Apparatus for endothermic process with improved burners arrangement

Abstract

A furnace for performing an endothermic process comprising tubes containing a catalyst for converting a gaseous feed, wherein tubes are positioned in rows inside the furnace, wherein burners are mounted between the tubes and between the tubes and the furnace walls parallel to the tubes row and wherein the burners rows and the tubes rows are ended by end walls and are divided into sections with the distance from the end burner to the end wall being B2W, the distance between two adjacent burners in the section being B2B, and half the distance in-between two sections being B2S, wherein the burners in the rows are arranged in such a way that the ratios B2B/B2W and B2B/B2S are greater than 1.3 thus limiting the occurrence of the flame merging phenomenon and reducing significantly the quadratic mean of the tube temperature profile.

Claims

1. A furnace for performing an endothermic process, the furnace having a set of parallel furnace walls and a set of end walls, wherein the furnace further comprises: tubes containing a catalyst for converting a gaseous feed, wherein the tubes are positioned in a plurality of rows inside the furnace, wherein each row of tubes is parallel with the furnace walls, wherein the plurality of rows of tubes comprises a first row of tubes, a last row of tubes, and a first inner row of tubes disposed between the first row of tubes and the last row of tubes; and a plurality of burners mounted in rows between each row of tubes and between the furnace walls and the first and last row of tubes, wherein the plurality of burners are mounted in parallel with the furnace walls; and at least one roof beam running orthogonal to the set of parallel furnace walls, wherein the at least one roof beam divides each row of burners and row of tubes thereby sections within the furnace; wherein the rows of burners and the rows of tubes are ended by the set of end walls and are divided into the sections with a distance from an end burner to the end wall being B2W, a distance between two adjacent burners in a common section being B2B, and half a distance in-between two adjacent sections being B2S, wherein the plurality of burners are configured such that the ratios B2B/B2W and B2B/B2S are greater than 1.3 thus limiting the occurrence of a flame merging phenomenon and reducing a quadratic mean of a tube temperature profile.

2. The furnace according to claim 1, wherein the ratios B2B/B2W and B2B/B2S are greater than 1.6.

3. The furnace according to claim 1, wherein the ratios B2B/B2W and B2B/B2S are greater than 1.8.

4. The furnace according to claim 1, wherein the ratios B2B/B2W and B2B/B2S are equals.

5. The furnace according to claim 1, wherein the burners are mounted to the furnace roof.

6. The furnace according to claim 1, wherein the burners are mounted to the floor of the furnace and fire vertically upwards.

7. The furnace according to claim 1, wherein the furnace is a steam methane reforming furnace.

8. An endothermic process to be performed in a furnace comprising tubes and burners, said process comprising: a) providing the furnace as claimed in claim 1; b) combusting fuel with air in the plurality of burners; c) introducing a gaseous feed and steam to the plurality of tubes under conditions effective for converting the gaseous feed and steam into products; and d) discharging the products at a lower end of the tubes.

9. The process according to claim 8, wherein the furnace is a steam methane reforming furnace.

10. The process according to claim 8, wherein the ratios B2B/B2W and B2B/B2S are greater than 1.6.

11. The process according to claim 8, wherein the ratios B2B/B2W and B2B/B2S are greater than 1.8.

12. The process according to claim 8, wherein the ratios B2B/B2W and B2B/B2S are equal.

13. The process according to claim 8, wherein the furnace is a top-fired furnace.

14. The process according to claim 8, wherein the furnace in a bottom-fired furnace.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The furnace of the present invention and its advantages will be described in more detail in the following examples and on the basis of the drawings, where:

(2) FIG. 1 shows the burners configuration for typical furnace designs;

(3) FIG. 2 shows a typical arrangement using a 3D representation of a top-fired furnace used for syngas synthesis;

(4) FIG. 3 shows a top view of a top-fired furnace, highlighting tubes and burners organization;

(5) FIG. 4 shows a top view of the same furnace highlighting representative bays at the furnace scale;

(6) FIG. 5a shows the flame jets merging for a chosen representative bay (with 4 burners and 18 tubes);

(7) FIG. 5b shows the maximum tube skin temperature profile for the 18 tubes of the same representative bay as FIG. 5a;

(8) FIG. 6 shows the key parametersaccording to the inventionfor the repartition of burners in the representative bay of FIG. 5a and FIG. 5b;

(9) FIG. 7 presents 3 different repartitions of the burners in the representative bay of FIG. 6;

(10) FIG. 8 illustrates the flame jets behaviour for the 3 cases presented on FIG. 7;

(11) FIG. 9 shows the maximum tube skin temperatures for the 18 tubes of the representative bay for the same 3 cases presented on FIG. 8;

(12) FIG. 10 presents a table giving the root mean square of the tubes temperature obtained from simulations applied to a range of representative bays

DETAILED DESCRIPTION OF THE INVENTION

(13) As stated above, the invention aims at proposing an improved design of a furnace of top-fired or bottom-fired typesuch furnaces are illustrated on FIG. 1for performing an endothermic process; the objective is to mitigate the temperature variations along a row of burners parallel to the rows of tubesalong X-axishaving the same power thanks to an improved repartition of the burners along said row.

