Modeling and Simulation for S.S. Re-Rolling Mills Waste Treatment

8/3/2019 Modeling and Simulation for S.S. Re-Rolling Mills Waste Treatment

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Modeling and Simulation for S.S. Re-Rolling Mills Waste Treatment

Document by: Bharadwaj

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Abstract: The S.S. Re-Rolling mills use mixture of acids to wash the plates during process. This acid

mixture becomes waste and is currently treated by lime which generates lot of solid sludge. A treatment

process of commercial importance has been developed to convert this effluent into a useful product. The

S.S. Re-Rolling mills are of different size and hence effluent generated are of varying magnitude ranging

from 4000 liters / day to 15,000 liters / day. The process developed therefore needs to be simplified to treat

different quantity of waste liquor. This paper offers computer program for the sizing of various equipments,

important components and certain important features of lay-out of the treatment plant. The treatment

process is briefly discussed first with flow diagram. With the help of equipment occupancy chart, the need

of various size of equipment is worked out and finally the model is presented. The simulation of the model

is done using C programming language.

Keywords: S.S. Re-Rolling Mill Waste, Waste Treatment, Algorithm, Mathematical

model, Simulation

Introduction

The industrial process for the treatment of the waste from S.S. Re-rolling mill has been

developed (1).The paper briefly describes the process with flow diagram. The details of

the process on industrial scale have been worked out during the exercise performed to

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submit the report to Department of Science and Technology (DST) under ‘Technology

Transfer Scheme’. The industries generate effluent of different magnitude and hence the

treatment plant required is also of different size. Since the cost of treatment may not be

affordable by a single unit, number of units can come together, form a cluster to generate

and treat the larger quantity of effluent. Thus the need for the size of the effluent

treatment plant will vary. Looking at the need the paper describes the modeling and

simulation for the above case. In the last segment of this paper the application of this

simulation is explained.

Process Description

The industrial process for said treatment is shown along with the flow diagram. Pl. refer

fig.1. The pickling liquor is treated for a day with the Mild Steel Scrap. The clear

supernatant liquor is then neutralized to pH 7 by adding pickling liquor to the

Ammonium hydroxide solution. This is done in a neutralizing tank. Neutralization takes

40 minutes. The slurry is then circulated through the spray reactor, three-phase separator

and then is returned to the neutralizing tank. Slurry gets sprayed in the reactor and there it

gets oxidized with air. The time for oxidation ranges from 20 to 45 minutes, judged by

the color change of the slurry to reddish brown. The mass then is separated in the three

phase separator into liquid and solid phase. The wet precipitates are collected, dried and

calcined in furnace to obtain red iron oxide.

Mathematical Model



The problem involves treatment of waste pickling liquor generated by industry. Normally

the quantity remains between 4000 and 15000 liters/day. The material flow is already

described. Now the problem remains to design the equipment used at various stages.

The liquor is available continuously and total collection in a day is, say, Q liters. The

segment of the process which involves circulation of pickling liquor from storage tank of

pickling liquor to oxidizer, to separator and then back to neutralizer; 1st segment of the

process, takes 2.5 hr. The steps of filtration, moulding, drying and calcinations then

follows. The quantity of the material to be handled changes from ‘1 st segment of the

process’ to different subsequent steps of the process. Hence selection of the size of the

equipment for ‘1st segment of the process’ is done separately and selection of the

equipment for each stage is done separately.

For ‘1st segment of the process’, per 8 hours three cycles can be conveniently completed

without any hassle. Therefore, in 24 hours, 9 cycles can be completed. Hence, the

capacity of the equipment in ‘1st segment of the process’ is chosen as compatible to 9 th

part of the total pickling liquor production.

