4_combustion air system
Post on 04-Jun-2018
215 Views
Preview:
TRANSCRIPT
8/13/2019 4_Combustion Air System
http://slidepdf.com/reader/full/4combustion-air-system 1/29
Combustion Air systemTommy Lundin
8/13/2019 4_Combustion Air System
http://slidepdf.com/reader/full/4combustion-air-system 2/29
© Metso
Requirements on a modern air system
• Good boiler control, allowing a wide range of load
and black liquor quality variations
Minimized emissions
High availability of boiler
Good and safe working environment
Flexibility for integration of NCG system
Good bed control with stable smelt flow
High reduction rate and low amount of unburned carbonin smelt
8/13/2019 4_Combustion Air System
http://slidepdf.com/reader/full/4combustion-air-system 3/29
© Metso
Combustion Air System
• Supply air to each air level at the correct:
• Temperature
• Pressure
• Flow
• Pattern
• In order to:
• Transport air to combustibles
• Mix air with combustibles
Page 3
8/13/2019 4_Combustion Air System
http://slidepdf.com/reader/full/4combustion-air-system 4/29
© Metso
Combustion Air System
•Affects:• Furnace temperature
• Reduction efficiency
• Carry-over
• Boiler deposits
• Running time
Page 4
8/13/2019 4_Combustion Air System
http://slidepdf.com/reader/full/4combustion-air-system 5/29
© Metso
Multilevel Air SystemTM combustion zones
Stable, undisturbed
liquor spraying zone
with even droplet
distribution
Final combustion
zone, completes
combustion and
ensure an even flow
pattern for optimal
superheaterperformance
Optimum drying,
pyrolysis and heat to
char bed reactions
Char bed control,reduced atmosphere
and smooth smelt
removal
8/13/2019 4_Combustion Air System
http://slidepdf.com/reader/full/4combustion-air-system 6/29
© Metso
Interlaced Air Jet Technology
Tertiary air High secondary air
Secondary air Primary air
8/13/2019 4_Combustion Air System
http://slidepdf.com/reader/full/4combustion-air-system 7/29
© Metso
Arrangements of air system, example
Primary air
Secondary air
High Secondary air
Tertiary air
Load burners
The Multilevel air system
offers a compact ducting
and air port design
resulting in a good andsafe working environment
8/13/2019 4_Combustion Air System
http://slidepdf.com/reader/full/4combustion-air-system 8/29
© Metso
POWER DIVISION
Multilevel air distribution system
8/13/2019 4_Combustion Air System
http://slidepdf.com/reader/full/4combustion-air-system 9/29
© Metso
Aire de Combustion – Valdivia RB
8/13/2019 4_Combustion Air System
http://slidepdf.com/reader/full/4combustion-air-system 10/29
© Metso
Celulosa Arauco y Constitución, Valdivia, Chile
Capacity 3100 t ds/24hSteam 131 kg/s
86 bar
485 °C
Start-up 2004
Air port layout:• Tertiary (4+3), 1000 cm²
• High Secondary on two walls *)
• Secondary on two walls *)
• Primary 132 pcs, 120 cm²
* 4 + 2 big ports 1000 cm²+ CNCG burner
* 3 + 4 small ports 240 cm²
•2 start-up burners/ each wall
•3 load burners on front wall
8/13/2019 4_Combustion Air System
http://slidepdf.com/reader/full/4combustion-air-system 11/29
© Metso 2010-08-09, Nueva Aldea, RB upgrade - Training material11
The next pages introduce the combustion air
system.
The pages thereafter give advices regarding
the combustion.
Introduction
The modern Multilevel Air System™ supplied by Metso has
been developed to enable a maximum burning rate of blackliquor for a given boiler size. At the same time, the availability is
maximized while the emissions from the boiler are minimized.
The combustion air system
8/13/2019 4_Combustion Air System
http://slidepdf.com/reader/full/4combustion-air-system 12/29
© Metso
The combustion
2010-08-09, Nueva Aldea, RB upgrade - Training material
INTERNAL
12
A stable combustion – air and liquor
The air contributes to the combustion of black liquor. The secondary air contributing to
the combustion at the front wall is coming from the back wall and vice versa.
