## 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

0

# Valve In Flash Vessel

valve pressure

20 replies to this topic
|

### #1 Usu

Usu

Junior Member

• Members
• 10 posts

Posted 02 March 2022 - 07:32 PM

Hi all,

I have some doubts I hope you can help me with.

The main scenario is this, there is a vessel at a certain pressure and then it flows to another vessel. The second is a flash vessel so it is expected to separate the flow into a vapor and a liquid stream. In PFD, in books or the like, I have seen this operation depicted as follows (Fig 1): there is a pipeline, then there is a valve, then there is a vessel with 2 outlet streams one from the top and one from the bottom, and that is pretty much it. However I would like you to clarify me what is really happening.

Since I have seen this depiction many times, in my mind there was the idea that the valve was a piece of equipment that somehow reduced the upstream pressure to the flash vessel pressure. Then, after reviewing some classes of fluid engineering I came across a formula that let us know how much pressure drop is having place in the valve Cv = Q (Sg /DP)^0.5, where Q is the volumetric flow, Sg, the specific gravity and DP the pressure drop across the valve. Then mixing this two pieces of information I thought that the change of pressure between the first vessel and the flash vessel was due to this pressure drop created in the valve. However, then, I thought it would be difficult for the valve to give exactly this much pressure drop equal to the differences of pressure between the first vessel and the flash vessel, lets say a 100 psi pressure drop.

Then I started looking for this on the internet but I couldn't find the exact answer I was looking for, yet, I found a video (Fig 2) that shows 3 valves, one in the entry stream to the flash vessel, one in the vapor stream and one in the liquid stream. They say that the valve in the inlet is used to control the inlet flow, the one in the liquid outlet stream is for controlling the liquid flow, and i guess the liquid level in the vessel, and the one in the vapor outlet is said to control the pressure of the vessel. So I thought maybe this is it, this is the way that the pressure from the first vessel (lets say 200 psia) changes to (lets say 100 psia) the pressure in the flash vessel. Now this arised another question on my mind. And is related to how this works, I am imagining that the tank is being filled, it gets to a desired level, then the liquid outlet valve is opened so it stabilizes and the vapor outlet valve is closed so the vapor is allowed to "build up" or be kept in the vessel, thus increasing the pressure, then the vapor valve is opened and then so the pressure is maintained. All of this meanwhile somehow the system reaches a steady state where the inlet mass flow equals the outlet mass flows. But then another question came to me, so if the pressure in the flash vessel is set, or controlled by the vapor in the vessel, then that pressure is kind of ... "moving" backwards upstream, so the pressure immediately after (downstream) the inlet valve should be almost the same as the one in the flash vessel. But then, why doesn't that pressure transmits up to the first vessel and reduces the pressure inside it to (100 psia). Do the valve "protects" the flow upstream from this effect on the pressure? or said in another way Do the pressure upstream the inlet valve is indeed 200 psia and downstream the valve is 100 psia? if so, why?

But then I was still looking after all this questions all mixed up in my head, and I found that there are some valves called pressure reducing valve, and backpressure valve that ingeniously have a set mechanical pressure inside the valve so i only opens when the desired pressure is below that set, kind of resisting, pressure.

So well, I hope you can clear this doubts. And tell me if there is indeed a valve that only by itself can reduce the pressure 100 psia, or if in reality there is a team of valves doing the work or it these pressure reducing or backpressure valves are used instead, or if something very different is occurring.

A friend of mine also have another question regarding flash tanks and it was that she thought of a flash tank as a big big big pipe it is connected to the pipeline upstream, so she was thinking if the change in area/volume from the pipe diameter to a vessel "diameter" had any effect on the pressure of the fluid and was this would be.

Thank you for your interest and feedback,

Usu~

#### Attached Files

Edited by Usu, 02 March 2022 - 08:11 PM.

