Tools for EfW sector to do its job

The next generation of Flue Gas Treatment (FGT) reagents for Energy from Waste (EfW) are evolving rapidly to meet the needs of the sector.

Here, my colleague - John Whitehurst, Lhoist UK’s FGT Market Manager, explains:

'Limestone is a very useful and diverse material, and used to construct roads and buildings, help make steel, treat water and help crops grow. High alkalinity means that lime is great for neutralizing acidic gases produced by combustion.

For this reason, historically, it is the main reagent used in FGT.

Reagents supplied all over the world

Lime can be used in its natural form, but when burnt it becomes calcium oxide, or quicklime. Add water and you produce hydrated lime. This is the main product, in some cases mixed with other reagents, which Lhoist supplies to EfW plants, all over the world - operating in 25 countries across four continents.

Today’s modern EfW and biomass plants are a far cry from the brick-built factories and power plants that used to emit acidic, particulate laden smoke into the sky. But hydrated lime, today as back then, is still performing the same function – reducing hydrogen chloride (HCl), sulphur dioxide (S02) and hydrogen fluoride (HFl) from flue gases, after being introduced into the gas flow at carefully selected parts of the process.

Many modern-day waste burning plants, municipal waste or biomass, require removal of more than one family of pollutants, each requiring different types of reagents. With this in mind Lhoist can assist by providing these with either separately or by a carefully blended product, so that one can do the same as two.

These blends offer the client certain benefits in terms of approved guarantees regarding pollutant removal and in all cases increase the safety aspect by diluting the organic component and reducing fire risk.

Reducing Pollution

Specialising in innovation over the last few decades, Lhoist has refined and adapted hydrated lime-based reagents to make them more efficient. We have helped power stations and incineration plants to stay within the ever-reducing pollution limits set from the early 1970s, by the EU and as dictated by the Industrial Emissions Directive (IED, 2010/75/EU).

Tightened Emissions

The recent changes in the Waste Incineration BREF document under this directive have tightened emissions further, of which existing plants have four years to amend their environmental permit.

Grate firing is the technology used for more than 90% of the industry but Sorbacal? reagents are also used by the latest generation of plants designed for gasification technology. This is a process in which thermal decomposition of waste at elevated temperatures occurs in a low/zero oxygen atmosphere to produce syngas. This is used to generate steam pressure that drive turbines, but which still needs to be treated afterwards.

Many other new technologies are now becoming available to convert waste streams into useful chemicals or fuels to support the circular economy and this trend is likely to grow over the coming years - meaning waste could become a key raw material for many industries.

Reducing Methane

As demanding EU-derived targets have been imposed to reduce the UK’s use of landfill, incineration has become an important policy tool. It is a vital technology for dealing with residual, unrecyclable waste and reducing the climate-damaging methane that would otherwise have come from landfilling, which until recently was the only outlet for it.

At the end of 2019, there were approximately 50 EfW facilities operating in the UK, representing 42% of the UK residual waste market. Significant new plant capacity is planned over the next decade to ensure diversion from landfill continues but also to deal with waste that would previously have been exported but is now facing taxation by importing countries. This set of scenarios has exposed a current capacity gap in EfW in the UK.

Refuse Derived Fuel

Feedstocks are also changing in line with recycling policies and targets being introduced meaning that many recyclables are being removed at intermediate materials recovery facilities, leaving unrecyclables to form the basis of fuel for EfW plants. This is mainly in the form of blended, waste bundles known as Refuse Derived Fuel (RDF).

For operators, RDF is far superior to unsorted Municipal Solid Waste (MSW). The varying calorific value of MSW leads to fluctuating process conditions as a result of changing fuel composition which is not helpful to plant operators. When RDF is used the peaks and troughs are evened out.

Removing Plastics

Thanks to the efficiency of MRF’s in removing recyclable materials, the amount of plastics with recycling potential being burnt is reducing significantly. This is then changing polluting gas compositions during the incineration process and we have seen evidence that ratio of HCl to SO2 in the dirty gas phase has reduced considerably in the last 3 years.

This trend is likely to continue until recycling levels reach a stable state and as RDF becomes the standard material used for incineration.

Continuous Monitoring

The new BREF has imposed tough demands across the industry and will push continuous monitoring of heavy metals such as mercury and continuous sampling of dioxins and furans.

Continuous monitoring will require the installation of more complex analytical equipment and possibly more focus on specialty reagents to ensure compliance. The industry will rise to this, but with the new emission limits for heavy metals and micro-pollutants set, the challenge could be to find suitable technology to accurately measure in values as low as nanograms and with the required accuracy to do so - concerns that have been raised by the industry already.

Tougher Emission Limits Welcomed

We welcome tougher emission limits, whether for acidic gases or heavy metals and dioxins. They are great for the environment and will hopefully ensure better acceptance for such facilities from protest groups. In addition tightening of limits will provide a growing market for the specialized and blended reagents that we are known for, produced by a constant pipeline of innovation.

For us, hydrated lime is not just a commodity – it is a resource that we can build on, for the benefit of our customers and we anticipate new and exciting reagents to be developed by Lhoist to cope with changing policies and conditions that this evolving industry currently faces.'