ES2360589T3 - IMPROVED PROCESS OF FUEL SCALE CONTRIBUTION FOR LOW NOx OPERATIONS. - Google Patents

Abstract

A method for diluting a fuel to reduce NOx uses a fuel dilution device, which includes: a first conduit having an inlet and an outlet, the first conduit adapted to transmit a stream of a fuel entering the inlet and exiting the outlet at a first thermodynamic state and a first fuel index; and a second conduit having an intake and an outtake, the second conduit adapted to transmit a stream of a fluid entering the intake and exiting the outtake at a second/different thermodynamic state and a second fuel index different from the first fuel index by at least about 0.1, whereby a potential for mixing exists between the two streams exiting the outlet and the outtake, and at least some of the fuel mixes with at least some of the fluid near the outlet and the outtake, thereby generating a diluted fuel stream having an intermediate fuel index. <IMAGE>

Description

Background of the invention

The present invention relates to processes and systems of stepped fuel input to reduce nitrogen oxide (NOx) emissions, and in particular to such processes and systems that use fuel dilution tips in low Nox burners.

One of the challenges facing the chemical process industry (CPI) is the combustion of residual fuels for economic reasons and that at the same time meet the requirements for low NOx and CO emissions. Residual fuels contain a mixture of higher C / H gases that burn with very bright flames due to carbon oxidation and also produce soot or carbon particles depending on the combustion process. The typical composition of the refinery fuel contains varying amounts of inert fuels and gases (for example, C1, C2, C3 Cn, olefins, hydrogen, nitrogen, CO2, water vapor). If carbon or soot particles form on the fuel tips, the soot structure generally grows under favorable conditions of pressure and temperature existing near the tip outlet. This could result in blockage of fuel injection, deflection of the fuel jet, and overheating of the tips and parts of the furnace, such as process tubes and refractory walls, and the potential shutdown of the operation of the burners and the oven. The shutdown of a furnace could lead to significant financial burdens, including the responsibility that arises from the interruption of subsequent processes.

Dirty refinery fuels consisting of higher carbon and containing gases such as acetylene, ethane, propane, butane and olefins (for example, ethylene and propylene) generally produce soot particles if the fuel tips are subjected to:

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 Inadequate mixing in the oven (depending on the number of jets, jet geometry, injection angles and injection speeds are not optimal) (generally classified as a burner design problem);

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 Lack of combustion or oxidant air available near the fuel jets (generally classified as a burner flow configuration problem);

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Inadequate cooling of the fuel tips (regular exposure to furnace radiation) (generally classified as a problem of burner design and fuel tip configuration);

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 Interruption of fuel flows (reliability of fuel equipment located upwards) (generally classified as a process problem);

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 Lower combustion operation (lower fuel flow rates due to lowering of the process) (generally classified as a process problem); or

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 Fluctuation of the composition of the refinery fuel in terms of carbon-containing species (generally classified as a problem of process requirements).

The design of the burner or the tips significantly affects the overheating of the tips, soot production, sealing of the tips, and frequent maintenance resulting from the burner equipment. These problems are complicated by changing process conditions, such as low end of the process drop and / or interruption of fuel flows, which affect the required cooling required at the fuel tips. Changing process conditions and changes in fuel composition are common in the operation of the refinery.

Another challenge that the ICC faces is the requirement of low NOx emissions to meet emission standards. There are several areas in the United States where NOx standards (according to the Pure Air Act of 1990) require that emissions from process heaters, boilers, gas turbines, and other stationary combustion equipment be less than 10 ppm. of NOx. The most common solution or BACT (best available control technology) in the ICC is to use a SCR (selective catalytic reactor) for post-cleaning flue gas to reduce the NOx content in the exhaust gas stream (converting NOx to N2) using ammonia injection into a large catalytic reactor. This process requires a lot of capital and requires significant amounts of ammonia, hot air and electricity for the operation of the ID fan.

Most refineries would like to avoid installing SCRs and instead use low Nox burners to meet their NOx requirements. However, low NOx burners have not consistently produced less than 10 ppm NOx in various process heating applications, such as methane steam reformers (SMR), crude heaters, ethylene crackers, or boilers. For this reason, the use of low Nox burners has not been certified by regulatory agencies such as the BACT. In other words, SCR is currently the only commercially viable solution to meet strict NOx levels in ozone compliance regions where ground level ozone concentration exceeds legal limits.

Typically, operators at the ICC use clean natural gas or an optimal mixture of natural gas and dirty refinery fuels to reduce the burden of maintenance problems. However, due to the shortage of natural gas and the high cost of fuels, it is not always possible for process industries to use clean natural gas for combustion. Refiners that can burn residual fuels typically have higher productivity and a relatively favorable competitive status compared to other refineries that underuse the potential of residual fuels.

With respect to NOx reduction, common NOx control methods include the use of low Nox burners equipped with higher levels of staggered fuel input and air / fuel dilution with flue gas recirculation (FGR). By injecting non-reactive or inert chemical species into the fuel / oxidant mixture, the average flame temperature is reduced and, therefore, NOx emissions are reduced. However, these methods require additional pipe and energy costs associated with the transport of combustion gases. In addition, there is an energy charge due to the required heating of the gases from room temperature to the process temperature. In addition, the field data published in the literature does not indicate that these methods achieve a yield of less than 10 ppm of NOx.

Several devices and methods have been developed that use phased fuel input with the aim of reducing NOx emissions. Several of them are explained below.

US Patent Application No. 2003/0148236 (Joshi et al.) Describes an ultra-low NOx burner that uses a stepped fuel nozzle. The burner has eight staggered fuel lances located around the main body of the burner. The central part of the burner is used to supply 100% of the combustion air and a very small amount of fuel (-10%) is injected for the overall stability of the flame. The rest of the fuel (- 90%) is injected using multiple lances of stepped fuel input. The staggered fuel lances have special fuel nozzle tips with two circular holes. As shown in Figures 1A-1C, these lances have axial and radial divergence angles for delayed mixing with combustion air and furnace entrainment due to a relatively high jet velocity (152 to 305 m / s ( 500 to 1,000 feet / second) or a fuel supply pressure of 34,500 to 103,000 N / m2 (5 to 15 psig) depending on the combustion rate).

