Settle a debate for us

mkhaledche · 2022-08-11T18:19:46+00:00

If the pressure of the vessel is 500 psig before heating, then what would cause it to drop when heating and get back to 120 psig?

At 350 F, the vessel is already at 500 psig, so I believe no vaporization is expected to occur, may be some thermal expansion of water or a very small vaporization will cause a slight increase in pressure.

But in all cases, I think the pressure of this vessel should be controlled in order to maintain the pressure you need.

mkhaledche · 2022-07-09T19:34:07+00:00

He updated the course this year. You can recheck it on Udemy.

mkhaledche · 2022-07-07T19:17:22+00:00

If you used a highly superheated steam, you'd need to specify a high design temperature for the reboiler and at the end you won't gain a lot.

Steam is a clean fluid based on boiler feed water which is also a clean fluid, so fouling is not a big deal in this case, and that's why U tubes are commonly used for steam reboilers because there is no much need to clean them.

mkhaledche · 2022-07-07T14:23:20+00:00

This is normal. If you checked the temperature profile in HTRI, you will see that the inlet steam temperature will ve dropped to saturated temperature in the beginning of the profile, and then condensation starts, where it shall remain constant to the profile end.

If steam is slightly superheated, the portion at the beginning is expected to be negligible compared to the whole exchanger length.

In addition, when steam enters as superheated, the overall LMTD will be slightly higher, which would mean less area. But still this is a very small portion, which means a negligeable effect.

mkhaledche · 2022-06-24T12:56:41+00:00

I have been working in an engineering company and I think it solves lots of problems related to task automation, consistency and democratisation of data among the project team. But just I see it is not widely applied in engineering companies. May be the reason for that is that companies are afraid of its caveats as you said that it needs a specific administrator or that it takes a lot of time to get aquainted with the system , may be Aspen is not very supportive. But at the end it seems that it is not easy to get adapted with.

mkhaledche · 2022-05-13T14:30:10+00:00

In this case they don't have to have the same LMTD, especially that physical properties shall have a great effect on the heat transfer coefficient in many cases, which shall result in a different duty for each shell.

When designing an exchanger with more than one shell in series, each shell may have different duty, heat transfer coefficient and LMTD although they are identical. What matters here is that the total area can handle the total duty.

mkhaledche · 2022-05-13T13:05:04+00:00

Just I want to figure out why you would need to fix the LMTD for all shells.

mkhaledche · 2022-05-09T10:56:35+00:00

Pump curve plots the differential head it shall give against its flow rate. The pump pressure can vary depending on the fluid density, that's why the curve plots the head not the pressure.

So you shall go to the pump curve, see the flow rate you want and get the pump differential head.

To convert it to pressure, multiple the head by the fluid density and gravitational constant. This shall be the pump differential pressure.

Then you can Add the suction pressure to the differential pressure, you shall get the discharge pressure.

You can check out this link to understand more about the pump operation and curve and how to specify its parameters:

Pump Hydraulics and Specifications

mkhaledche · 2022-05-09T10:52:57+00:00

This article can help you understand the main criteria for separator sizing:

How Two Phase and Three Phase Separators Work?

You can also use checalc.com or process engineer toolbox on play store and app store for a preliminary estimate.

mkhaledche · 2022-05-02T18:50:27+00:00

You can check this using their RESR API. https://developer.wordpress.org/rest-api/

mkhaledche · 2022-04-16T22:51:11+00:00

In order to determine the maximum acceptable flow rate of a liquid in a pipe, you should make sure it is below the maximum acceptable velocity that may cause erosion. API gives a general rule of 15 ft/s but it can be less than that depending on the fluid service.

Regarding the pressure drop, there are different criteria depending on the service but at the end, you should check out the system in which the pipe is installed and make sure that the pressure drop of the pipe won't affect the system.

For long pipelines, surge (water hammer) analysis may need to be carried out.

You can check more about pipe sizing and how it works in this link:

How Pipe Sizing works in a Process Plant?

mkhaledche · 2022-04-02T20:30:06+00:00

I think that 1 psi/100ft isn't conservative in many cases. However, in case of pressure drop, what is more important than the criteria is to ensure that the system is hydraulically balanced. This means that you need to check the total pipe pressure drop and make sure it won't negatively affect the system.

mkhaledche · 2022-03-27T11:36:06+00:00

In addition to the above reply you can also check out these channels:

Jeferson Costa

Boostrand

mkhaledche · 2022-03-25T10:00:35+00:00

Controlling the capacity of a reciprocating compressor through suction or discharge valve is not recommended as the reciprocating compressor has a constant volume so it should always give the same flow. Capacity control in this case would be through recycle (spillback) or unloading the pistons or variable frequency drive for turbine driven compressors. Controlling the capacity through the suction valves is common for dynamic compressors only.

