5 replies to this topic

[Ariel]

Hello everybody,

 

I have a problem I would like to shear with you.

We have 3 propane bullet and two pumps to fill LPG transport trailer.

 

The operator said to me that, in summer (40°C - 104°F ambient temperature) the efficiency of the pumps lows(need more time to fill the transport than in winter) and sometimes he needs to vent the suction pipe.

 

The composition of the propane ( C2 - 0.198 / C3 95.61 / iC4 2.00 / C4 0.041)

 

Can anybody help me with this? Which could be the causes? Do I need to install thermal insulation to the suction pipe?  The NPSH can be affected by temperature?

 

Thanks in advance.

 

Ariel

[Bobby Strain]

Why don't you provide your analysis of the problem? That's what engineers do. You should readily arrive at the cause with little effort once you do a bit of thinking. Otherwise you may get lots of answers from this diverse forum.

 

Bobby

[Ariel]

Bobby,

 

Thanks for the answers. Let me explain what I guess:

 

Problem description: I want to recall that the problem only arises on summer, where the operator need more time to fill the trailer. Sometimes the operator open the vent valve to take out gas

 

Causes:

1) NPSH - I guess vapor on piping suction could be because of that. I do the maths  and there´s no problem there.

 

2) Suction piping.

It is Far? YES de pump is 100 meters away from the bullet.

Slope? It seems that no slope (down or up) is present

Main or individual pipe? each pump has his own 6in pipe from bullet

 

Probably I could confirm that no line up exists to the pump (if any very small, no visible by eye)

 

3) Velocity?

Pump nominal flow is 45 m3/h - With 6in pipe we have 0.65 m/s. I think is a good velocity for suction piping.

 

4) Composition envelope?

Beside there´s more than one element, the behavior could be read as vapor -equilibrium data for the propane (hysys envelope attached)

 

at 40°C(104°F)  13.6 kg/cm2 (185 psi)

at 50°C (122 °F) 16.7 kg/cm2 (227psi)

al 52.5°C (125 °F) 17.5 kg/cm2 (241psi) PSV set on bullet.

 

If pipe is heated by solar radiation up to 52.5 °C and more, the psv would open to release pressure.

There´s any chance that a section of the pipe could vaporize? Need some help here-. Because I have doubt here, y asked if the installation of thermal insulation have benefits

 

Thanks again

Ariel

[Ariel]

I forgot to attach the envelope.

Attached Files

•  Envelope.JPG   76.65KB   0 downloads

[Bobby Strain]

You could have vapor accumulation in the inlet pipe. But, most likely the loading is slower because the tanker is warmer causing some vaporization in the tanker. This results in higher pressure drop in the vapor return line, thus requiring higher head for the pump. The propane density is also less which also raises the head required. But you can confirm this with some pressure measurements. And listen to the pump.

 

Bobby

[Ariel]

Thanks bobby. Good point. Let me see the return line and think a bit about what you just said.

I will calculate preddure drop in the return line,at winter and summer temperature to see the difference.

 

Thanks again.

Ariel