MXPA00006395A

MXPA00006395A - High performance heat exchangers

Info

Publication number: MXPA00006395A
Application number: MXPA/A/2000/006395A
Authority: MX
Inventors: Joseph Blanda Paul Jr; Stanley Decourcy Michael
Original assignee: Rohm And Haas Company
Priority date: 1999-06-30
Filing date: 2000-06-27
Publication date: 2001-11-21

Abstract

Disclosed are means for improving the service-life of indirect tubesheet type heat exchangers used in chemical reactors, particularly those exposed to reducing, nitridizing and/or carburizing environments. Such means include the use of certain ferrules (22) within the heat exchange tubes (2) and/or weld types used in construction of these heat exchangers.

Description

High Performance Heat Intervals BACKGROUND OF THE INVENTION This invention relates generally to elements for improving the service life and reliability of indirect heat exchangers used in chemical reaction systems that produce reactive effluent gases. In particular, this invention relates to elements for improving the service life of the indirect heat exchangers used in the production of hydrogen cyanide. In many chemical processes, the reaction effluent comprises, fluids and / or hot gases, reagents and / or abrasives. For many of these reactions, it is desirable to quench the reactor effluent to prevent decomposition of the product component (s). The tempering can be achieved through direct contact, as with the application of water spray, or more commonly through indirect methods such as through the use of indirect heat exchangers. Because indirect heat exchangers provide the added advantage that they can be configured to recover wasted heat, they are the most preferred method and have been used for many years. Typical indirect heat exchangers used in chemical processes consist of an armored design. In many of the systems, the thermal, kinetic and reactive properties of the effluent can serve individually or collectively to corrode, crack or otherwise degrade the materials used to form the heat exchange zone. In particular, the exchange tubes and the welding of the tube to the tubular sheet closest to the reaction zone observe the most severe conditions and those most susceptible to degradation. For example, the hot effluent can chemically react with the metal of the heat exchanger tube, thus causing erosion and / or corrosion, that is, dusting, carburization, and the like, which leads to the failure of the heat exchanger. The welding of the heat exchanger tubes is also susceptible to stress corrosion cracking, which leads to heat exchanger failure, which can be found, for example, in the production of hydrogen cyanide or acrylonitrile, in heat exchangers. for the recovery of nitric acid waste, in hydrocarbon cracking units, and in boilers and exchangers ignited by side tubes.The use of splints as a protective cover for heat exchanger tubes and armored capacitors is well known. They mainly insulate pipes and welds but they also protect the exchange tubes of heat against deterioration resulting from a chemical attack. Typically, heat exchangers are placed downstream of a reaction zone in a chemical reactor, such as a downstream of a catalyst. This is how the upper or upper portion of the heat exchange tubes are exposed to the hot effluent gases. Certain splints, such as alumina, are used to provide insulation against the heat of these gases. In a common application, first an exchange tube of a base material is constructed; a second, possibly different material, selected for its properties, such as resistance to erosion and / or chemical attack, is formed in a tube that slides into the inlet / upstream end of the heat exchanger tube. Depending on the severity of the conditions of the procedure, splints can provide a long period of maintenance-free service, or alternatively, can be sacrificed, requiring frequent replacement. In any case, the use of splints provides an economic method to extend the service life of the base material of the exchanger through the prevention of erosion and / or corrosion. For example, M. James, "Unexpected Metal Dus ting Fai lure of Waste Hea t Boiler Tubes" Unexpected Failure of Metal Dust from Waste Heat Boiler Tubes ", First International Symposium on Innovative Approaches to Improve Reliability, Procedures, and Materials Technology of the Heat Exchanger of the Institute of the Chemi cal Process Industri is, Inc., 1-13 (1998) discloses a ceramic splint designed in an armored reactor for use in a chemical process with reduction conditions, carburization and / or In this document, various nickel-chromium alloys (INCONEL) were used in the tubes of an exchanger, and in each case the INCONEL material experienced a severe waste, that is, metal dusting, at rates much higher than the known rates.Also in U.S. Patent No. 5,775,269 a boiler protective tube assembly with an inner ceramic sleeve, a block d is disclosed e ceramic and an outer ceramic sleeve. The ceramics disclosed in the U.S. Patent. 5,775,269 are aluminum and zirconium oxides. These ceramics were not practical for use in heat exchangers that require rapid tempering of a very hot effluent and these materials only lasted a relatively short time under these extreme temperatures. Ceramics, such as alumina, silica and zirconia, are effective as insulators in reactors such as methane vapor reformers. However, they suffer from poor resistance to thermal shock and can, in the case of silica, react with hydrogen that is present in many reducing environments. See, for example, M.S. Crowel, Reactions of Si l i ci o of Hi reeógeno in Refractarios, -J- * »- * - - ¡g ^ d ^ Ceramic Bulletin, Vol. 46, No. 7,679-682 (1967). This is how these ceramic materials are not suitable for use in chemical processes that require a rapid tempering of hot effluent gases and / or in reducing environments, of which both are in the production of hydrogen cyanide. In the typical armored reactor, the tubes of the heat exchanger are joined to a tubular sheet at each end of the tube. Typically, a tube passes through a hole in the tubular sheet until the end of the tube is approximately flush with the upper surface of the tubular sheet. Then, the tube is typically welded to the upper surface of the tubular sheet. Generally, the outer diameter of the tube is smaller than the inner diameter of the hole corresponding to the tubular sheet. This is how once the tube is welded to the tubular sheet, an annular space remains between the tube and the tube sheet under the weld. The Figure shows a typical solder 3 used in armored reactors, especially reactors used for chemical processes that have reducing environments, such as in the production of hydrogen cyanide. These tubes can also be fixed to the tubular sheet through alternative elements, such as rolling. Figure Ib shows a typical union of a tube to a tubular sheet through coiling. In the production of hydrogen cyanide, the hot effluent gases should be rapidly cooled from about 1000 ° to 1400 ° C to about 600 ° C or less, in order to prevent the decomposition of hydrogen cyanide. While these effluent gases cool the tubular sheet, the weld and the upper portion of the exchange tubes become very hot. As a result, any water that is present in the annular space 5 vaporizes and deposits any impurities contained in the water within the annular space 5. These impurities are typically ions and minerals in the water and the like. These impurities are also typically corrosive to the tubular sheet, the exchange tube, and particularly the weld. Over time, these corrosive materials accumulate in the annular space 5. The combination of the heat of the effluent gases and the corrosive materials with - ^ ^. ^, A.-a. ^, > .-- ^.-a, -, - -. - ... - ... ^^^ iñ ^ í ???? t ^^. | -___ ^ __ L efforts in the system leads to stress corrosion cracking in the pipe, weld and / or tubular sheet. This cracking by stress corrosion leads to failure and finally to the replacement of the heat exchanger. A number of designs of reactors for armored hydrogen cyanide have been developed to address the problem by minimizing the heat to which the tube plate, exchange tubes and welding are exposed. Figures 3A-E illustrate these reactors. Each of the reactors is designed with high rates of cooling water flow, turbulent cooling water flow, and refractories to insulate the tube plate. However, these designs do not completely prevent this cracking by stress corrosion. The welds at the bottom of the hole, or the full penetration welds, have been used in chemical processes that do not have reducing environments or so rapid tempering requirements. For example, Ahmed et al., Failure, Repair and Replacement of a Waste Heat Boiler, Safety of the Ammonia Plan and Relined Ins ta llations, American Institute of Chemical Engmeers, vol. 37, 100,110, discloses the use of a weld in a horizontal heat exchanger for use with a secondary ammonia reformer. This document does not disclose the use of this welding for any other procedure. It is thus, the problem to provide effective heat exchangers that have a long service life in the armored reactors used in chemical processes that have remnants of reducing environments. SUMMARY OF THE INVENTION It has been surprisingly found that the service life of heat exchangers in armored reactors for hydrogen cyanide can be extended by using a splint, particularly a splint that includes silicon nitride, and / or by using a precipitate weld to secure the heat exchange tubes to the tube plate. One aspect of the present invention is directed to a heat exchange apparatus for use in the reduction of a reducing, carbuporing and / or nitrifying environment, including: (1) a - - - ».. ~. ~. meuUlife iiM? i ^ coating having an inlet portion of the tubular sheet and an outlet portion of the tubular sheet, each of the tubular plates has a plurality of holes, where the coating has at least one intake and one mouth output for the heat exchange medium; (b) a plurality of tubes disposed within the cover where an inlet end of each of the tubes is fixed to the tubular inlet and outlet end of each of the tubes is fixed to the tubular outlet sheet that an ee of the tube and an axis of an inlet and outlet hole of the tubular sheet are coincident; and (c) a plurality of ferrules, wherein each of the ferules have an inlet end and an outlet end that extend through the inlet of the tubular sheet into a tube where the outlet end extends below the tubular inlet sheet, in which the ferrule includes silicon meter. In a second aspect, the present invention is directed to a heat exchanger apparatus that includes: (a) a coating having an inlet portion of the tubular sheet and a portion The output of the tubular sheet, each of the tubular sheets has a plurality of holes, where the coating has at least one intake and an outlet for the heat exchange medium, - (b) ) a plurality of tubes disposed within the coating where an inlet end of each of the tubes is fixed to the tubular inlet sheet and an outlet end of each of the tubes is fixed to the output tubular sheet in such a way that a tube axis and an axis of one of the inlet and outlet holes of the tubular sheet are coincident, each tube being formed of a metal including a nickel and chromium alloy; and (c) a plurality of splints, wherein each of the splints has an inlet end and an outlet end that extends through one of the inlet orifices of the tubular sheet into a tube where the The outlet end extends below the tubular inlet sheet, in which the splint includes a nickel-chromium alloy. In a third aspect, the present invention is directed to a splint for use within a heat exchange tube, where the splint * ~ * ** ~ * - ~. ... .... - ...... - - *? * ^ Mto¿ ^ -i- [| it has an entrance end and an exit end; the inlet end has a conically tapered opening within a pipe section, in which the outside diameter of the inlet end is larger than the inside diameter of the heat exchange pipe; the pipe section has an outer diameter of up to 99% of the inside diameter of the heat exchange pipe; The pipe section has an extended area with an outside diameter that is substantially equal to the inside diameter of the heat exchange pipe. In a fourth aspect, the present invention is directed to a splint for use within a heat exchange tube, wherein the splint has an inlet end and an outlet end; the inlet end has a conically tapered or trumpet-shaped opening within a pipe section, the outside diameter of the inlet end being greater than the internal diameter of the heat exchange pipe; the section of the pipe has an outer diameter that is substantially the same as the inner diameter of the heat exchange pipe; and where the splint has a venturi-shaped design in the longitudinal cross section.

