FIELD OF THE INVENTION:
The present invention generally relates to treatment of BOT water from coke oven
effluents. More particularly, the invention relates to a process for removing cd or
from BOT water of coke oven effluents.
BACKGROUND OF THE INVENTION
The wastewater produced during known carbonization and classification process of
fuel are as follows.
1. Water used for quenching the coke discharged from the retorts or ovens.
2. Waste formed during cooling and washing the gas.
3. Waste formed during the purification of by-products.
In the known process, a large amount of water is used. The waste waters include
waste waters from mining operations, from plating operations, from various
stripping operations, from various washing, scrubbing or flushing waters that are
used to wash chemical process off gases that contain various contaminants,
including cyanide, for example the off gases obtained from coke oven batteries
operating to manufacture coke used in steel mills.
Industrial wastewaters, containing various refractory organic pollutants, are often
discharged into the water environment without appropriate treatments. In order to
remove refractory organic pollutants effectively from industrial wastewaters, the
optimal treatment process with high quality effluent and low operating cost must be
selected and moreover appropriate operation of the wastewater treatment process is
required. Major components of coke-oven wastewaters are condensate of coke-oven
gases, which contain many refractory compounds in high concentration such as
phenol, thiocyanate, sulfide, cyanide, ammonia and so on. Furthermore, various
compounds such as fluorene, pyrene, acenaphthene, phenanthrene and
flouranthrene, can also be found in wastewaters (Littleton et al., 1992). Particularly,
phenolic compounds can easily migrate within different aqueous environments and
contaminate the groundwater because of their high solubility in water (Chang et al.,
1995).
A number of techniques for cyanide treatment, such as biomass treatment, chemical
oxidation, use of potassium permanganate, chlorine, and ozone, are known. It is
further known that certain metal ions, particularly iron, form complex compounds
with cyanide, which complex compounds can be soluble or insoluble in water and
the complexes are highly colored. However, some of these soluble or partially
soluble complexes do not allow removal of cyanide from waters through sludge or
precipitating process.
OBJECTS OF THE INVENTION:
It is therefore, an object of the invention to propose a process for treatment of
cyanide contaminated waters to remove therefrom cyanide by using a coke oven by-
product material.
Another object of the invention is to propose a process for treatment of cyanide
contaminated waters to remove therefrom cyanide by using a coke oven by-product
material which allows absorption of the cyanide compounds from coke oven waste
water by the coke-oven by product material.
A still another object of the invention is to propose a process for treatment of
cyanide contaminated waters to remove therefrom cyanide by using a coke oven by-
product material which enables reutilization of solid waste without adding chemicals.
A further object of the invention is to propose a process for treatment of cyanide
contaminated waters to remove therefrom cyanide by using a coke oven by-product
material cyanide removal which is cost effective;
SUMMARY OF THE INVENTION:
According to the invention, there is provided a process for removing colour from
BOT waterof coke oven effluents comprising: removing cyanide compounds from
the coke oven effluents by adding to the effluents a coke by-product material with
pH 8-9 at normal temperature; subjecting the soluble compounds to a step of
removing; and separating the treated fluid by one of Colum separation in a packed
bed column, and filtration in a mix reactor;
a surface modified coke oven by-product material is used for removing cyanide
anions from BOT effluent of coke oven wash water. Thus, the by-product material
of the invention is enabled to replace the known absorbents for cyanide removal
from Bot as well as other industrial effluents. A continuous mix reactor and absorber
column process can be adapted for efficient removal of cyanide from waste water
containing cyanide upto 100 mg/dm3. The inventive process is wholly effective
irrespective of pH value and temperature of the waste water. Thus, the
invention is capable of removing cyanide to the extent of at least 80%, relative
to initial cyanide concentrations, and preferably 99% removal or higher is
possible.
Cyanide wastes from ammonia pretreatment and BOT waters are particularly
waste waters treatable by the inventive process.
Further, according to inventive the process the adsorbent used is available cheaply,
easily and aplenty in steel plants and the output of the process can be easily
absorbed by the steel plants which interalia means the process entitles almost zero
raw material cost. Also, the process is capable of treating
cyanide contaminated waters containing from about 5 to about 1,000 parts per
million cyanide to remove at least 80, preferably at least 90% of the cyanide.
