Display large decimal number using seven segments display
Since the output of your ADC is binary and you need BCD to drive the BCD to 7- segment display drivers, you'll need a binary to BCD converter between the ADC output and the seven-segment drivers. 

One way to do the conversion in hardware is to load the ADC output into an 8 bit binary down counter and, at the same time, clear three BCD up counters.

Then, using the same clock for all of the counters, simultaneously clock all the counters. When the binary counter counts down to zero, stop the clock/disable the counters and -  VOILA! - the ADC's output, in BCD, will be held in the up counters' Q outputs.

Like this: