15 replies to this topic

[chemmu]

Dear Friends,

Good Day to all.

We have to store 33% HCl in storage tank. As you all know that HCl is so corrosive, we should not relieve the HCl vapour to atmosphere.

So relieved mixture (air + vapor) is sent to the scrubber for removing HCl vapour.

I have to give the HCl concenration in the inlet of Scrubber and outlet condition is as per Pollution Control Board (PCB).

To find out the HCl concenration, how to calculate the evaporation rate of 33%HCl in stagnant and working conditions ?

As per pump in and pump out rate, we can get the mixture (air + HCl Vapour) replacement data. But how to calculate the HCl Vapour in the mixture?.

I am getting some formulae in the search. But those formulae are for the spillage.

In our case, we are storing the solution in the tank.

The following are some design data.

Tank Diameter : 5m
Tank Height : 7m

Pump in rate : 5 m3/hr
Operating temperature : 45°C (Ambient Temperature)

Thanks in advance.

Edited by chemmurugan, 03 January 2013 - 08:11 AM.

[S.AHMAD]

1. The evaporation rate of HCL vapor is insignificant therefore you can assume it negligible. The main flowrate shall be the vapor/air mixture during pumping in operation as the liquid level rises, it displaces the air/HCL/water vapor mixture above the liquid level into scrubber.
2. The 33% HCL solution is in equilibrium with the vapor mixture. Therefore you can estimate the HCL/air/water composition in the gaseous mixture using Roult's and Dalton's law. But you need to know the vapor pressure of HCL and water at the storage temperature. I think Perry's has the table of HCL solution vapor pressure.

[breizh]

http://www.cheresour...uilibrium-data/

Consider this link to support your query.
Breizh

[kkala]

I think slightly negative gauge pressure has to be developed in gaseous phase of the HCl tank, to prevent diffusion of HCl "fumes" into ambient air around. Air will leak from ambient into the scrubber inlet, from any void on tank roof and connecting piping. This air will be additional to the one pushed to the scrubber by liquid displacement during tank filling.
This "parasitic" air may have been considered in the design, but it is not mentioned in post No 1. Its flow rate depends on how much "tight" to air ingression the structure upstream scrubber has been; it is not easy to be estimated without specific experience.
Above is based on seen examples of phosphoric acid reactor (~1978, no figures recalled), where air ingression was also used for cooling. Same principle is applied in phosphoric acid disk filters (no cooling); also in certain crashers, screens, etc, to prevent ambient air from dust.
I cannot think of a different system for the hydrochloric acid (atmospheric) tank, clarification would be appreciated.

Edited by kkala, 04 January 2013 - 06:20 PM.

[S.R.Shah]

Parry has tables of

Water vapor pressure over Hydrochloric Acid Solutions-Table 2.9,7th edition
HCl Vapor Pressure Over Hydrochloric Acid-Table 2.10,7th edition

SRShah

[chemmu]

Dear All,

Thank you so much for your valuable comments.

We will assume that the tank is having 33% of HCl.

We assume that the evaporated mixture flow rate is 100 kg/hr.

Shall we take that evaporated mixture also having 33% HCl??

As the evaporation rate of HCl is different and the evaporation rate of water is different, I hope that the mixture will not have the 33% HCl.. Please correct my understading.

Please advice, how to calculate the evaporation rate???

[S.AHMAD]

1. You do not understand the problem at hand.
2. Read and understand post#2.
3. Others have helped you by giving resources of HCL vapor/partial pressure. You already have enough information. We can guide you but you have to do the computation yourselves.

[chemmu]

Dear All,

Thank you so much for your reply.

I have done some calculation for the peak load.

Please give your views and correct in the calculation.

 33% HCl Vapour Loss Calculation.xlsx   20.01KB   559 downloads

Thanks in advance.

Regards,
Chem.M

Doing mistake is not a mistake. But not learning from the mistake is a mistake

Edited by chemmurugan, 10 January 2013 - 12:51 AM.

[S.AHMAD]

1. I have looked at your spreadsheet. Please use consistent unit for the volume either actual or Nm3/h or both. The calculation for determining the volumetric flowrate is OK.
2. The vapor composition that you assumed 33% HCL I think it is too much and apparently I believe you do not know what and how to apply Dalton's Law.
3. From the data supplied by others, determine the partial pressure of HCL and water at 45 degree C. Then calculate the mole fraction by dividing partial pressure with the total pressure. Then assume the balance component is air. Good luck.

Edited by S.AHMAD, 10 January 2013 - 02:17 AM.

[chemmu]

1. I have looked at your spreadsheet. Please use consistent unit for the volume either actual or Nm3/h or both. The calculation for determining the volumetric flowrate is OK.
2. The vapor composition that you assumed 33% HCL I think it is too much and apparently I believe you do not know what and how to apply Dalton's Law.
3. From the data supplied by others, determine the partial pressure of HCL and water at 45 degree C. Then calculate the mole fraction by dividing partial pressure with the total pressure. Then assume the balance component is air. Good luck.

Dear Sir,

Thank you so much for your immediate reply.

