Reduced maintenance and improved energy savings in chemical reaction product production with heat recovery

Abstract

A method for extending operating intervals between maintenance breaks in the production of chemical reaction products, comprising: directing at least one reactant stream to a reactor; reacting the reactants in the reactor at high temperature and pressure to obtain a chemical reaction product; removing a high temperature chemical reaction product stream from the reactor; and exchanging heat with at least one of the reactant streams, the heat exchange occurring in at least two shell-and-tube heat exchangers, each of the heat exchangers including a plurality of tubes and a shell-side heat exchange passageway, the high temperature chemical reaction products being directed through the tubes of the heat exchanger and the reactants being guided through the shell-side passageway, and at least two of the heat exchangers being connected in series for both the shell-side flow and the tube-side flow. The use of two or more heat exchangers reduces the impact of fouling in individual tubes on the overall heat exchange capacity, as compared to configurations in which only a single heat exchanger is used.

Description

[Technical field]

[0001] In chemical processes, various sources of waste heat may be available, for example, cooling of intermediate product streams or flue gases of any combustion process. It is highly desirable to recover heat during the production of chemical reaction products. Heat available at temperatures of at least 400-500°C is typically recovered by generating high temperature steam, which can be used in the process itself or expanded in a turbine to generate energy. Heat available at lower temperatures is generally not suitable for generating energy and can be recovered, for example, by preheating one or more process streams. Preheating typically occurs by indirect heat exchange of a high temperature chemical reaction product stream with a reactant stream, whereby heat is transferred to the reactant stream. [Background technology]

[0002] The temperature of the reactant stream, preheated by indirect heat exchange with the hot chemical reaction products, may be further adjusted, typically further increased in a heater, prior to introducing the reactant stream into the reactor. Any means for adjusting the temperature may be applied. Such means include, but are not limited to, electrical heating, direct combustion, and / or heat exchange against another medium, such as steam or thermal oil.

[0003] One type of heat exchanger commonly used in connection with commercial processes is the shell-and-tube heat exchanger. In this type of exchanger, one fluid flows through the inside of the tubes while the other fluid is forced around the outside of the tubes through the shell. Baffles are usually installed to support the tubes and force the fluids in a serpentine fashion across the tube bundle. Summary of the Invention [Problem to be solved by the invention]

[0004] One of the most problematic aspects associated with the use of heat exchangers is their tendency to develop fouling. Fouling refers to various deposits and coatings that form on the surfaces of the heat exchanger as a result of the flow of process fluids and heat transfer. There are various types of fouling, including corrosion, mineral deposits, polymerization, crystallization, coking, sedimentation, and biological. In the case of corrosion, the surfaces of the heat exchanger may corrode as a result of the interaction between the process fluid and the materials used to construct the heat exchanger. The situation is further aggravated by the fact that various types of fouling may interact with each other, causing even more fouling. Fouling creates additional resistance in terms of heat transfer, thus reducing performance in terms of heat transfer. Fouling also causes an increase in pressure drop associated with the fluid flowing inside the exchanger.

[0005] One particular area prone to fouling in conventional shell-and-tube heat exchangers is the tube area near the tubesheet, near the inlets where the tube-side fluid exits the individual tubes. Excessive fouling in this area can result in clogging of individual tubes and stagnation of fluid along the entire length of these tubes. Fluid stagnation generally results in reduced heat transfer performance.

[0006] A further consequence of the reduced heat transfer performance caused by fouling is the increased energy required by the heater to adjust the temperature of the preheated reactant stream to the desired reaction temperature, which results in more additional external heat being required, which is detrimental in terms of energy demand and process economics, and often negatively impacts the carbon dioxide footprint of the product.

[0007] A preferred, but not exclusive, application of the present invention is the expansion of heat recovery, more specifically, the extension of operating intervals between maintenance breaks in processes and plants for the synthesis of isoprenol. Isoprenol, or 3-methyl-3-buten-1-ol, is an important intermediate for pharmaceuticals and aroma compounds, with thousands of tons produced annually worldwide. Isoprenol is commercially synthesized by reacting formaldehyde with isobutylene. High temperatures are required to obtain high isoprenol yields in the uncatalyzed reaction of formaldehyde with isobutylene. Effective removal of heat is important for product quality and process safety. The heat removed from isoprenol is used to increase the temperature of isobutylene before it enters the reactor.