When black liquor load and air distribution changes, the velocity dampers should be
changed equivalently to keep the optimal air pressure in the port. Thus, the pressure
should remain while the flow in the ports changes with the load change.
The composition of chemicals in black liquor may vary, which affects the viscosity.
Viscosity is controlled by the temperature of the black liquor, and variations in the
liquor heat value requires changes in combustion air amount and distribution.
At hardwood liquor firing, the intensity is often higher in the furnace. In thesesituations, the secondary air flow should be reduced and the overfire air flow
increased. When the combustion is performed over the whole furnace cross section,
the result is better reduction ratio and lower emissions.
8/13/2019 4_Combustion Air System
http://slidepdf.com/reader/full/4combustion-air-system 13/29
© Metso
The combustion
• Proper air/liquor and fuel ratio, air distribution and a hot bed give the best result to
maintain a stabile combustion. One and often the best way to control the oxygen
content in the flue gas is to adjust the secondary and overfire air.
• Adjust the combustion so that the oxygen content (O2) in the flue gas after theeconomiser is about 2.8 % (dry, and depending on the load) and at the same time
check that there is a low carbon monoxide (CO) content in the flue gases, about
100 – 300 ppm.
• Adjustments of the combustion air amounts should be done very carefully andslowly. If a load increase is needed, add first air and after that add fuel. If a load
decrease is needed, reduce fuel first and after that reduce air.
2010-08-09, Nueva Aldea, RB upgrade - Training material
INTERNAL
13
A stable combustion – air and liquor
8/13/2019 4_Combustion Air System
http://slidepdf.com/reader/full/4combustion-air-system 14/29
© Metso 2010-08-09, Nueva Aldea, RB upgrade - Training material
INTERNAL
14
The combustion A stable combustion – optimization of the air system
To optimize the combustion and minimize the carry-over, it is important to
decrease the incoming air below the liquor guns as far as possible.
As to begin with, reduce the primary air flow to the benefit of the tertiary air flow,
which accordingly should be correspondingly increased. When it comes to a point
when the primary air flow cannot be further reduced, according to the shape of thechar bed and the amount of unburned smelt in the smelt spouts, reduce the
secondary air flow to the benefit of tertiary air instead.
When this is performed, it is important to have strict control over the optimization
and to follow the changes and affects in the boiler, to make sure that the amount
of air below the liquor guns is sufficient.
Control the content of sludge regularly, and check if there is much of unburned
smelt in the smelt spouts.
8/13/2019 4_Combustion Air System
http://slidepdf.com/reader/full/4combustion-air-system 15/29
© Metso
The furnace bed
The furnace bed must be observed regularly from the beginning of liquor firing. Someconditions can lead to unburned liquor in the furnace bed.
High turbulence while large bed
The new air system increases the possibility to fire a larger amount of liquor in the boiler
with good results in form of small amount of carry-over and high reduction efficiency.
At the same time, the powerful air jets and the turbulent mixing causes that the
combustion in the lower part of the furnace is sensitive for adjustment of air distribution
and air pressure. If there is a large bed in the boiler at the same time as the firing
intensity increases, the smelt flow from the bed will also increase drastically. That is why
it is important to have a controlled operation of the boiler.
2010-08-09, Nueva Aldea, RB upgrade - Training material
INTERNAL
15
8/13/2019 4_Combustion Air System
http://slidepdf.com/reader/full/4combustion-air-system 16/29
© Metso
The furnace bed
Liquor distribution
It is very important to achieve a good distribution of the liquor, to prevent development of
ridges in the outer edge of the bed with pools of smelt behind. The bed should also be
prevented from becoming unstable and collapse and cause surges. This can spurt out
through the smelt spout openings.
During the cold start-up, liquor may enter the furnace bottom unburned (wet) and
this can result in plugging in the primary air nozzles or in the spout. This can alsohappen if the furnace is too cold, the liquor spraying pressure is too low or the aiming ofthe liquor guns is incorrect.
In these cases, increase the load of the burners, then clean the air ports and increasethe combustion air by opening the dampers for a short period of time on both sides ofdark (wet) area so that the wet area starts to burn again. Also check the liquor guns and
clean them if needed. If there is mechanical failure in a nozzle, replace it.
If this does not help, stop liquor firing and burn off the wet bed with the burners. Whenthe situation is back to normal, start liquor firing again.
