Thermal Science 2012 Volume 16, Issue 3, Pages: 789-804
https://doi.org/10.2298/TSCI120120122S
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Co-firing Bosnian coals with woody biomass: Experimental studies on a laboratory-scale furnace and 110 MWe power unit
Smajevic Izet (JP Elektroprivreda BiH d.d. Sarajevo, Sarajevo, Bosnia and Herzegovina + University of Sarajevo, Faculty of Mechanical Engineering, Sarajevo, Bosnia and Herzegovina)
Kazagic Anes (JP Elektroprivreda BiH d.d. Sarajevo, Sarajevo, Bosnia and Herzegovina)
Music Mustafa (JP Elektroprivreda BiH d.d. Sarajevo, Sarajevo, Bosnia and Herzegovina)
Becic Kemal (JP Elektroprivreda BiH d.d. Sarajevo, Sarajevo, Bosnia and Herzegovina)
Hasanbegovic Ilijas (JP Elektroprivreda BiH d.d. Sarajevo, Sarajevo, Bosnia and Herzegovina)
Sokolovic Seval (JP Elektroprivreda BiH d.d. Sarajevo, Sarajevo, Bosnia and Herzegovina)
Delihasanovic Nermin (JP Elektroprivreda BiH d.d. Sarajevo, Sarajevo, Bosnia and Herzegovina)
Skopljak Almedin (JP Elektroprivreda BiH d.d. Sarajevo, Sarajevo, Bosnia and Herzegovina)
Hodzic Nihad (b University of Sarajevo, Faculty of Mechanical Engineering, Sarajevo, Bosnia and Herzegovina)
This paper presents the findings of research into cofiring two Bosnian cola
types, brown coal and lignite, with woody biomass, in this case spruce
sawdust. The aim of the research was to find the optimal blend of coal and
sawdust that may be substituted for 100% coal in large coal-fired power
stations in Bosnia and Herzegovina. Two groups of experimental tests were
performed in this study: laboratory testing of co-firing and trial runs on a
large-scale plant based on the laboratory research results. A laboratory
experiment was carried out in an electrically heated and entrained
pulverized-fuel flow furnace. Coal-sawdust blends of 93:7% by weight and
80:20% by weight were tested. Co-firing trials were conducted over a range of
the following process variables: process temperature, excess air ratio and
air distribution. Neither of the two coal-sawdust blends used produced any
significant ash-related problems provided the blend volume was 7% by weight
sawdust and the process temperature did not exceed 1250ºC. It was observed
that in addition to the nitrogen content in the co-fired blend, the volatile
content and particle size distribution of the mixture also influenced the
level of NOx emissions. The brown coal-sawdust blend generated a further
reduction of SO2 due to the higher sulphur capture rate than for coal alone.
Based on and following the laboratory research findings, a trial run was
carried out in a large-scale utility - the Kakanj power station, Unit 5 (110
MWe), using two mixtures; one in which 5%/wt and one in which 7%/wt of brown
coal was replaced with sawdust. Compared to a reference firing process with
100% coal, these co-firing trials produced a more intensive redistribution of
the alkaline components in the slag in the melting chamber, with a
consequential beneficial effect on the deposition of ash on the superheater
surfaces of the boiler. The outcome of the tests confirms the feasibility of
using 7%wt of sawdust in combination with coal without risk to the efficiency
of the unit, its combustion process and with the benefits of emissions
reductions. Furthermore, they show that no modification to the existing coal
transport system and boiler equipment is necessary to achieve this outcome.
Keywords: co-firing, coal, woody biomass, ash, deposits, slagging, NOx emission, SO2 emission