EU Project: Clean Selective
The scientific object of this project is the development of an integrated online tool to locally monitor and detect slagging and fouling in the whole boiler including convective and radiative part in order to allow an intelligent or selective cleaning by soot blowers or water cannons.
The control strategy is based on the interactions between the CFD of the flue gas flow, the thermodynamic calculations of the water-steam cycle, a detailed fuel analysis and the development of new sensors. These processes will provide a detailed and realistic picture of the slagging on the heat exchangers.
Project start: 01.07.2006
Project end: 30.06.2009
Duration: 36 months
The project is supported by the European Commission under the Research Fund for Coal and Steel with the contract number RFCR-CT-2006-00008.
INTELLIGENT MONITORING AND SELECTIVE CLEANING CONTROL OF DEPOSITS IN PULVERISED COAL BOILERS
Deposit formation is an enormous operational problem for all solid fuel fired boilers and increases emissions, costs and reduces efficiency as well as operability. It is a problem that cannot be avoided but only reduced by appropriate boiler design and operation. Slagging and fouling has a negative impact on the power plant performance:
- decrease of efficiency
- increase of emissions
- damages and outages of the plant
- increase of maintenance costs
In a coal fired steam power plant the investment costs of the boiler are about one third of the total investment costs, however the costs of maintenance of the boiler have a share of about 80 % of the total maintenance costs of the power plant. This high share is caused by operational problems like slagging, fouling and corrosion. The only way to handle and eliminate the negative impact of deposit formation is an efficient and intelligent cleaning of all heat exchangers in the boiler.
The goal of this EU research project is to combine the thermodynamic modelling (engineering tool) and CFD modelling (research tool) in order to be able to simulate the steam and the flue gas side of the boiler. The on-line model will use available on-line measurements on the steam side, available heat flux sensors and additional measurements on the flue gas side to improve the boiler diagnostic system. This approach has not yet been investigated and has not been addressed in an EU funded project but makes use of the experience which has been developed in previous EU funded projects and provides an innovative integrated approach for selective monitoring and control of boiler deposits. Novelties of this proposal in comparison to the above mentioned projects are:
- Utilization of sensors for fouling also in the convective heat exchangers; Sensors for convective, hanging heat exchangers by weight signal have not yet been used in Europe
- Diagnostic modelling tool for 3 dimensions: This allows the detection of deposits at the furnace wall and within the convective heat exchangers. This is required for selective or intelligent cleaning.
- Combination of diagnostic tool consisting of a coupled thermodynamic and CFD model, heat flux sensors in the furnace and convective heat exchangers and temperature distributions at the furnace exit; Combination of modelling and sensors is new!
- Cleaning strategy which allows selective cleaning of convective heat exchangers
TERUEL POWER PLANT
The thermal power plant Teruel is located close to Zargoza. Local lignite mines are located very close to the site and its characteristics is a high sulphur content. This fact leads to the dilution of the local coal with imported coal from South Africa and the installation of one of the worlds largest desulphurization plants. The power plant has a maximum electricity output of around 3 x 350 MW. The project will lead to new technologies which will be installed in the power plant for scientific purposes.
FORMATION MECHANISM OF SLAGGING AND FOULING
The formation mechanisms of slagging and fouling are very complex. To provide a better understanding a simple sketch is shown in the figure below.
The fuel, which is used in steam boilers, contains beside carbon and hydrogen also mineral constituents. These are present either as extraneous minerals or included into the organic structure of the fuel. The included minerals are released by vaporization of the fuel and fragmentation of the particles during the combustion process. These mineral molecules form particles by agglomeration, for characterization it is distinguished between two different sizes: <1μm and >1μm. The extraneous part descends with a certain percentage into the flue gas as fly ash.
The impurities contained in the flue gas are carried by the flow towards the heat exchangers and the walls of the steam generator, where they are likely to form deposits. Particle impaction and gas diffusion leads to a porous and molten structure of the deposits. These affect the efficiency of the heat exchangers and result in a material loss of the heat exchangers pipes. In order to improve the availability of the power plant and to reduce emissions the influence of these deposits has to be minimized.
Technische Universität München (Coordinator)
Endesa Generación, S.A.
C/ Ribera del Loira, 60
María de Luna, 3
Clyde Bergemann GmbH
Centre for Research and Technology Hellas
6th KM. Charilaou - Thermi Road
Energy research Centre of the Netherlands
P.O. Box 1