To develop methods to measure and predict gas-side fouling in a generic way. To that end, fouling monitors suitable for use by non-specialists will be developed and predictive mathematical models will be constructed for a range of environments. The potential application of the methodology to liquid-side fouling problems will also be assessed.
Extended surface exchangers offer many advantages over plain tube exchangers for gas side applications, but their use is currently limited to clean environments, due to uncertainty about the effects of fouling on their performance. In order to achieve a better understanding of fouling mechanisms, recent work has used a combination of theory and experimental measurements and industrial scale data to produce valid models for real process streams. The main objective was to obtain improved predictions for thermophoretically enhanced deposition onto extended surfaces. The core of the problem is identified as the determination of retention probability and the deposit removal mechanisms.
Previous approaches to the modelling of gas side fouling are based on calculation of the overall residence probabilities for particulate fouling. A methodology has been developed for quantifying nonparticulate mechanisms of deposition, based on measurements from a refuse incineration plant at Toulon. If the chemical composition of different size fractions of gas borne particulates is known and the compostion of deposits, then any difference between the 2 is the result of either uneven deposition from particulate species or nonparticulate deposition. Results show that depostion in refuse incineration is related to the gas stream temperature, with an increase at about 700 C which accords well with the observed melting behaviour of the deposited material. This deposition results from a complex set of processes including inertial impaction, enhanced retention of inertially impacted particles rich in calcium small particle deposition and condensation deposition.
Fouling of heat exchangers is a major problem which can lead to loss of heat exchanger efficiency. In view of the wide use of heat exchangers a decrease of fouling could lead to large energy savings. In this project, the following tasks are foreseen: model development; experimental tests and evaluation of the model.
An integrated fouling model for heat exchangers will be developed by NEL. A practical sensor for the detection of fouling deposits will be produced by TNO; acoustic, electric and optic techniques will be considered. Experimental work on fouling includes both measurements under laboratory and full scale operating conditions.
The measurement of the temperature distribution on exchanger fins of selected geometries will be carried out. Fouling in Diesel exhaust environments will be studied as a function of tube lay-out gas velocity (5-20 m/s), exhaust temperature (300-700 C), surface temperature (80-200 C) and particle concentration. Fouling as a function of particle size will also be investigated in an experimental facility simulating exhaust environments (GRETh).
CNIM will carry out studies in a refuse incinerator in order to measure mass accumulation rates and other fouling aspects as a function of gas velocity, gas temperature and operating conditions. The same experimental study will be carried out in gas streams of a cast steel furnace (HAMON-SOBELCO). These data will serve as an input for the evaluation of the fouling model developed by NEL. The potential of the gas-side methodology for liquid-side fouling problems will also be investigated.
The work on fouling in liquid systems has subsequently been considerably extended under a supplementary contract. With one new contractor (UNIVERSITY OF BIRMINGHAM) and some industrial collaboration (BRITISH SUGAR PLC, SOGELERG GTS and HI TRAN/CAL GAVIN), the possibilities for generic fouling modelling in liquid systems, with particular emphasis on industrial process fluids, is investigated.
The data are used within the project to assess the limitations of the present models and show how it may be possible to integrate physical with physico-chemical models to provide more generic prediction methods.
The development of a gas-side fouling monitor has been successfully completed.
Funding SchemeCSC - Cost-sharing contracts
B15 2TT Birmingham