Release of stored ammonia at start-up

A method of storing and dosing ammonia from a solid ammonia storage material capable of binding and releasing ammonia reversibly by adsorption/absorption: - heating a start-up storage unit (3) and a main storage unit (2), as a consequence of which the start-up storage unit (3) will reach a desired minimum pressure before the main storage unit (2) will reach that pressure, so that the at least one one-way valve (4) is then closed and thereby prevents any back-flow of ammonia from the start-up storage unit (3) to the main storage unit (2), - dosing ammonia according to the demand, - when the main storage unit (2) reaches a pressure higher than that downstream the one-way valve (4) opens and enables ammonia to pass through the at least one one-way valve (4).