MX2008007320A - Fluid heating method - Google Patents

Abstract

A method of heating a fluid utilizing a process heater having one or more first combustion zones and one or more second combustion zones. The combustion of a fuel is divided between the first and second combustion zones. The oxygen is provided for combustion within the first combustion zone by one or more oxygen transport membranes that contribute between about 50 and 99 percent of the stoichiometric amount of oxygen required for complete combustion of the fuel passing through the process heater. A supplemental or secondary oxidant is introduced into second combustion zone to complete combustion of the fuel and thereby produce a flue gas stream containing between about 1 and 3 percent oxygen. In this manner, the surface area of the oxygen transport membranes may be reduced below the surface area that otherwise would be required if 100 percent of the oxygen were contributed by the oxygen transport membranes .

Description

FLUID HEATING METHOD Field of the Invention The present invention relates to a method for heating a fluid. More particularly, the present invention relates to such a method wherein the fluid is heated inside a process heater that incorporates an oxygen transport membrane to provide the permeate oxygen to support the combustion and thereby increase the heat of the process. necessary to heat the fluid. Even more particularly, the present invention relates to such a method wherein combustion of the fuel is divided between a first heating zone incorporating the oxygen transport membrane and a second heating zone wherein a secondary oxidant is used to support the combustion. Background of the Invention The prior art has provided process heaters to heat fluids. A common example of a process heater is a boiler that is used to increase the steam of the feed water or to superheat the steam that has already been generated. Commonly, process heaters burn a fuel in the presence of an oxidant, for example, air, to increase the heat necessary to heat the process fluid. In recent years, it has been suggested to incorporate oxygen transport membranes in process heaters to produce permeate oxygen to support combustion, rather than air. The main advantage of using an oxygen transport membrane in a water heater process to supply oxygen for combustion, is that the vapor present inside the combustible gases that result from combustion, can be condensed at a higher temperature than in the combustible gases produced by combustion supported only by air The reason for this is that when combustion is supported by oxygen produced by the oxygen transport membrane, combustible gases essentially contain carbon dioxide and water When air is used as the combustion oxidant, combustible gases that also contain substantial amounts of nitrogen and water contained in such combustible gases will condense at a much lower, commonly about 25 ° C less than the case where the combustion is supported by oxygen Condensation of the steam at high temperature allows the heat that would otherwise be lost in the exhaust gases, recover and recycle for the use in the preheating of the feed for the process heater As such, a process heater that uses an oxygen transport membrane can be more thermally efficient than one that uses air In addition to the above, since the combustible gases essentially contain dioxide From carbon and water, carbon dioxide can be easily captured with conventional water removal. On the other hand, since only a small amount, if any, of nitrogen is present during combustion, very little NOx is produced from combustion. As is well known in the art, oxygen transport membranes can be made of ceramic materials that are formed in the plate or tubular elements that when heated to an operational temperature of between about 400 ° C and about 1000 ° C exhibit the transport of oxygen ions. When a gas containing oxygen, for example, air, comes into contact with one side of the membrane, known as the cathode side, oxygen is ionized by the acquired electrons. The resulting oxygen ions are transported through the membrane and emerge from an opposite side, known as the anode side, where the oxygen ions combine to form elemental oxygen and in doing so the electrons are produced. The electrons are transported again from the anode side to the cathode side to ionize the oxygen. If the ceramic material is a mixed conductor, commonly a perovskite, the electrons will be transported in the ceramic material by themselves. Other types of materials use dual phases of an ionic material, such as cerium or zirconium oxide stabilized with yttrium, which is capable of only transporting the oxygen ions and an electronically conductive phase. The electronically conducting phase is used to conduct the electrons. The transport