Abstract:
A method of discovering leakage in a heat exchanger, wherein the method is carried into effect on an intact heat exchanger which, together with surrounding conduits, is filled with water. The heat exchanger preferably has requisite pressure indicators mounted between each section, as well as requisite shut-off valves. The method comprises applying in each section of the heat exchanger an excess pressure on one side which is enclosed there, while the other side is at normal pressure. The pressure is enclosed during a period of time and is monitored during this period of time.

Description:
TECHNICAL FIELD 
     The present invention relates to a method of discovering leakage in a heat exchanger, the heat exchanger being, together with surrounding conduits, filled with water, and the method comprising the steps that, in each section of the heat exchanger, an excess pressure is applied on the one side and is closed in across the section during a period of time, while the other side in the section is at normal pressure, and that the pressure difference is monitored during the period of time. 
     BACKGROUND ART 
     In order to heat treat liquid products use is made of various types of heat exchangers in indirect heating. The most common types of heat exchangers are plate heat exchangers and tube heat exchangers. The method according to the present invention is applicable to both types, but is preferably intended for plate heat exchangers. Heat exchangers are also used to a considerable extent within the food industry, such as in dairies and in juice factories. Depending upon the temperature to which the product is heated, a pasteurised or a sterile product will be obtained. 
     A heat exchanger normally consists of different sections which all have two sides—one side for product and one side for a heating medium, such as water or other liquid at different temperature, or steam. Alternatively, the sections may be disposed regeneratively, so that a cold product is heated up by an already heated product. 
     It is naturally always desirable that both of the sides in each respective section are kept separate and discrete, but within the food industry this is extremely important. Otherwise, a ready-treated product may be reinfected by a heating medium or by untreated product. 
     Various methods of discovering leakage in a heat exchanger have been used with the passage of time, such as saline solutions and coloured water on the one side in a section and normal water on the other side, whereafter, by conductivity measurements of alternatively ocular observations, it has been possible to discover any possible leakage. These methods take up considerable time and another of their drawbacks is that it is difficult to discover minor leakage. 
     A further method is described in international Patent Specification WO 02/086438. This method implies that the heat exchanger is connected to an external unit with the aid of which different pressures are applied on the different sides in a section in a heat exchanger. The unit makes for the simultaneous testing of several sections. This method is effective as regards discovering minor leakage, but it is also time-consuming and involves external service costs, for example, for a dairy. 
     OBJECTS OF THE INVENTION 
     One object of the present invention is to realise a method which is rapid and reliable. 
     A further object of the present invention is to realise a method which may be carried out routinely, for example in connection with washing of the plant. 
     SOLUTION 
     These and other objects have been attained according to the present invention in that the method of the type described by way of introduction has been given the characterising feature that the method is carried out on an intact heat exchanger with requisite pressure indicator mounted between each section, as well as requisite shut-off valves. 
     Preferred embodiments of the present invention have further been given the characterising features as set forth in the appended subclaims. 
    
    
     
       BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING 
       One preferred embodiment of the present invention will now be described in greater detail hereinbelow, with reference to the accompanying Drawing. In the accompanying Drawing: 
         FIG. 1  shows a part of a flow diagram with a heat exchanger. 
     
    
    
