Method and apparatus for improving exhaust gases of a gas turbine installation

Claim 5

A method according to claim 2, characterized in that a decrease in the quantity of non-preheated admixed air beyond the middle partial load range proceeds to an admixture quantity of zero.

Claim 6

A method according to claim 3, characterized in that the point of zero admixture is reached at a point below an output adjustment corresponding to a rated output of the gas turbine installation.

Claim 11

A method according to claim 6, characterized in that a decrease in the quantity of non-preheated admixed air beyond the middle partial load range proceeds to an admixture quantity of zero.

Claim 12

A method according to claim 6, characterized in that the point of zero admixture is reached at a point below an output adjustment corresponding to a rated output of the gas turbine installation.

Claim 13

A gas turbine installation comprising compressor means for compressing air, heat-exchanger means for heating the compressed air by utilizing the exhaust gas heat of the gas turbine installation, combustion chamber means for combusting fuel with an excess of air under supply of compressed air constituting the primary air, means for thinning resulting gas of the combusted fuel by an admixture of compressed heated air constituting secondary air and cooling the same for producing gases for use in turbine means, and means including said turbine means for expanding the produced gases while producing a mechanical output, characterized in that a mixing chamber means is disposed outside of said combustion chamber means for intimately combining and mixing a more or less large quantity of substantially non-preheated air to the preheated primary air prior to the entry thereof into a combustion zone of the combustion chamber means at least within a lower partial load range, means operable as a function of the load of the gas turbine installation for controlling the amount of non-preheated air so that at most approximately 15% of the rate of air flow of the gas turbine installation is admixed in non-preheated air by said controlling means.

Claim 14

A gas turbine installation comprising compressor means for compressing air, heat-exchanger means for heating the compressed air by utilizing the exhaust gas heat of the gas turbine installation, combustion chamber means for combusting fuel with an excess of air under supply of compressed air constituting the primary air, means for thinning resulting gas of the combusted fuel by an admixture of compressed heated air constituting secondary air and cooling the same for producing gases for use in turbine means, and means including said turbine means for expanding the produced gases while producing a mechanical output, characterized in that a mixing chamber means is disposed outside of said combustion chamber means for intimately combining and mixing a more or less large quantity of substantially non-preheated air to the preheated primary air prior to the entry thereof into a combustion zone of the combustion chamber means at least within a lower partial load range, means operable as a function of the load of the gas turbine installation for controlling the amount of non-preheated air so that at most approximately 15% of the rate of air flow of the gas turbine installation is admixed in non-preheated air by said controlling means.

Claim 15

An installation according to claim 9, characterized in that said controlling means control the preheated air such that, starting with the idling output of the gas turbine installation, a relatively small amount of non-preheated air is admixed by said controlling means, that said relatively small quantity is increased with an increasing output adjustment of the gas turbine installation to a maximum value whereby this maximum value is reached in a middle partial load range, and that with a further increase of the output adjustment of the gas turbine installation beyond the middle partial load range, the quantity of non-preheated admixed air is again decreased by said controlling means up to an admixture quantity of at least approximately zero.

Claim 16

An installation according to claim 10, characterized in that said point of approximately zero admixture is reached at a point below the output adjustment corresponding to a rated output of the gas turbine installation.

Claim 17

A gas turbine installation comprising compressor means for compressing air, heat-exchanger means for heating the compressed air by utilizing the exhaust gas heat of the gas turbine installation, combustion chamber means for combusting fuel with an excess of air under supply of compressed air constituting the primary air, means for thinning resulting gas of the combusted fuel by an admixture of compressed heated air constituting secondary air and cooling the same for producing gases for use in turbine means, and means including said turbine means for expanding the produced gases while producing a mechanical output, characterized in that a mixing chamber means is disposed outside of said combustion chamber means for intimately combining and mixing a more or less large quantity of substantially non-preheated air to the preheated primary air prior to the entry thereof into a combustion zone of the combustion chamber means at least within a lower partial load range, and in that means are provided for controlling the amount of non-preheated air in the gas turbine installation so that, starting with the idling output of the gas turbine installation, a relatively small amount of non-preheated air is admixed by said controlling means, that said relatively small quantity is increased with an increasing output adjustment of the gas turbine installation to a maximum value whereby this maximum value is reached in a middle partial load range, and that with a further increase of the output adjustment of the gas turbine installation beyond the middle partial load range, the quantity of non-preheated admixed air is again decreased by said controlling means up to an admixture quantity of at least approximately zero.

