5 replies to this topic

[navneet2109]

Respected Sir,

I have attached the schematic with some problems. I just need an advice. if any more points you come up with this its very very welcome to enlighten me.

 

1. The criteria of Pressure drop of Pump Discharge Line is around 0.4 to 1 kg/ cm2 and velocity upto 5 m/s. But if I calculate Discharge to Truck Tanker 2" Line where flow rate is 34 m3/hr the pressure is high (around 3.52 kg/cm2g). If I increase the Size by 3" the pressure drop will come near to criteria. But we have to drop pressure to trunk tank working pressure so can we consider 2" line pressure drop??further pressure drop will be taken care by control valve. 3" will increase the cost. I want opinion on this.

 

2. I have studied there is a limitation in compression ratio and discharge temperature when we are selecting and designing compressor.But if we are using single stage compressor the compression ratio is approximately  16.5 and discharge temperature is more than 181 degC. But all thing is under review. I want an opinion in this.

 

3. I got the design for vacuum from storage tank's vendor is 50mmWCg. Is it Correct? Should it not be in minus or in absolute. Pls advice.

 

 

Tank design pressure is 0.14kg/cm2g+full of liquid (In drawing i did not mentioned gauge)

Attached Files

•  Ammonia refrgeration for cheresources Model (1).pdf   60.67KB   41 downloads

Edited by navneet2109, 27 January 2017 - 04:45 AM.

[Art Montemayor]

Navneet:

 

You did well by coming here for some free consulting and advice on your Ammonia storage project.  You basically have gone about the fundamental design in a wrong way.  I know nothing of where you obtained your process logic or technology on Ammonia storage and recovery, but it is a flawed design.  It won't work the way you have outlined it.  Is this your own concept or someone else's?

 

No one uses a centrifugal compressor for this kind of service.  Process engineers here in the USA have been doing this design for many decades, perhaps as much as 75 years ago.  The process logic and design has been honed down to a world-wide accepted process and is used wherever the need arises.  I highly recommend you follow the principles and basic design outlined and explained step-by-step in the attached document that was published some years ago by Dan Webb of CF Industries.  By guiding yourself with this technology you will avoid a lot of failures, mistakes, errors, and hazards.

 

With the Technical information outlined in the document you should be able to do a complete design heat and mass balance around the system.  I have furnished a lot of calculated examples of the NH₃ recovery cycle in our Forums in the past on this exact application and if you are interested, you can upload the calculations using our SEARCH engine.  If you need further help on developing the correct process calculations for the NH₃ vapor recovery, you should develop your calculations together with a flow diagram in an Excel workbook and submit it here so our members can review and help you out on any questions or problems you may come across.

 

 Large Scale Ammonia Storage and Handling.pdf   2.46MB   53 downloads

[navneet2109]

To,

Art Montemayor sir

 

Sorry for the wrong symbol of compressor which i have shown in the drawing. Its actually a screw compressor.

This project is in initial stage. The input that I have shown in the drawing, is from the OWNER. On the basis of there input i did preliminary calculation.

Right now my main concern is the given 3 points in drawing.

 

If i come up with any difficulty I will ask definitely because I did complete the design part of my previous job successfully. 

 

With Regards

Navneet

Attached Files

•  Ammonia refrgeration for cheresources Model (1).pdf   63.14KB   11 downloads

[Art Montemayor]

Navneet:

 

Thank God you are in the initial design stage at present.  Your main concern should be your basic design - and not "the given 3 points in drawing".  Your scheme will simply NOT WORK AS DEPICTED.  The type of compressor shown is not that important.  What is really alarming is that you are trying to recover the built-up storage vapors using a single-stage of compression (this is not possible mechanically or practically) and then connecting the resultant high pressure condensed liquid directly into the low pressure storage tank.

 

Your .pdf drawing schematic is showing a flawed process design.  As a process engineer you should show how you are condensing the produced tank vapors in a detailed manner.  That is what you should really be concerned about because the main, important issue in this storage of low pressure, low temperature ammonia is the tank heat leak that has to be controlled around-the-clock.  Without this ability, the storage tank will be a hazardous risk.

 

I made the prior recommendations because, as a very old and field-experienced engineer I can detect your design failings very quickly and I am concerned that you have not studied the document I attached to my previous post.  I am making these recommendations to you to help you with the accumulated years of experience I have and if you want to generate a design that works with confidence and safety, you would be wise to follow the recommendations made regarding submittal of your calculations and a design platform that allows our Forum members to easily and efficiently help you with recommendations, questions, and comments.  A .pdf document does not allow for that to occur.  

 

Your vapor compression will have to be made in a 2-stage compressor, and if your scope of work entails refrigeration efficiency then you should include an economizer intercooler.  It is not done the way you show it --- unless you are planning to constantly flare ammonia vapors (which nobody does).

 

Look at the attached example of a typical 2-stage ammonia compression and liquefaction schematic used to condense CO₂.  Your application involves replacing the shown CO₂ condenser with your storage tank and - voila! - you have a standard schematic diagram for vapor recovery from an ammonia storage tank.  If you employ a screw compressor it will obviously be an oil-flooded type.  A dry screw today is still not developed enough to ensure efficient, trouble-free operation.

 

I hope these details help you form a practical, dependable design.  My comments are not meant to criticize you or your design directly, but to help you with useful information that you obviously have not been made aware of due to lack of experience or the opportunity to work in this field yet.  If you submit your detailed calculations and further details, our Forum will help you with additional experienced comments.

 

 Ammonia Refrgeration Schematic.pdf   64.63KB   37 downloads

 2-Stage Ammonia Vapor Compression and Liquefaction.xlsx   34.9KB   31 downloads

 

[breizh]

Hi ,

You may find pointers reading this paper .

hope this helps.

 

Breizh

[navneet2109]

To,

Art Montemayor sir,

I am taking your points seriously and I've studied your attached document. All the comments here are important to me.

After taking all the points i will make the pfd and after completing, i will post it too in this thread.

 

To,

breizh sir

Thank you for your valuable information.

 

With Regards

Navneet