[0008] The problem underlying the present invention is seen in devising a process and plant for maintaining adequate heat transfer performance of shell-and-tube heat exchangers used for heat recovery in chemical processes even when individual tubes of the heat exchanger have failed due to fouling. The improved process should allow for extended operating intervals between maintenance breaks and reduce the energy demand for adjusting the temperature of preheated reactant streams to reaction temperatures, thus enhancing process economics. [Means for solving the problem]

[0009] The problem is a method for enhancing heat recovery during the production of chemical reaction products, more specifically a method for extending the operating intervals between maintenance breaks in such a method, - conducting at least one reactant stream into a reactor; - reacting reactants in a reactor at high temperature and pressure, thereby obtaining a chemical reaction product; - removing a hot chemical reaction product stream from the reactor; and - exchanging a hot chemical reaction product stream with at least one of the reactant streams; The problem is solved by a method comprising the steps of: wherein the heat exchange is performed in at least two shell-and-tube heat exchangers, preferably in a countercurrent mode, each of the heat exchangers including a plurality of tubes and a shell-side heat exchange passage; Hot chemical reaction products are directed through the tubes of the heat exchangers and reactants are guided through the shell-side passages, and at least two of the heat exchangers are connected in series for both the shell-side flow and the tube-side flow.

[0010] The term "maintenance break" is intended to mean a process shutdown that is periodically required to clean heat exchanger tubes that are clogged by fouling. An indication of the need for a maintenance break is usually when the reactants leaving the last heat exchanger are not preheated sufficiently and subsequent heaters are barely able to add additional external heat to the reactants to bring them to the required temperature before they enter the reactor. An aspect of the present invention is that the preheating of at least one reactant can be maintained at a sufficiently high level for a longer period of time so that the reactants can easily reach the desired temperature of the reactants before they enter the reactor.

[0011] According to the invention, the heat exchange takes place in at least two shell-and-tube heat exchangers connected in series for both shell-side and tube-side flows. Preferably, at least the first heat exchanger, and more preferably each of the heat exchangers, is operated in countercurrent mode. At least one reactant stream is conducted through the shell-side passages of the first heat exchanger and then through the shell-side passages of the second and all further heat exchangers, and the hot chemical reaction products are conducted to the tubes of the heat exchangers in reverse order relative to the direction of the at least one reactant stream.

[0012] The use of two or more heat exchangers reduces the impact of fouling in individual tubes on the overall heat exchange capacity compared to configurations where only a single heat exchanger is used. As a result, heat transfer rates are maintained at desired levels for longer periods, thus extending operational intervals between maintenance breaks, and preheating of at least one reactant stream requires less additional external heat compared to plants with a single heat exchanger in an advanced fouling state.

[0013] Shutdowns and maintenance process interruptions are expected to be required less frequently.

[0014] The physical state of the hot chemical reaction product is not particularly limited, so long as it is a fluid stream. The hot chemical reaction product may be in a gaseous state, a supercritical state, or a liquid state. In one embodiment, the hot chemical reaction product stream is a liquid stream.

[0015] The present invention addresses problems that can occur during indirect heat exchange in shell-and-tube heat exchangers when high temperature chemical reaction products are prone to fouling.

[0016] Chemical reaction products are considered "prone to fouling" if, in a fouling test, they form deposits on the tube walls when circulated through the tubes of a single shell-and-tube heat exchanger against a coolant directed through the shell side of the heat exchanger, e.g., a reactant stream requiring preheating, which may ultimately lead to clogging of individual tubes. As a result, the heat exchange effectiveness is reduced and the coolant outlet temperature is reduced. In a fouling test, the heat exchange reduces the temperature of the hot chemical reaction product stream by 150°C. The single heat exchanger has 300 tubes with an outer diameter of 14 mm, an inner diameter of 10 mm, and a length of 10 m, and has an (external) heat exchange surface of 130 m. 2 A means for determining whether a single heat exchanger has become clogged during operation may be to monitor the heat transfer coefficient k of the single heat exchanger over time during heat exchange at constant conditions. The heat transfer coefficient k may be determined as follows:

number

number

[0017] A chemical reaction product is considered to be "susceptible to fouling" if the heat transfer coefficient k of a single heat exchanger decreases by more than 15%, preferably more than 30%, within a period of 180 days, preferably 150 days, more preferably 120 days, and even more preferably 100 days.

