DE2708940A1 - METHOD OF OPERATING A GAS TURBINE AND IMPROVED GAS TURBINE COMBUSTION CHAMBER - Google Patents

Description

BEIL, WOLFF & BEIL

: iT ΛΜ MAIN 80

ADC ^! .o ^f . 6230 FR.

2708940 01. HSrs 1S77

Our no. 20 910

F / La

Exxon Research and Engineering Company Linden, N.Y., V.St.A.

Method of operating a gas turbine and improved gas turbine combustion chamber.

709837/0723

The need for gas turbine combustion processes that comply with air pollution regulations and ensuring optimal use of the fuel is of such importance that in this field a great deal Experimental work was done. It is known that a controlled mixing of excess air in the second Stage of a 2-stage combustion system is the key to limiting the formation of nitrogen oxides NO.

In a gas turbine engine, the incoming air is continuously compressed, mixed with fuel and then burned in a combustion device. Amounts of air which are in considerable excess over the stoichiometrically required amount are compressed and used to cool the liner of the combustion device and to dilute the gases emerging from the combustion device in order to avoid damage to the turbine blades and nozzle. As a rule, main sections of the combustion device are operated near stoichiometric conditions, which leads to gas temperatures of up to approximately 2,200 ^° C. in the combustion device. Secondary air is added to the combustion device further down, which increases the ratio of air to fuel and lowers the gas temperatures so that the gases leaving the combustion device are of the order of magnitude of 1,100 ^° C. The fuel injection pressure fluctuates; with full power it is typically 42 kg / cm, while under idle conditions it is between 1 and 7 kg / cm ² .

It is known that the formation of nitrogen oxides contributes to NO high temperatures is thermodynamically favored. Kinetic studies show that the rate of formation of NO is a has a high activation energy (about 115 kcal / mol), so that the

709837/0723

Major NO formation occurs in the high temperature primary combustion zone of conventional turbines got to. Since the reaction leading to the formation of NO is so strongly temperature-dependent, falling combustion peak temperatures are an effective means of lowering it of NO emissions from a combustion device. One of the easiest ways to lower temperatures and thus To achieve low NO emissions, the combustion is carried out under very lean conditions (i.e. with a high excess of air). Here you came across the Problems with ignition and combustion of very lean fuel-air mixtures; they were used for many control systems motor vehicle emissions and, in industrial incineration systems, from solvent off-gas. In both cases Catalysts are used to aid and complete the combustion process. On a similar one Catalysts can be used in gas turbines to produce efficient combustion in lean systems.

The present invention relates to methods of operating Gas turbine combustion equipment in which the formation and the leakage of pollutants such as NO »can be reduced to a minimum. In particular, the Invention to the use of a series of 2 or more catalysts to cause fuel oxidation at temperatures below flame temperatures, thereby minimizing the formation of NO.

In another embodiment of the invention, a staged catalytic combustion apparatus is operated, in the fuel in fuel-rich conditions in one

709837/0723

non-catalytic zone is burned, followed by a catalytic oxidation of the partially burned fuel in a 2nd zone, in which a catalyst is used _{to complete the fuel oxidation and reduce the emission of ΝΟ χ and other pollutants.}

The invention is also directed to the use of a new embodiment for the primary combustion zone, in which fuel is partially burned with amounts of air which are below the stoichiometric amounts, and the partially burned effluent from the primary zone is then mixed into the secondary airflow, without continuing the high temperature combustion. This has the effect that both the hot partially burned effluent from the primary zone is quenched and sufficient mixing of the partially burned fuel with secondary air is achieved so that complete combustion is maintained under conditions which do not _{allow the formation of Ν0 χ} favor. The operation of gas turbine combustion devices in accordance with the embodiments described above leads, in addition to the reduction in NO, to the following advantages: improved fuel efficiency and reduced emissions of carbon monoxide and unburned hydrocarbons.