As said before, in the subsequent operations, there are filtration, moulding, drying and

calcination. The rate of filtration, rate of drying and rate of calcination are all established

in the laboratory, providing necessary design data. Further, equipments for operation like

filtration, drying and calcination are available in standard sizes. Hence, equipment sizing

for all these operations are done depending upon batch size and commercially available

equipment size. Help of Equipment occupancy chart is taken. Pl refer fig. 2. From the

equipment occupancy chart also, it becomes clear that sizing of the set of equipment for



‘1st segment of the process’ should be done as a single unit and it should again match the

intake requirement and equipment availability of subsequent operations. The equipments

that are used subsequently are available with the standard sizes, hence they are chosen

such that they can treat the desired amount of material (either one, two three or any

integer no. of batches from ‘1st segment of the process.’)

The model is developed for the sizing of all the equipments that are used in entire

process. There are many assumptions and thumb rules to simplify the modeling

procedures. But this is based on the engineering judgment obtained while undertaking the

process at pilot scale and authors believe that it will be applicable at all scale.

Conventional design equations are used to develop the mathematical model for different

units of the entire plant.

Algorithm

1. Enter the amount of pickling liquor generated per day.

2. Amount of Scrap quantity required, decided based on experimental study, is calculated.

3. Storage tank: Storage tank volume is calculated. Based on tank volume, the

diameter and height of the tank is calculated.

4. Neutralizer: Quantity of Ammonium Hydroxide is calculated based on amount of

pickling liquor.

5. Volume of neutralizing tank which is volume required to tackle the neutralized liquid.

6. Pump Capacity: Based on the neutralizer volume and the number of times liquid is to

be circulated in the ‘1st segment of process’ (which is based on experimental

observations), the pump capacity is calculated.



7. Cross-sectional area and the Diameter of the liquid pipe is calculated using the

volumetric flowrate and the velocity of the entering liquid (assumed). Then after, nearest

standard pipe size for liquid is chosen.

8. Blower: Blower pipe diameter, is chosen from the available standard pipe and is taken

to be 2.5 to 3 times the liquid pipe diameter.

9. Volumetric flowrate of blower is calculated using the velocity of the gas (assumption

based on pilot plant study) and the cross-sectional area of the gas pipe.

10. Based on the volumetric flowrate and assumed volumetric efficiency of blower, the

blower capacity is calculated and the nearest standard blower is chosen.

11. Spray reactor: The cross-sectional area and the diameter of the spray reactor is

calculated using the velocity of the gas in the spray reactor (assumed) and volumetric

flowrate.

12. Flowarea for the gas is assumed to be 66% of the total available area and remaining is

assumed to be that of liquid.

13. Total flowarea is calculated based on the gas flowarea (gas flowarea is 66.6% of total

flowarea).

14. Total flowarea is also calculated based on the liquid flowarea (liquid flowarea is

33.3% of total flowarea). Liquid flowarea is calculated based on pump capacity and

entering velocity of liquid.

15. The higher value of the two total flowarea calculated in step 14 and step 15, is then

taken for subsequent calculations.

16. From the selected total flowarea, the liquid flowarea is calculated.



17. From this liquid flowarea and volumetric flowrate of liquid, final velocity of liquid in

spray reactor is calculated.

18. Initial Velocity of the liquid through nozzle (calculated) and the final velocity gives

the time required and from that distance traveled to acquire that final velocity is

calculated. This gives the cylindrical height of the spray reactor.

19. Standard cone with 60o angle is considered.

20. From the selected total flowarea, diameter of the outlet pipe of the spray reactor is

calculated.

21. The diameter of the pipe from ‘outlet of spray reactor to inlet of separator’ is

calculated assuming gas velocity and assuming that 66% of the total flowarea is occupied

by the gas.

22. Having known diameter of the pipe, diameter of the spray reactor and angle of cone,

the conical height of the reactor is calculated. Finally the total height is calculated which

is the total of cylindrical and conical height.

23. Separator: The diameter of inlet pipe of Separator is same as the outlet of the spray

reactor.

24. The diameter of top outlet of separator is to facilitate the gas flow and is taken to be

1” more than the inlet pipe of the gas to the spray reactor.

25. The diameter of separator is then taken to be 8” greater than the gas outlet of

separator.

26. Liquid is assumed to take two turns before settling. From the velocity of the liquid

and the horizontal distance traveled, time required is calculated.



