of 7
1.
Basic descriptions of two
processes
1)
via “Sulphuric Acid
Vacuum concentration
Ø
Typical Process:
Concentrating waste acid from 20% ~ 60% or even lower to
70% ~ 75% by pre
-
vacuum concentration
process; concentrating acid from
70% to 85% by intermediate
vacuum concentration
; concent
rating acid from
85% to 96% ~ 97% by high concentration process.
Concentration
w
H
2
SO
4
20%
→→
w
H
2
SO
4
70%
→→
w
H
2
SO
4
85%
→→
w
H
2
SO
4
95%
Phase
I
pretreatment
It can be operated at atmospheric pressure or in vacuum. Different materials and
types of heaters can be used according to the concentration of waste acid and
impurity characters. Multi
-
effect (or multi
-
stages)
vacuum concentration
will
undoubtedly save en
ergy, but because multi
-
effect
vacuum concentration
will
increase the investment cost of equipment, generally it is not recommended to
use more than three
-
effect pre
-
concentration processes.
Phase
II
Intermediate
vacuum concentration
of sulphuric acid
w
H
2
SO
4
20%
→→→
w
H
2
SO
4
85%
Generally, it operates under the absolute pressure of 8 ~ 10Kpa and the
operating temperature is 150~180
°C
. For the devices with high processing
capacity, it can be divided into two or more stages to reach the final required
product c
oncentrations.
Phase
III
Highly concentrated
w
H
2
SO
4
85%
→→→
w
H
2
SO
4
95%
The main equipment is metal tantalum, which is expensive. Steam consumption
is huge during this process.
Ø
About our task:
For the feed w (
H
2
SO
4
) 45%, theoretically, it is possible to be
concentrated to
various concentrations of acid in the range of 45% ~ 95%.
2)
v
ia “Spent sulphuric acid regeneration (SAR) process”
Ø
Process:
thermal decomposition
(
Fuel must be added
)
→→
gas clealing
→→
dring&absorbtion
→→
converte
Concentration
w
H
2
SO
4
60%
→→→
w
H
2
SO
4
98%
Generally, the feed concentration should be w (H
2
SO
4
) > 60%, because a large
amount of water and air are brought into the combustion process. If the feed
concentration is low, the heat balance of the conversion process will be affected.
At the same t
ime, if the water content is too high, the water balance in the dry
suction section will be unbalanced.
Electronic
Supplementary
Material
(ESI)
for
Energy
&
Environmental
Science.
This
journal
is
©
The
Royal
Society
of
Chemistry
2021
Ø
About our task:
The feed with 45% concentration of (H2SO4) appears to be low in concentration
by the above mentioned SAR method and may be necessary to
be concentrated
first. Then use SAR process for further concentration and purification.
w
H
2
SO
4
45%
→→
w
H
2
SO
4
65%
→→
w
H
2
SO
4
75%
w
H
2
SO
4
85%
w
H
2
SO
4
95%
Tab.1
Comparison of two processes
comparative content
two processes
Sulphuric
Acid vacuum Concentration
SAR
Impurity content in waste acid
It is more suitable for waste acid with low impurity
content. It is suggested that it is suitable for small
amount of acid and low impurity content.
Using calciner
to incinerate
and
electrostatic
precipitation to remove
burning dust, no matter how
much impurity content in
waste acid, the process can
be used to treat the acid to
reach high quality acid and it
can be used in a wide range.
Final product
Only sulphuric
acid with a concentration of less than
98% can be produced, because 98% of the sulphuric
acid is mixed with water during concentration, and
only 98% can be achieved regardless of any measures
taken. When the waste acid is concentrated, the solid
impuritie
s cannot be removed, but the water and
volatile organic compounds are evaporated. The
concentrated waste acid can only be reused by this
product. Due to the recycling of concentrated waste
acid, the pipeline is easy to be blocked after a long
time, and aci
d sludge is easy to deposit at the bottom
of the acid storage tank.
