urban's rave zone - chapter 1 download

they all follow the general principles of producer gas furnaces. Most ceramic kilns of this sort are built on the 66 CERAMIC CHEMISTRY. recuperative and not the regenerative principle. Re- generation consists of heating brickwork flues by passing hot exit gases through them, and subsequently passing the combustion air through the same passages so that the brickwork can communicate its heat. In recuperation the hot exit gases pass outside pipes, through which the combustion air flows, preferably in the opposite direction. Whatever type of kiln be used, three properties are requisite : (a) To obtain the temperature required in a proper interval of time and to hold it at pleasure ; (b) to control the temperature throughout the kiln by being able to advance or steady the heat in its different parts ; (c) to control at will the chemical character of the flame, whether oxidising, reducing, or neutral. A kiln fired by coal should be constructed on the down-draught principle that is, the flame should be made to travel up and then down the kiln after striking the crown, so that heat is conserved which would escape in the exit gases in an up-draught kiln. In an up-draught kiln there is probably an excess of air of 50 to 100 per cent. ; in a down-draught only 30 to 50 per cent. But in china biscuit ovens an excess of 50 per cent, is said to be necessary in order to avoid dis- coloration of the ware an example of the quality of the ware being more important than economy in fuel.