Energy from Waste - the Technology is getting Safer and Better.

July 9, 2018 7:15 PM
An EfW Plant on Teeside

An EfW plant on Teeside

The oldest and the most famous Energy from Waste (EfW) plant in UK started operation in 1971 in Edmonton, North London, near the North Circular Road. An industrial accident in Seveso in Italy in 1976 led to the exposure aof a significant proportion of the surrounding population to polychlorinated dioxins. This led over the years to an investigation into dioxins in the environment, either naturally occurring or due to combustion. It became realised that these chemicals were present in small amounts in the environment but more was produced, and in significant quantities, when organic material was burned - especially if the combustion was at low temperatures and/or inefficient. This led to a flurry of chemical research to understand the ways in which dioxins are produced and destroyed during different stages of waste combustion.

The breakthrough came around 1990 when amounts of dioxins in fly-ash, bottom ash, flue gas and in the quenching and adsorbtion materials were all measured and understood. This led to combustion cycles run at higher temperatures - sometimes with after-burners - to destroy the dioxins, followed by cooling and queching to lower the flue gas temperatures rapidly and prevent them reforming.

All EfW plants now have to hold emergency stocks of light fuel oil for injection into the furnace to ensure the requisite high temperatures are always maintained. The main use of this oil is, however, on those occasions when a plant is starting up and when being shut down.

All this meant that the newer post-1990 EfW plants actually reduce the amount of dioxins in the environment due to their improved combustion cycles. In particular, the emergent flue gasses contain less than 1% of the dioxins that used to be emitted into the atmosphere by the older plants before they were upgraded.

When it was realised that there was dioxin adsorbed onto the ash and fly-ash and in the various gas adsorbtion materials, the recycling of these materials - e.g. to make building blocks - was suspended and they went straight to landfill. Subsequently an re-processing industry arose and this has had great success in destroying or removing the dioxins so that the materials could be safely recycled. So once again metal can be recovered from the bottom ash and fly-ash can again be used to produce building materials. In addition the sulpur dioxide absobtion material can again be used to produce plasterboard.

So it then became feasible to set targets for EfW facilities of zero material sent to land fill.

Last year in a national first the local Lakeside EfW facility at Colnbrook near Slough became the first in the country to achieve that zero waste-to-landfill target. Everything fed in now either produces electricity or is recycled - and a combustion equivalent quantity of oil or gas can be left in the ground.

These plants are doing a good job at the moment. Not only do they produce electricity, but they clean up the environment by removing dirty un-recyclable plastic, pre-existing dioxins in the waste stream and offensive, putrescible waste. In addition they safely dispose of organic materials, such as waste wood, which is potentialy dioxin producing if burned inefficiently.Seemingly harmless activities such as garden or builders' bonfires or wood-burning stoves (sorry!) produce a lot of dioxins. In the future, as we get better at recycling plastic and more careful as to its use, EfW plants will become greener by supplementing any fuel shortfall with dry agricultural or forestry waste.

Lakeside Energy is a joint venture between Grundon Waste Management and Viridor and has been fully operational since 2012.

The local management is very pleased with their zero landfill success. For the last 8 years, the incinerator bottom ash (IBA) has been recycled by Brentford-based Day Aggregates for recycling to make sustainable, cost effective aggregates suitable for construction projects - and asphalt for road surfacing. More recently they have been sending the residue from the gas clean up process, called APCr (Air Pollution Control residues) to a company called Carbon8 Aggregates has been using this ash to make building blocks, precast and readymixed concrete and screed.

Lakeside Energy Plant Manager, Danny Coulston says,

"We are really excited that the Colnbrook EfW was the first in the UK to reach this industry milestone. It is a credit to the two partners in the business that they have been prepared to commit the time, effort and financial support needed to reach this sustainable achievement. To further enhance our green credentials we have also fitted 980 solar panels on the sloping southern face of the roof - and installed LED lighting - which uses only 42% of the total original consumption of lighting energy."

Lib Dem Herts County Councillor, Nick Hollinghurst, commented,

"We are faced with having to have an EfW plant over in the south east of the county. As local councillors we must ensure that communities are protected from lorry movements and that the project represents good value for money for HCC, since it will be used to dispose a proportion of the county's waste."

"However, I hope my council colleagues will at least be reassured by the technological improvements to EfW plants over the last couple of decades and encouraged by the enhanced proportion of recycling that these plants can now achieve."