of the oxygen ions is conducted by a different partial pressure of oxygen between the cathode and anode sides of the membrane. This difference in partial pressure can be created completely or partially by consuming the oxygen on the anode side through the combustion of a fuel. There have been a variety of designs for process heaters that incorporate the oxygen transport membranes proposed in the prior art. Such an example can be found in US Patent No. 6,394,043 which incorporates the oxygen transport membranes within a combustion chamber to provide oxygen to support combustion of the fuel and thereby generate heat. Part of the heat generated is used to heat the oxygen transport membrane to its operational temperature. The remaining portion of the heat is used to increase the steam or to superheat the steam that passes through the transfer passages that extend through the combustion chamber. The combustible gases produced from combustion can be recirculated and mixed with the fuel. In another example, US 6,552,104, a fuel is burned within a combustion chamber and the heated combustible gases pass in a cross-flow relationship to the oxygen transport membranes that are used to generate the oxygen. In one embodiment, the oxygen transport membranes and the vapor tubes are intermixed within a combustion chamber. In another embodiment, the oxygen transport membranes and the vapor tubes are separated. A combustion chamber contains the steam tubes and the resulting combustible gas passes to the oxygen transport membranes as a scavenging gas. The combustible gases are enriched in oxygen and then recirculated to the combustion chamber. The problem with an oxyfuel combustion system, which uses the oxygen transport membranes, is that the flow of oxygen in fuel-rich conditions is substantially greater than in low-fuel conditions by order of magnitude. Thus, to have complete combustion in such a system, a large membrane surface is required to contribute the oxygen necessary for stoichiometric combustion. As will be discussed, the present invention provides a method for heating a fluid through a process heater that integrates the oxygen transport membranes, which overcomes this problem by not using the oxygen transport membranes as the sole source of oxygen that is used. to withstand combustion. Brief Description of the Invention The present invention provides a method for heating a fluid. According to the method, a fuel stream is introduced into a process heater having at least a first combustion zone and at least a second combustion zone for combustion of the fuel contained in the fuel stream. The heat transfer passages extended through at least one first combustion zone so that the fluid passage is heated from the heat generated from combustion of the fuel. At least one first combustion zone and at least one second combustion zone are connected in series so that a first portion of the fuel can be burned in at least one first combustion zone and a second portion of unburned fuel. at least one first combustion zone can be burned in at least one second combustion zone. The fuel stream comes into contact with at least one oxygen transport membrane located within at least one first combustion zone. Oxygen is separated from at least one first gas stream containing oxygen with at least one oxygen transport membrane, such that the permeate oxygen supports the combustion of a first portion of the fuel and supplies between about 50 percent and about 99 percent of the amount of stoichiometric oxygen necessary for the complete combustion of the fuel present within at least a first zone of combustion. The combustion of the first fuel portion provides a driving force for oxygen separation. At least one second stream of oxygen-containing gas is introduced into at least one second combustion zone to support the combustion of the second part of the fuel so that a fuel gas is produced from the combustion of the second part of the fuel. fuel containing between about 1 and about 3 volume percent oxygen. The fuel gas is discharged from at least one second combustion zone. A process heater that uses the oxygen transport membranes in a way in which not all of the oxygen needed for combustion is contributed by the oxygen transport membranes, allows the number of oxygen transport membranes to be substantially reduced. that the use of oxygen transport membranes for the combustion of oxyfuel is economically attractive. Preferably, the permeate oxygen supplies between about 75 percent and about 95 percent of the amount of stoichiometric oxygen necessary for the complete combustion of the fuel present within at least one first combustion zone. At least one second gas stream containing oxygen may be air or air enriched in oxygen or an oxygen-containing stream containing at least 90 