Broadly, this invention is an improved absorbent process for treating wastewaters
containing cyanides compounds. It is a very effective separation of cyanides and
compounds from the wastewaters without adding any flocculent etc. Finally coke bye
products materials used as an absorbent and left over materials back to sinter
making processing
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Figure 1 is a block diagram illustrating a flow chart of the process according to the
present invention implemented.
Figure 2 shows a mix reactor of the invention.
DETAILED DESCRIPTION OF THE INVENTION
WASTEWATER SAMPLES
Coke-oven wastewater discharged from coking plants is used. Characteristics of
coke-oven wastewaters in terms of COD, BOD, CN, phenol, SCN, NH3 and dissolved
organic carbon (DOC) are analysed
TREATMENT EXPERIMENTS
The process is implementable in an absorbent column with continuous operation.
Main part of the apparatus is a transparent column.
Methodologies:
Packed bed method: As shown in figure 2, the color is removed by passing water
through a Pack bed column which is packed by coke breeze. This is very standard
equipment & easy to implement. Some results are mentioned below to have a better
perception.
a. 1 kg of coke is able to remove near about 8 litre of water (1:8
ratio).
b. -3.15 mm - 0.25 mm size coke breeze is found satisfactory to
remove color bodies.
Mixing method: As shown in figure 1, the coke breeze & effluent of BOT is mixed
thoroughly by a mixture having a stirrer arrangement. After providing some
residence time in the mixer, the slurry is separated through filtration means for
example a pressure filter or an vacuum belt filter. Some results having that kind of
treatment are explained below.
a. Raw Coke Breeze without any size fraction can be used with
1:7 ratio. That implies 1 kg coke is able to remove 7 litre of
water.
b. Stirring speed is maintained at 600 r.p.m.
c. Normal filtration technique is able to separate coke from clean
water.
The color can be removed completely by implementing any of the two
embodiments of the invention. The results are as follows :-
1. The color constituents are developed due to phenyl thiocyanate complex with
cyanide & other phenolic compounds linkage with sulphur.
2. >99% color is removed which is analysed by UV-visible spectra-photometer
3. >=97% Phenolic compound is removed from treated water.
4. >=99% cyanide compound is removed from treated water.
5. >96% thiocyanate compound is removed from treated water.
6. 1 ton of coke breeze adsorbed 50 gm of color bodies which implies 150 gm of
CO2 & NO2 can be generated.
WE CLAIM:
1. A process for removing colour from BOT water of coke oven effluents
comprising:
removing cyanide compounds from the coke oven effluents by adding to the
effluents a coke by-product material with pH 8-9 at normal temperature;
subjecting the soluble compounds to a step of removing; and
separating the treated fluid by one of Golum separation in a packed bed
column, and filtration in a mix reactor;
2. The process as claimed in claim 1, wherein the step of separation is carried out
for a period of about 2 hour or 3 minutes respectively in case of packed bed
column or a mix reactor with sequential sampling for checking cyanide.
3. The process as claimed in claim 1, wherein the absorbent used is selected form
one of carbon materials and rejected coke materials.
4. The process as claimed in claim 1, wherein the particle size of the absorbent is
between -3.15 mm - 0.25 mm.
5. The process as claimed in claim 1, wherein the concentration of the absorbent is
1:7 by weight.
6. The process as claimed in claim 1, wherein 99% of cyanide compounds are
removed.
7. The process as claimed in claim 1, wherein the absorbent 100 % reusable.
8. The process as claimed in claim 1, comprising preparing a slurry of absorbent by
dissolving in waste water in a ratio from 1:5 to 1:20 at a speed of 800 to 900 rpm
in the reactor for a period of maximiuml20 minutes to form cyanide compounds
precipitant.

The invention relates to a process for removing colour from BOT water of coke
oven effluents comprising: removing cyanide compounds from the coke oven
effluents by adding to the effluents a coke by-product material with pH 8-9 at
normal temperature; subjecting the soluble compounds to a step of removing;
and separating the treated fluid by one of Colum separation in a packed bed
column, and filtration in a mix reactor;