In accordance with the present invention, gas turbine combustors are operated using two or more catalysts in series to oxidize the fuel, wherein High temperature gas flows for the turbine are available, and the temperatures of the sustained gas flow are lower than the flame temperatures, so that relatively low NO concentrations occur. Such a catalyst system had the ability to produce hydrocarbons in the area to oxidize from 177 to about 1,315 ° C. The specific temperature range is related to durability and the

709837/0723

Activity properties of the catalysts and also corresponds to the operating modes of gas turbines with variable running speed.

Figure 1 is a schematic representation of a catalytic converter see hybrid combustion process and illustrates the different combustion zones;

Figure 2 is a graph representing the ratio of air to fuel and for different, shown in Figure 1, where as (1), (2), (3), ⁽¹ O and (5) designated zones, the adiabatic flame temperatures, which are plotted against a NO _x emission index, which is defined as kg NO (as NO ₂ ) per 1,000 kg of fuel;

FIG. 3 is a schematic representation of ¹ L catalyst systems which are useful in the process of the invention;

Figure 4 is a schematic diagram showing how that catalytic E belittles; and

catalytic hybrid system according to the invention N0 _x emissions

Figure 5 graphically illustrates the comparison of a conventional gas turbine combustor with one catalytic hybrid system and at the same time shows the importance of excess air concentrations.

As has been previously stated, present invention relates to a process to be operated at the gas turbine combustors using 2 or more catalysts in series, which latter ¹ oxidize the fuel and supply high-temperature gas flows to the turbine,

09837/0723

the maintained temperatures of the gas stream being lower than the flame temperatures, so that nitrogen oxides NO are only formed in low concentrations. This catalytic process uses 2 or more catalysts in series. These catalysts comprise a platinum catalyst for firing at temperatures of 177 to 65O ⁰ C, a copper-nickel catalyst joins that this helps in that the fuel-air mixtures are brought to about 87O ⁰ C, after which the oxidation of the fuel to temperatures above 870 ⁰ is up to 1,315 ° C, a nichrome mesh catalyst. Such a catalyst system has the ability to oxidize hydrocarbons in the range of 177 to about 1315C. The specific temperature range is related to the durability and activity properties of the catalysts and also corresponds to the operating modes of gas turbines with variable running speeds. For example, the various operating modes of an aircraft gas turbine engine change from low temperatures at idle to high temperatures at full power in order to reach peak temperatures during take-off. In one of the operating modes, a premixed and heated stream of a lean air-fuel mixture is passed over a noble metal catalyst in order to initiate the combustion of the fuel at the lower temperature (so-called "lightoff", ie starting point of the combustion reaction).

The noble metal catalyst is present in a thin zone the non-precious metal catalyst which the combustion complete, arranged. This dual catalyst system benefits from the higher reaction rates the inlet temperatures in the combustion device, which are favored by the precious metals such as platinum, does not suffer from the high temperatures

70983770723

occurring deactivation problems, which normally are found in precious metal catalysts. To prevent these problems, the volume of the precious metal catalyst is kept sufficiently small to avoid » that it is exposed to temperatures above 81.6 ° C. The use of 3 catalysts in series is that preferred embodiment, in order not to have those imposed on the catalyst material by its physical properties Exceeding limits. These used in series Catalysts were described above; they include metals from groups IB, UB, HIB, IVB, VB, VIB, VIIB and VIIIB of the periodic table can be selected.

In another embodiment of the present invention, employs a staged catalytic combustion device which offers certain advantages over catalytic oxidation of fuel-lean mixtures. At this Embodiment, the burner is operated under fuel-rich conditions, with the effluent mixed with air, and the oxidation is catalytically completed. Accordingly, the partially burned mixture from the primary zone, which was burned non-catalytically, passed through a secondary zone after the partially burned effluent was mixed into the air stream until a desired final equivalency ratio of about 0.3 was obtained. Of the unburned effluent from the primary zone is passed over an oxidation catalyst, such as one made of nickel-copper, Nickel oxide on ceramics, rare earth oxides, or nichrome screens, this catalyst preventing fuel oxidation at the desired turbine inlet temperature of about 1095 ° C completed. This embodiment can but can also be operated by mixing the partially burned stream with air over the catalyst in order to prevent

709837/0723

that the temperature rises excessively. Such an alternative is also within the scope of the invention.

