IMechE publishes energy efficiency report

A report launched on 4 December outlines a five-pronged action plan devised by the Institution of Mechanical Engineers (IMechE) urging the government to deal with waste and energy issues.

The report, entitled 'A Wasted Opportunity', offers a series of measures and advanced technologies that could help reach targets of an 80 per cent reduction in CO2 emissions by 2050 and produce a third of UK electricity from renewable sources by 2020.

In the past the UK has adopted the policy of burying all waste, but following legislation in 2002 (UK and England) it must reduce this by 25 per cent by 2010 and 50 per cent by 2013.

The report states this cannot be achieved by recycling alone as there are too few recycling plants.

There is also the issue that large quantities of recyclable products such as paper and plastics are being shipped off to other destinations with their future unknown - and this still counts towards UK and local targets.

The report also focuses on the benefits of the UK creating an energy-from-waste (EfW) network that would help power the nation and reduce the need for landfill, but the five action points listed in the report must be adopted if change is to happen.

An EfW plant works by taking waste and converting it into usable energy - the main forms of which are electricity, heating and transport fuels, in the same way that coal, oil and gas are used as fuels in fossil-fired power stations.

Sewage, domestic, commercial, industrial, construction and demolition (which currently accounts for 36 per cent of our household waste) waste can all be used in the processes - as long as they are combustible and/or biodegradable.

The IMechE is concerned that EfW plants should not be seen as a waste treatment plant but more accurately as a power station or even a combined heat and power (CHP) station.

A thermal EfW plant, in particular, treats waste in the same way that a coal-fired power station treats coal.

Any other benefit, such as volumetric reduction, is a useful by-product but is not the primary purpose of an EfW plant.

Unfortunately, most legislation over recent years has erroneously and dogmatically focused on EfW as waste treatment rather than as energy production, and has attempted to deal with an EfW plant as if it were an incinerator, rather than a power station.

The approach is very different in most other parts of Europe, where recycling and EfW are both used to their optimum potential and as a result, landfilling is successfully minimised.

The report states there is a massive public and government misunderstanding about EfW, which tends to conjure up images of huge incineration plants.

This thinking derives from seeing waste as a problem and not a resource.

IMechE said the issue here is that the UK government is itself very unclear on this.

Defra constantly refers to EfW plants as 'incinerators' and despite huge widespread public consultation has ignored the feedback.

There are four main processes used in EfW plants: combustion, gasification, pyrolysis and anaerobic digestion.

Combustion is the most common and well-proven thermal process using a wide variety of fuels.

The combustion process is that used in all the large coal-fired power stations in the UK and follows a process known as the Rankine Cycle.

Gasification is where oxygen in the form of air, steam or pure oxygen is reacted at high temperature with the available carbon in the waste to produce a gas, ash or slag, and a tar product.

The major benefit of gasification of bio-wastes is that the product gas can be used directly, after significant cleaning, to fuel a gas turbine generator.

Pyrolysis is also a thermal process and involves the thermal degradation of organic waste in the absence of oxygen to produce a carbonaceous char, oils and combustible gases.

Although pyrolysis is an age-old technology, its application to biomass and waste materials is a recent development.

Anaerobic digestion (AD) is a biological process that is a method most commonly used with liquid and semi-liquid slurries such as animal waste.

It is also used for obtaining gas from human sewage.

The main advantage of AD is that it deals well with 'wet' waste, which is a real problem for all other forms.

It is ideal for small-scale operations, such as farms, where enough energy (electricity and heat) can be produced to run the farm (including fuelling some of the vehicles) from what is produced on the farm.

Accurate statistics for total waste are notoriously hard to come by in the UK, but latest figures show it generates 307 million tonnes of waste annually.

Of that, Defra estimates that 46.4 million tonnes of household and similar waste was produced in the UK, with 60 per cent of this landfilled, 34 per cent 'recycled' and six per cent 'incinerated'.

According to the official statistics, none of this resource was used as fuel in EfW plants.

'In a climate where we currently have over a million people classed as being in fuel poverty, the IMechE believes this is simply unacceptable,' said Ian Arbon, IMechE.

It is extremely improbable that the UK's legally-binding energy commitments can be reached unless EfW plants are established and become regarded as the best-proven, safe, clean energy recovery solution available.

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