This invention relates to a bench scale plant for organo refining process.
This invention further relates to a bench scale plant for organo refining
process, which is economical and has optimum heat exchanger network
for effective use of waste heat, to produce low ash clean coal from high
ash coals for various metallurgical operations.
BACKGROUND OF THE INVENTION:
Organo refining process fundamentals are available In various
literatures, but hardly any attempts have been taken to design the
process in a techno economical way. Cobe steel of Japan has given some
thoughts for designing the process in bench scale level, but the works
are very limited and inadequate to prove the plant economics completely.
SUMMARY OF THE INVENTION
According to the invention, coal, solvent and co-solvent are mixed
thoroughly to produce coal slurry. The coal slurry is extracted with a
predetermined ratio of coal-solvent mixture. In extraction unit a
sufficient high temperature is maintained to facilitate the extraction at
high temperature. A high pressure is required to elevate the boiling point
of the liquid. The temperature and pressure range of variation is around
(200 °C to 300 °C) and (1.5 atm. to 5 atm.). Due to thermal impact coal
structure relaxed and extraction process is enhanced. Coal extract is
then released in a flasher unit at atmospheric pressure. Due to the
pressure drop 15% of the solvent will flash out leaving 85% of liquid at
the bottom of flash chamber, which is then sent to the evaporator. In
evaporator a further recovery of solvent is done and the concentrate
heavy material is then discharged into the precipitation tank. The
combination of evaporator and flash unit gives almost 70-80% of solvent
recovery. The rest of the solvent, which is still 20-30% in amount, can be
recovered from distillation unit. The immense quantity of heat comes
from flash chamber & evaporator top & bottom product. According to the
invention, it is possible to extract heat from waste heat streams. This
heat recovery is made possible by implementing a heat exchanger
network (HEN) with a sophisticated automation which is able to bridge
between continuous discrete heat sources. Therefore, the invention
relates to the HEN method and the logic to achieve continuous & discrete
heat to recover heat from waste heats and the methodology to integrate
the discrete & continuous heat sources to get a continuous heat
recovery.
OBJECTS OF THE INVENTION:
It is therefore an object of this invention to propose a bench scale plant
for organo refining process, which is economical.
It is a further object of this invention to propose a bench scale plant for
organo refining process, from which the solvents can be easily recovered
from the main process stream.
Another object of this invention to propose a bench scale plant for organo
refining process, wherein waste heat is very effectively recovered by
introducing a heat exchanger network.
These and other objects of the invention will be apparent from the
ensuing description.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Fig 1 shows a diagram of the organo refining process according to the
invention.
Fig 2 shows the different modes of heat available from reactor and
evaporator.
Fig 3 shows the details of heat exchanger network with 60 min next
cycle.
Fig 4. shows the details of heat exchanger network with 75 min next
cycle.
DETAILED DESCRIPTION OF THE INVENTION
Coal, solvent and co-solvent are mixed thoroughly In coal in feed
preparation zone. Coal slurry is then pumped to the reactor. In reactor a
temperature around 200 to 300°C, preferably around 220°C IS
maintained by circulating hot thermic fluid. The high pressure is
maintained by inducing high pressure about 1.5 to 5 atm, preferably, 3
to 4 atm. inside the reactor. High pressure elevates the boiling point of
the solvent. Residence time in the reactor may vary from 1 h to 1.5 h and
i.e. dictated by the techno economics of the process and its specific
requirement. Then the coal extract are send to the flasher unit. In
flasher due to the sudden pressure drop 15% of the solvent will be
flashed off as the temperature of the solvent is much more than the
atmospheric boiling point of the solvent. This way 15%is required of the
solvent without introducing any external heat source. Actually reactor
high pressure and temperature are being exploited for flashing. The
heavy material with some coal extracts is then fed to the evaporator.
Bottom part of the flasher also contains some amount of coal extract
which is again discharged into the evaporator. The residue is taken off
and stored for later use. The filtrate contains little but coal extracts
which is fed to the evaporator. In evaporator the "coal extract" IS
concentrated by boiling of most of the solvent. With the help of
evaporation a further 55- 65 % of solvent recovery is possible. This way
almost 70-80% of the solvents recovery is possible by the combination of
flasher and evaporation unit. In precipitating tank coal is precipitated as
water acts as an anti solvent. This slurry is filtered by another rotary
drum filter and the super clean coal is collected as residue. The filtrate
contains water and organic mixture which is fed to the distillation unit
and water and organic components are separated. In distillation unit the
remaining 20 to 30% of solvent is recovered. The proposed design helps
to recover 99% of the solvent by combination of flash unit, evaporation
unit and distillation unit with minimum energy consumption, hence it
proves the process feasibility.