Another embodiment for carrying out the present Invention consists in the application of a new training

primary combustion zone, with the chamber in the verse device

combustion / is operated under fuel-rich conditions with an air volume of 50 to 70 % of the stoichioraetrically required amount. The fuel-rich, high temperature stream from this chamber is mixed with make-up air in the incinerator to the desired final equivalence ratio to complete the combustion. A catalyst is used to complete the combustion of the partially oxidized fuel, if necessary, and such a catalyst is a narrower bed of non-noble metal catalyst since its purpose is to accelerate the completion of the final 50% or less of the oxidation. The main feature of this embodiment is the method of mixing the hot, partially burned effluent from the primary zone into the secondary air flow without continued combustion. The mechanical design of the jacket of the primary zone is critical to proper operation of the mixed catalytic combustion apparatus and such a design is described below with reference to the drawing.

The solid catalysts used in the embodiment of the catalytic combustion device according to the invention can have various shapes and compositions; they can be of the kind used to oxidize Fuels in the presence of molecular oxygen is used or is known. Preferably im includes generally the initial catalyst (under initial catalyst is understood here that catalyst with which the

709837/0723

Fuel comes into contact first) precious metals or mixtures of precious metals as sieves or on ceramic Substrates. The intermediate catalyst bed comprises substances such as transition metals, mixtures or alloys as sieves or on ceramic substrates and rare earth oxides on ceramic substrates. The 3rd catalyst used in series according to the preferred embodiment includes substances which generally as transition metals or alloys in the form of sieves or on ceramic substrates as well as oxides of Have rare earths described on ceramics. The latter are due to their resilience to a Degradation of their physical properties selected at the high temperatures of the last stage.

As a rule, the weight ratios of air to fuel in all catalytic processes are in the range of 500 to 30, preferably 150 to 30. The temperature for operating the catalytic process is in the range of 65 to 1.5 ^ 0, preferably 120 to 1.205, in particular 177 to l.O93 ° C. The operation of the catalytic embodiment suitable space velocities are generally in the range from 50,000 to 50,000,000, in particular from 500,000 to 5.OOO.OOO volume / volume / hour.

When operating the embodiment with graded catalytic Combustion apparatus can generally use the catalyst used in the second zone of the two-zone system Materials exist which are called transition metals, mixtures or alloys of the same are to be designated; the catalyst is in the form of sieves or such materials ceramic substrates; Rare earths on ceramic substrates can also be used. The one in the embodiment air-to-fuel ratios used with the staged catalytic combustion device and the

709837/0723

Applied temperatures can generally be described as being in the range of those used in conventional stationary and mobile gas turbines, including aircraft gas turbines.

The space velocities are not critical and can range from 50,000 to 50,000,000, preferably from 500,000 to 5,000,000 volumes / volumes / hour.

In the 3rd embodiment, the new primary zone combustion chamber and a catalyst is used in the secondary zone. The catalyst is usually one of the types that have been described for catalytic combustion at maximum temperatures.

The materials that make up the primary zone combustion chamber include ceramics or high temperature alloys such as Inconel and Hastelloy alloys or other materials suitable for construction. Those in the mixed catalytic combustion process The operating temperatures to be used are usually in the range of the operating conditions for conventional ones Gas turbines, and it is important to have air to fuel ratios in the range from 7 to 15 »preferably 10 to 1 * 1, apply. The space velocities used in carrying out this process are not critical and lie generally in the range of 50,000 to 50,000,000, preferably 500,000 to 5,000,000 volume / volume / hour.

Operation of the gas turbine combustion apparatus in any of the preferred embodiments previously described results in the combustion of fuel to power the Turbine, while at the same time the NO concentrations below about 10 ppm, preferably below about 5 ppm, in particular

709837/0723

especially below about lppm.

