BAN Waste Select Committee evidence

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Phase 1 Day 6 2001-10-15 Dan Grierson (on pyrolysis)

report from minutes of Select Committee

2. Dan Grierson - Pyrolysis

Submitted: evidence sheet from Dan Grierson and fact sheet on pyrolysis and gasification of waste circulated and copy in official minute book.

The Chair welcomed Dan Grierson to the meeting and asked him to make his presentation.

Mr Grierson explained that his knowledge of pyrolysis as a means of releasing energy stemmed from his MSC thesis completed last year which undertook a life cycle assessment of "pyrolysis as a new renewable", focussing on the environmental impact of: growing energy crops (willow, forestry waste), transporting this to pyrolysis plants, pyrolysing it into pyrolysis oil and then using the oil as a fuel for gas turbines linked to generators. In summary he indicated that the process involved be drying of wood using heat from further along in the process. The dryed wood was then feed into "pyrolysis vessels" were it was subjected to heat in a vacuum. These conditions caused the wood to degrade into charcoal and gaseous volatiles but most of the volatiles were then condensed forming pyrolysis oil, with the remaining gas been recycled to heat the pyrolysis vessels. Some of the charcoal was fed back into the process and used to heat water for powering low-pressure turbines. At this point wood had been turned into charcoal, gas (which was used to power the process) and pyrolysis oil. Advantages of the process over traditional combustion included its efficiency (high proportion of energy recovered from fuel) and the relatively low emission of complex molecules because of the high temperatures involved. Also there was a minimisation of ash production. He understood that pyrolysis was already being used to dispose of tyres, the bio-product of which was carbon black which was highly saleable; as well as oil fed gas turbines and created electricity; the process was better than landfill or incineration particularly as third generation plants were becoming very controlled. He acknowledged that at this stage very little work had been carried out on the use of pyrolysis in relation to household waste and acknowledged that there would be a need for clean separation.


The Chair thanked Dan Grierson for his presentation and questions/answers ensued:-

(Q1) Are you aware of any Government plans to support the development of newer or alternative technologies such as pyrolysis? (Eric Landau)

In answer Dan Grierson said that there was some support from NOFO for wood field schemes (e.g. Carlisle) but that the technology was still someway off. More recent findings for renewables were focussing on offshore wind although the DTI did have a stake in research into pyrolysis. The plant at Carlisle brought in forestry waste from Kielder and South West Scotland and the plant would turn all woodstock into charcoal and oil, half of which would be used on site to generate 10 megawatts and the other half taken away in tankers (as oil) to other plants elsewhere. He indicated that the plants were fairly small and that 10 megawatts would feed 10,000 households and bring power to 24,000 people. This could mean that in the future we could have far fewer large power stations and more smaller stations scattered around which would be more efficient.

(Q2) Do you know what work has been done on pyrolysis of the general waste stream rather than clean sources of fuel? - Pyrolysis seemed to depend on clean waste - was there any recent research on mixed household waste?

In answer Dan Grierson said that if you put dirty waste into pyrolysis it would come out the other end as ash and would include any heavy metals in it and confirmed that there was still of work to be done to use a mixed waste stream in pyrolysis.

(Q3) Was there justification for the current classing of pyrolysis (and the gasification) as renewable energies? Was this gasification likely to continue?

Dan Grierson said that the pyrolysis of bio-crops would be regarded as renewable in that the amount of CO2 omitted was equivalent to that taken out by the trees you are using. Waste was classified as renewable by NOFO scheme and that if part of the organic/clean waste was pyrolysised it would be regarded as renewable. Also the pyrolysis of tyres could be regarded as renewable in the form of recovery of energy.

Phil Capon suggested that it was really about how much energy that could be saved e.g. far more energy was saved if paper was recycled rather than burned.

Dan Grierson acknowledged this and mentioned that in his second paper there was mention of comparisons of relative energy efficiencies of these technologies and he emphasised that large-scale pyrolysis in future (15 megawatt plus) would be highly efficient in terms of the gas turbines.

(Q4) One of our witnesses last week talked of pyrolysis plants "lying like white elephants all over the planet". He quoted one which had been closed down in Germany last year. Why is this and does it discredit the technology, or the way it's applied? (June Wolf)

In response Dan Grierson said that from his studies and contacts in Europe he was aware that there were very few up and running pyrolysis plants but that this was a new technology and test plants had shown that it can work. The Canadians were well advanced in this matter but were keeping very quiet. It was likely that the principle would be a major success.

The Chair enquired what were the major problems in taking pyrolysis forward - were they technological, environmental or financial.

Dan Grierson said that it was likely to be a combination of all three, however in certain parts of the world pyrolysis had great potential and would prove to be very much economically viable e.g. outlying parts of Russia, Asia and North America in terms of replacing power lines - and using forestry waste.

Bob Stewart raised questions about emissions from charcoal.

In answer Dan Grierson said that if wood was pyrolysised before burning you would get far fewer particulates - the burning of charcoal produced a fraction of the particulates of burning green wood and was more efficient. In term of waste it would depend on the type of waste stream and could give a lot of smoke. The fuel produced after pyrolysis was changed and emissions were lower - it was a cleaner burn.

The Chair commented that the controls and regulations over emissions on pyrolysis were less strict than for the burning of waste.

Jenni Madison commented that city's waste stream was not harmozgous and that it sounded difficult for pyrolysis to cope with a mixed waste stream.

The Chair enquired whether if separation of the mixed stream took place, say to take out food waste, could pyrolysis cope?

Dan Grierson said that pyrolysis could cope very well with wet compounds and that separated food waste would not be a problem. He confirmed that the system could also cope with plastics in large volume. Also that one of the main advantages of the whole system was that the pyrolysis plants could have up to say eleven small vessels to deal with different waste streams so it would not be necessary to turndown plants as waste streams supply changed only to close off some vessels.

(Q5) In terms of the wider distribution of locations of these plants was there any evidence to say that some locations could affect the population in terms of emissions etc?

Dan Grierson said that in terms of pyrolysis of wood some planning applications had already gone in for plants. In Carlisle the emissions from the plant are far less than many other industrial processes. In his view the small 10-megawatt plants were entirely suitable for industrial estates (said to create emissions to 10 buses). He confirmed that dirty nappies, if separated, could be processed through pyrolysis.

(Q6) Were there any figures on how much municipal waste a 10-megawatt pyrolysis plant could handle? (Geoff Stokle)

Dan Grierson said that he did have the figures and would send them. He also confirmed that the plant could cope with mixed streams of plastic.

(Q7) Pyrolysis appeared to be a good idea for some waste (e.g. green bio-mass) but was it a sustainable use of land?

Dan Grierson said that the growing of bio-crop (willow) in low yield areas (e.g. East Anglia) with careful planning was a sustainable strategy.

The Chairman thanked Dan Grierson for his presentation.