10000×3500×3500mm Gas fired Bogie Hearth Furnace
1. Application
The gas fired bogie hearth furnace is mainly used for heat
treatment of metal parts.
2. Structural Introduction
2.1 furnace body
The furnace body steel structure is made from 12-18# U steel and
4-14mm
steel plates. The side pillar and back pillars are made from
sectional steel,
and are reinforced with sectional steel bracings. The external wall
of the
furnace is painted with 2 layers of primers, and 2 layers of
coating paint.
The key part of the furnace is painted with heat resistant paint.
The furnace
door edge is made of 14mm heat-resistant steel casting material in
several
pieces.
2.2 lining
The lining material is 1200 type 1000℃ high purity refractory fiber
compacted
block. This refractory lining structure has the advantages of low
heat conductivity,
strong anti-shock capacity, and anti-erosion. Aluminum silicate
fiber compression
block with thickness of 320mm is designed as the high temperature
refractory layer.
2.3 bogie
The bogie is comprised of heat preservation material, bogie frame
and moving
mechanism. The refractory layer is divided into 3 sub-layers, i.e.,
1st top
high-alumina brick layer, and 2nd and 3rd layer with both light
clay bricks.
The bogie framework is made of 20# U-steel and 20# I-steel. The
edges of the
bogie are made of 20mm I-steel. The bogie is equipped with 8 pieces
of wheels.
Each wheel diameter is 300mm.
The heat preservation material is divided into 3 layers, the top
layer being
high-alumina bricks, and 2nd and 3rd layer being both light clay
bricks.
The bogie is driven by motor reducer gear driving mechanism. The
moving speed
of the bogie is 6-8m/min.
2.4 Sealing System
Sealing between the furnace door and the furnace body is through
the electric
push-rod. Sealing between the bogie and the real wall is through
the spring
mechanism. When the bogie moves inside the hearth, the bogie
contacts tightly
with the rear wall to prevent heat loss.
2.5 furnace door
The furnace door is comprised of all-fiber lining and steel
structure shell.
The door is built with silicate aluminum compressed fiber blocks
same as that
for the furnace body. The shell is a welding structure from
sectional steel and
steel plates. The furnace door has the feature of simple,
practical, reliable and
convenient maintenance. The furnace door is fixed on the bogie.
2.6 burning system
The burning system is comprised of AGS 125HB high speed burners,
proportional
combustion control system, gas valve, solenoid valve, burner
control box, etc.
The burner has the functions of automatic ignition, flame
detection, and flame out alarm.
The burner controller receives the control signal of the
temperature controller and
controls the large/small fire status of the burner based on the
heat load requirement so
that adjustment of the temperature is realized.
A) The burner has adjustment function and the adjustment rate is
1:10 and the air
efficient is 1-5. The burner could meet the temperature uniformity
of the heat treatment
process and effectively control the air-gas ratio so that the fuel
consumption is reduced.
B) When the furnace is working, the burning system could
automatically cut off the
electrical gas valve and general safety valve in the case of power
failure detected by
the alarm system. When the power supply is resumed, the worker
needs to open
the safety valve and restart the ignition program after purging
function is confirmed.
The burner is set with a proportional control unit which enables
alternative burning
of large and small fire, fire out alarm, and re-ignition. The
burner control box has both
manual and self-run modes available. The worker could operate in
front of the furnace
or in the control cabinet.
C) The pipe before the burner is equipped with solenoid valve, and
manual gas
adjustment valve. The valve system could realize an ideal gas/air
supply ratio so
that the air excess efficient is lower than 1.1.
2.6.1 air system
The air piping system is comprised of high pressure centrifugal
fan, automatic
regulation valve, pressure gauge and pipes. The air volume is to
match the gas
volume, and the air excess rate is lower than 1.20.
2.6.2 gas supply system
The general gas supply pipe is equipped with a pressure regulation
device (equipped
with a filter), a low pressure switch and a pressure gauge. For the
sake of safety there
is one fast cut-off valve on the general gas pipe.
2.6.3 discharge system
The furnace takes direct fume discharge method. The fume is
directly vented out
through the flue pipe to the atmosphere. The fume conducts heat
exchange with
the heat exchanger before emission to the atmosphere.
2.6.4 Furnace pressure control system
The pressure on the working table in the furnace is kept at (+15
Pa), which is very
beneficial to the uniformity of temperature and the thermal
efficiency of the furnace.
When the pressure in the furnace is too high, the hot air in the
furnace will escape
from the furnace mouth and other unsealed places, resulting in the
heat loss caused
by the escape of the flue gas; because the high temperature flue
gas in the furnace
escapes to the outside of the furnace, it will affect the door, the
side seal and burner
of the furnace directly, which is related to the overall service
life of the furnace; when
the pressure in the furnace is too low, a large number of cold air
outside the furnace
will be absorbed into the furnace, as well. The heat loss of
off-furnace flue gas is increased.
The low pressure of the furnace causes the diffusion of cold air
outside the furnace into
the furnace, and secondary combustion is formed due to the entry of
oxygen-containing
cold air, which has adverse effects on the uniformity of furnace
temperature, oxidation
of workpiece and thermal efficiency of the furnace. Therefore,
effective technical
measures must be taken to control the furnace pressure with full
automatic control.
