Proceedings World Bioenergy 2010

EMISSIONS CHARACTERISTICS OF A RESIDENTIAL PELLET BOILER AND A STOVE
Kaung Myat Win, Tomas Persson
Solar Energy Research Center, Dalarna University, 781 88 Borlänge, Sweden
Tel: +46 23 778704, Fax: +46 23 778701, Email: kmw@du.se
ABSTRACT: Gaseous and particulate emissions from a residential pellet boiler and a stove are measured at a realistic 6day
operation sequence and during steady state operation. The aim is to characterize the emissions during each phase in
order to identify when the major part of the emissions occur to enable actions for emission reduction where the savings
can be highest. The characterized emissions comprised carbon monoxide (CO), nitrogen oxide (NO), total organic carbon
(TOC) and particulate matter (PM 2.5). In this study, emissions were characterised by mass concentration and emissions
during start-up and stop phases were also presented in accumulated mass. The influence of start-up and stop phases on
the emissions, average emission factors for the boiler and stove were analysed using the measured data from a six-days
test. The share of start-up and stop emissions are significant for CO and TOC contributing 95% and 89% respectively at
the 20kW boiler and 82% and 879% respectively at the 12 kW stove. NO and particles emissions are shown to dominate
during stationary operation.
Keywords: emissions, pellet boiler, stove, combustion, start-up, stop.
1 INTRODUCTION
Emission characteristics at each phase of pellet boiler
operations are important aspect to reduce the annual
emissions from residential pellet combustion.
Characterisation of the emissions during different
operation strategies makes it possible to identify the
phase when the major part of the emissions occur and
helps to take actions for emission reduction that can
achieve highest possible savings. A residential pellet
boiler may start and stop several thousand times [5] and a
considerable part of uncombusted are emitted during start
and stop periods [1, 2, 3]. Fiedler and Persson [2] and
Persson [4, 5] showed that the dominating part of the COemissions
in most pellet boilers were emitted during
start-up and stop phases of the burner. Several simulation
studies shows the possibility to substantially reduce the
annual CO-emissions by changing from ON/OFF control
to modulating operation, which results in fewer start-up
and longer operation periods with lower combustion
power [4, 5]. Good and Nussbaumer [3] have recently
reported gaseous and particles emission factors for two
pellet boilers.
2 MEASUREMENTS
A 20 kW wood pellet boiler and a 10 kW pellet stove
(extended room heater) were measured during steady
state operations and a six-days test. The six-days test was
developed for measuring of solar heating systems during
six days that should give results representative for annual
operation [5]. The steady state operations were measured
applying a constant heating load to avoid combustion
power modulation. In order to take the average, the
steady state measurement was repeated 3 times. In the
realistic six day test, the combustion devices were
connected to emulated domestic hot water and space
heating load and run according to a measurement
sequence developed by Bales [1] for comparable
measurements of solar-combi systems, which are
designed to give representative conditions of a full year
operation. The stove was connected to a storage tank with
a volume of 750 litres and an emulated 9 m 2 flat plate
solar collector.
The time of start-up and stop phases were chosen
according to the related emissions and combustion
power. Start-up phases commences after the ignition and
lasts until the emission concentrations and combustion
power have reached to the same level as a stationary
operation. Similarly, stop phase begins with a abrupt rises
of emissions followed by a slow decrease and continues
until the emissions are completed. In case of an
uncomplete stop phase followed by a start-up, the stop
phase is only taken to the beginning of the following
start-up.
2.1 Measurement set up
Figure 1: Schematic of the measurement set up
The measurement set up was shown in figure 1. A set
of multi-port averaging pitot-tubes calibrated in
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