Tube failure is the leading reason of forced boiler shutdowns and a major cost for the electric utilities. In the USA alone the costs are 6.9 bln USD annually. With the increasing interest in staged combustion introduced in order to limit NOx emissions, the problem of more pronounced reducing zones in the boiler became a significant issue. In the reducing zones corrosion proceeds quickly and deposits characterized by lower melting temperature compared to the respective deposits formed in over-stoichiometric conditions influence the heat exchange rates and waterwall-lifetime which in some cases can be shortened even to one year. The aspect of co-firing different blends of coals (to reduce the fuel price) or coal with other fuels such as biomass or RDF (to reduce the CO2 emissions), influences also the corrosion and slagging process in the boiler. An improper selection of fuel blend for the particular boiler is known to have causedsevere boiler damage even within a couple of weeks.
The innovative aspect of CERUBIS project is to combine existing, develop new and adopt sensors from application in other industries, to form an integrated on-line corrosion monitoring system for hard-coal and lignite-fired boilers, under very low NOx emissions operation. The scope of CERUBIS project is to obtain one combined online corrosion/slagging monitoring system - Common Intelligent Boiler Operation Platform (CIBOP). Also a conceptual integration of the CIBOP with the boiler’s switching system, allowing for a more automated operation, while keeping the corrosion and slagging risk down to a minimum and at the same safeguarding proper NOx emission will be attempted. Next aiding environmental standard compliance and lowering the overhaul cost, a better control of corrosion and slagging processes has also direct impact on the overall boiler efficiency and hence economy of the power generation process. This in turn results in a better competitive position of the coal-(co-)fired boilers. Therefore the CERUBIS-project aims at enhancing the flexibility, operability and environmental performance of coal-fired power stations, simultaneously avoiding great expenditures connected with an unexpected boiler breakdown.
Major novelties offered by the CERUBIS project are:
- Development and optimization of various online corrosion/slagging tools and their validation
- Incorporation of online corrosion/slagging monitoring tools into - Common Intelligent Boiler Operation Platform
- Investigation and validation of various available and newly-developed sensors for online corrosion monitoring in the robust environment of coal combustion.
- Development and implementation of intelligent software – CIBOP – at two utility boilers with different low NOx systems
- Development and investigation of dedicated CFD submodels for near wall numerical simulations
- Evaluation of results in respect to the potential of power plant operation
Project was devided into four technical Work Packages:
The first WP focuses on laboratory, pilot scale and full-scale investigations of corrosion and slagging phenomena. Main objectives are: determination of corrosion and slagging behaviour under different emission regime (NOx, CO2) for different types of tube materials with multi fuel criteria; obtaining multitude corrosion and slagging factors and data for utilization in newly-developed intelligent systems (in WP2 and WP3); obtaining multitude real scale data from two utility boilers in order to determine corrosion and slagging behaviour, and training and validation of the newly-developed sensing systems and validate CFD submodels. Additionally, reference in-boiler diagnostic data regarding the relevant boiler conditions will be obtained by carrying out two measurement campaign at the beginning and at the end of the project.
WP2 focuses on development and testing of the different sensors, sensor platforms and sensing systems. The main objectives are: obtaining a list of potentially available corrosion and flow sensors for present and future applications in utility boilers; selection of most promising sensors with particular attention to the severe power plant conditions; manufacture/procurement and validation of three integrated sensors platforms to be investigated in pilot and real scale conditions.
The WP3’s scope is on the integration of the earlier developed sensor platforms with the existing boiler control/diagnostic systems. Main objectives are: conceptual integration of sensing systems; conceptual design, realisation and pilot scale testing and validating of an integrated pilot scale sensing systems ready to be manufactured, installed and tested in WP4; development of an artificial intelligence software and intelligent systems; realisation, testing and validation of Common Intelligent Boiler Operation Platform – CIBOP; creation, testing and validation of CFD submodel(s) for boiler boundary layer simulations.
WP4 will focus on testing and optimisation of the newly-developed systems at real scale conditions. The envisaged workload encompasses:
- carrying out wall thickness measurements in order to validate and check sensing systems and intelligent software (CIBOP)
- testing and validating of sensors and sensing system performance in severe boiler conditions
- investigating of corrosion/slagging phenomena in the real scale conditions under low emission demands for hard and lignite coal combustion
- validating and further improving the intelligent software tools – CIBOP and supportive numerical models
To cover a broader fuel and technology portfolio, the testing and validation will be performed in two separate boilers, firing different coals: hard coal (Opole) and lignite (Bełchatów). Furthermore these boilers are equipped with different low NOx systems. Also, the high moisture flue gas resulting from the lignite combustion will add to the challenge of testing the mechanical durability and longevity of the sensors.