Reducing maintenance and increasing energy savings in chemical reaction product production involving heat recovery

Abstract

Disclosed is a method for extending the operating interval between maintenance interruptions in the production of chemical reaction products, the method comprising directing at least one reactant stream into a reactor; reacting the one or more reactants in a reactor at elevated temperature and pressure, thereby obtaining a chemical reaction product; withdrawing a thermochemical reaction product stream from the reactor; and subjecting the thermochemical reaction product stream to heat exchange with at least one of the reactant streams; wherein the heat exchange is carried out in at least two shell and tube heat exchangers; each of the heat exchangers includes a plurality of tubes and a shell-side heat exchange channel; wherein the thermochemical reaction product is directed through the tubes of the heat exchanger; and reactants are conducted through the shell-side channel, 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. By using two or more heat exchangers, the impact of fouling in individual tubes on the overall heat exchange capacity is reduced compared to an arrangement using only a single heat exchanger.

Description

[0001] In chemical processes, various waste heat sources may be available, for example, from cooling the intermediate product streams or flue gases of any combustion process. Heat recovery in the production process of chemical reaction products is highly desirable. The heat available at a temperature of at least 400° C. to 500° C. is typically recovered by producing hot steam, which can be used in the process itself, or expanded in a turbine to produce energy. The heat available at lower temperatures is generally not suitable for energy production, and may be recovered, for example, by preheating one or more process streams. Preheating typically occurs by indirect heat exchange of a thermochemical reaction product stream with a reactant stream, thereby transferring heat to the reactant stream.

[0002] The temperature of the reactant stream preheated by indirect heat exchange with the thermochemical reaction products can be further adjusted, typically by further increasing the temperature in a heater before the reactant stream is introduced into the reactor. Any means for adjusting the temperature can be applied. Such means include, but are not limited to, electrical heating, direct flame heating, and / or exchanging heat with another medium such as steam or hot oil.

[0003] One type of heat exchanger commonly used in conjunction 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 another fluid is forced through the shell and over the outside of the tubes. Baffles are typically installed to support the tubes and force the fluid to flow over the tube bundle in a serpentine manner.

[0004] One of the most problematic aspects associated with the use of heat exchangers is the tendency to foul. Fouling refers to various deposits and coatings that form on the surfaces of a heat exchanger as a result of process fluid flow and heat transfer. There are various types of fouling, including corrosion, mineral deposition, polymerization, crystallization, coking, sedimentation, and biofouling. In the case of corrosion, the surfaces of the heat exchanger may corrode due to the interaction between the process fluid and the materials used in the construction of the heat exchanger. The situation is even worse because the various fouling types may interact with each other to cause even more fouling. Fouling causes additional resistance in heat transfer and therefore reduces performance in terms of heat transfer. Fouling also causes an increase in the pressure drop associated with the fluid flowing inside the exchanger.

[0005] One particular area that is susceptible to fouling in conventional shell and tube heat exchangers is the area of ​​the tubes near the tube sheet, close to the inlet, where the tube side fluid leaves the individual tubes. Excessive fouling in this area can lead to plugging of individual tubes and fluid stagnation along the entire length of these tubes. Fluid stagnation generally results in reduced heat transfer performance.

[0006] As another consequence of the reduced heat transfer performance caused by fouling, the energy required in the heater to adjust the temperature of the preheated reactant stream to the desired reaction temperature increases. As a result, more additional external heat becomes necessary (which is disadvantageous in terms of energy requirements and process economics) and often has a negative impact on the carbon dioxide footprint of the product.

[0007] The preferred but non-exclusive application of the present invention is extended heat recovery, more particularly in the process and equipment of synthesizing prenol, extending the operating interval between maintenance interruptions. Prenol or 3-methyl-3-butene-1-ol is an important intermediate for medicines and aromatic compounds, with an annual global production of thousands of tons. Prenol is commercially synthesized by reacting formaldehyde with isobutylene. In the uncatalyzed reaction of formaldehyde with isobutylene, high temperatures are required to obtain high prenol yields. Effectively removing heat is critical for product quality and process safety. The heat removed from prenol is used to raise its temperature before isobutylene enters the reactor.