The present invention and its embodiments can be more easily understood with reference to FIGS. The basis of the present invention can be explained with reference to FIG. 2, where the circled numbers relate to FIG. 1 and the hybrid combustion system shown there. When primary zone combustion occurs at about 70 % of the stoichiometrically required air, the equilibrium NO emission index (EI _NQ ) is 2.2 kg per 1000 kg of fuel, while the adiabatic flame temperature is 2.120 ° C. As a result, a reasonably high temperature has been reached in zone 1, with the index E is small. The dilution air occurs on the outside of the

Primary zone container at about 5 ¹ IO ⁰ C and is called Zone 2

gas

designated. The hot, partially burned mixture is so diluted in zone 3 with the secondary air flow that a Passing through the stoichiometric combustion zone (0 = 1.0) is avoided. The mechanical design of the primary zone enclosure is critical to proper operation of the incinerator. The primary zone container can be made of high temperature alloys such as Hastelloy X or of ceramic exist. It should have small openings or chimneys for rapid injection of the primary zone gas into the air stream and also create a local turbulence to mix the 2 streams together quickly. It was found, that no flame propagation occurs if the quenching diameter, i.e. the hole size, is kept below 3 * 05 mm, or if the speed the hot gases leaving zone 1 are of the order of 30 m / sec. amounts to. The sheathing of the primary zone can, however can also be made of a porous material such as Rigimesh, which is effective by the external airflow is cooled, at the same time a flow of the primary gas

709837/0723

to the outside is made possible. (The commercial product "Rigimesh" is a rigid metal sieve which enables such "cooling" and prevents the flame from "flashing back".) The mixture obtained in zone Ί then flows through the catalyst bed. Otherwise, homogeneous oxidation occurs to a limited extent, with the desired inlet temperature for the turbine being reached. The exiting stream has to Zone 5 at an equivalence ratio of about 0.3 and about 93O ⁰ C at the specified pressure and at the specified preheat temperature. In the case of automotive gas turbine combustion, the preheat temperature is much higher; as a result, the stream exiting the incinerator approaches temperatures of 1095 ° C. The process of NO formation is kinetically limited and as a result the actual equilibrium NO emissions should be

Jw

index EI ™ will have a value much lower than the equilibrium predicted value of 15 kg per 1,000 kg of fuel. The effect of the "prompt NO" is higher in the case of a rich, ie fuel-rich, primary combustion and can reach 10% of the equilibrium value, ie 0.22 kg per 1,000 kg of fuel. This value represents prompt NO

Jv

one expected from the type of combustion proposed here Value (approx. 3 ppm).

The invention will now be explained in more detail by means of examples. Example 1

In this example, the performance of the various catalyst systems described herein and illustrated in Figure 3 are: tested in the operation of gas turbines.

The test results are summarized in Table I; they show a comparison of the catalyst systems according to the invention with a system with a single catalyst,

709837/0723

which was tested by the US Air Force (see Table I). It should be noted that the system with an iron single Catalyst was ineffective in maintaining the starting point of the burn at temperatures as low as it is to investigate the catalyst systems according to the invention were applied. The single catalyst system would likely produce good results in one operation run gas turbines under full power; however, it is ineffective to operate at lower force and consequently unsuitable for gas turbines. The system could, however, be used as a 2nd or 3rd catalyst in the systems described above be used.

Example 2

In this example, the inventive concept of a hybrid combustion was tested according to the invention. The test procedure used an experimental setup where some of the air was premixed with fuel in a commercial burner and the rest of the air was mixed in independently of the burner. The variables examined included the percentage of stoichiometric air in the burner zone (primary zone) and various types of physical barriers between the primary zone and the dilution air. The total percentage of stoichiometric air was kept constant at 400 % . The results of these tests are shown in Table II.

The first experimental group was run as a control, with no physical barrier between the primary zone and the dilution air was present. The test results show that with fuel-rich operation of the primary zone

709837/0723

(67 % of the stoichiometrically required air) an NO concentration occurred which was higher than that which was obtained with stoichiometric combustion.

