In conventional power plants, a hydrocarbon fuel, such as natural gas or distillate oil, is burned in air to produce a hot gas. In a gas turbine power plant, the hot gas, which is typically pressurized to about 1000-1500 kPa (150-200 psia) , is then expanded in a turbine to produce shaft power. In a steam turbine power plant, the hot gas transfers heat to feed water so as to generate steam, which is then expanded in a steam turbine to produce shaft power. In either case, the turbine drives a load, such as an electrical generator or compressor, so as to deliver useful shaft power.

Unfortunately, the combustion of hydrocarbon fuel in air results in the formation of oxides of nitrogen ("NOx"), considered an atmospheric pollutant. During combustion, NOx is generated primarily from three sources - - (i) the conversion of atmospheric nitrogen in the combustion air to NOx, typically referred to as "thermal NOx" (ii) the conversion of organically bound nitrogen compounds, such as HN ₃ (ammonia) and HCN, in the fuel to NOx, and (iii) the reaction between atmospheric nitrogen and hydrocarbon fragments formed from the breakdown of

hydrocarbons in the fuel, typically referred to as "prompt NOx" .

Burning hydrogen fuel in pure oxygen would eliminate Nox entirely since there would be no hydrocarbons to create prompt and fuel bound NOx and no atmospheric nitrogen. Combustors for rocket engines have traditionally operated by combusting liquid hydrogen in liquid oxygen. However, unlike rocket engines, power plant turbines must operate for extended periods of time without deterioration and must make as efficient use as possible of the energy available in the fuel.

It is therefore desirable to provide an efficient method of burning hydrogen fuel in oxygen in a turbine power plant, thereby producing shaft power without generating NOx.

SUMMARY OF THE INVENTION Accordingly, it is the general object of the current invention to provide an efficient method of burning hydrogen fuel in oxygen in a turbine power plant, thereby producing shaft power without generating NOx.

Briefly, this object, as well as other objects of the current invention, is accomplished in a method of generating rotating shaft power, comprising the steps of: (i) combusting a flow of pressurized hydrogen in a flow of pressurized oxygen in a combustor, thereby consuming at least a portion of the flow of pressurized oxygen and producing a flow of hot pressurized steam, (ii) expanding the flow of hot pressurized steam so as to produce a flow of at least partially expanded steam, at least a portion of the expansion being accomplished in a turbine, thereby producing shaft power, and (iii) transferring heat from the flow of at least partially expanded steam to at least one of the flows of pressurized hydrogen and pressurized oxygen prior to the combustion thereof. In a preferred embodiment of the invention, the flows of hydrogen and oxygen are pressurized above their critical pressures prior to the combustion thereof, and the

step of transferring heat from the flow of expanded steam comprises transferring heat to both the flows of pressurized hydrogen and oxygen.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic diagram of a first embodiment of the turbine power plant according to the current invention, in which all of the oxygen for combustion of the hydrogen fuel is supplied to the first combustor, after the oxygen has been passed through one or more cooling flow paths.

Figure 2 is a schematic diagram of a second embodiment of the turbine power plant according to the current invention, in which only the oxygen necessary for stoichiometric combustion of the hydrogen fuel is supplied to each combustor.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, wherein like numerals indicate like elements, there is shown in Figure 1 a schematic diagram of a first embodiment of the hydrogen fueled power plant of the current invention. The primary components of the power plant are an oxygen source 1, a hydrogen source 2, a recuperator 6, primary, secondary and tertiary combustora θ, 10, and 12, respectively, and high, intermediate and low pressure power turbines 14, 16, and ₁ 8, respectively, each of which drives a load ⁽ not shown ⁾ such as an electrical generator. The turbines are preferably of the conventional type and comprised of a plurality of alternating rows of stationary vanes and rotating blades. The stationary vanes are affixed to a cylinder and the rotating blades are affixed to a centrally disposed rotating shaft. The combustors may be of the conventional type used in gas turbines or may be of special design.