### #2 Art Montemayor

Art Montemayor

Gold Member

• 5,779 posts

Posted 02 March 2022 - 09:04 PM

Gerardo,

First of all, I’m going to assume that you are a first-year Chemical Engineering student who has recently been introduced to a flash process as used in process plants and elsewhere.  I make this assumption from what your lengthy description of your “doubts”.  I hope I can contribute to your understanding of what a flash vessel is, what it does, how it is controlled in a process operation, and some examples of industrial flash operations.

Before I start with my explanations, I have to advise you that you are very confused with the subject and you seem to lack a solid and detailed engineering or science background in looking for an understanding of this process.  So, I will try to be very simple and direct and hope that you understand what I explain.

You are confusing the “Cv equation” dealing with all valves as being related to a flashing operation.  Actually, the valve Flow Coefficient (Cv) defines the flow capability of a control valve at fully open conditions relative to the pressure drop across the valve.  It is defined as the volume of water (GPM in the US) at 60 °F that will flow through a fully open valve with a pressure differential of 1 psi across the valve.  You can forget this equation for now.  All fluids – whether gas, liquid, slurries, or mixtures – will flow when a driving force is applied to them.  This driving force is usually a pressure drop – fluids flow from a high pressure to a lower pressure.  The rate at which fluids flow depends to a large degree on the flow resistance that they meet – such as pipe friction, change of direction, and valve throttling (“estrangulación”).  The last item – the use of valve throttling – is a means of reducing the fluid flow but also used to reduce it’s downstream pressure.  When this happens – in some cases – you have a process that chemical engineers call a flashing operation.  It is that simple.

However, not all fluid throttling produces a “flash”.  Process operations where a flash operation is employed can be:

• A case where a high-pressure liquid is saturated with undesired dissolved gases;
• A case where a high-pressure liquid (such as a refrigerant) is expanded to produce a mixture of low-pressure gas and liquid at a lower temperature;
• A case where a high-pressure gas is expanded to produce a lower pressure gas at a lower temperature (the Joule-Thomson Effect);
• A case where a high-pressure, hot liquid is expanded to allow processing at a lower pressure.

The flash sketch you furnish lacks details and information to be fully understood.  You should identify the fluid being flashed (dropped in pressure) and its composition, pressure, and temperature.  Without a complete identity of the high pressure fluid, we can’t surmise what will be the effects resulting from the flash.  Please be detailed, accurate and direct in explaining your query.  Our forum members can be of tremendous help to engineering students, but you must communicate thoroughly with them, explaining your query in detail.  Sketches are very good input, but they must be complete in detail and basic data.  If you need a more specific explanation, let us know.

### #3 Bobby Strain

Bobby Strain

Gold Member

• Members
• 3,522 posts

Posted 02 March 2022 - 11:52 PM

I wouldn't worry about it at this stage of your education. Pay attention to what you should be learning, and don't get distracted by such as this.

Bobby

### #4 Usu

Usu

Junior Member

• Members
• 10 posts

Posted 24 March 2022 - 07:08 PM

Dear Art,

Thank you very much for your answer, it was made clear that flashing occurs, sometimes, when reducing the pressure with a valve. Also, the examples of when a flash is used were insightful. I also liked very much this statement "The rate at which fluids flow depends to a large degree on the flow resistance that they meet – such as pipe friction, change of direction, and valve throttling (“estrangulación”)."

It is true that I am confused with this topic, specially I think I lack of understanding of how calculations and PFD translate into real pieces of equipment. However, I am not a first year, but last year. I took a leave, so some concepts aren't as fresh as they could be.

I will try to approach the question in a different way and I hope I can give a more detailed explanation of my questions.

Part I

I updated the sketch I made for a more detailed one. It is a sketch of a PFD of a part of a refrigeration loop. It shows that a valve is used to cool the refrigerant, in this case ammonia. Let me try to explain my train of thoughts as I hope this will help me to address my questions.

