The pyrolysis always consists of several process stages:
Shredder. Degasification of the organic components in a pyrolysis reactor In most cases a rotary kiln with indirect heating is used. Treatment of pyrolysis-gas and coke. There are the following possibilities:
Incineration and energetic use
Condensation of the gas to get the oil- and tar- fraction. For example: pyrolysis of used tyres.
Incineration and energetic use,
Gasification with the gas to produce a synthesis gas.
T h e t e m p e r a t u r e o f t h e p y r o l y s i s - s t a g e i s b e t w e e n 4 0 0 o C a n d 7 0 0 o C .
This means a partial oxidation of the organic contents of the waste. The products are synthesis gas (without oil and tar – because of the high temperature) and solid residues (melted minerals and metals).The synthesis gas consists of carbonmonoxid, carbondioxid, hydrogen, water, some methane.
Also the gasification consists of several process stages:
Pre-treatment of the waste (mechanical or thermal) Gasification in the reactor Energetic- or material-recycling of the synthesis gas
(gas motor, gas turbine, incineration, synthesis of methanol)
Selected Recycling-Plants in Germany
ConTherm-Pyrolysis-Plant in Hamm (North Rhine Westphalia)
Example for „energetic-recycling“
In unit C of the power plant „Westfalen“ (high temperature about 1,500 degrees, melted slag) of the RWE-Power Company with a capacity of 769 Megawatt, about 9,5 % of the required hard coal are replaced by a special prepared substitute fuel. This is a matter of co-incineration of wastes. The wastes are energetic-recycled. But before the wastes can co-incinerated in a power plant, they had to be converted into a fuel with the characteristics of hard coal. For this purpose the pyrolysis is the only appropriate process. In Hamm the ConTherm-Process, which started the large-scale operation in connection to unit C of the power plant in the year 2001, is specially developed by RWE Power for the pyrolysis of wastes.
The centre of the ConTherm-Plant are two parallel operated external heated rotary kilns with a flow rate of altogether 100.000 t/a. There the shredded wastes are degassed at approx. 500 °C under exclusion of air. The inflammable pyrolysis gases are cleaned from dust and supplied then directly to the unit C and burned there. The carbon-rich fraction is separated from the solid residues and also given to the coal mill of unit C as substitute fuel. The metals are also separated and recovered
The advantages of the procedure in relation to the direct incineration are:
Use of the high energetic efficiency of the power station (approx. 38 %) with the employment of the wastes and thus saving of fossil sources of energy. The correspond efficiency of waste incineration is only about 20 %.
Separation and utilization of the metals in good quality,
Melting down of the remaining residues,
Safe destruction of organic pollutants at the high burn temperature of 1,500 °C in the power station,
Use of the existing infrastructure.