An apparatus for starting up and/or shutting down a plant for preparing nitric acid from ammonia and oxygenous gas may include at least one air compressor, at least one process gas cooler, at least one feed water preheater, and at least one residual gas turbine. The at least one process gas cooler and the at least one feed water preheater may include pipe coils, at least one of which is connected to a source for a heating medium such that the at least one pipe coil in the process gas cooler and/or the feed water preheater can be charged during startup and/or shutdown of the apparatus with the heating medium for heating the process gas flowing through the process gas cooler and feed water preheater. The apparatus may further include a heat exchanger downstream of the process gas cooler and/or the feed water preheater for transferring thermal energy from the heated process gas to the residual gas supplied to the residual gas turbine. Corresponding methods are also disclosed.