Coal, solvent and co-solvent are mixed thoroughly to produce coal slurry.
The coal slurry is extracted in reactor (1) with a predetermined ratio of
coal-solvent mixture. In extraction unit a sufficient high temperature is
maintained to facilitate the extraction at high temperature. The
temperature and pressure range of operation is around 200°C to 220°C
and 1.5 atm. to 3 atm .. Due to thermal impact coal structure relaxes and
extraction process is enhanced. Coal extract is then released in a flasher
unit at atmospheric pressure. Due to the pressure drop some fraction of
the solvent will flash out leaving extracted slurry at the bottom of flash
reactor. The slurry is then sent to the hot filtration unit (2) from where
residue (4) is sent to the washing unit (9) & then clean extracted part
coal (3) is carried forward to the evaporator as filtrate. In evaporator (5) a
further recovery of solvent is done and the concentrate heavy material is
then discharged into the precipitation tank (6). The combination of
evaporator and flasher gives almost 70-80% of solvent recovery. The rest
of the solvent, which is still 20-30% in amount, can be recovered from
distillation unit. The fundamental problem arises in implementing HEN
is the synchronization between batch & continuous process that means
heat recovered from reactor is batch mode & heat gained from evaporator
out going streams is in continuous mode. A technique is employed to
recover all the heat from waste heat stream the store it to impart it to the
other cold streams.
The heat exchanger network needs three heat exchangers in its loop.
Heat exchangers are required inevitably during process operation
1
irrespective of heat exchanger network. The function of HE1 is Reflux
condenser. The HE2 and HE3 are required for condensing -cooling
evaporator top and bottom product. If heat exchanger network had not
been there then all the heat exchangers would have been run by cooling
water and that amount of heat is wasted as water gives low temperature
heat and can't be used in any other place. So if heat exchanger network
is to be introduced then instead of water Thermic fluid oil is used as it
produces high temperature heat (750C to 1700C). The arrangement for
using that hot sink heat in different place is a bit complex and needs to
be automated intelligently. Fabrication wise there is no great difference of
keeping HEN or not. Anyway the exchangers are required by any mode
and thus the concept of HEN can be incorporated without any big capital
and operating cost. Benefit of heat economy can fetch substantial
amount of heat economy. Here we have devised a way to execute the
entire network in a very systematic manner.
Nowhere the main heat sources are
I.Hot fluid from Boiler
Heat is required in
I.Reactor
2. Evaporator
3. Distillation Reboiler
Distillation feed pre heater
So the waste heat can be obtained through cold thermic fluid heat sink
from
I.Flashed Product from the top of the reactor.
2.Evaporator Top & Bottom Product
The heat source is hot thermic fluid which is coming from boiler. For
preservation of heat, the heat sink concept has been introduced, Heat
sink is a cold thermic fluid stream which takes all the waste heats
coming from reactor top product & evaporator. The cold heat sink gets
heated and that secondary hot thermic fluid is then distributed among
different places like distillation columns to use that heat. Now the main
problem encountered in this heat preservation system is the mode of
containing heat. Figure 2 depicts the different modes of heat available
from reactor & evaporator. In Reactor (11 of figure 2) the heat is coming
in a discrete mode as the reactor is operated in batch mode. Again heat
is coming from evaporator (12 in figure 2) top & bottom product cooling
but in continuous mode. So there is mismanagement of heat extraction
9
as overlap takes place between discrete & continuous heat sources. Thus
a systematic algorithm is developed to conduct the heat exchange
operation smoothly.
The details of heat exchanger network and heat capturing methodology
are depicted in figure 3. There are two reservoirs implemented into the
system. One is hot sink (HS) which is for storing hot thermic fluid which
is being heated by taking heat from heat exchangers HE1, HE2 & HE3.
Likewise another heat sink, the cold heat sink (CS) is used to receive the
cold thermic fluid steam after delivering heat of HS to HE4 & HE5. Now
among the heat sources HE1 is discrete heat source and HE2 , HE3 are
the continuous heat sources. So fluid in CS is taking heat from HE1
where hot flushes of reactors (RV-01, RV-02, RV-03) are cooled down
periodically. This fluid in CS is getting hot and stored in HS. The hot
fluid in HS then provides heat through feed pre heater (HE4) of DISTl.