Claim 18

A gas turbine installation comprising compressor means for compressing air, heat-exchanger means for heating the compressed air by utilizing the exhaust gas heat of the gas turbine installation, combustion chamber means for combusting fuel with an excess of air under supply of compressed air constituting the primary air, means for thinning resulting gas of the combusted fuel by an admixture of compressed heated air constituting secondary air and cooling the same for producing gases for use in turbine means, and means including said turbine means for expanding the produced gases while producing a mechanical output, characterized in that a mixing chamber means is disposed outside of said combustion chamber means for intimately combining and mixing a more or less large quantity of substantially non-preheated air to the preheated primary air prior to the entry thereof into a combustion zone of the combustion chamber means at least within a lower partial load range, and in that means are provided for controlling the amount of non-preheated air in the gas turbine installation so that, starting with the idling output of the gas turbine installation, a relatively small amount of non-preheated air is admixed by said controlling means, that said relatively small quantity is increased with an increasing output adjustment of the gas turbine installation to a maximum value whereby this maximum value is reached in a middle partial load range, and that with a further increase of the output adjustment of the gas turbine installation beyond the middle partial load range, the quantity of non-preheated admixed air is again decreased by said controlling means up to an admixture quantity of at least approximately zero.

Claim 19

An installation according to claim 12, characterized in that said point of approximately zero admixture is reached at a point below the output adjustment corresponding to a rated output of the gas turbine installation.

Claim 20

A gas turbine installation which comprises a compressor means, at least one combustion chamber means having combustion chamber wall means and supplied with fuel, inlet aperture means for the supply of unheated primary air provided in the combustion chamber wall means within the area of a combustion zone arranged near the fuel supply and inlet aperture means for the supply of heated secondary air provided in the combustion chamber wall means within the area of a thinning zone arranged after the combustion zone, expansion means with at least one turbine wheel means connected downstream of the combustion chamber means and serving the drive of the compressor means and of a separate load of mechanical energy, heat-exchanger means traversed on the heat-absorbing side by the compressed air and acted upon by exhaust gases on the side giving off heat, said heat-exchanger means having outlet means for a heat-absorbing medium in communication with at least a portion of the inlet aperture means for the secondary air by way of at least one warm-air channel means, a feed line for the heat-absorbing medium of said heat-exchanger means in communication with at least a portion of the inlet aperture means for the primary air by way of a by-pass line, and control means for influencing the distribution of the flow to the by-pass line and the warm-air channel means, characterized in that a mixing chamber means is located outside of the combustion chamber means for intimately combining and mixing flow paths of the preheated and non-preheated air prior to entry in the combustion chamber means, at least one wall means is arranged between the mixing chamber means and the combustion zone of the combustion chamber means, and in that aperture means are provided in the at least one wall means for directing the flow of the combined and mixed preheated and non-preheated air from the mixing chamber means into the combustion chamber means.

Claim 21

A gas turbine installation which comprises a compressor means, at least one combustion chamber means having combustion chamber wall means and supplied with fuel, inlet aperture means for the supply of unheated primary air provided in the combustion chamber wall means within the area of a combustion zone arranged near the fuel supply and inlet aperture means for the supply of heated secondary air provided in the combustion chamber wall means within the area of a thinning zone arranged after the combustion zone, expansion means with at least one turbine wheel means connected downstream of the combustion chamber means and serving the drive of the compressor means and of a separate load of mechanical energy, heat-exchanger means traversed on the heat-absorbing side by the compressed air and acted upon by exhaust gases on the side giving off heat, said heat-exchanger means having outlet means for a heat-absorbing medium in communication with at least a portion of the inlet aperture means for the secondary air by way of at least one warm-air channel means, a feed line for the heat-absorbing medium of said heat-exchanger means in communication with at least a portion of the inlet aperture means for the primary air by way of a by-pass line, and control means for influencing the distribution of the flow to the by-pass line and the warm-air channel means, characterized in that a mixing chamber means is located outside of the combustion chamber means for intimately combining and mixing flow paths of the preheated and non-preheated air prior to entry in the combustion chamber means, at least one wall means is arranged between the mixing chamber means and the combustion zone of the combustion chamber means, and in that aperture means are provided in the at least one wall means for directing the flow of the combined and mixed preheated and non-preheated air from the mixing chamber means into the combustion chamber means.