Preferably, the oxygen 30 from the oxygen source 1 is at a temperature of approximately 143°K (258°R ⁾ or colder so that it is a cryogenic liquid. Preferably, a _b oost compressor 3 raises the pressure of the oxygen 30

above its supercritical pressure, which for oxygen in approximately 4970 kPa (720 psia) and, most preferably to about 34,500 kPa (5000 psia) . The pressurized oxygen 3 ₂ then flows through the recuperator 6, where it is heated, preferably to about 540°C (1000°F) . Since the oxygen 32 is preferably pressurized above its critical pressure, no change in state accompanies this heating so that the heated oxygen 34 discharged from the recuperator remains in essentially the liquid state. However, if sub-critical pressure oxygen, including gaseous oxygen, is supplied to the recuperator 6, the heated oxygen 34 will be in the gaseous state.

The recuperator has heat transfer surfaces formed therein that allow heat to flow from low pressure steam 76, discussed further below, to the pressurized oxygen 32 without contact between the oxygen and the steam. The recuperator 6 may be of the shell and tube type, with the pressurized oxygen 32 flowing through finned tubes and the low pressure steam 76 flowing over the tubes. From the recuperator 6, the heated pressurized oxygen 34 is divided into three streams 38, 40 and 42. Oxygen stream 38 flows through a cooling flow path 24 formed in the high pressure turbine 14, where it is used to cool the turbine components so that they are not excessively heated by the hot pressurized steam/oxygen mixture 71 that flows through the high pressure turbine 14. The turbine components through which the cooling flow path 24 extends may include the rotating blades and stationary vanes. Using principles well known in the art, the blades and vanes have cooling fluid passages formed within them that allow heat transferred to the blades and vanes from the hot steam/oxygen mixture 71 to be subsequently transferred to the oxygen 38 flowing through the cooling path 24, thereby heating the oxygen 38 and cooling the blades and vanes. The further heated oxygen 39, which has now been preferably heated to approximately 650°C (1200°F) , is then discharged from the cooling flow path 24 and exits

the turbine. Similarly, oxygen streams 40 and 42 flow through cooling flow paths 26 and 28 formed in the intermediate and low pressure turbines 16 and 18, respectively. Preferably, the cooling flow paths 24, 26 and ₂₈ are of the closed loop type so that all of the oxygen 38, 40 and 42 that enters the cooling flow paths is discharged from the turbines 14, 16 and 18. Alternatively, if desired to aid in effective cooling, a certain amount of the oxygen 38, 40 and 42 can be bled from the cooling flow paths 24, 26, and 28 into the steam/oxygen mixtures 71-76 flowing through the turbines.

Although in the preferred embodiment, the pressurized oxygen 34 is used as the cooling fluid for the turbine components, the turbine could also be cooled by the pressurized hydrogen 54, either exclusively, or in combination with the oxygen by employing separate oxygen and hydrogen cooling flow paths through selected turbine components. Alternatively, such cooling may be accomplished by recirculating steam from the recuperator, as discussed hereinafter.

Returning to Figure 1, the streams of further heated pressurized oxygen 39, 41 and 43 discharged from the turbines 14-18 are combined into a flow of oxygen 44, which is then directed to the primary combustor 8.

Preferably, the hydrogen 50 from the hydrogen source 1 is at a temperature of 17°K (30°R) or less so that it is also a cryogenic liquid. Preferably, a boost compressor 4 raises the pressure of the hydrogen 50 above the supercritical pressure, which for hydrogen in approximately 1280 kPa (185 psia) and, most preferably to about 34,500 kPa (5000 psia) . The pressurized hydrogen 52 then flows through the recuperator 6 in which it is heated, preferably to about 540 ^β C (1000°F) , in a manner similar to the pressurized oxygen 32. Since the hydrogen 32 is preferably pressurized above its critical pressure, no change in state accompanies this heating so that the heated

hydrogen 54 discharged from the recuperator remains in essentially the liquid state. However, if sub-critical pressure hydrogen, including gaseous hydrogen, is supplied to the recuperator 6, the heated hydrogen 54 will be in the gaseous state.

As in the case of the oxygen 32, the recuperator has heat transfer surfaces formed therein that allow heat to flow from the low pressure steam 76 to the pressurized hydrogen 52 without contact between the hydrogen and the steam.

