FIELD OF INVENTION
The present invention relates to a process of minimising level of impurities
present in spent wash oil (SWO) for utilising the same as an alternative source of
energy in replacement of light diesel oil (LDO).
BACKGROUND OF THE INVENTION
The wash oil is used for scrubbing of naphthalene to purify coke oven gas
generated during coal to coke conversion. After scrubbing the spent wash oil is
generated, which has calorific value similar to light diesel oil (LDO). The present
invention represents the innovation for further utilization of spent wash oil (SWO) as an
alternative source of energy by improving the performance of existing process. It is
necessary to minimize the level of impurity present in spent wash oil before its
utilization.
A huge volume of jute batching oil or wash oil is consumed in coke making
process scrubbing of naphthalene from coke oven gas. After scrubbing, wash oil is
regenerated by stripping out the naphthalene from the wash oil using steam distillation
as there is an appreciable amount of gap in boiling point of wash oil (Initial BP 2850C

and final BP 3710C) and naphthalene (2100C). Meanwhile, after some cycles the
regeneration cannot help to regain the adsorbing property of wash oil at initial stage
then such wash oil is called spent or used wash oil which is replaced by fresh wash oil.
Such type of spent oil can’t be discharge directly to the environment thus it is stored in
safe place. However, storage capacity is also limited. Therefore, in general practice,
SWO is sold in the market at very nominal price. Hence, discharge of this type of oil is
totally market dependent and storage of such kind of oil increases health hazard. Thus
in-situ utilization is best possible choice in such circumstances.
Several researchers have attempted to utilize different type of waste oil after
purification and some of them separated out different type of by-products form waste
wash oil. The term ‘wash oil’, present some of the inventions e.g. EP3026101 and
CN104087373 is very different physically and chemically form the term used in the
present study. Above those invention ‘wash oil’ refers an emulsion of water and oil
whereas in the present invention the commercial name of wash oil is ‘jute batching oil’.
In the invention US4206186, spent wash oil has been pyrolyzed for its further utilization
which is very energy consuming. Moreover, researchers have tried to purify spent wash
oil (CN103087763, BE826540, CN101333453, JPH01194908, PL162110) though such
process is very energy consuming and needs extra capital investment.
The present invention has been tried to develop a direct process of utilization of
SWO by enhancing the efficiency of existing system. Based on literature and preliminary

studies it has been predicted that SWO having high calorific value can be utilized as a
fuel for generation of energy. Hence, the present study has been conducted to reuse
SWO as fuel for boiler operation effectively without alternation of current system.
OBJECTS OF THE INVENTION
Therefore, it is an object of the invention to propose a process of minimising
level of impurities present in spent wash oil for utilising the same as an alternative
source of energy, which is capable of reducing level of contamination in SWO.
Another object of the invention is to propose a process of minimising level of
impurities present in spent wash oil for utilising the same as an alternative source of
energy, which is capable of regenerating used wash oil or jute batching oil by stripping
out naphthalene with the help of distillation.
SUMMARY OF THE INVENTION
The wash oil or jute batching oil is used for scrubbing of naphthalene from coke
oven gas. Scrubbing efficiency of wash oil is reduced after certain no of recycle
depending on process parameters, and then used or SWO is replaced by fresh wash oil.
The disposal of spent wash oil is market dependent as it is sold in the market at very

nominal price. Sometime due to insufficient market demand, disposal of such oil is very
difficult and thus it is essential to utilize spent wash oil insitu. However, that can
possible only after the separation of impurities from spent wash oil so that the
characteristics should be very similar to conventional fuel oil.
By improving naphthalene stripping process, it has been established that the
physiochemical properties of SWO is very similar with light diesel oil (LDO). LDO is
commonly used for boiler operation. Therefore, SWO can be used as replacement of
LDO or it can be used by mixing with LDO in different proportion.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Fig. 1: Shows circuit of utilization of wash oil and regeneration of spent wash oil.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
The current process of naphthalene scrubbing plant has been shown in the figure
1. The wash oil is delivered to the naphthalene scrubber (101) to adsorb naphthalene
and the naphthalene rich wash oil is transferred to decanter (102) where phase
separation takes place. Lean oil along with make again sent back to scrubber (101)
and rich oil send to naphthalene still (104) via preheater (103) to reach the temperature