Claim 22

A gas turbine installation according to claim 14, characterized in that the control means is operable in dependence on a load of the gas turbine installation.

Claim 23

A gas turbine installation according to claim 15, characterized in that discharge openings are provided for the flow paths of the preheated and non-preheated air at the mixing chamber means, said discharge openings being constructed so that there are two types of air flow into the mixing chamber means with each flow having at least one flow component of significant amount in substantially the same direction.

Claim 24

A gas turbine installation according to claim 15, characterized in that the discharge openings of the flow paths of the preheated and of the non-preheated air at the mixing chamber means are constructed so that the two types of air flow into the mixing chamber means at least approximately in the same direction.

Claim 25

A gas turbine installation according to claim 16, characterized in that the aperture means in the at least one wall means are discharge apertures constructed so that a flow deflection takes place between an entry of at least one of the non-preheated and preheated air and an outlet of the mixed air.

Claim 26

A gas turbine installation according to claim 16, characterized in that the aperture means in the at least one wall means are discharge apertures directed and constructed so that a flow deflection takes place between an inlet of the preheated air and an inlet of the non-preheated air and the discharge of the mixed air.

Claim 27

A gas turbine installation according to claim 18, with slot means for blowing air into the combustion chamber means, said slot means are so arranged and constructed that blown-in air flows along as cooling air in the form of an air veil flowing along an inner wall of the combustion chamber means, and flow channels for the cooling air branch off from flow channels of the compressed air, characterized in that a branching place of the cooling air is arranged upstream of a combining place of the flow paths for the preheated and non-preheated air, as viewed in the flow direction.

Claim 28

A gas turbine installation according to claim 20, characterized in that the control means for influencing the distribution of the air into the by-pass line and the warm air channel means includes one separate throttling means in each of the two flow paths.

Claim 29

A gas turbine installation which comprises a compressor means, at least one combustion chamber means having a combustion wall means and supplied with fuel, inlet aperture means for the supply of primary air provided in the combustion chamber wall means within the area of a combustion zone arranged near the fuel supply and inlet aperture means for the supply of secondary air provided in the combustion chamber wall means within the area of a thinning zone arranged after the combustion zone, expansion means with at least one turbine wheel means connected downstream of the combustion chamber means and serving the drive of the compressor means and of a separate load of mechanical energy, heat-exchanger means traversed on the heat-absorbing side by the compressed air and acted upon by exhaust gases on the side giving off heat, said heat-exchanger means having outlet means for a heat-absorbing medium in communication with at least a portion of the inlet aperture means for the secondary air by way of at least one warm air channel means, a feed line for the heat-absorbing medium of said heat-exchanger means in communication with at least a portion of the inlet aperture means for the primary air by way of a by-pass line means, and control means operable in dependence upon a load of the gas turbine installation influences the distribution of the flow to the by-pass line and the warm air channel means, characterized in that flow paths for a preheated and non-preheated air combine in a mixing chamber means located outside of the combustion zone, at least one wall means provided with aperture means is arranged between the mixing chamber means and the combustion zone, discharge openings are provided for the flow paths of the preheated and non-preheated air at the mixing chamber means, said discharge openings being constructed so that there are two types of air flow into the mixing chamber means with each flow having at least one flow component of significant amount in substantially the same direction, the aperture means in the at least one wall means are discharge apertures constructed so that a flow deflection takes place between an entry of at least one of the non-preheated and preheated air and an outlet of the mixed air, slot means are provided for blowing air into the combustion chamber means, said slot means are so arranged and constructed that blown-in air flows along as cooling air in the form of an air veil flowing along an inner wall of the combustion chamber means, and flow channels for the cooling air branch off from flow channels of the compressed air, a branching place of the cooling air is arranged upstream of a combining place of the flow paths for the preheated and non-preheated air, as viewed in the flow direction, the control means for influencing the distribution of the flow into the by-pass line means and the warm air channel means includes one separate throttling means in each of the two flow paths, both throttling means are constructed as rotary slide valves having movable parts, and in that means are provided for at least indirectly coupling the throttling means with one another.

