helps protect walls of the combustion chamber formed with the sio 2 coating application_number US 28821102 A description referring now to the figures of the drawing in detail and first particularly to fig1 and 2 thereof there is shown in both configurations a combustion chamber 10 in which a burner 11 is disposed the combustion chamber 10 is delimited by boundary surfaces 22 with a sio 2 coating 24 a combustion medium 25 is fed to a nozzle 12 via a line 17 with a shut off valve 18 it is ignited by a device that is not shown in more detail so that a combustion operation is formed in the form of a flame 14 the combustion gives rise to a formation of flue gases 15 which collect in the combustion chamber 10 and are discharged via a discharge 16 for example to a non illustrated steam generator furthermore an additive 26 is added in order to protect the sio 2 coating 24 on the boundary surfaces 22 the additive 26 is held in a vessel 21 and is added via a pump 20 and line 19 the pump 20 is used to meter the quantity of additive 26 that is added in the configuration shown in fig1 the additive 26 is added separately from the combustion medium 25 via a dedicated nozzle 13 it is therefore possible to select an additive.