volume percent oxygen. Such oxygen-containing stream can be produced by pressure swing adsorption or by cryogenic rectification. While the use of pressure swing adsorption or cryogenic rectification is on an illogical economic basis in which the cost would have been associated with obtaining oxygen from such sources, the use of such oxygen sources in the practice of the present invention, particularly in cases in which most of the fuel is consumed in the first combustion zone, can be economically attractive because very little oxygen contributed from such sources would be required. A fuel gas stream partially integrated from the fuel gas can also be introduced into at least one first combustion zone. The use of the fuel gas in at least one first combustion zone recaptures the combustion heat and also increases the vapor to the carbon ratio to help prevent deposition of carbon in the oxygen transport membrane. Another fuel gas stream partially integrated by the fuel gas can be introduced into at least one second combustion zone. In addition, another fuel stream is introduced into at least a second combustion zone. The fuel gas stream that is introduced into at least one first combustion zone can be heated in an in-line burner. Another possibility is to eliminate an intermediate fuel gas stream between at least a first combustion zone and at least one second combustion zone and combine the intermediate fuel gas stream with the fuel gas stream which is recirculated to at least a first combustion zone. The intermediate fuel gas stream is formed from the combustion gases produced in at least one first combustion zone. Any embodiment of the present invention could incorporate an oxidation catalyst contained in at least a second combustion zone to promote combustion of the second fuel portion. Brief Description of the Drawing While the specification is concluded with the claims that indicate differently the subject matter that the Requesters consider as their invention, it is believed that the invention will be better understood when taken with reference to the accompanying drawing in which the only figure is a schematic diagram of an apparatus for performing a method according to the present invention. Detailed Description of the Invention With reference to Figure 1 a process heater 1 is illustrated which for discussion purposes is a boiler designed to heat water or to superheat steam. As would be known to those skilled in the art, the process heaters could be used to heat other fluids, for example reagents such as steam and a feed containing a hydrocarbon for a steam methane reformer. In this regard, the term "process heater" as used herein and in the claims, is any device that through the combustion of a fuel indirectly warms any fluid passing through the localized heat exchange passages. in the process heater. The process heater 1 is provided with a first combustion zone 10 and a second combustion zone 12 which are designed to burn the fuel provided by a combined stream 14 for the conclusion. In the illustrated mode, the fuel provided is natural gas ("N.G.", for its acronym in English). The total heat generated is used to heat the process fluid, for example water passing through the heat exchange passages 16 located in the first combustion zone 10 and optionally in the heat exchange passages 18 located in the second combustion zone 12. The heat generated from the combustion of the fuel supplies the heat to the process fluid passing through the transfer passages 16 and 18. An oxygen transport membrane 20 is located within the first zone of combustion 10. The oxygen transport membrane 20 could be manufactured from known perovskites or from a dual phase conductor having an ionic phase for the transport of oxygen ions and an electronic phase for the passage of electrons. A common ionic conductor would be cerium dioxide or zirconium stabilized with yttrium. In addition, although only a single oxygen transport membrane 20 is illustrated, as would be known to those skilled in the art and as shown in the prior art discussed above, a series of oxygen transport membranes could be projected into the first zone. 10. A primary stream containing oxygen 22, for example air, is introduced into the first combustion zone 10 to come into contact with the cathode side 24 of the oxygen transport membrane 20. Oxygen is separated from the primary stream containing oxygen 22 to produce the permeated oxygen on one side of the anode 26 of the oxygen transport membrane 20 through transport of oxygen ions. The transport of oxygen ions is conducted by the combustion of the part of the fuel that is injected from the combined stream 14 in the zone 10 of combustion and also, the part of heat generated is used to elevate the oxygen transport membrane 20 at operational temperatures.