Our method is to control the furnace pressure effectively by using
a system consisting
of pressure taking device, pressure transmitter, intelligent
instrument and so on. The
furnace pressure is controlled in the optimum state (the surface of
the trolley is in a
slightly positive pressure). At this time, the exhaust gas is in a
dynamic equilibrium
state, which can not only ensure that the furnace gas does not
overflow, but also
ensure that the cold air outside the furnace is not sucked into the
furnace, so as to
save energy and maximize the efficiency of the furnace.
2.6.5 Heat exchanger and flue system
A flue is set at the back of the furnace, and it is carried out
with the heat exchanger
(according to the national standard GB3486-83). The flue leads to
the outside of the
factory building. The cold air is exchanged with the heat exchanger
to preheat the
combustion-supporting air before entering the burner, so as to
improve the heat efficiency
of the furnace.
Heat exchangers and flue gas exhaust pipes are insulated by
internal insulation (using
fiber castables) to ensure the service life of heat exchangers and
flues.
2.6.6 fault detection and alarm system
The furnace has a complete fault detection, alarm, diagnosis, and
safety protection
system. On the control cabinet there is an alarm lamp.
2.7 control system
control system has the following parts: Ⅰ. Burning control system;
Ⅱ. Electrical
power control system; Ⅲ.temperature control system .
Measures taken for burning control system:
K type thermal couple gets mV signal and sends it to temperature
PID controller
(SHIMADEN brand). The temperature controller calculates the signal
and outputs
4-20mADC control signal to the electrical actuator. The actuator
further sends a signal
to the burner controller after calculation.
The burner controller is mainly responsible for ignition and flame
detection. When the
terminal receives the ignition signal, the burner controller
carries out flame simulation
and self testing stage. If during this simulation and self-test
stage the burner couldn’t
detect the flame signal. The burner controller would open the gas
solenoid valve and
convert the voltage 220VAC to 5KV for ignition (ignition time about
3S). If the burner
detects the flame signal in the safe time period (about 8S), the
yellow indication light
of the burner would be on (ignition successful). If the burner
couldn’t detect the flame
signal, the red light would be on (ignition failed). The burner
controller is locked and
the gas solenoid valve is cut off.
B) electrical power control system: The electrical power control
system mainly controls
ON/OFF of the fan, and IN/OUT of the bogie.
C) temperature control and record system
The system has the functions of temperature setup, control and
digital display. And also
there is an audible and visual alarm at over-temperature
situations.
Temperature control zone arrangement
A:temperature control system
The furnace is equipped with 5 thermal couples and an intelligent
temperature controller.
The furnace is controlled by 5 zones.
B: instrument temperature control
The temperature controller allows setup of heating time, holding
time, and cooling time.
It has self-tuning and self-adjustment function, and displays SV
and PV.
3.Main Technical Parameters
| No. | Item | Technical Parameters |
| 1 | Fuel | Natural gas |
| 2 | fuel gases calorific value Gas pressure before furnace | 8600kcaL/Nm3 0.05-0.1Mpa |
| 3 | Rated temperature | 900℃ |
| 4 | Normal used temperature | 600℃ |
| 5 | Heating zone | 5 zones |
| 6 | Surface temperature of furnace body | ≤45℃+ room temperature |
| 7 | Surface temperature of furnace door | ≤55℃+ room temperature |
| 8 | Loading capacity | More than 50 ton/furnace |
| 9 | Temperature measurement accuracy | ±2℃ |
| 10 | Burner gas consumption | 300Nm3/h |
| 11 | Gas pipe total requirement | 350Nm3/h |
| 12 | Air consumption | 4160Nm3/h |
| 13 | Power of bogie motor | 5.5KW, 2sets |
| 14 | Power of combustion fan | Approx 11KW |
| 15 | Temperature uniformity | ≤±10℃ |
| 16 | Effective working size | 10000×3500×3500mm(L×W×H) |
| 17 | Hearth size | 10400×3800×4000mm(L×W×H) (the heigh excludes the base support) |
| 18 | Quantity and model of burner | 10pcs, 320KW/h, AGS 125HB burner |
| 19 | Temperature control method | PID regulation + PLC touch screen control (Siemens), manual control |
| 20 | Max temperature rise speed | 160℃/h at full capacity |
| 21 | Temperature record | K type thermal couple |
| 22 | Bogie move speed | 6-8m/min |
| 23 | Furnace lining | high quality heat-resistant fiber |
| 24 | Furnace door opening method | Electric up and down, speed 6-8m/min |
| 25 | Furnace door sealing method | Sealed by 4 sets electric push-rod |
| 26 | Bogie power supply | Coil of cable |
| 27 | Bogie driving power | motor reducer gear driving mechanism |
| 28 | Furnace side sealing method | Sealed by 4 sets electric push-rod |
| 29 | Furnace back sealing method | Sealed by a spring compacted fiber block |
| 30 | Consumption index | Heat efficiency at full load η≥40% |
