13. Holzenergie

www.holzenergie-symposium.ch!
13. Holzenergie-Symposium!
Leitung: !Prof. Dr. Thomas Nussbaumer!
!Verenum Zürich und Hochschule Luzern!
Patronat:!Bundesamt für Energie!
Ort:
!ETH Zürich!
Datum: !Zürich, 12. September 2014!
Verenum
Vergleich von Rost- und Wirbelschichtfeuerung
Technik, Kosten, Anwendungen
Philipp Kolbitsch
+43 1 79574 623
philipp.kolbitsch@bertsch.at
Business segments of BERTSCHenergy
Solid Fuel Boiler Plants
Electricity and Heat from Biomass
Process Heat Recovery
Systems and Pressure
Equipment
Steam, Heat and Equipment for
Process Plants
Combined-Cycle /
Cogeneration HRSG
Electricity and Heat from Gas and Oil
Waste Heat Recovery Boilers
Steam from Waste Heat in Industrial
Processes
Service
Optimal Maintenance and Service
Business segments of BERTSCHenergy
Solid Fuel Boiler Plants
Electricity and Heat from Biomass
•  design (from conception to detail)
•  Steam parameters: 15 – 80 t/h, 40 – 150 bar, 400 – 520°C
•  EPC solutions (lot wise or turnkey)
•  in house design
•  Air cooled grate
•  Bubbling fluidized bed
•  Water tube boiler
•  After sales services
•  24 references in 6 countries
Fuel Spectrum
Wood chips
Waste wood
Wood from Landscape preservation
RDF
Short-rotation plantation
Municipal waste
Criteria for choice of technology
Given fuel quality is the main
criteria for the choice of
combustion system
1.
Grate firing
Water content of
fuel
2.
Lower Heating
Value
3.
Ash content,
impurities,
Particle size
Bubbling fluidized bed
firing
Grate Firing
•  Air cooled reciprocating grate with optimized grate bar geometry
for highest availability and life time
•  Fuel input with pusher and chute onto fuel feeder grate
•  Active control of fire position on grate for highest efficiency
•  Each grate zone with variable controlled primary air supply
•  Staged combustion with primary and secondary air
•  Temperature control in combustion chamber with recirculated
flue gas (beneath and above grate)
Bubbling Fluidized Bed Firing
•  Bubbling fluidized bed integrated in boiler
•  “open nozzle floor”
•  Fluidization of bed with a mixture of air and recirculation
gas (temperature control)
•  Start up burners in freeboard
•  Staged combustion with primary and secondary air
•  Deashing with reliable conveyors
•  Sand classifier and sand recycling
Fuel quality
Grate
Technology
BFB
Technology
Reason
Economic
Effect
LHV max
15 MJ/kg
>20MJ/kg
wear on grate
maintenance cost
LHV min
5.5 - 6 MJ/kg
3 - 4 MJ/kg
intensified heat
transfer in BFB
choice of technology
Co-combustion of
wet fuel (LHV < 0)
low quantity possible
high quantity possible
intensified heat
transfer in BFB
choice of technology
Fuel grain size
(screen size)
< 350 mm
(max. pieces > 1m)
< 100 mm
(sum of edge length <
300mm)
fuel feeding / dosing
higher costs for fuel
treatment with BFB
Metal content
high content
acceptable
(depending on
species), removal
recommended
must be removed as
far as possible (spec.
Al, bulk particles)
agglomeration in
BFB; blocking of
deashing system
higher cost for fuel
preparation with BFB
Emissions - General
CO
NOx
Mean TOC
(ash)
N 2O
Grate
Technology
BFB
Technology
Reason
Economic
Effect
50 – 100 mg/Nm³
(6%O2, dry)
0 – 50 mg/Nm³
(6%O2, dry)
homogeneous combustion
with BFB
none (efficiency difference
is negligible)
lower combustion temperature
with fewer temperature peaks
for BFB
Investment and operating
costs for SNCR
Residence time,
Fluidized bed
normally low, can be
interesting for high ash
content in fuel
lower combustion temperature
for BFB
none
fuel dependant; BFB approx. 50% of
grate firing
3%
0 - 3%
slightly higher for BFB combustion
Emissions – Reference plants
Plant
Fuel
NOx emissions
[mg/Nm³, 6%O2 dry]
BFB, No 1
demolition wood, W25
250
BFB, No 2
natural biomass with 30% demolition wood, W35
180
BFB, No 3
natural biomass, W35
150
BFB, No 4
natural biomass with 30% demolition wood, W35
180
Grate firing, No 1
natural biomass, W50
350
Grate firing, No 2
natural biomass, W55
375
Grate firing, No 3
natural biomass (mostly bark), W60
375
Other figures
Grate
Technology
Boiler efficiency
BFB
Technology
slightly increased for BFB
Load change rate
low
moderate
Electric power
consumption
moderate
(1.0 – 2.0% of fuel
thermal input)
high
(1.5 – 2.5% of fuel
thermal input)
Investment cost
Reason
- 
- 
air / fuel ratio
unburnt in ash
fuel residence time on
grate / in BFB
- 
- 
BFB requires high
pressure primary air
BFB often has higher
rec. flue gas ratio
Economic
Effect
slightly lower fuel costs
for BFB
interesting for e.g. paper
industry and peak load
plants
net electricity production
The boiler including firing has more or less equal investment cost. The overall cost strongly
depend on the fuel type and fuel quality.
Resource consumption
Grate
Technology
Cleaning intervals of
soot blowers
BFB
Technology
- 
1 – 3 cycles / day
0 – 1 cycle / day
- 
- 
Quartz sand demand
none
Pressurized air
required
variable
- 
- 
reduced wear from
soot blowers
HP steam
consumption
costs for sand acquisition
BFB requires bed
material preheating to the
solid fuel ignition
temperature
fuel costs,
investment costs
- 
Start-up burners
combustion
temperature
“self-cleaning effect”
efficiency of sand
separation system
sand attrition
approx. 2 - 3kg/MWh
not required,
sometimes
executed
Economic
Effect
Reason
- 
- 
- 
- 
bag filter or ESP
SNCR
deashing system
etc.
costs for pressurized air
production
Disposal and maintenance costs
Slag (from grate),
bed ash
Grate
Technology
BFB
Technology
high
low
Reason
- 
- 
- 
Boiler / filter ash
Wear
low
high (depending
on fuel)
high
low
- 
- 
Economic
Effect
BFB: bed ash consists of
coarse particles only
BFB: all other ash is boiler /
filter ash
Grate: ash is only partially
discharged with the flue
gas; major fraction is slag
from grate
benefit of grate firing
since slag / bed ash is
usually easier / cheaper
disposable compared to
filter ash
BFB: no moving parts
Grate layer is a wear part
which needs to be changed
regularly (5 – 10 years)
wear parts and
maintenance costs
Summary
•  Main advantage of grate firing is low demand on fuel preparation
–  Fuel particle size
–  Inorganic impurities (ceramics, glass, Fe and non Fe)
•  Main advantages of bubbling fluidized bed are:
–  Emissions (usually no need for SNCR)
–  Efficiency
–  Wide LHV and water content range, high fine content in fuel possible
•  Operational costs are similar
•  Maintenance costs are lower for BFB
•  Investment costs depend very much on the overall situation
–  Boilers including firing have very similar investment costs
–  In case extensive fuel preparation is required, grate technology is
usually less expensive