As will be discussed, the first fuel portion is burned within the first combustion zone 10 to leave a second portion of the fuel and combustion products that will be injected as a stream 28 in the second combustion zone 12. The current 28 contains the combustion gases produced by the combustion that occurs in the first combustion zone 10 and the unburned fuel. The separation of the oxygen from the oxygen-containing gas 22 produces an oxygen transport membrane of the gas stream 30 which in the case of air is rich in nitrogen. Commonly, the operating temperature of the oxygen transport membrane 20 is between about 800 ° C and about 1000 ° C. It should be noted that while the first and second combustion zones 10 and 12 are illustrated separately and apart from each other, such combustion zones could actually be part of the same combustion zones. In such a case, the second combustion zone 12 would be located simply downward, with respect to the combustion gases and unburnt fuel, of the first combustion zone 10.

As discussed above, the oxygen transport membrane 20 has a sufficient area at any location that supplies between about 50 and about 99 percent of the stoichiometric amount of oxygen required to fully burn the fuel within the fuel stream 14. Preferably , the oxygen transport membrane 20 supplies between about 75 percent and about 95 percent of such stoichiometric amount of oxygen. As such, stream 28 still contains the unburnt fuel and, as will be discussed, the area savings for the oxygen transport membrane 20 are important under such circumstances. The current calculation of the required membrane surface area is determined by the transfer of oxygen through an oxygen transport membrane. Any calculation is a complicated modeling process with many intermediate steps that need to be considered, such as: the total transfer through the limited layers of the gas phase surrounding the oxygen transport membrane; exchange of surface area; ambipolar diffusion; oxidation of fuel; and total fuel transfer through the porous support of the membrane. The effect of temperature, pressure and gas composition in some of these intermediate stages are not well understood. The models developed by a particular membrane architecture will not be universally applicable. However, such modeling is well understood by those skilled in the art.

Thus, although modeling is possible, the following is a more direct and simpler method to determine such an area. An oxygen transport membrane, such as an oxygen transport membrane 20, is exposed to a high temperature and the fuel on the anode side to the oxygen-containing stream on the cathode side. These process currents can flow in uniform flow directions, countercurrent or crossed with respect to each other. The degree of fuel combustion is determined from the difference between the inlet and outlet gas composition and the flow rates in the fuel or on the anode side of the oxygen transport membrane. The average oxygen flow is calculated by dividing the amount of oxygen per unit time that has been removed from the oxygen-containing stream by the area of the membrane that was used in the experiment. When the flow rates of fuel and of the oxygen-containing stream vary experimentally, the average oxygen flow can be determined based on the degree of fuel combustion and the degree of oxygen recovery of the air stream. This determination will be limited to the particular membrane material used, the membrane architecture, flow configuration, temperature and pressure. The average oxygen flow value can then be used to calculate the membrane area requirement for the amount of stoichiometric oxygen that will be supplied by dividing the total oxygen requirement per unit time by the average oxygen flow. The following tables I, II and II show the examples of an average oxygen flow calculation of simulated results involving different degrees of combustion and for membrane areas of approximately 780.4 cm2.

Table I High degree of combustion (95%).

Table II Average degree of combustion (79%) Table III Low fuel combustion degree (66%) In these tables there are calculated amounts of the degree of fuel combustion, oxygen recovery and average oxygen flow on a unit basis. These quantities are determined as follows: The degree of fuel combustion (? As%) can be calculated from the tables as follows: rcombust? be, entry \ 2X 2-entry "*" 2 entry "*" "^ entry) ~ ^ x ^^ *, entry" * "^ x ^^ exit" * "¿? C ™ 4¿at? da )? = - r fuel, entry \ 2 X "2fintrada" * "2 e tra? a ¿x ^" 4 entry) Where: Fcombustibie input = molar flow rate of the fuel stream entering the process heater [mol / s] xH? input = mole fraction of hydrogen in the fuel [-] xCentry = mole fraction of carbon monoxide in the fuel [-] xCH4 input - mole fraction of methane in the fuel [-] Fgas fuel, outlet - molar flow rate of the fuel gas stream leaving the OTM section of the boiler [mol / s] H? sanda - mole fraction of hydrogen in the fuel gas [-] xCOsa da = mole fraction of carbon monoxide in the fuel gas [-] xCH4 output = mole fraction of methane in the fuel gas H- Oxygen recovery (R02 as%) can be calculated from table 1 as follows: r air, enter x ^ '2, input ~' held, outputx ^ 2, output G a? re, enter? j2, input Where: Faue enters a = molar flow index of the oxygen-containing stream entering the process heater [mol / s] xO2 input = molar fraction of oxygen in the oxygen-containing gas stream [-] Frequency output = oxygen molar flow rate of the oxygen-free current [mol / s] * 02, output = molar fraction of oxygen in the oxygen-free current [-].

