Practical rule-of-thumb for a 1 km tunnel
If your lining is relatively thin (5–15 cm) and you have several weeks of spraying time, a 10–15 m³/h unit can be sufficient.
If you need faster cycle times, thicker linings, or want one machine to finish in a short window, go 20–30 m³/h with a 12–16 m boom. Several manufacturers list 30 m³/h models recommended for tunnels up to ~1 km.