From the recuperator 6, the heated pressurized hydrogen 54 is divided into three streams 56, 58 and 60, which are directed to the primary, secondary and tertiary combustors 8, 10, and 12, respectively. As discussed below, the pressure of the steam/oxygen mixtures 73-76 flowing through the intermediate and low pressure turbines 16 and 18, respectively, is less than that flowing through the high pressure turbine 14. Therefore, in the preferred embodiment of the invention, the hydrogen streams 58 and 60 are partially expanded in small power turbines 20 and 22, respectively, prior to their introduction into the secondary and tertiary combustors 10 and 12. This allows a portion of the energy expended to compress the hydrogen 52 to be recovered as useful work. In the embodiment of the invention shown in

Figure 1, all of the oxygen 44 necessary for combustion of the three hydrogen steams 56, 58 and 60 in each of the three combustors 8, 10 and 12 is introduced into the primary combustor 8. Consequently, in the primary combustor 8, all of the first portion 56 of the hydrogen fuel is combusted with a portion of the oxygen 44 so that the combustion in the primary combustor 8 may be characterized as oxygen rich/fuel lean. Such combustion prevents the temperature from becoming excessively high, such as might occur if the hydrogen were combusted stoichiometrically.

The products of the combustion of the hydrogen and oxygen in the primary combustor 8 are pure water in the form of supercritical steam. Consequently, the primary combustor 8 discharges a hot pressurized gas 71 comprised of a mixture of supercritical steam and oxygen.

Preferably, sufficient hydrogen 56 is combusted in the primary combustor 8 to heat the high pressure steam/oxygen mixture 71 to approximately 1650°C (3000°F) .

From the primary combustor 8, the high pressure steam/oxygen mixture 71 is partially expanded to an intermediate pressure in the high pressure turbine 14 so as to produce useful shaft power. In so doing, the temperature of the steam/oxygen mixture 72 is reduced, preferably to about 810°C (1500°F) . The intermediate pressure steam/oxygen mixture 72 discharged from the high pressure turbine 14 is then reheated in the secondary combustor 10, in which the second portion 59 of the hydrogen fuel is combusted with a portion of the oxygen in the steam/oxygen mixture 72. Since not all of the remaining oxygen is consumed in the second combustor 10, the combustion may again be characterized as oxygen rich/fuel lean. The combustion in the secondary combustor 10 preferably raising the temperature of the intermediate pressure steam/oxygen mixture back to approximately 1650°C (3000 ^β F) .

The reheated intermediate steam/oxygen mixture 73 from the secondary combustor 10 is then further expanded to a low pressure in the intermediate pressure turbine 16, thereby producing additional shaft power. In so doing, its temperature is again reduced, preferably to about 810°C (1500°F) . The low pressure steam/oxygen mixture 74 discharged from the intermediate pressure turbine 16 is then reheated in the tertiary combustor 12, in which the third portion 57 of the hydrogen fuel is combusted with the remaining portion of the oxygen in the steam/oxygen mixture 74, preferably raising the temperature of the low pressure steam/oxygen mixture back to approximately 1650°C (3000°F) .

Since the oxygen is preferably depleted by the combustion in the tertiary combustor 12, this combustion may be characterized as stoichiometric and the fluid discharged _b y the tertiary combustor is essentially pure steam. The reheated low pressure steam 75 from the tertiary combustor 12 is then further expanded in the low pressure turbine 18, where its temperature is again reduced, preferably to about 810°C (1500°F) . Thus, the low pressure turbine 18 produces yet more shaft power. Preferably, the pressure of the expanded steam 76 discharged from the low pressure turbine 18 is at sub- atmospheric pressure, for example, about 7 kPa (1 psia) .

Preferably, the total pressure drop experienced by the fluid from the primary combustor 8 to the recuperator 6 is approximately evenly divided among the high, intermediate and low pressure turbines 14, 16 and 18, respectively, so that the expansion ratio in each turbine is the cube root of 3.

