DC Supply Load Dummy based on NPNs
Your circuit will not work.

1) 28 volts @ 24 amps is 672 watts. The 2N3773 is only rated for 150 watts, and this assumes a perfect heat sink capable of maintaining the transistor case at 25 C. Using a more reasonable thermal load of 100 watts, you'll need at least 7 transistors. You'll also need a bloody good heat sink with a fan.

2) Assuming ~8 transistors, this implies ~3 amps collector current per transistor max. If the transistor hfe is assumed (from the data sheet) to be about 20, you'll need about 150 mA per transistor base drive, or a total of about 1.2 amps total base current. An LM358 will never produce that kind of current, so you'll need a current booster for the base drive. 

3) In order to get down to 0 amps load current, you'll need a negative supply voltage. First, you need it to allow the op amp to operate reliably near zero volts input from the sense resistor, and second you need some way to bleed off leakage currents through the pass transistors. Note that, if you select an op amp with rail-to-rail inputs, you can still get in trouble with parasitic IR drops in your power circuitry, so unless you are rather more knowledgeable about pcb layout than I suspect, a negative supply is still indicated. 

4) Along this line, you should use a differential amplifier or instrumentation amplifier to sense your current - don't simply assume that the ground point of the sense resistor is at the same voltage as the ground point of your reference voltage. With 24 amps running around your circuit they almost certainly are not. And make sure you use a Kelvin connection on your sense resistor.

5) For stability, you'll need to provide small emitter resistors on each NPN. 0.1 ohm to 1 ohm will work well.