REDUCING MAINTENANCE AND INCREASING ENERGY SAVINGS IN THE PRODUCTION OF A CHEMICAL REACTION PRODUCT INVOLVING HEAT RECOVERY

Abstract

A method for prolonging operation intervals between maintenance disruptions in the production of a chemical reaction product, comprising directing at least one reactant stream into a reactor; reacting the reactant(s) in the reactor at elevated temperature and pressure, whereby the chemical reaction product is obtained; withdrawing a stream of a hot chemical reaction product from the reactor; and heat-exchanging the stream of hot chemical reaction product with at least one of the reactant streams; wherein heat-exchanging is performed in at least two shell-and-tube heat exchangers; each of the heat exchangers comprising a plurality of tubes and a shell-side heat exchange passage; wherein the hot chemical reaction product is directed through the tubes of the heat exchangers; and the reactant is guided through the shell-side passage, and at least two of the heat exchangers are connected in series with regard 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 in comparison to arrangements where only a single heat exchanger is used.

Claims

1.-19. (canceled)

20. A method for prolonging operation intervals between maintenance disruptions in the production of a chemical reaction product, comprising directing at least one reactant stream into a reactor; reacting the at least one reactant in the reactor at elevated temperature and pressure, whereby the chemical reaction product is obtained; withdrawing a stream of a hot chemical reaction product from the reactor; and heat-exchanging the stream of hot chemical reaction product with at least one of the reactant streams; wherein heat-exchanging is performed in at least two shell-and-tube heat exchangers; each of the heat exchangers comprising a plurality of tubes and a shell-side heat exchange passage; wherein the hot chemical reaction product is directed through the tubes of the heat exchangers; and the reactant is guided through the shell-side passage, and at least two of the heat exchangers are connected in series with regard to both the shell-side flow and the tube-side flow.

21. The method according to claim 20, wherein the hot chemical reaction product is prone to fouling during heat exchange.

22. The method according to claim 20, wherein the heat transfer of the first heat exchanger, relative to the direction of the at least one reactant stream, gradually deteriorates.

23. The method according to claim 20, wherein the reduction of the overall heat transfer coefficient k of all heat exchangers connected in series is less than the reduction of the heat transfer coefficient k of the first heat exchanger, relative to the direction of the at least one reactant stream, preferably by at least 10 percentage points.

24. The method according to claim 20, wherein the hot chemical reaction product undergoes an at least partial phase change during the heat exchange.

25. The method according to claim 20, wherein heat exchanging reduces the temperature of the stream of hot chemical reaction product by at least 100 C.

26. The method according to claim 20, 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.

27. The method according to claim 20, wherein heat-exchanging is performed in 2 to 4 heat exchangers connected in series.

28. The method according to claim 20, wherein the heat exchangers each comprise 50 to 5000 tubes with an inner diameter in the range of 6 to 25 mm and an overall tube length of 2 to 30 m.

29. The method according to claim 20, wherein the length of the heat exchangers 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.

30. The method according to claim 20, wherein the stream of the hot chemical reaction product has a temperature in the range of from 50 to 800 C. and an absolute pressure in the range of from 1 to 400 bar.

31. The method according to claim 20, which is a method for heat recovery during the production of isoprenol, wherein a first reactant stream is an isobutylene stream and a second reactant is a stream of a formaldehyde source, wherein the chemical reaction product is an isoprenol-containing product, and the isoprenol-containing product is heat-exchanged with the isobutylene stream.

32. The method according to claim 31, comprising reacting the formaldehyde source and isobutylene at a temperature of at least 220 C. and an absolute pressure of at least 200 bar.

33. The method according to claim 31, comprising reacting a molar excess of isobutylene with the formaldehyde source, calculated as formaldehyde.

34. The method according to claim 31, wherein the formaldehyde source is an aqueous formaldehyde solution.

35. The method according to claim 34, wherein the aqueous formaldehyde solution comprises at least 15 wt.-%, of formaldehyde, based on the total weight of the aqueous solution of formaldehyde.

36. The method according to claim 31, wherein the formaldehyde source and isobutylene are reacted in the essential absence of a catalyst.

37. 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 withdrawing a stream of a hot chemical reaction product from the reactor; at least two shell-and-tube heat exchangers, each of the heat exchangers comprising a plurality of tubes and a shell-side heat exchange passage; wherein the heat exchangers are connected in series with regard to both the shell-side flow and the tube-side flow; and are interconnected such that the hot chemical reaction product is directed through the tubes of the heat exchangers; and the reactant is guided through the shell-side passage; optionally, a heater for further increasing the temperature of the reactant stream; wherein the plant has prolonged operation intervals between maintenance disruptions and/or decreased energy consumption in case the heater is used; compared to an identical plant except for having a single shell-and-tube heat exchangers in place of at least two shell-and-tube heat exchangers in series.

38. The plant according to claim 37, wherein the hot reaction product from the reactor and the reactant are flowing countercurrently through the heat exchangers.