In a fifth aspect, the present invention is directed to a heat exchanger apparatus for use in a hydrogen cyanide reactor that includes; (a) a coating having an inlet portion of tubular sheet and an outlet portion of tubular sheet, in which each of the tubular sheets? they have a plurality of holes, where the coating has at least one intake and outlet for the heat exchange medium; and (b) a plurality of tubes disposed within the shell where an inlet end of each of the tubes is attached to the tubular inlet sheet and an outlet end of each of the tubes is attached to the tubular outlet sheet in such a way that an axis of the tube and an axis of an entrance orifice and an exit orifice of the tubular sheet are coincident, where each of the entrance ends of the tube is joined to the tubular entrance foil through welding of precipitate. In a sixth aspect, the present invention is directed to an apparatus for preparing hydrogen cyanide by reacting a hydrocarbon, ammonia and optionally a gas containing oxygen -kA-tthiÉ - diél in the presence of a catalyst containing platinum at a temperature in the range of 100 ° C to 1400 ° C, including a reaction zone, an optional refractory zone, and a heat exchange zone that it includes: (a) a coating having a portion of tubular inlet sheet and a portion of tubular outlet sheet, wherein each of the tubular sheets has a plurality of holes, wherein the coating has at least one outlet admission and an outlet for the heat exchange medium; (b) a plurality of tubes disposed within the coating where an inlet end of each of the tubes is fixed to the tubular inlet sheet and an outlet end of each of the tubes is fixed to the tubular output sheet such that a tube axis and an axis of the inlet and outlet hole of the tubular sheet are coincident; and (c) a plurality of splints, wherein each of the splints has an inlet end and an outlet end that extends through an inlet opening of the tubular sheet into a tube where the outlet end it extends below the tubular entrance foil, in which the ferrule includes silicon nitride.

In a seventh aspect, the present invention is directed to a process for preparing hydrogen cyanide which includes the steps of: feeding reaction gas to a reactor, wherein the reaction gas includes a hydrocarbon, ammonia and optionally a gas that contains oxygen; by reacting the reaction gas in the presence of a catalyst to give product gas; cooling the product gas in a heat exchange apparatus including (a) a coating having a tubular sheet inlet portion and a tubular sheet outlet portion, wherein each of the tubular sheets has a plurality of holes, wherein the covering has at least one intake port and an exit port for the heat exchange medium; (b) a plurality of tubes disposed within the coating wherein a feeler end of each of the tubes is fixed to the tubular inlet sheet and an outlet end of each of the tubes is fixed to the tubular output sheet such that one axis of the tube and one axis of an inlet and one outlet of the tubular sheet are coincident; and (c) a plurality of splints, wherein each of the splints has an inlet end and an outlet end that extend through an inlet opening of the tubular sheet into a tube where the outlet end it extends below the tubular entry sheet, in which the ferrule includes silica nitride; and recover the hydrogen cyanide from the cooled product gas. BRIEF DESCRIPTION OF THE DRAWINGS The Figure shows the schematic cross section of a typical exchange tube towards a tubular sheet weld used in hydrogen cyanide reactors having an exaggerated annular space. Figure Ib shows a schematic cross section of an exchange tube wound to a tubular sheet connection having an exaggerated annular space. Figure 2a shows a schematic cross section of a tubular sheet and a fixed exchange tube through a precipitate weld having an exaggerated annular space. Figure 2b shows a schematic cross-section of a tubular sheet and an exchange tube located for a precipitate weld aJjUttíÁiiíllí-i- gÜ &gj g that has an exaggerated annular space. Figures 3a to 3e show a schematic cross section of designs of a heat exchanger of a reactor for hydrogen cyanide. Figure 4a shows a schematic cross-section of a ferrule providing a gas insulating space. Figure 4b shows a schematic cross section of a ferrule having a tapered inlet end and a diameter expanded in one of the sections of the pipe. Figure 5 shows a schematic cross-section of a ferrule having a tapered inlet end and a straight outlet end. Figure 6 shows a schematic cross-section of a splint having a convergent / divergent design. Figure 7 shows a cross section of a splint having a straight hollow. Figure 8 shows a cross section of a coating and a tube heat exchanger including ferrules and sleeve ferrules. Figure 9 shows a cross section ^ - - ^^ J ^ - ^ »- ^ -..-. schematic of a two-splint system with a ferrule sleeve in a heat exchange tube. Detailed Description of the Invention As used throughout the specification, the following terms should have the following meanings, unless the context clearly indicates otherwise. The terms "heat exchange units" and "heat exchange containers" are used alternately. The terms "first" and "second" and "upper" and "lower" and "input" and "output" respectively are used alternately, although it is recognized that the reactor may have a vertical, horizontal or other configuration in which the terms "superior" and "inferior" are not apt to describe the relationship of the components to each other. The term "inlet" refers to the portion of the heat exchange apparatus that is closest to the reaction zone, that is, where the process gases enter the heat exchange apparatus. The term "output" refers to the portion of the heat exchange apparatus that is farthest from the reaction zone, that is, where the hot process gases exit the apparatus. heat exchange. The following abbreviations are used through the specification: C = Celsius and cm = cm. All ratios and quantities are by weight, unless otherwise indicated. All numerical ranges are inclusive, unless noted otherwise. The present invention provides a solution to the problem of short service life of shell and tube heat exchangers through the use of specific ferrules and / or welds. Preferably, the design of the ferrules of the present invention further serve to minimize the potentially damaging effects of the effluent flow rate of the reactor. In addition, the design of the heat exchanger and the use of welds down in the fixing of the exchange tubes to the tubular sheet of the apparatus simplifies the construction, maintenance and repair of the unit, minimizing idle time and increasing efficiency operative The weld of precipitate also eliminates the annular space between the exchange tube and the tubular sheet that can be used with a gap for ^ m ^ tma To concentrate corrosive agents. This is how the present invention is useful for extending the service life of any shell and tube heat exchanger. The ferrules and welds of the present invention are particularly useful for coating and tube heat exchangers that are exposed to hot reactive effluent gases, and preferably where the heat exchanger is exposed to a reducing, carbuporing or nitrifying environment, as in production of hydrogen cyanide. There are numerous designs of heat exchangers suitable for use with reactors that produce reactive effluent flow, high temperature and high abrasion. Particularly in connection with the production of hydrogen cyanide, the need to temper the hot process gases has been widely appreciated. When tempering the hot process or the effluent gases it means to cool the gases sufficiently in such a way that the products contained there do not degrade. For example, it is well known in the production of hydrogen cyanide that if the hot process gases are not cooled sufficiently, the hydrogen cyanide present will be degraded. Typical heat exchange units or containers, useful in the production of hydrogen cyanide, are illustrated in Figures 3a to 3e. These units have the following elements that are identified with a similar number in each of the figures: hot process gas inlets 1, cooled procedure gas outlets 6, Inlet 7 of cooling water of the exchanger, outlet 8 of cooling water of the intercalator, fan 9 of the tubular sheet, tubular sheet 4, heat exchange tubes 2, heat exchange container 10, reaction container 11, and refractory material 12. Refractory material 12 protects the tubular sheet from direct exposure to hot process gases. The arrows indicate the direction of the flow of the gases or the cooling water. The unit of Figure 3a is configured in such a way that the lower portion of the reactor container will extend inside and is surrounded by the heat exchange container. This allows the outlets of the cooling water to be placed above the level of -SHUa -. ^. ^. ^. ^. I »... ,,. . ... - ,. . ,. ..... .. ^ .. ^^ ^. ». ^,. splice the exchange tubes and the tubular sheet. The tubular sheet forms a convex inner upper surface of the heat exchange container. The flow of process gases down and through the exchange tubes that are surrounded by the cooling water. The exchange tubes pass through the tubular sheet and are welded to the tubular sheet using conventional solders in the interface between the upper tab of the exchange tube and the lower surface of the tubular sheet. The heated water and the bubbles formed there during the tempering of the hot process gases are generally directed away from the exchange tubes towards the cooling water outlet ports. The unit of Figure b has a flat tubular sheet, generally of relatively large thickness. Process gases pass through the tubular sheets and down into the exchange tubes. The cooling water enters the heat exchange container from the bottom and primarily exits through the outlet mouth of the cooling water in the upper portion of the container. The tubular sheet contains the integral channels that allow the cooling water to flow through them horizontally. There are also the fans of the tubular sheet of the exchanger placed in the upper part of the container, above the main outlet, which receives the water from the channels of the tubular sheet. These fans are designed to remove hotter water and bubbles that enter there. The unit of Figure 3c uses the reverse orientation for the output flow of the heat exchange medium. The tubular sheet is in the annular shape with the exchange tubes extending from there. The outlet of the cooling water is in the center of the ring and transports the heated water up and out of the heat exchange container through the center of the reaction vessel. The cooling water inlet intakes are located at the bottom of the heat exchange container. The upward flow of water is cooling, and the preferred slope of the tubular sheet, with an upward angle in the direction of the cooling water outlet, promotes the removal of heated water and the bubbles that enter from the sheet tubular and exchanger tubes. The unit of Figure 3d provides a tubular sheet with a flat top surface and forming a concave upper surface of the heat exchanger container. The cooling water enters the container of the heat exchanger towards the upper portion of the container and exits through the outlet mouth of the cooling water near the base of the container. The placement of the intake and outlet mouth, as well as the concave roof of the container container tends to direct the cooler water towards the surface of the tubular sheet and the exchanger tubes emerge from the tubular sheet. The fans of the tubular sheet of the exchanger with outlets placed near the vertex of the container serve to remove the heated water and bubbles away from the tubular sheet and the exchange tubes. In each of the units illustrated in Figures 3a to 3d, the process gases flow down through the units. In the In the unit of Figure 3e, the process gases flow upwards. In this orientation, the reaction container is located below the heat exchange container. The gases flow upwards passing the refractory material through the tubular sheet and into the exchange tubes. The cooling water enters the heat exchange container at the bottom of the container just below the tubular sheet, and is removed from one. outlet mouth near the top of that container. As a result of this, heated water and gas bubbles, such as vaporized water, rise to the surface of the container, which is remote from the tubular sheet. However, the solids in the cooling water, especially the minerals, can precipitate and accumulate on the exposed upper surface of the tubular sheet. These mineral deposits create localized hot spots that promote the degradation of the tubular sheet, the exchange tubes and the welds of the adjacent tubular sheet, to it. An advantage of this design is that the formation of the gas layer adjacent to the tubular sheet, that is, the heat exchange barrier is minimized.

