12 replies to this topic

[williammadella]

I read all comments, which helped a lot, thanks all but,

 

In my case  I’m working in a LPG pipeline transfer project composed of spheres > boosters (single stages centrifugal pumps of 55 kW each one, increase pressure around 2.6 kgf/cm2) > 8” diameter pipeline 1500 meters length and 15 m elevation until reach the main pump suction > main barrel pumps of 400kW > pipeline of around 170 km/8 inches diameter. I’m concerned about the transfer thought the 8”x1500m pipe (1 “thickness insulated) generate too much regasification and cause main pump severe cavitation. Some engineers tells me that I’m watching ghosts that we will never have problems and some says that of course I will have problems, The temperature of LPG inside the spheres are 12 to 38 C  kg/cm2 . I have indicated the severe risk of cavitation, many engineers told me that I was watching ghosts, are they right? Anyone may help me?

Thanks in advance.

[Ajay S. Satpute]

Williammadella,

 

Your concern is that due to heat absorption by liquid LPG, a part of the same could vaporize and lead to cavitation in the pump.

 

Please provide following details;

1. LPG composition

2. Minimum liquid head in the spherical vessel

3. Minimum operating pressure in the spherical vessel

4. Insulation type

5. Flow rate

6. System schematic

7. Is pipe in air or underground? If in air, then air max. temperature and air max. velocity. If underground, then ground conductivity and buried depth.

 

Regards.

 

Ajay S. Satpute

Edited by Ajay S. Satpute, 21 April 2014 - 11:23 PM.

[williammadella]

 Many thanks for your kindly help,  you are right, that’s what I’m concerned, bubble vaporization inside the transfer pipe and main pump cavitation, follow the answers:

 

1. the composition vary from 40% C2 and 60% C3 until 60% C2 and 40% C3 (follow attached the LPG pressure x temp data)
2. For the booster pump inlet is 3 meters but the main pump is settle down 15 meters higher with a 1,5 km x 8” transfer pipe (follow attached schematic)
3. It’s around 5 kgk/cm2 at 15 C temp;

4. 1” thickness of calcium silicate + 0.8 mm aluminum coat protection foil;

5. 120 to 250 m3 ( speed around 1 to 2 m/s)

6. Follow attached;

7. Airground trasnfer pipe, max air temp around 45C, speed around 1 to 2 m/s

Thanks a lot, regards,

                                   William Madella

Attached Files

•  preesao x temp.pdf   92.06KB   25 downloads
•  schematic.pdf   96.46KB   31 downloads

[Ajay S. Satpute]

 Hi,

 

Pl refer my comments in red.

 

Regards.

 

Ajay

 

 Many thanks for your kindly help,  you are right, that’s what I’m concerned, bubble vaporization inside the transfer pipe and main pump cavitation, follow the answers:

 

1. the composition vary from 40% C2 and 60% C3 until 60% C2 and 40% C3 (follow attached the LPG pressure x temp data)

Isn't LPG a mixture of C3 and C4? What is the unit of composition (mole % or wt. %)?

1. For the booster pump inlet is 3 meters but the main pump is settle down 15 meters higher with a 1,5 km x 8” transfer pipe (follow attached schematic)
2. It’s around 5 kgk/cm2 at 15 C temp;

Unit kg/cm2 or kg/cm2g?

1. 1” thickness of calcium silicate + 0.8 mm aluminum coat protection foil;

2. 120 to 250 m3 ( speed around 1 to 2 m/s)

Unit again? Do you have mass flow rate?

1. Follow attached;

2. Airground trasnfer pipe, max air temp around 45C, speed around 1 to 2 m/s

Thanks a lot, regards,

                                   William Madella

 

[Ajay S. Satpute]

Williammadella,

 

I've put some numbers in Hysys model to check if there is any vapor formation in the pipeline. Please check the attached snapshot, especially the input parameters and correct me so that Hysys file can be updated.

 

Nevertheless, it appears that there may not be any issue of pump cavitation due to vapor in pump suction.

 

Regards.

 

Ajay

Attached Files

•  Hysys_Snapshot.png   255.03KB   1 downloads

[williammadella]

Thanks onde again,

1. the composition vary from 40% C2 and 60% C3 until 60% C2 and 40% C3 (follow attached the LPG pressure x temp data)

Isn't LPG a mixture of C3 and C4? What is the unit of composition (mole % or wt. %)? excuse me for my error, it´s C3 and C4 , but the composition it's not always de same, the attached graffic for pressure x temperature is correct between the 2 curves, did you downloaded it?

1. For the booster pump inlet is 3 meters but the main pump is settle down 15 meters higher with a 1,5 km x 8” transfer pipe (follow attached schematic)
2. It’s around 5 kgk/cm2 at 15 C temp;

Unit kg/cm2 or kg/cm2g? kg/cm2

1. 1” thickness of calcium silicate + 0.8 mm aluminum coat protection foil;

2. 120 to 250 m3 ( speed around 1 to 2 m/s)

Unit again? Do you have mass flow rate? the considered density is 515 kg/m3, 61.8 ton/h until 128.75 ton/h

1. Follow attached;

2. Airground trasnfer pipe, max air temp around 45C, speed around 1 to 2 m/s

 

Best regards,

                    William Madella

[williammadella]

Dear Mr. Satpute,

 

 May you simulate at HYSYS the condition for 35.5 C temp x 10.5 kg/cm2 g at the sphere?

 

Regards,

             William

[Ajay S. Satpute]

William, 

 

PFA Hysys snapshot.

 

 

Regards.