Using the information provided in the sketch I am able to "solve" the diagram. By solving I mean I am able to calculate the conditions (flow, composition, temperature, pressure) in all the streams using mass and energy balances and thermodynamic relationships. I would do it roughly as follows:

Ammonia Cooler
Data: outlet V/F = 0, suppose recommended P drop for a condenser, suppose recommended CW inlet and outlet temperatures
Calculations:  Q, cooling water flow,

Flash
Data: Temperature at outlet = T in stream 6
Calculations: Pressure in stream 4: use Antoine equation to find P at T= 18°C, Find V/F = hF - hL / (hV - hL )

Process Cooler
Data: Q needed to cool the process stream, ΔHvap

Calculations: mass flow of liquid ammonia that evaporates, flow in stream 5 and 9

Up to this point I can handle it. And, from my point of view, besides knowing the stream conditions, this would be useful, from example, to observe the effect of the outlet pressure of the compressor in this system, that is, in the CW demand, the pressure drop in the valve, and the power required in the compressor.

Then, once the stream conditions are ok, I would proceed to size the equipments. I could "size" the cooler as a condenser and the process cooler as an evaporator following, for example, Kern's advice. For the Flash vessel I could find some insights in Ludwig. Finally, I think I can "size" or select the valve using the CV equation, correct me if i am mistaken.

But now, If I wanted to go from the paper to the real thing:

1. What would be the next steps a chemical engineer would have to do?
2. In what step I need to add the effect of the pressure drop in pipes using bernoulli equation?
3. To appropriately select the valve and the compressor I need the system curve analysis, don't I?

Part II

Further questions have to do with this input which I read and I couldn´t fully understand: https://www.cheresou...ingflash-drums/

quoting:
Your asserted knowledge is wrong. The resultant pressure drop is [/size]NOT produced from the smaller volume. The pressure drop across the throttle valve exists simply because the resultant products – primarily the produced vapor – are being continuously removed from the flash drum. This is a [/size]STEADY STATE process. The prerequisite condition is that there must be an existing steady state (continuous flow). Otherwise, the process cannot work. There is nothing "Bernoulli" about this simple fact. You must have systems downstream that are continuously taking your product vapor and the continuously drained liquid. It is that simple.[/size]

From my understanding the pressure drop (to achieve the flash) is due to the valve, I mean, without the valve, there would be no pressure drop is what I think. In my book, the pressure drop occurring in the valve is accounted for with the CV equation and is a frictional loss caused by the flow in this piece of equipment. (I do not share the view of the A.L.L. about the volume, though). But when I read about the explanation about the vapor being removed from the drum I got confused and started looking for further explanations. I watched this video and I thought it was depicting what you said in the other topic/post  https://bit.ly/3tyJ8W5

Could it be that you can give me some explanation about this? I mean the valve is a must, right? I cannot grasp the part of the vapor and liquid going out of the flash drum as an explanation of the pressure drop.

I apologize for the slow reply, but I had to think things over in my mind so I could reply, I hope, in a better way.

Thank you for your interest,
Usu~

Edited by Usu, 24 March 2022 - 11:43 PM.

### #5 Art Montemayor

Art Montemayor

Gold Member

• 5,779 posts

Posted 27 March 2022 - 10:39 PM

Usu:

I am more than glad to help out any student - if he/she demonstrate that they have done the work of studying the problem before them and make the appropriate and detailed calculations that show and clearly demonstrate the algorithm they use.

This should be done in a submitted Excel workbook if you want our Forum to peruse and check out your calculations.  You will certainly find that our Forum members will be more than willing to help you.  But you must do the work first.  We will not do the calculations for you.

For example, I have done complete and detailed ammonia refrigeration calculations many times before - as well as for other refrigerants.  I've even submitted some of them on this forum through the years.  I still preserve those files.  But I am not going to submit them if you don't show what calculations you have done.  Basically you are doing (or proposing) your calculations for a refrigeration system in the totally wrong way.  Your proposal doesn't make any sense.  Kindly give us some background as to your background in the subject.  Have you had any thermodynamic courses yet?

