A European Issue

Approximately 44 million tonnes of fly ash were produced in Europe (EU15) in 2003 of which 21.1 million tonnes (48%) were utilised, leaving about 23 million tonnes to dispose of.

Approximately 20 million tonnes of PFA were produced in the same year by the new 10 EU member states.

Production of PFA in the UK alone is in the region of 10 million tonnes per year

Construction

PFA has many uses in the construction industry: load bearing fill, concrete and cement manufacture, grouting, lightweight aggregate, cement-stabilised PFA for hard standings etc, building blocks as well as many other more specialised uses. Dry PFA combines with free lime released during the hydration of Portland cement by pozzolanic reaction. This allows it to replace part of the cement component in concrete, offering both technical and economic benefits. Technology has recently been developed to manufacture high quality bricks from PFA using a sintering process.

Industrial scale reprocessing of PFA into high quality building materials, such as high performance concretes, special cements, and blocks, is both technically feasible and well-proven and is being promoted in RWE's own home country, Germany. The resultant product(s) can be used as cement and concrete substitutes, and as substitutes for, or supplements to, traditional building materials, such as clay bricks and concrete blocks. Because of its low porosity and chemical resistance, it can be used as a liner for waste pits and as a means of immobilising toxic waste, at the same time as helping to solve the the PFA "waste" disposal problem itself.

In Britain, the RockTron beneficiation process, another well established technology which has been available for about 15 years, is capable of recovering saleable products from any power station ash ash with no waste, ie all the ash is recycled. Recovered products include high-grade carbon products, pozzolanic cementaceous products with <2% LOI, and cenospheres. The process can be applied to dry or wet ash, including ash recovered from landfill. The cementaceous products can replace products that would otherwise have to be produced by energy-expensive kilning of limestone and thus contribute to a low-carbon economy.

In Australia, scientists have developed ways of making bricks and aggregates entirely from fly ash, using a technology that has been licensed to British and US markets.

A promising new technology for the manufacture of concrete, without using any portland cement at all, is e-crete, which is a form of concrete in which the silicates and aluminates in fly ash and slag waste are polymerised by the addition of alkali. The manufacture of e-crete does not involve the large amounts of energy consumption and CO2 production involved in the production of ordinary concrete. It is therefore both cheap and 'green', and is currently being manufactured in Australia for use (initially) in small-scale low-performance-demand applications, until its durability and usability are better proven. A considerable amount of interest has been generated in this product by the article which appeared in New Scientist in January 2008. E-crete may not be a completely proven technology yet, although there is evidence from analyses of alkaline slag-based concretes used in 40-year old constructions in the Soviet Union that it will prove to be as durable as ordinary concrete. It also yet again serves to illustrate the potential of fly ash as a raw material.

Concrete step barriers (CSBs) are currently being constructed along Britain's motoways and trunk roads to replace the familiar steel safety barriers. CSBs offer improved performance, durability, and lifespan compared with steel barriers. They are maintenance free, do not generally need replacing or repairing following accidents, and are expected to last 50 years (compared with 20 years for steel barriers, which invariably need replacing following accidents.) They also offer improved safety performance due to greater impact strength and the absence of posts presents a reduced hazard to road users, especially motorcycles.

Concrete safety barriers are constructed by means of a continuous slip-forming process, which requires that the rheological properties of the concrete need to be tightly specified. Cement replacements, including fly ash, are deemed suitable for CSB applications. The specification also requires that the construction should be sustainable and that recyclable materials should be used. Many thousands of miles of CSBs must therefore be constructed over the next 15-20 years and we would expect that this would extensively exploit available supplies of PFA, and other cement substitutes, over that period.

The manufacture of bricks from PFA is now being promoted, in other countries, notably the USA (where building materials that contain coal ash are considered to be "green" products in a market that is receptive to green issues) as well as India and China, where PFA disposal is particularly problematic, as a means of reducing atmospheric pollution (from conventional brick manufacture) and water pollution (from disposal of PFA in landfill). It is being presented as a green and sustainable means of reducing the impact of coal burning on the environment.

This possibility is also important for the UK. The manufacture of bricks and light-weight aggregates from PFA is perhaps its single most important application. UK Government wishes to build around 300,000 new homes in the SE in the next 10 years, and bricks will undoubtedly be one of the main construction materials. Also, new infrastructure will be required to support the needs of the people that will occupy these homes. This will require concrete and aggregates. PFA bricks, for example, are superior, in virtually every every respect, to conventional clay bricks: they are stronger and lighter, adhere better to ordinary mortar and require less energy (and hence produce less CO2) for their manufacture and transportation. They possess low water absorbency, are highly resistent to frost and chemical attack. They can be manufactured in virtually any colour, shape and surface texture. Moreover the raw material, fly ash, comes at "zero cost". The potential of this application for exploiting PFA produced by Britain's power stations cannot be over emphasised. Unlike concrete manufacture, which cannot guarantee a steady a market for PFA and which requires major projects to take appreciable amounts of ash, brick manufacture can easily soak up all of the country's PFA production, both in the future as well as any that is currently "stockpiled" in mounds or landfill.

