Loesche Energy Systems Ltd was contracted by an American Utility to supply a new dynamic classifier as a retrofit for the existing static classifier on a pulverizer of a Plant. This Plant is a coal-fired power station owned and operated by an American Utility in Kentucky. The Unit generates 800MWe net and was constructed in 1969. First Published on www.greenbankenergy.com

1. Increased Pulverizer Performance with
Loesche’s High Efficiency Dynamic Classifier
S. Mutzenich
P. Garnham
Loesche Energy Systems Ltd.
Washington, Pennsylvania, USA
1 Introduction
Loesche Energy Systems Ltd was contracted by an
American Utility to supply a new dynamic classifier
as a retrofit for the existing static classifier on a
pulverizer of a Plant. This Plant is a coal-fired
power station owned and operated by an
American Utility in Kentucky. The Unit generates
800MWe net and was constructed in 1969.
The existing pulverizer is a Foster-Wheeler MBF
design which was later converted with B&W MPS-
89 internals. The new dynamic classifier was
supplied to Plant in August 2012 and was installed
and commissioned in the September outage with
final hot commissioning completed at the end of
2012.
The objective of retrofitting the Loesche dynamic
classifier to their MPS pulverizer was to improve
the pulverizer performance, coal throughput (by
15%) and pulverized fuel fineness whilst
maintaining operating levels.
1.1 Classifier functional description
The Loesche LSKS classifier is an air-flow classifier.
An upwardly flowing and rotating air-fuel mixture,
generated by the pulverizer and contained by the
classifier housing, enters the classifier in the zone
of the static guide vanes. These redirect the air-
fuel mixture into a tangential flow toward the
rotor. In the gap between the static guide vanes
and the spinning rotor the particles are subjected
to various forces (Figure 1).
Based on the particle’s mass, velocity and the
balance of the forces acting upon them, they
either do not pass through the rotor and return
through the grit cone to the pulverizer for further
grinding, or pass through the rotor and are carried
up in the air flow and out of the classifier to the
burners on the boiler. The size of particles passing
the rotor is related to its speed, whereby a lower
rotor speed gives a coarser pulverized fuel but
greater throughput, and a higher rotor speed gives
a finer pulverized fuel with a lower throughput.
Figure 1: Loesche LSKS High Performance Dynamic Classifier
2 Removal of existing classifier
During the fall outage of 2012 the installation /
removal began on Pulverizer 21. All the coal
piping, shutoff gates and walkways on top of the
pulverizer had to be removed to clear the top area

2. and the classifier reject chute was cut loose from
the inside. The existing seal air piping for the roll
wheels were removed to later be reinstalled going
thru the new classifier housing.
Once these items were removed, the top flange of
the classifier housing was all that needed to be
unbolted to remove the housing and classifier
assembly as a whole (Figure 2). Once removed
the reject chute was lifted up thru the top opening
of the pulverizer.
Figure 2: Removal of static classifier
No other internal parts had to be removed and
the large maintenance doors stayed closed on the
pulverizer. For safety reasons, the spring tension
was released for fear of not knowing what forces
could be on a 40 year old housing after removing
the top section. The yoke seal air piping on the
pulverizer next to this one had to be removed to
allow for room to lower the old classifier and
housing to the ground. There were only a few
inches on each side between the two pulverizers
when setting the old static classifier on the floor
(Figure 3).
During the outage no rebuilding or changes were
carried out on the pulverizer ensuring that all
improvements in performance could be tied to the
classifier retrofit.
Figure 3: Static on the ground between pulverizers
3 Installation of Loesche Dynamic
Classifier
The new classifier was made in two sections
(Figure 4 and Figure 5). This helped with the
installation since the overall height of the new
classifier was taller. The lower housing section
included the classifier lower cone which hung
below the flange line. This required this section to
be raised high to clear the housing on the
pulverizer. Loesche accounted for these issues in
the design and engineering and installed lifting
lugs such that the new lifting beams worked on
the two new sections.

