Hitachi Power Europe Service is an independent
subsidiary of Hitachi Group and bundles the service
activities of Hitachi Power Europe GmbH.
Mills and Components
Hitachi Power Europe Service GmbH
2
About Hitachi Power Europe Service
Hitachi Power Europe Service GmbH (HPES), with about 300 employees, is an inter nationally
active company in the field of power generation, steam generator construction, as well as
for environmental technologies and firing equipment. The companys head office is located
in Duisburg (Germany), with the departments of engineering, boiler and firing technology,
mills and components, erection and commissioning and flue gas cleaning. In addition,
Hitachi Power Europe Service GmbH operates a centre of excellence for surface engineering
(cladding) with a cooperation partner.
With service centres throughout Germany and branches in Europe, Middle East and Asia,
Hitachi Power Europe Service GmbH operates as closely to its customers as possible, provid-
ing its products and specialist skills.
Contents
Components in Typical Coal Power Plants 3
Mill Feeders 4
Pulverisers 6
Burn-Out Grate 13
Ash Removal 14
Other Ash Removal Components 15
Bevel Planetary Gear 16
Replacement Parts Service 17
References 18
HiTACHi POwER EuROPE SERviCE GMBH Head office in Duisburg, Germany German locations International locations
Mills and Components 3
Components in Typical Coal Power Plants
Lignite
Bituminous coal
A Steam generator
B Steam lines
C Coal bunker
D Mill feeder
E Coal mill
F Burn-out grate
G Ash removal
H FD fan
a
A Steam generator
B Steam lines
C Coal bunker
D Mill feeder
E Coal mill
F Ash removal
G PA fan
H FD fan
a
4
Mill Feeders
Reliability even under demanding requirements
Designed as coal bunker dischargers, the mill feeders supply the pulverisers with raw coal
evenly dosed and in keeping with boiler load requirements.
Even when faced with demanding requirements, the mill feeders designed by HPES operate
both reliably and safely.
Experienced HPES staff determine the optimum feeder in keeping with the requested
fuel quantity, design directives (including DIN EN 12952-9, NFPA 85 F) and customer
requirements (for instance, volumetric and gravimetric metering).
Other selection factors are the various bulk material properties, such as coal flow and erosion
behaviour.
Gravimetric coal feeder
Mills and Components 5
In hard coal boiler units, gravimetric coal feeders are used to discharge the raw coal from
the bunker. In lignite plants, drag-chain conveyors together with belt conveyors are used
to discharge the raw coal from the bunker.
Gravimetric coal feeders
The gravimetric coal feeders with corrugated edge belt ensures high outputs, uniform bunker
discharge and continuous mill charging even at low conveying rates. This design permits volu-
metric / gravimetric metering and quantities conveyed of up to 180 t / h. During normal operation
no conveyed material can fall to the bottom of the feeder due to the design of the corrugated edge
belt. Nevertheless a cleaning device is installed in the bottom section of the feeder to guarantee
the removal of dust deposit. The belt speed is determined by the quantity conveyed. Purge air is
supplied to the housing to stop condensate forming and, in turn, to stop corrosion.
Drag-chain conveyor
Drag-chain conveyors are meant for limited conveyed quantities of up to approx. 40 t / h this
can, in special cases, be raised to 120 t / h. The fuel is discharged opposite to the direction
of conveying. The drag-chain conveyor principle allows both a compact design with minimum
spacing between bunker discharge and conveyor dumping as well as a possible large spacing
between material charging and dumping.
DB
E
A
A
D
B
C
A Discharge of coal from the bunker
B Conveyance of coal
C Bed depth limitation
D Conveyance of coal
E Discharge to the mill
A Discharge of coal from the bunker
B Conveyance of coal
C Bed depth limitation
D Weighing of coal
E Discharge to the mill
6
Pulverisers for Bituminous Coal
Excellent results
In the mills, the raw coal is simultaneously pulverised, dried and evenly distributed to the
coal burners. Hot air or flue gases transfer the pulverised fuel to the burner and reduce the
moisture in the coal.