[0018] Phase changes of hot chemical reaction products upon cooling are often associated with a tendency to produce fouling. Thus, in embodiments, the hot chemical reaction products undergo at least a partial phase change during heat exchange. For example, the hot chemical reaction products may undergo a supercritical to liquid, gas to liquid, or liquid to suspension transition. A liquid to suspension transition may occur when the solubility limit of a component decreases upon cooling, causing precipitation of said component.

[0019] Cooling hot chemical reaction products across large temperature differences is often associated with a tendency to produce fouling. Thus, in embodiments, the heat exchange may reduce the temperature of the hot chemical reaction product stream by at least 100° C., preferably in the range of 120-180° C., more preferably in the range of 130-160° C. In this scenario, the hot chemical reaction product stream has a temperature difference that can be calculated from the inlet temperature of the tube side of the last heat exchanger, e.g., the second heat exchanger if two heat exchangers are connected in series, and the outlet temperature of the tube side of the first heat exchanger.

[0020] The use of two or more heat exchangers reduces the impact on the overall heat exchange capacity of the first heat exchanger of gradual deterioration over time of heat transfer caused by fouling within individual tubes of the first heat exchanger for at least one reactant stream direction, as compared to a configuration in which only a single heat exchanger is used.

[0021] In an embodiment, the reduction in the overall heat transfer coefficient k of all heat exchangers connected in series is preferably at least 10 percentage points less than the reduction in the heat transfer coefficient k of the first heat exchanger. For example, if the heat transfer coefficient k of the first heat exchanger is reduced by 35%, then the overall heat transfer coefficient k of all heat exchangers connected in series should be reduced by at least 10 percentage points less than 35%, i.e., by less than 25%. The "first" heat exchanger is the first heat exchanger seen in the direction of at least one reactant stream.

[0022] Hot chemical reaction products flow inside the tubes and reactants are forced outside the tubes through the shell. Hot chemical reaction products can be directed in either an upward or downward direction through the tubes, preferably downward. Baffles are typically positioned to support the tubes and force the reactants in a serpentine manner across the tube bundle. As the reactants pass through the shell-side passages, they will generally follow a serpentine path, most of which is horizontal, although the overall direction of movement of the reactants in the shell-side passages is vertical and countercurrent to the direction of flow of hot chemical reaction products inside the tubes.

[0023] According to the present invention, both the hot chemical reaction product stream flow path and the reactant stream flow path include at least two heat exchangers connected in series for both the shell-side flow and the tube-side flow. Two or more heat exchangers arranged in parallel can be connected in series with at least one heat exchanger.

[0024] This includes embodiments in which heat exchange occurs in three or more heat exchangers, where a first heat exchanger is connected in series with two or more second heat exchangers arranged in parallel with each other, in which the "first" and "second" heat exchangers are viewed in the direction of flow of the shell-side stream.

[0025] In a preferred embodiment, the heat exchange is carried out in 2 to 6 heat exchangers connected in series, preferably 2 to 5 heat exchangers, more preferably 2 to 4 heat exchangers, most preferably 2 to 3 heat exchangers. Two heat exchangers are generally preferred, taking into account the fact that any additional heat exchangers beyond two involve higher investment and maintenance costs and the benefits achievable by the use of more than two heat exchangers do not increase to the same extent.

[0026] The total required heat exchange surface area of ​​all shell-and-tube heat exchangers connected in series depends on the specific heat exchange task. The heat exchange surface area of ​​a heat exchanger corresponds to the sum of the tube walls in contact with the shell-side flow. The ratio of the heat exchange surface area of ​​each individual heat exchanger to the heat exchange surface area of ​​each other individual heat exchanger is preferably in the range of 1:10 to 10:1, preferably 1:4 to 4:1, more preferably 1:2 to 2:1. For example, if two shell-and-tube heat exchangers are connected in series, the ratio of their heat exchange surface areas is preferably in the range of 1:10 to 10:1, more preferably 1:4 to 4:1, most preferably 1:2 to 2:1.

[0027] The heat exchangers typically each contain from 50 to 5000 tubes, more preferably from 400 to 3000 tubes, and most preferably from 800 to 2000 tubes.

[0028] The tube preferably has an inner diameter in the range of 6 to 25 mm, more preferably 8 to 16 mm, and most preferably 8 to 12 mm.

[0029] Preferably, the tube has a length of 2 to 30 m, such as 2 to 25 m, preferably 2 to 20 m, most preferably 5 to 20 m, such as 5 to 15 m.