The cooling efficiency of the shell and tube heat exchangers, such as those shown in Figures 3a to 3e, can be improved through the use of baffles within the hull. These reflectors direct the flow of the heat exchange medium inside the helmet. The size, shape and placement of baffles inside the hull are specific to the design of the particular heat exchanger used. This design and placement of the deflector is within the skill of a person skilled in the technology and the deflectors can allow the water intake (s) and the outlet (s) to be reversed if is desired It will be appreciated that more than one heat exchanger can be connected in series, which can increase the cooling of the reactor effluent. In armored heat exchangers, the tubular sheet is typically about one-eighth of an inch (0.3 cm) to twenty inches (50 cm) thick. These tubular sheets are typically made of carbon steel, stainless steel, nickel alloys, nickel and chromium alloys, nickel and molybdenum alloys, and the like. In The heat exchanger tubes have a nominal diameter typically of the order of 0.5 inches (1.2 cm) to 2 inches (5 cm). The heat exchange tubes can have any length that allows the cooling of effluent gases or liquids. The length of the heat exchange tubes may vary depending on the design of the heat exchanger, the diameter of the tube, the flow of the cooler and the like. Thus, the length of the tube for a particular reactor design is within the skill of a person skilled in the technology. Typically the lengths of the tubes are in the range of 4 feet (1.2 m) to 30 feet (9 m). Tubes useful in armored heat exchangers are typically made of carbon steel, stainless steel, nickel alloy, nickel-chromium alloy, nickel-molybdenum alloy, and the like. It is preferred that the heat exchange tubes are made of carbon steel or nickel-chromium alloy. Nickel-chromium alloys suitable for use in heat exchange tubes contain 40 to 80% nickel and 12 to 28% J ^ -aM ** ^ - of chromium. The nickel-chromium alloys may optimally contain one or more other components, such as carbon, silicon, manganese, copper, sulfur, cobalt, aluminum, iron, titanium, boron, phosphorus, molybdenum, or niobium. Suitable commercially available alloys include those marketed under the INCONEL brand, available from Special Metals Corporation (New Hartford), NY) . INCONEL alloys include, but are not limited to INCONEL 600, INCONEL 601, INCONEL 617, INCONEL 625, INCONEL 718, INCONEL X-750, INCONEL 751 and INCONEL MA 754. It is preferred that the nickel-chromium alloy used in the tubes heat exchange contain 71-75% nickel, 15-17% chromium, 7-11% iron, 0.2-0.35% manganese, 0.2-0.35% silica, 0.1-0.3% copper, 0.003-0.04 % ca and 0.001-0.01% sulfur. The preferred nickel-chromium alloy which is suitable includes INCONEL 600. It is even more preferred that the tubular sheet and the heat exchange tubes are made of the same material. The gases of the hot process and / or the fluids passing through the heat-armored heat exchanger can be cooled by any means for heat exchange. This medium enters the ^^. «. ^. W ^ a. . . ...to". -... ^ ü ^^ - a- ^ a ^^ helmet through at least one intake intake, passes along the heat exchange tubes, and leaves the case through at least one exit mouth. The suitable heat exchange element is any that removes heat from process gases and / or fluids. The element of heat exchange suitable, but not limited, is: water, a mixture of water and steam, molten salt, glycol, a mixture of water and glycol, oil, as a natural or synthetic oil, gases, such as air and water. of process gas, and the like. The Figure illustrates a typical weld used to secure the heat exchange tubes to the tubular sheet in the heat-armored heat exchangers, such as those shown in Figures 3a to 3e. The figure has the following elements: hot process gas inlet 1, heat exchange tube 2, weld 3, tubular sheet 4, annular space 5, and cooled process gas outlet 6. The annular space 5 extends through the tubular sheet and terminates at the lower surface of the weld 3 which secures the exchange tube 2 to the tubular sheet 4. While the water = --- • - - - - - r. . ^. ^ .. .M ^, .. ^^^^^^ M? J1l¡? ^ I ?? i ^ ,. cooling between the annular space 5, vaporizes, and deposits any impurities contained in the water within the annular space 5. These impurities are typically ions and minerals in water and the like. These impurities are also typically corrosive to the tubular sheet, the exchange tube, and particularly the weld. Over time, these corrosive materials accumulate in the annular space 5. The heat combination of the effluent gases and the corrosive materials together with the stresses in the system lead to stress corrosion cracking in the tube, welding and / or the tubular sheet. The heat treatment of the welding area minimizes the potential for corrosion cracking with stress in welding, particularly in nickel and chromium alloy welds. However, this heat treatment does not eliminate stress corrosion cracking in the tubes and / or in the tubular sheet. Corrosion cracking with stress leads to failure and ultimately replacement of the heat exchanger. Other methods are known for fixing the exchange tubes to the tubular sheets, such as tí¡aj s¡á¡ í¡¡mM rolled. In winding, one end of the heat exchange tube is wound into an equalizing groove within the hole in the tubular sheet. Figure Ib shows a typical coiled connection of an exchange tube to a tubular sheet. These winding methods are well known to those skilled in the art. When a tube is attached to a tubular sheet through the coil, a small annular gap 5 remains between the exchange tube 2 and the tubular sheet 4 which can also result in stress corrosion cracking. This winding can be combined with welds as shown in Figure 1 to obtain additional mechanical strength. However, this combination does not eliminate stress corrosion cracking. The heat exchange containers used in reactors that have hot reactive process gases, such as hydrogen cyanide reactors, have been designed to minimize these stress corrosion cracks. For example, each of the heat exchange containers illustrated in Figures 3a through 3d have a design that facilitates cooling - * --- "-'-» -''-- of the effluent gases Each of the designs provides high rates of water flow for cooling, a flow of water for turbulent cooling and an optional refractory to isolate the sheet tubular top of the hot effluent gases, by efficiently cooling the effluent gases, these designs reduce the corrosion rate. However, these designs do not eliminate corrosion. The upstream orientation of the unit of Figure 3e reduces the particular problem mentioned above, that is, the concentration of corrosive agents in the annular space, since hot water and steam rise away from the tubular sheet, and the welds of the exchange tube. However, these configurations still suffer from the effect of mineral deposits and other precipitating agents in the cooling water. These materials can also find their way into the gap between the openings of the tubular sheet and the exchange tubes and cause damage to the components as well as welding. Therefore, the designs of the known heat exchange containers used in the reactors having hot reactive process gases do not solve the problem of the concentration of corrosive materials, and thus do not solve the problem of stress corrosion cracking. . The down-welding of the present invention significantly reduces stress corrosion cracking in heat exchangers having hot reactive process gases, such as hydrogen cyanide reactors, nitric acid waste recovery exchangers and acrylonitrile reactors. Figure 2a has the following elements: hot process gas inlet 1, heat exchange tube 2, welding 48, tubular sheet 4 and cooled process gas outlet 6. in a precipitate weld, the part The top of the heat exchange tube is fixed to the lower side of a tubular sheet with a full penetration weld. This is how the annular space is eliminated and the concentrations of corrosive materials are significantly reduced. The use of downward welds greatly increases the service life of armored heat exchangers, particularly those used in the production of hydrogen cyanide, by reducing cracking by stress corrosion. Precipitate solder is preferably used in reactors having heat exchange units as illustrated in Figures 3a to 3e, and more preferably as illustrated in Figures 3a to 3d. The precipitate solder useful in the present invention can be formed through any conventional element, such as that described in U.S. Patent No. 4,221,263. It will be appreciated that the exchange tubes can be adjusted to a variety of ways for welding the tubular sheet. For example, the tubes can be fitted within a widening or plug in the lower surface of the tubular sheet and can be welded from the inside of the tube to the tubular sheet or outside the tube to the lower surface of the tubular sheet. See, for example, U.S. Patent No. 4,221,263. It is preferred that the precipitate solder used be that illustrated in Figure 2a.