Bowl & roller mill type MPS
The MPS bowl & roller mill by Hitachi Power Europe Service grinds and dries hard coals and
difficult-to-grind lignite with a low moisture content to pulverised fuel and distributes them
evenly directly to the burners.
Mills of various sizes for throughputs ranging from 10 t/h to 200 t/h can be supplied. Constant
refinements and improvements have led to excellent crushing results with high fineness
grades from raw coal found throughout the world. The positive operating properties and low
energy requirements have contributed in no small measure to the success of these mills.
MPS mill
Mills and Components 7
The performance of vertical spindle mills depends on the geometric dimensions, revolution
speed of the grinding table and the grinding force itself.
By suitable measures at existing plants capacity increase and adaption of the load change
behavior are possible. For example for changed coal characteristics.
As a prerequisite for these mill upgrades, it needs to be ensured that sufficient primary air is
available and that the mill primary air pressure as well as the mill drive power have the required
margins. This necessitates also investigating the mill motor, PA fans and pf-piping in detail.
Implementation of the above measures for variable adjustment of dust fineness during op-
eration, by use of dynamic classifier (type SLS), also secures higher flexibility during load
changes and a temporary increase of pulverised fuel outlet capacity.
MPS Mill
U.S. Standard Sieve
Particle Size in m
V6
Pass
ing
(%)
Resi
due
R (%
)
400
63 90 20050 70 150 300 70050030
270 200 100 70 50 30
50
40
30
20
10
1.0
0.1
0.01
60
50.00
60.00
70.00
80.00
90.00
99.00
99.90
99.99
40.00140
V3 V1 V5
0 rpm
110
rpm
100
rpm
85 rp
m
SLS classifier
A Rotary classifier
B Classifier drive
C Grinding rollers
D Hydro-pneumatic system
E Grinding table
F Gear
G Motor
a
8
Pulverisers for Bituminous Coal
Long service life
Tube ball mill type RKD
The Hitachi Power Europe Service RKD tube ball mill grinds and dries difficult-to-pulverise
hard coals (particularly low-volatile coals such as lean coal and anthracite). This mill type
can deal with approx. 150 t / h of coal. Depending on size and space, the tube ball mill
can be designed with drum or neck bearing and be of the single or double pass type.
A Rotary classifier
B Oversize return
C Neck bearing
D Drive gear rim
E Grinding ball filling
F Feed spiral conveyor
G Classifier riser
RKD mill
a
Mills and Components 9
Maintenance of tube ball mill
The maintenance work at tube ball mills includes activities which are carried out while the
mill is in operation and work which requires shutdown of the mill.
Maintenance work during mill outage
Inlet screw conveyors
Inside lining of the inlet and outlet housing
Grinding space armoring
Air sealings
installation of wear plates
Replacement of screw spirals
10
Low energy requirements
Pulverising lignite is particularly challenging in view of its high moisture content and the
considerable throughputs involved.
Distributor fan beater mill type DGS
HPES supplies DGS mills of various sizes up to a 240 t / h throughput for drying and pulver-
ising raw lignite coals.
DGS technology involves the raw coal and flue gases being initially put through the pre-
crushing beater section of the beater wheel. This ensures excellent air and coal dust distribu-
tion into the beater wheel. Crushing in
the DGS mill is usually so intensive
that adequate grinding fineness can be
obtained in one working operation
without the need for an additional clas-
sifier. This both raises the pressure
balance and cuts back on energy re-
quirements. The DGS mill has stood
the test of time particularly with
difficult-to-work lignites something
that explains its considerable lifetime
and unrivalled properties.
a
Pulverisers for Lignite
A Flue gas gate valve
B Inlet housing
C Beater shaft
D Beater wheel
E Coupling
F Motor
G Bearing
DGS mill
Mills and Components 11
Easy maintenance
Wet fan mill type NV
The NV mills ranging from 10 t/h to 140 t/h throu ghputs are for crushing high moisture
co