[0030] In an embodiment, each heat exchanger includes 50-5000 tubes having an inner diameter in the range of 6-25 mm and a total tube length of 2-30 m.

[0031] In an embodiment, the length of the heat exchanger is in the range of 10 to 30 m and the diameter of the shell is in the range of 0.5 to 2 m.

[0032] The hot chemical reaction product stream contains sensible heat from the chemical reaction. Sensible heat is potentially renewable energy and can be reused. In an embodiment, the removed hot chemical reaction product stream has a temperature in the range of 50-800° C., preferably 50-400° C., and an absolute pressure in the range of 1-400 bar, preferably 20-400 bar, more preferably 50-400 bar.

[0033] In a preferred embodiment, the method of the present invention is a method for heat recovery during the production of isoprenol, more specifically for extending the operating interval between maintenance breaks in such a process. In this process, the first reactant stream is an isobutylene stream, the second reactant is a formaldehyde source stream, and the chemical reaction product is an isoprenol-containing product. The isoprenol-containing product is heat exchanged with the isobutylene stream.

[0034] Preferably, the production of isoprenol is carried out under supercritical conditions. Supercritical conditions exist when a substance or mixture of substances is exposed to temperatures and pressures that exceed the thermodynamic critical point of the substance or mixture. In this state, there is no distinction between the liquid and gas phases, and the fluid is called dense gas, where the saturated vapor and saturated liquid states are identical. It has been found that under supercritical conditions, the reactivity of isobutylene with formaldehyde is high enough to allow a smooth reaction even in the absence of extraneous solvents or catalysts. This leads to a reduction in the amount of by-products.

[0035] It is believed that the supercritical isobutylene acts as a supercritical solvent to solubilize at least a portion of the formaldehyde source and / or extract formaldehyde from the formaldehyde source. This allows the formaldehyde to be efficiently mixed with the isobutylene, reducing problems typically associated with mixing of multiple phases. For example, localized supersaturation of formaldehyde may be avoided. Thus, ideally, the entire reaction mixture containing the formaldehyde source and isobutylene will be a homogeneous single phase in the supercritical or near-supercritical region, although it is expected that some of the formaldehyde source will be present as a second liquid phase. Also, the isoprenol formed in the reaction may dissolve in the near-supercritical or supercritical reaction mixture or form another liquid phase.

[0036] To form a supercritical reaction mixture of isobutylene and formaldehyde, it is necessary at least to feed isobutylene, used in excess as both reactant and solvent, to the reactor at the necessary pressure and temperature. To achieve the required temperature of isobutylene, an energy-consuming heater is usually required. As preheating of isobutylene by heat exchange with hot isoprenol product gradually decreases due to rapid and progressive fouling of the single heat exchanger usually used, more and more additional energy is required.

[0037] Phase diagrams of the reactants are readily available to those skilled in the art. Furthermore, the critical point of a compound or mixture can be determined by calculating or experimentally obtaining the phase diagram of the compound or mixture. From the above, it is clear that the pressure and temperature of the process must be at least sufficient to maintain isobutylene in a supercritical state. The critical temperature Tc and pressure Pc of isobutylene are Tc=417.9 K and Pc=40.00 bar (Tsonopoulos, C.; Ambrose, D., Vapor-Liquid Critical Properties of Elements and Compounds. 6. Unsaturated Aliphatic Hydrocarbons, J. Chem. Eng. Data, 1996, 41, 645-656).

[0038] To achieve supercritical conditions, the formaldehyde and isobutylene are preferably reacted at a temperature of at least 220° C., e.g., in the range of 220-290° C., and a pressure of at least 200 bar absolute, more preferably at a temperature of at least 250° C., e.g., in the range of 250-280° C., and a pressure of at least 220 bar absolute, and most preferably at a temperature of at least 260° C., e.g., in the range of 260-275° C., and a pressure of at least 250 bar absolute. Unless otherwise stated, all pressures quoted herein are absolute pressures.

[0039] Preferably, a molar excess of isobutylene is reacted with formaldehyde. The term "molar excess of isobutylene" is understood to mean a molar excess of isobutylene relative to formaldehyde. This results in a relatively low concentration of formaldehyde in the reaction mixture, thereby reducing the possibility of localized supersaturation of formaldehyde. Thus, the amount of by-products obtained is reduced. Furthermore, it has been found that the greater the molar ratio of isobutylene to formaldehyde, the less prone the reaction mixture is to form multiple phases.