US Patent No. 6,383,462 (Lang) describes a method and an apparatus that has a mixing chamber outside the "burner and oven" for mixing combustion gases of the furnace with the combustible gas, as shown in Figure 2. A divergent convergent venturi mixer is used to further dilute the combustible gas with additional flow promotion gas. The resulting mixture (fuel diluted with combustion gases) is subsequently sent to the burner where the mixture is combined with combustion air and burns in the oven. Depending on the level of dilution of the flue gases, a reduction of NOx emissions from 26 ppm to 14 ppm can be obtained. This apparatus and method do not reduce NOx emissions below 10 ppm and the results are not comparable to those typically achieved with SCR technology.

US Patent No. 6,481,209 (Johnson et al.) Describes a stepped fuel delivery system suitable for gas turbine engines. Efficient combustion is achieved with air with lower NOx and CO emissions by dividing the fuel injection into two stages: 1) injectors installed in eddy mixers, and 2) injectors installed in the trapped whirlwind region of the combustor. However, this injection scheme is not suitable for large ovens where trapped vortex zones are not possible due to the furnace geometry and load.

US Patent No. 6,558,154 (Eroglu et al.) Describes a control-based staggered fuel supply strategy for an air motor in which two separate staggered fuel input nozzles are used. A set of emission sensors and downward pulsation of each step zone has been installed. These sensors measure the quality of combustion products from each stepping zone and subsequently a control unit varies the relative amounts of fuels injected into each zone depending on changing operating and environmental conditions.

US Patent No. 5,601,424 (Bernstein et al.) Describes a method for reducing NOx using atomizing vapor injection control. NOx levels are reduced by adding atomizing steam to the burner flame, which is available for fuel oil atomization. For a reduction of 30% and NOx, approximately 0.227 kg of steam / 0.454 kg of fuel flow (0.5 pounds of steam / pounds of fuel flow) is required. A large amount of steam is needed to reduce the flame temperature and obtain a required NOx reduction. In addition, if a large amount of steam is used to rapidly cool the flame, there is a possibility of flame instability and cathodic deposition. Thus, there is an upper limit for steam injection for reasons of flame stability.

The gas turbine industry also uses a similar steam injection technique for NOx control. However, due to an inefficient mode of steam injection, a large economic charge is paid to reduce NOx emissions. The steam consumption is very large, and the technique is relatively inefficient and of unreasonable cost for NOx control.

It is desired to have a reasonable cost reconversion apparatus and method for the reduction of NOx emissions, which provide the ability to burn refinery waste gases without excessive NOx emissions.

It is also desired to have an apparatus and method that reduce the maintenance of the equipment due to problems such as plugging of the burner tips and overheating of the process pipes, and providing additional benefits of improved fuel efficiency and kiln productivity.

It is also desired to have an apparatus and method that allows low Nox current burners to meet the requirements of the NOx level of SCR allowing refineries to comply with NOx standards without using SCR technology of high capital cost.

It is also desired to have an apparatus and method that allow the process industries to consume cheaper residual fuel without incurring loads of maintenance problems such as tip seals, equipment overheating, process interruptions, etc., while complying with the NOx standards producing emissions of less than 10 ppm NOx.

It is also desired to have an apparatus and method for burning a fuel that provide better performance than the prior art, and which also overcome many of the difficulties and disadvantages of the prior art in order to obtain better and more advantageous results.

Brief Summary of the Invention

The present invention is a method and system for diluting a fuel to reduce nitrogen oxide emissions through staggered fuel delivery. The invention also includes a fuel dilution device that can be used in the method or system.

There are multiple steps in a first embodiment of the method for diluting a fuel to reduce nitrogen oxide emissions through phased fuel input. The first step is to provide a fuel dilution device, which includes: a first conduit having an inlet and an outlet spaced from the inlet, the first conduit being adapted to transmit a stream of fuel entering the inlet and leaving the output in a first thermodynamic state and a first fuel index; and a second conduit having an intake and a spaced outflow of the intake, the second conduit being adapted to transmit a current of a fluid entering the intake and exiting the evacuation in a second thermodynamic state and a second fuel index , the second fuel index being different from the first fuel index by at least about 0.1 and the second thermodynamic state being different from the first thermodynamic state, whereby there is a potential for mixing between the current of the fuel leaving the outlet of the first conduit and the flow of the fluid that comes out of the evacuation of the second conduit. The second step is to feed the fuel stream to the inlet of the first duct, said fuel stream leaving the outlet of the first duct in the first thermodynamic state and the first fuel index. The third step is to feed the fluid stream to the admission of the second duct, said stream flowing out of the outlet of the second duct in the second thermodynamic state and the second fuel index, whereby at least a portion of the stream of the fuel leaving the outlet of the first duct is mixed with at least a portion of the fluid stream that comes out of the evacuation of the second duct in a position close to the outlet and the evacuation, thereby generating at least one stream of diluted fuel which has an intermediate fuel index between the first fuel index and the second fuel index. The fourth step is to provide a source of an oxidant. The fifth step is to burn a portion of the oxidant with at least a portion of at least one of the fuel stream, or the fluid stream, or the diluted fuel stream, thereby generating a gas containing a reduced amount of nitrogen oxide. , said reduced amount of nitrogen oxide being less than a higher amount of nitrogen oxide that would be generated by burning the fuel using means other than the fuel dilution device.

There are many variations of the first embodiment of the method. In a variation, the fluid is a fuel. In another variation, the fluid is selected from a group consisting of steam, flue gases, carbon dioxide, nitrogen, argon, helium, xenon, krypton, other inert fluids, and mixtures or combinations thereof.

In another variation of the first embodiment of the method, the first conduit is adjacent to the second conduit. In another variation, at least a substantial portion of the second conduit is disposed in the first conduit. In another variation, the second conduit has an equivalent diameter (Dc) and the evacuation of the second conduit is located at a distance behind the exit of the first conduit, said distance being in a range of approximately (2 Dc) to approximately (20 Dc ).

