Title of Invention

A ARRANGEMENT FOR INDIRECTLY TRANSFERRING HEAT TO A FLOWING PROCESS MEDIUM

Abstract

(57) Abstract: The invention relates to an arrangement for indirectly transferring heat to a flowing process medium, especially for carrying out steam reformation of hydrocarbons, with a heating chamber (1), which can be heated from above by burners (2) arranged in multiple rows and through which run, on vertical longitudinal planes, a plurality of rows of heat exchanger tubes (3) through which the process medium can be conducted, whereby the combustion waste gasses of the burners (2) can be extracted laterally from the heating chamber (1) through waste gas ducts (4) arranged on the floor of the heating chamber (l) parallel to each other and to the rows of heat exchanger tubes (3), and whereby the waste gas ducts (4) are made of refractory-grad material and have a substantially rectangular cross-section constant in the axial direction and are equipped on their longitudinal sides in the region near the floor with openings (5) distributed over their entire axial length for the passage of waste gases out of the heating chamber ( l) into the interior of each respective verse gas duct (4), characterized by the fact that to devitalize. the flow conditions of the waste gas, flow-bodies are arranged in the interior of the waste gas ducts (4) in the region of the lower part of the row of heat exchanger tubes (3), and that the flow bodies have, by section, flow baffles (6, 6a) running substantially hori-rontally, and are arranged in a step-like configuration relative to each other, whereby the step-like form is directed downward in the direction of the lateral output of the waste gas duct C4). PRICE: THIRTY RUPEES

