Pyrolysis and Gasification
Pyrolysis is what happens when something (nomrally organic) is heated up in the absence of oxygen to the point of thermal degredation. It results in the starting material being converted into "permanent" gasses (some flammable, some not), tarry materials (which condense from the gas phase at lower temperatures) and a solid residue (normally a char or coke which also contains any inorganic materials - the latter usually being referred to as "ash").
Gasification on the other hand, is perhaps better defined as partial combustion: the material to be gasified is exposed at elevated temperatures to sufficient air (or oxygen) for a proportion to combust. This process generates heat which i) serves to dry the substrate, ii) pyrolyses it (i.e. reduces the volatiles content to zero), and ii) cracks/combusts any tars. The result is hot gas (normally a mixture of CO2 and H2O) and hot char which acts as a reducing agent, converting the gasses into combustible CO and H2. In this way, up to 75% of the calorific value of a solid (e.g. wood) can be converted into a gaseous fuel for e.g. an internal combustion engine.
Pyrolysis and gasification have rôles to play in alternative energy production in third-world countries, but in Europe they are more suited to tackling the problems of refuse disposal.
Quicksilver Engineering Ltd. has extensive knowledge of both the theory and practice of pyrolysis and gasification, especially when it comes to manipulating the balance between the possible products of gas, tar and solids. The techniques all revolve around residence times, both in the direct vicinity of the pyrolysing solid and in the "hot zone" of a reactor (e.g. the freeboard of a fluidised bed).
The combination of pyrolysis or gasification with vacuum engineering opens up a whole new world of interesting possibilities. If you would like more information on this subject, please do not hesitate to contact Quicksilver Engineering Ltd..