Thermodynamic Prime Mover With Heat Exchanger

The present invention relates to a thermodynamic prime mover with a heat exchanger. More particularly, the invention relates to a gas turbine with a heat exchanger, which turbine is especially suitable for motor vehicles.

Prior art gas turbines comprise heat exchangers for supplying a portion of the heat contained in the exhaust gas, to the relatively cold compressed air in order to save fuel. It is this preheating of the compressed combustion air which makes possible an economical operation of a gas turbine, especially one that is employed as the prime mover in a motor vehicle.

However, the temperature of the air entering the combustion chamber of such gas turbines using heat exchange means in rather high, for example in the range from 700.degree. C and even higher. Where no heat exchange means are used in gas turbines the temperature of the air entering the combustion chamber is customarily in the range of 200.degree. C to 400.degree. C. It has been found that the preheated air, that is air having a temperature of 700.degree. C or more, does not have a sufficient cooling ability to adequately cool the flame pipe, which is conventionally made of sheet metal. As a result, the useful life of the flame pipe becomes rather short in gas turbines using heat exchange means whereby an economical operation again becomes questionable.

Attempts have been made heretofore to solve the above problem by providing complicated cooling slot configurations for the flame pipe. However, tests have shown that a satisfactory improvement in the cooling efficiency cannot be attained by means of such cooling slot configurations.

In view of the foregoing, it is the aim of the invention to achieve the following objects, singly or in combination:

TO PROVIDE AN EFFICIENT COOLING OF THE FLAME PIPE OF A HEAT EXCHANGER GAS TURBINE WHEREBY THE DISADVANTAGES OF THE PRIOR ART ARE TO BE AVOIDED, MORE SPECIFICALLY, TO AVOID A COSTLY FLAME PIPE CONSTRUCTION WHILE SIMULTANEOUSLY ASSURING THAT THE FLAME PIPE WILL BE ABLE TO WITHSTAND HIGH TEMPERATURE LOADS EVEN DURING CONTINUOUS OPERATION;

TO PROVIDE COOLING MEANS FOR THE FLAME PIPE WHICH COOL THE LATTER EXTERNALLY AS WOULD NORMALLY BE POSSIBLE WHERE THE TURBINE DOES NOT USE A HEAT EXCHANGER;

TO USE A PROPORTION OF THE COMPRESSED AIR FOR THE COOLING OF THE FLAME PIPE WHILE AVOIDING THE LOSS OF THAT PROPORTION OF COMPRESSED AIR FOR ITS MAIN PURPOSE, NAMELY THE SUSTAINING OF THE COMBUSTION;

TO GUIDE A PROPORTION OF THE COMPRESSED AIR AS CLOSE AS POSSIBLE TO AND AROUND AT LEAST THE UPSTREAM END OF THE FLAME PIPE, AND

TO GUIDE A PROPORTION OF THE COMPRESSED AIR CLOSE TO AND AROUND THE FLAME PIPE SUBSTANTIALLY ALONG ITS ENTIRE LENGTH.

The above objects have been achieved in a gas turbine with a heat exchanger, a flame pipe in a combustion chamber and a compressor by branching off a small proportion, for example 3 to 10%, of the compressed combustion air, upstream of the heat exchanger by means of a separate or second conduit which directs the branchedoff air directly into the combustion chamber and onto the flame pipe so that the branched-off air flows in a cooling manner at least over and around the upstream end of the flame pipe without substantially participating in the combustion at this point.

The foregoing teaching makes it now possible to cool the flame pipe externally or from the outside substantially as efficiently as is possible in a turbine without heat exchanger. In addition, there is the advantage that the branched-off compressed air is not lost because, although this air does not participate in the combustion at the point of cooling, it is used for the combustion in the turbine by re-entering this air into the hot gas stream upstream of the turbine inlet port means.

In order that invention may be clearly understood, it will now be described, by way of example, with reference to the accompanying drawings, wherein:

FIG. 1 illustrates schematically a gas turbine prime mover with a heat exchanger and with cooling of the flame pipe by means of blowing cool compressor air onto the upstream end of the flame pipe;

FIG. 2 illustrates another embodiment wherein the cooling air is guided about and into contact with the upstream end of the flame pipe; and

FIG. 3 shows a further embodiment wherein cooling air guide means extend substantially along the entire length of the flame pipe.

FIG. 1 illustrates schematically a prime mover according to the invention including a compressor 1, a turbine 2, a combustion chamber 3, and heat exchanger means 6. First conduit means 7 connect the compressor outlet port 9 with the inlet of the heat exchanger 6. The first conduit means also include a connection 8 operatively arranged between the heat exchanger 6 and an air inlet port 15 of the combustion chamber 3. The combustion chamber exit 14 is connected to the turbine 2 in a conventional manner. Similarly, the compressor 1 is also connected conventionally to the turbine 2. Further, the turbine exhaust 12 is connected by conventional means 10 to the heat exchanger 6 which has an exhaust port 11.

