What's the maximum size of orifice for minimum flow line?
What's the maximum size of orifice for minimum flow line?
(OP)
Hi All,
What could be the maximum size of orifice for minimum flow lines? Because control valve could save energy once minimum flow lines are big enough? Thanks for any comments in advance..
What could be the maximum size of orifice for minimum flow lines? Because control valve could save energy once minimum flow lines are big enough? Thanks for any comments in advance..





RE: What's the maximum size of orifice for minimum flow line?
The classic paper in this regard is Hooper, Chem Eng, Nov 7, 1988, pgs 89-92 and he does not specify any limits for his correlations.
Katmar Software - Engineering & Risk Analysis Software
http://katmarsoftware.com
"An undefined problem has an infinite number of solutions"
RE: What's the maximum size of orifice for minimum flow line?
Thanks for the reply. But what if the size is large enough and the energy savings would be great if converted from orifice to control valve?
RE: What's the maximum size of orifice for minimum flow line?
Put a simple manual globe valve in the minimum flow bypass line.
You will have the ability to "play" with the flow till you get it right. It is not fixed and you did not endure the cost of the full Control valve and all of the control loop hardware.
RE: What's the maximum size of orifice for minimum flow line?
You could install a self-contained and self-powered automatic spill-back valve. The most common manufacturer we use has a brand name of Yarway. This will close off the minimum flow line when the outgoing flow is above the required minimum and open it only when the outgoing flow is below the required minimum.
If, on the other hand, your outgoing flow is constant, then there is little or no value in an automated valve. An orifice or a manual globe valve would be more than adequate.
Johnny Pellin
RE: What's the maximum size of orifice for minimum flow line?
Don't look to save money by replacing an orifice with a control valve. Look to replace an orifice with a control valve to cut minimuze the noise and flashing.
We are more connected to everyone in the world than we've ever been before, except to the person sitting next to us. Lisa Gansky
RE: What's the maximum size of orifice for minimum flow line?
Katmar Software - Engineering & Risk Analysis Software
http://katmarsoftware.com
"An undefined problem has an infinite number of solutions"
RE: What's the maximum size of orifice for minimum flow line?
We are more connected to everyone in the world than we've ever been before, except to the person sitting next to us. Lisa Gansky
RE: What's the maximum size of orifice for minimum flow line?
information related to these pumps is listed below:
Item Rated Capacity Motor P Est. Recycle Power
G-0405A/B 8.9 + 3.3 15 4.1
G-0407A/B 8.2 + 3.3 45 12.9
G-0502A/B 17.7 + 8.6 75 24.5
G-0503A/B 35.2 + 17.2 22 7.2
G-0509A/B 20.7 + 7.8 22 6.0
G-0903A/B 37.8 + 22.1 45 16.6
G-0405 Wash Gasoline Pump, G-0407 Gas Oil Stripper Bottoms Pump, G-0502 Charge Gas Comp 3rd stage suction drum pump, G-0503 Charge Gas Comp 3rd stage discharge drum pump, G-0509 Medium Gasoline Pump, G-0903 PGH Depentanizer Reflux Pump. As you can see, estimated recycle power is an energy savings. This pump were purchased and to be installed according to API 610 Standard. On our Boiler Feed Pump application, we are using ARV (Automatic Recirculation Valve) which will automatically switch to main line once minimum flow is reached. These pump are all inside the process area of an Ethylene Cracker Plant which we are ongoing construction. Target commissioning of the plant will be on 2013. What i think is that 4kw above of recycle power should be change to control valve, which will shut-off at predetermined flow.
RE: What's the maximum size of orifice for minimum flow line?
Assuming the pumps are constant speed, the energy consumed at full flow, or half flow, or any flow will be Power = Qt*ρ*g*h/eff. Where Qt is the total flow to downstream, Qd if any, plus flow to recycle, Qr. H is the head shown on the pump's curve at the same total flow, Qt. Whether the flow is going to recycle, via an orifice, or via a control valve, will make no difference to the energy consumption of these pumps. It is still P = Qt*ρ*g*h/eff. Because Qt remains constant no matter how much is going to recycle or how much is going downstream, but if you reduce Qt, no matter how you do it, by reducing Qr or Qd, pump Power will drop accordingly.
What you don't want to do is to have the recycle lines open when you are trying to move all of the design flowrate downstream, assuming your pumps are sized with the correct head for your design flow at BEP. You are the one wasting energy in that case, because you are not using that high pressure recycled fluid in your process, but the pump has no choice, it must use whatever Power happens to equal = Qt*ρ*g*h/eff.
There is no more energy savings possible here than what you would get if you simply reduce the total flowrate through the plant. To save energy, perhaps by considering VFDs, the next step would be to see how much you could save. Then you would see that they would cost you 5% more at full flow and you would save no energy running at design capacity. Then you would also see that you have to operate at reduced capacity for the VFDs to have any chance of saving money. Then you see, that if you reduce flow, you also reduce INCOME from the plant and that there is no future in that VFD logic. Its pretty much like saying, "Humm... If I shut this plant down, I will be able to save a lot of energy."
We are more connected to everyone in the world than we've ever been before, except to the person sitting next to us. Lisa Gansky
RE: What's the maximum size of orifice for minimum flow line?
RE: What's the maximum size of orifice for minimum flow line?
With VFDs, pump energy essentially increases to 5% more than what you would use with simple constant flow at the optimum BEP speed design flow.
At around 50% flow, your energy consumption is obviously roughly 1/2, based on 1/2 Q alone, Power = qρh/e, neglecting some efficiency decrease. You have a potential to save money, if you can also cut H, but with VFDs you must be able to cut H by the drop in speed squared to move any flow. So, that's 1/4 H at design speed, a drop to 0.5 squared. Lots of plants can't do that.
So, generally speaking again, you can't drop to 50% with VFDs in many applications. If you do, you don't save all that much over constant speed operation, because you've already saved half anyway simply by cutting plant output in half, so there's only a max you will save around 25% at best, not half.
Here's the killer. Yes, if you operated the plant at half flow you might could save money with VFDs, but do you want to operate at half flow? NO! You've already cut your profit in half. There is no business reason to do it, so if you do, you will only run at half flow for the smallest amount of time possible, or your boss will kill you. Now let's push up toward higher flowrates again.
As you get to 75% to 85% operation, there is some potential to save money with VFDs, you're in the good range for that, but if you move to operation at 80 to 90% design for enough time where it makes it attractive to use VFDs, I've found that you should really review your design flow criteria and most likely lower that to the point where you can go back to running the plant continuously at a full speed operation again, just at 90% of the design flowrate that you thought you needed before. When applying VFDs to new plant design, if it looks attractive, it could easily turn out that you probably made a bad choice of original design flowrate and you should reduce that by 10 percent or so and run at constant speed. If you selected your design flowrate conservatively to have some easy future expansion capacity, then, if you were so optimistic then, you shouldn't now be looking at running at 75% or less design flowrates where VFDs make sense. VFDs have some potential to save in closed loop systems, where you may never want to operate at maximum flow for a very long time, otherwise ... well .... look elsewhere for energy savings. There ain't any there.
We are more connected to everyone in the world than we've ever been before, except to the person sitting next to us. Lisa Gansky
RE: What's the maximum size of orifice for minimum flow line?
RE: What's the maximum size of orifice for minimum flow line?
RE: What's the maximum size of orifice for minimum flow line?