Full Text

The invention relates to an arrangement for the indirect transmission of heat to a fluid process medium, in particular suitable for carrying out steam reforming of hydrocarbons, and comprising a heating chamber which is beatable from above by means of burners which are arranged in a plurality of burner banks and through which a plurality of rows of heat exchanger tubes are directed in vertical planes, process medium in use flowing along the interiors of said heat exchanger tubes and waste gases from the burners being directed laterally out of the heating chamber via waste gas ducts which are arranged at the bottom of the heating chamber, parallel to one another and parallel to the rows of heat exchanger tubes, and in which the waste gas ducts„are composed of refractory material, have a constant cross-section in the lengthwise direction and are provided on their longitudinal sides in close proximity to floors thereof with openings, which are distributed along the full lengths of the waste gas ducts, for the passage of the waste gases from the heating chamber into the interiors of the respective waste gas ducts. Arrangements, which have the design of the example illustrated in different views and partial sections in Figures 5 to 7, are frequently used for the steam reforming of hydrocarbons. Such arrangements comprise an essentially parallelepiped-shaped heating chamber 1 which is beatable by a plurality of burners 2, which are grouped to form burner banks and ara arranged in the top of the parallelepiped of the heating chamber to have a flame direction which is directed vertically downward. Rows of heat exchanger pipes 3, through which fluid process medium to be subjected to an endothermic chemical reaction is designed to pass, are arranged in a vertical plane between the banks of burners. The heating of the process medium is carried out predominantly by radiant heat produced by burning, but partially also by convection. Waste gas ducts 4, which are closed at their tops and extend parallel to the rows of heat exchanger tubes 3 and parallel to the burner banks 2, are provided at the bottom of the heating chamber 1 for the removal of the waste gases from the heating chamber 1. These waste gas ducts 4 have a substantially rectangular cross-section. They are produced from a refractory material (e.g. refractory brickwork). Numerous openings 5, through which waste gas can reach the interiors of the waste gas ducts 4 from the heating chamber 1, are arranged in the lower parts of the side walls of the waste gas ducts 4, along the full length thereof. Waste gas can thus flow laterally (horizontally) out of the heating chamber along the waste gas ducts 4, to arrive in a collecting duct 8, Into which all the waste gas ducts 4 feed, and can thence be conveyed away for further utilization of residual heat still contained in the waste gas, prior to subsequent discharge into the atmosphere. With regard to the practical operation of an arrangement of the kind described above, it is noted that conditions prevailing on the heat exchanger tubes during the transmission of heat are not uniform. This is apparent during maintenance work from the stresses to which such an arrangement is subjected. When certain of the heat exchanger tubes are exposed to relatively great thermal influences, they age relatively rapidly and must be replaced relatively soon. In a situation of this kind, there is a choice between the option either to replace all the heat exchanger tubes, including those tubes which do not in fact need to be replaced, or the option merely to replace a number of the heat exchanger tubes. The latter option results in frequent interruptions of operation in order to carry out maintenance and repair work. Since the heating of the heat exchanger tubes is predominantly by means of radiant heat, it is of substantial significance that the heat exchanger tubes be arranged in a manner such that all the heat exchanger tubes are exposed to the same condlTlbns, as far as the effect thereon by heat from the radiation source is concerned. When the waste ducts are rectangular in cross-section, this is,, in principle, the case. A rectangular duct of this kind is illustrated diagrammatically n more detail in Figure 8, which shows a panel-like portion of a heating chamber I. Openings through which waste gases pass in the side walls of the waste gas juct 4 are designated by reference number 5. Another known design of a waste gas duct is illustrated in Figure 9. Although, in cross-section, this waste gas duct, designated 4a, also has a rectangular cross-section, this cross-section changes Drogressively in the direction of the waste gas outlet (collecting duct 8). The i/vaste gas duct 4a has a roof which is stepped to slope such that said cross-section progressively increases in the direction of the collecting duct 8. By means of this design of the waste gas duct 4a, it is intended to ensure that the flow of waste gas into the waste duct is uniform along the length of the waste gas duct. It is clear that this is not the case in the waste gas duct 4 of Figure 8, which is parallelepiped-shaped because of changes in pressure in the waste duct. Yet even the stepped shape of the waste gas duct 4a provides no effective improvement in this regard, and a non-uniform heating of the heat exchanger tubes takes place in the cases of both Figures 8 and 9. If it were possible to ensure a uniform heat distribution during the transmission of heat to the heat exchanger tubes, it would be possible for the heat exchanger tubes to be designed to have a thinner wall thickness, because higher wall temperatures in certain tubes, such as occur in non-uniform heat distribution, would no longer be a factor for consideration. Accordingly, it would be possible to operate under relatively harsh operating conditions, or the service life of the heat exchangers would be increased under normal operating conditions. It is the object of the invention to provide a further development of an arrangement of the kind comprising a heating chamber which is beatable from above by means of burners which are arranged in a plurality of burner banks and through which a plurality of rows of heat exchanger tubes are directed in vertical planes, process medium in use flowing along the interiors of said heat exchanger tubes and waste gases from the burners being directed laterally out of the heating chamber via waste gas ducts which are arranged at the bottom of the heating chamber, parallel to one another and parallel to the rows of heat exchanger tubes, and in which the waste gas ducts are composed of refractory material, having a constant cross-section in the lengthwise direction and being provided on their longitudinal sides in