NZ619980B2 - Gas/gas heat exchanger - Google Patents

Abstract

heat exchanger for use in sulphuric acid plants is described. The heat exchanger seeks to provide a uniform heat transfer by offsetting its tube bundle (12) within the chamber (2), thus reducing corrosion. The tube bundle (12) is a circular ring within the chamber (2). Gas is introduced into the gas space (15) in the chamber via an inlet (6), heat is diffused, and gas exits through the outlet (3), which is linked to the interior chamber of the bundle (16). The sulphuric acid condensate collects at the drainage outlet (18). as space (15) in the chamber via an inlet (6), heat is diffused, and gas exits through the outlet (3), which is linked to the interior chamber of the bundle (16). The sulphuric acid condensate collects at the drainage outlet (18).

Description

Gas/Gas Heat ger This invention relates to a heat exchanger, in particular for use in the contact group of a sulfuric acid plant, with a chamber in which a tube bundle is arranged on a circular ring, wherein between the tube bundle and a chamber casing sur- rounding the tube bundle a gas space is formed, a gas supply opening provided in the r casing for introducing a gas into the gas space substantially radially relative to the tube bundle, and a gas outlet opening which adjoins an interior space enclosed by the tube bundle in substantially axial direction.

Within the contact group of sulfuric acid plants tube bundle heat exchangers usually are employed, which are installed in a vertical configuration, so that possibly ed sulfuric acid condensate can flow off towards the bottom tray and can be withdrawn there to avoid corrosion. In general, the 802 gas is guided on the casing side and the 802/803 gas is guided on the tube side. In commercial plants over 1,500 tato MH, disk-and-doughnut heat exchangers are used (of. Winnacker/K'Lichler, Chemische Technik: Prozesse und te, edited by Roland Dittmeyer et al., Vol. 3: nische Grundstoffe, enprodukte, p. 96 f., Wiley-VCH Verlag, Weinheim, 2005).

The cold 802 gas lly is guided in counterflow to the SOg—containing gas to be cooled. it was found out that the sulfuric acid sate leads to a strong corrosion in particular in the first chamber of the heat exchanger, so that high- alloy and expensive stainless steel materials must be used. To reduce the costs, the heat exchanger was divided into two parts, so that in the case of excessive corrosion not the entire heat exchanger, but merely the region exposed to cold gas, in which a particularly high ion occurs, must be replaced. While initially assuming a uniform division of the heat er region, the applicant recently has employed heat exchangers in which in the cold heat-exchange section (tst chamber) only a minor part of the entire heat transfer surface was provided. Moreover, instead of an arrangement in which two vertically oriented heat exchangers are arranged one beside the other and which creates problems in terms of drainage, there was now used an arrangement in which the chamber, to which the cold 802 gas is supplied, is arranged horizontally. From this first chamber, the sulfuric acid condensate can simply be withdrawn at the bottom.

The SOz—containing gas then was transferred into the adjoining vertical section with a greater heat transfer surface. It was found out, however, that in the case of the radial approach flow of the tube bundle in the horizontal section of the heat exchanger a non-uniform gas flow and as a result an impairment of the 1O heat er can occur.

Therefore, it is the object of the invention to achieve a uniform heat transfer, or to at least provide a useful alternative. Falling below the dew point temperature of the sulfuric acid should be avoided as far as le.

This object substantially is solved by the invention with the es as described herein in that the center of the tube bundle is offset with respect to the center of the chamber casing in a direction opposite to the gas supply opening.

In particular, the present ion provides a heat exchanger (1), in particular for use in the t group of a sulfuric acid plant, with a chamber (2) in which a tube bundle (12) is ed on a circular ring, wherein between the tube bundle (12) and a chamber casing (13) surrounding the tube bundle (12) a gas space (15) is formed, with a gas supply opening (6) provided in the chamber casing (13) for introducing a gas into the gas space (15) substantially radially to the tube bundle (12), and with a gas outlet opening which s an interior space (16) ed by the tube bundle (12) in substantially axial ion, wherein the center (ZR) of the tube bundle (12) is offset with respect to the center (ZK) of the chamber casing (13) in a direction opposite to the gas supply opening (6).