A second embodiment of the method for diluting a fuel to reduce nitrogen oxide emissions through phased fuel input is similar to the first embodiment, but includes two additional steps. The first additional step is to provide a turbulence arranged in the second conduit. The second additional step is to transmit at least a portion of the fluid stream through the turbulence, thereby swirling at least a portion of the fluid exiting the second conduit.

According to the invention, a rack nozzle is arranged in fluid communication with the outlet of the first conduit. This allows at least a portion of a stream of diluted fuel to be transmitted through the rack nozzle.

Another embodiment of the method is similar to the first embodiment, but includes the additional step of placing the fuel dilution device in fluid communication with an oven containing an amount of an oven gas, whereby at least a portion of the amount of the oven gas is mixed with at least a portion of the diluted fuel stream.

Another embodiment of a method for diluting a fuel to reduce nitrogen oxide emissions through phased fuel input includes multiple steps. The first step is to provide a fuel dilution device, which includes: a first conduit having an inlet and an outlet spaced from the inlet, the first conduit being adapted to transmit a stream of fuel entering the inlet and leaving the output at a first pressure, a first speed, and a first fuel index; and a second conduit having an intake and a spaced outflow of the intake, the second conduit being adapted to transmit a current of a fluid entering the intake and exiting the evacuation at a second pressure, a second speed, and a second fuel index, the second fuel index being different from the first fuel index by at least about 0.1 and at least one of the second pressure and the second speed being different from at least one of the first pressure and the first speed , so there is a potential for mixing between the fuel stream leaving the first duct outlet and the fluid stream exiting the second duct drain. The second step is to feed the fuel stream to the inlet of the first duct, said fuel stream leaving the outlet of the first duct at the first pressure, the first speed, and the first fuel index. The third step is to feed the fluid stream to the admission of the second conduit, said flow of the fluid flowing from the evacuation of the second conduit to the second pressure, the second velocity, and the second fuel index, whereby at least a portion of the fuel stream leaving the outlet of the first conduit is mixed with at least a portion of the fluid flow leaving the evacuation of the second conduit in a position close to the outlet and the evacuation, thereby generating at least one diluted fuel stream having an intermediate fuel index between the first fuel index and the second fuel index. The fourth step is to provide a source of an oxidant. The fifth step is to burn a portion of the oxidant with at least a portion of at least one of the fuel stream, or the fluid stream, or the diluted fuel stream, thereby generating a gas containing a reduced amount of nitrogen oxide. , said reduced amount of nitrogen oxide being less than a higher amount of nitrogen oxide that would be generated by burning the fuel using means other than the fuel dilution device.

There are multiple elements in a first embodiment of a fuel dilution device to dilute a fuel to reduce nitrogen oxide emissions through phased fuel input. The first element is a first conduit that has an input and an output spaced from the input, the first conduit being adapted to transmit a current of a fuel entering the input and leaving the output in a first thermodynamic state and a first fuel index The second element is a second conduit that has an admission and a spaced evacuation of the admission, the second conduit being adapted to transmit a current of a fluid entering the admission and exiting the evacuation in a second thermodynamic state and a second fuel index, the second fuel index being different from the first fuel index by at least about 0.1 and the second thermodynamic state being different from the first thermodynamic state, whereby there is a potential for mixing between the current of the fuel leaving of the outlet of the first duct and the flow of the fluid that comes out of the evacuation of the second duct, whereby at least a portion of the fuel stream that exits the outlet of the first duct is mixed with at least a portion of the stream of the fluid that comes out of the evacuation of the second conduit in a position close to the exit and the evacuation, generating therefore at least one diluted fuel stream having an intermediate fuel index between the first fuel index and the second fuel index. The third element is a source of an oxidant. The fourth element is means for burning a portion of the oxidant with at least a portion of at least one of the fuel stream, or the fluid stream, or the diluted fuel stream, thereby generating a gas containing a reduced amount of nitrogen oxide, said reduced amount of nitrogen oxide being less than a higher amount of nitrogen oxide that would be generated by burning the fuel using means other than the fuel dilution device.

There are many variations of the first embodiment of the fuel dilution device. In a variation, the fluid is a fuel. In another variation, the fluid is selected from a group consisting of steam, flue gases, carbon dioxide, nitrogen, argon, helium, xenon, krypton, other inert fluids, and mixtures or combinations thereof.

In another variation, the first conduit is adjacent to the second conduit. In another variation, at least a substantial portion of the second conduit is disposed in the first conduit. In another variation, the second conduit has an equivalent diameter (Dc) and the evacuation of the second conduit is located at a distance behind the exit of the first conduit, said distance being in a range of approximately (2 x Dc) to approximately (20 x Dc).

In another variation of the first embodiment, the fuel dilution device is in fluid communication with an oven containing an amount of an oven gas, whereby at least a portion of the amount of the oven gas is mixed with at least a portion of the diluted fuel stream.

A second embodiment of the fuel dilution device is similar to the first embodiment, but includes a turbulence arranged in the second conduit. According to the invention, the fuel dilution device includes a zipper nozzle in fluid communication with the outlet of the first conduit.

Another embodiment of the fuel dilution device for diluting a fuel to reduce nitrogen oxide emissions through staggered fuel delivery includes multiple elements. The first element is a first conduit that has a spaced inlet and outlet of the inlet, the first conduit being adapted to transmit a stream of a fuel entering the inlet and leaving the outlet at a first pressure, a first speed , and a first fuel index. The second element is a second conduit that has an intake and a spaced evacuation of the admission, the second conduit being adapted to transmit a current of a fluid entering the intake and leaving the evacuation at a second pressure, a second speed , and a second fuel index, the second fuel index being different from the first fuel index by at least about 0.1 and at least one of the second pressure and the second speed being different from at least one of the first pressure and the first velocity, so there is a potential for mixing between the fuel stream leaving the outlet of the first duct and the fluid stream exiting the evacuation of the second duct, whereby at least a portion of the stream of the fuel leaving the outlet of the first duct is mixed with at least a portion of the fluid stream that comes out of the evacuation of the second duct in a position close to the exit and the evacuation, thereby generating at least one stream of diluted fuel having an intermediate fuel index between the first fuel index and the second fuel index. The third element is a source of an oxidant. The fourth element is means for burning a portion of the oxidant with at least a portion of at least one of the fuel stream, or the fluid stream, or the diluted fuel stream, thereby generating a gas containing a reduced amount of nitrogen oxide, said reduced amount of nitrogen oxide being less than a higher amount of nitrogen oxide that would be generated by burning the fuel using means other than the fuel dilution device.