[0008] The problem faced by the present invention can be seen in designing a process and apparatus to maintain adequate heat transfer performance of a shell and tube heat exchanger used for heat recovery in a chemical process, even in the event of failure of individual tubes of the heat exchanger due to fouling. The improved process should enable extended operating intervals between maintenance interruptions, reduced energy requirements for adjusting the temperature of the preheated reactant stream to the reaction temperature, and thus improved process economics.

[0009] The problem is solved by a method for extended heat recovery in a chemical reaction product production process, more particularly in such a method to extend the operating intervals between maintenance interruptions, the method comprising

[0010] - directing at least one reactant stream into a reactor;

[0011] - reacting the one or more reactants in a reactor at high temperature and high pressure, thereby obtaining a chemical reaction product;

[0012] - withdrawing a thermochemical reaction product stream from the reactor; and

[0013] - exchanging heat between a thermochemical reaction product stream and at least one of the reactant streams;

[0014] wherein heat exchange is performed in at least two shell and tube heat exchangers, preferably in countercurrent mode; each of the heat exchangers comprising a plurality of tubes and shell side heat exchange channels;

[0015] wherein the thermochemical reaction products are directed through tubes of the heat exchangers; and the reactants are directed through shell side channels, 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.

[0016] The term "maintenance disruption" is intended to mean the need to stop the process at intervals in order to clean the tubes of a heat exchanger that is clogged with scaling. Typically, a maintenance disruption is indicated when the reactants leaving the last heat exchanger are insufficiently preheated and even subsequent heaters are barely able to add additional external heat to the reactants to bring them to the desired temperature before they enter the reactor. One aspect of the invention is that the preheating of the at least one reactant can be maintained at a sufficiently high level for a longer period of time so that the desired temperature of the one or more reactants can be readily reached before the one or more reactants enter the reactor.

[0017] According to the invention, the heat exchange is carried out in at least two shell and tube heat exchangers which are connected in series with respect to both the shell side flow and the tube side flow. Preferably, at least the first heat exchanger, more preferably each of the heat exchangers, is operated in countercurrent mode. The at least one reactant stream is directed through the shell side channels of the first heat exchanger and subsequently through the shell side channels of the second and all further heat exchangers; and the thermochemical reaction products are directed to the tubes of the heat exchangers in reverse order with respect to the direction of the at least one reactant stream.

[0018] By using two or more heat exchangers, the effect of fouling in individual tubes on the overall heat exchange capacity is reduced compared to an arrangement using only a single heat exchanger. Thus, the heat transfer rate is maintained at a desired level for a longer period of time, thereby extending the operating interval between maintenance interruptions, and less additional external heat is required for preheating of the at least one reactant stream compared to an apparatus having a single heat exchanger in a severely fouled state.

[0019] It is envisioned that process interruptions for shutdowns and maintenance will not be required as frequently.

[0020] The physical state of the thermochemical reaction product is not particularly limited as long as it is a fluid stream. The thermochemical reaction product may be in a gaseous state, a supercritical state or a liquid state. In one embodiment, the thermochemical reaction product stream is a liquid stream.

[0021] The present invention solves the problem that may occur during indirect heat exchange in a shell and tube heat exchanger when the thermochemical reaction products are susceptible to fouling.

[0022] A chemical reaction product is considered "prone to fouling" if, in a fouling test, the chemical reaction products, as they circulate through the tubes of a single shell and tube heat exchanger relative to a coolant directed through the shell side of the heat exchanger (e.g., a reactant stream that requires preheating), form deposits on the tube walls, ultimately causing the individual tubes to become plugged. As a result, the heat exchange efficiency is reduced and the outlet temperature of the coolant is reduced. In a fouling test, the heat exchange reduces the temperature of the hot chemical reaction product stream by 150°C. A single heat exchanger may be one having 300 tubes having an outer diameter of 14 mm, an inner diameter of 10 mm, and a length of 10 m, resulting in a 130 m 2 The (external) heat exchange surface of the heat exchanger. A means for determining whether a single heat exchanger is blocked during operation may be to monitor the heat transfer coefficient k of the single heat exchanger over time during heat exchange under constant conditions. The heat transfer coefficient k may be determined as follows:

[0023]

[0024] in

[0025]

[0026] A = heat exchange surface

[0027] ΔT log = logarithmic temperature difference between hot and cold streams

[0028] A chemical reaction product is considered "prone to fouling" if the heat transfer coefficient k of a single heat exchanger decreases by more than 15%, preferably by more than 30% over a period of 180 days, preferably 150 days, more preferably 120 days and even more preferably 100 days.