Description

[0066] The invention is further illustrated by the examples and figures that follow.

[0067] FIG. 1(A) to (C) depict schematic illustrations of different operational states and arrangements of shell-and-tube heat exchangers.

[0068] FIG. 1(A) depicts a schematic illustration of a shell-and-tube heat exchanger 1 comprising a cylindrical shell and a plurality of tubes 2, 2, 2 arranged within the shell. A shell-side heat exchange passage 3 allows for circulating a heat transfer liquid in the space between the tubes and within the shell. The heat exchange passage 3 may comprise baffles (not shown) to optimize flow of the heat transfer liquid through the heat exchange passage 3.

[0069] A stream of a hot chemical reaction product, e.g. obtained from a chemical reaction in a reactor (not shown), is introduced via line 6 and distributed via an upper tube sheet to the tubes 2, 2, 2 of the shell-and-tube heat exchanger 1. The tubes 2, 2, 2 have an overall length L from the upper tube sheet to the lower tube sheet. Simultaneously, a reactant is introduced via line 4 into and guided through the shell-side passage 3 of the shell-and-tube heat exchanger 1. Heat is transferred from the hot chemical reaction product to the reactant stream through the walls of the tubes 2, 2, 2.

[0070] The stream of the chemical reaction product is withdrawn through line 7 of the shell-and-tube heat exchanger 1 at the bottom part of the shell-and-tube heat exchanger 1, wherein said stream withdrawn through line 7 has a lower temperature than the stream of the hot chemical reaction product introduced via line 6. The pre-heated reactant is withdrawn through line 5 of the shell-and-tube heat exchanger 1 at the top part of the shell-and-tube heat exchanger 1 and can be directed to the reactor (not shown) or further heated if required. The reactant withdrawn through line 5 has a higher temperature than the reactant introduced via line 4.

[0071] FIG. 1(B) depicts the same shell-and-tube heat exchanger 1 as shown in FIG. 1(A) and illustrates an operational situation wherein the tube 2 is clogged near to the lower tube sheet by a blockage 8. This results in a reduced flow of the stream of the hot chemical reaction product through the tube 2 or liquid stagnation in the tube 2 above the lower tube sheet. Thus, essentially the entire wall surface of the tube 2 is no longer available for heat transfer and the heat transfer efficacy of the shell-and-tube heat exchanger 1 is reduced.

[0072] FIG. 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.

[0073] Seen in the flow direction of the at least one reactant, the first shell-and-tube heat exchanger 1B comprises a plurality of tubes 2B, 2B, 2B and a shell-side heat exchange passage 3B. The tubes 2B, 2B, 2B of the first shell-and-tube heat exchanger 1B have an overall length L2 from the upper tube sheet to the lower tube sheet.

[0074] The second shell-and-tube heat exchanger 1A in the flow direction of the one or more reactants comprises a plurality of tubes 2A, 2A, 2A and a shell-side heat exchange passage 3A. The tubes 2A, 2A, 2A of the second shell-and-tube heat exchanger 1A have an overall length L1 from the upper tube sheet to the lower tube sheet.

[0075] Each of the lengths L1 and L2 is less than the length L. In the illustrated embodiment, the sum of L1 and L2 approximately equals L.

[0076] The first shell-and-tube heat exchanger 1B and the second shell-and-tube heat exchanger 1A are connected in series with regard 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 line 6A and distributed via an upper tube sheet to tubes 2A, 2A, 2A. The partially cooled down product emerging from the tubes 2A, 2A, 2A of the second shell-and-tube heat exchanger 1A is introduced via line 7A into the first shell-and-tube heat exchanger 1B and distributed via an upper tube sheet to the tubes 2B, 2B, 2B. Conversely, the reactant to be pre-heated is introduced via line 4B into the shell-side passage 3B of the first shell-and-tube heat exchanger 1B and after leaving the same is directed into the shell-side passage 3A of the second shell-and-tube heat exchanger 1A via line 5B. The pre-heated reactant is withdrawn through line 5A.

[0077] During operation, fouling may occur, causing a blockage 8B in the tube 2B. This results in the tube 2B being partially blocked or fully blocked, i.e. in a reduced flow of the stream of a hot chemical reaction product through the tube 2B. Only the wall surface of tube 2B is no longer available for heat transfer. Thus, in comparison to FIG. 1(B), a larger surface of the tube wall is still available for heat transfer even in case of a blockage of an individual tube.

[0078] It is also possible in some chemical production processes that the fouling may occur by partial or fully blocking of a tube in the heat exchanger 1A, for example 2A. That would analogously be 8A if it would be included in the FIGURE. In such a case, the invention allows the still partially hot reaction product to make use of the full wall surface of the heat exchanger 1B including the tube 2B, while in the case of a single shell-and-tube heat exchanger as shown in FIG. 1(A), fouling in the upper half of a tube like 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 to the at least one reactant stream in the shell surrounding tube 2.

