Proceedings World Bioenergy 2010

combination with pressure transducers specifically to the
installed chimney is used to measure the transient flue
gas flow in the chimney during start-up and stop phases.
The whole set of the boiler/stove was installed on a scale
and the fuel consumption was continuously monitored.
However, the fuel consumption during the start-up and
stop period was too small relative to the scale’s
measurement resolution. Therefore, the fuel consumption
during start-up and stop phases are calculated using
measured flue gas flow with the combustion calculation
according to Wester [6].
The sample flue gas is extracted from the chimney
and transported via a heated tube (180°C). Carbon
dioxide (CO 2), carbon monoxide (CO) and nitrogen oxide
(NO) are measured with an non- dispersive infra-red gas
analyser, oxygen (O 2) with a paramagnetic gas analyser
and total organic carbon (TOC) with a flame ionisation
detector (FID). The emissions of TOC are presented in
propane equivalent. The particle emissions are sampled
in the dilution channel (Figure 1) with an electrical low
pressure impactor (ELPI). Particulate matters are
measured in number concentration and size distribution
in the range of 7 nm to 10 µm and are characterized for
PM 2.5.
2.2 Combustion devices
Both boiler and stove are modern pellet heating
devices with electrical ignition and automatic pellet
feeding from above. The 20 kW boiler has an integrated
hot water preparation unit with water volume of 150
liters. The maximum combustion power was set to 80%
of the nominal power and combustion air supply and. The
boiler has a cleaning routine during a stop phase in which
the glowing pellet are blown with compressed air into the
ash box and the stove has 1.5 cleaning routine at every
1.5 hours of operation.
2.3 Pellet
Only a brand of soft wood pellet were used.
However, two batch or order were made through all the
measurements. The composition of the pellet fuel used in
the measurements are listed in table I.
Table I: Fuel composition of the pellet
86 world bioenergy 2010
Element Unit Start-up Stop
Carbon wt% dry 51.20 50.74
Hydrogen wt% dry 42.00 42.52
Oxygen wt% dry 6.30 6.23
Nitrogen wt% dry 0.20 0.10
Ash wt% dry 0.30 0.41
Moisture wt% dry 8.20 6.80
Lower heating
value
3 RESULTS
MJ/kg 19.14 18.99
The accumulated emissions measured during start-up
and stop phase of the boiler and stove are presented in
table II. The duration of the start-up phase and stop phase
of the boiler are 5 minutes and 24 minutes. Comparing
with the boiler, the stove has higher accumulated
emissions during start-up with 12 minutes duration and
lower emissions during stop phase with 25 minutes.
Cleaning with compressed air during stop phases of the
boiler caused glowing in the ash box resulting higher
emissions for stop phase.
Table II: Accumulated emissions of start-up and stop
phase of 20 kW boiler and 12 kW stove
Boiler* Stove
Start-up Stop Start-up Stop
CO (g) 0.72 8.99 1.05 6.78
NO (g) 0.10 0.04 0.35 0.03
TOC (g) 0.15 0.43 0.12 0.01
PM 2.5 (g) 0.23 0.41 0.35 0.17
Energy (MJ) 2.12 1.22 6.81 1.02
* Win,. et al.[7]
Emission concentrations during start-up, steady state and
stop phases are compared in figure 2. Steady state
emissions characterised per MJ combusted fuel are in
general lower than start-up and stop emissions. CO
emissions during steady state operation of the stove is
higher than from the boiler due to the cleaning routine at
every 1.5 hours occurred during long steady state periods.
Figure 2: Average emission concentrations during startup,
stationary periods and during stop periods
Steady state emissions are lower than from start-up
and stop periods, significantly in CO and TOC. Cleaning
with compressed air during stop phases of the boiler
caused the accumulation of uncombusted pellet in the ash
box leading to glowing in the ash box resulting in higher
stop emissions. The 1.5 hourly cleaning routine of the
stove was taken into the steady state. Both the boiler and
the stove has near zero TOC emissions during steady state.