ACARP Project Number: C3091
Ashley Conroy, Philip Bennett
This project examines the ability of CQIM
(version 1.2) to predict the performance of Australian coals in
some of the many processes that occur in a modern coal-fired power
station. The continued growth in the world thermal coal market is
resulting in greater diversity in thermal coal suppliers. The
operators of coal-fired power stations are looking at computer
software to assist in the evaluation of the impact of coal
properties on the operating and maintenance costs.
One such computer software is EPRI's Coal Quality
Impact Model (CQIM) developed by Black & Veatch. CQIM is a
computer model designed to facilitate the prediction of performance
and cost impacts of firing alternative coals at an existing or
proposed power generating station. This project examines the
ability of CQIM (version 1.2) to predict the performance of
Australian coals in some of the many processes that occur in a
modern coal-fired power station. The processes examined in this
project were limited to ones where full or pilot scale data was
available for comparison.
The processes that were examined in this project
maintenance and availability of milling and ash handling plant
The full scale data used in this evaluation was
supplied by Pacific Power, and pertained to equipment at Eraring
Eraring Power Station operates four 660 MW IHI
designed generating units. These units are single furnace,
twin-drum type using natural circulation with a divided back pass
and balanced draught. Each unit is fed by seven tube mills.
The pilot scale data was taken from the testing
of 38 coals in ACIRL's 150kW pilot scale boiler simulation furnace.
Eleven of the coals were blends.
The adjustment, based on one coal's performance,
of the mill performance curves used by CQIM is a satisfactory
approach to predict mill capacity for the coals being evaluated.
CQIM does not attempt to predict the size distribution of the coal
or mineral matter.
To determine the combustion performance of a
coal, CQIM allows the user to select either a simple model or
The simple unburned carbon model is based on
empirical correlations. The detailed unburned carbon model uses
estimates of the char kinetic parameters with a detailed
determination of the time temperature history of the particle to
estimate the unburned carbon loss.
CQIM's simple unburned carbon model gives a good
estimate of the carbon burnout for a wide range of coals as shown
by the comparison with pilot scale data. The detailed burnout model
suffers from instability problems which could reduce its
The use of indices, determined from the bulk ash
properties, to predict slagging and fouling characteristics of a
coal does not fully account for the impact of individual minerals
or the influence of fluid dynamics. CQIM failed to predict the
reduced heat absorption by the waterwall that was recorded during
one of the tests at Eraring. This was due to the coal's unusually
low ash absorptivity.
The power of CQIM is its ability to relate coal
quality to fuel costs, maintenance costs and the availability of a
This ability of CQIM to model the large number of
interacting processes that occur within a power station depends on
the use of correlations relating these processes to coal
CQIM reduces the possible errors in using
empirical correlations by using the known performance of one coal
to calibrate its predictions for other coals fired in the same
This means the user has to be careful about the
choice of the calibration coal, ensuring that this calibration coal
is similar to the other coals that are to be evaluated, the
completeness of its performance data.
With the improvements that are planned for future
versions of CQIM, it is likely that its use by power station
operators to evaluate potential coal supplies will increase.
Australian producers should continue to evaluate future versions of