I have no idea what a "current loop primer" is.
I could take a guess, but I have never heared the expression before.
What you need is a constant current generator of some sort.
Have a look at the attachment, just using two components, an LM317 voltage regulator and a variable resistor, you can make a nice little constant current generator.
To calculate the required resistance:
resistance = 1.25/current
Note that the output voltage will not be fixed at 24v, but will vary depending on the load resistance and the current flowing.
Does that help?
Jimb