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Future Thinking: Equipment and Processes

ef w emissions

NO-ONE LIKES WASTE BEING burnt and even policy-makers tend to this view this option as a necessary evil. But the truth is, at the moment, we have no choice.

There are two main reasons. First, the Government’s resources and waste strategy contains a target dramatically reducing municipal waste going to landfill (to 10% or less by 2035). Second, the options of exporting our waste are narrowing.

That is why the waste strategy from Defra admits that “incineration currently plays a significant role in waste management in the UK, and the Government expects this to continue”. In fact, the strategy predicts an additional two million tonnes of energy-from-waste (EfW) capacity to come on-stream by 2020.

Incineration has grown exponentially in recent years. In 2012, there were only 24 EfW plants in England but, today, we have almost double that number. The latest UK statistics show that the tonnage of waste being incinerated for energy has quadrupled in the past four years, and a significant milestone was reached last year when more tonnage went to EfW than landfill.

Most councils which are waste disposal authorities either already have an EfW facility or are planning to get one. Investors and waste companies take the view that the UK still has considerable under-capacity for EfW.

But with lots of recycling and reuse targets now being set – in part to decrease the amount of plastic waste – we have to ask ourselves what is the composition of waste going to be in five years’ time and what will that mean for the sector?

In general, we are seeing a trend that is moving away from burning rubbish from traditional black bags in the form of municipal solid waste. The newest plants are signing contracts to use refuse-derived fuel (RDF) or solid recovered fuel (SRF), which comes from MRFs.

The waste is shredded, baled and ready to go. It has been produced to a specific calorific value and offers consistent burning characteristics.

Lhoist is the world’s largest lime producer, supplying products for flue treatment for EfW and biomass plants all over the UK, so the chemical composition of waste is of significant interest.

As you take plastic out of the waste, you can incorporate other materials which also have a high calorific value but their combustion will produce different by-products. These will potentially need new techniques and reagents to reduce unwanted emissions.

In EfW plants, the main pollutants that hydrated lime deals with are the acidic pollutants: hydrogen chloride (HCl), sulphur dioxide (SO2) and hydrogen fluoride (HF). Burning a high proportion of plastics produces more HCl and less SO2. For existing operational plants, the ratio of HCl to SO2 is typically about six or seven-to-one.

In my view, if you look at projects coming on-stream in the next three to five years, that ratio is going to be much closer to one-to-one. In fact, Lhoist has just provided reagent estimates for a series of EfW plants that will see more SO2 than HCl in their waste streams, an indication that fuel contracts for future projects are being proposed with significant changes to waste compositions.

Plants coming on-stream now are signing contracts with fuel suppliers based on more waste being sorted and there being less plastic in the feedstock, but it is difficult to predict exactly what the changes will be.

Fortunately, Lhoist has a strong focus on innovation. It is already bringing to market the next generation of reagents, designed to assist plants to cope with varying proportions of sulphur, chlorine and fluoride in their emissions, as well as making the most of existing flue gas treatment technologies and newer technologies that are becoming more common.

This will help to ensure that plants remain within their permitted emission limits and the conditions set by performance warranties, as their feedstock fluctuates.

There is an additional challenge coming down the line. Maximum emission levels set by the Environment Agency (EA) will inevitably become more demanding, not less, reflecting tighter EU rules. In my view, unless some of the older, legacy EfW plants invest in new technology now, they could face the prospect of needing expensive bolt-on solutions in three to five years’ time or will even risk going out of business.

We will need solutions that require innovation both in flue gas treatment technology and reagents, but the industry has a reputation for ‘silo working’. To be ready for the future, we will need far more collaboration across the EfW sector. Government support may also be forthcoming.

Defra’s waste strategy says: “We continue to welcome further market investment in residual waste treatment infrastructure. We particularly encourage developments that increase plant efficiency and minimise environmental impacts while upholding our existing high standards of emissions control.”

Lhoist supplies its hydrated lime-based products to the most high-tech EfW plants, using advanced conversion technology (ACT). Here, waste is heated to high temperatures in low- or no-oxygen environments, so that it breaks down and produces syngas, a combustible by-product which can be used to generate electricity.

This process, known as gasification or pyrolysis, was encouraged by subsidies and seemed to promise a cleaner method of operation, but it is currently used by fewer than 25% of EfW plants.

Many struggled to run on a consistent and reliable basis and some plants that were originally permitted for ACT have, during the permitting process, changed back to traditional incineration. I think it’s fair to say that it has not taken off as quickly as people thought and the jury is still out.

As Defra’s strategy acknowledges, waste should be viewed as a commodity from which value can be extracted – not as a cost drag. You could ask why the UK is currently exporting three million tonnes of RDF a year to other countries to feed into their industrial furnaces and power stations? Why aren’t we gaining the economic benefit ourselves?

There is a growing view that we can do something more useful with unwanted plastic than turning it into heat to make steam and power. Exciting start-up companies are developing processes that can make plastic into biofuels and other valuable products.

British Airways, for example, has partnered with Velocys to design plants that convert waste, including plastic, into a clean-burning jet fuel. The initiative will contribute to the airline reducing its net greenhouse gas emission (GHG) by 50% by 2050.

It is true that the EfW sector has a steep hill to climb in terms of public perception. Most people are unaware that plants work to strict emissions standards, tightly enforced by the EA, and that firework displays are more harmful to the environment than waste incinerators in terms of particulates and dioxins.

Even when members of the public understand the difference between steam and smoke, and are not basing their opposition on myth or misconception, they may have other environment concerns and these may be justified.

Location is important. Plants need to be sensitively sited if they are to avoid inevitable objections, for example on the basis of intrusive lorry movements.

john whitehurst

john whitehurst

“We will need innovation in both flue gas treatment technology and reagents.”

John Whitehurst

There is far more acceptance of EfW plants in Scandinavia and that is not because they are smaller and less visible – some of them are very large. You could even say that they are popular. The reason is that the plants are nearly all used to provide people with cheap heating from district heating systems. That’s an option that we too rarely take up in the UK. We install the pipework to fulfil permitting requirements but do not usually connect it to anything. That is a terrible waste.

That missed opportunity is acknowledged by the waste strategy. Defra notes that much higher efficiency levels – typically around 40% – can be achieved if an EfW plant harnesses its heat output in addition to generating electricity. Very few do – often because they cannot find a customer for waste heat.

The strategy draws attention to the Heat Networks Investment Project from the Department for Business, Energy and Industrial Strategy, a £320m capital fund to help develop waste-powered district heat schemes.

The strategy also says that Defra will work with the Ministry of Housing, Communities and Local Government so that the national planning policy framework supports the Waste Management Plan for England.

The waste strategy makes clear that incineration, especially when providing combined heat and power, has a vital role in meeting the UK’s medium-term strategic requirements. By 2025, there will be no more coal-fired power stations in operation and it is widely predicted that the UK will struggle to make up the energy shortfall.

Currently, the EfW sector contributes less than 10% of energy to the grid. With a predicted doubling of the number of EfW plants in the next 10 years, that number could go into double figures – reducing the significant GHGs that are inevitable as a result of methane generation when waste is buried in landfill. It is another valuable contribution that incineration could make to the circular economy.

John Whitehurst is UK business manager at Lhoist

hci vs so2

Pilot plant conditions only using Sorbacal SP; real time gas conditions could influence the above comparison slightly

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