Another aspect of the invention is a system for diluting a fuel to reduce nitrogen oxide emissions through phased fuel delivery. The system includes multiple elements. The first element is a fuel dilution device, which includes: a first conduit having an inlet and an outlet spaced from the inlet, the first conduit being adapted to transmit a stream of fuel entering the inlet and exiting the output in a first thermodynamic state and a first fuel index; and a second conduit having an intake and a spaced outflow of the intake, the second conduit being adapted to transmit a current of a fluid entering the intake and exiting the evacuation in a second thermodynamic state and a second fuel index , the second fuel index being different from the first fuel index by at least about 0.1 and the second thermodynamic state being different from the first thermodynamic state, whereby there is a potential for mixing between the current of the fuel leaving the outlet of the first conduit and the flow of the fluid that comes out of the evacuation of the second conduit. The second element is means for feeding the fuel stream to the inlet of the first duct, said fuel stream leaving the outlet of the first duct in the first thermodynamic state and the first fuel index. The third element is a means for feeding the fluid stream to the admission of the second duct, said stream flowing out of the evacuation of the second duct in the second thermodynamic state and the second fuel index, whereby at least a portion of the fuel stream leaving the outlet of the first conduit is mixed with at least a portion of the fluid flow leaving the evacuation of the second conduit in a position close to the outlet and the evacuation, thereby generating at least one current of diluted fuel that has an intermediate fuel index between the first fuel index and the second fuel index. The fourth element is a source of an oxidant. The fifth element is means for burning a portion of the oxidant with at least a portion of at least one of the fuel stream, or the fluid stream, or the diluted fuel stream, thereby generating a gas containing a reduced amount of nitrogen oxide, said reduced amount of nitrogen oxide being less than the high amount of nitrogen oxide that would be generated by burning the fuel using means other than the fuel dilution device.

Another embodiment of the system for diluting a fuel to reduce nitrogen oxide emissions through phased fuel input includes multiple elements. The first element is a fuel dilution device, which includes: a first conduit having an inlet and an outlet spaced from the inlet, the first conduit being adapted to transmit a stream of fuel entering the inlet and exiting the output at a first pressure, a first speed, and a first fuel index; and a second conduit having an intake and a spaced outflow of the intake, the second conduit being adapted to transmit a current of a fluid entering the intake and exiting the evacuation at a second pressure, a second speed, and a second fuel index, the second fuel index being different from the first fuel index by at least about 0.1 and at least one of the second pressure and the second speed being different from at least one of the first pressure and the first speed , so there is a potential for mixing between the fuel stream leaving the first duct outlet and the fluid stream exiting the second duct drain. The second element is means for feeding the fuel stream to the inlet of the first duct, said fuel stream leaving the outlet of the first duct at the first pressure, the first speed, and the first fuel index. The third element is a means for feeding the fluid stream to the admission of the second conduit, said fluid flow leaving the evacuation of the second conduit at the second pressure, the second velocity, and the second fuel index, so that at least a portion of the fuel stream leaving the outlet of the first conduit is mixed with at least a portion of the fluid stream exiting the evacuation of the second conduit in a position close to the outlet and the evacuation, thereby generating the minus a dilute fuel stream that has an intermediate fuel index between the first fuel index and the second fuel index. The fourth element is a source of an oxidant. The fifth element is means for burning a portion of the oxidant with at least a portion of at least one of the fuel stream, or the fluid stream, or the diluted fuel stream, thereby generating a gas containing a reduced amount of nitrogen oxide, said reduced amount of nitrogen oxide being less than a higher amount of nitrogen oxide that would be generated by burning the fuel using means other than the fuel dilution device.

Brief description of the drawings

The invention will be described by way of example with reference to the accompanying drawings, in which:

Figure 1A is a cross-sectional plan view of a stepped nozzle of prior art fuel used in an ultra-low NOx burner.

Figure 1B is a cross-sectional elevational view of the stepped fuel inlet nozzle of the prior art of Figure 1A.

Figure 1C is a side view of the prior art stepped fuel nozzle of Figure 1 B.

Figure 2 is a cross-sectional elevational view of a mixing chamber of the prior art for mixing flue gases from an oven and a flow promotion gas with a combustible gas.

Figure 3 is a schematic diagram illustrating a cross-sectional view of an embodiment according to the prior art.

Figure 4 is a schematic diagram illustrating a cross-sectional view of another embodiment according to the prior art.

Figure 5A is a schematic diagram illustrating another embodiment according to the prior art using strong jet-weak jet drag.

Figure 5B is a schematic diagram illustrating a cross-sectional view of another embodiment according to the prior art, which uses a swirl-induced drag.

Figure 6 is a schematic diagram illustrating a cross-sectional view of another embodiment according to the prior art.

Figure 7 is a schematic diagram illustrating a cross-sectional view of an embodiment of the invention that includes a zipper tip or nozzle.

Figure 8A is a schematic diagram illustrating a front view of a tip or rack nozzle.

Figure 8B is a schematic diagram illustrating a side view of a tip or zipper nozzle attached to a lance, such as that shown in Figure 7.

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fifteen

twenty

25

30

35

40

Figure 8C is a schematic diagram illustrating a plan view of a tip or rack nozzle.

Figure 8D is a schematic diagram illustrating a portion of the front view of the tip or rack nozzle in Figure 8A in detail for sizing.

And Figure 9 is a schematic diagram illustrating a cross-sectional view of another embodiment of the invention that includes a zipper tip or nozzle.