The same stream after delivering heat to HE4 cools down and returns
back to the CS. Similarly another hot stream from HS is used as hot
medium in Reboiler of DIST2. The return hot outlet is then sent to the
CS to further processing. The basic problem arises due to the heat
available in (RV-01, RV-02, RV-03). This heat is available only for a short
time span (15 minutes interval of each). This heat along with continuous
10
heat available from evaporator top & bottom product cooler (HE2 & HE3),
are stored in HS. The fluid in HS then delivers heat (as explained above)
in different capacity. So the capacity of fluid transported from CS and the
fluid pumped from HS is different. But the total flow in a cycle is
constant according to the mass balance. This means that if 1000 kg of
CS fluid is used in 60 minute cycle, HS has to maintain 1000 Kg of fluid
in that cycle but in different capacity. The proposed algorithm helps to
get rid of the synchronizing problem & the all the heat exchanger is
synchronized without harming total mass balance of the system.
Basis:Distillation should start 30 min prior to reflux condenser. PI & P2
should be considered in such a way that flow rate passing through line
14 should be exactly two times equal to flow rate of fluid passes through
line 13.
Time = 1 hr
PI Flow rate 500 Kgjhr, P2 Flow rate 1000 Kgjhr
HS contains 250 Kg hot 170°C fluid
CS contains 250 Kg 75°C cold fluid
Time (Min)
o
Mass in HS
250
Mass in CS
250
~I
The solenoid valve S5 opens after 30 minutes and the line 13 allows a
flow rate of 500 Kgjhr coming from HS through pump PI. So after 30
minutes the scenario is like this
30 o 500
Likewise the solenoid valve S4 is open after 30 minutes and the line 14
receives a flow rate of 1000 Kg per hour of CS fluid pumped from P2.
This will continue to next 30 minutes & after 30 minutes the HS receives
a flow of 500 Kg coming from CS fluid through pump P2. At the same
time 250 Kg of fluid is being pumped from HS through pump PI and
going ultimately to CS. So after 60 minutes from starting the scenario is
like this.
60 250 250
Again after 60 minutes S5 is on and allows another 500 kgjhr of fluid
from HS to next 30 minutes while keeping the S4 off.
90 o 500
After 90 minutes S4 is on and S5 is off and line 14 receives a flow rate of
1000 Kg per hour of CS fluid pumped from P2 to next 30 minutes. So
after 120 minutes of operation the mass distribution is as follows.
120
250
Mass in HS can be calculated by the equation 1 &2.
Mass in HS= Mass in HS previously - flow rate in line 13*(~tj60 )+ flow
rate in line 2*(~tj 60) (1)
250
rL
Mass in CS= Mass in CS previously + flow rate in line 13*(~tj60) - flow
rate in line 2*(~tj 60)
Where ~t= time span in min
(2)
The tabulated data is shown in Table 1:
Time Sl S2 S3 S4 S5 Flow Flow Mass Mass
(Min) Status Status Status Status Status rate in rate in in HS in CS
line 1 line 2 (kg) (Kg)
(Kgjhr) (Kgjhr)
0 0 0 0 0 0 0 0 250 250
10 0 0 0 0 1 500 0 166.67 333.33
20 0 0 0 0 1 500 0 83.33 416.67
30 0 a 0 0 1 500 0 0 500
40 1 0 0 1 1 500 1000 83.33 416.67
50 0 1 0 1 1 500 1000 166.67 333.33
60 0 0 1 1 1 500 1000 250 250
10 0 0 0 0 1 500 0 166.67 333.33
20 0 0 0 0 1 500 0 83.33 416.67
30 0 0 0 0 1 500 0 0 500
40 1 0 0 1 1 500 1000 83.33 416.67
50 0 1 0 1 1 500 1000 166.67 333.33
60 0 0 1 1 1 500 1000 250 250
\3
Table 1: Status of the valves & storage tanks in a 60 minute cycle of
operation
In the second case, an uneven heat cycle is considered i.e. complete cycle
of batch operation is considered to be 75 minutes. In 15 minutes
interval S1, S2 & S3 will open alternatively to pass hot flush which
actually opened the valve S4 too. So altogether 45 minute is taken to cool
down hot flush and thus S4 is open for 45 minutes in 75 minutes total
batch cycle. The entire HEN is shown in figure 4
Basis:Distillation should start 30 min prior to reflux condenser. PI & P2
should be considered such a way that flow rate passing through line 14
should be exactly two times equal to flow rate of fluid passes through line
13.