[0029] Typically, the phase change of the thermochemical reaction product upon cooling is associated with a tendency to foul. Thus, in an embodiment, the thermochemical reaction product undergoes at least a partial phase change during the heat exchange process. For example, the thermochemical reaction product may undergo a transition from supercritical to liquid, from gas to liquid, or from liquid to suspension. A transition from liquid to suspension may occur if the solubility limit of a component decreases upon cooling, resulting in the precipitation of the component.

[0030] Generally, cooling the thermochemical reaction product to a large extent is associated with a tendency to fouling. Therefore, in an embodiment, the heat exchange can reduce the temperature of the thermochemical reaction product stream by at least 100° C., preferably in the range of 120° C. to 180° C., more preferably in the range of 130° C. to 160° C. In this case, the thermochemical reaction product stream has a temperature difference, which can be calculated by the tube side inlet temperature of the last heat exchanger (e.g., the second heat exchanger if two heat exchangers are connected in series) and the tube side outlet temperature of the first heat exchanger.

[0031] By using two or more heat exchangers, the effect of gradual degradation of the heat transfer of the first heat exchanger over time (relative to the direction of the at least one reactant flow) caused by fouling in individual tubes in the first heat exchanger on the overall heat exchange capacity is reduced compared to an arrangement using only a single heat exchanger.

[0032] In an embodiment, the reduction in the total heat transfer coefficient k of all heat exchangers connected in series is less than the reduction in the heat transfer coefficient k of the first heat exchanger, preferably at least 10 percentage points less. For example, if the heat transfer coefficient k of the first heat exchanger is reduced by 35%, the total heat transfer coefficient k of all heat exchangers connected in series should be reduced by a value at least 10 percentage points lower than 35%, i.e. by less than 25%. The "first" heat exchanger is the first heat exchanger seen in the direction of the at least one reactant stream.

[0033] The thermochemical reaction products flow inside the tubes, while the reactants are forced to pass through the shell and flow through the outside of the tubes. The thermochemical reaction products can be directed through the tubes in an upward direction or a downward direction, preferably in a downward direction. Typically, baffles are placed to support the tubes and force the reactants to flow over the tube bundle in a serpentine manner. In their travel through the shell-side channels, the reactants are usually made to follow a tortuous path, the major part of which is horizontal, while the overall direction of travel of the reactants in the shell-side channels is vertical, countercurrent to the flow direction of the thermochemical reaction products inside the tubes.

[0034] According to the invention, both the flow path of the thermochemical reaction product stream and the reactant stream flow path comprise at least two heat exchangers connected in series with respect to both the shell side stream and the tube side stream. Two or more heat exchangers placed in parallel may be connected in series with at least one heat exchanger.

[0035] This includes embodiments in which heat exchange is performed in three or more heat exchangers, wherein a first heat exchanger is connected in series with two or more second heat exchangers arranged in parallel with each other. In this regard, a "first" heat exchanger and a "second" heat exchanger are observed in the flow direction of the shell side stream.

[0036] In a preferred embodiment, the heat exchange is carried out in 2 to 6 heat exchangers connected in series, preferably in 2 to 5 heat exchangers, more preferably in 2 to 4 heat exchangers, and most preferably in 2 to 3 heat exchangers. In view of the fact that any additional heat exchangers beyond two require higher investment and maintenance costs, and the benefits that can be achieved by using more than two heat exchangers do not increase to the same extent, 2 heat exchangers are generally preferred.

[0037] The required total 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 ​​the heat exchanger corresponds to the sum of the tube wall surfaces in contact with the shell side flow. The ratio of the heat exchange surface area of ​​each individual heat exchanger relative to the heat exchange surface area of ​​each of the other individual heat exchangers 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, in the case of two shell and tube heat exchangers 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.

[0038] The heat exchangers typically each comprise from 50 to 5000 tubes, more preferably from 400 to 3000 tubes, most preferably from 800 to 2000 tubes.