In the tional heat exchanger, the tube bundle arranged as circular ring is arranged trically relative to the se ntially cylindrically formed chamber of the heat exchanger. The present invention, however, s from this concentricity and the tube bundle is offset with respect to the chamber casing, so that the gas space formed between the tube bundle and the chamber casing tapers to an increasing extent from a maximum width facing the gas supply opening to the opposite side of the tube bundle. During the approach flow of the gas supplied to the heat exchanger, the pressure in the gas space is more and more increased due to the taper up to a maximum on the side facing away from the gas supply opening. The increase in pressure during impingement of the gas onto the tube bundle in the region of the gas supply g thereby can be compensated, so that over the entire circumference of the tube bundle the gas passes through the tube bundle and enters into the interior space enclosed by said tube bundle with uniform velocity. A uniform heat transfer can be ensured in all regions of the tube bundle.

In accordance with the invention, a ularly uniform flow distribution in par- ticular is obtained when the center of the tube bundle is offset with respect to the center of the chamber casing by 30 to 70%, preferably by about 50% of the width of the centric gas space. "Centric gas space" here is understood to be the gas space as it would be achieved with a concentric arrangement of the tube bundle with respect to the chamber casing. With a cylindrical design of the chamber, the tube bundle in this case would have a uniform distance to the chamber wall over its entire circumference. The gas space also would have a uniform width. From this position, the tube bundle now is shifted by about 30 to 70% of the width of the gas space. if instead of a cylindrical chamber a polygonal or differently shaped chamber is employed, the m distances to the chamber wall are ve for shifting the tube bundle. Polygon shaped chambers, however, involve disadvantages with regard to the flow distribution.

In accordance with a preferred embodiment of the invention the gas supply opening has an oval cross-section, wherein the maximum diameter of the gas supply opening preferably s to 70 to 95%, more preferably 85 to 90%, of the distance of tube plates defining the tube bundle in axial direction. Thus, the gas supply opening extends along the substantial length of the tube bundle.

In accordance with the invention, the main axis of the r is oriented sub- stantially horizontally, so that an easy ge of sulfuric acid accumulating in the lower region is possible. For this purpose, a drainage outlet is provided in the lower region of the chamber in accordance with the ion.

In accordance with a preferred aspect of the invention, the first chamber of the heat exchanger only includes about 10 to 30%, preferably 15 to 20%, of the entire heat-exchange surface of the heat exchanger. As a result, the temperature increase of the sulfur dioxide (802) can be limited to about 5-30 K, preferably 15-20 K, so that falling below the dew point temperature of the ic acid y is avoided. Correspondingly, a minimized condensation of sulfuric acid is obtained.

In accordance with a development of the invention, a vertical heat exchange section adjoins the chamber, in which a plurality of tubes are arranged in sub- ally vertical direction. in accordance with the invention, the vertical heat- exchange section includes about 70 to 90% of the heat-exchange e of the heat exchanger. As in this region only minor corrosion risks exist due to the higher temperatures, the vertical heat-exchange section can be made of less expensive materials. r objectives, features and possible applications of the invention can be taken from the following description of an exemplary embodiment and the draw- ing. All features described and/or illustrated form the subject-matter of the inven- tion per se or in any combination, independent of their inclusion in the claims or their back-reference.

In the drawing: Fig. 1 schematically shows a section through a heat exchanger according to the invention, 1O Fig. 2 schematically shows a n through the first chamber of the heat exchangen The gas/gas heat exchanger 1 according to the invention comprises a substan- tially horizontal chamber 2 which via a gas discharge tube 3 adjoining a gas outlet opening is connected with a vertical heat-exchange section 4. The hori- zontal chamber 2 and the vertical heat-exchange section 4 are attached to the bottom via corresponding bearings 5.

When the heat exchanger 1 is ed in a contact group of a sulfuric acid plant, cold SOg-containing gas is ed to the horizontal chamber 2 via a gas supply opening 6. in the chamber 2, a disk-and-doughnut heat exchanger 7 is provided. The chamber 2 is closed by covers 8, 9, wherein the cover 9 facing the vertical heat—exchange section 4 is penetrated by the gas discharge tube 3.

The vertical heat-exchange section 4 also is formed as disk-and-doughnut heat exchanger, as is schematically shown in Fig. 1. The gas centrally ed through the gas discharge tube 3 is radially deflected to the e and passes through tube s 10 only schematically indicated here, in which 803— containing gas to be cooled flows. Behind a disk 11 the SOg—containing gas is again deflected to the , wherein it again passes through a tube bundle 10.

