Title of Invention

PLATE-TYPE HEAT EXCHANGER

Abstract

A plate-type heat exchanger comprising numerous parallel metal plates, between which there are alternatively formed permeable cold chambers for cooling liquid and permeable hot chambers for the hot liquid to be cooled, comprising a housing surrounding the plates, which housing has supply lines and discharge lines for the liquids, comprising a first distribution passage for supplying the hot liquid to the hot chambers, and a second distribution passage for supplying the cooling liquid to the cold chambers, and comprising a first collecting passage for discharging the hot-cooled liquid and a second collecting passage for discharging the cooling liquid, wherein the metal plates and the housing are designed for the passage of sulphuric acid as hot liquid and for the passage of water as cooling liquid, wherein the region through which flows sulphuric acid has at least one metal cathode and one reference electrode, wherein at least half the metal plates have a plurality of electric contacts connected with the anode of a d.c. voltage source of variable electric voltage, wherein the metal cathode likewise is electrically connected with the d.c. voltage source, and wherein the d.c. voltage source belongs to a potentiostat which is electrically connected with the reference electrode.

Full Text

FORM-2 THE PATENTS ACT, 1970 (39 of 1970) COMPLETE (Section -10, rule 13) PLATE-TYPE HEAT EXCHANGER OUTOKUMPU OYJ of Riihitontuntie 7, FIN-02200 Espoo, Finland a Finnish public limited Company THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE NATURE OF THIS INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED:- Description: This invention relates to a plate-type heat exchanger comprising numerous parallel metal plates, between which there are alternately formed permeable cold chambers for cooling liquid and permeable hot chambers for the hot liquid to be cooled, comprising a housing surrounding the plates, which housing has supply lines and discharge lines for the liquids, comprising a first distribution passage for supplying the hot liquid to the hot chambers, comprising a second distribution passage for supplying the cooling liquid to the cold chambers, and comprising a first collecting passage for discharging the hot, cooled liquid and a second collecting passage for discharging the cooling liquid. International patent application WO 86/01837 Al discloses a plate-type heat exchanger comprising numerous parallel metal plates and providing an anodic corrosion protection, wherein the metal plates are connected with the direct positive current output of a rectifier via a single connection provided at the top end of the metal plate block. However, this arrangement create problems because the plates cannot be uniformly protected against corrosion in all regions. Therefore, the object underlying the invention is to provide a plate-type heat exchanger in which the metal plates are protected more uniformly against corrosion due to the attach of sulphuric acid. In accordance with the invention, this is achieved in that the metal plates and the housing are designed for the passage of sulphuric acid as hot liquid and for the passage of water as cooling liquid, that the region through which flows 2 sulphuric acid has at least one metal cathode and one reference electrode, that at least half the metal plates have an electric contact which is connected with the anode of a d.c. voltage source of variable electric voltage, that the metal cathode likewise is electrically connected with the d.c. voltage source, and that the d.c. voltage source belongs to a potentiostat which is electrically connected with the reference electrode. Expediently, a metal cathode is disposed in the first distribution passage and/or in the first collecting passage, where it gets in direct contact with the sulphuric acid. In particular in the case of large-surface metal plates it may be expedient to pass a metal cathode through a plurality of hot chambers, which metal cathode is sealed against the metal plates and electrically insulated. There is thus obtained contact with the sulphuric acid flowing in the chambers. The anodically protected metal plates, which are equipped with associated electric contacts, can for instance also have 2 to 5 electric contacts per plate, when the plates should rather uniformly be protected against corrosion in all regions. The housing can also have one or more electric contacts which are connected with the variable d.c. voltage source, in order to achieve an anodic protection. Expediently, all metal plates will be protected anodically. By means of the anodic protection, a metal oxide layer is produced on the side against which flows the sulphuric acid, which metal oxide layer prevents the corrosion attack. The plate-type heat exchanger protected against corrosion in accordance with the invention can be used for instance in plants for producing sulphuric acid, in which sulphuric acid with a H2S04 content in the range from 90 to 100 wt-% and temperatures in the range from 140° C to the 3 boiling point must be cooled by indirect heat exchange. The plates may be made of alloyed steel which apart from iron in particular has the alloying components chromium, nickel and molybdenum. Embodiments of the plate-type heat exchanger will be explained with reference to the drawing, in which: Fig.l shows a section through the plate-type heat exchanger in a schematic representation, Fig.2 shows a variant of the arrangement of a metal cathode, and Fig.3 shows a reference electrode in a longitudinal section in a schematic representation. The plate-type heat exchanger (1) of Fig. 1 has a housing (2) comprising a supply line (3) and a discharge line (4) for the hot sulphuric acid to be cooled as well as a supply line (5) and a discharge line (6) for the cooling water. In the housing (2), parallel metal plates (7) are provided, between which there are disposed hot chambers (8) for the passage of sulphuric acid to be cooled and cold chambers (9) for the passage of cooling water. The acid enters through the supply line (3) and first of all gets into a first distribution passage (10), from where it flows through the hot chambers (8) to a first collecting line (11) and leaves the exchanger (1) through the discharge line (4). The cooling water enters the exchanger (1) through the supply line (5) and is supplied by the second distribution passage (13) to the cold chambers (9), reaches the second collecting passage (4) and then the discharge line (6). A first metal cathode (16) is provided in the first distribution passage (10), and the insulated metal cathode extends through the housing (2). 