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Waste to Energy

Discussion in 'Speaker's Corner' started by PlacidCasual, 19 Jan 2006.

  1. PlacidCasual

    Soldato

    Joined: 13 May 2003

    Posts: 6,984

    http://news.bbc.co.uk/1/hi/uk/4621710.stm

    I was discussing this at work with the head of generation for one of the big six energy providers yesterday. It seems that the Government in its latest Energy White Paper (how many in how many years?) is intending to burn more waste as fuel in general power stations and purpose built waste to electricity plants to reduce the burden on land fill. Now as someone that works in the industry this just highlights the lack of joined up thinking on environmental and energy issues. Most plants in the UK have triialled burning tallow and re-firing ash (because a proportion still has high carbon content that can be burnt) the EA (in all its regional forms) however has at various times decided that tallow is a fuel and then that it is a waste. Now tallow is a good replacement for heavy fuel oil (a petro-chem product) with a high specific heat. When it is classified as fuel we can burn it and extract valuable MWh from it but when it is classified as waste it has to be sent for incineration with no energy recovery. Longannet power station in Scotland built a sewage treatment plant that turned 40% of southern Scotland’s (Glasgow – Edinburgh area) into pellets that could be fired in the boiler to create electricity. The Scottish EA decided waste must be incinerated and the plant has stood dormant after an expensive investment. The irony is that previously most of this waste was simply dumped in the sea which was acceptable, but if you build a plant to get energy from it you can’t use for that purpose and you must now incinerate the pellets at your own cost. So genuine fuel opportunities have regularly been turned down by the EA but now we are going to burn genuine waste in power stations and that is ok so why were these other valuable projects rejected?
    Part of the reason for the new loveof incineration is that we have reduced massively the number of special waste land fill sites so their volume is at a premium and cannot be spared for regular waste and regular land fill sites are being closed over water concerns. Basically all those ni-cad batteries we chuck in the bin are rotting and the tiny amounts of cadmium are getting into the drinking water breaking some EU legislation and requiring their closure.
    Now I agree with the Friends of the Earth that the aim should be to recycle and cut down waste but whatever happens there will always be some waste and some of it will be suitable for waste to energy. The furore that will no doubt break out will completely overlook the fact that uber-green countries like Germany already burn most of their waste in regular power plants that have been designed and built with ability to do so. To them the anathema is to bury waste, the solution of which we approve.

    So when you hear about this don’t be alarmed this is the norm in many countries it’s only places like Britain where the jobsworths and nimby’s rule that the sensible option can’t be followed. When someone mentions dioxins point out that at 1160 degC the typical boiler temperature for a coal station they don’t form.
     
  2. William

    Capodecina

    Joined: 26 Jul 2003

    Posts: 10,948

    Location: Derby

    A waste incineration power plant is being built in Maidstone, but its really quite a farce, the amount of energy it will generate from raw waste compared to the amount of crap it will pump out is well, pretty damn inefficent. The main problem is that the government is unwilling to give any real funding towards green power sources, proper recycling protocol like in Germany or even towards Nuclear. It seems to be happy at this moment to sit along doing the bare minimum to fall within the already vague objectives it sets itself.

    I think coal powerplants do pump out some pretty nasty stuff, dioxins could prehaps form at cooler temperatures past the boilers in the chimneys? I know that Eggbourough powerstation had a flu-gas treatment plant installed recently.
     
  3. PlacidCasual

    Soldato

    Joined: 13 May 2003

    Posts: 6,984

    Out of curiosity what crap do you think a waste to power plant will emit? I also have great difficulty imagining that a regular power plant burning waste (only as a small proportion of its fuel) would produce dioxins in the chimney. Surely by the time the gases reach that point the complex molecules necessary for dioxin formation will have been converted to simpler molecules like H2O, CO and CO2. Recycling is important though especially to remove unwanted materials like metals from the fuel lest they “pollute” the gases and ash. If the reliance on petro-chem based packaging is tackled much of the remaining waste will be organic so burning it is only part of a loop anyway.
    Eggborough has flu gas de-sulphurisation (FGD) where you take high quality limestone (also known as Buxton) turn it into slurry (mix with water) and spray into the flue gas. The limestone and SOx react to form building gypsum which you then find difficult to sell because the market is flooded. FGD merely removes the sulphur from the gases a process that is proved to reduce acid rain.
    Another good environmental story here. To meet some asinine bureaucrats idea of reality power stations are defined on the number of stacks they have (not chimneys or flues which are something different). So Eggborough has 4 units each operationally independent but one stack, Ferrybridge has 4 units each operationally independent but two stacks. Eggborough has 2 units with FGD Ferrybridge has 2 units with FGD. Eggborough has to treat its entire station as one unit for the new environmental laws Ferrybridge gets treated as two. This has massive operational impact with regard to environmental limits and remaining station life. So British Energy are shafted to the tune of ££££££’s and Ferrybridge’s owners aren’t despite there being only very minor differences in the environmental impact of running each station all because some person that has never worked at a power station is making the law.
     
  4. William

    Capodecina

    Joined: 26 Jul 2003

    Posts: 10,948

    Location: Derby

    I imagined the harmful waste as you say to be petro-chem packaging, I am not a chemist so I don't know the exact products of burning such things. As to the organic waste that is fine, it probably just is not that great a thing to burn raw, it might be processed into pellets at Maidstone, I can't really can't remember what they planned to do with it. Do they constantly run coal plants over 1000c or are they run at a lower temperature because it is cheaper? Do you know what the cost of modifying plants to burn waste would be? (I am guessing burning pellets would need very little) I am not being rhetorical, I am interested in how it all works. :)


    Thanks for reminding me about what the FGD does, my dad works on the FGD in Eggbourough at the moment. I have an odd egg-timer thing with some of the first Gypsum from the FGD plant in it.
     
  5. PlacidCasual

    Soldato

    Joined: 13 May 2003

    Posts: 6,984

    The physics of a conventionally fired coal boiler mean that in the superheater section the gases are in the 1100-1200 deg C range. Most things break down to fairly simple waste gases at those temperatures. I know dioxins are produced from organic waste at lower temperatures but your regular power station will far exceed those to meet the required steam conditions and efficiency. Like I say the uber-green Germans treat this as the norm not the exception.
    Generally the waste would be pre treated to meet our technical requirements then ground to talc powder sort of sizes in the mills before being blown into the boiler. When we burn wood products for instance we don't even get as high a 10% wood by energy mixed in with the coal because each boiler is specifically designed to burn a certain type of fuel and the further your stray from that the bigger the operational problems you have.
     
  6. William

    Capodecina

    Joined: 26 Jul 2003

    Posts: 10,948

    Location: Derby

    Ah I see, would the waste be blown in as a mixture with coal dust to try and avoid those operational problems?