[0039] The tube preferably has an internal diameter in the range of 6 to 25 mm, more preferably 8 to 16 mm, most preferably 8 to 12 mm.

[0040] Preferably, the tube has a length of 2 to 30 m, for example 2 to 25 m, preferably 2 to 20 m, most preferably 5 to 20 m, such as 5 to 15 m.

[0041] In an embodiment, the heat exchangers each comprise 50 to 5000 tubes having an inner diameter in the range of 6 to 25 mm and a total tube length of 2 to 30 m.

[0042] 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.

[0043] The thermochemical reaction product stream contains sensible heat from the chemical reaction. Sensible heat is potentially recoverable energy that can be reused. In an embodiment, the withdrawn thermochemical reaction product stream has a temperature in the range of 50°C to 800°C, preferably 50°C to 400°C, and an absolute pressure in the range of 1 to 400 bar, preferably 20 to 400 bar, more preferably 50 to 400 bar.

[0044] In a preferred embodiment, the inventive method is a method for heat recovery in a production process of prenol, more particularly to extend the operating interval between maintenance interruptions in such a method. In the process, the first reactant stream is an isobutylene stream, and the second reactant is a stream of a formaldehyde source, and the chemical reaction product is a product containing prenol. The product containing prenol is heat exchanged with the isobutylene stream.

[0045] Preferably, the production of isopentenol is carried out under supercritical conditions. Supercritical conditions exist when a substance or a mixture of substances is subjected to a temperature and pressure exceeding the thermodynamic critical point of the substance or mixture. In this state, there is no distinction between the liquid phase and the gas phase, and the fluid is called a dense gas, in which the saturated vapor and saturated liquid states are the same. It has been found that under supercritical conditions, the reactivity of isobutylene to formaldehyde is high enough to allow a smooth reaction even in the absence of an external solvent or catalyst. This results in a reduced amount of by-products.

[0046] It is believed that supercritical isobutylene acts as a supercritical solvent, which dissolves at least a portion of the formaldehyde source and / or extracts formaldehyde from the formaldehyde source. This allows formaldehyde to be effectively mixed with isobutylene, thereby alleviating the problems usually associated with mixed multiphases. For example, local supersaturation of formaldehyde can be avoided. Therefore, although ideally, the entire reaction mixture (including the formaldehyde source and isobutylene) becomes a uniform single phase in the supercritical or near-supercritical region, it is also envisioned that part of the formaldehyde source exists as a second liquid phase. Moreover, the prenol formed in the reaction can be dissolved in the near-supercritical or supercritical reaction mixture, or cause the formation of a separate liquid phase.

[0047] The formation of a supercritical reaction mixture of isobutene and formaldehyde requires that at least the isobutene used in excess be supplied to the reactor both as reactant and as solvent at the necessary pressure and temperature. To achieve the necessary temperature of the isobutene, energy-consuming heaters are typically required. If the preheating of the isobutene by heat exchange with the hot prenol product is gradually reduced due to rapid and severe fouling of the single heat exchanger typically used, more and more additional energy is required.

[0048] Phase diagrams of the reaction components are readily available to those skilled in the art. In addition, the critical point of a compound or mixture can be determined by calculating or experimentally obtaining a phase diagram of the compound or mixture. From the above, it is apparent that the pressure and temperature required for the process are sufficient to maintain at least isobutylene in a supercritical state. The critical temperature Tc and pressure Pc of isobutylene are Tc=417.9K 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).

[0049] To achieve supercritical conditions, formaldehyde and isobutylene are preferably reacted at a temperature of at least 220°C (e.g. in the range of 220°C to 290°C) and an absolute pressure of at least 200 bar, more preferably at a temperature of at least 250°C (e.g. in the range of 250°C to 280°C) and an absolute pressure of at least 220 bar, and most preferably at a temperature of at least 260°C (e.g. in the range of 260°C to 275°C) and an absolute pressure of at least 250 bar. Unless otherwise stated, all pressures quoted herein are absolute pressures.

