Emissions of Hoffman kiln during production
The following typical releases to air are produced in this process:
Particulates: 60 – 70 mg/Nm3 (18% O2 dry)
CO: 100 mg/Nm3 (18% O2 dry)
Concrete emission data was not available at the time of the visit and a formal request for this information has been made in writing to Geoff Bowler.
From observation, the chimney emitted a white exhaust for most of the time. However, most of this will be air and water vapour (generated during the drying process) and is not due to poor combustion within the kiln. The organic content of the clay as well as the coal (support fuel) have a high sulphur content and so it is assumed that SO2 and SO3 will be the main gases emitted.
Products of incomplete combustion including some odourless compounds are emitted specifically from the ‘Coming Hot’ and ‘Main Drier’ phase of the process.
Once the temperature in the chamber has reached soaking temperature (960°C approximately) the combustion of the organic content in the clay and of the support fuel (coal) is thought to be complete, giving rise to no significant releases of products of incomplete combustion.
It is important to note that the emission characteristics of the Stewartby kiln are directly related to the brick material and firing regime and do not necessarily reflect the performance of a comparable design used to incinerate MSW.