Claim 30

A gas turbine installation which comprises a compressor means, at least one combustion chamber means having a combustion wall means and supplied with fuel, inlet aperture means for the supply of primary air provided in the combustion chamber wall means within the area of a combustion zone arranged near the fuel supply and inlet aperture means for the supply of secondary air provided in the combustion chamber wall means within the area of a thinning zone arranged after the combustion zone, expansion means with at least one turbine wheel means connected downstream of the combustion chamber means and serving the drive of the compressor means and of a separate load of mechanical energy, heat-exchanger means traversed on the heat-absorbing side by the compressed air and acted upon by exhaust gases on the side giving off heat, said heat-exchanger means having outlet means for a heat-absorbing medium in communication with at least a portion of the inlet aperture means for the secondary air by way of at least one warm air channel means, a feed line for the heat-absorbing medium of said heat-exchanger means in communication with at least a portion of the inlet aperture means for the primary air by way of a by-pass line means, and control means operable in dependence upon a load of the gas turbine installation influences the distribution of the flow to the by-pass line and the warm air channel means, characterized in that flow paths for a preheated and non-preheated air combine in a mixing chamber means located outside of the combustion zone, at least one wall means provided with aperture means is arranged between the mixing chamber means and the combustion zone, discharge openings are provided for the flow paths of the preheated and non-preheated air at the mixing chamber means, said discharge openings being constructed so that there are two types of air flow into the mixing chamber means with each flow having at least one flow component of significant amount in substantially the same direction, the aperture means in the at least one wall means are discharge apertures constructed so that a flow deflection takes place between an entry of at least one of the non-preheated and preheated air and an outlet of the mixed air, slot means are provided for blowing air into the combustion chamber means, said slot means are so arranged and constructed that blown-in air flows along as cooling air in the form of an air veil flowing along an inner wall of the combustion chamber means, and flow channels for the cooling air branch off from flow channels of the compressed air, a branching place of the cooling air is arranged upstream of a combining place of the flow paths for the preheated and non-preheated air, as viewed in the flow direction, the control means for influencing the distribution of the flow into the by-pass line means and the warm air channel means includes one separate throttling means in each of the two flow paths, both throttling means are constructed as rotary slide valves having movable parts, and in that means are provided for at least indirectly coupling the throttling means with one another.

Claim 31

A gas turbine installation according to claim 22, characterized in that the rotary slide valve means are arranged coaxially to each other.

Claim 32

A gas turbine installation according to claim 23, characterized in that the two flow paths within the area of the throttling means extend coaxially to one another.

Claim 33

A gas turbine installation according to claim 24, with at least one pair of rotary slide valve means, characterized in that the combustion chamber means are of circular construction and that the rotary slide valve pair surrounds concentrically the combustion chamber means.

Claim 34

A gas turbine installation according to claim 25, characterized in that the mixing chamber means is constructed of a hollow annular shape and is arranged concentrically to the combustion chamber means.

Claim 35

An installation according to claim 26, characterized in that the mixing chamber means is arranged at an end face of the combustion chamber means at which is arranged the fuel supply and which is traversed by the primary air radially inwardly.

Claim 36

A gas turbine installation according to claim 27, characterized in that means are provided for mutually coupling the two throttling means in such a manner that the two throttling means are moved simultaneously.

Claim 37

A gas turbine installation according to claim 27, characterized in that an adjusting drive means is provided for at least indirectly connecting the two throttling means said adjusting drive means adjusting the throttling means in accordance with an operating magnitude which changes unequivocally in dependence upon an adjusted output of the installation.

Claim 38

A gas turbine installation according to claim 28, characterized in that the throttling means include active elements, and in that means are provided for changing a mutual relative position of the active elements.

Claim 39

A gas turbine installation according to claim 28, characterized in that a mutual coupling means is provided for coupling the two throttling means to each other, said coupling means is so constructed that opening cross sections of the two throttling means change analogously in the same direction during actuation thereof.

Claim 40

A gas turbine installation according to claim 31, characterized in that the throttling means are so constructed that when traversing in the same direction through an entire movement range of an actuating element of the throttling means, the open cross section of both throttling means, starting with a respective small flow cross section at the beginning of the actuating path, assume a maximum value of the flow cross section in a middle area of the actuating path and toward the end of the actuating path, return again to a small flow cross section.

Claim 41

A gas turbine installation according to claim 32, characterized in that the small flow cross section of the throttling means for the non-preheated air reaches the value of about zero and that the small flow cross section of the throttling means for preheated air has a value of about 50% to about 85%.