(14) In order to be able to identify and propose the best arrangements of burners along a row, numerical simulations have been performed for different arrangements of the burnershaving the same poweralong a row of burners, for several SMR plants.

(15) The tool used to identify the best repartitions of the burners in representative bay is the tool used here above for putting forward the lack of homogeneity of the flame jets and tube temperatures resulting from existing designs.

(16) The numerical simulations are made on top-fired SMR representative bays using a 3-D Computational Fluid Dynamic (CFD) solver intended for calculation of the heat transfer between the combustion chamber and the tubular catalytic reactors.

(17) For a given furnace, representative bays are chosen; the representative bays defined would have to be representative of repeated sections, and also have to take into account the presence of the walls and also the voids between sections for furnaces with two sections or more. The modular standard reformer with the desired capacity would then be composed by assembling a suitable number of representative bays.

(18) Reading the following more detailed description of the figures will help understanding the invention.

(19) FIG. 2 is a 3-D perspective view of a furnace; more exactly, it shows a typical arrangement of a top-fired furnace 1 used to produce a synthesis gas from a feed containing methane and steam. Catalyst tubes 2 are arranged in rows within the furnace 1. The feed is supplied through tubes 2 from the top to the bottom; the synthesis gas produced containing hydrogen and carbon monoxide as major components, and residuals, is withdrawn from the bottom part of the tubes 2. Burners 3 are arranged in rows between the tubes rows and between tubes rows and the walls along X axis. Resulting flue gases are withdrawn through exhaust tunnels 4.

(20) FIG. 3 presents a top view of a top-fired furnace 1 with 8 rows 9 of 54 tubes, each row being arranged in 3 sections 10 of 18 tubes eachand 9 rows 5 of 12 burners 6 arranged in 3 sections 10 of 4 burners each, and parallel to the tubes rows. The rows 5 of burners 6 are ended by a wall 7 (wall along Y axis also identified as end walls). For all rows 5 of burners 6, the end burners 8a facing the wall 7 are identified as wall end burners.

(21) As already stated, an important number of tubes and burners make it necessary to add support beams to ensure safety of the furnace; said supports divide the rows in several parts (also known as sections or bays 10). The sections 10 end either by a wall 7 or by a symmetry plane 11 separating two adjacent sections. The end burners 8b closest to the symmetry planes 11 are identified as symmetry end burners. This division in sections 10 induces dissimilar boundary conditions leading to merging of the flame jets towards the center of the sections.

(22) FIG. 4 shows a top view of the furnace highlighting four representative bays at the furnace scalesee grey rectangles. The representative bay 12 is composed of a subset of 18 aligned tubes, heated by 2 rows of 4 burners of same power, one end W being a wall representative of end wall 7, and the second end S being representative of the symmetry plane 11 in the middle of the void between 2 sections 10. The configuration of the representative bay 12 will be used for the simulations intended to describe the invention and presented hereafter in relation with the figures.

(23) FIG. 5a presents the temperature field in a plane cut in the middle of the burners. It results from the numerical simulation applied to the representative bay 12 of FIG. 4 with the burner arrangement characteristics B2B/B2W=1.1 and B2B/B2W=1.2; it illustrates the flame merging effect towards the center of the bay due to the deflection of the flame jets from end burners 8a close to a wall 7 and end burners 8b close to the symmetry plane 11.

(24) Due to this flame jets merging behavior, the heat transferred to the tubes lacks homogeneity, the tubes in the middle of the representative bay reach a higher skin-temperature as shown on FIG. 5b which presents the profile of the maximum tube temperature calculated thanks to the 3-D CFD model; this clearly illustrates that the heat transfer to the tubes is not homogeneous. A higher skin-temperature is observed for the tubes placed in the middle of the representative bay, the difference between the maximum and minimum skin temperature value within this representative bay reaching 30 C.

(25) As stated above, the invention aims at controlling the heat flux inhomogeneities in a representative bay so as to consequently control the heat flux all along the row, and finally to improve the heat flux control in the whole furnace. To achieve this result, the invention aims at limiting the flame jets merging thanks to an improved burners arrangement design along rows of burners of same power.

(26) In order to optimize the arrangements of the burners, numerical simulations of the behavior of different SMR plants have been performed.

(27) As already stated, the arrangement of the burners along a row can be defined by the three distances (in meter) B2B, B2W and B2S. Identified on FIG. 6, the distances correspond to the following: B2B is the distance between two adjacent burners in the representative bay; B2W is the distance between the end wall 7 and the burner 8a in the representative bay; B2S is the distance between the symmetry plane 11 and the burner 8b in the representative bay;

(28) The three distances listed above have been identified as being of great importance and representative of the row, more precisely in the form of the two ratios B2B/B2S and B2B/B2W.