[0079] It has to be understood that the inventive arrangement of at least two shell-and-tube heat exchangers in series as shown in FIG. 1 is not limiting the invention to physically separated at least two such heat exchangers in series. For example, these might be within one casing. Also, in one aspect of the invention said at least two heat exchangers in series is to be understood to comprise a set-up that resembles a single heat exchanger at first glance, except that it has in the middle portion a zone where the partially cooled reaction product streams running through the tubes of one part of a heat exchange unit are reunited and then again split into streams fed through further tubes in the other part of the shell-and-tube heat exchange unit for further transfer of heat to the at least one reactant entering that part of the heat exchange unit in need of pre-heatingby this creating two shell-and-tube heat exchangers in a single heat exchange unit.

EXAMPLE

[0080] For the industrially important conversion of isobutylene and formaldehyde yielding isoprenol, isobutylene must be pre-heated. For this purpose, the hot product isoprenol is heat exchanged with isobutylene.

[0081] The heat exchange performance between a hot isoprenol stream and a cold isobutylene stream was calculated by applying correlations of heat transfer which are documented in VDI-Wrmeatlas, VDI-Gesellschaft Verfahrenstechnik und Chemieingenieurwesen Hrsg., 11., bearbeitete und erweiterte Auflage (e.g. chapter G1 Durchstrmte Rohre; Volker Gnielinski, Institut fr thermische Verfahrenstechnik, Karlsruher Institut far Technologie, page 785-791).

[0082] Heat exchange was simulated according to the following scenarios: [0083] (1) single shell-and-tube heat exchanger (reference example) having 1942 tubes with an outer diameter of 14 mm, an inner diameter of 8 mm and a length of 14 m, resulting in a heat exchange surface of 1025 m.sup.2, [0084] (2) two shell-and-tube heat exchangers connected in series (example in accordance with the invention) with a total heat exchange surface area of 1025 m.sup.2: [0085] first shell-and-tube heat exchanger having 1942 tubes with an outer diameter of 14 mm, an inner diameter of 8 mm and a length of 7 m, resulting in a heat exchange surface of 512.5 m.sup.2, and [0086] second shell-and-tube heat exchanger having 1942 tubes with an outer diameter of 14 mm, an inner diameter of 8 mm and a length of 7 m, resulting in a heat exchange surface of 512.5 m.sup.2.

[0087] The following specifications apply: [0088] isobutylene: mass flow=81.1 t/h, and [0089] isoprenol: mass flow=87.9 t/h.

[0090] The results of the simulation are shown in Table 1. Blockage relates to the percentage of tubes failing due to fouling. These tubes were deemed to contribute no longer to the heat exchange performance.

TABLE-US-00001 TABLE 1 isobutylene (reactant) isoprenol (product) blockage T inlet T outlet T inlet T outlet heat exchange h.e. .sup.[1] k-value # Scenario [%] [ C.] [ C.] [ C.] [ C.] [kW] [%] [W/(m.sup.2 .Math. K)] 1 (1) 0 60.0 276.2 285.0 122.4 13391 0 477 2 (1) 60 60.0 264.2 285.0 133.5 12567 6.2 293 3 (1) 80 60.0 246.9 285.0 148.8 11391 14.9 185 4 (2) 0 (1.sup.st h.e. .sup.[2]) 60.0 219.7 238.6 122.4 9577 0 513 0 (2.sup.nd h.e. .sup.[3]) 219.7 276.2 285.0 238.6 3815 563 (total) 13392 477 5 (2) 60 (1.sup.st h.e. .sup.[2]) 60.0 184.9 214.6 126.5 7326 2.2 313 0 (2.sup.nd h.e. .sup.[3]) 184.9 271.8 285.0 214.6 5768 554 (total) 13094 388 6 (2) 0 (1.sup.st h.e. .sup.[2]) 60.0 230.1 250.7 126.6 10269 2.3 511 60 (2.sup.nd h.e. .sup.[3]) 230.1 271.7 285.0 250.7 2819 330 (total) 13088 386 7 (2) 60 (1.sup.st h.e. .sup.[2]) 60.0 197.0 230.5 133.6 8097 6.1 310 60 (2.sup.nd h.e. .sup.[3]) 197.0 264.2 285.0 230.5 4473 327 (total) 12570 293 8 (2) 80 (1.sup.st h.e. .sup.[2]) 60.0 154.2 193.8 129.8 5409 4.1 198 0 (2.sup.nd h.e. .sup.[3]) 154.2 268.2 285.0 193.8 7438 546 (total) 12847 337 9 (2) 95 (1.sup.st h.e. .sup.[2]) 60.0 99.2 161.9 134.9 2163 6.8 62 0 (2.sup.nd h.e. .sup.[3]) 99.2 262.8 285.0 161.9 10311 516 (total) 12474 281 .sup.[1] h.e. (heat exchange): reduction of heat exchange [kW] compared to 0% blockage. .sup.[2] first heat exchanger .sup.[3] second heat exchanger