moving to ensure billets to be discharged stops at the right position for the extractor to discharge.
The upward and downward travel stroke of the walking beam is 200mm and its horizontal
travel stroke is 500mm. the minimum period of motion of the walking beam mechanism is 50
seconds.
In normal operation, the walking beam settles at the lowest and full back position.
2.3 Discharging
The slabs heated by the furnace shall be discharged as per the requirements of the rolling
pace.
When heated to the required rolling temperature, the billets shall be conveyed to the
discharging end for discharging. If the heat-insulated time of the furnace is very long, it is required
that the walking beam stops at the middle position which is of the same elevation with the fixed
beam (called middle position holding) or stepping in place to protect billets against bending
deformation.
When receiving the discharging signal from the level 2 computer of the rolling mill, the control
system of the reheating furnace will calculate the travel stroke of the supporting arm of the
extractor moves based on the position and dimension of billets settling on the discharging position,
the discharging roller outside the furnace stops rotating, the furnace door for discharging is
opened, the extractor moves from the its lower place into the furnace, stops at the calculation
position and discharge billets, and put billets on the discharging roller table. The discharging roller
table then will be actuated to convey the billets to the rolling mill for rolling. At the same time, the
extractor returns to its initial position for next discharging.
The whole discharging process shall be subject to the monitoring of the high-temperature
industrial television mounted at the furnace end head.
2.4 Interlocking
Timing, sequencing, interlocking and logic control of billets charging, discharging, counting
and material tracing as well as data exchange with the rolling mill shall be achieved with the
automatic control system to realize operation automation and level 2 computer management.
The interlock relationship among the charging and discharging processes and conveyance
inside the furnace is as follows:
--When the charging roller table is in operation, billets are still not to be positioned , the
pusher will not work;
--When there is no Vacant position at the charging end, the pusher will not work;
--When the walking beam is at the upper position or moving upward, the pusher will not work.
--When the pusher is in charging operation, walking beam is at its lower position and can
not work.
--When the billets have not been detected by the laser detector at the discharging end, the
discharging door is closed or half opened, the walking beam is at its upper position, the
extractor can not get unlocked to getting into the furnace.
--When the extractor is in discharging operation, the walking beam is at its lower position
and can not work;
--When the extractor is in discharging operation and the billets are not stable on the rollers,
the discharging roller table cannot work;
3 Furnace Plan Layout and Furnace Structure
3.1 Furnace Plan Layout
The reheating furnace is located between the Bay B-C and C-D, the span length of Bay B-C is
28m, the span length of Bay C-D is 36m, the center line of furnace coincides with the line of
No.7 column.
The detail plan layout sees the attached drawing: plan layout drawing
3.2 Furnace Foundation and Structures
The civil foundation and structures for the slab reheating furnace of India LSIL Steel include:
furnace proper, flue duct, chimney and its foundation, underground hydraulic station,
evaporation cooling building (including underground pump station and overground steam
drum platform), charging pulpit, distribution room, furnace control room, blower house,
equipments foundation, foundation of operating platform, pipe supports and foundation, etc.
All above will be designed by the supplier(According to Chinese national standards) and
constructed by the Buyer(
Including the foundation treatment of above foundation).
a. Furnace proper: depth of the furnace pit is -7.5m, the plash depth of furnace pit is -8.5m
(deepest point). The ventilation ducts are arranged on both sides of furnace pit along the width
of furnace, a layer of RC platform and a layer of steel platform are on the ventilation ducts. On
both sides of furnace pit along the length of furnace respectively lay out: the foundation of
charging roll table (including sluiceway), foundation of pusher and foundation of discharging
roll table (including sluiceway), the foundation of extractor.
b. Foundation of flue duct: the bottom level of flue duct foundation is -5.8m, the inner width
before recuperator is 5.4m, inner width after recuperator is 5m, inner width at recuperator is8.5m.
the requirement of temperature resistance needs to be considered at the foundation of
recuperator, the steel plate is covered on the flue duct. In the passing area of charging roll
table and slab storage area, the load requirement also needs to be considered. The ramming
RC cover plate is selected.
c. Chimney: select the RC chimney, the inner diameter of upper port of chimney is
Φ3000mm,the height is 80m, the bottom level of foundation is about -8.6m.