The average oxygen flow (J02 in mol O2 / m2 / s) results from the following equation: '' air, entry ^^ '2, entry ~' ltetenido, saüdaX '^ 2 ^ alida Where: A = oxygen transport membrane area [m2]. The area of oxygen transport membrane that is required for a process heater can then be calculated by dividing the required amount of oxygen for fuel combustion determined by a stoichiometric ratio by the experimental value of the average oxygen flow that has been determined from the manner set forth above for the same degree of combustion, oxygen recovery, and other process conditions (e.g., temperature, pressure, fuel, oxygen-containing stream composition, and flow rates). For example, assuming the hydrogen where the fuel was required and the fuel combustion degree of 50 percent, the amount of oxygen required for that purpose would be half the amount of fuel required. The required oxygen flow would then be divided by the experimental value of the average flow "Jo2" as established above to determine the required area. If tables I, II and III are reviewed, it can be observed that while the degree of combustion increases the flow per unit area decreases. This is because, as mentioned above, more area is required for higher degrees of combustion but the driving force along the length of the membrane is decreased to result in a lower value of flow per unit area. Returning again to the illustrated embodiment, the stream 28 is introduced into the second combustion zone 12 together with a secondary gas stream containing oxygen 32 to supply the additional oxygen required to completely burn the fuel remaining in the stream 28. When a The load is placed in the second combustion zone 12 such as the exchange passages 18, an additional fuel stream 34 can also be introduced into the second combustion zone 12 to meet the heating requirements for the load. This, however, it is optional as well as the heat exchange passages 18. In situations in which the combustion occurring within the first combustion zone 10 is almost stoichiometric, combustion of the fuel remaining inside the combustion chamber can be hindered. the stream 28 within the second combustion zone 12. In such cases, an oxidation catalyst 36 can be provided to promote the reaction of the fuel with the oxygen contained within the gas stream containing oxygen 32. The oxidation catalyst 36 can be any of numerous catalysts which are well known in the art and which could consist of a perovskite oxide. It is necessary that sufficient oxygen, by means of the second gas stream containing oxygen 32, be supplied such that a stream of fuel gas 38 is discharged from the second combustion zone 12 which contains anywhere from about 1 percent to about 3 percent by volume of oxygen. This ensures that the fuel supplied by the combined stream 14 and optionally, a combined stream 34 containing the fuel has been totally burned.

The secondary gas stream containing oxygen 32 can be air. This is the least expensive proposal and would be practical at high stoichiometric oxygen rates within the first combustion zone 10. Thus, very little nitrogen is contributed and the fuel gas stream 38 containing a sufficiently low concentration of nitrogen that the water contained within the fuel gas stream 38, it can be condensed at a higher temperature than the case where the oxidant would have been conventionally supplied by air through the process heater. As will also be discussed, other sources of oxidant could be used such as those generated by pressure swing adsorption or even by cryogenic distillation. The amount of oxygen that would be required would be quite small and such units could be extremely compact and therefore would be economically justifiable. The exact limit of course is an economic one that depends on the price of the oxygen contained within the secondary gas stream containing oxygen 32. In any case, the secondary gas stream containing oxygen 32 preferably has an oxygen concentration of at least approximately 90 percent by volume and therefore, it could be air enriched in oxygen.

