5 replies to this topic

[Abhishek Hota]

Hi everyone

I work in a shampoo manufacturing unit. While transfer of shampoo taken place from manufacturing vessel to storage vessel, some quantity remains in the pipelines as hold-up. How can I calculate this hold up? On what factors does it depend?
The shampoo is transferred with a lobe pump and the connecting pipes consist of both horizontal and vertical sections.

[daryon]

Liquid hold up is not relevant for single phase flow in pipelines. Whatever liquid (shampoo) goes into your pipeline will come out the other end, where else can it go?

Liquid hold up occurs in 2-phase (gas and liquid) flow through pipelines where the gas superficial velocity is higher than the liquid and some degree of liquid inventory is held up in the pipeline. The liquid hold up is dependant of the gas velocity relative to the liquid velocity as well as fluid properties (density and viscosity), interfacial tension between the fluids, and pipe diameter. There are correlations to predict liquid hold up in 2-phase pipelines, I suggest you try the GPSA Engineering Databook as a 1st reference.

Good luck

[chemsac2]

Abhishek,

Whay Daryon refers to is for two-phase flow which I think is not what you are looking for. I think you want to know how much volume would be trapped in pipe. I presume your system to be liquid full.

If assumptions are valid, you just need to calculate pipe volume. If D is inside diameter of pipe and L is total physical length, liquid hold-up in m3 would be pi*D*D*L/4.

Use actual length of pipe. You will have to be carefull with elbows. If you have isometrics, you can get dimensions of elbow to calculate volume held-up there. For valves, it would be tricky, but you can approximate by length.

Regards,

Sachin

[fallah]

With a little bit information you mentioned as above it is hard to submit a helpful answer.Assumed you mean liquid hold up at the end of loading and after that the pump to be stopped.

What can be presented as the main factors affect amount of hold up would be as below:

-Viscosity of the fluid
-Size of transfer line
-Overall slope of transfer line (between pump discharge and inlet of storage tank)
-If low point(s) existed in pipelines or it completely is to be free drain

[Abhishek Hota]

The pump cannot transfer 100% of the shampoo since it is a displacement pump. Once the shampoo on side of the pump is over, it cannot push the quantity remaining on the other side. Also, since the other side has vertical as well as horizontal sections, there is shampoo trapped in these.
The approximate hold-up after following a few transfers comes out to be around 70%-75% of the volume of the pipeline covered.

Now, I am trying to find out on what factors does it depend. And if for given pipe info. like length, diameter, no. of bends etc(complete structure), can I calculte theoretically the actual hold-up.

[ankur2061]

Abhishek,

The volume of any hollow cylindrical geometrical shape (in your case pipe) is calculated as the product of the cross-sectional area to the length of the pipe section.

For fittings (elbows, bends etc.). the equivalent straight length can be used to add to the straight length & the total length thus calculated used for the volume calculation.

After transfer of any batch of liquid, the left out liquid volume in the pipe can thus be calculated. This leftout inventory of liquid is useful when doing a plant wise inventory calculation & the finished product cost.

In certain cases where the product is sensitive to time induced degradation or a different product grade is required to be produced, it is important that the product be drained from the pipe & recylced or disposed off.

Hope this helps.

Regards,
Ankur.

Edited by ankur2061, 30 June 2010 - 09:01 AM.