High pressure gas cycle and power plant

Details High pressure gas cycle and power plant High pressure gas cycle and power plant

2001-08-24

2002-11-19

Freay, Charles G. (Department: 3746)

Power plants

Combustion products used as motive fluid

Plural combustion products generators in ring coaxial with...

C060S039770, C060S806000

Reexamination Certificate

active

06481197

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a high pressure gas cycle for use in an engine. The invention also relates to an electrical power generating plant.
2. Background of Related Art
The Otto cycle shown diagrammatically in
FIG. 1
[Prior Art], with pressure as the ordinate and volume as the abscissa, is a cycle that closely represents the explosion and compression stages of a gasoline automobile engine. In the Otto cycle, the air is drawn in at atmospheric pressure, shown at 1, then compressed isentropically to a high pressure with fuel mixed in the air, shown at 2. The fuel air mixture explodes at a theoretically constant volume to form a combustion gas having an increased pressure, shown at 3. The combustion gas expands isentropically back to the original inlet volume, shown at 4, where the combustion gas is then discharged. As shown in
FIG. 1
, the combustion gas discharges at a pressure above atmosphere, shown at 4, and then the pressure drops to atmosphere as it exhausts from the engine, not shown. The energy that could be available by expanding from exhaust pressure to atmospheric pressure, represented by the difference between 4 and 1 shown in
FIG. 1
, is wasted.
The theoretical efficiency of the Otto Cycle is defined by the relationship 1−(V
2
/V
11
)
(K-1)
where V
1
/V
2
is the ratio of the volume before compression to the volume after compression, commonly called the compression ratio. K=ratio of specific heat at constant pressure to specific heat at constant volume=C
p
/C
v
.
Another cycle commonly used in automobile engines is the Diesel cycle. The pressure vs. volume diagram for a Diesel cycle is shown in
FIG. 2
[Prior Art]. In a Diesel cycle, air is drawn in at atmospheric pressure, shown at 5, and then the air is compressed, shown at 6. The fuel is injected after the air is compressed and burns at somewhere near constant pressure to form a combustion gas, shown at 7. The combustion gas expands isentropically back to the original inlet volume, shown at 8, where the combustion gas is then discharged. As shown in
FIG. 2
, the combustion gas discharges at a pressure above atmosphere, shown at 8, and then the pressure drops to atmosphere as it exhausts from the engine, not shown. The energy that could be available by expanding from exhaust pressure to atmospheric pressure, represented by the difference between 8 and 5 shown in
FIG. 5
, is wasted.
The advantage of the Diesel cycle compared to the Otto cycle is that the compression ratio can be made much higher than that for the Otto Cycle, because the fuel is not mixed in the air, and therefore the rise during compression in temperature will not ignite the fuel until after the fuel is injected at the high pressure. In general, this increase in compression ratio for the Diesel Cycle enables the Diesel cycle to achieve higher efficiencies than are possible with the Otto Cycle.
The compression ratio for the Otto Cycle is usually limited to about 10 to 1, corresponding to a pressure ratio of about 25 to 1. The reason for this is that at higher ratios the fuel air mixture becomes so hot that the explosion occurs before the mixture is fully compressed. This preignition or detonation actually decreases the power output.
In the Diesel engine the fuel injection occurs after compression, and only air is being compressed during the compression cycle. Therefore, typical compression ratios are 23 to 1, corresponding to pressure ratios of 82 to 1. This is the basic reason why the Diesel cycle is more efficient than the Otto cycle.
A further cycle is the Brayton or Joule cycle, as shown in
FIG. 3