     The drawing shows only those details and parts essential to an understanding of the present invention, and the remaining part of the plant in which the heat exchanger is included has been omitted. 
     DESCRIPTION OF PREFERRED EMBODIMENT 
     The method according to the present invention is intended to be employed to detect leakage in a heat exchanger. The method is primarily intended for a plate heat exchanger, as shown in  FIG. 1 , but the method may also be used for other types of heat exchangers, such as tube heat exchangers, which process liquid foods. 
     The method may be employed in connection with an existing heat exchanger without it needing to be disconnected or without the need to disconnect connecting conduits. Preferably, the method may be used directly in conjunction with washing of the plant in which the heat exchanger is included. Directly in conjunction with the washing, the heat exchanger and connecting conduits are filled with rinsing water from the washing operation. Naturally, the method may be carried into effect on other occasions, for example, before start up of production, but then conduits and the heat exchanger must first be filled with water. 
     Given that the method may be carried on an intact heat exchanger, this implies that it is rapid, approx. 30 minutes. This implies that the method may be employed routinely at, for example, a dairy, which contributes in increased product safety. Previous methods have involved the separate planning of service inputs which have taken up to half a day to complete. 
     The heat exchanger  1  in  FIG. 1  has three sections  2 ,  3 ,  4 , but the method may naturally also be employed for both more and fewer sections  2 ,  3 ,  4 . Each section  2 ,  3 ,  4  is provided with respective pressure indicator  5 - 10  indicators  5 - 6 ,  7 - 8 ,  9 - 10 . The pressure indicators  5 - 10  are preferably electric, but also other types of pressure indicators  5 - 10  may occur. The pressure indicators  5 - 10  emit signals to the master or control unit of the plant. Conventional heat exchangers  1  may perhaps need to be retrofitted with pressure indicators  5 - 10 , but in those cases where one or more of the sections  2 ,  3 ,  4  is used regeneratively, pressure indicators  5 - 10  must already be in position in compliance with the legislation of certain countries. 
     For carrying the method into effect, a number of shut-off valves  11 ,  12 ,  13  are also required. A pump  14  which normally pumps product into the heat exchanger  1  is also used in the method. The pump  14  which normally consists of a circulation pump must be frequency controlled. 
     In the first section  2  there is, on production, hot water on one side which enters into the heat exchanger  1  through the conduit  15 . The water pressure in this conduit  15  is monitored using the pressure indicator  5 . On the other side in the first section  2 , there is a part  16  of the product conduit which is monitored using the pressure indicator  6 . 
     In the second section  3 , there are product conduits on both sides. The upstream side has a part  17  of the product conduit which is monitored using the pressure indicator  7 . The downstream side has another part  18  of the product conduit which is monitored using the pressure indicator  8 . 
     In the third section  4  there is, on production, on the one side ice water which enters into the heat exchanger  1  through the conduit  19 . The water pressure in this conduit  19  is monitored using the pressure indicator  9 . On the other side in the third section  4 , there is a part  20  of the product conduit which is monitored using the pressure indicator  10 . 
     When the method is to be carried into effect, the heat exchanger  1  and connecting conduits are to be filled with water. The pressure of the water through the heat exchanger  1  and the conduits should be approx. 2 bar, which is normal pressure on production and washing. 
     When the method is to be put into effect, the first step is to close the shut-off valve  11 . Thereafter, the pump  14  is accelerated in order to give a pressure increase to the conduit system. When the pressure indicator  10  shows approx. 6 bar, the valve  12  closes so that an excess pressure of approx. 67 bar is enclosed on the downstream side in the third section  4 . 
     Thereafter, the pump  14  is decelerated somewhat and when the pressure indicator  8  shows approx. 5.5 bar, the shut-off valve  13  closes so that an excess pressure of approx. 5.5 bar is enclosed on the downstream side in the second section  3  of the heat exchanger  1 . 
     The pump  14  is decelerated slightly further and when the pressure indicator  6  shows approx. 5.5 bar, the pump  14  is completely decelerated. An excess pressure of approx. 5.5 bar has now been enclosed on the upstream side in the first heat exchanger section  2 . 
     The downstream side in the first section  2  and the upstream sides in the second and third sections  3 ,  4  have a normal pressure of approx. 2 bar, which can be read off with the aid of the pressure indicators  5 ,  7  and  9 , respectively. 
     The values of the pressure indicators  5 - 10  are registered in the master or control unit of the plant during a given, predetermined period of time, for example 30 minutes. The entire read-off period may suitably be printed out so that there will by such means be obtained different graphs of the pressurised sides of each respective section  2 ,  3 ,  4 . By pressurising the different sections  2 ,  3 ,  4  in steps, it is simple to distinguish the different sections  2 ,  3 ,  4  from one another. Steps between the different sections may be larger or smaller than 0.5 bar. However, the difference must be distinguishable on a graph. 
     If leakage were to occur in some section  2 ,  3 ,  4 , the pressure in the pressurised side will fall and begin to approach the pressure in the unpressurised side. Large leakages show a rapid pressure equalisation. For minor leakage it is important to use a relatively long measurement period, since the pressure equalisation in such a case is considerably slower. 
     The excess pressure is preferably laid on the downstream side of the heat exchanger  1  and preferably on the main conduit through the heat exchanger  1 , i.e. on that side where the product is led. 
     After the carrying out of the method, the shut-off valves  11 ,  12 ,  13  are opened, the water is emptied from the conduits and heat exchanger  1  and, if no leakage is present, the heat exchanger  1  is now ready for production. 
     In those cases where the heat exchanger  1  has more or fewer sections, more or fewer pressure indicators  5 - 10  and shut-off valves  11 ,  12 ,  13  must naturally be used so that it is possible in a corresponding manner to enclose an excess pressure on one side of each respective section  2 ,  3 ,  4  in the heat exchanger  1 . 
     As will have been apparent from the foregoing description, the present invention realises a method for discovering leakage which is rapid and reliable. Since the method is carried out on an intact heat exchanger, the method may be put into effect routinely, preferably in conjunction with washing of the plant. Given that the leakage monitoring may be carried out often and regularly, this contributes to increased product safety and reliability which is of vital importance above all in the food industry.