 

Ajay S. Satpute

 

Dear Mr. Satpute,

 

 May you simulate at HYSYS the condition for 35.5 C temp x 10.5 kg/cm2 g at the sphere?

 

Regards,

             William

 

 

Attached Files

•  Hysys_Snapshot_2.png   349.61KB   2 downloads

[williammadella]

 Flow_curve.pdf   86.92KB   22 downloads Dear Mr. Satpute,

 

Thanks once again. I´m mechanical engineer, so I take a look at the system with a mechanical eye, so I must consider some possible critical flow conditions.

 If possible please help me understand better the limitation of the HYSYS software. I guess the HYSYS software does not consider the pressure drop caused by all pipe construction elements such as curves, check valves, flow rate meters and others ( I received the project finished and didn´t find this evaluation or calculation memory).

Otherwise a fluid flow speed inside a pipe has a curve similar like that attached, where we have different speeds along the radius of flow, so near the pipe wall we have  a very low speed and a long time fluid contact with the heated pipe wall, where I’m concerned of bubbles of regasification formation near the pipe wall. as information I have measured the temperature over the insulation surface, 62 C and in the external pipe surface of 48 C.

 

Regards,

                William Madella

 

 

 

[Ajay S. Satpute]

William,

 

You mentioned air max. temperature as 45 oC in post no. 6. Why you should read 62 oC or 48 oC temperatures at/near your pipe? Do you need to correct your input parameters?

 

You wanted to know if pump suction line would have any vapor generation at given operating parameters and due to heat absorption from hotter ambient air. Hysys calculation provides you the favorable news. I wonder why you don't believe it.

 

With all due respect, I would request you to kindly leave the process calculations, hysys limitations etc. to process engineers.

 

 

 

Regards.

 

Ajay S. Satpute

[williammadella]

Mr Satput,

 

 Thanks to go along with me in this case, I will try to clarify my informations:

 

Parameter is all right. The maximum air temperature is around 45C, but in the surface of the foil over the insulation goes to 62 due the solar radiation, and 48C in the pipe due to the insulation, and only 35 C in the mass of LPG at the spheres due to the amount of LPG inside and the necessary time to the heat transfer (at night we have temperature inversion). 

 

.  I believe in the HYSYS software, but I guess it works with the RMS speed, and do not consider the different speeds lines inside the pipe, but the HYSYS information is valuable for me as preliminary analysis.

 

   I will now perform the pressure drop calculation and return the information, I guess that all information that was possible to have from HYSYS software you’ve provided me, many thanks.

Regards,

                 William 

[Ajay S. Satpute]

William,

 

1. You may kindly go through a few topics discussed in this forum regarding solar radiation. Mr. Ankur has provided several useful links to understand the subject better.

 

2. During flowing condition, solar radiation heat into the liquid through insulation and foil is very very less (not enough heat to raise the liquid temperature to Tsat). However, when one starts the pump after a shut down (as the pipe and pump temperatures would be high), one can expect vaporization of a part of liquid, causing pump cavitation.

 

3. If the liquid flow rate drops below a value, where heat in from solar radiation matches sensible heat of liquid causing it to reach Tsat, one can expect vaporization in such line.

 

4. Solar radiation subjected on Al sheet shall absorb a part and reflect the rest. Assuming all the heat absorbed by Al sheet is available for LPG to get heated up;

 

alpha_s = 0.15

Emmissivity = 0.05

G_solar = 1000 W/m2

Sigma = 5.67 e-8

T_s = 62 + 273 = 335 K

T_sky = 280 K

 

Qnet_radiation = alpha_s * G_solar - Emissivity * Sigma * (T_s^4 - T_sky^4) ............. Equation 1

Qnet_radiation = 132 W/m2

 

A. 50 kW suction pipe:

10 m length

219.1 mm od + 25.4 mm insulation = 244.2 mm is net diameter

Total surface area = 3.142 * 0.2442 * 10 = 7.7 m2

Q_absorbed_1 = 132 * 7.7 = 1016 W

Now let's check if this heat is high enough to raise LPG temperature to its Tsat.

Tsat at 10.5 kg/cm2g = 48.1 oC.

LPG temperature = 35.5 oC

m = 61948 kg/h (120 m3/h)

Q_1 = m*Cp_1 * (Tsat - T) = 61948 / 3600 * 2710 * (48.1 - 35.5) = 5.9 e5 W

As Q_absorbed_1 << Q_1, therefore no vapor formation in liquid.

 

B. 400 kW suction pipe:

1500 m length

219.1 mm od + 25.4 mm insulation = 244.2 mm is net diameter

Total surface area = 3.142 * 0.2442 * 1500 = 1146 m2

Q_absorbed_2 = 132 * 1500 = 151272 W

 

Now let's check if this heat is high enough to raise LPG temperature to its Tsat.

Tsat at 14.2 kg/cm2g = 60.93 oC.

LPG temperature = 35.87 oC

m = 61948 kg/h (120 m3/h)

Q_2 = m*Cp_2 * (Tsat - T) = 61948 / 3600 * 2702 * (60.93 - 35.87) = 1.2 e6 W

As Q_absorbed_2 << Q_2, therefore no vapor formation in liquid.

 

C. For flow rate 8043 kg/h (15.6 m3/h), Q_absorbed shall equal Q.

 

Regards.

 

Ajay S. Satpute

[williammadella]

Ajay S. Satpute

 

Dear Mr. Satput,

  I guess now only remains the work of calculate the pressure drop due the geometry, pipe construction elements. Will perform these and publish here.

Bests regards,

 

                          William madella