You shouldn't waste time with the Cv of the expansion valve.

There is no "system curve analysis" needed or required to fully size and specify a refrigeration system.  What do you mean by "system curve analysis"?

There are many questions that need to be answered due to your long query.  You have to fully define what the problem is that you have before you.  Be specific in defining your case.

### #6 Usu

Usu

Junior Member

• Members
• 10 posts

Posted 28 March 2022 - 01:07 PM

Dear Art,

Thank you for your reply, I will do the calculations and submit them in an Excel file as you told me to. It may take me a little some time, but I wanted to reply and do not leave the topic unanswered meanwhile I am doing the calculations.

About the system curve analysis, well that is where I am most confused. But, I will first do the calculations, and then progressively ask the questions I still have, I hope that makes sense to you.

Sincerely,

~Usu

Edited by Usu, 28 March 2022 - 05:40 PM.

### #7 Pilesar

Pilesar

Gold Member

• Members
• 1,325 posts

Posted 28 March 2022 - 03:22 PM

Pressure in the downstream flash drum will not be controlled by the valve between the source vessel and the flash vessel. Remember the gas law relating pressure, volume and moles of gas. The volume of the flash vessel is fixed (assuming constant liquid level.) Therefore the flash drum pressure will be directly related to how many vapor molecules are kept inside the vessel.

### #8 Pilesar

Pilesar

Gold Member

• Members
• 1,325 posts

Posted 29 March 2022 - 08:57 PM

Process vessels generally have some controls for inventory. Typically, a valve on the outlet liquid is set up to keep the liquid inventory constant as indicated by a continuous level measurement. A valve on the outlet vapor controls the vapor inventory. As more vapor molecules are retained in the vessel, the higher the vessel internal pressure. Simple process controls never see the incoming feed and the valves are adjusted while only considering pressure measurement and level measurement. Good control schemes will make the necessary adjustments whenever there is a disturbance in the feed flow rate. When more vapor feeds the vessel, the pressure will start to trend higher so the vapor outlet valve will respond by opening more. When less liquid enters the vessel, the level will begin to fall below its set point and the liquid valve will pinch back. These control schemes have to be designed into the process with a programmed response for the expected disturbances. For vessels operating near atmospheric pressure, the vapor vent may not have a valve and the vapor flow will adjust automatically to keep the vessel internal pressure the same as the external pressure. Vessels with feedback controllers have no direct indication of what enters the vessel and only respond to the effects (pressure and level) produced by changes in the feed.

### #9 Usu

Usu

Junior Member

• Members
• 10 posts

Posted 29 March 2022 - 11:13 PM

Dear Pilesar,

I appreciate very much your input in this topic.

You've helped me to understand a little better the control of the pressure in a flash vessel.

I hope what I am about to write makes sense. The way I see it is this: The flashing occurs when suddenly reducing the pressure in a stream. In this case, we have a liquid (ammonia) near saturation and then its pressure is decreased in an isoenthalpic process. This gives a second state in which we have a stream with a mixture of vapor and liquid ammonia at a lower temperature and pressure.

I cannot understand the role that the (1) valve between the source vessel and the flash vessel, and the (2) valve controlling the pressure of the flash vessel play into reducing the pressure. And this is one of the things I am trying to grasp.

I still will make the calculations as I told Art, but I wanted to do follow up to your replies since they were so helpful.

Thanks again,

~Usu

### #10 Pilesar

Pilesar

Gold Member

• Members
• 1,325 posts

Posted 30 March 2022 - 01:15 AM   Best Answer

Become familiar with how to read a pressure-enthalpy diagram. https://imgv2-2-f.sc.../1595838359?v=1 The liquid ammonia at your source conditions can be found on such a diagram. The flash drum conditions can also be found on such a diagram. No matter how the flash drum conditions are reached, the point on the diagram is the same and the amount of vapor and liquid will be the same as long as the pressure and enthalpy are the same. So what does the valve in between do? It helps describe the path the fluid will take from one condition to the other. The fluid at the new pressure will have the same enthalpy as the fluid in the source tank but at a lower pressure. This allows you to trace the path from the source point and find the new location on the chart! You can calculate the amount of vapor and liquid at the new point based on the enthalpy and pressure.