Although in the preferred embodiment, the combustion in the tertiary combustor 12 consumes all of the remaining oxygen, it may be desirable in some circumstance to employ lean combustion in the tertiary combustor 12 as well, so that the fluid discharged from the tertiary combustor will contain some excess oxygen. Moreover, although the embodiment shown in Figure 1 employs three turbines 24, 16 and 18, a greater or lesser number of turbines could also be utilized in order to optimize thermodynamic efficiency and cost.

The steam 76 discharged from low pressure turbine 18 is directed to the recuperator 6, where its temperature is further reduced by transferring heat to the incoming flows of cryogenic oxygen and hydrogen 32 and 52, respectively. By transferring heat from the steam exhausting from the low pressure turbine 16 to the oxygen 32 and hydrogen 52 fuel, optimum use is made of the energy input into the cycle, thereby maximizing thermal efficiency. The temperature of the steam 77 discharged

from the recuperator 6 will be a function of the temperature and mass flow rate of the incoming steam 76 as well as the inlet and outlet temperatures and flow rates of the oxygen and hydrogen. Preferably, the steam 77 will be sufficiently cooled in the recuperator 6 so that it is condensed. The condensate 77 is then discharged for use as process water or discharged to the environment. Alternately, the recuperator 6 may only partially cool the steam 76, in which case the partially cooled expanded steam discharged from the recuperator will then be directed to a condenser (not shown) .

Thus, according to the current invention, rotating shaft power is efficiently produced without the generation of NOx. Indeed, the only emission from the power plant is pure water, which can be safely discharged to the environment after, at most, a slight cooling.

Figure 2 shows a second embodiment of the current invention. In this embodiment, oxygen 132 and hydrogen 152 are supplied by oxygen and hydrogen sources 101 and 102, respectively. Preferably, the oxygen 132 and hydrogen 152 are pressurized above their critical pressures but are not cryogenic -- e.g., ambient temperature and approximately 20,500 kPa (3000 psia). The oxygen 132 and hydrogen 152 are heated in a recuperator 106 by the transfer of heat from the low pressure steam 176, as before. In this embodiment, the oxygen 134 and hydrogen 154 are preferably heated to approximately 260-540°C (500-1000°F) .

From the recuperator 6, the heated oxygen 134 and heated hydrogen 154 are each divided into three streams. The first portion 144 of the oxygen and the first portion of the hydrogen 160 are combusted in a primary combustor 108. However, in this embodiment, the combustion is carried out essentially stoichiometrically so that essentially all of the oxygen 144 is consumed in combusting all of the hydrogen 160. As a result, the primary combustor 108 discharges a flow of high pressure supercritical essentially pure steam 171 -- i.e., steam at

a pressure greater than the supercritical pressure of steam, which is approximately 21,840 kPa (3168 psia) .

Despite the stoichiometric nature of the combustion, the temperature is prevented from becoming excessive by the introduction of flows of supercritical steam 181 and 188 into the primary combustor 108, as discussed below, that moderate the combustion temperature. Consequently, the high pressure supercritical steam 17 ₁ discharged from the primary combustor 108 is comprised of the steam formed by the combustion of the oxygen 144 and hydrogen 160, as well as the injection of steam 181 and 188. Preferably, the supercritical steam 171 discharged by the primary combustor 108 is at a pressure and temperature of approximately 20,500 kPa (3000 psia) and 1650°C (3000°F) , respectively.

From the primary combustor 108, the high pressure supercritical steam 171 is partially expanded to an intermediate pressure in the high pressure turbine 114 so as to produce useful shaft power. In so doing, the temperature of the steam is reduced, preferably to about 810°C (1500°F) . The intermediate pressure steam 172 discharged from the high pressure turbine 114 is then reheated in the secondary combustor 110, in which the second portion 159 of the hydrogen fuel is combusted with the second portion 136 of the oxygen. Again, the combustion in the secondary combustor 110 is preferably carried out under essentially stoichiometric conditions so that essentially pure intermediate pressure steam 173 is produced. The combustion in the secondary combustor 110 preferably raises the temperature of the intermediate pressure steam 173 back to approximately 1650°C (3000°F) .

