1 AN ASSESSEMENT OF THE CORRELATION BETWEEN FUELS AND DEPOSITIONS IN THE COMBUSTION CHAMBER OF THE MISKOLC BIOMASS HEATING PLANT Péter Kókai, Csaba Póliska, Bernadett Csordás University of Miskolc Abstract Modern district heating systems represent an attractive alternative in the view of inhabitants accomodating their demand for thermal energy. Production of thermal energy in biomass combustion boilers contributes to the reduction of pollutant emission associated with the combustion of fossile fuels. This article focuses on a wood chip boiler of 3MW output, in the combustion chamber of which depositions were produced on the chamotte lining reducing boiler performance. Our aim was to explore the exact reasons leading to formation and continuous growth of slags during operation. We were looking for correlations between various fuels combusted in our boiler, the operational parameters of the boiler and the slags formed. We defined the combustion features of various fuels, the softening features of fuel ashes and deposition samples as well as the structure and composition of ash samples by using a scanning electrone microscope; based on our findings we have drawn consequences and proposed potential measures. 1. Introduction How to provide buildings with heating and domestic hot water is a central issue in many countries of the world. It has been hotly debated which energy system would be the best solution for the future, but the issue that has generally been agreed on is that combustion of fossile fuels is to be reduced. Some go as far as working out systems based on 100% renewable fuels. [1]. One view is that buildings must be built with a low energy consumption, while the other view is that renewable energy resources and waste heat, the byproduct of various branches of the industry must be utilized at a higher level of efficiency. In this latter case the thermal energy produced centrally needs to be transported to end-users via some district heating system. The district heating system (DHS) is a central heating plant, which provides the neighbouring buildings with thermal energy and domestic hot water [2]. State of the art biomass boilers ensure high operating efficiency; the primary energy consumption of the district is reduced while energy efficacy is linearly growing. These benefits compensate for the environmental damage associated with the operation of the boiler [3][4]. Carbohydrates, more specifically natural gas dominates the energy structure of Hungary; it has a significant role in heat production as well, mainly in households, 90% of which are dependent on natural gas. Most district heating plants (>80%) operate with this fuel, while Hungary has no effect whatsoever on the constantly growing prices of fossile fuels. Because prices have been rising faster and faster leaving Hungary at the mercy of gas suppliers, it is absolutely necessary to at least partly substitute the purely natural gas based heat prodution with renewing fuels. One of the potential ways of substitution is involving biomass as fuel into district heat production. Biomass based district heating systems have been operated successfully all over Europe and more and more Hungarian towns have been considering a similar expansion [5] [6] [7] [8]. Furthermore, while reducing fossile fuel dependency, it is also important to emphasize that utilization of biomass fuels creates new workplaces in any given community thus furthering social and economical improvement of the community [9]. DOI: 10.26649/musci.2015.016
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1
AN ASSESSEMENT OF THE CORRELATION BETWEEN FUELS AND
DEPOSITIONS IN THE COMBUSTION CHAMBER OF THE MISKOLC BIOMASS
HEATING PLANT
Péter Kókai, Csaba Póliska, Bernadett Csordás University of Miskolc
Abstract
Modern district heating systems represent an attractive alternative in the view of inhabitants
accomodating their demand for thermal energy. Production of thermal energy in biomass
combustion boilers contributes to the reduction of pollutant emission associated with the
combustion of fossile fuels.
This article focuses on a wood chip boiler of 3MW output, in the combustion chamber of
which depositions were produced on the chamotte lining reducing boiler performance. Our
aim was to explore the exact reasons leading to formation and continuous growth of slags
during operation. We were looking for correlations between various fuels combusted in our
boiler, the operational parameters of the boiler and the slags formed.
We defined the combustion features of various fuels, the softening features of fuel ashes and
deposition samples as well as the structure and composition of ash samples by using a
scanning electrone microscope; based on our findings we have drawn consequences and
proposed potential measures.
1. Introduction
How to provide buildings with heating and domestic hot water is a central issue in many
countries of the world. It has been hotly debated which energy system would be the best
solution for the future, but the issue that has generally been agreed on is that combustion of
fossile fuels is to be reduced. Some go as far as working out systems based on 100%
renewable fuels. [1]. One view is that buildings must be built with a low energy consumption,
while the other view is that renewable energy resources and waste heat, the byproduct of
various branches of the industry must be utilized at a higher level of efficiency. In this latter
case the thermal energy produced centrally needs to be transported to end-users via some
district heating system. The district heating system (DHS) is a central heating plant, which
provides the neighbouring buildings with thermal energy and domestic hot water [2]. State of
the art biomass boilers ensure high operating efficiency; the primary energy consumption of
the district is reduced while energy efficacy is linearly growing. These benefits compensate
for the environmental damage associated with the operation of the boiler [3][4].
Carbohydrates, more specifically natural gas dominates the energy structure of Hungary; it
has a significant role in heat production as well, mainly in households, 90% of which are
dependent on natural gas. Most district heating plants (>80%) operate with this fuel, while
Hungary has no effect whatsoever on the constantly growing prices of fossile fuels. Because
prices have been rising faster and faster leaving Hungary at the mercy of gas suppliers, it is
absolutely necessary to at least partly substitute the purely natural gas based heat prodution
with renewing fuels. One of the potential ways of substitution is involving biomass as fuel
into district heat production. Biomass based district heating systems have been operated
successfully all over Europe and more and more Hungarian towns have been considering a
similar expansion [5] [6] [7] [8]. Furthermore, while reducing fossile fuel dependency, it is
also important to emphasize that utilization of biomass fuels creates new workplaces in any
given community thus furthering social and economical improvement of the community [9].
DOI: 10.26649/musci.2015.016
2
MIHŐ short for Miskolci Hőszolgáltató Kft. (Miskolc District Heating Supplier LLC) is a
public service provider operating the second biggest district heating system in Hungary
producing and providing heat for about 32,000 end-users in homes and 1,200 public
institutions.
District heat supply in Miskolc was exclusively covered by natural gas until 2008, with hardly
more than 0.1% improvement on it when the heating system based on depot gas fuel in the
Hejőcsaba housing area of Miskolc was installed. In 2009 the town decided that natural gas
based thermal energy must be substituted by alternative fuels.The first step on the road was a
green-field investment, the construction of a 3MW boiler based on wood chip combustion in
the Kenderföld district of Miskolc. Planned technical and operational parameters of the boiler
are tabulated below in Table 1.
Table 1. Planned technical and operational parameters of the boiler based on wood chip
combustion
Technical parameters Planned values
Heat generating capacity 41 087 GJ/year
Heat fed in with fuel 51 470 GJ/year
Boiler efficiency rating 80%
Amount of input fuel 4 500 t/year
Wood chip usage per hour 900 kg/h
Nominal heat output 3 MWt
Temperature of produced hot water max. 110 °C
Number of operating hours about 5 000/évyear
1.1. The biomass boiler of the Kenderföld heating plant
The Binder RRK 2500-3000/6 wood chip fire boiler is equipped with a grate shaker and a
multicyclone flue gas filter. Figure 1 illustrates a cross sectional view of the boiler and below
we shall give a short overview of the most important features of the appliance.
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Fig. 1. Cross sectional view of the boiler (1. Fuel inlet: Stoker screw; 2. Walking grate; 3.