1400C before distillation. After distillation naphthalene is separated out from condenser
(105) and certain portion of wash oil is returned back to still (104) for further
distillation. The bottom product of still (104) is enriched with wash oil from which
maximum portion recycled back to decanter (102) via cooler (108) to reach
temperature 350C and rest amount sent to regenerator (107) for separation of
maximum impurities. In regenerator (107) steam is supplied to maintain temperature
1600C and vapor phase again sent back to still (104). Spent wash oil is discarded from
decanter (102) by replacing fresh make up to maintain impurity (percentage of
naphthalene) level less than 0.005% in lean oil. The spent wash oil is stored in storage
tank (109) having naphthalene percentage 2.3 to 2.5% and time to time it is sold into
the market. Insufficient market demand causes serious discharge problem, thus insitu
utilization is only way to remove such limitations. Before utilization as fuel it is essential
to remove impurities as much as possible for reduction of viscosity spent wash oil.
The used wash oil or jute batching oil is regenerated by stripping out the
naphthalene with help of steam distillation (104) as wash oil (Initial BP 2850C and final
BP 3710C) and naphthalene (2100C) have good boiling point difference. However, after
some time the regeneration is not possible due to saturation and then spent or used
wash oil is replaced by fresh wash oil.
Lab scale distillation of SWO had been conducted to enhance the quality of the
SWO and remove the organic impurities. It was observed that after distillation, the

impurity level (percentage of naphthalene) was less than 0.05% but at higher
temperature than the temperature at which the plant is operated. Therefore, based on
the lab scale study, the plant trial was conducted by increasing the temperature of
preheater (103) from 1400C to 1500C and in regenerator (107) from 1600C to 1750C
(figure 1). Hence, the impurity level became less than 0.05-0.06% in SWO, whereas
earlier the impurity level was greater than 2%. Such changes have also ensured the
reduction of percentage of polymerized oil present in SWO.
CHARACTERIZATION OF SPENT WASH OIL:
There are several impurities mainly naphthalene and polymerized oil present in
spent wash oil as mentioned in table 1, thus for further utilization SWO, it is essential to
reduce the level of contamination. It is mandatory to compare different fuel properties
of SWO with LDO for its further utilization as fuel. Those properties of SWO were
estimated and compared with LDO as shown in the table 1. It had been observed that
most of the properties of SWO after the process modification were very similar and in
some cases SWO was better than LDO as fuel. It was also noted that the amount of
naphthalene and other polymerized oil present in SWO was reduced appreciably after
alternation of process parameter (table 1). Such comparative study ensured that SWO
could be utilized as replacement of LDO in existing system. Moreover, SWO was mixed
with LDO in different proportions and after characterizations of those blend (table 2), it
had been confirmed SWO could be used at any proportion with LDO.

TRIAL WITH SPENT WASH OIL:
Plant trials were conducted using only SWO and different blends of LDO and
SWO in boilers of power houses. Initially trial was failed during the use of SWO in boiler
operation and it was observed due to higher density and viscosity of SWO than LDO,
atomization during burning of SWO could not take place properly. Therefore, poor flame
stability was obtained in the boiler. Steam atomizers are used in boilers. In atomizer,
the steam pressure was adjusted in such a manner so that atomization took place
properly. After proper atomization, both SWO and its blends with LDO at different
proportion were successfully used in boiler operation and the flame stability was
constant.
Moreover, the impact of utilization of SWO as fuel on the environment had been
studied and it had been observed there were similar effects on environment as compare
to other fuel like LDO.
The present invention reduces the disposal problem SWO as earlier disposal is
totally market dependent, health hazard and other material handling problem. This also
ensures huge amount of financial benefit along with the reduction of use of fossil fuel
and carbon foot print.

WE CLAIM
1. A process of minimising level of impurities present in spent wash oil for utilising
the same as an alternative source of energy comprising;
delivering wash oil to a naphthalene scrubber (101) to adsorb naphthalene;
transferring naphthalene rich wash oil to a decanter (102) to allow phase
separation;
transferring lean oil back to said scrubber (101);
delivering rich oil from the decanter (102) to a naphthalene still (104) through a
preheater (103) reaching a temperature of 1400C before distillation;
introducing low pressure steam (LP steam) to the said naphthalene still (104) for
distillation; wherein distilled oil goes to a condenser (105) where naphthalene is
separated out from condenser (105) and certain portion of wash oil is returned back to
still (104) for further distillation, when maximum portion of bottom product of still (104)
being enriched with wash oil is returned back to the decanter (102) via a cooler (108)
reaching a temperature of 350C, when rest amount of oil is sent to a regenerator (107)
to separate maximum impurities, wherein steam is supplied to maintain a temperature
of 1600C and oil in vapour phase is again sent back to still (104) when spent wash oil is
discarded from decanter (102) by replacing fresh oil to maintain impurity level less than
0.005% in lean oil, wherein the spent wash oil is stored in storage tank (109) having
naphthalene percentage 2.3 to 2.5 %, wherein the temperature of preheater (103) is

increased from 1400C to 1500C and that of regenerator from 1600C to 1700C to reduce
the level of impurities below 0.05% - 0.06% ensuring reduction of percentage of
polymerized oil present in spent wash oil.
2. The process as claimed in claim 1, wherein steam pressure is adjusted for proper
atomization during burning of spent wash oil (SWO) and its blends with LDO at different
proportion are successfully used in boiler operation having the flame stability constant.
3. The process as claimed in claim 1, wherein after few number of regeneration,
the said regeneration becomes saturated, when spent or used wash oil is replaced by
fresh wash oil.