste material, prior to incineration.

The Government’s Renewable Obligation Certificates (ROCs) scheme places an obligation on UK electricity suppliers to demonstrate the biomass content, or fraction, of mixed fuels.

It also offers incentives for sourcing an increasing proportion of the electricity they supply to customers from renewable sources.

However, calculating the renewable content of waste conventionally involves manual sorting of waste into individual components, which is time-consuming and carries issues regarding labour costs as well as health & safety concerns.