In the preparation of the downstream weld preferably of the present invention, an orifice with a diameter m is almost completely pierced through the tubular sheet together with an y-axis, see FIG. 2b. A smaller hole is then drilled with a diameter n through the remainder of the tubular sheet along the y-axis. The diameter n is sufficiently long that the exchange tube 2 can be inserted through the hole. The exchange tube is then inserted into the tubular sheet in such a way that the x-axis of the exchange tube and the y-axis of the orifice of the tubular sheet are coincident. The exchange tube 2 is inserted into the orifice of the tubular sheet at the distance p from the lower face of the tubular sheet. The distance p is equal to the length of the hole in the tubular sheet having the diameter n. The distance p can be of any length that provides a sufficient area to weld the tube to the tubular sheet. Typically, the distance p is less than half the thickness of the tubular sheet. Once the tube is inserted into the tubular sheet, a full penetration weld is formed between the tube and the tubular sheet through any conventional element. It will be appreciated by those skilled in the art that the holes in the tubular sheet having diameters m and n can be made in one or more perforation steps. The down welds of the present invention are typically heat treated. In these heat treatments, the weld and the surrounding metal area are heated. The heat treatment methods used are the correct ones for these welded metals in particular. These heat treatment methods are well known to those skilled in the art. The reactor components are also subject to thermal, chemical and physical destructive agents resulting from them. various chemical procedures used. Heat exchange tubes are particularly exposed to these agents. For example, in the production of hydrogen cyanide, the produced hydrogen cyanide gas must be rapidly cooled in order to minimize degradation. In these reactors, the unit and heat exchange is placed as close to the catalyst and reaction zone as possible. Thus, the upper portion of the heat exchange tubes, that is, the nearest portion of the catalyst and the reaction zone, is continuously exposed to the hot, reactive, effluent gases which have a reducing environment, carburization and / or nitrurization. The optional refractory material, such as ceramic, is placed on the upper surface of the tubular sheet, that is, the closest to the catalyst and to the reaction zone. This optional refractory material isolates the tubular sheet from the heat of the reaction. However, this optional refractory material typically does not cover heat exchange tubes, which is thus exposed to heat and chemical species generated by the reactor. One approach to increasing the service life of heat exchangers exposed to harsh environments is to isolate the heat exchange tubes, typically by placing ceramic splints through the tubular sheet into the upper end of the tubes. heat exchange. These splints typically only protect the tubes from heat, but not necessarily from the chemical and physical agents. For example, ceramic splints of silica, alumina and zirconia are known to provide thermal protection. However, these splints do not provide adequate protection against chemical and physical agents under harsh environments of hydrogen cyanide reactors, nitric acid waste recovery exchangers, acrylonitrile reactors, side flame tube heaters, exchangers of lateral flame tubes or catalytic stills. Under these environments, splints typically used, include known ceramic splints, such as sacrificed, meaning that they are degraded and should be monitored and replaced on a regular basis. Another approach to increasing the service life of heat exchange tubes exposes that these harsh environments is to manufacture the exchange tubes of an alloy resistant to the reactor environment, such as nickel chromium alloys. However, heat exchanger tubes made of nickel-chromium alloys are still susceptible to these problems since the metal is powdered.