Note that the new flash drum conditions might be reached by a different method depending on the starting point by adding heat, adding pressure, reducing pressure through a turbine, etc. Once the fluid was at the same pressure and enthalpy conditions, the amount of vapor and liquid would be the same. The purpose of the valve in real life is to allow the ammonia to exist in the system at two different points on the diagram. The upstream vessel would need some way to control its inventory (keep a constant pressure or liquid level) and this valve might serve that purpose for the upstream vessel just as the downstream vessel also has a liquid control valve.

I don't think the actual controls are part of what you are studying since they aren't shown on your diagram. In brief, a valve can only help control one thing at a time such as pressure, flow, temperature. The control designer chooses which parameter is modified by each control element. For example in your sketch, if the in-between valve were missing, the vapor might blow through the exchanger without condensing which would affect both the compressor operation and the conditions downstream. I think of the valve as a boundary between the two points on the pressure-enthalpy diagram.

Don't stress over not fully understanding what is happening in your system and why. It will come to you eventually and you will find an explanation that makes sense to you. Have you tried watching some video tutorials on the web? Search for 'refrigeration cycle' and see what you find. If you can understand how a car air conditioner works, you will understand the ammonia refrigeration cycle.

### #11 Usu

Usu

Junior Member

• Members
• 10 posts

Posted 30 March 2022 - 11:36 PM

Dear Pilesar,

I really liked the explanation you gave me, I think, hopefully, I am understanding this topic a little better. I really liked how you visualize the valve as describing the conceptual path the process is taking thermodynamically, and I get that "abstract" part, but when it comes down to the real life equipments and what they physically do I usually get confused. It really made sense that the valve in the middle should be controlling the inventory of the upstream vessel, which I realized is the heat exchanger/condenser in this case.

Also, the suggestion about the videos was also a good idea. I had already search for "flash valve" or something similar, I had little results from that, though. "Refrigeration cycle" was indeed way better to get useful results.

Thank you very much,

~Usu

### #12 Usu

Usu

Junior Member

• Members
• 10 posts

Posted 20 May 2022 - 01:04 AM

Hi again,

I have done the calculations for the flash I sketched before, I attach it in an Excel file as Art told me to do. I made the calculations as I understood the problem could be solved given the data and diagram I attached. I focused on the thermodynamic flash calculations, the flash vessel and the valve. However I did not delve into the heat exchangers since my question is not directly related to those.

I hope you can check the Excel file and comment on it. I think it would be evident the way I used the CV equation, this was how I originally thought the pressure drop for the flashing to happen was explained in terms of equipment affecting the system.

I will appreciate your kind inputs,

~Usu

P.D. I corrected the data in stream 6, it was 8.0 kg/cm2

Note1: Updated spreadsheet with some suggestions from Pilesar

#### Attached Files

Edited by Usu, 20 May 2022 - 01:41 PM.

### #13 Pilesar

Pilesar

Gold Member

• Members
• 1,325 posts

Posted 20 May 2022 - 09:37 AM

I think streams 6 and 7 should be liquid instead of vapor. And stream 8 should be vapor instead of liquid. In real life, streams 4, 5, 6, 7, 8, 9 will not have the exact same pressure. I did not go through your sizing sheets point by point, but I will suggest at minimum you clearly state your final size selection (e.g. vertical vessel with x diameter, y length.) It is good engineering practice to document your calcs and conclusions in a way that another can look at this later (after you leave to start your own consulting company) and understand the specifications. A heading with description seems like a waste of time until you pick up the calcs months later and wonder what you did all these calculations for. In your case, I would put name, date, class, assignment number, process application, equipment number, equipment type, etc. These details will look good to a professor also. See an example generic vessel datasheet here: http://processprinci...-Sheet-Form.pdf

A real vessel data sheet will include materials of construction, pressure and temperature rating, nozzle sizes, locations and quantities, head type, etc. You can know and specify the location of your feed nozzle. Determine the height of your normal liquid level, your high liquid level, your low liquid level. Give the sizes of your vapor and liquid nozzles. If I were your professor and you spent two months working on this, I would want to see a more thorough design. I have not seen your assignment statement, but putting a bit of effort into polishing the presentation may help you get the grade you want.