This design of the vertical heat exchanger 4 is common practice, so that it will not be discussed here in detail. in Fig. 2, the construction of the first xchange chamber 2 is shown in detail. in the substantially cylindrically formed chamber 2 a tube bundle 12 formed as circular ring is provided, which is formed by a plurality of tubes 14 extending parallel to the chamber casing 13 of the chamber 2. n the r casing 13 and the tube bundle 12 a gas space 15 is provided. In the interior of the ring-shaped tube bundle 12 an interior space 16 is provided, which 1O merges into the gas rge tube 3. in axial direction, the tube bundle 12 is defined by tube plates (disks) 17 indicated in Fig. 1. Since the tube plates 17 are arranged vertically, sulfuric acid condensate formed can flow off downwards and an accumulation of the sate on the tube plates causing corrosion is avoided. in the lower region of the chamber 2 at least one drainage outlet 18 is provided, in order to withdraw accumulating sulfuric acid condensate.

The gas supply opening 6 is of oval shape, wherein the largest diameter of the oval gas supply opening 6 amounts to about 70 to 95% of the ce of the tube plates 17 and hence of the length of the tube bundle 12. As a result, the SOg-containing gas supplied through the gas supply opening 6 is introduced into the gas space 15 substantially along the entire length of the tube bundle 10.

As is clearly shown in Fig. 2, the tube bundle 12 is offset with respect to the chamber casing 13. In accordance with the invention, the offset here is chosen such that the center ZR of the tube bundle is offset with respect to the center ZK of the chamber 2 by 30 to 70%, in ular by about 50% of the width B of the centric gas space (determined with a tube bundle 12 fictitiously concentrically arranged in the chamber 2).

When the SOz-containing gas now is introduced into the chamber 2 through the gas supply g 6, it is spread in the gas space 15 and subsequently radially flows between the tubes 14 of the tube bundle 12 into the or space 16. Due to the offset arrangement of the tube bundle with respect to the chamber casing 13, a uniform radial flow of the gas is obtained over the entire circumference of the tube bundle 12. As a result, a m heat transfer over the entire circum— ference of the tube bundle and hence a more effective heat exchange is achieved.

The SOg-containing gas entering into the interior space 16 and heated by heat exchange with the gas flowing in the tube bundle 12 is introduced into the verti- cal heat-exchange section 4 via the gas discharge tube 3 and further heated in counterflow to the SOs-containing gas mostly introduced from above into the vertical heat-exchange section 4.

List of Reference Numerals CONGO-wa—A heat exchanger chamber gas discharge tube vertical heat-exchange section beaflng gas supply opening disk~and~doughnut heat exchanger covers 44444444.; COVGUW-POJN—‘O‘Co tube bundle disks tube bundle chamber casing tubes gas space interior space tube plates drainage outlet main axis of the r 2 width of the gas space 15 ZK center of the chamber 2 ZR center of the tube bundle 12

Claims (11)

What is claimed is:
1. A heat exchanger with a chamber in which a tube bundle is arranged on a circular ring, wherein between the tube bundle and a chamber casing surrounding the tube bundle a gas space is formed, with a gas supply opening ed in the chamber casing for introducing a gas into the gas space ntially radially to the tube , and with a gas outlet opening which adjoins an interior space enclosed by the tube bundle in substantially axial ion, wherein the center of the tube bundle is offset 10 with respect to the center of the chamber casing in a direction te to the gas supply opening.
2. The heat ger according to claim 1, wherein the heat exchanger is for use in the contact group of a sulfuric acid plant.
3. The heat exchanger according to claim 1 or 2, wherein the center of the tube bundle is offset with respect to the center of the chamber casing by 30 to 70% of the width of the centric gas space.
4. 20 The heat exchanger according to any one of claims 1 to 3, wherein the gas supply opening has an oval cross-section.
5. The heat exchanger according to any one of the preceding claims, wherein the maximum diameter of the gas supply opening amounts to 70 to 95% of 25 the distance of tube plates limiting the tube bundle in axial direction.
6. The heat exchanger according to any one of the preceding claims, wherein the main axis of the chamber is oriented substantially horizontally. _10_
7. The heat exchanger according to any one of the preceding claims, wherein a drainage outlet is provided at the chamber.
8. The heat exchanger according to any one of the preceding claims, wherein the chamber of the heat exchanger es about 10 to 30% of the heat- exchange surface of the heat exchanger.
9. The heat exchanger ing to any one of the preceding claims, wherein subsequent to the gas outlet opening of the chamber a vertical heat— 10 exchange n is provided, in which a plurality of tubes are arranged in substantially vertical direction.
10. 10. The heat exchanger according to claim 9, wherein the vertical heat- exchange section includes about 70 to 90 % of the heat-exchange e 15 of the heat exchanger.
11. 11. A heat exchanger substantially as herein bed with reference to any one of the embodiments shown in