Regenerative preheater and method of operating the same

The regenerative preheater includes a heat accumulator (6) and a catalyst (4). During operation, a crude gas (R) containing a pollutant component (for example NOx) and a clean gas (G) alternately flow through the heat accumulator (6) and the catalyst (4). A first addition point (24) for a gaseous reactant (M; for example NH3) is provided, which point is situated in the flow route of the crude gas (R) prior to the catalyst (4). In addition, a second addition point (34A, 34B) is provided for the reactant (M; NH3), which point lies in the flow route of the clean gas (G) prior to the catalyst (4). During operation therefore, the reactant (M) is introduced into both flow routes. As a result it is possible to decrease the unconsumed portion of the reactant (M) and simultaneously to increase the degree of reaction of the catalyst (4).