Claim 42

A gas turbine installation according to claim 33, characterized in that the slight flow cross section of the throttling means for the preheated air has a value of about 2/3 of the maximum value.

Claim 43

A gas turbine installation according to claim 33, characterized in that a cross section/adjusting path-cycle of the throttling means for non-preheated air is slightly phase-displaced with respect to a cross section/adjusting path-cycle of the throttling means for preheated air in a direction toward small adjusting paths.

Claim 44

A gas turbine installation according to claim 14, characterized in that the aperture means in the at least one wall means are discharge apertures constructed so that a flow deflection takes place between an entry of at least one of the non-preheated and preheated air and an outlet of the mixed air.

Claim 45

A gas turbine installation according to claim 14, with slot means for blowing air into the combustion chamber means, said slot means are so arranged and constructed that blown-in air flows along as cooling air in the form of an air veil flowing along an inner wall of the combustion chamber means, and flow channels for the cooling air branch off from flow channels of the compressed air, characterized in that a branching place of the cooling air is arranged upstream of a combining place of the flow paths for the preheated and non-preheated air, as viewed in the flow direction.

Claim 46

A gas turbine installation according to claim 14, characterized in that the control means for influencing the distribution of the air into the by-pass line and the warm air channel means includes one separate throttling means in each of the two flow paths.

Claim 47

A gas turbine installation which comprises a compressor means, at least one combustion chamber means having a combustion wall means and supplied with fuel, inlet aperture means for the supply of primary air provided in the combustion chamber wall means within the area of a combustion zone arranged near the fuel supply and inlet aperture means for the supply of secondary air provided in the combustion chamber wall means within the area of a thinning zone arranged after the combustion zone, expansion means with at least one turbine wheel means connected downstream of the combustion chamber means and serving the drive of the compressor means and of a separate load of mechanical energy, heat-exchanger means traversed on the heat-absorbing side by the compressed air and acted upon by exhaust gases on the side giving off heat, said heat-exchanger means having outlet means for a heat-absorbing medium in communication with at least a portion of the inlet aperture means for the secondary air by way of at least one warm air channel means, a feed line for the heat-absorbing medium of said heat-exchanger means in communication with at least a portion of the inlet aperture means for the primary air by way of a by-pass line means, and control means operable in dependence upon a load of the gas turbine installation influences the distribution of the flow to the by-pass line and the warm air channel means, characterized in that flow paths for a preheated and non-preheated air combine in a mixing chamber means located outside of the combustion zone, at least one wall means provided with aperture means is arranged between the mixing chamber means and the combustion zone, discharge openings are provided for the flow paths of the preheated and non-preheated air at the mixing chamber means, said discharge openings being constructed so that there are two types of air flow into the mixing chamber means with each flow having at least one flow component of significant amount in substantially the same direction, the aperture means in the at least one wall means are discharge apertures constructed so that a flow deflection takes place between an entry of at least one of the non-preheated and preheated air and an outlet of the mixed air, slot means are provided for blowing air into the combustion chamber means, said slot means are so arranged and constructed that blown-in air flows along as cooling air in the form of an air veil flowing along an inner wall of the combustion chamber means, and flow channels for the cooling air branch off from flow channels of the compressed air, a branching place of the cooling air is arranged upstream of a combining place of the flow paths for the preheated and non-preheated air, as viewed in the flow direction, the control means for influencing the distribution of the flow into the by-pass line and the warm air channel means includes one separate throttling means in each of the two flow paths, both throttling means are constructed as rotary slide valves having movable parts, and in that means are provided for at least indirectly coupling the throttling means with one another.

