Biomass Cofiring and Torrefaction - Biomass Gasification, Pyrolysis and Torrefaction - page 357

percentage amount of biomass fired (Z). For the set of plant for which
Eq. (10.1) was developed, it was correlated as (Tillman 2000):

Reduction in NO x emission 0 : 75Z% (10.2)

5

Reduction is measured in kg/GJ input and Z is in mass percentage of bio-
mass in feed.
Adding biomass to the coal could also decrease the nitrous oxide (N 2 O)
emission, a strong GHG (about 300 times more potent than CO 2 ), from the
boiler due to the higher oxygen carbon (O/C) ratio of biomass and probably

due to catalytic effects of relatively high amount of calcium, potassium, and
sodium in biomass (EUBIONET, 2003, p. 21).

10.3.1 CO 2 Reduction
Biomass being a carbon neutral fuel, the CO 2 released from the combustion
of biomass in a cofired boiler does not make any net contribution to the
global CO 2 inventory (see Section 1.3.2). Additionally, owing to its high
hydrogen carbon (H/C) molar ratio, biomass combustion releases lesser

amount of CO 2 than that by lower H/C ratio fuels like coal or oil.

10.4 CARBON CAPTURE AND STORAGE (CCS) VERSUS
BIOMASS FIRING
Generation of power without much or no addition to the atmospheric inven-
tory of CO 2 can be achieved through one of the following two options:
1. Carbon dioxide capture and its sequestration from existing or new coal-
fired power plants (CCS).
2. Conversion of existing coal-based power plant into 100% biomass firing.

The first option (CCS) is most talked about and researched as it provides
a lasting and complete solution to the emission of GHG from coal-fired
plants. In this option, efforts are being made to retrofit existing coal-fired
units with a CCS plant as a CO 2 scrubbing system. The CCS option allows
generation of electric power from coal in conventional means, while largely
avoiding the release of the CO 2 to the atmosphere. This is done by removing
carbon dioxide from the flue gas by amine scrubbing or other techniques and
sequestering it appropriately. One option for CO 2 scrubbing involves separa-
tion of carbon dioxide by using oxygen instead of air for combustion. This
option, known as “oxy-firing,” requires complete change in the entire firing
system of the boiler such that the flue gas is free from nitrogen and it con-
tains mostly CO 2 . The flue gas being primarily made of CO 2 it permits easy
compression and its eventual sequestration in appropriate storage.
The CCS technology when fully developed would require additional
energy for separating CO 2 (or for generating O 2 for oxy-firing) from flue gas