Size of orifice / Pressure drop across Multiple Discharge lines

[dungarah]

Hi all,

I am trying to come up with an excel spreadsheet that allows me to calculate pressure drop across a system having multiple discharge lines; a recycle line, an IBC filling point & a tanker loading point from a single pump. I have attached calculations that i have done to show pressure drop if you treat the process as a series, one route as a time, and am looking for help how to link the 3 into 1.
My aim is also to find out the size of orifice needed within the recirc line to be able to push just enough flow into the IBC packing point.
Its my first time posting, so i may not have put across all the details needed. I will post back asap.

thanks , any help would be appreciated.

 

[chemebabak]

Your excel file shows three branches, each on its own tab, and each branch has its own pump. According to your description, you have one pump that provides positive pressure to impulse phosphorous trichloride flow through each branch. You need to add another tab to your excel file and use that to calculate the pump head. I have done that and highlighted all of the changes I have made to your file.

For your reference, the solution is:

1. calculate the line loss from the pump discharge to the end point of each branch. That is, at end point of head tank loading, the pressure required is P1. Let us say P1 = 100 psig. Add the line loss to P1 and you have Pd (pump discharge pressure). Let us say that the line loss is 10 psi. Pd = P1 + line loss = 100 psig + 10 psi = 110 psig required pump discharge pressure. Do the same for branches 2 and three. Select whichever Pd is the highest as the design discharge pressure for the pump.
2. Calculate line loss from Storage vessel Pa (pressure a) to pump suction for the total flow (sum of flow 1, flow 2 and flow 3).
3. the difference between pump suction and pump discharge pressures is your total head required for the pump.

You should adjust each branch to include a control valve and you should also include a minimum flow bypass for the pump.

 

[chemebabak]

dungarah,

OK, it took me awhile to understand what it was you really wanted. As you said, you want to size the orifice to adjust the flow. This is even easier. Use the Goal Seek function. Select an orifice size (any size) and set discharge pressure cell G55 to 31.74 (this is the pump pressure required on the recycle line) by changing the flow rate cell F12.

This is the calculation method to simulate reality. In reality your system will adjust the flow to meet the pressure available. It does not matter what orifice size you select. The smaller the orifice, the lower the flow. Even if you do not select an orifice, the system will only be able to force as much flow through each branch as the pump pressure makes possible.

On the other hand, if you size the pump for 60 m head, your corresponding branches will increase in flow. Please understand that reality is a dynamic system. As you increase the flow (by increasing the orifice size or the opening of a control valve) the pump pressure will decrease along the curve. All three branches will react to the new pressure and the flow and pressure will adjust along the curve.

My advice is to size the pump for 32 m at 40 m3/hr and forget about it.