[0040] In a preferred embodiment, the molar ratio of isobutylene to formaldehyde under supercritical conditions is at least 7:1, particularly preferably at least 10:1, most preferably at least 12:1, such as at least 12.5:1.

[0041] Formaldehyde can be provided as a liquid, for example as a solution of paraformaldehyde.Preferably, the formaldehyde source is an aqueous formaldehyde solution.When formaldehyde is provided as an aqueous solution, the solution preferably comprises at least 15% by weight, more preferably at least 25% by weight, most preferably at least 35% by weight, for example at least 45% by weight, or at least 50% by weight, based on the total weight of the aqueous formaldehyde solution.

[0042] Proper fluid mixing is important in the production of isoprenol. Thus, the production of isoprenol preferably involves mixing and injecting a formaldehyde source and isobutylene into a reactor through multiple nozzles operated in parallel. Preferably, the multiple nozzles are located on the lid of the reactor. To allow a high degree of mixing and avoid dead zones, the nozzles should be flush with the lid.

[0043] Upon injection and mixing with the reactor contents, the formaldehyde source and isobutylene form a homogeneous single phase in the supercritical region. The isobutylene is either a supercritical fluid prior to injection into the reactor, or is in a liquefied or gaseous phase near its supercritical state prior to injection into the reactor. In either case, it is necessary to heat the isobutylene prior to injection, usually by a combination of preheating by heat exchange with hot isoprenol product, followed by an energy-consuming heater immediately prior to injection, increasing energy consumption if preheating by heat exchange is hindered by poor heat transfer due to fouled heat exchangers.

[0044] Further details regarding reactor design and reaction conditions can be found, for example, in WO 2020 / 049111 A1.

[0045] The present invention further provides a plant for the production of a chemical reaction product, comprising: - a reactor having at least one reactant inlet for receiving at least one reactant stream and a reaction product outlet for removing a high temperature chemical reaction product stream from the reactor; - at least two shell-and-tube heat exchangers, each of which includes a plurality of tubes and shell-side heat exchange passages, the heat exchangers being connected in series with respect to both shell-side flow and tube-side flow, and interconnected such that hot chemical reaction products are directed through the tubes of the heat exchanger and reactants are directed through the shell-side passages; - optionally, a heater to further increase the temperature of the reactant stream; The present invention relates to a plant comprising:

[0046] The plant may have extended operating intervals between maintenance breaks and / or reduced energy consumption when heaters are used, compared to an otherwise identical plant having a single shell-and-tube heat exchanger instead of at least two shell-and-tube heat exchangers in series.

[0047] In an embodiment, the plant is adapted to allow counter-flow of hot reaction products from the reactor and reactants through a heat exchanger.

[0048] One aspect of the invention relates to a plant for the production of chemical reaction products with an extended operating interval, said plant including a heat exchange step between a hot chemical reaction product stream and at least one reactant stream, and preferably a subsequent heater of at least one reactant stream prior to introduction of the reactant stream or streams into a reactor, wherein the plant has at least two shell-and-tube heat exchangers in series for heat exchanging the hot chemical reaction product stream with at least one of the reactant streams, and the operating interval is extended compared to an otherwise identical plant having a single shell-and-tube heat exchanger instead of the at least two shell-and-tube heat exchangers in series of the plant of the invention.

[0049] A further aspect of the invention relates to a plant for the production of chemical reaction products with reduced energy consumption, said plant comprising a heat exchange step between a hot chemical reaction product stream and at least one reactant stream, and preferably a subsequent heater of at least one reactant stream prior to introduction of the reactant stream or streams into the reactor, wherein the plant has at least two shell-and-tube heat exchangers in series for heat exchanging the hot chemical reaction product stream with at least one of the reactant streams, and wherein the energy consumption is reduced compared to an otherwise identical plant having a single shell-and-tube heat exchanger instead of the at least two shell-and-tube heat exchangers in series of the plant of the invention.

[0050] Where applicable, the above-mentioned embodiments relating to the process of the invention are also valid for the plant of the invention.

[0051] A further embodiment is the use of at least two shell-and-tube heat exchangers in series in a plant for the production of a chemical reaction product, which includes a heat exchange step of a hot chemical reaction product stream with another stream, e.g., a reactant stream, to increase the interval between maintenance breaks compared to an otherwise identical plant having a single shell-and-tube heat exchanger instead of at least two shell-and-tube heat exchangers in series.

