POWER May 2021 - 33

COAL POWER
such as heavy metals will also enter the
flue gas during the combustion process,
and later turn into water pollution through
the desulfurization process.
FGD wastewater mainly comes from
the concentrated filtrate of the secondary
cyclone separator. It is an inorganic wastewater
with high salinity and high hardness.
The pH is about 4 to 6. The composition is
quite complex, containing large amounts
of suspended solids, chloride salts, heavy
metals, and excessive boron.
In the past, the traditional chemical
precipitation method was used for FGD
wastewater treatment. Chemical coagulation
precipitation is a standard solid-liquid
separation procedure, which is widely
used in various industrial wastewater applications
and has a good removal effect
on heavy metals in the water. The sources
of boron in FGD wastewater include coal
used for power generation and combustion,
and limestone powder used in FGD
equipment to remove SOx
from flue gas.
The original FGD wastewater treatment
process had extremely low removal rates
for boron, which led to the release of boron
in the water. The concentration was often
much higher than the discharge water control
standard of 5 milligrams/liter.
Boron removal technology can be
roughly divided into five types, namely
chemical precipitation, ion exchange,
adsorption, reverse osmosis, and extraction,
but each method has its limitations.
The method of reverse osmosis is currently
the most widely commercialized
technology, but it is limited to low-concentration
boron-containing wastewater
or seawater desalination.
Both the chemical precipitation method
and the extraction method are very
suitable for the treatment of high-concentration
boron-containing wastewater. The
solvents used in the extraction method
are mostly diols, but the toxicity of the
solvent and subsequent treatment are
relatively tricky. The chemical precipitation
method is the most widely used in the industry.
It is an accepted technology, but
the traditional coagulation precipitation
method often requires high-temperature
conditions to simulate the hydrothermal
method to produce insoluble species.
The present invention relates to a
method for treating high concentrations
of boron-containing wastewater. The
method includes one stage of pretreatment
that uses hydrogen peroxides to
react with borate ions and one stage of
precipitation that uses precipitant (such
as barium hydroxide and barium chloride)
to extensively remove boron from
May 2021 | POWER
boron-containing wastewater as perborate
precipitants. The method of present
invention is effective to high concentrations
of boron-containing wastewater
and capable of reducing boron level to
less than 5 ppm, which is the average
concentration of seawater.
TCPP engineers were so stressed in this
situation that they were constantly seeking
and eager to find an appropriate solution.
They worked together with the Industrial
Technology Research Institute (ITRI), which
has professional experience in technology
research and development. They used a
patented fluidized bed to treat the boroncontaining
wastewater (Figure 1).
A fluidized-bed crystallization wastewater
treatment device includes a reaction
tank containing a carrier. The waste water
to be treated enters from the bottom of
the reaction tank and flows upward, and
the reaction tank is connected with a firstrate
water circuit. Part of the wastewater
is pressurized and returned to fluidize the
above-mentioned support, and part of it
is brought into the reaction tank due to
the siphon effect. The reaction tank is
also connected with a medicament inlet
for injecting medicament, so that the
pollutants in the wastewater are on the
fluidized support crystallization, and the
treated wastewater flows out from the
outlet on the top of the reaction tank.
According to a present invention, the
method for treating
wastewater includes pre-treatment
high-concentration
of
boron-containing wastewater and a precipitation
step of applying the pretreated
wastewater to the wastewater. A proper
ratio of hydrogen peroxide is stirred and reacted
for a period of time. The precipitation
step is to use a barium-containing compound
to mix with the pretreated wastewater
to produce perborate precipitation,
and stir for a period of time. In a preferred
embodiment, the method for treating highconcentration
boron-containing wastewater
further includes a pH control step, a
mixing and stirring step to fully mix the solution,
and the proper operating conditions
of the pretreatment tank.
Ecological Environment
Fireflies appeared at the TCPP in the early
days when larvae arrived with the planting
earth when the facility was built. As TCPP
maintains 50% of the land green and has
a lot of trees planted around it, and there
is low human interference in other areas,
the environment has allowed the fireflies
to gradually multiply for decades.
In the ecological pond water intake
test and analysis, it is believed that the
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2. The ecological environment around the
Taichung Power Plant supports fireflies and
many types of bird species, including terns,
such as the one pictured here. Courtesy:
Taipower
artificial repopulation technology will be
stable, and the aquatic yellow firefly can
grow up twice a year. The ecological pond
was refurbished to build an isolated area
with embankments, filled with treated
water from the circulated fluidized bed.
At the same time, Wu Guo fish, shrimp,
and crabs that swallowed firefly larvae
were removed. Native plants, such as
Ficus and Jinxinmu ginger, create a suitable
growth environment for the yellowrimmed
firefly. A black net was set up by
the pool to block the street lights and car
lights in order to reduce the damage to
fireflies from incandescent.
Rehabilitation experts have said: " It
takes at least three to five years for
fireflies to repopulate to be stable. Of
course, the environment must continue
to maintain a good ecology to cultivate
stable populations. "
The coal sinking pond and the forest
on the southwest side of the factory are
far away from the generator set and people.
There are few cars passing by, there
are not many street lights, and the green
belt forms a suitable growth environment
for Taiwanese window fireflies.
In addition, little terns (Figure 2) were
observed circling, drinking water, and
wetting their belly feathers around the
coal sink, and then returning to the nest to
cool their bird eggs. TCPP chose to build
and maintain artificial breeding grounds
for small terns near the wind turbines and
on the roof of the warehouse, including
laying gravel habitat, drainage design,
vegetation and power grid maintenance,
and installation of fake birds.
After more than 15 status records, 73
species were found inside and outside
the factory. Furthermore, more than 5,000
species of birds were active, carrying out
breeding and nesting behaviors. TCPP intends
to continue striking a delicate balance
between plant development and
ecological environment maintenance. ■
-Hsu ChiaHao is genernal manager and
Liao ZiFeng is an environmental engineer
at Taipower's Taichung Power Plant.
33
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