The
new plant shall supply the following blast furnaces,
| No. 2 |
6.000 |
t HM/d |
| No. 4 |
6.000 |
t HM/d |
| No. 1 |
6.000 |
t HM/d |
| No. 6 |
10.000 |
t HM/d |
|
|
|
in the final phase of development,
with 5,616 t/d of pulverised coal.
Each of the three milling
systems has a raw coal storage capacity of 470 tons and produces 80 t/h
of pulverised coal. The pulverised coal is stored in five storage silos
of 550 t capacity each.
Each mill system is connected
via drag chain feeder to the five storage silos. The total storage capacity
(raw coal and pulverised coal) is 4,010 tons and represents 17.1 hours
of blast furnace operation at the maximum pulverised coal injection rate.
The above ensures a high
availability of the total system.
The four members of
the consortium are responsible for the following:
* VAI, Linz, Austria:
Civil engineering for building foundations Civil
engineering for buildings and raw material silos
Building site, erection and erection supervision
Consortium leader
* Klöckner Stahitechnik,
Hamburg:
Responsible for the pulverised coal injection
system into the four blast furnaces
* Italimpianti S.P.A.,
Genoa:
Supply of the foundations Supply of the buildings
and raw material silos Supply of high and low
voltage switch-gear Electricals for the entire
project. Electrical cabling for the entire project
Installation of the high and low voltage switch-gear
as well as the electricals
* LOESCHE GmbH, Duesseldorf:
Engineering Delivery of the machinery Milling
process control and control loops Erection
supervision Commissioning Training of the site
personnell for the three mill systems utilising the
largest tc date LOESCHE coal mills, type LM
28.325 D.
Milling system technical
data:
| Number of milling systems |
3 |
| Mill type: |
3 x LOESCHE Roller Mill
LM 28.325 D |
| Capacity (puleverized coal) |
3 x 80 t/h |
| turn-down capacity per system
(100-40%) |
80 t/h, 100%;180.000 m³/h
32 t/h, 70%;126.000 m³/h |
| Product fineness |
20% R; 0,09 mm |
| Raw coal data |
|
| Feed size |
0-50 mm (max. 80 mm) |
| Volatile matter content |
30 % maximum |
| Ash content |
12 % maximum |
| Hardgrove index |
45 °H |
| Surface moisture |
12 % maximum |
| Chloride content |
less than 0,2 % |
| Heat source |
|
| Blast furnace gas |
approx. 3.000 kJ/m³ |
| Natural gas |
approx. 30.000 kJ/m³ |
| Inert gas |
|
| Nitrogen |
N2 |
| Process gas |
CO2, N2, Steam an O2 |
Process data of one mill
system:
| Output capacity |
80 t/h |
| Product fineness |
20%R; 0,09mm |
| Raw coal moisture |
12% |
| Pulverised coal moisture |
less than 1% |
| Gas volume at mill outlet |
180.000 m³/h |
| Temperature at mill outlet |
approx 95 °C |
| Dew point ot mill outlet |
approx 65°C |
| Oxygen content at mill outlet |
9% (wet) |
| Gas volume at mill inlet |
222.700 m³/h |
| Temperature at mill inlet |
approx. 320 °C |
| Dew point at mill inlet |
approx. 56°C |
| Exhaust gas volume |
approx. 75.300 m³/h |
| Exhaust gas temperature |
approx. 106°C |
| Dewpoint temperature of
exhaust gases |
approx. 65 °C |
| Dust content of exhaust
gases |
10 mg/Nm³ |
| Sound level |
85 db (A) 1m |
| Mill Motor |
950 kW |
| Specific power consumption
at mill motor |
11 kWh/t |
| Mill fan motor |
950 kW |
Scope of LOESCHE equipment
supply
| 3x1 |
Raw coal feed ststem |
|
|
Drag chain feeder and associated
auxiliary equipment, capacity 100 t/h |
|
| 3x1 |
LOESCHE Roller Mill |
|
|
Type LM 28.325D |
|
|
Bevel gear gearbox |
950 kW |
|
Static integral mill separator |
|
| 3x1 |
Fabric filter |
|
|
Pulse Jet Filter |
|
|
Gas volume |
186.000 m³/h |
|
Temperature |
94-120 °C |
|
Filter exit gas content |
10 mg/m³ (dry) |
| 3x1 |
Mill fan |
|
|
Gas volume |
205.000 m³/h |
|
Temperature |
94-120 °C |
|
Mill fan motor |
P=950 kW |
| 3x1 |
Pulverised coal transport
system |
|
| 3x1 |
Hot gas producer |
|
|
with a heat generating capacity
of |
30 x 10^6 kJ/h |
|
heating source |
bf gas approx 3.000 kJ/m³ |
| 3x1 |
Mill system duct work |
|
|
with dampers and slides |
|
| 3x1 |
Gas analysis system |
|
|
for N2 and CO measurement |
|
| 3x1 |
N2-Inertisation /safety
system |
|
| 3x1 |
Hoistung equipment |
|
|
for service function on
mills |
|
| 3x1 |
Necessary motors |
|
|
as well as electricals and
control system |
|
| 3x1 |
Necessary insulation |
|
|
and equipment painting |
|
|
The
low and high voltage switch-gear as well as electrical control and analysis
equipment is to be installed by Italimpianti to LOESCHE-Engineering specifications.