(29) Remark: depending on its dimension and geometry, a furnace can be represented by different representative baysas can be deduced from FIG. 4; a bay can be characterized by a pair of the following ratios: (B2B/B2W and B2B/B2S) for a bay close to an end wall 7 on one end and a symmetry plane on the other end. (B2B/B2S and B2B/B2S) for a middle section with symmetry planes 11 on both ends (B2B/B2W and B2B/B2W) for a section with end walls 7 on both ends in the case of a small reformer with only one section.

(30) The three following figures present the different repartitions of the burners for the representative bay 12 to which simulations have been applied and the results obtained.

(31) FIG. 7 shows 3 different repartitions of the 4 burners of the bay 12 of FIG. 6; for each case, the two ratios B2B/B2S and B2B/B2W are indicated and the burners are represented as lozenge, triangle or square according to the repartition. The same shapes will be used to differentiate the 3 cases in the following related figures. For the three cases, the repartition of the 18 tubes remains sensibly the same.

(32) FIG. 8 shows the temperature field in a plane cut through the middle of the burners for the same 3 cases.

(33) The numerical simulation results highlight that the flame jets from the end burners 8a and 8b are more or less deflected, depending on the repartition of the burners. The more regular shape is observed for the triangle referenced case with the ratios B2B/B2S=B2B/B2W=1.8; the maximum merging effect is observed for the square referenced case with B2B/B2S=1.2 and B2B/B2W=1.1, with the flame jets of end burners deflected toward the middle of the bay; the lozenge referenced case with B2B/B2S=2.1 and B2B/B2W=1.9 being intermediate with slightly visible deflection effect toward the adjacent bay increasing the fluid temperature close to the symmetry side.

(34) FIG. 9 shows the maximum tube skin temperature profile along a tube row for the same 3 cases. The comparison of the three profiles confirms the observations made on the flame shapes: triangle referenced tubes temperature profile is the more uniform and regular with a temperature spread between the hottest and coldest tube of around 10 C., while lozenge referenced tubes temperature profile is regular (no maximum in the center of the bay) but not uniform (temperature appears globally higher on the symmetry side than on the wall side) due to unequal ratios B2B/B2S=2.1 and B2B/B2W=1.9 leading to a temperature spread of 28 C., and square referenced tubes temperature profile presents an outstanding parabola shape profile with a maximum in the center of the bay and the highest temperature spread of 30 C.

(35) To retrieve general design rules, a parametric study has been performed on 14 examples of reference bays with different values for the B2B, B2S and B2W distances, and various numbers of tubes and burners so as to represent a large variety of possible designs. This study allowed identifying the best ratios B2B/B2W and B2B/B2S, leading thus to define the best design rules, thanks to this study, it has been also to estimate the gain in term of temperature homogenization among the tubes.

(36) FIG. 10 presents a table that summarizes the study presented here above, with the impact of the burner arrangement on the quadratic mean square (also known as root mean square RMS) of the tube temperature profile within different reference bays. The quadratic mean of the tube maximum temperature will quantify the dispersion of the tubes temperatures within a reference bay.

(37) As the main objective of the invention is to solve the problem of non-uniformity of the temperatures along a row of tubes, this means that the best examples are those giving a RMS value as low as possible; in the examples presented, the highest RMS values are around 10, while the lower are close to 1 C. Such a low standard deviation (not far from 0) indicates that the tubes have similar temperatures while a high standard deviationclose to 10 or even moreindicates that the tube temperatures are spread out over a wider range of values. Thus, the lower the RMS of the tube maximum temperature in a bay, the better the performances of a steam methane reformer are.

(38) Based upon the study performed, the hereafter burner ratio rules were defined: in order to have a RMS value lower than 5 the ratios B2B/B2W and B2B/B2S should be higher than 1.3 with ratios B2B/B2W and B2B/B2S higher than 1.6, the RMS value are expected to be lower than 3 furthermore if the ratios B2B/B2W and B2B/B2S are higher than 1.8 then the RMS values are expected to be usually lower than 2.

(39) Another trend that is revealed by this examples is that the tube temperature RMS in a representative bay is lowered when the ratios B2B/B2W and B2B/B2S are more and more similar, preferably equal. This trend is observed for all values of the ratios.

(40) Finally, the number of tubes or burners in the representative bays has no impact on the ratios rules. Therefore, by applying the burners ratios rules of the invention when designing a furnace, the number of burners per section can be lowered while having a good homogenization in heat transfer from the burners to the tubes.

(41) The above results put forward design rules that need to be applied to the arrangement of the burners all along the rows in order to obtain more regular tubes temperatures all along the rows. Thanks to the observance of these rules, hot tubesfrequently observed in the center of the sectionsmay be avoided; failure, replacement of tubes and shutdown will therefore decrease.

(42) While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

(43) The singular forms a, an and the include plural referents, unless the context clearly dictates otherwise.

(44) Comprising in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of comprising). Comprising as used herein may be replaced by the more limited transitional terms consisting essentially of and consisting of unless otherwise indicated herein.

(45) Providing in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

(46) Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

(47) Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.

(48) All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.