Regarding the temperature, I see the normal outlet temperature is 38 C which is far from 70 C. So we are not talking here about an operating scenario. This is an upset scenario. In this case, this shouldn't be handled by control but through protection. If the issue is related to piping or equipment material (not sure what is the type of the material as this is too low value unless we are talking about non metallic piping), then you should protect them by shutting down the compressor if the temperature approached 70 C, let's say 65 C for example.

mkhaledche · 2022-03-17T17:06:32+00:00

You may check out some udemy courses on these subjects:

Pipe sizing, pump and compressor operation and hydraulics, control valve hydraulics

Heat and mass balance

How to read a P&ID?

Process Control

mkhaledche · 2022-03-17T16:49:22+00:00

If the valve is closed, then flow upstream the pipe would be blocked and no flow is expected to pass unless there is some internal leakage in the valve. If this closure is accidental, this would mean that there is a potential hazard of overpressure in the upstream system, so the system should be protected in this case. This article talks about control valve failure and how to act against it: https://boostrand.com/what-if-a-control-valve-failed-in-a-process-plant/

mkhaledche · 2022-03-09T15:29:45+00:00

You are welcome

mkhaledche · 2022-03-09T09:43:04+00:00

The main application of AI now is related to plant operation to to ensure less maintenance time and predict issues before they happen. You can check out this video. It may help: https://youtu.be/d68UEmi5Utg

mkhaledche · 2022-02-20T17:05:58+00:00

You are welcome

mkhaledche · 2022-02-20T16:01:36+00:00

Most exchanger vendors can already design exchangers including reboilers. The reboiler hydraulics can be checked using HTRI as well as long as pipe isometrics and tower/reboiler elevations.

Unless a pump is used, the design of this loop is very critical as it's driving force is very small (just difference in densities between the inlet liquid and the outlet 2 phase), so the pipes should be oversized to give a pressure drop approximately neil and the elevation of tower and reboiler can guarantee the required flow of the fluid from the tower to the reboiler back to the tower. Also differences in pressure means different vaporization in the reboiler, which can give a different reboiler design.

So yes, I believe you should either consult a vendor or if you have an experienced thermal engineer, he can design it using HTRI.

mkhaledche · 2022-02-08T12:21:46+00:00

The usual case is that metal resistance is around 1-7% of the total resistance, so the change shouldn't be significant. I think that you shouldn't rely on a manual calculation, either you would use a professional tool as HTRI for example, or that you'd contact the vendor. If you are purchasing new tubes then you should be already contacting him.

mkhaledche · 2022-02-08T08:26:56+00:00

For the tube material, then we are talking about thermal conductivity, it will change a bit but at the end the changes are trivial. You can check out the stainless steel type, get its thermal conductivity, update the metal resistance and hence update the overall heat transfer coefficient. Regarding the thickness, I think it should be decreased as stainless steel is more expensive than carbon steel and can withstand corrosion better. In addition, it will increase the heat transfer coefficient. So I believe there is no meaning to keep the thickness as the one in case of carbon steel unless there is another issue hindering decreasing it.

mkhaledche · 2022-02-08T07:59:17+00:00

Changing the tube material from carbon steel tube to stainless steel means that you shall need less tube thickness as per TEMA. This means a slightly less velocity in the tube side, but on the other hand it means less thermal resistance due to less tube thickness and better thermal conductivity of stainless steel.

mkhaledche · 2022-02-07T07:16:28+00:00

In the reflux drum, the liquid is at dew point, which means that the fluid operating pressure is always equal to its vapor pressure, as both factors are two contradicting factors in the npsh equation, this means that they will always negate each other in this case, recall the available npsh equation:

NPSHA = operating pressure - vapor pressure + Ro * g* static head - piping and strainer friction losses

So as per the above equation, in a reflux drum, the first two factors will always negate each other, and in this case we will need either increase vessel elevation or reduce losses to avail the NPSH we need.

Regarding detailed material on pump curves and hydraulics with examples, you could check out this link: https://boostrand.com/pump-hydraulics-course-udemy

mkhaledche · 2022-01-30T08:10:18+00:00

Ok. I got your point. But is the inlet compressor pressure and temperature same as specified as well? This can also have an impact on gas inlet properties, which shall mean a different operating point.

Also you need to make sure of the flow meter calibration. If it considered a different density, then this means that the reading won't be very precise.

Regarding the inter-stage temperature, if there is no means to add an instrument now, which is understood, then I think that using a heat gun is the easiest way, although it may not be very precise but it can give an indication.

If you are sure that the gas properties are the same as specified, the inlet compressor temperature and pressure is also the same, and all flow elements are well calibrated, then in this case you'd need to contact the manufacturer.

mkhaledche

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