[0050] Preferably, a molar excess of isobutene is reacted with formaldehyde. The term "molar excess of isobutene" is understood to mean a molar excess of isobutene compared to formaldehyde. This leads to a relatively low concentration of formaldehyde in the reaction mixture, thereby reducing the likelihood of local supersaturation of formaldehyde. As a result, the amount of by-products obtained is reduced. In addition, it was found that the greater the molar ratio of isobutene to formaldehyde, the lower the tendency of the reaction mixture to form multiple phases.

[0051] 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, and most preferably at least 12:1, such as at least 12.5:1.

[0052] The formaldehyde may be provided as a liquid, for example as a solution of paraformaldehyde. Preferably, the formaldehyde source is an aqueous formaldehyde solution. When the formaldehyde is provided as an aqueous solution, the solution preferably comprises at least 15 wt.-%, more preferably at least 25 wt.-% and most preferably at least 35 wt.-%, e.g. at least 45 wt.-% or at least 50 wt.-% formaldehyde, based on the total weight of the aqueous formaldehyde solution.

[0053] Sufficient fluid mixing is important in the production of prenol. Therefore, the production of prenol preferably involves mixing and injecting a formaldehyde source and isobutylene into the reactor by a plurality of nozzles running in parallel. Preferably, a plurality of nozzles are arranged in the lid of the reactor. In order to allow high mixing and avoid dead zones, the nozzle should be flush with the lid.

[0054] 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 its injection into the reactor, or a liquefied or gaseous phase close to its supercritical state prior to injection into the reactor. Either way, the isobutylene needs to be heated before it is injected, typically by a combination of preheating via heat exchange with the hot prenol product and then passing through an energy consuming heater directly prior to injection, wherein energy consumption increases if preheating by heat exchange is hampered by reduced heat transfer due to heat exchanger fouling.

[0055] Further details on reactor design and reaction conditions can be found, for example, in WO 2020 / 049111 A1.

[0056] Furthermore, the present invention relates to an apparatus for producing a chemical reaction product, the apparatus comprising:

[0057] - a reactor having at least one reactant inlet for receiving at least one reactant stream and a reaction product outlet for withdrawing a thermochemical reaction product stream from the reactor;

[0058] - at least two shell and tube heat exchangers, each of which comprises a plurality of tube and shell side heat exchange channels; wherein the heat exchangers are connected in series with respect to both the shell side flow and the tube side flow; and are interconnected such that the thermochemical reaction products are directed through the tubes of the heat exchangers; and the reactants are directed through the shell side channels;

[0059] - Optionally, a heater for further increasing the temperature of the reactant stream.

[0060] Where a heater is used, the apparatus may have extended operating intervals between maintenance interruptions and / or reduced energy consumption; this is compared to the same apparatus except having a single shell and tube heat exchanger instead of at least two shell and tube heat exchangers in series.

[0061] In an embodiment, the apparatus is adapted to enable countercurrent flow of hot reaction products from the reactor and reactants through the heat exchanger.

[0062] One aspect of the present invention relates to an apparatus for producing chemical reaction products having an extended operating interval, wherein the apparatus comprises a step of heat exchanging a hot chemical reaction product stream with one or more reactant streams before introducing at least one reactant stream into a reactor, and preferably a subsequent heater for the at least one reactant stream, and wherein the apparatus 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 operating interval is extended compared to an apparatus that is identical except that it has a single shell and tube heat exchanger instead of the at least two shell and tube heat exchangers in series of the apparatus of the present invention.

[0063] A further aspect of the present invention relates to an apparatus for producing chemical reaction products with reduced energy consumption, wherein the apparatus comprises a step of heat exchanging a hot chemical reaction product stream with one or more reactant streams before introducing at least one reactant stream into a reactor, and preferably a subsequent heater for the at least one reactant stream, and wherein the apparatus 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 identical apparatus except that it has a single shell and tube heat exchanger instead of the at least two shell and tube heat exchangers in series of the apparatus of the present invention.

[0064] Where applicable, the above embodiments concerning the process of the invention are also valid for the apparatus of the invention.

[0065] Another embodiment is the use of at least two shell and tube heat exchangers in series in an apparatus for producing a chemical reaction product that includes a step of heat exchanging a hot chemical reaction product stream with another stream (e.g., a reactant stream) to increase the intervals between maintenance interruptions compared to the same apparatus except having a single shell and tube heat exchanger instead of the at least two shell and tube heat exchangers in series.

