TM 5-815-1/AFR 19-6
f. Approach to fuel substitution. An approach to fuel
-- adjusting turbine control valves to insure
substitution should proceed in the following manner:
proper lift
(1) Determine the availability of low sulfur fuels.
-- adjusting preheater seals and feedwater heat-
(2) For each, determine which would have sulfur
ers
emissions allowable under appropriate
-- insuring cleanliness of heat transfer surfaces,
regulations.
such as condensers, superheaters, reheaters,
(3) Determine the effect of each on particulate
and air heaters.
h. Limestone injection. One of the earliest tech-
emissions, boiler capacity and gas tem-
peratures, boiler fouling and slagging, and
niques used to reduce sulfur oxide emission was the
existing particulate control devices.
use of limestone as a fuel additive. This technique
(4) Identify the required equipment modifica-
involves limestone injection into the boiler with the
tions, including transport, storage, handling,
coal or into the high temperature zone of the furnace.
preparation, combustion, and control equip-
The limestone is calcined by the heat and reacts with
ment.
the SO2 in the boiler to form calcium sulfate. The
(5) For the required heat output calculate the
unreacted limestone, and the fly ash are then collected
appropriate fuel feed rate.
in an electrostatic precipitator, fabric bag filter, or
(6) Determine fuel costs.
other particulate control device. There are a number of
(7) Determine the cost of boiler and equipment
problems associated with this approach:
(1) The sulfur oxide removal efficiency of the
modification in terms of capital investment
additive approach is in the range of 50 to
and operation.
70% in field applications. However, it is
(8) Annualize fuel costs, capital charges, and
considered feasible that when combined with
operating and maintenance costs.
coal cleaning, it is possible to achieve an
(9) With the original fuel as a baseline, compare
overall SO2 reduction of 80 percent.
emissions and costs for alternate fuels.
(2) The limestone used in the process cannot be
(g. Modification to boiler operations and mainte-
recovered.
nance.
(3) The addition of limestone increases
(1) A method of reducing sulfur oxides emissions
particulate loadings. In the precipitator this
is to improve the boiler use of the available
adversely affects collection efficiency.
heat. If the useful energy release from the
(4) The effects of an increased ash load on
boiler per unit of energy input to the boiler
slagging and fouling as well as on particulate
can be increased, the total fuel consumption
collection equipment present a group of
and emissions will also be reduced.
problems which must be carefully considered.
(2) An improvement in the boiler release of
(5) The high particulate loadings and potential
useful energy per unit of energy input can be
boiler tube fouling in high heat release boilers
achieved by increasing boiler steam pressure
tend to cause additional expense and technical
and temperature. Doubling the steam drum
problems associated with handling large par-
pressure can increase the useful heat release
ticulate loadings in the collection equipment.
per unit of energy input by seven percent.
(6) There have been many claims over the years
Increasing the steam temperature from 900 to
regarding the applicability of fuel additives to
1000 degrees Fahrenheit can result in an
the reduction of sulfur oxide emissions. The
improvement in the heat release per unit of
United States Environmental Protection
energy input of about 3.5 percent.
Agency has tested the effect of additives on
(3) Another way to maximize the boiler's output
residual and distillate oil-fired furnaces. They
per unit of energy input is to increase the
conclude that the additives have little or no
attention given to maintenance of the correct
effect.
fuel to air ratio. Proper automatic controls
i. Flue gas desulfurization (FGD). There are a
can perform this function with a high degree
variety of processes which have demonstrated the
of accuracy.
ability to remove sulfur oxides from exhaust gases.
(4) If additional emphasis can be put on mainte-
Although this technology has been demonstrated for
nance tasks which directly effect the boilers
some time, its reduction to sound engineering practice
ability to release more energy per unit of
and widespread acceptance has been slow. This is
energy input they should be considered a
particularly true from the standpoint of high system
modification of boiler operations. Items
reliability. The most promising systems and their
which fall into this category are:
performance characteristics are shown in table 10-2.
-- Washing turbine blades
j. Boiler injection of limestone with wet scrubber. In
-- adjusting for maximum throttle pressure
this system limestone is injected into the boiler and is
10-2
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