[Prior Art]. In the Brayton cycle, air is drawn into a compressor at atmospheric pressure, shown at 9, and then compressed to a high pressure, shown at 10. Fuel is injected into the compressed air in the combustor, where it burns at nearly a constant pressure (except for friction losses in the combustor) to form a combustion gas, shown at 11. The combustion gas expands isentropically back to atmospheric pressure, shown at 12. In this case, the expansion to atmospheric pressure is advantageous, and the theoretical efficiency is like the Otto cycle above in that the theoretical efficiency is equal to 1−(V
2
/V
1
)
(K-1)
where V
1
/V
2
is again the volume ratio of specific volume at atmospheric pressure divided by the specific volume at the pressure at which burning starts. The Brayton cycle is the cycle commonly used in gas turbines, and is limited in efficiency by the fact that the temperature of the gas entering the turbine is nearly the same as the combustion temperature. Therefore the combustion temperatures possible in a gas turbine system are usually limited to approximately 2300 to 2600° F. However, the Brayton cycle does have an advantage over the Otto cycle in that complete expansion back to essentially atmosphere is achieved.
A disadvantage of the Brayton cycle is that as pressure ratios or compression ratios are increased the temperature leaving the compressor and entering the combustor becomes higher. Therefore, less fuel energy can be added because of the temperature limit of the turbine. For this reason, although efficiency can be increased by increasing the pressure ratio in a gas turbine cycle, the output gradually decreases as higher pressure ratios are used. Therefore, it is common practice to limit the pressure ratio in industrial gas turbines to about 10 to 20 atmospheres.
Table 1 shows typical theoretical performance calculations for the Brayton cycle, based on air standard data and constant mass flow through the cycle.
TABLE 1
A
B
C
D
E
F
G
H
I
1
P2/P1
32
32
32
32
32
32
32
32
2
T1
520
520
520
520
520
520
520
520
3
T3
2810
2810
2810
2810
2810
2810
2810
2810
4
P1/J
2.7201
2.7201
2.7201
2.7201
2.7201
2.7201
2.7201
2.7201
5
V1
13.089
13.089
13.089
13.089
13.089
13.089
13.089
13.089
6
EFF COMP
1
0.9
0.85
0.9
0.9
0.9
0.9
0.9
7
COOL FACT
1
1
1
0.9
0.8
0.7
0.6
0.5
8
N/(N-1) CO
3.463
3.1167
2.94355
3.463
3.895876
4.462429
5.1945
6.2334
9
(N-1)/N CO
0.288767
0.320852
0.339726
0.288767
0.256682
0.224597
0.192511
0.160428
10
N COMP
1.406009
1.472434
1.514522
1.406009
1.345319
1.289651
1.238407
1.19108
11
EFF TURB
1
0.9
0.85
0.9
0.9
0.9
0.9
0.9
12
N/(N-1) TU
3.463
3.847778
4.074118
3.847778
3.847778
3.847778
3.847778
3.847778
13
(N-1) N TU
0.288767
0.25989
0.245452
0.25989
0.25989
0.25989
0.25989
0.25989
14
N TURB
1.406009
1.351151
1.325297
1.351151
1.351151
1.351151
1.351151
1.351151
15
W IN
212.1196
251.5701
276.9102
235.6885
221.0261
207.4814
194.9616
183.3819
16
V1/V2
11.76285
10.52493
9.858518
11.76285
13.14636
14.6926
16.4207
18.35205
17
T2/T1
2.72043
3.0404
3.245924
2.72043
2.434134
2.177968
1.94876
1.743674
18
T2
1414.624
1581.008
1687.88
1414.624
1265.75
1132.543
1013.355
906.7106
19
HEAT IN
330.8437
291.3941
266.0545
330.8437
366.1417
397.725
425.9845
451.2699
20
V3
2.210342
2.210342
2.210342
2.210342
2.210342
2.210342
2.210342
2.210342
21
W EXPAN
421.3532
395.5742
381.6844
395.5742
395.5742
395.5742
395.5742
395.5742
22
NET WORK
209.2335
144.0041
104.7742
159.8857
174.5481
188.0928
200.6127
212.1923
23
EFF
0.632424
0.49419
0.393807
0.483267
0.476723
0.472922
0.470939
0.470212
A
J
K
L
M
N
O
P
1
P2/P1
32
32
32
32
32
32
32
2
T1
520
520
520
520
520
520
520
3
T3
2810
2810
2810
2810
2810
2810
2810
4
P1/J
2.7201
2.7201
2.7201
2.7201
2.7201
2.7201
2.7201
5
V1
13.089
13.089
13.089
13.089
13.089
13.089
13.089
6
EFF COMP
0.9
0.9
0.9
0.9
0.9
0.9
0.9
7
COOL FACT
0.4
0.3
0.2
0.1
0.05
0.04
0.03
8
N/(N-1) CO
7.79175
10.389
15.5835
31.167
62.334
77.9175
103.89
9
(N-1)/N CO
0.128341
0.096256
0.06417
0.032085
0.016043
0.012834
0.009626
10
N COMP
1.147237
1.106508
1.068571
1.033149
1.016304
1.013001
1.009719
11
EFF TURB
0.9
0.9
0.9
0.9
0.9
0.9
0.9
12
N/(N-1) TU
3.847778
3.847778
3.847778
3.847778
3.847778
3.847778
3.847778
13
(N-1) N TU
0.25989
0.25989
0.25989
0.25989
0.25989
0.25989
0.25989
14
N TURB
1.351151
1.351151
1.351151
1.351151
1.351151
1.351151
1.351151
15
W IN
172.6651
162.7406
153.5437
145.0155
140.9852
140.197
139.414

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