[0066] Yet another embodiment of the present invention is the use of at least two shell and tube heat exchangers in series in an apparatus for producing a chemical reaction product comprising the step of heat exchanging a hot chemical reaction product stream and at least one reactant stream and subsequently a heater for the at least one reactant stream to reduce energy consumption compared to the same apparatus except having a single shell and tube heat exchanger instead of the at least two shell and tube heat exchangers in series.

[0067] The present invention is further illustrated by the following examples and drawings.

[0068] Figure 1 (A) to Figure 1 (C) Schematic diagram depicting different operating states and arrangements of a shell and tube heat exchanger.

[0069] Figure 1 (A) depicts a schematic diagram of a shell and tube heat exchanger 1, which includes a cylindrical shell and a plurality of tubes 2', 2", 2'" arranged within the shell. Shell-side heat exchange channels 3 allow heat transfer liquid to circulate in the spaces between the tubes and within the shell. The heat exchange channels 3 may include baffles (not shown) to optimize the flow of the heat transfer liquid through the heat exchange channels 3.

[0070] A stream of thermochemical reaction products, obtained, for example, from a chemical reaction in a reactor (not shown), is introduced via line 6 and distributed via the upper tube sheet to the tubes 2', 2", 2'" of the shell and tube heat exchanger 1. The tubes 2', 2", 2'" have a total length L from the upper tube sheet to the lower tube sheet. At the same time, reactants are introduced via line 4 and conducted through the shell-side channels 3 of the shell and tube heat exchanger 1. Heat is transferred from the thermochemical reaction products to the reactant stream via the walls of the tubes 2', 2", 2'".

[0071] The chemical reaction product stream is withdrawn at the bottom of the shell and tube heat exchanger 1 through line 7 of the shell and tube heat exchanger 1, wherein the stream withdrawn through line 7 has a lower temperature than the hot chemical reaction product stream introduced via line 6. The preheated reactants are withdrawn at the top of the shell and tube heat exchanger 1 through line 5 of the shell and tube heat exchanger 1 and can be directed to a reactor (not shown) or further heated if necessary. The reactants withdrawn through line 5 have a higher temperature than the reactants introduced via line 4.

[0072] Figure 1 (B) depicts the Figure 1 The same shell and tube heat exchanger 1 shown in (A) is shown in operation in which the tube 2" is blocked by a blockage 8 near the lower tube sheet. This results in a reduced flow of the thermochemical reaction product stream through the tube 2", or stagnation of liquid above the lower tube sheet in the tube 2". As a result, substantially the entire wall surface of the tube 2" is no longer available for heat transfer, and the heat transfer efficiency of the shell and tube heat exchanger 1 is reduced.

[0073] Figure 1 (C) depicts an arrangement of two shell and tube heat exchangers in series, comprising a first shell and tube heat exchanger 1B and a second shell and tube heat exchanger 1A.

[0074] In terms of the flow direction of the at least one reactant, the first shell and tube heat exchanger 1B includes a plurality of tubes 2B', 2B", 2B"' and a shell side heat exchange channel 3B. The tubes 2B', 2B", 2B"' of the first shell and tube heat exchanger 1B have a total length L2 from the upper tube sheet to the lower tube sheet.

[0075] The second shell and tube heat exchanger 1A includes a plurality of tubes 2A', 2A", 2A"' and shell side heat exchange channels 3A in the flow direction of the one or more reactants. The tubes 2A', 2A", 2A"' of the second shell and tube heat exchanger 1A have a total length L1 from the upper tube sheet to the lower tube sheet.

[0076] 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.

[0077] The first shell and tube heat exchanger 1B and the second shell and tube heat exchanger 1A are connected in series with respect to both the shell side flow and the tube side flow. The hot reaction product is introduced into the second shell and tube heat exchanger 1A via pipeline 6A and distributed to tubes 2A', 2A", 2A"' via the upper tube sheet. The partially cooled product produced from the tubes 2A', 2A", 2A"' of the second shell and tube heat exchanger 1A is introduced into the first shell and tube heat exchanger 1B via pipeline 7A and distributed to tubes 2B', 2B", 2B"' via the upper tube sheet. Conversely, the reactant to be preheated is introduced into the shell side channel 3B of the first shell and tube heat exchanger 1B via pipeline 4B and, after leaving the shell side channel 3B, is directed to the shell side channel 3A of the second shell and tube heat exchanger 1A via pipeline 5B. The preheated reactant is extracted through pipeline 5A.