Detailed description of the invention

The present invention solves several problems encountered in the design of combustion equipment, such as burners used to heat reformers, process heaters, boilers, ethylene crackers, or other ovens at high temperature. The invention relates to an improved process of phased fuel delivery. In particular, the two approaches that provide rapid dilution and mixing, depending on the required process objectives, are:

I. Step-by-step contribution of fuel with another fuel (F-F): high-pressure refinery residual fuel, atomized liquid fuel, etc., is injected near a relatively clean and low-pressure gaseous fuel for clean, maintenance-free operation of low NOx; Y

II. Staggered supply of fuel with inert gas (F-I): high pressure inert fluids such as steam, nitrogen, CO2 are injected near a low pressure gaseous fuel for NOx reduction.

In the sense that it is used here, the term "fuel index" (FI) is defined as the weighted sum of the atomic number of the combustible carbon where molecular H2 is assigned a carbon number 1.3, the weights being the molar fractions of component: Fl = ΣCi / Σxi, where Ci and xi are the number of carbon atoms and the molar fraction of component i, respectively. The fuel indices of a number of fuels and inerts are listed in Table I. Generally, a fuel with a higher fuel index cracks more easily and produces more NOx through the indicated NOx mechanism. H2 is a special case in this definition. Although H2 does not have carbon atoms, it is well known that the addition of H2 in natural gas increases NOx emissions. The literature suggests that approximately 30% more NOx emissions occur with pure H2 flames compared to methane flames. The higher NOx emission of H2 flames is attributable to higher flame temperatures through the thermal NOx mechanism. Since the fuel index is used here as an indicator for NOx emissions, a value of 1.3 is assigned to H2 to be consistent with its potential for NOx emissions.

Table I: Fuel indices for selected fuels and inerts

Fuels or inert

Fuel index

H2

 1.3

H2O

0

CO2

0

CO

one

N2

 0

CH4

 one

C3H8

 3

ROG (1)

1,434

PSA discharge gas (2)

0.57

Natural gas (3)

1.08

Natural gas (4)

1.14

(1) ROG: H2 18%, CH4 44%, C2H2 38%. (2) PSA discharge gas: H2 30%. CH4 18%, CO2 52%. (3) Natural gas: CH4 91%, C2H6 4%, C3H8 3%, N2 1%, CO2% (4) Natural gas: CH4 84%, C2H6 12%, C3H8 2%, N2 2%.

As explained here, the term "thermodynamic state" is defined as a state of existence of a matter. This definition is based on the concept of generally known thermodynamics, but with an extension including not only the usual temperature and pressure, but also the speed, concentration, composition, volume fraction, flow rate, electrical potential, etc., to fully characterize a current. This definition is used to define exactly the mixture as the result of a difference in the thermodynamic state between two currents.

The two approaches are explained in detail later.

I. Staggered contribution of fuel with another fuel (F-F):

This approach can be used to burn waste refinery fuels at a high supply pressure that contain a mixture of hydrogen and more high C / H fuels (ethane, propane, butane, olefins, etc.) with a second low pressure fuel gas , relatively cleaner. Maintenance problems arise with said refinery residual fuel due to high cracking of high C / H fuels and subsequent accumulation of soot at the burner fuel tips. In addition, the combustion of such fuels results in higher than normal NOx emissions.

To improve combustion of high C / H refinery residual fuels, the dirty fuel is diluted with a relatively cleaner secondary fuel stream) (e.g. hydrogen, synthesis gas, natural gas, or a kg fuel mixture low (BTU)). In an embodiment depicted in Figure 3, a high pressure refinery fuel gas (containing combustible gases of high C / H ratio) is injected through a central lance 32 and a relatively clean low pressure combustible gas, such as gas natural, synthesis gas, process gas, PSA discharge gas (recycled fuel gas after removing the hydrogen produced from PSA adsorbent beds), etc., is injected through an annular region 33 between the central lance 32 and a lance exterior 34. As shown in Figure 3, the outlet 36 of the central lance is reduced a preferred distance from the outlet 38 of the outer lance. This distance is preferably 2 to 20 times the equivalent diameter (Dc) of the central lance. Depending on the fuel divided between the high pressure refinery fuel gas and the cleanest fuel gas at low pressure, the distance is preferably from 1.59 to 25.4 mm (approximately 1/16 to 1 inch).

Those skilled in the art will recognize that the reference to "high pressure" in Figures 3-7 and 9 could also say "high speed" or "high pressure or high speed". Similarly, the reference to "low pressure" in said figures could say "low speed" or "low pressure or low speed".

The arrangement shown in Figure 3 allows the dirty refinery fuel gas at high pressure to be mixed with the cleanest fuel gas at low pressure due to turbulent jet interaction. The velocity of the high pressure refinery fuel gas through the central lance 32 is preferably 274 to 427 m / s (approximately 900 to 1400 feet / second) (preferably sonic or strangulated speed). The velocity of the low pressure fuel gas through the annular region 33 between the central lance 32 and the outer lance 34 is preferably 30.5 to 274 m / s (approximately 100 to 900 feet / second), depending on the pressure of available gas supply at low pressure. The higher velocity gas stream leaving exit 36 of the central lance drags the lower velocity gas stream approaching exit 38 of the outer lance and performs "first stage" mixing before the currents leave through a hole or holes 40. The hole geometry, angles, etc., of the outer lance are designed for optimum "second stage" mixing in the oven atmosphere. A very large amount of furnace gas 42 is entrained for second stage dilution, thereby decreasing maximum flame temperatures and the subsequent reduction of NOx emissions.

Figure 4 illustrates an arrangement for phased supply of liquid fuel (F-F). In this embodiment, a high pressure liquid fuel (and high C / H ratio) (for example, fuel oil, diesel, C bunker, residual liquid fuel, etc.) is diluted using a low pressure fuel gas before being injected to an oven atmosphere for further dilution. For example, heavy fuel oil can be atomized with an atomizing fluid, such as steam, and then diluted with a low pressure fuel gas for combustion without soot (clean) inside the oven. This embodiment also decreases NOx emissions due to lower maximum flame temperatures.

In Fig. 4, X is the distance from the outlet of the central lance 32 to the rear face of the outlet for the outer lance 34. Dc is the equivalent flow area diameter of the central lance outlet, that is, The total flow areas of the central lance outlet is the same as a circle of diameter Dc. Of is the equivalent flow area diameter of the outer lance, that is, the total flow area of the lance outlet is the same as a circle of diameter De.

