Main components
• The
bigger the need of heat output is.
the bigger the components (storage.
boiler. chimney etc.)
• In private houses the output need of the
boiler is about 25–40 kW and in farms
from 60 kW-
Chimney
Fuel supply
Boiler
Exhaust gas
handling
Feeding
equipment
Fuel handling
equipment
Combustion
equipment
Ash handling
• Buying all components from same manufacturer or reseller it guarantees
better compatible and service if something happens
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Storage
• 500–1000 litres in private homes
=> filling manually
=> risk of dust and farmer's lung disease
• Made from steel/metal. lid and locks in it
• If the system works with one feeding screw. the storage
must be airtight
– remember to shut the lid to avoid back fire
– In the bottom there is a plate or a string for
emptying
• Main principle for sizing the storage is that it is big
enough for two days using with maximum output
• In farms and bigger buildings the storage is few m3
=> filling with a tractor and front loader
– usually there is bar discharger (two rakes moving
back and front)
– district heating plants have usually walking floor
systems
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Photo: Ala-Talkkari Ltd.
Photos: Thermia Ltd.
2
Fuel need bulk-m3 / day
( in wintertime when maximum output is needed
Output, kW
Wood pellets
bulk-m3
Sod peat
bulk-m3
Wood chips
bulk-m3
40
0.3
0.8
1.1
60
0.5
1.0
1.6
80
0.6
1.5
2.1
120
1.0
2.2
3.2
150
1.2
2.8
3.6
200
1.6
3.7
4.8
300
2.4
5.5
8.0
400
3.2
7.4
10.7
500
4.0
9.2
13.3
Example: Maximum output 300 kW, using wood chips. Refilling once/week
=> storage size (8.0 bulk-m3 /day * 7 days ) = 56 bulk-m3
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Feeding screw
• Made of steel
• Usually one-screw or two-screw system. Gets the
power from electric motor
• In a one-screw system, the burner head and the
bottom of the fuel storage are in the same level
•The pipe around the screw can be rounded or
square
• In small units usually pulse and pause based
feeding system
–
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In bigger sites frequency transformer based
system, i.e. feeding screw is moving all the
time little by little
Photo: Ala-Talkkari Ltd.
4
Two-screw system
• In a two-screw system there are more alternatives to connect
them in different angles
– it has better back-fire protection, because there is free
drop between screws
– In a two-screw system the end of the screw is in a
higher position than the start. It also protects against
the back-fire
lock–roller, lock-feeder
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Photo: Ala-Talkkari Ltd.
5
Burner head (stoker)
• Different models, usually round
• Made of iron. Bigger burners have also ceramic parts in it
•Possible to use wood chips, peat, pellets, briquettes
Photo: Ala-Talkkari Ltd.
A good burner head?
• Can reach a high temperature (up to 1000°C)
–
better combustion, lower emissions
• Low air coefficient
–
High air coefficient means lower efficiency
• Low CO-emissions (< 100 ppm)
• Low NOx-emissions
• Wide using range (20-100% of total output)
• Good back-fire protection
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Whole
system
Photos: Thermia Ltd.
6
Air fans (=blower)
• In small units there is only one blower to both primary and
secondary air
• Primary air is fed from below the burner head (=or grate)
• Secondary air is fed right to the flame
Primary air
Adjusting manually by using own eyes
Pictures: Thermia Ltd.
•The colour of flame must be orange – red
–
–
–
not transparent or blue;
it indicates that there is too much air
not red – brown; it means that there is too little air
adjusting manually by using own eyes
Adjusting by using flue gas analyser
Secondary air
⇒ better result
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Boiler
Arimax 340 Bio is compatible with bio burner
–
effective hot water spiral
•
–
–
burning openings and cleaning hatches on
both sides
ceramic wall in fire chamber
•
•
–
–
no need for an accumulator tank
increases the boiler effectiveness
clean and effective burning
working pressure usually 1.5 bar
negative pressure in burning chamber must
be 20–30 Pa
Good boiler?