close proximity to floors thereof with openings, which are distributed along the full lengths of the waste gas ducts, for the passage of the waste gases from the heating chamber into the interiors of the respective waste gas ducts such that the most uniform possible heat distribution to the heat exchanger tubes is encouraged during the transmission of heat. According to the invention, this object is met by employing flow-conducting bodies arranged in the interiors of the waste gas ducts for the purpose of encouraging uniform flow conditions of waste gas in the vicinity of the lower parts of the rows of heat exchanger tubes. Advantageously, the flow-conducting bodies at least in part comprise substantially horizontally extending guide plates and are arranged in a vertically spaced stepped configuration, the stepped configuration extending downwardly in a direction towards a laterally located outlet from the waste gas duct. Furthermore, the guide plates of each immediately adjacent pair thereof may partially overlap each other; and the flow-conducting bodies may each comprise a partitioning plate which extends from the floor of the associated waste gas duct substantially transversely relative to the longitudinal direction of said waste gas duct, being connected to a respective guide plate at that end of the guide plate which points away from the waste gas outlet of the duct. Accordingly, the present invention provides an arrangement for indirectly transferring heat to a flowing process medium, especially for carrying out steam reformation of hydrocarbons, with a heating chamber, which can be heated from above by burners arranged in multiple rows and through which run, on vertical longitudinal planes, a plurality of rows of heat exchanger tubes through which the process medium can be conducted, whereby the combustion waste gasses of the burners can be extracted laterally from the heating chamber through waste gas ducts arranged on the floor of the heating chamber parallel to each other and to the rows of heat exchanger tubes, and whereby the waste gas ducts are made of refractory-grade material and have a substantially rectangular cross-section constant in the axial direction and are equipped on their longitudinal sides in the region near the floor with openings distributed over their entire axial length for the passage of waste gases out of the heating chamber into the interior of each respective waste gas duct, characterized by the fact that to equalize the flow conditions of the waste gas, flow bodies are arranged in the interior of the waste gas ducts in the region of the lower part of the row of heat exchanger tubes, and that the flow bodies have, by section, flow baffles running substantially horizontally, and are arranged in a step-like configuration relative to each other, whereby the step-like form is directed downward in the direction of the lateral output of the waste gas duct. The invention will be described in more detail hereinafter with reference to the drawings, in which: Figure 1 shows a panel-like portion of a heating chamber comprising a waste gas duct according to the invention. Figure 2 shows a modification of the embodiment of Figure 1, Figure 3 is a diagram of the vertical components of the waste gas flow rate in the vicinity of a bank of heat exchanger tubes along a waste gas duct, as a factor depending on the height above the bottom of the heating chamber in an arrangement according to the invention, and Figure 4 is a comparative diagram in respect of Figure 3 for an arrangement comprising a conventional waste gas duct, and, as the state of the art: Figure 5 shows a side view of a steam reforming plant (partially in cross-section). Figure 6 shows a plan view of the plant according to Figure 5 (partially in cross-section). Figure 7 shows a front end view of the plant according to Figure 5 (partially in cross-section). Figure 8 shows a pane-like diagrammatic section of a heating chamber comprising a parallelepiped-shaped waste gas duct. Figure 9 shows a pane-like section of a heating chamber comprising a sloping waste gas duct. It is possible to meet the object of the present invention by a surprisingly simple means. A particularly simple embodiment of the invention is diagrammatically illustrated in Figure 1 in the form of a panel-like portion of a heating chamber alongside a waste gas duct 4. A single row of flow-conducting bodies, in the form of guide plates 6, is arranged in the interior of the waste gas duct 4. The guide plates 6 are flat (planar) bodies, which extend substantially horizontally in the lengthwise direction (direction of flow) of the waste gas duct 4, and, in comparison to the duct cross-section, have a relatively thin wall thickness. They extend between the iongituuinai wajis of the waste gas duct 4 across its entire width. They are made from a heat-resistant material appropriate for the conditions of use, for example a refractory material or a heat-resistant metal material. Accordingly, the term guide plate does not, of necessity, refer only to metal materials. Indeed, this term is intended to indicate that the flow of waste gases within the waste gas duct 4 is influenced thereby in the sense of rendering the flow uniform in the lengthwise direction. The length of the guide plates 6 is, in each case, only a small fraction of the total length of the waste gas duct 4. The various guide plates 6 are, overall, arranged in a vertically spaced stepped arrangement having stepped levels descending in the direction towards the collecting duct 8. Each pair of immediately adjacent individual guide plates 6 conveniently overlap each other to a small degree. Waste gas can reach in the interior of the waste gas duct 4 through waste gas openings 5, which are arranged in the same manner as those in Figure 5, i.e. they are located in the vicinity of the bottom of the heating chamber 1. In the interior of the waste gas duct, the waste gas can flow upward to be deflected into a horizontal flow direction by the associated respective guide plate 6, which is disposed in the vicinity of the openings through which the gas has entered the duct 4. In this manner, a horizontal flow, which extends across its entire cross-section and is substantially uniform, is promoted in the interior of the waste gas duct 4 in the direction towards the collecting duct 8. Figure 2 shows a modification of the embodiment of Figure 1. It differs only from that shown in Figure 1 in that the individual guide plates 6a are each connected, in each case at their ends which point away from the collecting duct 8, to a substantially vertically extending partitioning plate 6b. This partitioning plate 6b extends all the way down to the floor of the waste gas duct 4. In