It has been surprisingly found that using ferrules including the nickel-chromium alloy or silicon nitride greatly increases the service life of armored heat exchangers, particularly those used in the production of hydrogen cyanide. It is preferred that the splints useful in the present invention include silicon nitride. Suitable nickel-chromium alloys for use in the ferrules of the present invention are those disclosed in U.S. Patent No. 5,354,543, or any other commercially available alloy. It is preferred that the nickel-chromium alloys useful in the present invention contain from 40 to 80% nickel and from 12 to 28% chromium. The nickel-chromium alloys may optionally contain one or more other components, such as carbon, silicon, manganese, copper, sulfur, cobalt, aluminum, iron, titanium, boron, phosphorus, molybdenum or niobium. Suitable commercially available nickel-chromium alloys useful in the present invention include those sold under the trademark INCONE, available from Special Metals Corporation (New Hartford, New York). INCONE alloys include, but are not limited to INCONEL 600, INCONEL 601, INCONEL 617, INCONEL 625, INCONEL 718, INCONE X-750, INCONE 751 and INCONEL MA 754. It is preferred that the nickel-chromium alloy contains 71- 75% nickel, 15-17% chromium, 7-11% iron, 0.2-0.35% manganese, 0.2-0.35% silica, 0.1-0.3 copper, 0.003-0.04% carbon and 0.001-0.01% of sulfur. The preferred nickel-chromium alloy which is suitable includes INCONEL 600. The silicon nitride ferrules useful in the present invention are any which include silicon nitride (Si3N4) or silicon nitride alloys. Suitable materials of silicon nitride useful in the ferrules of the present invention include, but are not limited to: silicon nitride, ceramics containing silicon nitride barbels or silicon nitride alloys. Suitable ceramics containing silicon nitride barbels include, but are not limited to: alumina, zirconia, and the like. Any silicon nitride alloy is suitable for use in the present invention. These silicon nitride alloys include those containing up to 5% carbon, such as those disclosed in U.S. Patent No. 4,036,653, incorporated herein by reference to the extent that it teaches the preparation of these silicon nitride alloys. It is preferable that the silicon nitride splint contains at least 95% silicon nitride (Si3N4), and more preferably at least 97% silicon nitride, and even more preferably at least 99% silicon nitride. Additionally it is preferred that the silicon nitride be hot pressed during manufacture. The ferrules of the present invention can have any shape that fits into a heat exchange tube of an armored heat exchanger. Thus, it will be appreciated by a person skilled in the art that the outer diameter of the ferrule is smaller than the inner diameter of the heat exchange tube. The external diameter of the splint can be in any of its parts of substantially the same diameter as the inner diameter of the exchange tube in such a way that a comfortable fit is provided to one significantly smaller than the inner diameter of the tube and exchange so that a very loose fit is provided. A person skilled in the technology will be able to easily determine the outer diameter of the splint that is necessary for a particular heat exchange tube design. By substantially the same it is meant that an outer diameter of a splint or any part thereof that is small enough to fit within an exchange tube or an orifice of a tubular sheet while providing an effective seal between the splint or part of the same and the exchange tube or the orifice of the tubular sheet. The splints of the present invention typically have a nominal diameter in the range of 0.5 to 2 inches (1.2 to 5 cm) and preferably 0.75 to 1.75 inches (1.9 to 4.4 cm). The splints of the present invention are inserted into the heat exchange tubes such that the upper surface of the inlet ends of the splints, that is, the ends closest to the reaction zone of the reactor are at least flush with the upper surface of the input tubular sheet. It is preferred that the inlet ends of the ferrules of the present invention extend over the upper surface of the tubular sheet. It is further preferred that the ends of the splint inlets extend over the optional refractory layer. When employed, this refractory layer is typically 1 to 24 inches (2.5 to 60 cm) in thickness. By extending the splint above the optional refractory layer, the erosion of the optional refractory layer by the hot effluent is reduced. Thus, the length of the splint depends on the design of the heat exchanger and the amount and type of refractory material used, if any. It will also be appreciated by any person skilled in the art that the splint is mounted or inserted into an exchange tube in such a way as to prevent the splint from sliding down the tube, that is, away from where the protection provided needed. It is preferred that the inlet end of the ferrules of the present invention, which is the end closest to the reaction zone of the reactor, has elements for holding the ferule in place. Suitable fasteners include, but are not limited to: tabs, tabs, trestles, flares, flanges, clamps or the like. It is preferred that the ferrules of the present invention have a flared or tapered inlet tongue or end. The ferrules of the present invention must have a length at least equal to the thickness of the tubular inlet sheet used in the heat exchanger. Otherwise, the length of the splint is not critical. If the splint is a sacrificial splint, meaning that it is expected to wear during use, it is preferred that the splint be longer than necessary to prolong the operating time of the reactor before having to replace the splint. The actual length of the splint depends on the effluent gases in the reactor as well as the design of the heat exchanger, and this is within the capacity of a person in the technology. It is preferred that the ferrules of the present invention have a length sufficient to extend below the tubular sheet. It will be appreciated that the more efficient the cooling medium, the shorter the length of the splint that extends below the tubular sheet. It is preferred that the splint extends from 0.5 to 4 inches (1.2 to 10 cm) below the tubular sheet. Typically, splints useful in the present invention have a general length in the range of 1 to 30 inches (2.5 to 76 cm), preferably 2 to 20 inches (5 to 50 cm). The ferrules of the present invention can be used as they are or can be wrapped with an additional insulator layer. Any material of the fiber type with low thermal conductivity is suitable for use as an insulating wrapper. Suitable insulation includes, but is not limited to: alumina, zirconia, silica and the like. This insulation can be in the form of blanket, gauze, tape and the like. For example, suitable insulation includes silica paper, Fiberfrax®-Durablanket manufactured by Unifrax Corporation of Niagara Falls, New York, and Altra® Refractory Blanket of Rath Performance Fibers, Inc., of Wilmington, Delaware, and the like. Suitable splint designs are illustrated in Figures 4 to 7. These splints have the following elements that are identified by similar number in each figure: inlet end 13, outlet end 14, hot process gas inlet 15, and outlet of cooled process gas 16. Arrows indicate the direction of gas flow. Splints suitable for use in the present invention include those that have an insulating design. These insulating ferrules have an inlet end and an outlet end; the inlet end has a conically tapered opening within the section of the pipe, the outside diameter of the inlet end is larger, than the inside diameter of the heat exchange pipe; the pipe section has an outside diameter that is not more than 99% of the inside diameter of the heat exchange pipe; The pipe section has an area that expands with an outside diameter that is substantially the same as the inside diameter of the heat exchange pipe. Examples of alternative embodiments of the insulating ferrules are illustrated in Figures 4a and 4b. The ferrules of Figures 4a and 4b have a tapered inlet end 13 having an outer diameter q which is generally larger than the inner diameter of the heat exchange tube or the hole of the corresponding tubular sheet and is thus subject the splint in position. The ferrules of Figures 4a and 4b have sections of tubing having a length t and an outside diameter r that is up to 99% of the inside diameter of the heat exchange tube. In Figure 4a, the expanded area is the exit end 14 and has an outer diameter s that is substantially the same as the inner diameter of the heat exchange tube such that an effective seal is formed around the splint when Place in the heat exchange tube. In Figure 4b, the ferrule has an expanded area 38 disposed between the section of the pipe and the outlet end 14. The expanded area 38 has an outside diameter s that is substantially the same as the inside diameter of the heat exchange pipe. in such a way that an effective seal is formed around the splint when it is placed in the heat exchange tube. In Figure 4b, the exit end 14 is a distance d from the expanded area. This distance d is not critical. It will be appreciated by someone skilled in the art that the expanded area of the insulating ferrules of the present invention can be arranged anywhere along the length of the ferrule. The closer the expanded area is to the entrance end, the shorter the insulation layer will be. More than one expanded area can be arranged along the length of the splint. The expanded areas of the insulating ferrules of the present invention can be bulbous projections, trestles, tabs, flanges, flares, and the like. When the expanded area is not at the outlet end, it is preferred that the ends curve slightly inward, as shown in Figure 4b. This inwardly curved end is particularly useful as an outer splint in a two-splint system. These expanded areas may be integrated with the splint or may be separate components that are subsequently fixed, such as by cementing the splints before placing them in an exchange tube. The insulating ferrules of the present invention have the advantage of trapping the gas in an annular space defined by the outer pipe section of the ferrule and the inner wall of the pipe. This trapped gas provides an insulating layer to protect the heat exchange tube, and possibly the hole and the weld of the tubular sheet, from the heat of the process gases. The width of the annular space is equal to the difference between the outer diameter of the section r of the ferrule pipe and the inner diameter of the heat exchange pipe. It is preferred that the pipe section of the insulating ferrules of the present invention have an outside diameter in the range of 85 to 99% of the inner diameter of the heat exchange tube, and preferably in the range of 90 to 98%. The insulating ferrules of the present invention may be of any metal, including bimetallic, ceramic or metal ceramic coating. Suitable metals or ceramics include, but are not limited to: nickel-molybdenum alloy, nickel-chromium alloy, silicon nitride, zirconia, alumina, carbon steel, 300 series stainless steel, 400 series stainless steel, monel and the like. Preferred metals or ceramics include silicon nitride, carbon steel or nickel-chromium alloy. If the outer surface of the ferrules of the present invention have a convergent / divergent shape, it will be appreciated that these can also provide an annular insulating space for the trapped gas, equivalent to that illustrated in Figures 4a and 4b. In another embodiment, the ferrules of Figures 4 and 4b can be wrapped with insulators along the length of the pipe section t. Any suitable fiber type material can be used as insulation for the splints as described above. This sheath can increase the insulating capabilities of the splint. The splint of Figure 5 has a conical entrance with an outside diameter q that is generally greater than the inside diameter of the heat exchange tube or the hole of the corresponding