A first portion 40 of the fuel gas stream 38 can be recirculated as a recirculation stream combined with a fuel stream 42 to form the combined stream 14. It is possible to separately inject the fuel stream 42 and the first portion 40 of the fuel stream 42. the fuel gas stream 38 in the first combustion zone 10. The use of recirculated fuel gas is optional, but advantageous, in that it preheats the fuel stream 14 and also supplies the vapor to prevent deposition of carbon in the transport membrane of oxygen 20 increasing the steam to the carbon ratio of combustion. Optionally, the fuel stream 44 can be burned within an in-line burner 46, for example, a duct burner. The combustion inside the in-line burner 46 is supported by a tertiary gas stream containing oxygen 48, for example air. Optionally, an intermediate fuel gas stream 50 formed from part of the stream 28 can be added to the fuel gas recirculation stream to also burn the fuel part. The advantage of this is to achieve a higher flow rate to promote a higher total transfer and more uniform temperature distributions. Still an additional option is to provide a second portion 52 of the fuel gas stream 38 to supply heat to the second combustion zone 12. As mentioned above, the combined stream 34 can be produced by combining a fuel stream 54 with the second portion. 52 of the fuel gas stream 38. The gas stream 54 and the second portion 52 of the fuel gas stream 38 could be injected separately.

A fuel gas stream 56 is then introduced into a carbon dioxide capture system 58 to produce a carbon dioxide product 60 for capture in a waste stream 62 that would consist mainly of water. The carbon dioxide capture system 58 consists of a phase separator, compressor and intermediate radiators used in a manner well known in the art. The fuel gas stream 56 could consist of the entire amount of fuel gas stream 38 or the remainder after providing the first and second portions 40 and 52 of the fuel gas stream 38.

As can be seen several combustion zones, such as the combustion zone 10, could be used in a larger installation. This would allow the heating of the heat exchange passages 16 to be more uniform. In such installation, although not illustrated, not all of the fuel stream 14 would be introduced into an initial zone of the first combustion zones, in fact, the fuel would be divided between the first combustion zones so that the generated heat would be equal. In addition, zones of more than a second combustion zone, such as combustion zone 12, could be provided. For example, in a case in which only 50 percent of the fuel was burned in the first combustion zone 10, there would be enough fuel to superheat the steam and in the first of the second combustion zones 12 and then in an area of downward combustion 12, the steam could be increased from the feed water. Although they were not illustrated, descending heat exchangers could be provided to reduce the temperature of the fuel gas stream 38.

The following table IV illustrates the calculated examples to demonstrate the effect on the reduction in the area of the membrane or oxygen transport membranes used in the first combustion zone 10 with the use of rich fuel, the sub-stoichiometric combustion occurring within the first combustion zone 10 followed by the addition of supplementary oxygen by means of the secondary gas stream containing oxygen 32. The system considered here is for a heat input of 120 MM BTU / hours that burns natural gas (equivalent to a boiler that produces approximately 100,000 Ib / h of saturated steam). It is assumed that the membrane or oxygen transport membranes operate between about 850 ° C and about 1000 ° C. The base case was generated assuming that the oxygen flow of the oxygen transport membrane 20 was constant in an initial section of the furnace, where there was an excess of fuel. Once all the fuel was consumed, it was assumed that the oxygen flow decreased substantially and since there was no more fuel, the oxygen transport membrane would operate in a similar way to the patents mentioned above where the combustion products act as a sweeping gas. Other assumptions used in the generation of the table are that: (a) the oxygen transport membranes supply 100 percent stoichiometric oxygen; (b) Oxygen beyond the stoichiometric requirement is supplied by the direct injection of secondary oxygen oxidant as illustrated above by the secondary gas stream containing oxygen 32; (c) the oxygen flow is constant at 10 sccm / cm2-min; and (d) the oxygen flow is constant at 0.5 sccm / cm2-min when excess oxygen is present by secondary oxygen injection.

Table IV Table V illustrates the additional calculated examples and is analogous to Table IV, but shows the effect of changing the amount of total oxygen replaced in the system by direct injection. The base case for table V is the same as that in table IV (all oxygen is supplied by the transport of oxygen ions through one or more membranes). In these cases, the assumptions are that: (a) the excess oxygen in the fuel gas is 1 percent (humidity); (b) the oxygen of up to the given percentage of the total required in relation to the base case (column 1) is supplied through the transportation of oxygen ions; (c) the remaining stoichiometric oxygen as well as the excess oxygen is supplied by the direct injection of a secondary oxygen; (d) the oxygen flow is constant at 10 sccm / cm2-min in the combustion zone; and (e) the oxygen flow is constant at 0.5 sccm / cm2-min when the excess O2 is present.