Time = 1 hr
Flow rate through line 14 =800 Kgjhr pumped by P2
Flow rate through line 13 = 320 Kgjhr pumped by PI
HS contains 160 Kg hot 170°C fluid
CS contains 240 Kg 75°C cold fluid
160
Mass in CS
240
Time (Min)
o
Mass in HS
The solenoid valve S5 opens after 30 minutes and the line 13 allows a
flow rate of 320 Kgjhr coming from HS through pump PI. So after 30
minutes the scenario is like this
30 o 400
Likewise the solenoid valve S4 is open after 30 minutes and the line 14
receives a flow rate of 800 Kg per hour of CS fluid pumped from P2. So
well before 45 minutes 400 kg material will deliver to HS by pump P2. At
the same time in 45 minute time duration through pump PI pumped
240 Kg liquid through line 13 at 320 Kgjhr flow rate. So after 75 minute
time elapsed from starting situation becomes.
75 160 240
Again after 75 minutes S5 is on and allows another 320 kgjhr of fluid
from HS to next 30 minutes while keeping the S4 off.
105 o 400
After 105 minutes S4 is on and S5 is off and line 14 receives a flow rate
of 800 Kg per hour of CS fluid pumped from P2 by 45 minutes. So after
150 minutes of operation the mass distribution is as follows.
150 160 240
The whole process operation is tabulated in table 2:
Mass in HS can be calculated by the equation 3,4 & 5.
Mass in HS= Mass in HS previously - flow rate in line 13*(~tj60 )+ flow
rate in line 2*(~tj 60) (3)
Mass in CS= Mass in CS previously + flow rate in line 13*(~t/60) - flow
rate in line 2*(~t/ 60)=
Mass in CS +Mass in HS = 400
Where ~t= time span in min (most of case ~t IS appearing to be 10
(4)
minutes)
Time SI S2 S3 S4 S5 Flow Flow Mass in Mass in
(Min) Status Status Status Status Status rate in rate in HS CS
line 1 line 2 (kg) (Kg)
(Kg/hr) (Kg/hr)
0 0 0 0 0 0 0 0 160 240
10 0 0 0 0 1 320 0 106.67 293.33
20 0 0 0 0 1 320 0 53.33 346.67
30 0 0 0 0 1 320 0 0 400
40 1 0 0 1 1 320 800 80 320
50 0 1 0 1 1 320 800 160 240
60 0 0 1 1 1 320 800 240 160
70 0 0 0 0 1 320 0 186.67 213.33
75 0 0 0 0 1 320 0 160 240
85 0 0 0 0 1 320 0 106.67 293.33
95 0 0 0 0 1 320 0 53.33 346.67
105 0 0 0 0 1 320 0 0 400
115 1 0 0 1 1 320 800 80 320
125 0 1 0 1 1 320 800 160 240
135 0 0 1 1 1 320 800 240 160
145 0 0 0 0 1 320 0 186.67 213.33
150 0 0 0 0 1 320 0 160 240
l6
Table 2: Status of the valves & storage tanks in a 75 minute cycle of
operation
So this way the entire mass preservation system is well maintained and
the operation will be continuing without any disturbance.
WE CLAIM:
1. A process for the organo refining of coal uSIng an integrated heat
exchanger network, comprising the steps of mixing coal, solvent and cosolvent
in the coal feed preparation zone of a reactor to obtain coal
extract,
transferring the coal extract to a flasher unit, wherein there is a sudden
pressure drop which boils off 15% of the sovent, leaving a heavy material
with coal extracts,
feeding the heavy material with coal extracts to an evaporator, boiling the
coal extracts therein to recover 55 to 65% solvent, to yield a slurry,
transferring the slurry to a precipitating tank, where the coal gets
precipitated to provide a slurry of coal in water, filtering the
slurry through a rotary drum filter, to obtain super clean coal,
the heat required for the process being hot thermic fluid which is stored
in the hot sink (HS), the heat being supplied from the reactor top and
bottom products, and the evaporator top and bottom products.
2. The process as claimed in claim 1, wherein the temperature in the
reactor is maintained between 200 to 300°C.
3. The process as claimed in claim 1, wherein the pressure in the reactor
is maintained between 1.5 to 5 atm.
'8
4.The process as claimed in claim 1, wherein the residence time in the
reactor is from 1 hour to 1.5 hours.
5. The process as claimed in claim 1, wherein 99% of the solvent is
recovered by a combination of the flasher unit, evaporator and
distillation unit.
6. The process as claimed in claim 1, wherein the hot thermic fluid is
heated by taking heat from heat exchangers HE1, HE2 and HE3.
7. The process as claimed in claim 1, wherein the HS delivers heat to
HE4 and HE5 and results in a cold thermic fluid, which is delivered to
the cold heat sink (CS).
8. The process as claimed in claim 1, wherein the fluid in CS takes heat
from HE1.