South China Morning Post – 17 Jan 2012
Alexander Luedi has a second letter in today’s paper in which he takes us to task for disagreeing with him over the choice of technology for the government’s proposed integrated waste management facility on Shek Wu Chau, off Lantau.
We suggested plasma arc technology should be considered, since it produces very low emissions compared with the conventional moving-grate incinerator the government is proposing to use.
Luedi refers to plasma arc technology as “something we consider about as expensive and, given the good track record of moving-grate incinerators, as unnecessary as sending the garbage to the sun”. He has called for “facts” to support our view, which is something his own lofty observations could benefit from.
The government is proposing a moving-grate incinerator to burn 3,000 tonnes of municipal solid waste per day, making it the biggest plant of its kind in the world.
Incinerators produce bottom ash and fly ash amounting to 30 to 50 per cent by volume of the original waste, which will have to be stabilised, loaded on to barges and dumped. Fly ash is toxic and has to be treated as a hazardous waste. According to the British Society for Ecological Medicine, it is one of the most toxic materials on the planet.
“Abatement equipment in modern incinerators merely transfers the toxic load, notably that of dioxins and heavy metals, from airborne emissions to the fly ash,” it said. “This fly ash is light, readily windborne and mostly of low particle size. It represents a considerable and poorly understood health hazard.”
Plasma arc technology, by contrast, produces virtually no emissions, no toxic ash or solid waste effluent. It produces small quantities of vitrified slag, which can be used in making concrete, road fill, bricks and other manufacturing uses.
The synthesis gas, or syngas, that is captured in the process can be variously used for producing electricity, or converted into jet fuel, or bio-diesel, depending on the technology employed, which in turn offsets the capital costs and waste disposal fees. Nor does it require a 130-metre stack.
As for the “good track record” of moving-grate incinerators that Luedi talks of, we see that a team from Imperial College London has been commissioned to carry out a survey after fears emerged about the health risks posed by incinerators, particularly for young children. This came after alarming discoveries of a higher incidence of infant deaths among those living downwind of a number of incinerators in Britain.
The good people of Detroit, home to the world’s largest incinerator, are three times as likely to be hospitalised for asthma compared with Michigan as a whole, and asthma death rates in the city are two times that for the state. There are plenty of other examples of incinerators being fined or closed down for exceeding emission caps.
Luedi says plasma arc is expensive compared with traditional moving-grate incinerators. An incinerator in Harrisburg, Pennsylvania, for example, has become so expensive to run it has bankrupted the town.
Meanwhile, a study in the US shows that a plasma arc gasification facility is near break-even at a capacity of about 180 to 270 tonnes of waste per day and generated net revenue using higher levels of waste. Traditional mass burn incineration produced negative net annual returns.
The study is by Dr Gary Young, an expert in industrial processes and the author of the recently published Municipal Solid Waste To Energy Conversion Processes; Economic, Technical and Renewable Comparisons.
He concludes “plasma arc gasification is an economically viable technology for managing municipal solid waste”, adding that the process is a “technologically advanced and environmentally friendly method of disposing of waste, converting it into commercially usable by-products”.
This is why we feel it should be considered for Hong Kong. The scheme favoured by Luedi is on the verge of obsolescence.