Different concentrations of
waste acid can be produced.
Similar to sulphur burning
sulphuric acid, the quality of
sulphuric acid produced
could reach the national
standard.
equipment
investment
The use of tantalum material in the acid evaporating
tower
,
with enamel glass lining in the washing tower,
and the investment of the two equipment are
relatively high.
The process
es
from calciner
to transformation
and dust
removal is gas flow. T
he
equipment volume and pipe
size are large, the occupied
area (or footprint) is large,
and the equipment
investment is large.
operational
cost
Daily
maintenance of
equipment
Vacuum concentration of waste acid is easy to leak
under the condition of unstab
le temperature control
and sharp change of temperature due to the use of
some glass equipment pipes.
industrial
wastes
management
It mainly deals with acidic wastewater produced by
condensation and acidic wastewater from vacuum
pump.
Control the
content of sulfur
dioxide in waste gas, treat or
use acid wastewater, and
waste residue from
electrostatic precipitator.
Site
environment
and staffing
Depending on the size of the device, several full
-
time
staff members are required.
The installation site is neat
and clean, and the labor
intensity of workers is not
heavy.
Consumption of
waste acid
treatment
Steam or heat transfer oil is needed to vaporize water
under vacuum condition.
A large amount of natural
gas is needed. The
calciner
temperature is controlled at
about 1000
°C
, and the
water in the waste acid is
vaporized.
Other
consumption
Waste acid, low pressure steam, electricity, by
-
product medium pressure steam, water,
deoxidizing water, circulating water, analysis costs
, maintenance costs, equipment
depreciation, personnel wages, management costs
2.
investigation of industrial waste acid treatment plant
Tab.2
Concentration of industrial waste acids from different sources and their usual
treatment processes
Various kinds
of waste acid from
different industrial processes
Waste acid concentration
Treatment process
Titanium dioxide waste acid
w
H
2
SO
4
19%~23%
concentration
Aromatics nitrification waste acid
w
H
2
SO
4
60%~70%
concentration
Dyestuff waste acid
w
H
2
SO
4
10%~50%
Partly neutralization
or ”concentration
Steel
cleaning
waste acid
w
H
2
SO
4
5%~10%
Recycling
FeSO4
Fe
2
(SO
4
)
3
n
Alkylation waste acid
w
H
2
SO
4
85%~90%
regeneration (SAR)
MMA
w
H
2
SO
4
40%
w
(NH
4
)
2
SO
4
35%
concentration + regeneration
(SAR)
Hydrofluoric
acid drying waste acid
w
H
2
SO
4
75%~85%
concentration
Chlor alkali waste acid
w
H
2
SO
4
75%~80%
concentration
or ” Air lift
Acetylene purifying waste acid
w
H
2
SO
4
80%~90%
concentration
or
regeneration (SAR)
or
neutralization
Tab.3 operational cost
of
Sulphuric Acid Concentration (45%
→→→
96%)
(
A device in Nanjing
,china)
unit consumption
Unit Price
Unit cost
(yuan/t)
Sulphuric acid 45%
2155
kg/t
Alkali (in kind)
180
kg/t
550
yuan/1000kg
99
Qing River water
200
kg/t
0.85
yuan/kg
170
circulating water
100
t/t
0.18
yuan/t
18
electric
69
kWh/t
0.65
yuan/kWh
44.85
Medium pressure steam
0.45
t/t
150
yuan/t
67.5
1.1MPa
1.2
t/t
140
yuan/t
168
Cost analysis
3
maintenance costs
10
Depreciation of equipment
20
Personnel wages
28.7
Management cost
10
operational cost
639.05
The vacuum concentration process needs two stages of enrichment, from 45% to 65%
or 65% to 96%. The operational cost is about 600 yuan
/ ton (including depreciation).
