Steam/steam generator 1

[Yobbo]

Hi,
I am confronted with the challenge to generate process steam for a paper factory within our power plant. As the condensate does not abide our strict quality requirements I would like to investigate whether it is possible and feasible to generate steam of 8,5 bar and 182 C with superheated steam of 15 bar and 290 C. From the viewpoint of enthalpy it shouldn't be a problem. I think however that it will be some kind of specialty as I cannot find any comparable application on the internet. And I seem to have learned at some point in my studies that it is not possible to transfer heat from a condensing fluid to a boiling fluid in a controlled way. But I am not sure about this. I would like to know whether anyone of you has ever been confronted with the same kind of challenge and may give me some hints or directions about where I should look for a practical solution. I would like to strive for the least pitch temperature difference as this heat exchanger is merely meant to eliminate the condensate quality problem.

Awaiting any interesting hints, directions, literature references or supplier references for this particular case.

Thanking you in advance,

Karel Postulart

Karel Postulart, The Netherlands
Nuon Power Generation

 

[Afox88]

This is a very common solution for generating high purity steam.

I would suggest using a BKU design (kettle) with the high pressure steam in the tube side. Due note if you are running this per ASME VIII-1, this falls under special service case UW-2(c).

 

[crshears]

Hello Yobbo, if you are new here, welcome to the forums.

I'm not entirely clear on your query...

"Condensate quality problem" - which condensate?

Is your question in regard to using higher-pressure and temperature steam as the heat source for a surface-type shell-and-tube or similar boiler?

Is your concern that the HP steam has impurities that you do not want to see carried over into the LP steam? If so, what LP feedwater source are you intending to employ?

Could you polish the dirtier HP feedwater to make it clean enough for your LP steam purposes?

tot straks [until later] ,

CR



CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[MJCronin]

I am not quite sure if I understand your question......

If you have a source of acceptable condensate, you might consider installing a steam conditioning valve, rather than a larger and more expensive heat exchanger.

Emerson (and many others) offer them:

http://www2.emersonprocess.com/en-u...nditioning/pages/fishersteamconditioning.aspx

They are smaller, much more adjustable and more efficient than a heat exchanger !

Please keep us informed and tell us about your final choice....


MJCronin
Sr. Process Engineer

 

[gruntguru]

Not sure if I am interpreting your problem correctly.

If you have steam at 15 bar, 290*C and you merely want to convert it to steam at 8.5 bar, 182*C, it can be done without a heat exchanger. Expand the steam to 8.5 bar then add (by spray) sufficient liquid water to acchieve the required temperature.

je suis charlie

 

[georgeverghese]

Desuperheater nozzle with 9barg BFW injection should do?

 

[FredRosse]

The power plant has condensate quality requirements that are more strict than the condensate that can be recovered from the paper mill, so you want to have a reboiler such that your heat source steam (power plant steam) is condensed and returned to the power plant without contamination of impurities. The LP side of the reboiler will have very low quality requirements because it is such a low pressure. For example, the power plant might have condensate purity requirement less than a fraction of a PPM (part per million) dissolved solids, while the LP side of the reboiler can have 1000 PPM dissolved solids, and low quality feed to the low pressure side of the reboiler is OK.

Steam to steam reboiler is well established technology, and very common, and controllable.

 

[Yobbo]

Thanks for your reactions. I have to say that some of the given solutions still involve the direct use of our process steam for exporting to a costumer. As I think I mentioned due to the fouled return condensate from the costumer this option is out of the question, unless great effort is being put into cleaning the return condensate. The strict condensate requirements for our process plant make that very costly. Maybe I should have added a small sketch of the situation. I think that the suggestion FredRosse made is for me the most usefull one. I will pursue that option further.
Thanks again and if I can be of service with another question I will be glad to join in.

Karel Postulart

Karel Postulart, The Netherlands
Nuon Power Generation

 

[EdStainless]

Another option that would take less equipment, but cost you more high purity steam would to reheat the condensate by direct injection. There are a number of these units available (pickheaters.com). These units are very efficient.
You will have issues with a steam heated boiler. Getting the correct sizing and heat transfer can be very tricky.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[mbt22]

I seem to have learned at some point in my studies that it is not possible to transfer heat from a condensing fluid to a boiling fluid in a controlled way.

This at least isn't correct. Pretty much every steam reboiler does just this, controlling via condensate level or supply flow control.

Matt

 

[plantprowler]

Steam to steam reboiler is well established technology, and very common, and controllable.

So in a situation like this would one send in the superheated high quality. high presssure steam directly to the reboiler or get rid of the superheat first externally perhaps by using high quality BFW injection and then send in the now saturated steam to the High Pressure Side of the reboiler?