Claim 48

A gas turbine installation which comprises a compressor means, at least one combustion chamber means having a combustion wall means and supplied with fuel, inlet aperture means for the supply of primary air provided in the combustion chamber wall means within the area of a combustion zone arranged near the fuel supply and inlet aperture means for the supply of secondary air provided in the combustion chamber wall means within the area of a thinning zone arranged after the combustion zone, expansion means with at least one turbine wheel means connected downstream of the combustion chamber means and serving the drive of the compressor means and of a separate load of mechanical energy, heat-exchanger means traversed on the heat-absorbing side by the compressed air and acted upon by exhaust gases on the side giving off heat, said heat-exchanger means having outlet means for a heat-absorbing medium in communication with at least a portion of the inlet aperture means for the secondary air by way of at least one warm air channel means, a feed line for the heat-absorbing medium of said heat-exchanger means in communication with at least a portion of the inlet aperture means for the primary air by way of a by-pass line means, and control means operable in dependence upon a load of the gas turbine installation influences the distribution of the flow to the by-pass line and the warm air channel means, characterized in that flow paths for a preheated and non-preheated air combine in a mixing chamber means located outside of the combustion zone, at least one wall means provided with aperture means is arranged between the mixing chamber means and the combustion zone, discharge openings are provided for the flow paths of the preheated and non-preheated air at the mixing chamber means, said discharge openings being constructed so that there are two types of air flow into the mixing chamber means with each flow having at least one flow component of significant amount in substantially the same direction, the aperture means in the at least one wall means are discharge apertures constructed so that a flow deflection takes place between an entry of at least one of the non-preheated and preheated air and an outlet of the mixed air, slot means are provided for blowing air into the combustion chamber means, said slot means are so arranged and constructed that blown-in air flows along as cooling air in the form of an air veil flowing along an inner wall of the combustion chamber means, and flow channels for the cooling air branch off from flow channels of the compressed air, a branching place of the cooling air is arranged upstream of a combining place of the flow paths for the preheated and non-preheated air, as viewed in the flow direction, the control means for influencing the distribution of the flow into the by-pass line and the warm air channel means includes one separate throttling means in each of the two flow paths, both throttling means are constructed as rotary slide valves having movable parts, and in that means are provided for at least indirectly coupling the throttling means with one another.

Claim 49

A gas turbine installation according to claim 39, characterized in that the rotary slide valve means are arranged coaxially to each other.

Claim 50

A gas turbine installation according to claim 39, characterized in that the two flow paths within the area of the throttling means extend coaxially to one another.

Claim 51

A gas turbine installation according to claim 39, with at least one pair of rotary slide valve means, characterized in that the combustion chamber means are of circular construction and that the rotary slide valve pair surrounds concentrically the combustion chamber means.

Claim 52

A gas turbine installation according to claim 42, characterized in that the mixing chamber means is constructed of a hollow annular shape and is arranged concentrically to the combustion chamber means.

Claim 53

A gas turbine installation according to claim 43, characterized in that the mixing chamber means is arranged at an end face of the combustion chamber means at which is arranged the fuel supply and which is traversed by the primary air radially inwardly.

Claim 54

A gas turbine installation according to claim 38, characterized in that means are provided for mutually coupling the two throttling means in such a manner that the two throttling means are moved simultaneously.

Claim 55

A gas turbine installation according to claim 45, characterized in that the throttling means includes active elements, and in that means are provided for changing a mutual relative position of the active elements.

Claim 56

A gas turbine installation according to claim 45, characterized in that a mutual coupling means is provided for coupling the two throttling means to each other, said coupling means is so constructed that opening cross sections of the two throttling means change analogously in the same direction during actuation thereof.

Claim 57

A gas turbine installation according to claim 38, characterized in that an adjusting drive means is provided for at least indirectly connecting the two throttling means said adjusting drive means adjusting the throttling means in accordance with an operating magnitude which changes unequivocally in dependence upon an adjusted output of the installation.

Claim 58

A gas turbine installation according to claim 38, characterized in that the throttling means are so constructed that when traversing in the same direction through an entire movement range of an actuating element of the throttling means, the open cross section of both throttling means, starting with a respective small flow cross section at the beginning of the actuating path, assume a maximum value of the flow cross section in the middle area of the actuating path and toward a end of the actuating path, return again to a small flow cross section.

Claim 59

A gas turbine installation according to claim 49, characterized in that the small flow cross section of the throttling means for the non-preheated air reaches the value of about zero and that the small flow cross section of the throttling means for preheated air has a value of about 50 to about 85%.

Claim 60

A gas turbine installation according to claim 50, characterized in that the slight flow cross section of the throttling means for the preheated air has a value of about 2/3 of the maximum value.

Claim 61

A gas turbine installation according to claim 49, characterized in that a cross section/adjusting path-cycle of the throttling means for non-preheated air is slightly phase-displaced with respect to a cross section/adjusting path-cycle of the throttling means for preheated air in a direction toward small adjusting paths.