•Strong structure; made of steel (5-8 mm)
• High burning temperature (up to 1000 0C )
• Enough secondary air that pyrolysis gases can burn
at last in the convection part
• Good insulation
– Small radiation losses
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– Vertical convection part
Photo: Ala-Talkkari Ltd.
8
Convection part
• Vertical convection part won't get dirty as
easy as a horizontal one
• As the output of the boiler increases, the
amount of flue gas rotations (goes up and
down more times) increases also
• The convection part should decrease the
exhaust gas temperature from 1000 0C to at
least 250 0C before the chimney
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Chimney
• the diameter and length depend on the boiler output
– A 40 kW boiler needs a chimney with diameter 150 mm and height 5 m
– If there is one meter horizontal part after boiler and before vertical
chimney
⇒ There must be two meters higher chimney
⇒ other possibility is to use flue gas fan
⇒ especially when chimney can't be long enough
• made from steel or bricks
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Chimney
Natural draught
No flue gas fan
Output, kW
∅, mm
Height, m
20 - 50
150
4
120
180
8
150
200
9
200
230
10
250
270
12
300
300
14
400
330
15
Depends on the flue gas fan
(flow speed 16m/s)
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Control system
•Tiimi 5301 control system has
– Flame control system
• feeding screw stops if the temperature drops down to an adjusted
level (in this case …)
– Backfire control system
• runs the feeding screw ahead adjusted time (40 s)
– Overheating of the boiler
• system stops when temperature is higher than set level - usually
100oC
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Control system
• Tiimi 5301 control system has
–
control the air fan (primary & secondary at the same time)
•
–
controls the feeding;
•
•
•
–
Blows only during the pulse level (same time with feeding)
length of efficiency pulse and pause
length of upkeep pulse and pause
four basic programmes / levels for chips, pellets and peat
check hysteresis between Upkeep and High operation level
• Efficiency / upkeep –system (on / off –system)
- Works perfectly with steady output need and stabile fuel
- Simple and profitable
- In upkeep level the combustion is incomplete
- Needs knowledge how to use and adjust
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Energy measuring
• Shows
– the total produced amount of energy
– water temperatures of output into network and return from
network
– amount of water flow
– produced energy at this moment (output kW)
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Safety systems
BACKFIRE
•
Sensor in feeding screw which measures the temperature
– If it is higher than adjusted level, control system runs the feeding screw ahead
for example 40-60 seconds
– There is a piece of beeswax which will melt because of high temperature and
the tank of water will douse the backfire
– It is quite usual nowadays that there is pressure water connected to the feeding
screw (valve that opens in high temperature. works also in during electric
blackout)
•
In two-screw feeding system there is a free drop between screws
– It is also back fire protection
– Usually there is the lock–roller, lock-feeder
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Maintenance
REMEMBER to USE GAS-MASK + clothes
Boiler room
•
Cleaning (once per month) and washing (once per year)
•
Change broken lights etc.
Storage
•
grease the chains and bearings
•
check that lid and locks are OK
Feeding screw and air fans
•
check that everything works
Burner head
•
Open the lid below the burner head. Clean it once per year by using metal stick
•
brush the burner head a few times per year
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Maintenance
Boiler
•
Sweep the combustion chamber a few times per year
•
Sweep the convection part once per week
– 2 mm layer of ash in the convection part decreases the efficiency with 8 %
Ash removal
•
Manually in small scale units a couple of times per month
– By hands or by a vacuum cleaner
•
In bigger heating plants there are automatic ash removal system (screw)
Chimney
•
Sweep couple of times per year. In Finland one of these sweepings must be done by
the official chimney sweeper. Otherwise the fire insurance won’t be in force…
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How to light the fire in the system
1.
Set the control system in manual use
2.
Feed the fuel in burner head by pressing screw feeding ahead
3.
Light the fire using for example lighter fluid
4.
When the fire is lit, switch on the air fan
5.
Set the system in automatic use and make sure that it works properly
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