Installing a Non Return Valve in the discharge line of a centrifugal pump (having a plug valve already in the discharge line) is the right thing to do?

plug valve is for isolating the pump from the line or the line itself , the NRV is to prevent reverse flow when the pump is stopped

The answer is yes, that it is the correct design. When a pump is deadheaded it doesn't do the impeller or the drive any good. Many engineers use relief valves to cycle the discharge back to the pump suction of centrifugal pumps. I was taught this was not correct and that the fluid should be return to the supply tank. Many times a flow switch is installed in the discharge of the relief valve to give operators an indication of relief valve action.

But if we install NRV, won't there be a problem relating to the pipeline draining? Since the solution cannot flow backwards.

And for isolating the pump I believe even a butterfly valve can do the job, right?

you can position a drainline between the NRV discharge and plug or isolation valve. as much a s possible avoid butterfly valve for isolation better use gate valve, ball valve

Select the type of isolation valve depending on the media and process conditions. For ex. a ball valve has a volume which could be liquid filled when closed. If the media is hazardous it could be a safety issue if this is not recognized during maintenance. Also think of thermal expansion if liquid is trapped inside the valve. I would recommend to look into litterature for how to choose valves for your process.

I wouldn't trust a butterfly valve for isolation in hazardous service. Gate valves are what I am familiar with for isolation. I have never seen a non-return valve on a pump discharge, but it is an interesting idea. I am familiar with ordinary swing checks on pump discharges, but they will stick open on occasion. Unfortunately a sticking check is not a rare event. A non-return valve would give the flexibility to force the check closed.

Becareful putting valves and fittings on either side of the pump without consideration to its impact on the pumps system curve.

The fittings will shift the system curve to the left and away from the pumps bep. This creates forces in the volute that can cause shaft deflection.

This shaft deflection leads to premature seal failure and increased maitenace intervals and "tool time."

The are minimum L/D's away from the discharge and suction. The suction side is more sensitive for more than one reason.

So, appropriate placement as well as selection is important. Even valve selection...use full port ball valves for instance to minimize resistances.

So a NRV is fine. Account for it in your system curve calculations. Compare to the pump curve. Ensure the pump will operate within the shift away from the pumps bep.

Another thing that can and will help is to buy pumps with low L3D4s, or stiffness ratios. Below 60. The lower the better.

Changing the pipe network in even small ways can have significant impact to its reliability and over all life time operational cost that manifests in real dollars.

Is there any tool or application available to do these system curve calculations?

Before spending time to investigate valve type for isolation, check if this work has been done already. For new facility, the engineering contractor usually has piping spec. for the fluid handled. For existing facility, there should also be piping specification already established. For some application, tapping a hole on the flap of the check valve for drainage is acceptable. This allowance will also be on the piping spec.