2010-08-09, Nueva Aldea, RB upgrade - Training material
INTERNAL
16
8/13/2019 4_Combustion Air System
http://slidepdf.com/reader/full/4combustion-air-system 17/29
© Metso
The furnace bed
Note!
It is very important to prevent a sudden opening of plugged smelt spouts since this willresult in large, uncontrolled smelt discharge through the open spouts which might causeexplosions or splashes in the smelt dissolving tanks.
To avoid the described problems, monitor the bed and the combustion all the time.
Do not let unburned liquor flow through the smelt spouts to the dissolving tank.
2010-08-09, Nueva Aldea, RB upgrade - Training material
INTERNAL
17
8/13/2019 4_Combustion Air System
http://slidepdf.com/reader/full/4combustion-air-system 18/29
© Metso
POWER DIVISION
Primary air port design
Benefits
• Cast iron ports
• Proven design
• Low maintenance
8/13/2019 4_Combustion Air System
http://slidepdf.com/reader/full/4combustion-air-system 19/29
© Metso
POWER DIVISION
Secondary and High Secondary air level
Benefits• Non welded sleeve
design
• Easy to change
sleeve
• Pressure control
possibilities
Valdivia, Chile Billerud,Gruvön, Sweden
8/13/2019 4_Combustion Air System
http://slidepdf.com/reader/full/4combustion-air-system 20/29
© Metso
POWER DIVISION
Tertiary air level
Valdivia, Chile
Benefits• Non welded sleeve
design
• Easy to change
sleeve
• Pressure control
possibilities
Billerud,Gruvön, Sweden
8/13/2019 4_Combustion Air System
http://slidepdf.com/reader/full/4combustion-air-system 21/29
© Metso
POWER DIVISION
• DNCG, CNCG, vent- and mix tank gas can be
integrated optimally with Multilevel Air System to form
Multifuel Combustion System.
NCG and Vent Gas
CNCG at secondary air level DNCG and vent gas at tertiary air level
8/13/2019 4_Combustion Air System
http://slidepdf.com/reader/full/4combustion-air-system 22/29
© Metso
POWER DIVISION
Summary – Benefits of Multilevel Air SystemTM
• Each air level is located anddesigned for optimal boiler
control , using 2-wall interlaced
and 4-wall primary air patterns
• Ensures vigorous mixing and
efficient final combustion withlow CO, TRS and VOC
emissions
• High availability through a well-
proven design and arrangement
0721
8/13/2019 4_Combustion Air System
http://slidepdf.com/reader/full/4combustion-air-system 23/29
© Metso
POWER DIVISIONTypical air elevations
8/13/2019 4_Combustion Air System
http://slidepdf.com/reader/full/4combustion-air-system 24/29
© Metso
POWER DIVISIONWide operation range
8/13/2019 4_Combustion Air System
http://slidepdf.com/reader/full/4combustion-air-system 25/29
8/13/2019 4_Combustion Air System
http://slidepdf.com/reader/full/4combustion-air-system 26/29
Air curves monocrome
8/13/2019 4_Combustion Air System
http://slidepdf.com/reader/full/4combustion-air-system 27/29
© Metso
POWER DIVISION
Forced draft fans
Primary air fan: Net Test block• Air flow nm3 /s 28.6 37.8
• Total pressure Pa 2380 3100
Secondary air fan: Net Test block
• Air flow nm3 /s 52.7 75.1
• Total pressure Pa 4660 6060
Tertiary air fan: Net Test block
•Air flow nm3 /s 33.2 51
• Total pressure Pa 5460 7100
Flow control type: Inlet vane, with pneumatic or electric
actuator
8/13/2019 4_Combustion Air System
http://slidepdf.com/reader/full/4combustion-air-system 28/29
© Metso
POWER DIVISIONFlue gas system
8/13/2019 4_Combustion Air System
http://slidepdf.com/reader/full/4combustion-air-system 29/29
© Metso
POWER DIVISION
Induced draft fans
• Number pcs 3• Drive type variable-frequency drive
• Induced draft fan 33.3 % MCR Test block
55 % MCR
• Flue gas flow / fan nm3 /s 55.0 91.0
• Total pressure Pa 2580 4350
• Temperature °C 180 180
top related