60
3 Advanced Technologies (Biological and Thermochemical) …
before milling or is fed and milled with coal. They are burned in the same boiler
or gasifier with the same or different burners. The operations of direct co-firing are
usually limited to low co-firing ratios because of the inferior quality of biomass fuels
such as higher moisture content and lower bulk density [11]. It is, however, less
costly compared to the other methods, and it is a straightforward and commonly
applied approach. The indirect co-firing process consists of gasification of the solid
biomass into fuel gas and then co-combustion of the fuel gas with the coal in the
coal boiler furnace. This method is also suitable for co-firing of biomass with natural
gas and it has a higher degree of fuel flexibility especially when using biomass and
wastes of a lower quality [11]. However, it commonly needs the fuel gas cleanup
before co-combustion, a challenging and costly step. The parallel co-firing provides
the burning of the biomass in a completely separate boiler for steam generation. The
steam is then utilized in a coal power plant system. This process is most common in
the pulp and paper industry.
3.1.1.2 Parameters Affecting the Combustion
Biomass properties such as moisture, volatile matter and ash content can largely
affect the biomass combustion process in terms of flame stability and combustion
efficiency in both phases of combustion: a fast volatile matter combustion and the
relatively slower combustion of stable char [19]. The combustion characteristics of
biomass could be affected by pre-treatments such as the addition of Ca-containing
compounds to the agricultural biomass during storage [20]. The pre-treatments can
alter the composition of the ash deposits and affect the flue gas composition.
3.1.1.3 Industrial Applications of Combustion and Co-firing
Biomass combustion is widely applied in many countries around the world on
different scales. Small-scale combustion processes such as manually operated stoves
and boilers are mainly used for residential heating and have a capacity of ≤100 kW th
[21]. An example of the small-scale combustion system is diesel generators used
for vegetable oil-based power production, which is very well-known and requires
little or no adaptation. Medium-scale combustion technologies have a capacity range
from 100 kW th to 10 MW th and are mostly used for district heating (heat network),
process heating and cooling and Combined Heat and Power (CHP) production [21].
Industrial application of the combustion system mostly in capacities higher than 10
MW th , includes co-firing in large-scale coal-fired generation plants, which is the
most cost-effective use of biomass for power generation [21].
Table 3.1 lists some of the biomass co-firing plants operating in different countries.
In the Netherlands, for example, there are around eight biomass co-firing plants.
Co-firing is regarded as an important strategy to meet the renewable energy goals
in the Netherlands, where direct co-firing is the most commonly used technology
with most units having a capacity range of 420–650 MWe. The most often used
3 Advanced Technologies (Biological and Thermochemical) …
before milling or is fed and milled with coal. They are burned in the same boiler
or gasifier with the same or different burners. The operations of direct co-firing are
usually limited to low co-firing ratios because of the inferior quality of biomass fuels
such as higher moisture content and lower bulk density [11]. It is, however, less
costly compared to the other methods, and it is a straightforward and commonly
applied approach. The indirect co-firing process consists of gasification of the solid
biomass into fuel gas and then co-combustion of the fuel gas with the coal in the
coal boiler furnace. This method is also suitable for co-firing of biomass with natural
gas and it has a higher degree of fuel flexibility especially when using biomass and
wastes of a lower quality [11]. However, it commonly needs the fuel gas cleanup
before co-combustion, a challenging and costly step. The parallel co-firing provides
the burning of the biomass in a completely separate boiler for steam generation. The
steam is then utilized in a coal power plant system. This process is most common in
the pulp and paper industry.
3.1.1.2 Parameters Affecting the Combustion
Biomass properties such as moisture, volatile matter and ash content can largely
affect the biomass combustion process in terms of flame stability and combustion
efficiency in both phases of combustion: a fast volatile matter combustion and the
relatively slower combustion of stable char [19]. The combustion characteristics of
biomass could be affected by pre-treatments such as the addition of Ca-containing
compounds to the agricultural biomass during storage [20]. The pre-treatments can
alter the composition of the ash deposits and affect the flue gas composition.
3.1.1.3 Industrial Applications of Combustion and Co-firing
Biomass combustion is widely applied in many countries around the world on
different scales. Small-scale combustion processes such as manually operated stoves
and boilers are mainly used for residential heating and have a capacity of ≤100 kW th
[21]. An example of the small-scale combustion system is diesel generators used
for vegetable oil-based power production, which is very well-known and requires
little or no adaptation. Medium-scale combustion technologies have a capacity range
from 100 kW th to 10 MW th and are mostly used for district heating (heat network),
process heating and cooling and Combined Heat and Power (CHP) production [21].
Industrial application of the combustion system mostly in capacities higher than 10
MW th , includes co-firing in large-scale coal-fired generation plants, which is the
most cost-effective use of biomass for power generation [21].
Table 3.1 lists some of the biomass co-firing plants operating in different countries.
In the Netherlands, for example, there are around eight biomass co-firing plants.
Co-firing is regarded as an important strategy to meet the renewable energy goals
in the Netherlands, where direct co-firing is the most commonly used technology
with most units having a capacity range of 420–650 MWe. The most often used