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|Phase 1 Day 8||2001-10-29||William Prescott (Energy From Waste Association)|
William Prescott BSc. (Hons) Newcastle University
The Benefits of Thermal Treatment of Waste.
Man has always either Buried or Burned his Waste.
This remains a truism even if 'Recycling' is taken into account, since recycling will give rise to waste at some stage- either the recycled material (or a non-recyclable part of it) will eventually become waste or waste is produced in the process of recycling the original material and must be disposed of. 'Composting' can be classed as a form of 'Burial' in this context.
The impending Landfill Directive will increasingly restrict what we currently 'Bury'.
I would like to consider Recycling first. Technically there are limits on Recycling.
100% recycling of all of our 'Waste' is not technically feasible, much less economically sensible.
The arguments in favour of recycling are often Energy related as well as resource related.
For example, Glass recycling is environmentally beneficial not because of the resource saving (where sand and alkali chemicals are abundant enough and will remain so) but because the energy saved by recycling glass is significant. The same holds for Aluminium.
The arguments around plastics have much to do with the energy/ cost of collection, separation, and clean-up together with the distance to the Recycling Reprocessor but remain, substantially energy related. When >90% of oil is burned (for heating, power, or transportation), the effect of recycling the ~4% used in plastics is questionable especially where the overall energy balance for recycling is negative.
Plastics are light( which gives energy savings on transportation when they are used as packaging), they are resistant to water, knocks, and air-borne bacteria hence making excellent material for packaging. These properties also make them useful as disposable nappies for example.
The resistance to water and bacterial attack, however, makes them difficult to break down within landfill sites where they will often remain indefinitely thus losing the 'latent energy' locked up inside the material.
Paper recycling is also not quite so simple in terms of environmental benefits. Where managed forests are used for the pulp production there is little 'resource' depletion and, again, energy becomes the biggest factor on whether recycling is environmentally beneficial or not.
Distance to the Recycling Reprocessor becomes important as does the work involved in Recycling, the markets for the Recycled products (We would not accept newspapers printed on cardboard) and the economics of the equation are often affected by global market conditions.
There are further limits to other forms of 'Recycling'.
Home composting could, theoretically, produce around � tonne of compost per family per year.
With a small garden some families would quickly become knee deep. What about flat-dwellers?
Against this difficult to comprehend (for the householder) backdrop is the clear need for local authorities to develop sensible waste strategies to manage our growing production of waste.
Rather than re-inventing wheels we should look to the best examples of waste management that exist and also to the newer technologies to see if they might offer some further improvements.
Most experts in Municipal Waste recycling place a 'ceiling' on recycling at around 50%.
The most successful nations and cities can achieve around 40%. Only small, controlled, experiments have exceeded these figures. In some examples these high figures have fallen back when the experiment has finished or funding been withdrawn, e.g. Washington Seattle (USA), Guelph (Canada).
The highest sustained rates tend to be in Europe by conventional wisdom (Ironically higher rates are often achieved in third world countries by waste scavenging!).It is to Europe, therefore, that I propose we should look for tried and tested recycling models under similar conditions to the UK. Judicious use of 'Bring Banks' has been shown to significantly lower pre-sorted collection costs. This should be linked to Bin size/charging methods to optimise.
I will now consider the existing and impending legal requirements on the local authority and I will comment on the contribution to be made by 'Thermal Treatments' along the way.
The UK faces several new EC Directives that do or will control our waste management activities.
The current Packaging Waste Directive says we should recover or recycle >50% of our Packaging waste.( Interestingly this also says that the Maximum amount that can be 'recycled' to comply is 45% .
This implies that at least 5% must be recovered' not recycled. To my knowledge this can only be by thermal treatment.) The % to be recovered/ recycled will almost certainly increase.
The Landfill Directive will, within a few years, restrict our land filling activities to 85% of 1995 levels and will continuously reduce levels thereafter for some years to below 50% of these earlier levels.
In the 20+ years that this will take, our waste volumes will probably double thereby making these targets significantly harder to achieve.
The End of Life Vehicle Directive and Waste Electrical & Electronic Equipment Directive will have more implications on waste management- particularly on Recycling- and they may adversely affect the available markets and processing capacities for recyclate.
Some materials, food packaging, disposable nappies, dressings, etc. have difficulty in, or are prohibited from, recycling.
A careful analysis of the available options set against the above waste Directives will lead to the conclusion that 'something else' must be done to supplement recycling and for the period when recycling and reduction needs to grow.
From my first statement that 'something' has traditionally been to 'Burn'.
Incineration is now a well developed, proven, and safe process. While incineration is a known emitter of Dioxins it does so under an increasingly controlled regime. SELCHP in SE London currently emits at the rate of 1 gram of Dioxins (TEQ) in ~100 years during which time it would have destroyed some 2kg. from the incoming waste stream (which also contains dioxins).
Waste burnt generates around 600kwh/tonne of waste. In Scandinavia Incinerators also provide district heating for communities at aroundtwice this electrical energy output. Increasingly they are being fitted out to do both.
Incineration is fully compatible with recycling. Those countries doing the most recycling also carry out the most incineration. Denmark, for example, has 32 incinerators all providing local district heating.
Incineration makes ferrous metal and aluminium recovery relatively easier and Incinerators in the UK are the largest source of Steel cans for recycling.
Bottom ash containing up to 1/3 Glass can be readily and safely recycled, dioxin and heavy metal contents both at or below typical urban soil levels. Final volumes are, in any case, only ~10% of input and only ~25% of input weight.
Interestingly, recycling benefits incineration. The removal of materials such as glass, metals and compostible items will stabilize, and even increase, the residual calorific value. Less non-combustible material will reduce the ash generation. Recycling the ash after prior waste recycling could bring residual landfill levels down towards zero.
Sensible approaches to collection with the recovery methods fully evaluated, will allow for reasonably high levels of recycling which, coupled with incineration, will enable the waste targets to be met or exceeded at affordable cost.
Other thermal treatments, esp. Pyrolysis and Gasification, release products that can generate energy (gas or oil) without necessarily burning these products on site. However in my opinion, they require extensive and extended development before they can be selected as reliable processes.
Their potential benefits in handling waste are, their potentially smaller size thereby being more flexible and offering the possibility of more local treatment, their lack of need for large oxygen (air) volumes thereby requiring smaller plant size, emitting less flue gas (even if the gas is combusted on site), and hence less dust emissions, their potentially more efficient use of energy by providing a fuel which can generate energy direct, e.g. through an engine or turbine, without the need for a waste heat boiler system. Several are undergoing trials and they are promising technologies to destroy waste thermally without large air volumes and, often, chimneys.
They are often classed as new technologies but, in fact, replicate what the old gas-works used to do with coal.
Their use with waste as a fuel is relatively new. The EC Waste Incineration Directive will govern any emissions from these plants but, as yet, how this will be policed is undecided. Unknowns include the emissions from numerous users of the gas or oil products, the suitability of ash products for recycling, the safety record of numerous plants for both the operational staff and nearby populace. If the plant is well operated where does its obligations end if a third party uses the gas generated from the waste?
These emerging techniques and technologies should be seen as offering more flexibility for the future in selecting an appropriate waste management strategy.
For the present a sensible mix of Considered Collection coupled with Recycling, Composting and Thermal treatment will enable all local authorities to meet their targets at affordable costs. Any single route is unlikely to do so.