[0052] Yet a further embodiment of the present invention is the use of at least two shell-and-tube heat exchangers in series in a plant for the production of a chemical reaction product, comprising a heat exchange step between a hot chemical reaction product stream and at least one reactant stream, and a subsequent heater for the at least one reactant stream, to increase energy consumption compared to an otherwise identical plant having a single shell-and-tube heat exchanger instead of at least two shell-and-tube heat exchangers in series.

[0053] The invention is further illustrated by the following examples and figures. [Brief description of the drawings]

[0054] [Figure 1] (A)-(C) show schematic diagrams of different operating conditions and configurations of a shell-and-tube heat exchanger. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0055] FIG. 1(A) shows a schematic diagram of a shell-and-tube heat exchanger 1 including a cylindrical shell and multiple tubes 2′, 2″, 2′″ disposed within the shell. Heat exchange passages 3 on the shell side allow for circulation of heat transfer liquid between the tubes and in the space within the shell. The heat exchange passages 3 may include baffles (not shown) to optimize the flow of heat transfer liquid through the heat exchange passages 3.

[0056] A stream of hot chemical reaction products, e.g., a stream resulting from a chemical reaction in a reactor (not shown), is introduced via line 6 and distributed to tubes 2', 2", 2'" of shell-and-tube heat exchanger 1 through the upper tubesheet. Tubes 2', 2", 2'" have a total length L from the upper tubesheet to the lower tubesheet. At the same time, reactants are introduced via line 4 into passage 3 on the shell side of shell-and-tube heat exchanger 1 and guided therethrough. Heat is transferred from the hot chemical reaction products to the reactant streams through the walls of tubes 2', 2", 2'".

[0057] A stream of chemical reaction products is removed from the shell-and-tube heat exchanger 1 at the bottom through line 7, said stream removed through line 7 having a lower temperature than the hot stream of chemical reaction products introduced through line 6. Preheated reactants are removed from the shell-and-tube heat exchanger 1 at the top through line 5 and can be directed to a reactor (not shown) or further heated as required. The reactants removed through line 5 have a higher temperature than the reactants introduced through line 4.

[0058] FIG. 1(B) shows the same shell-and-tube heat exchanger 1 shown in FIG. 1(A) but in an operating condition where tube 2″ is clogged near the lower tubesheet by an obstruction 8. This reduces the flow of the hot chemical reaction product stream through tube 2″ or causes stagnation of liquid within tube 2″ above the lower tubesheet. Thus, essentially the entire wall surface of tube 2″ is no longer available for heat transfer, reducing the heat transfer effectiveness of the shell-and-tube heat exchanger 1.

[0059] FIG. 1(C) shows a configuration of two shell-and-tube heat exchangers in series, including a first shell-and-tube heat exchanger 1B and a second shell-and-tube heat exchanger 1A.

[0060] Viewed in the direction of flow of at least one reactant, the first shell-and-tube heat exchanger 1B includes a plurality of tubes 2B', 2B", 2B'" and shell-side heat exchange passages 3B. The tubes 2B', 2B", 2B'" of the first shell-and-tube heat exchanger 1B have an overall length L2 from the upper tubesheet to the lower tubesheet.

[0061] The second shell-and-tube heat exchanger 1A in the direction of flow of one or more reactants includes a plurality of tubes 2A', 2A", 2A'" and shell-side heat exchange passages 3A. The tubes 2A', 2A", 2A'" of the second shell-and-tube heat exchanger 1A have a total length L1 from the upper tubesheet to the lower tubesheet.

[0062] Each of the lengths L1 and L2 is less than the length L. In the illustrated embodiment, the sum of L1 and L2 is approximately equal to L.

[0063] The first shell-and-tube heat exchanger 1B and the second shell-and-tube heat exchanger 1A are connected in series for both shell-side and tube-side flow. The hot reaction products are introduced into the second shell-and-tube heat exchanger 1A via line 6A and distributed to the tubes 2A', 2A", 2A'" via the upper tubesheet. The partially cooled products emerging from the tubes 2A', 2A", 2A'" of the second shell-and-tube heat exchanger 1A are introduced into the first shell-and-tube heat exchanger 1B via line 7A and distributed to the tubes 2B', 2B", 2B'" via the upper tubesheet. Conversely, the reactants to be preheated are introduced into the shell-side passage 3B of the first shell-and-tube heat exchanger 1B via line 4B and, after exiting therefrom, are led to the shell-side passage 3A of the second shell-and-tube heat exchanger 1A via line 5B. The preheated reactants are removed through line 5A.

