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I know from shop talk among previous colleagues that waste incinerators often need natural gas to sustain firing. AFAIK this is mostly because mixed household wastes have a high moisture content, making them a bad fuel. However, I found no data on this. For some reason, the incineration industry does not advertise this fact. The only tidbit I found was on a site advertising natural gas, of all things. I want to understand this issue more.

Obviously not all waste fractions are equally interesting as fuel. Light plastics and some packaging are close to brown coal in caloric content and usually pretty dry, organic waste is also okayish from a caloric point of view but has a high moisture content while some other trash basically does not burn. Paper would make a good fuel but makes better pulp. So when asking about whether natural gas or other fuel is used for co-firing, we need to know what waste fractions are in fact incinerated or the answer is meaningless.

  • Is it actually true that many/most incinerators for unsorted household waste use additional fuel for co-firing?

  • What sorting steps are neccessary to arrive at a waste stream (Starting from household waste) that can be burnt without additional fuel?

With the latter question, I want to be able to look at the input waste streams into an inceration plant and be able to make an educated guess wether it uses additional fuels or not. I don't see natural gas used purely for thermal exhaust aftertreatment as co firing for this question.

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    I cannot find much in the time I'm willing to spend on this, but it is the case that combustion has to happen at high enough temperatures to prevent pollution by half-burned or intermediate (gaseous) products. The Wikipedia article on incineration states that not only air is injected, but it is required to install backup auxiliary burners (often fueled by oil), which are fired into the boiler in case the heating value of the waste becomes too low to reach this temperature alone ....
    – user2451
    Commented Oct 20, 2015 at 11:44
  • ... Link to Waste Incineration Directive
    – user2451
    Commented Oct 20, 2015 at 11:47
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    "What sorting steps are neccessary to arrive at a waste stream (Starting from household waste) that can be burnt without additional fuel?" The obvious thing is to remove moisture. I know that when we started separating organic waste from the rest of the household waste in The Netherlands, there were complaints about the cladding of the incinerator ovens deteriorating too fast because of the much higher temperatures that were reached (sorry, could not find link), so I assume we have a self-sustaining burn since that time (apart from start-up).
    – user2451
    Commented Oct 20, 2015 at 11:54

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Contact City of Edmonton Waste Treatment. They have one of the best diversion systems in the world, at present removing better than 70% of the waste stream:

  • Yard waste is composted. The compost is sold commercially.
  • Plastic bags slitted, emptied, and vacuumed out of the stream. Baled and recycled.
  • Starting to do this with styrofoam too, but they still don't have an outlet.
  • Large plastic items are sorted out by type, shredded and bagged.
  • Newspaper and cardboard are baled and recycled.
  • ferrous metals are removed by magnet.
  • Wet waste may be in a different compost stream. Not sure.

The technology is changing constantly. They export expertise all over the world.

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