d. Underground hydraulic station is underground RC ramming structure, bottom level is -7.4m,
length × width × height: 9.000x7.000x6.600,a hole is left to cover the grid plate on the top,
terrazzo floor, the side wall is interconnected with furnace pit.
e. Evaporation cooling platform and water pump room are the RC frame structure, the lower
part is water pump room ( length × width × height: 15.000x5.500x6.600), the bottom level in
the pump room is -7.4m; the upper part is steam drum platform, its top surface elevation is ±
0 m.
f. Blower house: 10.000x8.000x4.500(height), RC ramming frame structure, RC isolated
foundation, terrazzo floor, ramming reinforced concrete roof boarding, RC equipment
foundation, sliding sash window of double-layer aluminium alloy.
g. Charging operation room: 5.000x3.000x4.000 (height), the operation room is made of light
steel structure, antistatic floor, the bottom level is +1.5m.
h. Distribution room: 13.000x4.500x4.500(height), one-storey brick-concrete cabin, bottom
level is +0m, concrete band-shaped foundation, 370 brick wall, terrazzo floor, constructional
column, ring beam, ramming reinforced concrete roof boarding, sliding sash window of
double-layer aluminium alloy.
i. Control room of furnace: 7.000x6.000x4.000 (height), the control room is made of light
steel structure, antistatic floor, the bottom level is +1.5m.
j. Fuel room: the buyer is responsible for the design and construction of this part.
3.3 Furnace Profile Structure
This plan is to build a new walking beam reheating furnace for the medium-wide strip mill ,
which adopts preheated-air combustion technology and evaporation cooling with forced
circulation.
As the fuel of the first phase is heavy oil and one year later is coke oven gas, the profile curve
of the furnace and burner, even burner arrangement should be compatible to the fuel features.
Reasonable furnace profile should be adopted to ensure slab heating quality and production
continuity, reducing inspecting, repairing and maintaining time.
This design will adopt firing for 4 sections i.e. No.1 and 2 heating section, top and bottom
soaking section. And No.1 and 2 heating section will adopt the completely side firing with
oil-gas dual fuel burners, the bottom soaking section will still adopt side firing with oil-gas dual
fuel burners. And the top soaking section will adopt end firing (arrange oil-gas dual fuel
burners along the width of furnace), so that ensure a good temperature uniformity within the
width of furnace, the simple furnace profile and good operation condition.
The height of upper hearth of heating and soaking section is 1800mm, that of preheating
section is 900mm, height of bottom hearth for all sections is 2200mm.
According to the plan layout of the furnace, the reheating furnace adopts upper flue
discharging method at the end of the furnace tail.
The furnace will adopt end charging and discharging.
3.4 Major Dimensions of Reheating Furnace
Distance between Center Lines of charging and discharging roller table ----------- 40000mm
Effective length of reheating furnace------------------------------------------------------------ 34600mm
Width of masonry of reheating furnace---------------------------------------------------------- 12864mm
Inner width of reheating furnace ------------------------------------------------------------------11800mm
Elevation of top surface of charging roller table ---------------------------------------------- +900mm
Elevation of top surface of discharging roller table---------------------------------------- +900mm
Depth of furnace pit ----------------------------------------------------------------------------- -7500mm
4 Technical Specifications of Equipment and Facilities of The Reheating Furnace
4.1 Steel Structure of The Furnace Body
The steel structure of the furnace body is a weldment made of plain carbon steel plate and a
variety of steels, and it is used to install and support the refractory material of the furnace, to
support the bottom beam of the furnace, to install the burners, furnace door and accessories
on both sides of the furnace, equipments and pipes of combustion system, and to install
maintenance platform of meter automation etc..
The steel structure of the furnace body contains the steel structure of the hearth, the steel
structure of the side wall, the steel structure of the end wall, the steel structure of the furnace
roof. All these parts form a box frame structure.
4.1.1
Steel structure of the hearth
The bottom steel structure consists of three parts: the bottom frame and steel plate, bottom
longitudinal girder and steel columns. The bottom frame of the furnace is formed with I beam,
channel steel and steel plate by welding, and it's used to support the masonry materials on the
bottom of the furnace and install fixed column. There are also openings for the movable
columns and seal case for fixing and sealing the furnace.