27. From the time calculated, the final outlet velocity of the liquid at the bottom is

calculated. Based on which the cylindrical height for the lower part is calculated.

28. The upper part of the separator (from the inlet pipe) is taken to be double than the

lower part and the total height is calculated.

29. Standard cone with 60o angle is considered.

30. Liquid Outlet pipe diameter from separator is calculated from the liquid flowrate and

the calculated velocity.

31. From the diameter of the separator, diameter of the outlet pipe of separator and cone

angle, height of the conical part is calculated.

32. Finally the total height is calculated which is the total of cylindrical and conical

height.

33. Service tank: This tank will accommodate filtered liquor for entire day, because,

filtration would be conducted during day time only (either in one or two shift). So, from

the total volume of liquor collected, diameter and height of the flat bottom tank is

calculated.

34. Filter press: Weight of dry cake per day is calculated based on dry cake obtained per

liter of pickling liquor during experimental work.

35. From the known characteristic values of the cake, initial moisture content and final

moisture content, the volume of the wet cake is calculated.

36. The volume required to accommodate the wet cake and volume available in the

standard filter press is compared and right size of the standard filter press is chosen.

37. Dryer: The batch fluidized bed dryer is used for operation.



38. Wet cake generated in a day can be dried in a single operation of smallest available

size of batch fluidized bed dryer.

39. Calcinator: Weight and volume of the material to be calcined is calculated. Since it

is less as compared to the available standard size of furnaces, for the calcination

operation batch size for material produced during entire day is considered.

40. Accordingly the size of the furnace required is calculated.

Discussion on Simulation

The model equations were first formulated and then simulated using programming

language ‘C’. The pilot plant study has already been carried out for this process and the

data used has been validated. The process involved different equipments like neutralizer,

spray reactor, separator, calcinator, dryer, filter press, etc. for which the mathematical

model was developed using conventional design equations. The basis for the process was

taken to be 10,000 ltrs/day pickling liquor (a validated data as mentioned earlier). Taking

this basis, all the necessary mathematical equations were designed for the respective

equipments with suitable assumptions which are included in algorithm. The entire

process was divided into two major segments. In the first segment three equipments were

considered together and in the second segment all equipments were treated as separate

unit and then the mathematical equations were designed for convenience. This model was

then simulated so that we can get the appropriate size of all the equipments by just

entering the amount of the pickling liquor.



Conclusions

The S.S Re-Rolling plants are of various capacities. The pickling liquor coming out

ranges in size. The program developed and run can be used to design the plant for various

output of the pickling liquor. The program was verified for different amount of pickling

liquor and was found to be appropriate. The utility of this program could be immense

looking at the need of the treatment plants for effluent of S.S. Re-Rolling Mills.

References

1. Desai M.G., ’Treatment of waste Pickling Liquor from S.S.Rolling Mill,’ Indian

Chemical Engineer, Vol. 47/No.2,April-June,2005.

2. Desai M.G., ’Project – Proposal Report on Iron Oxide from Waste Pickling

Liquor from S.S. Re-Rolling Mills,’ Department of Chemical Engineering,

V.G.E.C., Chandkheda.2009

List of figures

1. Process flow Diagram

2. Equipment occupancy chart.



1,2,3,4 Pickling Liquor Tanks

5 A Neutraliser 5 B Spray Reactor 5 C TPS-3 5 D Filter Press

6 A Heater 6 B Blower 7 Mould Making

8 Calcinator

9 Drier 10 Treated liquor tank

Fig. 1 Process Flow Diagram



1 Tank 1

2 Tank 2

3 Tank 3

4 Tank 4

5 Neutraliser / Spray Reactor /TPS-3 /Filter Press

6 Heater & Blower

7 Mould Making and Packing

8 Calcination

9 Drier

10 Treated Liquor Tank

11 Timing of General Shift

Fig. 2 Equipment Occupancy Chart

4

6

Da

Documents

Modeling and Simulation for S.S. Re-Rolling Mills Waste Treatment