Biomedical Engineering Reference
In-Depth Information
the combustion and physical handling characteristics of biomass and coal.
Such a fuel switch could reduce the output of an existing plant by as much
as 40%. The major inhibiting factors for 100% fuel switch are therefore:
1. Large capital investment for replacing the entire coal-firing and handling
system with biomass firing.
2. Long downtime of the existing plant for replacement of its firing system
with loss of revenues.
3. Reduction in output of the plant and in some cases lower overall effi-
ciency for operation of the steam cycle at reduced capacity.
4. The availability of large quantities of biomass at an affordable price could
also be an issue.
The extent of the above problems could be reduced by partial fuel switch
or cofiring such that the coal-fired plant can continue to fire coal along with
a modest amount of biomass.
10.5 COFIRING OPTIONS
Biomass cofiring has been successfully demonstrated in the large number of
installations worldwide for most combinations of fuels and boiler types.
There are three major options for cofiring in coal-fired boilers ( Figure 10.3 ):
1. Direct cofiring of raw or torrefied biomass
2. Gasification cofiring
3. Parallel cofiring
10.5.1 Direct Cofiring of Raw or Torrefied Biomass
In direct cofiring, the raw biomass and coal are fed directly into the boiler
furnace using the same or separate set of mills and burners ( Figure 10.3A ).
For this reason, it is simplest, least expensive, and most widely used. In
direct cofiring, there are several options like below:
1. Dried or raw biomass is mixed with coal upstream of the coal feeders.
They are then co-milled in the pulverizers.
2. Biomass is pulverized in separate mills and injected into the furnace
through existing coal burners.
3. Separate burner, mills, and other feed preparation are used for biomass.
In the first option, the dried and sized biomass is mixed with coal upstream
of the feeders. The mixture is then sent to the coal pulverizing mills, where it is
pulverized along with coal. The mixture of pulverized biomass and coal is dis-
tributed among all coal burners. It is the simplest option requiring least capital
investment, but it involves the highest risk of interference with the coal-firing
capability of the boiler unit. Thus, it is applicable to a limited range of biomass
Search WWH ::




Custom Search