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Coal and biomass cofiring: fundamentals and future trends 135

The ignition temperature, burnout, and NO emissions of blends of a semianthracite
and a high-volatile bituminous coal with 10e20 wt.% of olive waste have also been
studied under oxy-fuel combustion conditions in an EFR (Riaza et al., 2012). A sig-
nificant reduction in ignition temperature and a slight increase in the burnout value
were observed after the addition of biomass, this trend becoming more noticeable as
the biomass concentration increased. Emissions of NO were significantly reduced
by the addition of biomass to the bituminous coal, although this effect was less notice-
able in the case of the semianthracite.

5.8 Future trends of biomass cofiring

The main challenges of biomass cofiring could be summarized as follows: (1) biomass
cannot compete on an economic point of view with coal (or other fossil energies) due
to low thermal efficiency, high cost, and variable impacts on boiler and milling equip-
ment; (2) biomass typically has low bulk energy density, is wet, and is strongly hydro-
philic, and therefore, requires a great deal of fuel handling technology compared with
its heating contribution; (3) fuel costs may be low, but transportation, preparation,
handling, and storage costs for biomass can rapidly exceed total fuel costs for other
fossil options; (4) potential for increased corrosion rates in boilers due to higher alkali
levels in biomass fuel; (5) biomass fuels can have as much as 50% moisture, which will
reduce efficiencies in the boiler; (6) there is higher possibility that the rate and extent of
boiler slagging will increase because ash fusion temperatures for most biomass fuels
o

are low (750 C to 1000 C); and finally, (7) potential emissions and gas cleaning
equipment should be considered, as well as ash utilization.
Regarding the possibilities of increasing the scale of biomass cofiring, incentives
and favorable regulatory and environmental policies will probably be the major factors
encouraging the interest in power generation and cogeneration from biomass energy
sources in the future. Moreover, the guarantee of a stable and cheap supply of biomass,
together with an optimum biomass delivery system, could influence the increase in the
number of cofiring power plants. A dedicated biomass infrastructure (e.g., feeding,
milling, storage, conveying) needs to be introduced into the existing coal system
(Tumuluru et al., 2012). The economic feasibility of cofiring biomass with coal is
determined by the costs of biomass acquisition and transportation. Support by govern-
ments to develop biomass supply chains would be necessary.
Coal-fired power stations that provide both power and heat to district heating net-
works or even industrial facilities may significantly increase the efficiency and the eco-
nomics of biomass cofiring. Cofiring in combined heat and power (CHP) plants is
currently the most competitive option to exploit the biomass energy potential for
both electricity and heat production. Appropriate policies are needed to achieve an effi-
cient use of the available biomass resource by encouraging the use of cofiring in
connection with CHP, as well as incentives for the conversion of power plants into
cofired CHP plants. Likewise, policies should also take into account the cobenefits