The reheated intermediate pressure steam 173 from the secondary combustor 110 is then further expanded to a low pressure in the intermediate pressure turbine 116, thereby producing additional shaft power. In so doing, its temperature is again reduced, preferably to about 810°C (1500°F) . The low pressure steam 174 discharged from the

intermediate pressure turbine 116 is then reheated in the tertiary combustor 112, in which the third portion 157 of the hydrogen fuel is combusted with the third portion 135 of the oxygen. Again, the combustion in the tertiary combustor 112 is preferably carried out under essentially stoichiometric conditions so that essentially pure low pressure steam 175 is produced. The combustion in the tertiary combustor 112 preferably raises the temperature of the low pressure steam 175 back to approximately 1650°C (3000°F) . The reheated low pressure steam 175 from the tertiary combustor 112 is then further expanded in the low pressure turbine 18, where its temperature is again reduced, preferably to about 810°C (1500°F) . Thus, the low pressure turbine 118 produces yet more shaft power. Preferably, the pressure of the expanded steam 176 discharged from the low pressure turbine 118 is at sub- atmospheric pressure as before, with the total pressure drop experienced by the fluid being approximately evenly divided among the high, intermediate and low pressure turbines 114, 116 and 118, respectively. Moreover, although the embodiment shown in Figure 2 employs three turbines 14, 16 and 18, a greater or lesser number of turbines could also be utilized, as previously discussed. The steam 176 discharged from the low pressure turbine 118 is directed to the recuperator 106, where its temperature is further reduced by transferring heat to the incoming flows of oxygen 132 and hydrogen 152, respectively, as before, but also to pressurized water 179, as discussed below. The cooled steam 177 is then directed to a condenser 198. The condensate from the condenser 198 is divided into two steams 178 and 199. The stream 199 is discharged for other uses or to the environment .

The condensate stream 178 is pressurized by a pump 200 to a pressure greater than its critical pressure, and preferably to approximately 20,500 kPa (3000 psia) . Although the pressurized water 179 could be injected

directly into the primary combustor 108 in order to control the combustion temperature, the pressurized water ₁₇₉ preferably first flows through the recuperator ₁ 0 ₆ where its temperature is raised by the transfer of heat from the expanded steam 176. Within the recuperator 106, the water 179 is divided into two streams 180 and 181.

The first stream 180 is discharged from the recuperator 6 as a flow of supercritical steam after having flowed through only a portion of the heat transfer apparatus. Preferably its temperature is raised to approximately 260°C (500°F) . The steam 180 discharged from the recuperator 106 is then divided into three streams ₁ 82, 184 and 186, each of which flows through one of the cooling flow paths 124, 126 and 128 formed in the components of the high, intermediate and low pressure turbines 114, 116 and 118, as previously discussed. In each of the cooling flow paths, heat is transferred to the steam, preferably raising its temperature to approximately 540°C (1000°F) . The streams of heated supercritical steam 183, 185, and 187 discharged from the turbines is then introduced into the primary combustor 108 in order to control the combustion temperature, as previously discussed. Although Figure 2 shows a closed loop turbine steam cooling arrangement, all or a portion of the steam directed to the cooling flow paths 124, 126 and 128 could be discharged directly into the steam flowing through its respective turbine.

The second stream of supercritical steam 181 from the recuperator 106 is discharged after having flowed through the entirety of the heat transfer apparatus so that its temperature is raised beyond that of the steam 180, and preferably to approximately the same temperature as the steam flows 183, 185 and 187 discharged from the turbine cooling flow paths 124, 126 and 128 -- i.e., to approximately 540°C (1000 ^β F) . From the recuperator 106, the second flow of heated supercritical steam is directed directly to the primary combustor 108.

Although in the embodiment shown in Figure 2, the recuperator 106 is located downstream of the low pressure turbine 118, the recuperator could also be advantageously located upstream of the low pressure turbine. This would reduce the pressure differential between the flows of pressurized oxygen 132, hydrogen 152 and water 179 flowing through the recuperator 106 on the one hand and the steam 176 flowing through the recuperator on the other hand, thereby reducing the stresses imposed on the heat transfer components. In such an embodiment, the low pressure turbine 118 may be of the condensing type, and the low pressure combustor may be eliminated.

As the foregoing indicates, the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.