this manner, a controlled orientation of the flow of waste gas is encouraged from the outset, since waste gas, which enters between two immediately adjacent partitioning plates 6b, is completely enclosed by the walls of the waste gas duct 4 and by these two partitioning plates 6b, and can flow only through the longitudinally directed space provided between the two guide plates 6a associated respectively with the two partitioning walls 6b, i.e. it must, perforce, flow horizontally. The embodiment of Figure 2 does not, however, in use provide any noteworthy improvement over the embodiment of Figure 1. In an extreme case in the present invention, it would be possible for the waste gas duct to be composed of a plurality of individual pipes, each extending from one of the waste gas openings 5 to the collecting duct 8. In this regard, the concept ofYTIow-conducting body within the scope of the present invention also includes an embodiment of this kind, although it is allocated a lesser priority because of the structural outlay (cost) associated therewith. As a result of the invention, it is possible to alleviate non-uniform flow of waste gas from the interior of the heating chamber 1, as observed previously in a design of the waste gas duct 4 as shown in Figure 8 (or the waste gas duct 4a as shown in Figure 9). With the prior design, pressure drops occurring in the waste gas duct 4, or 4a, resulted in a distinctly stronger flow of waste gas in that part of the heating chamber 1 which was disposed in relative close proximity to the collecting duct 8, than elsewhere in the heating chamber. In the more remote regions of the heating chamber , the flow of waste gas was distinctly weaker, such that heat distribution was non-uniform. The extent to which the concept according to the invention, namely the installation of flow-conducting bodies in the waste gas duct, is effective is shown in the analysis of the flow of waste gas in the form of a flow profile, as illustrated in Figure 3. In this graph, the vertical components of the waste gas flow rate are illustrated (marked as parameter values) in the immediate vicinity of a row of heat exchanger tubes 3 in a cross-section of the heating chamber parallel to the plane of the row of heat exchanger tubes 3. Lines of more or less identical flow rate are recorded, in relation to position L along the length LI of the waste gas duct and in relation to the height H from the bottom of the heating chamber (relative to overall height HI). The negative values of the flow rate show that, in the top part of the heating chamber, in the immediate vicinity of the heat exchanger tubes, the flow of the waste gas is in an upward direcUon from below, since cylindrical fiow streams are formed between adjacent rows of heat exchanger tubes, which flow streams are directed centrally downwardly (in the region of the plane of the burners). It is only in the lower part of the heating chamber that the waste gas flows downwardly over the heat exchanger tubes to the openings in the side wall of the associated waste gas duct. It is clearly to be seen that, in a direction towards the waste gas duct, at a constant height above the bottom of the heating chamber, only very minor differences occur in the vertical component of the flow rate, which is a measure of the intensity of the heat transmission by convection taking place. By contrast, as illustrated in the comparative diagram of Figure 4 which shows a corresponding evaluation for a heating chamber comprising a waste gas duct of the conventional design according to Figure 8, these differences are very pronounced. The bottom right-hand part of this graph represents the region having by far the highest positive (i.e. downwardly directed) vertical velocity component. This means that, at this point in the heating chamber cross-section, i.e. in the immediate vicinity of the of position where the waste gas duct leaves the heating chamber, by far the strongest flow density of waste gas prevails, i.e. that, in this region, a distinctly greater heating of the heat exchanger tubes must take place by the relatively intensive convection, than in the other regions. WE CLAIM: 1. An arrangement for indirectly transferring heat to a flowing process medium, especially for carrying out steam reformation of hydrocarbons, with a heating chamber (1), which can be heated from above by burners (2) arranged in multiple rows and through which run, on vertical longitudinal planes, a plurality of rows of heat exchanger tubes (3) through which the process medium can be conducted, whereby the combustion waste gasses of the burners (2) can be extracted laterally from the heating chamber (1) through waste gas ducts (4) arranged on the floor of the heating chamber (1) parallel to each other and to the rows of heat exchanger tubes (3), and whereby the waste gas ducts (4) are made of refractory-grade material and have a substantially rectangular cross-section constant in the axial direction and are equipped on their longitudinal sides in the region near the floor with openings (5) distributed over their entire axial length for the passage of waste gases out of the heating chamber (1) into the interior of each respective waste gas duct (4), characterized by the fact that to equalize the flow conditions of the waste gas, flow bodies are arranged in the interior of the waste gas ducts (4) in the region of the lower part of the row of heat exchanger tubes (3), and that the flow bodies have, by section, flow baffles (6, 6a) running substantially horizontally, and are arranged in a step-like configuration relative to each other, whereby the step-like form is directed downward in the direction of the lateral output of the waste gas duct (4). 2. The arrangement as claimed in claim 1, wherein the individual directly adjacent flow baffles (6, 6a) partially overlap each other. 3. The arrangement as claimed in any one of the claims 1 or 2, wherein each flow body has a dividing baffle (6b) extending out of the floor at a substantially right angle to the longitudinal direction of the waste gas duct (4), which dividing baffle (6b) is connected to the flow baffle (6a) on the side facing away from the side of the waste gas extraction. 4. An arrangement for indirectly transferring heat to a flowing process medium substantially as herein described with reference to the accompanying drawings.

Documents:

447-mas-96 others.pdf

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447-mas-96 abstract.pdf

447-mas-96 claims.pdf

447-mas-96 correspondence others.pdf

447-mas-96 correspondence po.pdf

447-mas-96 description (complete).pdf

447-mas-96 drawings.pdf

447-mas-96 form-1.pdf

447-mas-96 form-26.pdf

447-mas-96 form-4.pdf

447-mas-96 petition.pdf