3. Figure 4: Dynamic Classifier section 1: grit cone lifted
The classifier fit perfectly (Figure 6). No classifier
modifications were needed. Loesche performed a
laser survey of the area prior to the project and
used it in the design all of the equipment.
However, there were still some modifications
necessary.
Figure 5: Dynamic Classifier section 2: Rotor assembly
Loesche provided quick assistance on correcting
these and any other problems or issues that would
arise. Loesche had an engineer on site to help
oversee the installation, startup and testing during
the project. They provided guidance, answered
questions and found solutions to any issue.
To assess the improvements gained from
retrofitting a Loesche dynamic classifier fineness
samples/readings of the pulverized fuel were
taken before and after the conversion. Pre-
conversion testing of the pulverizer and static
classifier was carried out in August 2012 and post-
conversion testing of the pulverizer and dynamic
classifier was carried out in January 2013.
During the outage no rebuilding or changes were
carried out on the pulverizer ensuring that all
improvements in performance could be tied to the
classifier retrofit.
Figure 6: Loesche Dynamic Classifier installed
4 Test Procedure
The measurements/sampling carried out for the
tests was undertaken by the utility with
representatives from Loesche in attendance for
witnessing. The tests were carried out in

4. accordance with the Plant project specific test
procedure.
4.1 Pre-conversion testing
Both the pre-conversion and post-conversion tests
were set to be carried out in the same manner
using the EUcoalsizer equipment so that an easy
comparison could be made between the two
tests.
However due to an issue with the sample ports
the pre-conversion tests were carried out using
the standard power station method of sampling
with an ASME probe in accordance with the
relevant utility test procedures.
Extensive testing by the utility and independent
parties indicates that the EUcoalsizer is a reliable
and accurate method of recording fineness
results. The conclusion indicated any deviations in
test results taken using the EUcoalsizer compared
to the ASME probe are considered to be relatively
small.
The pre-conversion tests were carried out on the
27th August 2012. An ASME probe was used to
take PF samples at the maximum pulverizer
throughput (87,000 lb./hr.) which was limited by
the dribbling of coal off the pulverizer table. PF
samples were taken from the pulverizer’s six
outlets and sent to the utility laboratories for
sieving.
Raw coal samples were also taken at the feeder
during the PF sampling tests and sent to the utility
laboratories for proximate and HGI analysis.
4.2 Post-conversion testing
The post-conversion tests were carried out over
two days (22nd January 2013 and 23rd January
2013). The EUcoalsizer equipment was used to
determine PF fineness in situ. Data is obtained
during the test without the requirement of a
sample being physically removed from the pipe.
The pipes sampled were situated at the corners of
boiler and were designated as A and F (as shown
in Figure 7).
Each pipe had two sample ports and fineness was
measured using the EUcoalsizer at 4 locations per
port (as shown in Figure 8).
Figure 7: Pulverizer and Pipe configuration
The post-conversion tests were performed at
various pulverizer throughputs and classifier
speeds to establish the improved pulverizer
operating envelope by retrofitting a Loesche
dynamic classifier. The objective of these tests
was to evaluate any improvement offered by this
retrofit regarding the maximum coal throughput
at similar or better fineness levels along with
establishing an improvement in pulverizer
fineness available at the same throughput as the
pre-conversion test.
Figure 8: EUcoalsizer sampling locations

5. 5 Results
5.1 Pre-conversion results
The sampling was carried out on the 27th August
using an ASME probe to take samples from the six
PF pipe outlets. The wear life of the pulverizer was
approximately 4,200 hours. The coal flow during
testing was 87,000lb/hr as this was the maximum
that could be achieved without the pulverizer
starting to dribble. The plant readings taken
during the tests are shown in Table 1.
Plant (Imperial) Metric
Pulverizer amps 86A
PA diff 2.24 IWC 5.6mbar
Pulverizer diff 19.38 IWC 48.3mbar
Coal flow 87,000lb/hr 39.5t/h
Outlet temp 170o
F 77o
C
Inlet temp 377o
F 192o
C
Table 1: Pre-conversion plant readings (averages across test)
Moisture 2.65%
Dry Ash 10.4%
Dry BTU 13,212BTU
Dry Sulphur 1.01%
HGI 42
Table 2: Pre-conversion test coal properties
Sieving and coal analysis was done in the utility
laboratory. The coal analysis is shown in Table 2
and the fineness results are shown in Table 3 and
Figure 9.
200 mesh 100 mesh 50 mesh
50.8% 86.5% 99.35%
Table 3: Pre-Conversion fineness results
Figure 9: Rosin Rammler Chart - Pre-Conversion results
5.2 Post-conversion testing
Over the two days of sampling nine complete tests
were undertaken.
During testing plant readings and measurements
were recorded in three separate manners.
1. PI Data – Readings for PA differential,
pulverizer differential, coal flow,
pulverizer outlet temperature and
pulverizer inlet temperature.
2. Manual readings – Readings for Pulverizer
motor Amps, Classifier rpm, Seal air
differential, coal flow, upper bearing
temperature, lower bearing temperature
and classifier motor winding temperature.
3. EUcoalsizer measurements – Readings for
PF fineness and pipe velocities.
Seven tests were undertaken at different loads
and classifier speeds. Fineness improvement
shown from Test 3 is shown in comparison to the
pre-conversion test in the Rosin Rammler chart
shown in Figure 10.
Figure 10: Rosin Rammler Chart - Test 3 compared against
Pre-conversion test
6 Technical Review
6.1 Increased Pulverizer
Performance - Throughput
For a proper analysis of the results found from the
seven tests it is necessary to compare from the
same basis. For this we must use the correction
curves from the pulverizer OEM and our
experience from other similar pulverizers. The
OEM pulverizer correction curves were received