Two other embodiments of step contribution (F-F) are shown in Figures 5A and 5B. In Figure 5A a strong jet-weak jet interaction takes place between the high pressure refinery fuel gas and the low pressure fuel gas. The high pressure refinery fuel gas is injected into a high pressure lance 52 at a high speed of 274 to 427 m / s (approximately 900 to 1400 feet / second) in a preferred direction, and a low pressure fuel gas , which is injected into a low pressure lance 54, is carried by the high pressure refinery fuel gas.

In Fig. 5B, the high pressure refinery fuel gas is swirled in a central lance 32 using a fuel turbulence 56, and the low pressure fuel gas is drawn into the crushed region (central region) of the high speed whirlpool. This allows a good mixture of the high pressure refinery fuel gas and the low pressure fuel gas before they leave the outer lance 34 and enter the furnace (not shown), where further dilution takes place with the furnace gases 42 This approach is beneficial for applications that require a short flame profile or a smaller combustion space.

An application for step contribution (F-F) is found in methane vapor reformers (SMR) where high-pressure fuel gas is generally a natural gas supply or a refinery discharge gas that is generally classified as an adjusted fuel. With reference to Figure 6, the high pressure combustible gas is injected into the central lance 32. The low pressure combustible gas injected into the annular region 33 between the central lance 32 and the outer lance 34 is generally PSA discharge gas ( pressure swing adsorption)

or PSA clean ventilated stream containing CO2 (~ 45%), hydrogen (~ 30%), methane (~ 15%), and CO (~ 10 ° / 0) with a fuel index of approximately 0.64. The PSA discharge gas leaves the adsorption bed after separating the hydrogen product. Fuel set at high pressure means between 10% and 30% of total energy for typical reformers that have PSA for hydrogen separation.

A secondary advantage of this staggered contribution application is to improve PSA recovery by increasing the range of the PSA pressure cycle, particularly at the low end. With reference to Figure 7, this is achieved by creating a low pressure region within the outer lance 34. The high speed central jet 72 shown in Figure 7 creates a low pressure region around the jet body where the fuel gas at low pressure that moves slower it is dragged by the central jet of faster movement. Due to an active entrainment process, the supply pressure for the low pressure fuel gas is reduced for the same fuel flow rate.

In a laboratory combustion experiment, the PSA discharge gas supply pressure at low pressure was reduced from 13800 to 11000 N / m2 (from 2 psig to 1.6 psig) (20% reduction). This was achieved by injecting the high pressure fuel gas at 172000 N / m2 / 396 m / s (25 psig) (a speed of 1300 feet / second). The combustion energy divided between the high pressure fuel gas and the low pressure fuel gas was 30:70 respectively.

To better quantify the details of the phased contribution process (F-F), laboratory test results using a low NOx burner were considered. The burner had 10 fuel lances distributed around a circle of 457 mm (18 inch) in diameter. Of the 10 fuel lances, two lances were reserved for the staggered type (F-F) configuration. The lances had special fuel tips and multiple divergent grooves (74 rack tips) to improve passive mixing. A schematic diagram of the staggered fuel input (FF) configuration using rack tips 74 is shown in Figure 7. The burner was rated at a combustion rate of 8.44,106 kg / h (8 MM Btu / h) using preheating with air at 340 ° C (644 ° F) and was designed to use two types of fuels. The details of the two fuels are set out below:

*

 High pressure refinery fuel gas: H2 (18%), natural gas (44%) and ethylene (38%). This fuel has a fuel index of 1.43 and accounts for 30% of the total energy input.

*

 Low pressure fuel gas: CO2 (52%), natural gas (18%) and H2 (30). It has a fuel index of 0.57, and accounts for approximately 70% of the total energy input.

With reference to the arrangement illustrated in Figure 7, the high pressure fuel gas was injected into a central lance 32 made of standard tubes with a diameter of 9.53 mm (3/8 inch) x 0.88 mm (0.035 inch) of wall thickness, which were concentrically placed in an outer lance 34 made of 3/4 inch (19.1 mm) tube 40. A zipper tip 74 was mounted at the end of the tube. The zipper tip was sized for 13 mm (0.51 inch) of equivalent diameter and, as shown in Figures 8A-8D, had four vertical grooves and a horizontal groove. The divergence angles (α1 and α2) for the vertical grooves were 18 ° and 6 ° respectively for the axial tip geometry of the zip nozzle as follows: 1) a series of vertical structures in intersecting planes between adjacent primary shapes; 2) instabilities of induced downward flow; and 3) a high level of molecular mixture (small scale) between the first fluid (fuels) and the second fluid (furnace gases). The previous mixture was also achieved at the shortest axial distance. The low NOx burner laboratory experiments performed with the lance lance configuration of Figure 7 (including rack tips) indicate rapid axial mixing, greater dragging of oven gas with the divergence angle β at 7 °.

The general fluid processes according to the arrangement of Figure 7 resulted in more uniform heat transfer to the load and ultra-low NOx and CO emissions (<15 ppmv) at a fuel pressure below 13800 N / m2 (2 psig ). It was also observed that, without the spear lance process, the combustion of high pressure fuel and a high C / H ratio produces a flame rich in visible soot. In addition, NOx emissions were up to 25 to 30 ppm. This experiment showed that the F-F phased contribution process could drastically reduce NOx emissions. The F-I phased contribution process could reduce emissions even more with inert.

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twenty

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40

The visual test of the improved mixture was observed in a furnace in a laboratory provided that the lagged fuel lance (F-F) lance configuration was used for refinery fuels consisting of butane (C4H10) of up to 50%. Individual flames were found to mix much more rapidly with furnace gases and create a spacious or flameless combustion. On the other hand, single lances with cylindrical nozzle lances created a rather visible (bluish) and relatively longer flame, indicating less dilution of furnace gas and mixing, and at the same time produced relatively more NOx and CO emission levels. high at a given fuel supply pressure.

