Processing of mixed household waste, pyrolysis

Processing of mixed household waste, pyrolysis

Mixed household waste is most often disposed of in landfills, and in some cases it is burned in thermal power plants for energy production. Such waste usually contains up to 30 percent plastic. The plastic melts at a temperature of 180 to 200 degrees Celsius, and upon cooling it turns into a solid mass, which occupies a much smaller volume than the initial raw material. Shown in this shot. Larger pieces of waste can trap air and gases when heated, and empty spaces can appear in the resulting mass. In order to prevent this, the waste must be finely chopped before processing.
After grinding into small granules and mixing from the mixed household waste, the metals are extracted with strong magnetic fields. The remaining shredded waste must be mixed well and melted in a furnace for melting waste.
Such a furnace (1) is shown in the picture above.
A long steel pipe (2) is placed horizontally through the furnace (1), which is placed at a slight incline of 5 to 15 degrees. Shredded mixed household waste is inserted into the upper part of the pipe. Under the steel pipe (2) there is a firebox (6) on which a fire burns and heats the thrown waste. By heating the waste, the water first evaporates from it and turns it into water vapor. At 100 degrees Celsius, biological waste dehydrates and small pores form in it. When the plastic melts, it enters the pores and thus turns these biological remains into inert waste. At temperatures between 100 and 200 degrees Celsius, various oils, fats, paint solvents and the like evaporate from the waste. There may be a small amount of discarded batteries in the waste, and various gases may be released from them. Also, part of the biological waste is oxidized and turned into carbon monoxide. In order to prevent all these gases from escaping into the environment, they need to be burned in an incinerator (6). For this purpose, a gas discharge pipe (3) is placed on the upper part of the steel pipe (2), which is connected at the other end to an electric fan (4), which draws waste gases from the metal pipe (2) and inserts them through the outlet pipe (5) below fireplaces (6). These waste gases, together with hot air, pass through the openings in the reservoir (6) and pass through the embers of the fire, which is the hottest at its bottom because the strongest oxidation takes place there. It is possible to regulate the speed of fuel burning and the power of the fire by changing the power of the fan (4) and by injecting more or less fuel into the combustion chamber (6). Wood separated from large household waste, usually old furniture, can be used as fuel, but other fuels such as gas or coal can also be used.

In order to prevent the waste from igniting, there must be covers at the entrance and exit that prevent the entry of air into the long pipe (2). They are opened when waste is put in or out. The waste also needs to be stirred occasionally.
When the plastic starts to melt, it immediately slides towards the lower part of the steel tube (2) and comes out, which prevents it from heating up to too high a temperature where toxic gases could be formed. Along with the melted plastic, suspended small particles of paper, dehydrated biological waste, dust, glass, sand, textiles and the like come out of the steel pipe. Part of the textile is made of soluble plastic, and these parts also melt. After exiting the steel pipe (2), all this suspension of liquid plastic and solid particles is poured into a mobile sludge (7) which is placed next to this kind of furnace (1) under the exit part of the steel pipe (2). When the mobile mold (7) is filled, it is brought to the place for cooling, and another mobile mold (7) is placed in its place.
When the mixture in the mobile mold (7) cools down, a hard solid object is removed from it, inside which there are many small particles that are not plastic. There is air inside these particles, which makes this object as light as wood. Such objects can be made as large solid panels for garden benches and tables, for large work tables and the like.
If a larger amount of finely chopped straw were added to the waste, then very light panels could be obtained that could be used for thermal insulation.
If the melted suspension of plastic and solid particles is inserted into strong presses instead of mobile molds (7), then various long profiles could be produced that could be cut to a certain length. The weight of such profiles would be somewhat heavier, and the strength would be higher. Such profiles could be used as posts for fences, as boards or beams, as stakes in gardening and vegetable growing, for sticks for various purposes and the like.
Objects produced in this way could replace many objects that are made of wood. Therefore, the demand, consumption and memory of wood would be reduced. The area under forests would increase, which would have a positive effect on the climate and the survival of various endangered species. And the areas for waste disposal would also be reduced, and those areas could be used for other purposes.