tubular sheet and thus holds the splint in place. The tubing section of the splint has the same diameter as the outlet end 14 having an outside diameter s that is substantially the same as the inside diameter of the heat exchange tubing. The inner diameter u of the pipe section is uniform along the length of the pipe section. The silicon nitride splints useful in the present invention and having the general shape illustrated in Figure 5 are generally available commercially as sandblasting or abrasive nozzles, such as those from Ceradyne, Inc. (Costa Mesa, California). Figure 6 shows an embodiment of a venturi splint having a conical entrance end 13 with an outside diameter q that is generally greater than the inside diameter of the heat exchange tube or the hole of the corresponding tubular sheet and this is how you hold the splint in position. The tubing section of the splint has the same outer diameter as the outlet end 14 having an outside diameter s that is substantially the same as the inside diameter of the heat exchange tubing. The inner diameter of the pipe section is gradually increased from the base of the tapered inlet end to the outlet end 14. The inner geometry of the ventup shaped splints of the present invention is that of a converging / diverging nozzle. In these venturi-shaped splints, the inlet end may be conical or trumpet shaped, and preferably conical. In venturi-shaped ferrules, which have a tapered end, the cone angle is typically in the order of 19 to 23 degrees. The diverging angle in the venturi-shaped ferrules of the present invention is typically less than 30 degrees. The diverging angle is preferably of the order of 5 to 7 degrees. These Venturi splints have the advantage of minimizing the erosion of the tube wall by reducing turbulence in the gases and / or effluent liquids that enter the heat exchange tubes, as well as the drop in the low pressure through the splint. Venturi splints of the present invention may be made of any metal, including bimetallic, ceramic or ceramic coating metal. The metals o? Suitable ceramics include, but are not limited to: nickel-molybdenum alloy. nickel alloy - chromium silicon nitride, zirconia, alumina, carbon steel, 300 series stainless steel, 400 series stainless steel, monel and the like. Preferred metals or ceramics include silicon nitride, carbon steel or nickel-chromium alloy. Figure 7 shows a splint having a straight gap and an outer tongue 35. The internal diameter of the inlet end 13 and the outlet end 14 are substantially the same. The internal diameter of the splint is substantially uniform along its length. The outer tab 35 provides an element to hold the splint in position, either in the upper part of the tubular sheet or in the upper part of the refractory layer. Thus, this outer tongue 35 has an outer diameter that is greater than the inner diameter of the heat exchange tube used. it will be appreciated that the outer tongue 35 can be placed anywhere along the length of the splint. However, this splint design is susceptible to fractures when subjected to thermal shock, such as that found in a hydrogen cyanide reactor. The nickel-chromium alloy and silicon nitride ferrules of the present invention can be used effectively with tubular sheets and tubes made of carbon steel, stainless steel, nickel alloys, nickel-chromium alloy, nickel alloy - molybdenum, and the like. It is preferred that the nickel-chromium alloy ferrules of the present invention be used in heat exchangers having tubular sheets and nickel-chromium alloy heat exchange tubes. The nickel-chromium splints of the present invention are effective in providing chemical, physical and thermal protection to the tubes. Silicon nitride splints are very effective in providing thermal protection as well as chemical and physical protection to the tubular sheet, welding and exchange tubes, virtually without degradation in all environments. The silicon mtride ferrules of the present invention are particularly effective in protecting tubular sheets, tubes and welds from chemical and physical degradation in reducing, carburizing, and / or nitrifying environments, such as in hydrogen cyanide reactors. In another embodiment, turbulators, also called twisted tape, may be added to the ferrules of the present invention that are not venturi-shaped, in the longitudinal cross-section. These turbulators are typically a separate element that slides in, or otherwise inserts into, the ferrules of the present invention and may extend past the outlet of the ferrules within the tubes. These turbulators impart a corkscrew flow pattern to the effluent gases that enter the heat exchanger. This flow pattern reduces the formation of a stagnant boundary layer of gas in the tube wall, thereby improving the overall heat transfer of the exchanger tube. It's like that >; As, the process gases will be tempered more quickly. Suitable turbulators include double helical and helical inserts. These inserts can be made of metal, such as carbon steel, stainless steel, nickel alloy, nickel-molybdenum alloy and nickel-chromium alloy. In yet another form of embodiment, the ferrules of the present invention can be grooved. By grooves is meant that a helical groove, an 'easel or other protuberances are added to the inside of the ferrule. This ridge has the advantage of imparting a corkscrew flow pattern to the effluent gases entering the heat exchanger. This groove typically has the shape of a helix or a double helix. This grooving can be achieved by grinding, grooving or similarly the inner wall of the ferrules of the present invention. Alternatively, the stand may be formed during the casting of the splint. In yet another embodiment, the splints are placed in sleeves before inserting the splints into the heat exchange tubes. These sleeves usable with the ferrules of the present invention are typically a hollow short cylinder, such as a section of the exchanger tube. These sleeves have the advantage of holding the splints at a specific height on the tubular sheet while the refractory is installed. This allows the splint to expand on the surface or on top of the optional refractory material placed on top of the tubular sheet. When the ferrule sleeves are used, the length of the splint must be increased to account for the length of the splint on the tubular sheet, so that the outlet end of the splint extends at least from the bottom of the sheet. tubular. The sleeves can be made of any material that can hold the splint until the refractory material is put in place. Thus, the sleeves of the splint can be ceramic, such as alumina, silica, zirconia, silicon nitride, and ceramic reinforced with silicon nitride barbels; metal, such as carbon steel, stainless steel, nickel alloy, nickel chrome alloys, nickel-molybdenum alloys; wax; plastic, paper, cardboard and the like. It is preferred that the sleeves be ceramic or metal, and more preferably silicon nitride or nickel-chromium alloy. These sleeves only need to support the splint until the refractory material is added to the upper part of the tubular sheet. When using pre-cast refractory, splint sleeves are not required. In certain applications or reactor designs, it may be desirable to use a multiple splint system, such as a two-splint system. A two-splint system includes an inner splint, typically chosen for its insulating ability and / or chemical resistance, and an outer splint, chosen primarily for its durability. Suitable interior splints include ceramics such as alumina, zirconia, silicon nitride, alumina reinforced with silicon nitride barbels, reinforced zirconia, silicon nitride barbels and the like. It is preferred that the inner splint be made of silicon nitride. The outer splint can be made of any other material. Suitable material of the outer splint includes, but is not limited to: carbon steel, stainless steel, nickel, nickel-chromium alloy, nickel-molybdenum alloy, silicon nitride, and the like. It is preferred that the outer splint be carbon steel, stainless steel, nickel-chromium alloy and silicon nitride. It is preferred that the outer splint be an insulating splint in the present invention. Figure 9 illustrates a two-splint system having an inner splint 40 disposed within an outer insulating splint 42 having an expanded area 46. The two-splint system is supported by a splint sleeve 31 and lies in an opening in the splint. refractory layer 44. The two ferrule system passes through an opening in the tubular inlet sheet 4 and enters the inlet end of the exchange tube 2. The exchange tube 2 is fixed to the upper surface of the tubular sheet entry 4 through conventional welding 3. One of the advantages of silicon nitride splints is that they are chemically compatible with the atmospheres of the effluent gases in many chemical reactors. further, the silicon nitride splints of the present invention can be used in systems where the effluent gases are decomposed by exposure to the catalyst metals in the heat exchange tubes, for example, in certain hydrogen cyanide reactors. The silicon nitride splints of the present invention are particularly useful in reactors which may contain one or more of the following effluent gases: hydrogen, nitrogen, nitrogen oxides, oxygen, carbon monoxide, carbon dioxide, ammonia, methane and other gaseous hydrocarbons. In this way, the ferrules and / or downward welding of the present invention are preferably used to extend the service life of armored heat exchangers used in hydrogen cyanide reactors, such as in the Andrussow or Degussa processes. BMA, heat exchangers for nitric acid waste heat, acrylonitrile reactors, titanium dioxide reaction systems, ammonia reaction and / or boiler systems, phosphoric acid reaction systems, systems of sulfuric acid reaction, waste heat exchangers, side flame tube boilers, flame side tube heat exchangers, waste incinerators or catalytic stills. It is more preferred that the present invention be used to extend the life of armored heat exchangers in hydrogen cyanide reactors, nitric acid waste recovery exchangers and acrylonitrile reactors, and more preferably in cyanide reactors. hydrogen. Thus, the invention is well suited to reactors that produce hydrogen cyanide to react hydrocarbons, ammonia and optionally an oxygen-containing gas in the presence of a catalyst containing platinum. In one embodiment it provides a heat exchange apparatus having an increased service life including (a) a hull having a portion of tubular inlet sheet and a portion of tubular outlet sheet, each of the sheets tubular have a plurality of holes, where the hull has at least one intake intake and one exit mouth for the heat exchange medium: (b) a plurality of tubes is disposed within the hull where one entry end of each one of the tubes is fixed to the tubular inlet sheet and one outlet end of each of the tubes is fixed to the tubular outlet sheet in such a way that one axis of the tube and one axis of the inlet and the orifice of the tube. The output of the tubular sheet are coincident, where each of the entrance ends of the tube is fixed to the tubular entrance foil through a precipitate weld; and (c) a plurality of splints, wherein each of the splints has an inlet end and an outlet end that extend through an orifice of the tubular entry sheet into a tube, where the end of the splint The outlet extends below the tubular inlet sheet, in which the splint includes silicon nitride, or a nickel-chromium alloy. It is preferred that the exchange tubes include a nickel chromium alloy. It is further preferred that the splint includes silicon nitride. In another embodiment, the present invention provides a heat exchange apparatus that increases service life by including (a) a helmet having a tubular inlet sheet portion and a tubular outlet sheet portion, each of which tubular sheets have a plurality of holes, wherein the helmet has at least one intake and outlet for the heat exchange medium; (b) a plurality of tubes arranged