### #14 Usu

Usu

Junior Member

• Members
• 10 posts

Posted 20 May 2022 - 12:47 PM

Dear Pilesar,

Thank you for your comments. Indeed, I inverted the 0 and 1 in streams 5 to 9, thank you for noting this. About streams 4 to 9 not having the same pressure, Do you know what can be done to estimate more real pressures? The only thing I can think of is the pressure drop from stream 7 to 8 having place in the heat exchanger.

I will add some of the information you suggested, like stating the final selection, date, process application, equipment number, and type.

About the vessel, and valve, I did the calculations as far as my knowledge and some researching went. I will try to check the location and size of the nozzles and the liquid level. As a chemical engineer do you suggest I should add more calculations, or are they added by other specialist (mechanical engineers, piping, instrumentist)?
Fact is I have not done assignments regarding vessel sizing so am not not sure to what extend I need to size/specify, but I will be glad to learn more.

Just to clarify, this was not a assignment, so there is no assignment statement, I did this for the sole purpose of clarifying my doubts. This DFP was used in class for other purposes, in fact that part of the DFP was not used a lot. However, I reused it to give Art a more detailed sketch of the process, and now, to make this calculations.

~Usu

### #15 breizh

breizh

Gold Member

• 6,260 posts

Posted 21 May 2022 - 08:08 AM

Hi,

To add to the previous reply , let you consider this guide :

https://www.red-bag....sel-sizing.html

Nh3 properties :

https://www.cheric.o....php?cmpid=1918

Good luck

Breizh

### #16 Pilesar

Pilesar

Gold Member

• Members
• 1,325 posts

Posted 21 May 2022 - 10:05 AM

The red-bag guide breizh referenced is a great place! Chemical design engineers do those calcs and provide those specs. The answer does not come all at once but is found step by step with perhaps some re-do required during an iteration, Steadily and methodically, an optimal design is specified. Near the end of that guide is a worked calculation example. Follow that for better understanding and realize that there may have been dead end branch calculation paths not shown.

Rules of thumb and company design standards help use successful previous experience in new equipment design. The subjective component in engineering is what makes it fun for me. Question one: Does the new equipment work as desired? Question two: Were company resources (money, plot space, project implementation cost, project schedule, design time, etc) used in the most efficient manner? Often the client only grades the first question and has little clue about how to answer the second question. The engineer's professional pride is sometimes the only judge of the second question and you have to pat yourself on the back since no one else will notice. I find that to be sufficiently satisfying. It helps to have an experienced engineer available to provide feedback when possible.

### #17 Pilesar

Pilesar

Gold Member

• Members
• 1,325 posts

Posted 21 May 2022 - 10:33 AM

I don't know where you are in your education, but you don't have to learn everything at once. Detailed equipment design may not even be covered in college like it is practiced in industry. Learn the principles from your class studies. For example, the stream pressure estimation should be covered in the fluid flow class (Bernoulli Equation) so don't sleep through that one. It takes time and repeated application of principles to 'learn' chemical engineering. Just being told once may not be enough and learning it the second or third time will help make it more real.

If it is the 'real life' applications causing your concern, consider taking some plant operator training. Operators have to know basic physics and how to control plant processes. Some is available at reasonable cost on line: https://www.udemy.co...duction-course/ I have not taken this course and there may be free resources available.