The bottom steel longitudinal girder runs through the overall furnace length of the hearth to
support the bottom frame.
The column is made of H-section steel and steel plate, its function is to support the bottom
longitudinal girder.
4.1.2
Steel structure of the side wall
The steel structure of the side wall is a frame structure which is welded with I beam, channel
steel and steel plate. The lower part of it is fixed by bolts in the bottom steel structure of the
furnace, and the top is connected with channel steel gird beam to form a rectangle frame.
The accessories of the furnace, such as burner of the furnace, side furnace door, access door,
industrial TV, laser detector and peephole, are all fixed on the steel structure of the furnace
wall.
4.1.3
Steel structure of the end wall
The steel structure of the end wall is welded with I-section steel, channel steel and steel plate.
The lower part of it is fixed by bolts in the bottom steel frame. The charging and discharging door
and its driving device are installed on the head end of the steel structure.
4.1.4
Steel structure of the furnace roof
The main part of the steel structure of the furnace roof is the cross beam which is made of
hot-rolled H-section steel. The hanging beam of furnace roof anchor brick hangs on the lower
flange of the H-section steel, and the two ends of the cross beam of the H-section steel stand
on the ring beam of upper steel structure (the steel structure of the side wall). To maintain the
integral stability of the H-section steel, a certain amount of reinforcements between the top
and lower flanges are configured.
4.1.5
Platforms, stairs, railings
Movable steel plate platforms on both sides of furnace
Concrete platforms leading to the hearth on both sides of furnace.
Steel plate walkways leading to the control valves and burners in each section.
Stairs at the connection of diversed platforms and walkways
Railings on the margin of platform and walkway
Fully consider the multiple factors, such as appearance, safety operation.
4.2 Masonry Structure of Reheating Furnace
The properties of the reheating furnace depend to a great extent on the selection of
refractories and its use condition;
The furnace wall adopts integral pouring construction with complex lining;
The furnace roof adopts integral pouring composite with castables;
The hearth adopts mold brick composite laying;
All the designs ensure that the average temperature of the external surface of the
furnace roof except for burner area is no higher than 120ºC and the temperature of
the external surface of the side wall is no higher than 105ºC;
The holes on the bottom of the furnace, which supporting beam and walking beam
go through, are constructed with castables.
The structural design and material selection for the furnace body (except for special
positions such as water pipe packing at the bottom of the furnace) shall secure the
overall service life of the furnace body not less than eight years.
Refractories selection for various parts of reheating furnace:
The contact surface temperature between top surface of 100mm-high Co40 pad and billet
can reach up to 1100ºC,which is close to the discharging temperature. So the effect of the
"water pipe black mark" is less.
The structure of pad adopts optimal type and quantity to minimize the pressed mark of pad,
so that accommodate the requirement for the slab heating.
The fixed beams in soaking, heating and preheating zone adopt staggered arrangement to
avoid the "skid mark" effectively.
To ensure the heat exchange between skids and pads and increase the service life of pads
effectively, the directly welded structure will be adopted for the pads and skids.
4.4 Water seal trough and scale removal system
The walking beam post runs through the furnace bottom, and is fixed on the transfer frame. In
order to seal the holes on the movable post and the furnace bottom, a water seal trough is set at
the lower part of the walking beam and is fixed on the transfer frame.
Part of the small amount of scale produced by heating the slabs in the furnace enter into the water
seal trough through the opening of the furnace bottom, be delivered to the charging end by the
scraper fixed on the bottom steel structure with the movement of the walking beams, be collected
into the pit slag hopper, and then craned away by the crane through the hoisting hole. The post of
the walking beam goes through the bottom of the furnace and fixed on the transfer frame.
Long-round hole was opened in the bottom according to the translation distance of the walking
beam. In order to prevent the cold air from being sucked in the furnace, the water seal trough was
designed between the steel structure in the bottom and the translation frame, apron-type water
seal blade is also designed between them to insert into the water seal trough to seal.