inside the hull where an inlet end of each of the tubes is fixed to the output tubular sheet, such that an axis of the tube and an axis of an inlet and an orifice of exit of the tubular sheet are coincident, where each of the tubes of the input end is fixed to the tubular input sheet through a precipitate weld; and (c) a plurality of splints, wherein each of the splints has an inlet end and an outlet end extending through a hole in the tubular inlet sheet into a tube where the outlet end it extends below the tubular inlet sheet, in which the splint has a ventup design in a longitudinal cross section and includes silicon nitride or, a nickel-chromium alloy. It is preferred that the exchange tubes include a nickel-chromium alloy. It is further preferred that the splint includes silicon nitride. In yet another embodiment, the present invention provides a heat exchange apparatus that increases service life by including (a) a hull having a portion of tubular inlet sheet and a portion of tubular outlet sheet, in the that each tubular sheet has a plurality of holes, where the helmet has at least one intake and outlet for the heat exchange medium; (b) a plurality of tubes disposed within the hull where an inlet end of each of the tubes is fixed to the tubular inlet sheet and an outlet end of each of the tubes is fixed to the tubular output sheet such that an axis of the tube and an axis of an inlet orifice and an outlet of the tubular sheet are coincident, where each of the ends of the tube inlet is fixed to the tubular inlet sheet by welding of precipitate; and (c) a plurality of splints, wherein each of the splints has an inlet end and an outlet end extend through a hole in the tubular inlet sheet into a tube where the outlet end is extends below the tubular entry sheet, where the splint has an inlet end and an outlet end; the inlet end has a conically tapered or trumpet-shaped opening within a pipe section, wherein the outside diameter of the inlet end is greater than the inside diameter of the heat exchange pipe; the pipe section has an outer diameter of up to 99% of the inside diameter of the heat exchange pipe; the outlet end of the splint has an outer diameter that is substantially the same as the inner diameter of the heat exchange tube; and where the splint includes silicon nitride or a nickel-chromium alloy. It is preferred that the splint includes silicon meter. It is also preferred that the splint be wrapped in an insulator. It is further preferred that the heat exchange tubes include a nickel-chromium alloy. In a typical system for the production of hydrogen cyanide, the reaction gas includes hydrocarbon (s), such as methane, ethane, methanol, and the like, ammonia and optionally an oxygen-containing gas are fed into a reactor and reacted in the presence of a catalyst, for example, a catalyst containing platinum, at a temperature in the range of about 1000 ° to about 1400 ° C. When the reaction includes an oxygen-containing gas, it is preferred that the catalyst be an ammoxidation catalyst. The reagents are generally heated to the reaction temperature in the presence of the catalyst. The effluent gases at high temperature, that is the product gases, contain the product of hydrogen cyanide. However, as discussed above, the effluent gases must be tempered to bring the temperature below 600 ° C in order to lessen the decomposition of hydrogen cyanide. This is done by passing the effluent gases out of the reaction zone in a heat exchange zone, through one or more ferrules communicating with the exchange tubes of the heat exchange zone. In the heat exchange zone, the heat of the effluent is transferred from the material to the exchange tubes and then to the heat exchange medium surrounding the outer surface of the exchange tubes, thus lowering the effluent fluid to a temperature adequate and capturing again the thermal energy of the system for later use in the reactor or elsewhere in the operations. This procedure is illustrated in Figure 8 which shows that the reagents 17 enter the reaction zone 18. in the reaction zone 18, the reagents come into contact with the catalyst 19, for example a heated platinum metal gauze catalyst. In the present case, they are layers 20 and 34. The catalyst support can be, for example, in the shape of a honeycomb with or without a stand or a foam with or without a stand. Suitable support material for the catalyst includes, but is not limited to, a metallic support screen, pre-cast ceramic or refractory, a cast-in-place refractory, ceramic foam, ceramic packing, silicon dioxide, (silica-SiO2), silicon (SiC), silicon nitride (Si3N4), silicon boride, silicon boronitride, aluminum oxide (alumina -A1203), aluminosilicate (mulite-3Al203-2Si02), aluminoborosilicate, carbon fiber, refractory fiber, zirconium oxide (Ze02), Yttrium oxide (Y203), calcium oxide (CaO), magnesium oxide (MgO), Cordite (MgO-Al203-Si02) or combinations thereof. The hot reactive effluent, containing hydrogen cyanide, leaves the reaction zone 18, entering the heat exchange zone 21 through the ferrules 22. The hot reactive effluent passes through the ferrules 22 into the the exchange tubes 2 surrounding the heat exchange medium 24. While passing through the exchange tubes 2, the effluent gases are rapidly cooled from a temperature in the range of about 1000 ° to about 1400 ° C at a temperature below 600 ° C. The cooled effluent gas 23 then passes out of the exchange zone 21 through the outlet ends of the exchange tubes 2 and the hydrogen cyanide product is separated from the effluent stream through conventional elements not shown. As further shown in Figure 8, the exchange zone 21 may be composed of a refractory layer 27 with openings extending therefrom, and that these openings are aligned with the openings in the inlet tubular sheet 4. The tubular sheet 4 forms a wall of the heat exchange container 26 containing the heat exchange means 24. The heat exchange means 24, preferably is water or a mixture of water and steam, but may be of other fluids, as described above, suitable for absorbing the energy transferred from the heated exchange tubes 2. The ferrules 22 lying in the openings of the refractory layer 27, it passes through the openings in the inlet tubular sheet 4, and enters the inlet ends of the exchange tubes 2. Preferably, the openings in the refractory layer 27 are formed to complement the outer shape of the ferrule 22. The splint 22 is preferably surrounded by a detachable or integrated splint sleeve 31 positioned along the longitudinal axis of the splint 22. By "integrated" it is meant that the sleeve can be formed as a single piece of common material, or fixedly attached to the splint. It is preferred that the sleeve of the ferrule 31 be a separate component to accommodate any movement of the ferrule 22 relative to the sleeve of the ferrule 31, for example due to differential expansion during operations, without creating undesired stresses within the ferrule. the materials. The sleeve of the splint 31 serves as a physical cushion between the splint 22 and the interior of the surrounding refractory layer 27. The sleeves of the splint 31 can also serve to place the splints 22 in the desired orientation on the entry end of the splints. exchange tubes 2. In the installation, the outside of the splint 22 and the inside of the sleeve of the splint 31 can be covered with a thin layer of wax to aid in the subsequent removal of the splint. In a conventional configuration, included within the scope of the invention, the ends of the exchange tubes 2 extend through the inlet tubular sheet 4 within the container of the reactor 33. In this embodiment, shown in Figure 8 , the exchange tubes 2 are fixed by a weld formed between the outside of the exchange tube 2 and the upper surface of the input tubular sheet 4. The following examples are presented to further illustrate various aspects of the present invention, but do not have the intention to limit the scope of the invention in any respect. Example 1 A hydrogen cyanide reactor was constructed with an armored heat exchanger. The input tubular sheet and the heat exchange tubes of the heat exchanger were prepared with a nickel-chromium alloy (I CONEL 600). The inlet end of the exchange tubes were flush with the upper surface of the input tubular sheet or with the ends of the tube extending slightly beyond the upper surface of the input tubular sheet. The exchange tubes were welded to the upper surface of the input tubular sheet. A mixture of silicon nitside splints and nickel-chrome alloy splints (INCONEL 600) was placed in nickel-chromium alloy splint sleeves (INCONEL 600) and the splints were inserted at the inlet end of the exchange tubes. After about 4 months (about 2700 hours) of operation, with 15 operating cycles, this is thermal shocks, and several high temperature operating periods (> 1200 ° C), one of the silicon mtride splints was removed and One of the nickel-chromium alloy ferrules was inspected for wear. Each of the operating cycles consisted of heating the splints during light removal from about 150 ° to 500 ° C to the order of 1200 ° to 1400 ° C in about 1 minute and a subsequent period of nitrogen tempering of the splints of the order of 1000 ° C to 1400 ° C up to 25 ° C. The nickel splint - as it was difficult to remove from the exchange tube and showed a considerable loss of length, approximately 2 inch (1.27 cm) of its original length. Large amounts of carbon / nitrogen deposits were also present on the surface of this splint. The splint was physically trapped inside the sleeve of the splint. This splint also swelled by carbon / nitrogen absorption, suddenly narrowing the inside diameter of the splint. The silicon nitride splint was easily removed from the exchange tube and showed no loss in length. Some cyanide metal deposits were noted at the outer outlet end of the splint. There was no visible internal wear or ^^^ ¡¡m swelling inside the silicon nitride splint. In this way, the inner diameter of the silicon nitride splint remained unchanged. It can be observed, in this way, that any of the nickel-chromium ferrules or silicon nitride ferrules protect the exchange tubes of an armored heat exchanger from the reactive, hot effluent gases, particularly the effluent gases. in a hydrogen cyanide reactor. Example 2 The hydrogen cyanide reactor of example 1 was operated for an additional 5 months. They were again removed from the reactor and a silicon nitride splint and a nickel-chromium alloy splint were evaluated. The nickel-chromium splint was difficult to remove from the exchange tube and showed a considerable loss in length, approximately 1 inch (2.54 cm) from its original length. There were large amounts of carbon / nitrogen deposits on the surface of this splint. Erosion patterns were also visible (thinning of ij ^ y ^^^ the wall) inside the splint. The silicon nitride splint was easily removed from the exchange tube and showed no loss in length. Some deposits of corrosion, similar to deposits of cyanide in metal were noted on the outside of the splint. A deposit of dark carbon was noted on the outside of the outlet portion of the splint. There was a slight erosion on the ridge of the spigot intake. There was no visible internal wear or swelling inside silicon nitride splint. This is how the inner diameter of the silicon nitride splint remained unchanged. In this way it can be seen that any of the nickel-chromium splint or the silicon nitride splint protects the exchange tubes of an armored heat exchanger from the hot reactive effluent gases, particularly the effluent gases in a reactor of hydrogen cyanide. Example 3 The splints of Examples 1 and 3 were analyzed for weight loss and change in volume. These results are reported in the Table a 1lggj ^ lg¡t¡lujSM ^^? ^ Í ^ tt ^ M M continued. The percentages reported were estimated by comparing the weight and volume of the splints of Examples 1 and 2 with those corresponding to a new splint.