A second test group was carried out using an open pipe to separate the primary zone from the evaporation air. The results show that in the case of a hybrid-type operating mode, the NO concentration measured was 30% lower than that of a stoichiometric or "conventional" operating mode.

A hybrid burner similar to that shown in FIG. 1 was used in a third test group. The burner was made of Hastelloy X and was perforated with small holes. When this burner was operated in a hybrid manner, a 40 % reduction in NO concentration was measured compared to stoichiometric combustion.

This concept has been illustrated on a larger technical scale in a tubular (cannular) incinerator of 3> O8 cm using an open ended can (can) made of perforated Hastelloy X. The combustion air was split into primary air for fuel-rich combustion and secondary air for cooling the hybrid can, with the stoichiometry of the fuel-rich gas mixture also being changed to the lean side before the catalyst was applied. The results of one of these tests are shown in Table III. It should be noted that a combustion efficiency which is better than 99 % was achieved by operating with the hybrid pre-burner. The center line temperature leading into the catalyst bed was 1.153 ° K, which is considerably above the catalyst temperature, with the combustion reaction beginning the light-of-temperature).

709837/0723

The remaining trace amounts of CO and unburned light hydrocarbons were slightly oxidized over the catalyst, with a combustion efficiency of the order of 99 * 9 % being achieved '. The amount of NO was 2.2 g / kg fuel or 1.98 g / 10 ⁶ kcal (0.11 lb./10* Btu); it was thus below the maximum limits of the current environmental protection regulations.

709837/0723

A. B.
201 " a catalytic C.
201 C. combustion USAP ⁶ <0.16 <0.11 B.
? "201 ■" - ■ cO, l <0, l "377 <0.22 Table I. 6.2 1.0 <O, 23 « 1.3 2.0 <O, 22 900 Experimental evaluation 550 700 5.0 750 900 900 50 . ^. ... _ '. . A.
Temperature at start
burn point (° C) 201 127 316 700 288 288 50 1066 0 at this point <0.21 113 927 CO 1.2 Unburned coals
hydrogen 500 Exit temperature ( ⁰ C) 332

282'201 V

co space velocity
■ - * (at standard temp.
^ and pressure) ² 261000 523000 261000 523000 261000 523000 82OOOO 820000 820000

- »0 for leaving

£ Peak temperature 0.50 0.50 0.60 0.60 0.60 0.60 0.11

CO 0.6 68 3, O ³ 3.0 1.3 ⁴ 50 15

Unburned coal, ·.

Hydrogen 310 310 100 ^ lOO about 0.1 800 0.35

Outlet temperature ( ⁰ C) 1201 1201 1201 1093 1260 927 1201 1260 1232

Space velocity

(at standard temp.

and pressure) ² 261000 523000 262000 523000 261000 523000 820000 820000 820000 ^

The NOx emissions were always less than 1.5 ppm or 0.22 kg N0 _5/1000 kg of fuel. O

O r \ OO

Standard temperature and pressure of OC and 1 atmosphere, respectively; Units: volume / volume / hour. CD

³ Estimated, actual data at 0 = 0.19 are iCO = 20 kg / 1000 kg fuel, unburned ^ hydrocarbons = 250 kg (as CH ₁₁ ) 1000 kg fuel, 2nd outlet temperature = 1093 ° C

Estimated actual data at 0 = 0.55 are: CO = 25 kg / 1000 kg fuel, unburned hydrocarbons = 10 kg (as CHi,) / 1000 kg fuel, 2nd outlet temperature = 1093 ° C

Catalysts A-D are described in FIG. ÜS-Air Force.