[0064] During operation, fouling can occur, resulting in blockages 8B in tubes 2B″. This causes tubes 2B″ to become partially or completely blocked, i.e., reducing the flow of the hot chemical reaction product stream through tubes 2B″. Only the walls of tubes 2B″ are no longer available for heat transfer. Thus, in comparison to FIG. 1(B), even if an individual tube becomes blocked, a larger tube wall surface is still available for heat transfer.

[0065] It is also possible that in some chemical manufacturing processes, fouling can occur due to partial or complete blockage of a tube, e.g., 2A″, of heat exchanger 1A, which could similarly be 8A if included in the drawing. In such a case, the present invention allows the still partially hot reaction products to use the entire wall of heat exchanger 1B, including tube 2B″, whereas in the case of a single shell-and-tube heat exchanger shown in FIG. 1(A), fouling of the top half of a tube, such as tube 2″, can effectively result in the loss of the entire wall of tube 2″ over the entire length of the heat exchanger for heat transfer to at least one reactant stream in the shell surrounding tube 2″.

[0066] It should be understood that the inventive configuration of at least two shell-and-tube heat exchangers in series as shown in FIG. 1 does not limit the invention to at least two such heat exchangers in series being physically separated. For example, they may be in one case. Also, in one embodiment of the invention, said at least two heat exchangers in series should be understood to include an apparatus that at first glance resembles a single heat exchanger, except that it has a zone in the middle part where the partially cooled reaction product streams flowing through the tubes of one part of the heat exchange unit are recombined and then subdivided into streams for further transfer of heat to at least one reactant entering that part of the heat exchange unit requiring preheating that is supplied through further tubes of another part of the shell-and-tube heat exchange unit, thereby providing two shell-and-tube heat exchangers in a single heat exchange unit. EXAMPLES

[0067] For the industrially important conversion of isobutylene and formaldehyde to produce isoprenol, the isobutylene must be preheated. For this purpose, the hot product isoprenol is heat exchanged with isobutylene.

[0068] The heat exchange performance between the hot isoprenol stream and the cold isobutylene stream was calculated by applying the heat transfer correlations described in VDI-Waermeatlas, VDI-Gesellschaft Verfahrenstechnik und Chemistry Engineering Laboratories, 11., bearbeitete und erweiterte Auflage (e.g., Chapter G1 “Durchstroemte Rohre”; Volker Gnielinski, Institut fur thermische Verfahrenstechnik, Karlsruher Institut fur Technologie”, pages 785-791).

[0069] The heat exchange was simulated according to the following scenarios: (1) It has 1942 tubes with an outer diameter of 14 mm, an inner diameter of 8 mm, and a length of 14 m, and has a heat exchange surface of 1025 m 2 A single shell-and-tube heat exchanger (reference example) (2) Total heat exchange surface area is 1025 m 2 Two shell-and-tube heat exchangers connected in series (example according to the invention): - It has 1942 tubes with an outer diameter of 14 mm, an inner diameter of 8 mm and a length of 7 m, giving a heat exchange surface of 512.5 m 2 A first shell-and-tube heat exchanger, - It has 1942 tubes with an outer diameter of 14 mm, an inner diameter of 8 mm and a length of 7 m, giving a heat exchange surface of 512.5 m 2 The second shell-and-tube heat exchanger becomes

[0070] The following specifications apply: - isobutylene: mass flow rate = 81.1 t / h, and - Isoprenol: mass flow rate = 87.9 t / h.

[0071] The results of the simulation are shown in Table 1. "Clogging" refers to the percentage of tubes that are non-functional due to fouling. These tubes were considered to no longer contribute to the heat exchange performance.

[0072] [Table 1]

[0073] [Table 2]

Claims

1. 1. A method for extending operational intervals between maintenance breaks in the production of a chemical reaction product, comprising: - conducting at least one reactant stream into a reactor; reacting reactants in said reactor at elevated temperature and pressure, thereby obtaining said chemical reaction product; - removing a hot chemical reaction product stream from said reactor; - exchanging said hot chemical reaction product stream with at least one of said reactant streams; Including, wherein the heat exchange is performed in at least two shell-and-tube heat exchangers, each of said heat exchangers including a plurality of tubes and a shell-side heat exchange passage; the hot chemical reaction products are directed through tubes of the heat exchanger and the reactants are guided through shell-side passages, and at least two of the heat exchangers are connected in series with respect to both the shell-side flow and the tube-side flow.

