Ever thought that all the refuse and junk that you throw out of our kitchens and homes everyday could ever turn out useful and provide the energy to light up millions of homes? Well now, maybe not millions of homes, at least not yet, maybe a few thousands for now. Let me introduce you to RDFs, refuse derived fuels, don't start thinking the world's turning over on its head yet, you can't use them to power your car yet, so you'd better stop thinking of emptying the garbage can into your gas tanks, but who knows, in this world of ours anything is possible.
Refuse derived fuels are a good substitute for more commercially and environmentally expensive fossil fuels used in most of our high energy demand industrial processes, cement industries, power plants. Refuse derived fuels mostly refer to high calorific fraction of our municipal solid waste that can either be domestic or industrial in its origins. Obtaining this high calorific fraction is the objective of the processing the waste has to go through. It's the reason any RDF processing facility has to have a material sorting facility.
There are generally two industrial processes for obtaining our RDF right now, the mechanical heat treatment and the mechanical biological treatment methods. RDF production facilities like other industries are best situated close to their sources of raw materials which in this case is municipal solid waste, basically that's the refuse you and I generate from our homes, so the regular RDF plant is next or as close as possible to the landfill site. Let's take a closer look at one of our processes for obtaining our RDF, let's take the mechanical heat treatment process or MHT first.
The first stage of this process involves a mechanical sorting of the MSW, the main objective is to remove the non combustible, materials, materials which are generally heat and fire resistant, glass, plastics, metals and the likes, this is mostly done by passing the refuse on a conveyor belt through shredders, trommel, screens, magnets and sometimes for a more refined and specific sorting process, through a hand picking process.
By the time we're through with these processes our MSW should have attained preset standard, which depends on many factors including the use to which we'd like to put the fuel to once it has been produced. The materials removed through the sorting process are mostly sent off for recycling. Any other rejects are usually only good for the landfill. The remaining material to undergo processing pass through the next stage. This involves, as the name might imply, a treatment with heat to yield the desired product. Refuse derived fuels. This heat treatment process is often referred to as an autoclave process, waste autoclave process in this case. Let me shed a little light on what an autoclave refers to, it simply refers to the process of treating waste, or any other feed material for that matter, with steam and heat under a certain amount of pressure. Waste autoclaves utilize injections of steam at high temperatures, usually up to about 160c, and at pressures of about 5 bars, these processes might take place in as little as an hour.
The major effects of the autoclaving process are:
o It sterilizes our refuse and neutralizes harmful microorganisms.
o It reduces considerably the volume of our waste that eventually has to go the landfill.
The autoclaving process breaks down most of the waste, breaking down and flattening plastics, while pulp, paper and other fibrous materials are reduced to a more fluid fibrous form. Autoclaving generally reduces the mass of waste by an average of about 50%. When it is done the chamber can be depressurized and the materials taken out to undergo another series of separation and recovery processes. The fiber fibrous materials obtained from this process can be burned as fuels in electricity generating plants.
Energy From Our Waste - A Dawning Reality? Part 1
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