4 Analogously, a second metal cathode (17) is provided in the first collecting passage (11). During the operation of the exchanger (1), both cathodes (16) and (17) are in contact with the sulphuric acid, whose corrosion attack must be stopped. In the vicinity of the contact with the sulphuric acid, the cathodes are made of stainless steel, for instance, which has a high resistance to hydrogen embrittlement, and outside the housing (2) they are connected with the negative poles (19) and (19a) of a potentiostat (20) by electric lines (18) or (18a). In a manner known per se, the potentiostat has a variable d.c. voltage source, whose positive pole (21) is connected with the electric contacts (23) of the metal plates (7) to be protected via the electric line (22). The housing (2) also has an electric contact (23a), in order to obtain an anodic corrosion protection. In contrast to the drawing, each of the plates (7) to be protected can have a plurality of electric contacts (23) connected with the positive pole (21), e.g. 2 to 5 electric contacts per plate. Mostly, it is expedient to dispose the contacts (23) at the edges of the plates, in order to achieve a constructionally simple realization of the anodic protection. The potentiostat (20) has a connection (25) for an electric line (26) which leads to a reference electrode (27). This reference electrode (27) provides the measurement basis for the potentiostat (20), and in a manner known per se it may constitute e.g. a calomel electrode, a Hg/Hg2S04 electrode, or a cadmium bar as shown in Fig. 3. Surrounded by an electric insulation (31), the cadmium bar (30) is provided in a housing (32) which has a diaphragm (33). This diaphragm is permeable for the sulphuric acid, so that the cadmium bar (30) is constantly immersed in the sulphuric acid flowing past the same. The potential developed thereby is supplied to the potentiostat (20) by the electric line (26). 5 In the case of large metal plates the anodic protection in the middle region of the plate surface can possible be smaller than in the vicinity of the plate edge. To provide sufficient anode current for the desired corrosion protection in this case as well, it may be expedient to pass a metal cathode through the middle region of the plates (7), as is schematically represented by means of Fig. 2. The cathode constitutes a metal bar (16a), and the sealed and electrically insulated cathode extends through the plates (7). In this way, the anode current necessary in the plate region susceptible to corrosion can precisely be determined. 6 We Claim: 1. A plate-type heat exchanger comprising numerous parallel metal plates, between which there are alternatively formed permeable cold chambers for cooling liquid and permeable hot chambers for the hot liquid to be cooled, comprising a housing surrounding the plates, which housing has supply lines and discharge lines for the liquids, comprising a first distribution passage for supplying the hot liquid to the hot chambers, and a second distribution passage for supplying the cooling liquid to the cold chambers, and comprising a first collecting passage for discharging the hot-cooled liquid and a second collecting passage for discharging the cooling liquid, wherein the metal plates and the housing are designed for the passage of sulphuric acid as hot liquid and for the passage of water as cooling liquid, wherein the region through which flows sulphuric acid has at least one metal cathode and one reference electrode, wherein at least half the metal plates have a plurality of electric contacts connected with the anode of a d.c. voltage source of variable electric voltage, wherein the metal cathode likewise is electrically connected with the d.c. voltage source, and wherein the d.c. voltage source belongs to a potentiostat which is electrically connected with the reference electrode. 2. The plate-type heat exchanger as claimed in claim 1, wherein a metal cathode is disposed in the first distribution passage. 3. The plate-type heat exchanger as claimed in claim 1 or 2, wherein a metal cathode is disposed in the first collecting passage. 7 4. The plate-type heat exchanger as claimed in claim 1 or any of the preceding claims, wherein a metal cathode extends through a plurality of hot chambers, which metal cathode is sealed against the metal plates and electrically insulated. 5. The plate-type heat exchanger as claimed in claim 1 or any of the preceding claims, wherein a plurality of metal plates have 2 to 5 electric contacts per plate. 7* Dated this 27th day of October 2003. MOHAN DEWAN OF R.K.DEWAN & COMPANY APPLICANTS PATENT ATTORNEY 8

Documents:

1002-mumnp-2003-cancelled pages(18-03-2005).pdf

1002-mumnp-2003-claims(granted)-(18-03-2005).doc

1002-mumnp-2003-claims(granted)-(18-03-2005).pdf

1002-mumnp-2003-correspondence(16-11-2005).pdf

1002-mumnp-2003-correspondence(ipo)-(09-05-2007).pdf

1002-mumnp-2003-form 1(28-10-2003).pdf

1002-mumnp-2003-form 13(16-11-2005).pdf

1002-mumnp-2003-form 19(19-10-2004).pdf

1002-mumnp-2003-form 2(granted)-(18-03-2005).doc

1002-mumnp-2003-form 2(granted)-(18-03-2005).pdf

1002-mumnp-2003-form 26(16-11-2005).pdf

1002-mumnp-2003-form 3(28-10-2003).pdf

1002-mumnp-2003-form 5(28-10-2003).pdf

1002-mumnp-2003-pct-ipea-409(28-10-2003).pdf

1002-mumnp-2003-pct-isa-210(28-10-2003).pdf

1002-mumnp-2003-petition under rule 138(15-03-2004).pdf