[0078] During operation, fouling may occur, resulting in obstructions 8B in tube 2B". This results in partial or complete obstruction of tube 2B", i.e., in a reduction in the flow of the thermochemical reaction product stream through tube 2B". Only the wall surface of tube 2B" is no longer available for heat transfer. Therefore, Figure 1 (B) Compared to the case where individual tubes are blocked, there is still a larger tube wall surface available for heat transfer.

[0079] It is also possible that in some chemical production processes, fouling may occur by partially or completely blocking the tubes (e.g. 2A") in the heat exchanger 1A. If it were included in the figure, it would similarly be 8A. In this case, the invention allows the still partially hot reaction products to utilize the full wall surface of the heat exchanger 1B including the tubes 2B", while in the case of Figure 1 In the case of a single shell and tube heat exchanger shown in (A), fouling in the upper half of a tube such as tube 2" will effectively result in the loss of the entire wall surface of tube 2" over the full length of the heat exchanger with respect to heat transfer with the at least one reactant flow in the shell surrounding tube 2".

[0080] It must be understood that if Figure 1The arrangement in series of at least two shell-and-tube heat exchangers of the invention shown in does not limit the invention to physically separated at least two such heat exchangers in series. For example, these can be in one housing. Moreover, in one aspect of the invention, the at least two heat exchangers in series are understood to include a device that is similar to a single heat exchanger at first glance, except that it has such a region in the middle part, in which the partially cooled reaction product flow running through the tubes of one part of the heat exchange unit is recombined and then divided again into a flow fed by further tubes in another part of the shell-and-tube heat exchange unit for further transferring heat to the at least one reactant that needs preheating entering this part of the heat exchange unit - by this, two shell-and-tube heat exchangers are formed in a single heat exchange unit.

[0081] Examples

[0082] For the industrially important conversion of isobutene and formaldehyde to prenol, the isobutene must be preheated. For this purpose, the hot product prenol is heat exchanged with the isobutene.

[0083] The heat exchange performance between the hot isopentanol stream and the cold isobutylene stream was calculated by applying the heat transfer correlation, which is given in [VDI Heat Transfer Atlas], VDI-Gesellschaft Verfahrenstechnik und Chemieingenieurwesen Hrsg. [VDI-Society for Process Engineering and Chemical Engineering], 11., bearbeitete und erweiterte Auflage [revised and supplemented edition] (e.g. Chapter G1 "Durchstrδmte Rohre [Flow Pipe]"; Volker Gnielinski, Institut für thermische Verfahrenstechnik [Institute for Thermal Process Engineering], Karlsruher Institut für Technologie [Karlsruhe Institute of Technology]", pp. 785-791).

[0084] Simulate heat exchange based on the following scenarios:

[0085] (1) A single shell and tube heat exchanger (reference example) with 1942 tubes having an outer diameter of 14 mm, an inner diameter of 8 mm, and a length of 14 m, resulting in 1025 m 2 The heat exchange surface

[0086] (2) Two shell and tube heat exchangers connected in series (according to an example of the present invention) with a 1025m 2 Total heat exchange surface area:

[0087] - A first shell and tube heat exchanger with 1942 tubes having an outer diameter of 14 mm, an inner diameter of 8 mm and a length of 7 m, resulting in 512.5 m 2 of heat exchange surface, and

[0088] - A second shell and tube heat exchanger with 1942 tubes having an outer diameter of 14 mm, an inner diameter of 8 mm and a length of 7 m, resulting in 512.5 m 2 heat exchange surface.

[0089] The following specifications apply:

[0090] - isobutylene: mass flow rate = 81.1 t / h, and

[0091] -Isopentenol: mass flow rate = 87.9 t / h.

[0092] The simulation results are shown in Table 1. "Blockage" is related to the percentage of tubes that failed due to fouling. These tubes are considered to no longer contribute to the heat exchange performance.

