Paper presented at the 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Mauritius, 11-13 July, 2011.
This paper presents and discusses various aspects of fouling
in case of heavily polluted flue gas (and/or off-gas) coming
especially from incinerators/waste-to-energy systems.
A long-term experience and know-how from this area as
well as continuing research and development brings new
insights into manufacturing of equipment and their operating.
Polluted off-gas causes high propensity to fouling and necessity
of consequent cleaning. In some cases, it is not possible to
utilize a conventional approach.
Introductory part of the paper provides a description of
various types of units for thermal processing of wastes
(including sludge and contaminated biomass). Fouling is
classified according to various cases of industrial applications
connected with easy/difficult cleaning. It is shown how fouling
can influence geometry of heat exchangers and their selection.
In the following part, several industrial cases are shown
taking into account aspects like:
• solid particles (ash and flying ash) in the gas, and
adapting design according to their concentration;
• species contained in flue gas which can chemically react
and create fouling deposits on heat transfer surfaces;
• potential corrosion between the fouling layer and heat
transfer surface caused by local temperature decrease.
The above aspects are clearly illustrated through industrial
applications as follows:
• heat recovery system of unit for the thermal treatment of
sludge coming from pulp and paper production;
• boiler systems in incineration plants and chemical
industry plants.
There are various methods to reduce fouling. We have
utilized very efficient approach combining intuitive design and
sophisticated tools based on CFD (Computational Fluid
Dynamics). However, fouling cannot be eliminated completely
therefore various efficient methods (mostly tailor-made ones)
are utilized (like common mechanical cleaning, air guns,
controlled local explosion) for cleaning of surfaces.
There is also an effort to develop a mathematical model for
fouling prediction, and selection of the most economically
acceptable systems connected with current research and
development in the field. However, it is difficult to validate the
models.
Fouling in the field described in the paper is in fact a “never
ending story”.