Tab.4
operational
cost
of
SAR
(
45
%
→→→
96
%)
(
A device in Nanjing
,
C
hina)
unit raw material
consumption
Unit Price
Unit cost
(yuan/t)
waste acid
45.00%
2155
kg/t
Low pressure steam
0.8MPa
80
kg/t
130
yuan
/1000kg
10.4
electric
95
kWh/t
0.65
yuan/kWh
61.75
By
-
product medium
pressure steam
3.2MPa
-
800
kg/t
150
yuan/1000kg
-
120
Qingjiang River water
500
kg/t
0.85
yuan/1000kg
0.425
De
-
oxygen water
1160
kg/t
24
yuan/1000kg
27.84
circulating water
82000
kg/t
0.18
yuan/1000kg
14.76
Natural gas
230
Nm3/t
2.8
yuan/Nm3
644
Cost analysis
3
maintenance costs
3
Depreciation of
equipment
40
Personnel wages
28.7
Management cost
10
operational cost
723.875
The operational cost of waste acid regeneration process is about 1000 yuan / ton.
The investigation of the industrial waste acid treatment plant has found that the
source of waste acid, the type of impurity content, the initial concentration of waste
acid, the concentration of finished acid, the amount of treatment, the steam used,
the
combustion gas and so on are the factors affecting the process combination,
investment and operational cost of the treatment plant. Therefore, it is difficult to
collect enough data from the completed
project
s in line with our task requirements.
In the fo
llowing work, I intend to set the preconditions for a certain type of waste
acid with a starting concentration of 45% w (H
2
SO
4
), daily
treatment amount
, steam,
and burning gas (calorific value), and ask experts to give rough estimations based on
personal e
xperience of different final sulphuric acid concentrations, investment and
operating costs.
3.
Waste sulfuric acid treatment and
vacuum concentration
process and its
operational cost and investment analysis
Setting up the process condition of waste sulfuric
acid concentration, analyzing
different final sulfuric acid concentration, its investment and operational
cost
1)
cost estimation of waste sulfuric acid vacuum concentration
process
Tab.5
cost estimation of waste sulfuric acid vacuum concentration process
Primary
concentration
final
concentration
yield
(ton / day)
CapEx
(10000 yuan)
OpEx
(yuan / ton)
Remarks
45%
55%
500
1070
114.3
1000
1800
112
45%
65%
500
1400
202.5
1000
2350
200
45%
75%
500
1550
286
1000
2630
283
45%
85%
500
1870
354.6
1000
3170
350
45%
95%
500
2670
450
1000
4070
445
3D
graph
2)
cost estimation of Spent sulphuric acid regeneration (SAR) process
The feed with 45% concentration of (H
2
SO
4
) appears to be low in
concentration by
Spent sulphuric acid regeneration (SAR) process method and can be concentrated
first
t
hen use SAR mode.
Because of it’s high investment cost,
professionals give the following suggestions
and estimate the related costs
f
or our task,
.
w
H
2
SO
4
45%
→→
w
H
2
SO
4
65%
using waste acid concentration process;
w
H
2
SO
4
45%
→→
w
H
2
SO
4
75%
using waste acid concentration process;
w
H
2
SO
4
45%
→→
w
H
2
SO
4
85%
using two stage concentration process.
w
H
2
SO
4
45%
→→
w
H
2
SO
4
95%
us
in
g
two stage
concentration and regeneration
process(SAR)
Tab.6
cost estimation
of
spent acid regeneration
(SAR)
processes
Primary
concentration
final
concentration
yield
(ton / day)
CapEx
(10000
yuan)
OpEx
(yuan / ton)
备注
45%
65%
500
1441
215
vacuum
concentration
1000
2420
212
45%
75%
500
1610
300
vacuum
concentration
1000
2720
297
45%
85%
500
1970
3
6
4.6
2 stage
1000
3320
3
58
vacuum
concentration
45%
95%
500
3600
7
50
2 stage
vacuum
concentration
+ regeneration
(SAR)
1000
6
070
745
3D
graph