Table II provides a preferred combustion range, dimensions, dimensionless ratios and injection angles for a proposed lance configuration. Simple circular tubes were used for high pressure refinery fuel while a zipper tip was used for low pressure PSA discharge gas fuel. These lances are critical components of a low NOx burner because the reliability of the burner's performance directly affects the methane steam reformer in the current performance.

Table II: Dimensional parameters for staggered lance fuel lance tips

Low pressure zipper tip

High pressure cylindrical tip

(H)

(W) (R0 / R1) (H / R0) (α1, α2) (β) L / Of  Dc  X / Dc

Burner combustion capacity (MM Btu / h)

Groove Height (in) mm Groove Width (in) mm End-to-center slot radius ratio Slot height ratio to corner radius Axial Division Angle (°) Radial division angle (°) Ratio of zipper tip thickness to equivalent diameter Tube diameter (inch) mm Distance to zipper tip input

8

(1 / 32-1) 0.79-25.4 (1/4 -2) 0.25-50.8 1.6 (1-3) 3.7 (2-6) 15 (0 30) 7 (0-30) 0.625 (0.05-3) (0.305) (1 / 16-2) 7.75 1.59-50.8 4 (2-20)

5.2

 (1 / 32-1) 0.79-25.4 (1 / 4-2) 0.25-50.8 1.6 (1-3) 3.7 (2-6) 15 (0 30) 7 (0 -30) 0.625 (0.05-3) (0.277) (1 / 16-2) 7.04 1.59-50.8 4 (2-10)

The above dimensional ranges are valid for various fuels, such as natural gas, propane, refinery discharge gases, low kg (BTU) fuels, etc. The nozzles are optimally sized depending on the composition of the fuel, flow rate (or combustion rate) and the supply pressure available at the burner inlet in Table II, the dimensions, ratios and ranges have been estimated for a Burner combustion rate of 2.11 · 106 to 10.6 · 106 kg / h (2 to 10 MM Btu / h). However, these dimensions and ranges can be scaled for burners with a higher combustion rate> 10.6 · 106 kg / h (> 10 MM Btu / h) using standard engineering practice to maintain similar flow rate ranges. II. Stepped fuel supply with inert gas (F-I):

The best staggered contribution of the fuel with high pressure inert gases, such as steam (dry or saturated, CO2, combustion gases, nitrogen or other inert gases) is carried out with low pressure combustible gases to reduce NOx emissions. Step-by-step inputs that may be used include, but are not limited to, natural gas; low kg (BTU) process gas (consisting of hydrogen and other refinery fuels); and PSA discharge gas. Injection tip configurations are similar to those depicted in Figures 3-7 The main objective is to further reduce NOx emissions A preferred embodiment is illustrated in Figure 9.

Referring to Figure 9, a saturated or dry high pressure steam of 207,000 to 689,000 N / m2 (30 to 100 psig) is sent through the central lance 32 at approximately 274 to 427 m / s (900 to 1400 feet / second) and low pressure fuel gas is sent through the annular region 33 between the central lance 32 and the outer lance 34. A high speed steam jet 92 drags the combustible gas for first stage dilution (and mixing) within the annular region. The resulting mixture subsequently exits through a zipper tip 74 at a high speed of about 183 to 427 m / s (about 600 to 1400 ft / second) for second stage dilution in the oven (not shown) using oven gases (not represented). The second stage dilution is very effective due to the high steam velocities and the drag loops established by individual flames formed by the zipper tip. Due to the geometry of the zipper tip and the steam assistance, better fuel dilution is obtained. Maximum flame temperatures are further reduced and ultra obtained

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Four. Five

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low NOx ultra low NOx emissions. Table III offers estimated steam consumption figures for a large methane steam reformer oven.

Table III: Economy of steam consumption with the proposed phased contribution process (F-I)

Steam injection rate kg steam / kg fuel

(lb_stm / lb_fuel) 0.02 0.05

Combustion Rate kg / h

(mmbtu / h LHV) 89,108, (850) 89,108, (850)

Oven heating value mg / Nm3

(btu / scf, LHV) 37.2 (1000) 37.2 (1000)

Fuel cost $ / 1.06106 kg

($ / mmbtu, LHV) 6 6

Molecular weight of fuel

18 18

Required steam kg / h m3

 (lb / h) (mmscfd) 366 (806) (0.408) 0.9 (2,016) (1,02)

11600

28900

Energy required to generate steam at 689000 N / m2 (100 psia) and 204.4 ° C (400 ° F) of water at 15.5 ° C (60 ° F)

(btu / scf) mg / Nm3 (btu / lb) kg / kg 2.12 (57.1) 2798.6 (1203.2) 2.12 (57.1) 2798.6 (1203.2)

Steam cost

$ / day $ / year 140 50,992 349 127,480

As set forth in Table III, due to the unique method of phasing the fuel with an inert gas such as steam, the amount of steam required for fuel dilution is extremely low. The amount of steam needed for staggered contribution (F-I) is approximately 2% to 10% based on kg per kg (lb per lb) compared to low pressure fuel. The high steam velocity is used for a two-stage dilution process: 1) inside the spear tube using steam and low pressure fuel gas, and 2) in the furnace space using high speed fuel-steam mixture and oven gases

Laboratory experiments using an inert gas, such as nitrogen, have shown that NOx reductions of approximately 30% to 40% are possible based on a comparison between the simple lance configuration of the prior art (rack or circular tips only without lance lance arrangement) and the lance lance configuration of Figure 9. For example, using a low NOx burner, at a combustion rate of 5.28 · 106 kg / h (5 MM btu / h) , using combustion ambient air, an oven operating at an average temperature of 871.1 ° C (1600 ° F), exhaust gases at 1093.3 ° C (2000 ° F), using a nitrogen flow rate of 10% by weight, the NOx emission is reduced from approximately 10 ppm (corrected to 3% O2) for non-inert gas in the center to approximately 7 ppm (corrected to 3% O2) with nitrogen gas in the center.

In each of the embodiments explained above, the favorable results achieved by the present invention are promoted by two differences in the currents leaving the two ducts. The first difference is a difference in the thermodynamic states of the respective currents, and the second difference is a difference in the fuel indices of the respective currents. Specifically, for there to be a potential for mixing between the two currents leaving the two conduits, there must be a difference in the thermodynamic states of the two currents, and there must be a difference of at least 0.1, and preferably at least 0 , 2, between the fuel rates of the two streams for a significant reduction of NOx.