Table II Try a hybrid system

Basis; Propane fuel no preheating atmospheric pressure

the
% / stoichiometrically required air too Training the
Can kg NO / 1000 kg
fuel Primary zone total too no 1.3 100 400 no 2.0 67 400 open end 2.4 100 400 open end 1.6 67 400 Hybrid burner 1.7 100 Hybrid burner 1.0 67

709837/0723

Table III

Experimental results relating to the open-ended hybrid catalytic combustion device

Combustion device pressure (atm.) 3 »3

Preheating temperature of the primary and secondary air ( ⁰ K) 400 primary equivalence ratio 1.5

Total equivalence ratio 0.3 Reference speed (m / s) ⁽¹⁾ 24.4 JP-4 flow rate (g / sec) 2.718 Primary air flow rate (g / s) 26.66

Secondary air flow rate (g / s) 106.61 Primary injector speed (m / s) 65.6

Secondary air speed around the pre-burner (m / s) 70 Secondary air injection speed

at the combustion outlet (m / s) X2) 19.5

Temperature profile at catalyst bed inlet ( ⁰ K)

Thermocouple (C) 924 at the catalyst bed inlet CO ₂ 5 14, ) Ν0 _χ (ppm) XW ⁺ Jppm) Thermocouple (D) 1083 CO (ppm) 5 4th 32 50 Thermocouple (E) 1153 395 4, 6th 4th 33 70 Thermocouple (F) 1143 345 2 14, 8th 26th 120 Concentration profile 350 1. 6th 29 48 365 Exam (C) Exam (D) Exam (E) Exam (F)

(1) Calculated for an air preheating of 400 ° K in a catalyst chamber with a diameter of 5.08 cm.

(2) No heat input with the exception of preheating

400 ⁰ K _.;

709837/0723

27089A0

(3) That is, the flow rate of the commercially available jet fuel " ¹ JP-I" to the incinerator.

'= Hydrocarbons.

For: Exxon Research and

Engineering Company Linden, N.J., V.St.A.

Dr HjXhi.Beil

Lawyer

709837/0723

Blank page

Claims (5)

Patent claims: Process for operating a gas turbine, characterized in that a propellant is brought into contact with air in a proportion of propellant to air of 0.001 to 0.03 in the presence of a primary catalyst bed which, as a catalyst, contains elements of groups IB, IIB, IHB, IVB, VB , VIB, VIIB or VIIIB as mixtures or alloys on sieves or ceramic substrates, in order to partially burn the fuel to an extent of less than 70% of the complete oxidation, the partially burned primary exit stream passes over 1 or more secondary catalyst beds, which act as catalysts Elements of groups IB, HB, IHB, IVB, VB, VIB, VIIB or VIIIB of the periodic table contain as mixtures or alloys on sieves or ceramic substrates in order to completely oxidize the partially burned part of the fuel, with the formation of KO on a concentration is reduced below about 10 ppm, this oxidation at a temperature of approx a 65 to 15 ¹ IO ⁰ C carries out, and that the gases emerging from these catalytic oxidations are passed through a gas turbine in order to make them rotate. 2. The method according to claim 1 ,, characterized in that a primary catalyst bed is used which is a Platinum, copper-nickel or a nichrome screen includes. 3. The method according to claim 1, characterized in that the fuel is brought into contact with air in the presence of 3 catalysts, namely with a platinum catalyst at a temperature of 117 to 649 ° C, a copper-nickel catalyst at a Temperature of up to 871 ⁰ C and a nichrome mesh catalyst at a temperature above 871 ⁰ C and up to 1316 ° C. Ϋ09837 / 0723 4. A method for operating a gas turbine, characterized in that one under fuel-rich conditions Brings fuel and air into contact in the non-catalytic primary part of a gas turbine and, after mixing with an air stream, passes the exiting partially burned gas stream to the desired final equivalence ratio of about 0.3 over an oxidation catalyst made of nickel-copper and nickel oxide , Ceramic .. Rare earth oxide or composed of a nichrome sieve to complete the fuel oxidation at a temperature up to 1538 ° C. 5. Improved gas turbine combustion chamber for the continuous partial oxidation of fuel for propulsion the gas turbine, characterized by a casing the primary zone, which has a sufficient number of openings through which the primary zone gases quickly be blown into a secondary air stream without continued combustion, the mixture from the from the The gas flow exiting the primary zone and the secondary air flow is further oxidized to completion over one or more non-noble metal catalysts, while the formation of NO is kept at a concentration below about 5 ppm. 709837/0723