2. The method of claim 1 , wherein the high temperature chemical reaction products are susceptible to fouling during heat exchange.

3. 3. The method of claim 1 or 2, wherein the heat transfer in the first heat exchanger deteriorates gradually with respect to the direction of the at least one reactant stream.

4. 4. The method according to claim 1, wherein the reduction in the overall heat transfer coefficient k of all heat exchangers connected in series is preferably at least 10 percentage points smaller than the reduction in the heat transfer coefficient k of the first heat exchanger in the direction of at least one reactant stream.

5. The method of any one of claims 1 to 4, wherein the hot chemical reaction product undergoes at least a partial phase change during the heat exchange.

6. 6. The method according to any one of claims 1 to 5, wherein by heat exchange the temperature of the hot chemical reaction product stream is reduced by at least 100°C, preferably in the range of 120 to 180°C, more preferably in the range of 130 to 160°C.

7. 7. The method according to any one of the preceding claims, wherein the ratio of the heat exchange surface area of ​​each individual heat exchanger to the heat exchange surface area of ​​each other individual heat exchanger is in the range of 1:10 to 10:1, preferably 1:4 to 4:1, more preferably 1:2 to 2:

1.

8. The method according to any one of claims 1 to 7, wherein the heat exchange is carried out in 2 to 4 heat exchangers, preferably 2 to 3 heat exchangers, connected in series.

9. 9. The method according to any one of claims 1 to 8, wherein each of the heat exchangers comprises 50 to 5000 tubes having an internal diameter in the range of 6 to 25 mm and a total tube length of 2 to 30 m.

10. The method according to any one of claims 1 to 9, wherein the length of the heat exchanger is in the range of 10 to 30 m and the diameter of the shell is in the range of 0.5 to 2 m.

11. 11. The method of any one of claims 1 to 10, wherein the hot chemical reaction product stream has a temperature in the range of 50 to 800°C and an absolute pressure in the range of 1 to 400 bar.

12. 12. The method of any one of claims 1 to 11, for heat recovery during the production of isoprenol, wherein a first reactant stream is an isobutylene stream, a second reactant is a formaldehyde source stream, the chemical reaction product is an isoprenol-containing product, and the isoprenol-containing product is heat exchanged with the isobutylene stream.

13. 13. The method of claim 12 comprising reacting the formaldehyde source with isobutylene at a temperature of at least 220°C and an absolute pressure of at least 200 bar.

14. 14. The method of claim 12 or 13 comprising reacting a molar excess of isobutylene with the formaldehyde source, calculated as formaldehyde.

15. The method according to any one of claims 12 to 14, wherein the formaldehyde source is an aqueous formaldehyde solution.

16. 16. The method of claim 15, wherein the aqueous formaldehyde solution comprises at least 15 wt.-%, preferably at least 25 wt.-%, more preferably at least 35 wt.-%, and most preferably at least 45 wt.-% or at least 50 wt.-% formaldehyde, based on the total weight of the aqueous formaldehyde solution.

17. The method of any one of claims 12 to 16, wherein the formaldehyde source and isobutylene are reacted essentially in the absence of a catalyst.

18. 1. A plant for the production of a chemical reaction product, comprising: a reactor having at least one reactant inlet for receiving at least one reactant stream and a reaction product outlet for removing a high temperature chemical reaction product stream from said reactor; at least two shell-and-tube heat exchangers, each of said heat exchangers comprising a plurality of tubes and shell-side heat exchange passages, said heat exchangers being connected in series with respect to both said shell-side flow and said tube-side flow and being interconnected such that said hot chemical reaction products are conducted through the tubes of said heat exchangers and said reactants are conducted through the shell-side passages; optionally a heater for further increasing the temperature of said reactant stream, wherein the plant has an extended operating interval between maintenance breaks and / or reduced energy consumption when said heater is used, compared to an otherwise identical plant having a single shell-and-tube heat exchanger instead of at least two shell-and-tube heat exchangers in series.

19. 20. The plant of claim 18, wherein the hot reaction products from the reactor and the reactants flow countercurrently through the heat exchanger.

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