counting replace the entire RBC population

Is it 2,400,000?

Oke, i'm going to assume a few things:
- the age of the RBC's is equally divided, so there is 1/120 part 1 day old, 1/120 part 2 days etc.
- RBC's only live for 120 days, then they die, no exceptions

Then: first we calculate the amount of RBC's in 5 liters of blood: 5*10^6 (RBC's in 5 micro liters of blood) * 5*10^6 (amount of micro liters of blood) = 25 * 10^12

Divide by 120 to get the amount that dies: 208333333333,33333......
assuming you want to keep the same amount of RBC's per day you have 24 hours to replace those that died so:
208333333333,33333 / (24*60*60) = 2.411.265, 432....

So per second you need to make about 2,4 million RBC's