The envisaged commissioning
timetable is as follows:
-
1. Mill system: May 1991
-
2. Mill system: June 1991
-
3. Mill system: July 1991
Description of self inertised
grinding plant
The raw coal is transported
by conveyor belt from the raw coal stockpile to the coal milling system.
The raw coal is distributed to the three raw coal silos which are cledusted
by bag filters.
Raw coal feed control to
the mill is facilitated by a drag chain feeder. The drag chain feeder discharges
into the centrally positioned (through separator) feed pipe.
In the LOESCHE Roller Mill,
raw coal is milled between the rotating grinding table and the rollers,
by the application of pressure to the rollers. The grinding table is driven
through a three-stage gearbox, where the grinding forces are absorbed by
a segmented thrust bearing. In the absence of a material bed on the grinding
table, contact between grinding table and rollers is avoided by accurately
positioned buffers. The grinding forces to the rollers are generated by
a hydropneumatic spring system. The grinding pressure is, within operating
limits, infinitely variable, even during mill operation. The milled material
is thrown outwards as a result of the grinding table rotation, where it
is dried and classified by the gas flow through the louvre ring. The pulverised
coal/gas mixture leaves the mill via the static separator.
The mill is equipped with
a sealed reject box for removal of foreign objects in the coal, such as
tramp iron, bricks, steel wire etc..
A bag filter with a precollecting
system and high pressure bag cleaning is employed for recovery of the pulverised
coal from the mill gas stream. These modern filters are devoid of coal
dust deposition areas and are therefore safe from smouldering coal fires.
The filter is of a welded, sealed construction. The filter bags are cleaned
cyclically by high pressure N 2 gas jets. This ensures that a consistent
quantity and fineness of pulverised coal is transported via rotary valve,
by the drag chain feeder to the fine coal storage.
The mill fan delivers the
required gas volume of approximately 186,000 m³/h for the mill system.
The volume of gas is damper controlled.
The drying of the coal employs
hot gases of up to
350 °C. To ensure that
the temperature before filter exceeds 105 °C, a portion of the process
gas is heated. The hot gas producer combustion chamber has a refractory
lined muffle in which the flame achieves complete burn-out.
A portion of the gas stream,
consisting of combustion gas, in-leak and water vapour from drying, needs
to be diverted from the mill system. A control damper after the mill fan
facilitates this function.
The pulverised coal from
the fabric filter is transported via rotary valve and drag chain feeder
to the pulverised coal storage. Each silo has a live volume of 1,200 m³.
Measurement of CO at the top of the silos, and temperature measurements
ensure a hazard free operation. N 2 gas is employed for inertisation of
the silos.
The mill system is operated
as a self-inertised system by virtue of the process gases used. For start-up
of the mill system, N2 flooding is employed as the initial inert atmosphere.
The mill system warm-up
procedures commence when the 0,2 content (wet) reaches 8 %.
During normal operation,
the inert atmosphere is derived from:
* hot-gas producer combustion
gases required for
drying
* water vapour liberated
during the drying /
milling process
* N2 originating from the
fabric filter cleaning system.
During heated, non-production
periods, N2 is available for system inertisation.
The above holds also for
the shutdown of the mill system.
Technical data of entire
system
| Blast furnaces |
|
2
|
4
|
1
|
5
|
| Blast furnace output (hot
metal) |
t/d
|
6.000
|
6.000
|
6.000
|
10.000
|
| Furnace diameter |
m
|
10,3
|
10,6
|
10,6
|
14,4
|
| No. of injection points |
pcs.
|
25
|
27
|
27
|
36
|
| Injection rate |
t/h
|
50
|
50
|
50
|
84
|
Total injection rate: t/h 234
Raw coal silo
Silo capacity:
-
(moist coal): 3 x 470 t
-
(dry coal): 1,260 t
Pulverised coal storage
Silo capacity: 5 x 550 t
= 2,750 t
Total capacity (pulverised
coal): 4,010 t
Operation time at full injection
rate 200 kg/t HM: 17.1 h
Mill system
| Mill type |
Vertical Roller Mill |
| Supplier |
LOESCHE |
| Mill size |
LM 28.325D |
| Grinding Table diameter |
2.800 mm |
| Number of rollers |
3 |
| Number of mills |
3 |
| Capacity |
3 x 80 t/h |
| Product fineness |
20% R; 0,09 mm |
| Fine coal moisture |
less than 1,0 % |
| Mill motor |
950 kW |
| Mill fan motor |
950 kW |
Injection system
| Supplier |
Kloeckner Stahltechnik GmbH |
| Pulverised coal storage
silo |
5 x 1.200 m³ (550t) |
| Pressure vessel |
2 per blast furnace |
| Number of blast furnaces |
4 |
| N2 consumption at full injection
rate |
14.180 Nm³/h |
| N2 presure |
20 bar |
|