In the embodiments illustrated in the figures and explained above, the difference between the thermodynamic states of the two streams is expressed in terms of the differential pressure (ie, a "high pressure" fluid in a conduit, and a "low fluid" pressure ”in the other duct). However, those skilled in the art will recognize that the differential in thermodynamic states can also be expressed in terms of, and achieved as a result of, differences in speed, temperature, concentration, composition, volume fraction, flow rate, electrical potential, etc.

Therefore, the present invention includes many other embodiments and variations that are not illustrated in the figures.

or are explained in the detailed description of the invention. However, said embodiments and variations fall within the scope of the appended claims and their equivalents.

Those skilled in the art will also recognize that the embodiments and variations illustrated in the drawings and explained in the detailed description of the invention do not describe all possible provisions of the present invention, and that other arrangements are possible. Accordingly, all other arrangements are contemplated by the present invention and fall within the scope of the present invention. For example, in each of the embodiments illustrated in Figures 7 and 9, the arrangement of the low pressure and high pressure currents can be reversed (ie, the low pressure lance can be the inner lance, and the lance of high pressure can be the outer lance).

In addition to reduced NOx emissions, there are other advantages and benefits of the present invention, some of which are explained below:

*

 The proposed method of phased fuel input allows the cooling of active tip due to staggered contribution (F-F) or staggered contribution (F-I). For fuel tips that have a relatively large outlet from the tip area, the nozzle tips are actively cooled by high speed outgoing fuel gas or inert current. This is a significant improvement over conventional circular nozzles.

*

 Due to relatively poor drag efficiency and higher operating temperature, conventional tips have serious maintenance problems and soot seal problems using high C / H fuels. In comparison, the present invention has the following advantages:

-

 Reduced tendency to coke while using higher carbon content fuels

-

 Ability to use lower flow rates or higher heating value fuels

-

 Ability to use cheaper fuel nozzle material (304 or 310 stainless steel is suitable)

Thermal cracking is a major concern in many refinery furnaces where fuel compositions contain hydrocarbons in the range of C1 to C4. It has been found that cracked carbon clogs the burner nozzles and creates overheating of burner parts, reduced productivity and poor thermal efficiency. Thus, a maintenance-free operation (using phased input F-F or F-I) is a critical advantage for the refinery operator.

Although it has been illustrated and described herein with reference to some specific embodiments, it is not intended, however, that the present invention be limited to the details shown. Rather, several modifications to the details can be made within the scope and range of equivalents of the claims.

Claims (9)

1. A fuel dilution device to dilute a fuel to reduce nitrogen oxide emissions through phased fuel input, including: a first conduit (32) having an input and an outlet spaced from the input, the first conduit (32) being adapted to transmit a stream of a fuel entering the entrance and exiting through the exit and a second conduit (34) having an intake and a spaced outlet evacuation, the second conduit (34) being adapted to transmit a current of a fluid entering the intake and exiting through the evacuation, defining the exit of the first conduit (32) and the evacuation of the second conduit (34) a mixing position close to the outlet and the evacuation, characterized in that the device also includes a rack nozzle (74) in fluid communication down with the first duct outlet (34) and the mixing position.

2.

 A fuel dilution device according to claim 1, wherein the first conduit (32) is adjacent to the second conduit (34),

3.

 A fuel dilution device according to claim 1, wherein the second conduit (34) is disposed in the first conduit (32).

Four.

 A fuel dilution device according to any one of claims 1 to 3, further including a turbulence (54) disposed in the second conduit (34).

5.

 A fuel dilution device according to any one of claims 1 to 4, wherein the second conduit (34) has an equivalent diameter (Dc) and the evacuation of the second conduit (34) is located at a distance behind the outlet of the first conduit (32), said distance being in a range of approximately (2 x Dc) to approximately (20 x Dc), and / or

where the fuel dilution device is in fluid communication with an oven containing an amount of an oven gas.

6.

 A method for diluting a fuel to reduce nitrogen oxide emissions through staggered fuel delivery using a fuel dilution device according to any one of claims 1 to 5, including the steps of:

a) feeding a fuel stream to the inlet of the first duct (32), transmitting the stream of the fuel entering the inlet through the first duct (32); said fuel stream leaving the outlet of the first conduit (32) in a first thermodynamic state and a first fuel index; b) feeding a current of a fluid to the admission of a second conduit (34); transmitting the current of the fluid entering the intake through the second conduit (34), said current flowing from the evacuation fluid of the second conduit (34) in a second thermodynamic state and a second fuel index, the second index being fuel different from the first fuel index by at least about 0.1 and the second thermodynamic state being different from the first thermodynamic state; c) thereby providing a potential for mixing between the fuel stream that exits the first duct (32) and the fluid stream that exits the second duct (34); d) mixing at least a portion of the fuel stream that exits through the outlet of the first duct (32) with at least a portion of the fluid stream that exits through the evacuation of the second duct (34) in a position close to exit and evacuation e) thereby generating at least one diluted fuel stream having an intermediate fuel index between the first fuel index and the second fuel index; f) transmit at least a portion of the diluted fuel stream through the rack nozzle; g) provide a source of an oxidant; Y h) burn a portion of the oxidant with at least a portion of the diluted fuel stream.

7.

 A method according to claim 6, wherein the fluid is a fuel, or wherein the fluid is selected from a group consisting of steam, flue gases, carbon dioxide, nitrogen, argon, helium, xenon, krypton, other inert fluids, and their mixtures or combinations.

8.

 A method according to claim 6 or 7 using a device as defined in claim 4, including the additional step of:

5 transmit at least a portion of the fluid flow through the turbulence (56), thereby swirling at least a portion of the fluid flowing out of the second conduit. A method according to any one of claims 6 to 8, using a fuel dilution device as defined in claim 5, including the additional step of placing the dilution device of 10 fuel in fluid communication with an oven containing an amount of an oven gas, thereby mixing at least a portion of the amount of the oven gas with at least a portion of the diluted fuel stream.