The calculated distance (air line) between Blanchardstown and Droichead Nua is approximately 22 miles respectively 36 kilometers.
By car or train, the actual journey to Droichead Nua is certainly longer, as only the direct route (as the crow flies) between Blanchardstown and Droichead Nua has been calculated here.
Air line (approximately)
36 kilometers
20 nautical miles