Jump to content



Featured Articles

Check out the latest featured articles.

File Library

Check out the latest downloads available in the File Library.

New Article

Product Viscosity vs. Shear

Featured File

Vertical Tank Selection

New Blog Entry

Low Flow in Pipes- posted in Ankur's blog

Calculating The Steam Usage Of A Vessel

steam calculations usage vessel reactor jacket heat capacity

This topic has been archived. This means that you cannot reply to this topic.
6 replies to this topic
Share this topic:
| More

#1 Shaj1

Shaj1

    Brand New Member

  • Members
  • 2 posts

Posted 07 May 2015 - 05:11 AM

Hi,

 

I am currently on placement, and one of my tasks is to calculate the usage of steam on our main production vessels. The way I am going to go about it is to use the formulas of Q=UadT and Q=McPdT. Say if the vessel needs to be heated up to 80oC, i will input that into the UAdT formula, using the U value for stainless steel. I am having issues as to when to apply the formulas and what numbers to use. For example, there is a mix of chemicals in the vessel, so what assumptions do I make when calulating the cP value to be used in the formula? How do I take things like vessel and jacket thickness into consideration?

 

I look forward to hearing from you all. I will provide more information if necesary.

 

Thanks,

 

Shaj


Edited by Shaj1, 07 May 2015 - 06:19 AM.


#2 shan

shan

    Gold Member

  • ChE Plus Subscriber
  • 692 posts

Posted 07 May 2015 - 06:44 AM

You should use calculate the mix of chemicals cP with the sum of each individual component cP multiplied its mole fraction (cP =cP1*MFr1+cP2*MFr2+...+cPn*MFrn).

 

The heat transfer characteristics of vessel and jacket wall thickness is included in U (Overall Heat Transfer Coefficient).



#3 Shaj1

Shaj1

    Brand New Member

  • Members
  • 2 posts

Posted 07 May 2015 - 10:36 AM

You should use calculate the mix of chemicals cP with the sum of each individual component cP multiplied its mole fraction (cP =cP1*MFr1+cP2*MFr2+...+cPn*MFrn).

 

The heat transfer characteristics of vessel and jacket wall thickness is included in U (Overall Heat Transfer Coefficient).

 How should I go about finding the usage of steam in a vessel. I will use UAdt to get q for the initial steam load to get up to temperature. I will then use McPdT to find the q value for the liquid in the vessel to be maintained under a specific amount of steam load. I will do the same for maintaining the vessel temperature with whatever the steam load is on operating procedures. However, my procedure seems flawed. Any assistance?

 

Thanks



#4 latexman

latexman

    Gold Member

  • Admin
  • 1,672 posts

Posted 07 May 2015 - 11:05 AM

Try to borrow someone's book by Kern, Process Heat Transfer.  Find an example similar to what you are doing and study his solution.  I think that would be good for you.



#5 shan

shan

    Gold Member

  • ChE Plus Subscriber
  • 692 posts

Posted 07 May 2015 - 11:19 AM

Please clarify your McPdt is for the vessel contents or the steam. What is your dt? "dt" is 0 for maintaining the vessel constant temperature and "dt" is 0 too for transferring steam latent heat.



#6 ColinR33

ColinR33

    Gold Member

  • Members
  • 106 posts

Posted 07 May 2015 - 03:07 PM

Further to Shan's comment regarding latent heat, when using steam be very careful about using Q=UadT and Q=McPdT for steam - they will give you the heat duty required, but don't use for calculating steam flow, if you only take a temperature drop into account with no phase change you will end up with a huge steam load. The bulk of the heat duty obtained using steam as a heat source comes from the latent heat of the steam - ie. the heat that is released when the steam condenses. Any addition "sensible" heat from temperature change is minor in comparison. For example, saturated steam at 50 psig has a latent heat of vaporization of about 913 Btu/lb (sorry, I'm more familiar with English Units), so if you have a heat load of 1MMBtu/hr, you will need (1,000,000Btu/hr)/(913Btu/lb)= 1,095 lb/hr of 50# steam (at 298F). This will vary depending on the steam pressure and to a much lesser extent on the temperature (ie. is it saturated or superheated), process temperature requirements will dictate the steam pressure (and therefore temperature) you will need.

#7 juche

juche

    Junior Member

  • Members
  • 17 posts

Posted 07 May 2015 - 11:52 PM

Further to Colin's comment, for the vessel fluid please see what is the temperature at the inlet of the vessel and what is the temperature at out let of the vessel fluid. Increase in temperature can be considered for calculating the energy/Heat to be supplied by steam. As rightly said Sensible heat is only a fraction of total heat provided by Steam for heating.

 

 

Thanks






Similar Topics