[0093]

Claims

1. A method for extending operating intervals between maintenance interruptions in the production of a chemical reaction product, the method comprising: - directing at least one reactant stream into a reactor; - reacting the one or more reactants in the reactor at high temperature and high pressure, thereby obtaining the chemical reaction product; - withdrawing a stream of thermochemical reaction products from the reactor; as well as - exchanging heat between the thermochemical reaction product stream and at least one of the reactant streams; wherein the heat exchange is performed in at least two shell and tube heat exchangers; each of these heat exchangers comprises a plurality of tubes and shell side heat exchange channels; wherein the thermochemical reaction product is directed through the tubes of the heat exchangers; and the reactants are directed through the shell side channel, and at least two of the heat exchangers are connected in series with respect to both shell side flow and tube side flow.

2. The method according to claim 1, wherein: The thermochemical reaction products are susceptible to scaling during heat exchange processes.

3. The method according to claim 1 or 2, wherein: The heat transfer of the first heat exchanger progressively degrades relative to the direction of the at least one reactant stream.

4. A method according to any one of the preceding claims, wherein: The reduction in the total heat transfer coefficient k of all heat exchangers connected in series relative to the direction of the at least one reactant stream is smaller than the reduction in the heat transfer coefficient k of the first heat exchanger, preferably at least 10 percentage points smaller.

5. A method according to any one of the preceding claims, wherein: The thermochemical reaction product undergoes at least a partial phase change during the heat exchange process.

6. A method according to any one of the preceding claims, wherein: The heat exchange reduces the temperature of the thermochemical reaction product stream by at least 100°C, preferably in the range of 120°C to 180°C, more preferably in the range of 130°C to 160°C.

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

1.

8. A method according to any one of the preceding claims, wherein: The heat exchange is carried out in 2 to 4 heat exchangers, preferably in 2 to 3 heat exchangers, which are connected in series.

9. A method according to any one of the preceding claims, wherein: These heat exchangers each comprise 50 to 5000 tubes having an inner diameter in the range of 6 to 25 mm and a total tube length of 2 to 30 m.

10. A method according to any one of the preceding claims, wherein: The length of the heat exchangers ranges from 10 to 30 m and the diameter of the shell ranges from 0.5 to 2 m.

11. A method according to any one of the preceding claims, wherein: The thermochemical reaction product stream has a temperature in the range of 50°C to 800°C and a pressure in the range of 1 to 400 bar absolute.

12. The method according to any one of the preceding claims, which is a method for heat recovery in the production process of prenol, wherein the first reactant stream is an isobutylene stream and the second reactant is a formaldehyde source stream, wherein the chemical reaction product is a prenol-containing product, and the prenol-containing product is heat exchanged with the isobutylene stream.

13. A process according to claim 12, comprising reacting the formaldehyde source with isobutylene at a temperature of at least 220°C and a pressure of at least 200 bar absolute.

14. A process according to 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. The method according to claim 15, wherein: The aqueous formaldehyde solution comprises at least 15 wt.-%, preferably at least 25 wt.-%, more preferably at least 35 wt.-%, 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 according to any one of claims 12 to 16, wherein: The formaldehyde source and isobutylene are reacted in the substantial absence of a catalyst.

18. An apparatus for producing a chemical reaction product, the apparatus comprising: - a reactor having at least one reactant inlet for receiving at least one reactant stream and a reaction product outlet for withdrawing a thermochemical reaction product stream from the reactor; - at least two shell and tube heat exchangers, each of the heat exchangers comprising a plurality of tubes and shell-side heat exchange channels; wherein the heat exchangers are connected in series with respect to both shell-side and tube-side flows; and are interconnected such that the thermochemical reaction products are directed through the tubes of the heat exchangers; and the reactants are directed through the shell-side channels; - optionally, a heater for further increasing the temperature of the reactant stream; Wherein with the heater the apparatus has extended operating intervals between maintenance interruptions and / or reduced energy consumption; this is compared to the same apparatus except having a single shell and tube heat exchanger instead of at least two shell and tube heat exchangers in series.

19. The apparatus according to claim 18, wherein: The hot reaction products from the reactor and the reactants flow countercurrently through the heat exchangers.

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