5 replies to this topic

[processengbd]

We are contacting Silica Gel supplier for Natural gas Hydrocarbon dew point control operation. ( Process is chosen by client)

 

Problem 1

Now supplier is suggesting to use wet gas for cooling the tower saying that it will reduce the complexity of the process. That means "Regeneration gas is untreated feed gas which is first used for cooling. With heat recovered from the cooling bed the gas goes to the heater and then to the tower on heating." The supplier is saying that they have been using this process for past ten years. (Does not agrees with suggestions from the most prominent engineers in this forum.)

 

Above mentioned process is creating confusion in the mind of our client. They are saying to use dry gas in for cooling,

 

Problem  2

Silica Gel supplier has agreed to use dry gas for cooling but they are saying they don't have the database which they can use for this configuration (really!). They have suggested us a heater which is much bigger then normally needed. According to our calculation heat duty they are suggesting is to heat the regeneration gas from atmospheric temperature to the desired regeneration temperature. Simple MCpDelT. But as we know we have an economiser which preheat the regeneration gas before entering to heater, So  we don't need this big heater. When we are asking about the main understanding of Silica Gel supplier but they are saying that they have considered the economizer and came to this heater.

 

 

problem 3

Gas temperature of well is pretty high, 144 deg F. at wellhead will be reduced after pressure reduction. Even then it will be 115 deg F. This is causing higher load at tower. As it is difficult to cool the gas at 115 deg F as temperature gradient with air is very low we will be needing a big air cooler with very little temperature drop.

 

 

Thank you

Attached Files

•  Untitled 2.jpg   121.97KB   1 downloads

Edited by processengbd, 17 September 2014 - 10:16 PM.

[Bobby Strain]

Your discussion leads me to conclude that the silica gel supplier is giving you a design for free. You get what you pay for. This technology is so old that I have forgotten what I ever knew about it.

 

Good luck,

Bobby

[processengbd]

silica gel supplier is saying they cannot gurantee the process if we don't follow their procedure. As they are the only one prominent supplier we don't have any choice.

[PingPong]

PFD shows stream numbers, but without the accompanying heat and mass balance there is not much for outsiders to review/comment./recommend.

 

"Regeneration gas is untreated feed gas which is first used for cooling. With heat recovered from the cooling bed the gas goes to the heater and then to the tower on heating."

That is not what the PFD shows.

 

problem 2 could easily be solved if a heat and material balance was available. Heater absorbed duty is simply enthalpy difference between streams <16> and <15>

 

problem 3: what do you expect from us? You do not even mention the ambient air temperature, or whether cooling water is available. If you would replace the pressure reduction control valve by an expander you could achieve a much lower wet gas temperature, and generate some power, but expanders are not cheap.

Besides, if the design takes into account the rather high wet gas temperature, what does it matter?

[processengbd]

Thank you very much fro your reply & sorry for the confusion that was created.

 

1. It was supplier suggestion to use wet gas. But our PFD was built according to or client directive so it used dry gas.

Now supplier is suggesting to use wet gas for cooling the tower saying that it will reduce the complexity of the process. That means "Regeneration gas is untreated feed gas which is first used for cooling. With heat recovered from the cooling bed the gas goes to the heater and then to the tower on heating." The supplier is saying that they have been using this process for past ten years. (Does not agrees with suggestions from the most prominent engineers in this forum.)

 

2. From heat and material balance we found the heater duty would be 1206 KW (400 deg F to 560 deg F). Where supplier is suggesting to use 2450 KW heater.(We can get this exact value when we heat the same gas from atmospheric temperature to desired regeneration 560 deg F temperature). The logic behind the increased heat duty according to our consideration was at startup each tower has to regenerate before adsorption can go on.  So as there is no heated gas available we need the gas go to regeneration straight to temperature by heater only. When asked to supplier they did not provide any logic behind their heater duty calculation.

 

3. Air temperature is at 35 deg C. Cooling water is available but have to use cooling tower to cool the water back to desired temperature. We were also thinking about Expander cost will be too much. Higher temperature causes too much load in the adsorption tower which is also increased the size of heater to 3350 KW.

 

Regards

 

[PingPong]

Again: without a heat and mass balance outsiders can not .....

 

So the PFD is yours, not the vendors?

 

Note that the towers should be regenerated from bottom to top, if the normal wet gas flows from top to bottom.

 

What exactly is the scope of supply of the silica gel vendor? Only the silica gel, and a heater duty?

Or a complete design package including PFD, heat and mass balance, equipment datasheets, instrument datasheets, P&ID's, line schedule?

And what exactly does the vendor guarantee?

 

It seems to me that you need a serious design review meeting with this vendor, in the presence of the client. Vendor is more likely to listen to (obey) a dissatisfied client than a contractor.

Edited by PingPong, 18 September 2014 - 09:57 AM.