As the post tube goes through around the opening of furnace bottom, an enclosure wall above the
furnace bottom shall be rammed with the castable to prevent furnace slag from dropping into the
water seal trough. Since a small amount of scale drops into the water seal trough, a scraper is
mounted under the apron water seal blade, in this way the scale will be automatically scraped to
the charging end of the furnace tail in the lifting and moving process of the walking beam. The
water seal trough and the scraper at the furnace tail end are lifting gradually, which may get the
scraped scale dried and scraped into the slag chute at the furnace tail end and slag be carried
away periodically.
The water seal trough and the scraping plate shall be made of the steel plate, and the internal
surface of the trough shall be painted with phenolic resin.
4.5 Furnace Door and The Observation Hole
4.5.1
Charging door
The charging furnace door adopts the welded structure of profile steel and steel plate, with
two furnace doors, which can be operated synchronously or respectively. They adopt
non-water cooling, integral casting structure. The furnace door on left and right side are
equipped with a hydraulic lifting device individually.
4.5.2
Discharging door
The furnace width direction is formed of two furnace doors (left and right) which can be
operated synchronously or respectively with each furnace door has a water-cooling system,
constructed from welded profile steel and steel plate, with the inner lining castable. Each
furnace door is equipped with a hydraulic lifting device.
4.5.3
Sight hole
There are six sight holes set on the side wall of the reheating furnace for observing conditions
in the furnace and burner flame, mounted on the level of fixed beam with a shelter plate and a
high temperature glass observation hole.
4.5.4
Access door
There are four access door set on the side wall of the reheating furnace for passing in and out
of the materials during the maintenance, and is convenient for the test and laying the
temporary dry-out pipe during drying out. The access door is sealed by loose face masonry
with refractories, and a steel plate door is mounted outside.
4.6 Combustion System of Reheating Furnace
The reheating furnace will use the heavy oil in phase 1 (within 1 year after putting into
production) and coke oven gas in phase 2 (1 year later after putting into production) as the
fuel, therefore the design of reheating furnace has to be suitable for this kind of condition to
satisfy the using of reheating furnace in phase 1 and 2, and not effect the life of furnace body,
so that the furnace shutdown time for secondary reforming is short and the reforming cost is
low.
The combustion system of reheating furnace mainly includes: oil and gas dual-fuel burner,
heavy oil system in phase 1 (including steam atomizing, heat tracing, purging), coke oven gas
system in phase 2 (including nitrogen purging, bleeding system), combustion air system, flue
duct system, chimney and ignition heating system. The ignition heating system is needed for
the first time dry-out and restarting the furnace each time in phase 1 when using the heavy oil
as the fuel.
5 Mechanical Equipments in Reheating Furnace Area
The mechanical equipments in the area of reheating furnace mainly consist of charging roller
table and discharging roller table within the range of furnace width, pusher and extractor,
charging/discharging furnace door and their elevating mechanism, hearth walking machinery,
hydraulic system, grease centralized lubrication system etc.
6 Evaporation Cooling System and Thermal Facilities of Reheating Furnace
For the slab reheating furnace provided to Indian LSTL steel plant, evaporation cooling and
forced circulation are adopted for skid cooling.
The designed rated cold charging capacity of reheating furnace is 250t/h. Evaporation
cooling is adopted for horizontal beam and post of walking beam reheating furnace. The beam and
post are pipe structure, which can bear high pressure.
steam parameters:
pressure of input steam
1.27MPa
temperature of input steam
190ºC
The cooling capacity of vaporization cooling system is designed according to the following
conditions:
Heat preservation system falling-off of skid of whole furnace
max.10%
Heat preservation system falling-off of skid of single cooling loop
max.40%
Heat preservation system falling-off of post of single cooling loop
max.10%
7 Level-1 Automation Control System
(1) System Overview
The slab walking beam type reheating furnace has high requirements for response speed and
resolution of the control system. In order to guarantee the test control accuracy of the walking
beam and reduce the tracking error of billets from charging to discharging. According to our
experience, the electrical control system has strict requirements for control cycle of PLC
analog quantity, resolution of analog quantity and sampling refreshing cycle. Therefore, the
software design must be optimized so as to guarantee failure-free operation of the system
while high-speed PLC is adopted.