In this way it is possible to ensure that the silicon nitride splints of the present invention are very effective in protecting the heat exchange tubes for long periods without any significant change in the dimensions of the splint. Example 4 - Comparative In the hydrogen cyanide reactor of Example 1, 4 aluminum oxide splints having the design shown in Figure 5 were used in place of the silicon nitride or nickel alloy rings. chrome. two of the splints had a purity of 95% and the other two ^^^ utátigim had a purity of 97%. After 4-5 months of operation, the 4 alumina splints were removed and inspected. In each case, the splint cracked or fractured in the region of the neck, that is, where the flared inlet end meets the section of the pipe. In some cases, the section of the tubing has completely separated from the flared section of the splint. & gjjj ^ j &

Claims

CLAIMS 1. A heat exchange apparatus for use in a reducing, carburizing, and / or mtrurizing environment comprising: (a) a hull having a portion of tubular inlet sheet and a portion of tubular outlet sheet, in the that the tubular sheet has a plurality of holes, where the hull has at least one intake inlet and one exit outlet of the heat exchange means, - (b) a plurality of tubes disposed within the cover where one inlet end of each of the tubes is fixed to the tubular inlet sheet and outlet end of each of the tubes is fixed to the output tubular sheet so that a tube axis and an axis of an inlet and outlet of the tubular sheet are commidentes: and (c) a plurality of splints, where each of the splints have an entrance end and an exit end that extend through the entrance orifice of the tubular sheet inside a tube where the former The outlet tube extends below the tubular entrance plate, in which the splint includes silicon nitride.
2. The apparatus of Claim 1 where i t iEMeMi the tubes are made of carbon steel, stainless steel, nickel alloy, nickel-chromium alloy or nickel-molybdenum alloy.
3. The apparatus of Claim 2 wherein the tubes are composed of carbon steel or a nickel-chromium alloy.
4. The apparatus of Claim 2 wherein the nickel-chromium alloy comprises 40 to 80% nickel and 12 to 28% chromium.
5. The apparatus of Claim 1 wherein the splint has a convergent / divergent design in a longitudinal cross section.
6. A heat exchange apparatus comprising: (a) a hull having a tubular inlet sheet portion and a tubular outlet sheet portion, each of the tubular sheets having a plurality of holes, wherein the hull has at least one inlet and outlet for the heat exchange medium: (b) a plurality of tubes is disposed within the hull where an inlet end of each of the tubes is fixed to the tubular sheet inlet and one outlet end of each of the tubes is fixed to the ásimM- - - < tubular exit sheet in such a way that an axis of the tube and an axis of the entrance orifice and the exit orifice of the tubular sheet are coincident, where each of the entrance ends of the tube is fixed to the tubular entrance foil to through precipitate welding; and (c) a plurality of splints, wherein each of the splints has an inlet end and an outlet end that extend through an orifice of the tubular entry sheet into a tube, where the end of the splint The outlet extends below the tubular inlet sheet, in which the splint includes silicon nitride, or a nickel-chromium alloy.
7. The apparatus of Claim 6 wherein the nickel-chromium alloy splint is composed of 40 to 80% nickel and 12 to 28% chromium.
8. The apparatus of Claim 6 wherein the splint has an inlet end and an outlet end; the inlet end has a conically tapered opening within a section of pipe in which the outside diameter of the inlet end is greater than the inside diameter of the heat exchange pipe; the pipe section has an outer diameter of up to 99% of the inside diameter of the heat exchange pipe; the outlet end of the splint has an outer diameter that is substantially the same as the inner diameter of the heat exchange tube.
9. A splint for use in a heat exchange tube where the splint has an inlet end and an outlet end; the inlet end has a conically tapered opening within the pipe section, in which the diameter of the inlet end is greater than the inside diameter of the heat exchange pipe; the pipe section has an outside diameter that is not more than 99% of the inside diameter of the heat exchange pipe; The pipe section has an expanded area with an outside diameter that is substantially the same as the inside diameter of the heat exchange pipe.
The splint of Claim 9 wherein the splint is composed of silicon nitride or a nickel-chromium alloy.
11. The splint of Claim 10 wherein the splint is composed of silicon mtride.
The splint of claim 10 wherein the nickel-chromium alloy is composed of 40 to 80% nickel and 12 to 28% chromium.
13. A splint for use in a heat exchange tube where the splint has an inlet end and an outlet end; the inlet end has a conically tapered or trumpet-shaped opening within a pipe section, wherein the outer diameter of the inlet end is larger than the outer diameter which is substantially the same as the inner diameter of the pipe of heat exchange; and where the splint has a convergent / divergent design in a longitudinal cross section.
14. The splint of Claim 13 wherein the splint is composed of ceramic, carbon steel, nickel alloy, nickel-molybdenum alloy, nickel-chromium alloy.
15. The splint of Claim 13 wherein the splint is comprised of silicon nitride, nickel-chromium alloy, carbon steel or stainless steel.
16. The splint of Claim 14 wherein the nickel-like alloy consists of 40 to 80% nickel and 12 to 28% chromium. g ^ tt ^
17. An apparatus for heat exchange that is used in a hydrogen cyanide reactor includes: (a) a hull having a portion of tubular inlet sheet and a portion of tubular outlet sheet, in which each of the tubular sheets they have a plurality of holes, where the hull has at least one intake port and one outlet port of the heat exchange means; and (b) a plurality of tubes disposed within the hull with an inlet end of each of the tubes being fixed to the tubular inlet sheet and an outlet end of each of the tubes being fixed to the output tubular sheet so that an axis of the tube and an axis of the entrance orifice and of the exit orifice of the tubular sheet are coincident, where each of the entrance ends of the tube is fixed to the tubular entrance foil through welding of precipitate.
18. The apparatus of Claim 17 wherein the tubes are composed of carbon mite, stainless steel, nickel alloy, nickel-chromium alloy, or nickel-molybdenum alloy.
19. The apparatus of Claim 18 wherein the tubes are composed of carbon steel or nickel-chromium alloy.
20. The apparatus of Claim 18 wherein the nickel-chromium alloy is composed of 40 to 80% nickel and 12 to 28% chromium.
21. The apparatus of Claim 17 wherein the precipitated solder is heat treated.
22. The apparatus of Claim 17 further is comprised of a plurality of splints, wherein each of the splints has an inlet end and an outlet end extending through the inlet opening of the tubular sheet within a tube where the outlet end extends below the tubular inlet sheet.
23. An apparatus of Claim 22 wherein the splint is composed of silicon nitride or a nickel-chromium alloy.
24. The splint of Claim 23 wherein the nickel-chromium alloy consists of 40 to 80% nickel and 12 to 28% chromium.
25. An apparatus for preparing hydrogen cyanide by reacting hydrocarbons, ammonia and optionally an oxygen-containing gas in the presence of a catalyst containing platinum at a temperature in the range from 1000 ° to 1400 °, which includes a reaction zone, an optional refractory zone and a heat exchange zone including: (a) a helmet having a portion of tubular inlet sheet and a portion of tubular outlet sheet, wherein each of the tubular sheets has a plurality of holes, where the helmet has at least one intake and outlet for the heat exchange medium; (b) a plurality of tubes disposed within the hull where an inlet end of each of the tubes is fixed to the tubular inlet sheet and an outlet end of each of the tubes is fixed to the tubular output sheet such that a tube axis and an axis of the inlet orifice and of the exit orifice of the tubular sheet are coincident; and (c) a plurality of splints, wherein each of the splints has an inlet end and an outlet end extending through the orifice of the tubular inlet sheet in a tube where the outlet end extends. under the tubular entrance foil, in which the splint is composed of silicon nitride.
26. The apparatus of Claim 25 wherein the tubes are composed of carbon steel, stainless steel, nickel alloy, nickel-chromium alloy, or nickel-molybdenum alloy.
27. The apparatus of Claim 26 wherein the tubes are composed of carbon steel or a nickel-chromium alloy.
28. The apparatus of Claim 27 wherein the nickel-chromium alloy is comprised of 40 to 80% nickel and 12 to 28% chromium.
29. The apparatus of Claim 25 wherein each of the inlet ends of the tube is fixed to the inlet tubular sheet through a precipitate weld.
30. A process for preparing hydrogen cyanide comprising the steps of: feeding reaction gas to a reactor, wherein the reaction gas is comprised of hydrocarbon, ammonia and optionally an oxygen-containing gas; reacting the reaction gas in the presence of a catalyst to give product gas; cooling the product gas in a heat exchange apparatus comprising (a) a hull having a tubular inlet sheet portion and a tubular outlet sheet portion, wherein each of the tubular sheets has a plurality of holes, where the helmet has at least one intake and outlet for the heat exchange medium; (b) a plurality of tubes disposed within the hull where an inlet end of each of the tubes is fixed to the tubular inlet sheet and an outlet end of each of the tubes is fixed to the tubular output sheet such that one axis of the tube and one axis of the inlet and the exit orifice of the tubular sheet are coincident; and (c) a plurality of splints, wherein each of the splints has an inlet end and an outlet end that extend through the orifice of the inlet tubular sheet into the tube where the outlet end extends. under the tubular entrance sheet, in which the splint is composed of silicon nitride; a recovery of hydrogen cyanide from the cooled product gas.