6. and have been applied to give an approximate
relationship of HGI, 200 mesh fineness and total
moisture versus pulverizer throughput.
An example of using the correction curves is
shown below and is based on the pre-conversion
and Test 1 results in Table 4.
Table 4: Pre-conversion and Test 1 results for correction
example
All seven post-conversion tests have been
corrected using the method stated and are
summarized in Table 6.
Test 3 achieved the highest coal throughput while
still maintaining the fineness at both the 200 mesh
and 50 mesh levels. Using the correction curves
the Loesche dynamic classifier has improved
pulverizer performance throughput by 19.3% over
the original static classifier.
6.2 Specific power
Pulverizer motor amperage was recorded during
tests and then power was calculated using an
assumed motor efficiency of 90% and a power
factor of 85% so that comparisons between the
different tests could be made. The power
calculations in Table 5 show an increase in power
consumption across most of the tests. However
these power calculations are viewed only in
relation to the coal flow itself. Table 5 shows the
power consumption figures in the form of specific
power consumption (however this is still
uncorrected for any changes in HGI and fineness
to the baseline test).
Table 5: Uncorrected specific power
Table 7 shows the coal flow corrected for fineness
and HGI against the pre-conversion test and then
the associated specific power per test. This shows
that the dynamic classifier is consistently reducing
the specific power consumption of the pulverizer
in the order of about a 10% savings in power per
Tonne (or Ton) of coal.
Table 6: Post-conversion corrected throughput results
Table 7: Specific power corrected for HGI and Fineness

7. 7 Conclusion
The retrofit of a Loesche dynamic classifier onto
Pulverizer #1 Unit 2 has successfully:
• Increased the throughput of the pulverizer
by 19.3%
• Eliminated the pulverizer reject/dribbling
issues
• Reduced the specific power consumption
of the pulverizer by over 10%
The ability to vary the speed of the classifier also
gives good flexibility in the operation of the
pulverizer by allowing increasing throughput or
fineness depending on the requirements of the
plant. Figure 11 shows operational flexibility of
the pulverizer by changing the classifier RPM and
its impact on performance on either throughput
or fineness (based on the test results). This
flexibility also allows the operators to react to
changes in the coal diet.
The retrofit of a complete boiler unit’s worth of
Loesche dynamic classifiers will afford the utility
full benefit of pulverizer optimization and
conceivably allow a return to an N+1 basis (spare
pulverizer).
8 Discussion
The differential pressure across the pulverizer can
have a major effect on the performance of the
pulverizer in terms of throughput and fineness.
Pressure drop across the pulverizer is influenced
by the physical layout of the pulverizer mainly due
velocities and the efficiency with which the
classifier sorts fine/coarse particles. As an
approximate guide the pressure drop is affected
equally by the physical layout and classification
efficiency.
The Loesche Dynamic Classifier has been designed
to decrease the physical layout pressure drop by
lowering velocities at the classifier inlet and up
into the PF outlets. The rotating classification
process used by Loesche also provides a higher
efficiency of classification which decreases the
burden on the pulverizer by reducing the
regrinding of fine particles and recirculation of PF
particles. It is this decrease in recirculation of PF
particles that contributes most to pressure drop
decrease as less pneumatic lifting energy is
needed. For an air limited pulverizer or one prone
to dribbling this added benefit can greatly improve
maximum throughput capabilities.
Figure 11: Pulverizer Operational Benefits
Dynamic Classifier
operational boundary
(limited by pressure drop,
mill plugging, mill amps or
rejects, etc)
Fineness
Increase from
DC (eg 75%)
Static
Classifier
(eg 70%)
UBC (& possible
Nox, Flyash and
SCR) benefits
Load Impact Savings
Possible spare mill
Decreased mill motor power
consumption
Decreased wear on grinding
elements
100%
Mill MCR
15% Throughput
Increase form DC
200mesh (75um)
fineness
Mill
Throughput
Loesche Dynamic Classifier - Operational Benefits

8. Loesche Energy Systems Ltd.
2 Horsham gates
North Street
Horsham, RH 13 5PJ, United Kingdom
Phone +44 1403 223 101
Fax +44 1403 223 102
Email loesche@loesche.co.uk