### #18 Usu

Usu

Junior Member

• Members
• 10 posts

Posted 24 May 2022 - 10:19 PM

breizh, the red-bag link to vessel design I really through, it will come extremely handy! I also did not know the database you shared, it is great to be able to estimate viscosities and other variables using a correlation instead of a nomogram. I am grateful for both resources.

Pilesar, thank you for thoughts about design engineering. And, again, I think your suggestion is helpful. I'll check a plant operator training course and see what's in.

Thank you both for your remarks,

~Usu

### #19 Art Montemayor

Art Montemayor

Gold Member

• 5,779 posts

Posted 25 May 2022 - 07:28 PM

Usu:

I have not been on the Forums for a couple of weeks due to grandchildren's graduations and I apologize for not joining in this thread any sooner.

I have reviewed part of your submitted workbook and find far too many wrong and erroneous assumptions or calculations.  Your mistaken concept of what a mechanical refrigeration system is and how it operates starts with your flow diagram.

Your calculations are not the type or sort of calculations done to define and specify the size, conditions, duty, and efficiency of an ammonia refrigeration system.

I am attaching a workbook some basic information that describes the beginning of what you are trying to do.  If you are interested I can start to describe - step by step - how an ammonia refrigeration system is calculated and designed.   However, in order to start this exercise you must furnish COMPLETE BASIC DATA  of what you are trying to do or what is your objective.  No engineering design work can start until there is a complete and detailed description of the objective Scope of Work.  If you don't understand what these terms mean, let me know and I will describe at length and in detail what I mean.

After defining the above information, design and calculations can commence, step by step.  Are you game?

Let me know.

### #20 Usu

Usu

Junior Member

• Members
• 10 posts

Posted 27 May 2022 - 01:31 AM

Art,

No need to worry about not posting before. Thank you very much for your comments and for sharing the spreadsheet, I took a look at it and it is a really nice example of a refrigeration system. The cycle is clearly identifiable.

I will try to give a little more information about my flow diagram:

The objective of what I sketched is to cool an ammonia stream of 248100 kg/h at 150 kg/cm2 from 45 to 25 °C. So in that diagram ammonia is being cooled with ammonia. This cooling is taking place in the heat exchanger on the right of the flash vessel which has the data Q = 24 GJ/h (where Q is the exchanger duty). I simplified the diagram by only showing part of the process, since I wanted to focus first on only one flash operation, and one valve, trying to not complicate myself with more pieces of equipment and the stream recirculations before I could grasp that part first. Full diagram is a little too much for me to calculate by hand (excel) since my question had to do with any one of the valves in the refrigeration loop, so I thought that any one of them worked just fine. The rest of the diagram involves stream 5 recycling into stream 1, and stream 9 going into another valve and another flash vessel, and more.

I am very interested in your offer, I am sure I would be able to learn and hopefully see where I was mistaken in my train of thoughts. However, I am not really sure it can be done on my example, for I understand the goal you are setting is to fully design the whole refrigeration loop, and the full diagram on my example gets complicated, but that was the example I had on hand. Maybe it would be better to work with the system of the CO2 condensation.

About your question I am not really sure what to understand from complete basic data and scope of work.

In short, I am in for the step by step calculations. I am sure I'll get a lot out of it, and from there I'll clarify some doubts and ask any remaining questions on the system.

By the way, congratulations on your grandchildren graduations!

Sincerely,

~Usu

Edited by Usu, 31 May 2022 - 10:15 PM.

### #21 Usu

Usu

Junior Member

• Members
• 10 posts

Posted 31 May 2022 - 10:58 PM

Art,

I found an example of an application that might work. The purpose of the refrigeration cycle is to cool down a process stream from 30°C to -12°C, so that a stream of a least 99% of ammonia can be recovered as liquid. We know that to do so 1700 MJ/h should be removed in a heat exchanger. An open ended problem here would be to design from scratch the refrigeration cycle to provide the cooling service to that heat exchanger.

I think this problem has enough information to design an ammonia refrigeration system.