The control of analog quantity of reheating furnace instrumentation system is comparatively
complex, while the control of switching value is relatively simple. So, with regard to the
instrument control, the DCS system should be adopted.
With regard to the reheating furnace that is comparatively independent, the control system
should be simplified as much as possible, so as to share resources and reduce costs. The
reasonable scheme is to adopt an electrical and instrumentation integrated system.
a)Two sets of control system devices shall be set up for each reheating furnace of the
whole basic automation system. Electrical control system will use one set of PLC system ,
which is used for the control and material tracing of reheating furnace proper equipments and
charging/discharging furnace door; the other DCS system is used for combustion control and
vaporization cooling system.
b)Three HMI stations shall be adopted for the reheating furnace control system. One engineer
station shall be set up in the reheating furnace control room by the electric system to observe
the blank operation and tracking inside the furnace; the parameter setup, operation, state
display, error supervision, alarming and report printing shall be carried out through the LCD
picture, and at the same time the sigils shall be transmitted to the DCS operating room
through communication; the other 2 HMI stations are also set up in the operating room in the
furnace area to control the combustion system and evaporating cooling system.
c)The I/O configuration of the control system should be reserved for 10 over measure.
d)The control system and the primary instrumentation are set on the linear UPS, with the
working time with not less than 30-minute delay.
(2) Hardware Configuration of Level-1 Automation Control System
One set of PLC system shall be equipped for the electric control of reheating furnace proper,
which mainly controls the charging furnace door, discharging furnace door, walking beam and
hydraulic station etc. The S7-300 device shall be adopted and its configuration is as follows:
5A power template PS307
Central processor CPU315-2DP
Counter Module FM350-2
Analog quantity output module SM331
Digital input module SM321 DC24V×DI32
Digital output module SM322 DC24V×DO32
Communication
The entire system sets up two layers of communication buses: DCS system adopts the
SINECHI of Ethernet to progress communications and driving PLC systems aopts the on-site
bus PROFIBUS to progress communications. DCS system progresses data communication with
driving PLC system through its DP communication template. Driving devices progress
communication using the on-site bus PROFIBUS; meanwhile connecting with rolling line
Ethernet to progress data communication.
(3) Main Electric Application Function of Base Automation System
a)Survey of equipment acting process
After the slabs which complete length-measurement, width-measurement, ID identification enter
onto roller table, the slab will be positioned along the width of furnace; When the charging
conditions are satisfied, the charging door will open, the pusher will push the slabs on the preset
position of fixed beam in furnace in accordance with the calculated stroke.
With the movement of walking beam, the slabs will pass No.1 heating section, No.2 heating
section, soaking section in turn, and will be fully heated upto the expected discharging
temperature to wait for discharge at any moment.
When there is the request to discharge, the discharging door will open, the extractor will extend
into the preset position in furnace according to the calculated stroke and lift up the heated slab,
the slabs are pulled out and placed on the center line of discharging roller table, at the same
time the extractor will return to the initial position to wait for next action.
During above charging and discharging process, the operation status, electrical fault, equipment
malfunction of all electrical-control equipments shall be monitored on line by electrical control
system, and make the alarm classification by major error and minor error, and prompt by means
of sound/light alarm, then print out the record of alarm type.
b)Main control functions of the primary sequence control of the reheating furnace
--Main functions of sequence control of reheating furnace:
Setting of travel distance of charging and discharing machine
Control of charging and discharging furnace doors.
Setting and control of the travel stroke of walking beam.
Control of positive cycle, reverse cycle and middle holding of the walking beam.
Detecting and control of discharging locations of slabs.
Tracking of slabs in the furnace area.Control of hydraulic station and lubrication station.
Interlocking among all devices in the furnace area.
--Functions of workstation (HMI)
Running preparation
Parameter setting and operation
Running monitoring
Fault monitoring and alarm
Simulation running of equipment
Log and saving
Report forms printing
Data communication between level-1 sequence control system of the furnace area and
other relevant system
(4) Operating Mode
There are three operating modes: automatic, semiautomatic and manual.
Automatic: various working sequence and operations and interlocks between the
devices will be automatically carried out in accordance with operational conditions of
various mechanical devices. All controls will be set up through the computer and carried
out by the basic automation system.
