Pump sizing

With the little bit of info you provide ...
Is this for water?

That is a wide operating flow rate range.
It would be helpful to know what the average flow rate is.
That could make a significant difference in what pumps you select.

The pumps are the correct size for peak flow of 3285m3/d, both working.
You will need a head capacity of 40 to 50m.
You do not mention the efficiency, so that 45kW could even need to be maybe 25% higher.

One pump is quite large for minimum flow, about 2X the minimum capacity and has excessive power.

Use of 2 pumps with VFD should be investigated further.
OR
Maybe 3 or even 4 fixed speed pumps could have advantages as, if the average flow rate is closer to the minimum flow, the 2 pump solution might be too large for the avg flow.
It is essential to know the average flow rate to go any further.
It may nor be the mathematical average, but rather a flow rate that you will be close to almost all the time.

Is the pipeline flat and outlet to open air discharge?




--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

Dunno - Try giving us proper details such as what the pumping pressure is at your max flow rate.

Less than 1km really shouldn't need much more than 2-3 bar with 0.5 bar static head, but you're not giving us all the data.

Start with the pump quote.

So 45kW on that basis looks very high.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

It's a 3bar dP +0.5
In round numbers,
150m3/h
say 50kg/s x 40m =2000 kg-m/s = 20kW
1 operating, 1 standby
Total Water Power 40kW
Eff?

For a 2 pump Total it's OK.
But if it is "a" =1 pump, it's a lot too high.

So is 45kW a total of 2 pumps?
Or is it for each pump and they have a 50% efficiency?

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

Yes, it is correct. At the peak flow, you have 60 meters of head including the 5 meters of static head.

How did you arrive at the average flow vs. peak flow? That is where you made the mistake. The low flow will provide the 2 ft/sec minimum flow, but the peak flow is too large for the 150 mm pipe. Pipelines of this nature normally pump at 3-5 ft/sec.

I'm having a hard time believing there isn't already a design professional involved in this who would be the person who would respond to the concerns of the official. For the amount of infrastructure investment we're talking about here, it can't all be in the hands of the pump vendor like it's a residential sewage pump. Are you by chance the owner, contractor, or the building official... and you are really looking to independently assure yourself? If so, just say so, it's ok to want 2nd opinions. I agree with the others... the peak flow rate doesn't make any sense and pump designers talk about flows in volume/minute so my spidey-sense is tingling just by seeing it talked about in daily flows. I suspect there is a large tank involved to regulate flows and you are just telling us the numbers you know.... Nobody is moving a million gallons a day of liquid through a 6-inch pipe.