1. As per API 2000, the calculated relief rate is in Nm3/hr (Temp.0°C and Pressure.1atm). So I converted that flowrate in m3/hr for getting actual flowrate.

2. As per our requirement, the solution is 33% HCl only.

3. The operating temperature of the process is 60°C. So I had taken the partial pressue value for H2O and HCl at operating temperature from Perry. And also i had taken the Vapour Pressure of the Pure water component at the operating temperatue. From these data, I calculated the mole fraction. I assumed that there is no air in the mixture as the tank is not a open tank.

Please advice the calculation procedure is corret or not as the storage fluid is not a petroleum products.

Shall we take this peak vapour flow rate for the sizing of scrubber ??.

Thanks in advance ..

Edited by chemmurugan, 10 January 2013 - 04:34 AM.

[breizh]

Part 2 :

You need to calculate the composition of the gas at 60C :
PH2O =# 20Kpa =0.2 bar
PH2O +PHcl # 0.46 bar ( data Solvay)

* typo (0.46 instead of 0.24 bar)

Pt=PHcl +PH2O +Pair # 1 Bar

Ymol Hcl= PHcl/Ptot

Hope this helps

Breizh

Edited by breizh, 11 January 2013 - 08:26 AM.

[S.AHMAD]

1. Breizh has given you the method.
2. There is air in your system since based on the scrubber diagram, the venting is to atmosphere. Whether you like or not, air will be sucked in.
3. If you assume no air then the system is under vacuum at 60^oC.that is 0.46 bar as per Breizh figures. Since scrubber is vented to atmosphere then air will be sucked in due to formation of vacuum in your system. and the final total pressure should be 1 atmosphere.
4. You can use any units that you are confortable with, as long as you know how to convert them into mole/hr. In dsigning, we use molar basis.

Edited by S.AHMAD, 15 January 2013 - 06:56 PM.

[kkala]

1. H2O+HCl vapor pressure = 0.46 bar a for 33% w/w aqueous HCl at 60 oC, http://www.solvaychemicals.com/Chemicals%20Literature%20Documents/Chlorinated_inorganics/PCH-1300-0009-W-EN_WW_.pdf. If there were no air, hydrochloric acid tank would be under vacuum (-0.553 bar g). But this is an atmospheric tank contacting ambient air (mainly) through the scrubber piping. Air partial pressure in it will be 0.553 bar a. Assumption that "the tank is not open to atmosphere" has to be revised.
2. Post no 4 (by kkala) supposes a fan downstream the tank, which is not the case here (see sketch in "33% HCl Vapour Loss Calculation.xlsx). http://www.epa.gov/t.../hcl/c_rdoc.pdf '> http://www.epa.gov/t.../hcl/c_rdoc.pdf (*) does not report any fan, indicating treatment without it.
In this case tank pressure in gas phase will increase by gas ΔP along scrubber and its piping (tank will operate in higher overpressure to be checked).

(*) Interesting info can be seen in the document, e.g. at paras 2.3.5, 2.3.7, 2.3.8, 2.4.4

[chemmu]

Dear All,

Thank you so much for your valuable information and guidance..

Still the vaporization is going in my mind. It did not reach the saturation..

Soon I will come with answer.

Once again thank you so much to Mr.breizh, Mr.S.AHMAD, Mr.kkala

Regards,
Chem.M

[S.R.Shah]

Chhemu;

Please resolve your problem with all advice from experts in your spreadsheet and keep on forum.

This shall make problem more defined and exact solutin shall come out.

SRShah

[chemmu]

Part 2 :

You need to calculate the composition of the gas at 60C :
PH2O =# 20Kpa =0.2 bar
PH2O +PHcl # 0.46 bar ( data Solvay)

* typo (0.46 instead of 0.24 bar)

Pt=PHcl +PH2O +Pair # 1 Bar

Ymol Hcl= PHcl/Ptot

Hope this helps

Breizh

Dear Sir,

Thank you so much for your valuable guidance.

I have done some calculation

All the data given are at 60°C

Parial Pressure of HCl on Aqueous solution of HCl is 327.91 mmHg
Parial Pressure of H2O on Aqueous solution of HCl is 43.47 mmHg

Vapour pressure of HCl is 67865.68 mmHg
Vapour Pressue of H2O is 149.38 mmHg

As per Dalton's Law , If two or more gases are enclosed in a vessel, the total pressure exerted by them is equal to the sum of their partial pressure

As per Raoult's Law, The partial vapour pressure of a component in a mixture is equal to the vapour pressure of the pure component at that temperature multiplied by its mole fraction in the mixture.

Mole fraction of HCl = 327.91 / 67865.68
= 0.0048

Mole fraction of H2O = 43.47 / 149.38
= 0.2910

So the mole fraction of Air = 1-0.0048-0.2910 = 0.7041 ( Assumed that the mixture contains H2O,HCl and Air)

We assume that the relief rate of the mixture is 100 m3/hr.
So the relief rate of the HCl vapour is 0.48 m3/hr.

Please correct the calculations and assumptions..

Regards,
Chem.M