Semiautomatic: the working sequence of partial single devices will be carried out by
themselves, and the interlock relationships between devices and the starting order to
operation will be given by operators, and its controls will be accomplished by the basic
automation system.
Manual: the single operations are carried out by the operator through the operating desk
and operating cabinet, especially emergency operations when the machinery is in repair
or failure.
(5) Operating Equipment and Detector
a)Operating desk
Main operating desk of the reheating furnace (adopted material is stainless steel and high
quality components) is placed in the operating room of the reheating furnace system,
including the operator station used for installation of primary control
system and the
operating elements used for installation of hardware.
b)Site control box
It is used for side operation of hydraulic devices,walking beam,fan and drain pumps in pit of
the reheating furnace, to satisfy the requirements of maintenance and debugging.
c)Detecting element
Main detecting elements, such as pulse coder, linear displacement transducer, etc., adopt the
high quality products.
Detecting element of reheating furnace
--2 linear transducers, used for furnace bottom machinery;
--2 laser detectors, used for width verify for charging slabs and detecting the position for
discharging slabs.
(6) Other Electrical Devices
a)Lighting distribution box
The C65N circuit breaker is installed inside; and the lighting power supply is from the lighting
distribution box in the reheating furnace area, used for hearth lighting.
b)Examining power cabinet and power box
Four examining power cabinet shall be set up in the site of area of reheating furnace. The power
shall be provided by the customers for distribution of all examining power boxes in the area of
reheating furnace. One three phase 415V socket, two single phase 230V sockets, one suit of three
phase 415V connecting terminals of electric welding machine are installed inside the examining
box. The leakage protecting circuit breakers are installed in all return circuits.
7.1 Combustion Control System:
7.2.1
Summary
Combustion Control Instruments DCS various test items to complete the circuit control, data
acquisition, data processing, operator station stoves needed for the production of all operations,
and monitoring of parameters, including overall and packet flow screen, circuit adjustment and
display, fault alarm screen, instantaneous images and historical trends, fault alarm printing,
parameters printing and production table printing etc.
8 Technical Performance Sheet of the Walking Beam Reheating Furnace
Usage of furnace:heating the slabs before rolling
Type of furnace:top & bottom fired walking beam type reheating furnace
Heating steel grade:
low carbon steel,medium carbon steel, including pipeline steel C-60 and X-70
Dimensions of billets:
Length: 4.5~11m ,Width: 900~1270mm,Thickness: 200,210mm
The proportion of billets:
A) 4.5 meter length slab charging: Maximum 5.0%
B) 6.0 to 8.0 meter length slab charging: Maximum 5.0%
C) 11.0 meter length slab charging: 90%
We can know from the charging diagram, the billet size of 7-8m is not suitable for
charging
Charging temperature:cold charging, room temperature, completely hot charging
600~900ºC
discharging temperature 1250±30ºC
Production capacity:
Rated output is 250t/h ( cold charging, room temperature, 210 mm×1270mm
×11000mm,common carbon steel, discharging temperature 1250ºC)
Rated output is 300t/h ( completely hot charging, 600 ~ 900 ºC
×11000mm, common carbon steel, discharging temperature 1250ºC)
Fuel and low heat value:Heavy oil with heat value of 10200 Kcal/kg
Heating mode:No.1 & No. 2 heating zones and bottom of soaking zone will
adopt side heating, the top of soaking zone will adopt end heating, totally divided into 4
zones to control.
Rated Specific Fuel consumption:
1.35GJ/t ( Rated output, carbon structural steel, cold packed, standard blank, stable
production, new furnace lining, stable quality of heavy oil , steel billet discharge
temperature~1250ºC)
scale loss:
0.8% ( Rated output, carbon structural steel, cold charging, standard billet, stable
production, new furnace lining, the quality of heavy oil satisfied the requirement, steel
billet discharging temperature~1250ºC)
Air preheating temperature : 480 ºC ( when flue gas temperature before
recuperator is 800ºC)
Stepping machinery type:
two wheels on slop rail, hydraulic drive
Stepping lifting travel stroke
200mm
Stepping translation travel stroke 500mm
Stepping period 50s
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