Techniques fossil fuel based power plant with

Techniques
to Reduce the Environmental Impacts

          In order to reduce the
environmental impacts there should be a moratorium for coal-fired power plants
that do not capture their CO2 emissions and sequests CO2 “. The zero
emission (emissionless) is achieved by carbon capture and sequester. An example
of this type of plant is Elsam power station at Esbjerg, Denmark (European
Communities, 2006). One recommendation is that the coal used for power plants
should be clean coal. “Clean coal” is a term used by coal industry to
describe a type of coal from where minerals and impurities are chemically
washed of and processed (gasified, steam treated). In order to run coal-fired
power plants effectively, a cost-effective method is to run the plant on a diverse
type of fuel, such as conversions to biomass or municipal waste based power
plants. The emission level from this type of plants is estimated to be 20% less
CO2 than a coal fired unit operating at a same capacity

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Combined
heat and power

          Combined Heat and Power (CHP)
is a process to generate electricity and process heat. Instead of discharging
heat at a higher than ambient temperature, it is used to heat the buildings.
This expertise is commonly practiced in some countries, for example Denmark and
other Scandinavian countries and parts of Germany. Hansen 18 has shown that
CHPDH is the low-cost method of reduction in carbon emissions.

Options for
fossil fuel power plants

          The choices other than
coal-fired power plants include hydroelectric power, nuclear power, solar
power, wind power, geothermal power, tidal and new renewable energy techniques.
Some of the power production technologies are proven on large industrial scale
(i.e., hydroelectric, nuclear, wind, and tidal power) while others are in
prototype stage.

Cost by
power generation source

          The costs for a fossil fuel
based power plant with a life of 30 years to 50 years is charming for investor
due to the low initial investment i.e., around $1000 to $1300 per kilowatt
electricity as compared to $2000 per kilowatt from an onshore wind farm. This
cost calculation is only true when it strictly includes the cost of electricity
production and does not consider the indirect costs supplementary to the
pollutants generated due to fossil fuels burning (e.g., increased respiratory
diseases).

Particulate
matter control

          Particulate matter (PM) is
often classified as PM 2.5 and PM 10. PM 2.5 is particulate matter of size 2.5
µm and less. PM 10 is particulate matter 10 µm and less and it includes PM 2.5.
PM 2.5 is considered to have more harmful health effects than the relatively
coarser particles.

A particulate matter (PM) control
device (equipment) remove the PM from the exhaust gas stream, stop the PM from
re-entering the exhaust gases, and remove the collected PM. The main PM control
equipment in use are Electrostatic Precipitators (ESP), Fabric Filters (FF),
Mechanical Collectors (MC) and Venturi Scrubbers (VS). Each type of PM control
equipment is based on a different PM collection technique. The FF contains baghouse
which collects the particulate matter by using finely netted filters,
electrostatic precipitators creates an electromagnetic field to catch
particles, and centrifugal force is used by cyclone collectors to separate
particles ESP and FF are good to meet stringent EPA requirements of high
efficiency and reliability. A FF consists of a number of joint enclosures. Each
enclosure contains up to over a thousand fabric bags made of small diameters
and are attached with vertical supports. The flue gas passes through the fabric
bags and PM from the flue gas is accumulated on the bag surface. The cake
formed can contribute significantly to remove other constituents of flue gas,
such as SO2 and mercury

NOx control

          The original coal burners are
replaced with new Low NOx burners. The Low NOx burner apply advance fluid
dynamics and flame thermodynamics techniques to reduce flame temperature,
hence, less NOx. NOx is controlled by using Selective Catalytic Reduction (SCR)
systems and/or Non-Catalytic Reduction (SNCR) system. In these technical
treatment systems through a series of reactions with a chemical reagent
injected into the flue gas, NOx is reduced to N2 and H2 O. The most commonly
used chemical agents are NH3 and urea ((NH2 )2 CO) for SNCR. SNCR system introduce
urea into temperature range of 760°C to 1100°C (1400°F to 2012 °F). Within this
range, urea may react with available oxygen to form NOx and in this way the NOx
removed ranges from 15% to 35%.

SO2 control

          The emissions of SO2 can be
controlled by three approaches: 1) blending of fuel, 2) switching fuel, with a
fuel having lower sulfur contents, or 3) removing the SO2 from the flue gases.
SOx emission limits set by various countries are given in Table 7. A variety of
technologies are available to remove SO2 . Among these technologies the
prominent are: wet flue gas desulphurization (FGD), dry flue gas
desulphurization. The dry FDG use a spray dryer absorber (SDA) or circulating
dry scrubber (CDS), or dry sorbent injection (DSI). Conventionally used wet FGD
systems include a wet limestone process which forced oxidized S to remove as
SO2 and gypsum is obtained as a byproduct. SO2 removal efficiency achieved by
Limestone process is 98%.

 Wet FGD systems are designed for various types
of chemicals including magnesium-enriched lime, seawater, and soda ash (sodium
carbonate, Na2 CO3 ). Some limestone-based systems use an organic acid to
enhance SO2 removal. Wet FGDs was successfully used for coals such as lignite,
anthracite, bituminous, and sub-bituminous types. Figure 6 shows the locations
of the flue gas desulfurization (FGD) option in plant. It may be of interest
that in China, the installed capacity of FGD systems is increasing from 379 GWe
at end 2008 to 723 GWe in 2020 which represents 75% of all the new FGD to be
installed worldwide each year 20. A Spray Dry Flue Gas Desulfurization
Systems (SDA) is an example of dry FGD system. In SDA, lime slurry is atomized
and applied over the exhaust gases to absorb the SO2 and other gases. The
subsequent dry material with absorbed gases is collected in a downstream PM
control equipment, such as a FF or ESP. A small quantity of the dry material
can be recycled to minimize the usage of lime. The SDA cools the flue gas from
340 K to 350 K before the flue gas passes through the FF. Extremely low PM
emissions are possible, including PM2.5. Approximately 96% of SO2 can be
removed with the use of this technology which make it suitable to for
compliance of new emission limits. Advantages of dry FGD as compare to wet FGD
include: 1) Low construction cost, 2) Simple unit operations, 3) Less water
consumption, 4) lLss power consumption, 5) Use of alkalinity to control the fly
ash for SO2 absorption as well, and 6) Dry solid byproduct (easy to manage)