The current practice of digging up the countryside to extract primary aggregates, and clay (for brick manufacture) only to have to fill the holes back up with PFA, is madness. Government needs to follow the example of other countries and introduce stronger incentives to ensure the take up of fly-ash-based materials by the construction industry, in line with existing policy.

PFA is not waste. It is in fact a valuable raw material that is being allowed to go to waste at the expense of causing unnecessary further damage to the environment by clay, sand and gravel extraction.

Other Applications

Other uses of PFA include

• Mineral filler for plastics, paints, resins etc

• Soil conditioning

Cenospheres

Cenospheres are a particularly valuable product used in pattern and mould making, foam-filled glass-fibre panels, fire-resistant coatings, urethanes, PVC frames, putty etc etc. Cenospheres are used in the manufacture of the Space Shuttle's heat shield.

Some Options for Didcot

The following list some alternative options for RWE npower to consider. The list is not intended to be exhaustive.

With the Government set to expand house building in the Southeast to around 30,000 homes per year, demand for primary building materials can be expected to rise sharply. An estimated 2-3 million tonnes of "bricks and mortar" per year will be required to meet the demand for the construction of the houses alone, while road and other infrastructure construction could easily double this figure. Rather than throwing a valuable material away as waste, and damaging the environment in the process, Didcot should be looking to how it can best take advantage of its situation to meet much of this anticipated demand.

Investing in the RockTron separation process is one way to go. Scottish and Southern Electricity have already agreed to proceed with a project to construct and operate a RockTron plant at the Fiddler's Ferry Power Station in Cheshire.

Another is to look into the possibility of manufacturing bricks and aggregates at Didcot. While this requires a larger investment (by around a factor of 3) than would be required for a Rocktron plant, the finished products (bricks) are of significantly higher value and demand is more assured, particularly in SE England.

Both of the above processes can utilise the ash in any condition, even after lengthy storage in lagoons. Brick and aggregate manufacture, for example, involve sintering and do not rely on pozzolanic reaction. This means that ash can be stockpiled in the environs of the power station (landfill at Sutton Courtenay for example) for as long as necessary while the reprocessing plant is commissioned. As any disposal at Sutton Courtenay would be temporary, costs would be anticipated to be much smaller than for permanent disposal. The power station would effectively be leasing, rather than consuming, the disposal resource. The end result is win-win for all: the power station saves some of its disposal costs (including, presumably, landfill tax) and could benefit from the profits from the product sales; the reprocessing plant owner would have a profitable business, people would benefit from extra jobs; the environment would benefit from building construction using greener more easliy transported materials, and the Radley Lakes would be saved from further damage.

After the power station has closed and all the ash has been used up, the reprocessing plant can be moved to another site. It is not necessary to write of its entire cost over the current projected life of the power station.

Any use of PFA for landfill should be restricted to the beneficial infilling of unwanted voids, provided that any pollution risk from leachate is properly understood and managed. For example, PFA from Drax Power Station is being used in a £33M project to stabilise the Northwich Salt Mines in Cheshire, much to the relief of the citizens of Northwich whose homes were becoming increasingly at risk from the mines collapsing under them.

The current Oxfordshire Structure Plan (section 8.15) refers to an anticipated need to extract gravel from the Wallingford-Benson area of South Oxfordshire without creating gravel pits, even temporarily, which would attract birds that would present an unacceptable hazard to operations at RAF Benson. This would require fuel ash from Didcot.

Above ground disposal or stockpiling should be preferred to "below ground-level" disposal, since this results in significantly reduced pollution of groundwater, and makes the PFA more readily available for future recovery should this be required in the future. This is the preferred disposal method used by several other power stations, such as Drax where, making virtue out of necessity, the Power Station operators have used their ash to enhance the natural landscape rather than destroy it. (Click here to see aerial photo of the award-winning Barlow Mound at Drax. (Compare this with the situation at Radley.) Above-ground disposal on land close to the Didcot Power Station is another option that should be given more serious consideration. Experience of operating the large mound at Drax has shown that dust emissions, provided proper measures are put in place, are not a problem.

Finally, stricter measures need to be taken by power station operators, as well as by Government and its agencies, to limit damage done to the environment by PFA disposal, where this is necessary, by ensuring the adoption of appropriate waste minimisation policies and ensuring that the process is managed sensitively with proper monitoring and control of all its aspects.