This page provides a short overview of the "path" followed by waste within the De Montfort double chamber incinerators. To help the reader visualize what is described below, each step number refers to those present on the cross section drawing.
1. Waste is loaded through the loading door at the top of the primary combustion chamber, which is then closed on an airtight sand seal.
2. In the primary combustion chamber the waste is heated by radiation from the hot firebricks in the absence of air. As the previous load or fuel is burned away, the load falls down the chamber by gravity and progressively dries.
3. As the waste nears the combustion zone at the level of the air inlets, it is pyrolized and burned.
4. The ash will then fall through the fire grate…
5. …before being removed through the ash door once the incineration process is finished.
6. During this primary combustion process some of the products are given off as combustible gases such as carbon monoxide. These combustible gases are forced to go through the gas transfer tunnel…
7. …and reach the secondary combustion chamber where they meet a further supply of air from the air hole in the back of the incinerator (in the case of the Mark 9), or from air not used in the primary process (in the case of the Mark 8a). They then undergo secondary combustion, raising the temperature even higher, and reducing the gases to stable compounds such as carbon dioxide. This flame can be stabilized by turbulence caused by wire mesh in the secondary chamber, which also glows red hot to reignite the flame should it be extinguished for any reason.
Correct operation of the incinerator can be checked by looking (with great precaution!) through the air holes in the secondary chamber to observe visible flames in the secondary chamber. The secondary chamber is built as large as the primary chamber to maximise the retention time of the gases in the hottest zone, thus killing off any pathogens and also breaking down some of the particulates in the outlet gases.
8. The hot gases in the chimney are less dense than the surrounding air and this difference provides the driving force to induce more air into the combustion chambers. This driving force requires the chimney to be at least 4m high.
Major components and areas of a De Montfort double chamber incinerator.