According to the invention there are provided second conduit means 13 branching off from the first conduit member 7 upstream of the heat exchanger 6. The second conduit means 13 connect the outlet port 9 of the compressor 1 directly to the combustion chamber 3 at a fresh air inlet port 16 located so that fresh air from the first or fresh air conduit 7 is directed onto the upstream end of the flame pipe 17 located coaxially in the combustion chamber 3. The quantity of not yet preheated fresh air directed onto the upstream end of the flame pipe 17 amounts to about 3 to 10% of the entire quantity of air supplied by the compressor 1. It has been found that this relatively small quantity of fresh, not yet preheated air efficiently cools the flame pipe to prolong the useful life of the latter.

According to the invention, a plurality of apertures 18 are provided in the flame pipe 17 at the upstream end thereof where the branched-off fresh cooling air hits the flame pipe 17. Thus, a small proportion of the branched-off not yet preheated fresh air may enter into a border zone of the combustion chamber 3, whereas most of the branched-off fresh, not yet preheated air flows along the outer surface of the flame pipe 17 to intensively cool the flame pipe. The dashed line 19 indicates the outer envelope of the cooling air flow 20 which itself is shown by the dash-dotted line. This envelope 20 of cooling air 19 extends all around the flame pipe 17 almost to its downstream end 17' where holes 26 permit the entry of the cooling air into the flame pipe 17. This flow is assured because the inlet ports 21 near the upstream end of the flame pipe 17 are provided with pipe extensions 22 which admit the secondary air 27 from the heat exchanger 6 into the flame pipe 17. A portion of the branched-off air will also enter through the pipe extensions 22 but due to the radially directed pipe extensions 22 most of this branched-off air will flow along the outer surface of the flame pipe 17 to cool it effectively. Thus it will be appreciated that there is substantially no loss of the branched-off air since this air is returned into the hot gas stream prior to entry into the turbine 2. FIG. 2 illustrates a further embodiment of the invention wherein the flame pipe 28 in the combustion chamber 4 is provided with guide means 23 for the branched-off cooling air coming from the second conduit means 13 into the inlet port 16 of the combustion chamber 4. The guide means 23 are formed as a sheet metal casing in the shape of a bonnet which extends from the inlet port 16 to surround the upstream end of the flame pipe 28. The downstream end of the guide means 23 is open to permit the flow of the cooling air 20 as shown by the dash-dotted line in FIG. 2. However, some of the branched-off cooling air also enters into the flame pipe 28 through openings 18 in the upstream end of the flame pipe 28. These openings 18 extend substantially radially inwardly. A further small proportion of cooling air also enters the flame pipe 28 through the port holes 21 but most of the cooling air will flow along the outer surface of the flame pipe 28 and enter it through apertures 29 as shown, where it is combined with the secondary air from the heat exchanger and mixed with the hot combustion gas. The guide bonnet 23 has the advantage that the cooling air must flow in close contact with the surface of the flame pipe 28. In addition, it facilitates the cooling of the inner and outer surface of the flame pipe 28 whereby an efficient cooling is made possible with even less branched-off air whereby the efficiency of the heat exchanger 6 is improved.

Incidentally, the guide bonnet 23 for the cooling air is spaced from the outer surface of the upstream end of the flame pipe 28 just sufficiently to provide a flow passage for the cooling air. The guide bonnet 23 extends to a point just downstream of the inlet ports 21 for the combustion air and the ends of the bonnet 23 are open to permit the flow 20 of cooling air as shown in FIG. 2. The upstream end of the flame pipe 28 is also provided with small apertures 18 for the cooling air to improve the cooling effect.

FIG. 3 illustrates a further embodiment of the invention in which a sheet metal housing 24 envelopes the flame pipe 30 in the combustion chamber 5 substantially along the entire length of the flame pipe 30. The upstream end of the housing 24 has substantially the same shape as the bonnet 23, however, the housing 24 extends almost to the exit end of the flame pipe 30. In addition, the housing 24 is closed at its downstream end. Radially extending bores 25 substantially adjacent to the downstream end of the flame pipe 30, interconnect the space between the guide housing 24 and the inside of the flame pipe 30 whereby substantially all of the branched-off cooling air is introduced into the mixing chamber of the flame pipe 30.

The embodiment of FIG. 3 has the advantage that even the downstream portions of the flame pipe 30 are cooled more intensively than in the other embodiments. This feature is especially important because these downstream portions are heated to a high degree particularly at full power output of the prime mover. Thus, the intensive cooling accomplished according to the invention presents damage to the downstream end of the flame pipe even where a continuous operation is involved.

Although the invention has been described with reference to specific example embodiments, it is to be understood, that it is intended to cover all modifications and equivalents within the scope of the appended claims.