Table V Although the invention has been described with reference to a preferred embodiment, as will be the case with those skilled in the art, numerous changes, additions and omissions can be made without departing from the spirit and scope of the present invention as cited in the claims currently pending. .

Claims (17)

1. A method for heating a fluid, comprising: introducing a fuel stream into a process heater having at least a first combustion zone and at least a second combustion zone for combustion of a fuel contained in the fuel stream fuel and the heat transfer passages extend through at least a first combustion zone for the passage of the fluid that will be heated from the heat generated by the combustion of fuel; at least one first combustion zone and at least one second combustion zone which are connected in series so that a first fuel portion is capable of being burned in at least one first combustion zone and so that a second portion of the combustion zone unburned fuel in at least one first combustion zone can be burned in at least one second combustion zone; the contact of the fuel stream with at least one oxygen transport membrane located in at least one first combustion zone and the separation of the oxygen from at least one first stream of oxygen-containing gas with at least one membrane of oxygen transport such that the permeate oxygen supports the combustion of the first fuel portion and sups approximately 50 percent and approximately 99 percent of a stoichiometric oxygen amount necessary for the complete combustion of the fuel present within at least a first combustion zone and combustion of the first fuel portion provides a driving force for oxygen separation; the introduction of at least a second gas stream containing oxygen to at least one of the second combustion zones to support the combustion of the second fuel part so as to produce a combustible gas from the combustion of the second part of fuel containing between about 1 and about 3 volume percent oxygen; and the discharge of the fuel gas from at least one second combustion zone.

The method of claim 1, wherein the permeate oxygen sups between about 75 percent and about 95 percent of a stoichiometric amount of oxygen necessary for complete combustion of the fuel present within at least one first combustion zone.

The method of claim 1 or 2, wherein at least a second stream of oxygen-containing gas is air or air enriched with oxygen or an oxygen-containing stream containing at least 90 percent oxygen by volume.

4. The method of claim 1, wherein the heat transfer passages also extend through at least a second combustion zone.

The method of claim 1, wherein a fuel gas stream integrated by a part of the fuel gas is also introduced into at least one first combustion zone.

The method of claim 5, wherein another stream of fuel gas integrated by another part of fuel gas is introduced into at least one second combustion zone.

The method of claim 6, wherein another fuel stream is introduced into at least a second combustion zone.

The method of claim 6, wherein the fuel gas stream is heated in an in-line burner.

9. The method of claim 6, further comprising removing a stream of intermediate fuel gas between at least one first combustion zone and at least one second combustion zone, the intermediate fuel gas stream is formed by the combustion gases. combustion produced in at least one first combustion zone, and combining intermediate fuel gas stream with the fuel gas stream that is recirculated to at least one first combustion zone.

10. The method of claim 1, wherein at least a second combustion zone contains an oxidation catalyst to promote combustion of the second fuel portion.

The method of claim 3, wherein the heat transfer passages also extend through at least a second combustion zone.

The method of claim 11, wherein a fuel gas stream integrated by a fuel gas part is also introduced into at least a first combustion zone.

The method of claim 12, wherein the fuel gas stream is heated in an in-line burner.

14. The method of claim 13, further comprising removing a stream of intermediate fuel gas between at least a first combustion zone and at least a second combustion zone, the intermediate fuel gas stream is formed by the combustion gases. combustion produced in at least one first combustion zone, and combining intermediate fuel gas stream with the fuel gas stream that is recirculated to at least one first combustion zone.

The method of claim 14, wherein another stream of fuel gas integrated by another part of fuel gas is introduced into at least one second combustion zone.

16. The method of claim 15, wherein another fuel stream is introduced into at least a second combustion zone. The method of claim 15, wherein at least a second combustion zone contains an oxidation catalyst to promote combustion of the second fuel portion.