to read the full report - Ecolateral by Peter Jones
to read the full report - Ecolateral by Peter Jones
to read the full report - Ecolateral by Peter Jones
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110<br />
Evaluation of Opportunities for Converting Indigenous UK Wastes <strong>to</strong> Wastes and Energy<br />
AEA/ED45551/Issue 1<br />
Table 55 Pollution and <strong>the</strong> abatement methods for combustion of waste<br />
Pollutant Method of removal<br />
Particulates or aerosols Fabric or electrostatic filters, for smaller<br />
boilers and cleaner fuel cyclones or<br />
multiclone.<br />
Acid gasses mainly from sulphur and Dry or liquid carbonate wash or dry<br />
chlorine<br />
absorber.<br />
Dioxin and o<strong>the</strong>r organic compounds Active carbon absorber, can be combined<br />
with dry carbonate scrub<br />
Oxides of nitrogen. Injection of ammonia or urea in<strong>to</strong><br />
combustion zone. Catalytic removal from<br />
<strong>the</strong> flue gas.<br />
The main concerns on pollution from incinera<strong>to</strong>rs relate <strong>to</strong> <strong>the</strong> health effects of dioxins and o<strong>the</strong>r<br />
chemicals such as PCBs (poly chlorinated biphenyls) and PAHs (poly aromatic hydrocarbons). These<br />
compounds accumulate in body fat and are persistent.<br />
Dioxins are not present in nature. The term is loosely used <strong>to</strong> describe <strong>the</strong> whole family of <strong>to</strong>xic organic<br />
micro-pollutant emissions that may be formed during and after combustion. They have been associated<br />
with poorly run incineration in <strong>the</strong> past when chlorine containing wastes such as PVC, paper and card and<br />
treated wood were burnt, and this association persists.<br />
Understanding of how dioxins are formed has led <strong>to</strong> advances in process design and control that have<br />
resulted in <strong>the</strong> emissions from <strong>the</strong> incineration sec<strong>to</strong>r falling dramatically in <strong>the</strong> UK. Scientific studies<br />
have shown that <strong>the</strong> impact of emissions from an individual plant is very low. Dioxin emissions have<br />
reduced <strong>by</strong> more than 90% in <strong>the</strong> UK in <strong>the</strong> past 20 years. Never<strong>the</strong>less <strong>the</strong>re remains acute public<br />
concern over <strong>the</strong> issue, despite <strong>the</strong> fact that local authorities have access <strong>to</strong> this information.<br />
PCBs are classified as persistent in <strong>the</strong> environment and as being probably carcinogenic <strong>to</strong> humans.<br />
They have also been linked <strong>to</strong> sub-chronic effects such as reduced male fertility and long-term<br />
behavioural and learning impairment. They may originate from flexible plastic waste, paint waste, as well<br />
as transformers and capaci<strong>to</strong>rs. PAHs are a large group of chemical compounds and are carcinogenic.<br />
They may originate from waste wood, tar or fat waste for example.<br />
Sampling and analysis costs for all of <strong>the</strong>se compounds are high due <strong>to</strong> <strong>the</strong> specialised nature of <strong>the</strong><br />
equipment and trained labora<strong>to</strong>ry personnel required. This restricts <strong>the</strong> frequency of data collection. For<br />
this reason <strong>the</strong> public express concern regarding <strong>the</strong> reliability of data. A simpler, on-line test would be<br />
more satisfac<strong>to</strong>ry but due <strong>to</strong> <strong>the</strong> nature of dioxins this is a long way off.<br />
Smaller installations burning wood that do not have particulate removal equipment have also given rise <strong>to</strong><br />
concern recently. This is due <strong>to</strong> <strong>the</strong> nature of emissions from wood firing. The ash composition contains<br />
alkali components that vaporise at <strong>the</strong> furnace temperature <strong>to</strong> later condense in <strong>the</strong> cold atmosphere as<br />
aerosols with a size that is respirable. There is a similar problem with condensable organics in batch fed<br />
wood combustion devices where poor combustion control allows <strong>the</strong> formation of aerosols of organic<br />
compounds and soot. These are particularly worrying as <strong>the</strong>y contain carcinogenic materials such as<br />
furans and aromatics. This is only likely <strong>to</strong> be a problem in urban areas where <strong>the</strong> aggregate effect of<br />
several installations in a small area coupled with o<strong>the</strong>r sources such as diesel traffic could give<br />
unacceptable impacts. Local Authorities are being issued with revised guidelines on this issue and this<br />
should resolve <strong>the</strong> situation.<br />
The ash leaves <strong>the</strong> process as two distinct streams – bot<strong>to</strong>m ash that falls out of <strong>the</strong> combustion grate or<br />
bed, and fly ash that is separated from <strong>the</strong> flue gases. Bot<strong>to</strong>m ash is considered <strong>to</strong> be inert and, after <strong>the</strong><br />
separation of metals, is ei<strong>the</strong>r disposed of <strong>to</strong> general landfill or used as aggregate. Fly ash, however, can<br />
contain heavy metal contamination and, with certain chlorine containing wastes, dioxin so must be