Patent Publication Number: US-2009220223-A1

Title: Multi-layer piping for conveying and heating a fluid

Description:
TECHNICAL FIELD 
     The present invention relates to a multi-layer piping for conveying and heating a fluid, in particular an aqueous urea solution. 
     BACKGROUND FIELD 
     To comply with the new anti-pollution standards, which impose more restrictive exhaust gas emission limits with respect to the existent, it is known the use of the so-called purification system by selective catalytic reduction, also known under the acronymic SCR (“Selective Catalytic Reduction”) of the vehicle exhaust gases. Such system is adopted, in particular, for reducing the emission into the atmosphere of nitrogen oxides. 
     Preferably, the SCR system is used in light-duty and heavy-duty vehicles. 
     The SCR system consists of injecting by compressed air at the catalyser inlet an aqueous solution of urea or equivalent product capable of reacting with the nitrogen oxides. Generally, it is preferred an aqueous solution of 32.5% of urea, for example the solution commonly marketed by Basf under the name AdBlue. The catalyser is arranged at the exhaust gas muffler and, inside it, the introduced urea reacts with the nitrogen oxides, also commonly called NO x , eliminating them from the atmospheric emissions. 
     The aqueous urea solution is generally contained in a tank from where it is taken to be injected into the catalyser, after being mixed to compressed air, according to times and modes defined by an electronic control unit which accounts for various parameters such as for example temperature, humidity, engine operation and number of revolutions. 
     A known problem of the SCR system is that during the parking of vehicles at temperatures lower than −12° C. the urea solution freezes. For this reason when the engine is ignited after parking, the pipings containing the urea solution are immediately heated up by passage of electrical current. 
     For example it is felt the need to reach a temperature of at least +5° C. for the urea solution at least ten minutes after the engine is ignited, with the SCR system initially placed at an ambient temperature of 35° C. 
     Furthermore, the pipings which convey the aqueous urea solution must allow the passage of fluid in the working temperature range, that is from −40° C. to 80° C., must be flexible and must ensure that, in −40° C. conditions, the aqueous urea solution does not freeze in any part in all flow rate conditions, that is from 0 to 5.5 l/h. 
     For heating up the aqueous solution there are therefore generally used electrically heated pipings and pipe fittings. 
     For example, it is known the use of heated pipings comprising TEFLON® fluid conveying pipes, with an electrical resistance externally wound on a polyethylene heat-shrink sheath which also has the function of electrical insulation and is further covered by a corrugated polyamide tube. 
     Such solution however does not allow to obtain a sufficiently rapid defrosting of the aqueous solution to respond to the aforementioned requirements due to the fact that the TEFLON® does not allow sufficient conduction of heat to warm up the inside of the pipe. The TEFLON® pipes also present problems in use in mating of couplings and are also very costly. 
     DISCLOSURE OF INVENTION 
     It was therefore sought a piping for a SCR system which allows to avoid the aforementioned drawbacks and consequently allows to rapidly defrost an aqueous urea solution. 
     A piping capable of rapidly and efficiently heating the fluid to be conveyed may also be advantageously used in a number of other applications, in particular both for domestic applications and on vehicles. 
     According to the present invention a piping  1  is made according to claim  1 . 
     Preferably, the piping  1  comprises:
         a fluid conveying pipe  2  comprising a thermoplastic elastomer;   a heating element  3 ;   a sealing element  4 ;   an insulating layer  5 ;   an anti-abrasive layer  6 .       

     Preferably, the piping  1  of the present invention is used for conveying an aqueous urea solution. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the present invention, it is further described with reference to the accompanying figures, which show: 
         FIG. 1  is a sectional and partial view of a piping made according to the present invention; and 
         FIG. 2  a graph showing the temperature value pattern in time of a 32% aqueous urea solution contained in a piping made according to the invention compared with a piping made according to the known art. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     In particular, the conveying pipe comprises a thermoplastic elastomer also known under the acronym TPE. For thermoplastic elastomer it is meant a polymeric material which behaves like an elastomer, but when heated can be worked like a thermoplastic. 
     Preferably, it is used a thermoplastic elastomer with polyolefinic matrix based in which is intimately dispersed a dynamically vulcanised elastomeric phase. 
     More preferably, the polyolefinic matrix is a polypropylene and the elastomeric phase is EPDM. 
     Even more preferably, the thermoplastic elastomer is a Forprene®. 
     Preferably, the conveying pipe  2  consists of a thermoplastic elastomer made thermally conductive by integration of appropriate fillers in the compound. 
     Preferably, such fillers are metallic fillers. 
     Advantageously, the thermal conductivity of the thermoplastic elastomer is comprised from 1.2 W/mK to 40 W/mK according to the ASTM E1461 test standards. More advantageously, thermal conductivity is approximately 20 W/mK. 
     Preferably, the pipe presents an internal diameter larger than 5 mm. 
     Preferably, the thickness of the conveying pipe  2  is comprised from 2 to 4 mm. 
     The heating element is preferably made of an electrical resistor  3  wound around the conveying pipe. 
     Even more preferably, it is used a heating wire, for example of the type marketed under the code NiCr8020 by Shanghai Anhing Alloy Material Co. Ltd. The electrical resistor can be bipolar or monopolar. Preferably, bipolar. 
     The geometries and the dimensions of the electrical resistive elements depend on the features required by specific use and moreover depend on the dimensions of the components in the whole piping. 
     Preferably, the heating element  3  is electrically insulated, preferably by use of TEFLON®. Alternatively, it is possible to use for example silicon or polyamide. 
     Preferably, the maintenance element  4  consists of a heat-shrink plastic sheath  4 . 
     The heat-shrink sheath  4  is preferably made of polyethylene, because this material has excellent elastic memory features. The polyethylene used is generally heated to a temperature higher than 100° C. and then cooled down, and increases its dimensions preserving elasticity nevertheless. The polyethylene sheets are then heated to over 100° C. again and the second heating causes in the radiated polyethylene the return to the original dimensions, adhering perfectly to the layers underneath. 
     The heat-shrinkability depends on the degree of deformation of the material and may vary from 50 to 300% of the original dimensions. 
     The insulating layer  5  is preferably made of polyurethane. More preferably, it is made of open or closed cell expanded polyurethane. More preferably, it is made of closed cell expanded polyurethane. 
     Preferably, the insulating layer  5  presents a thickness higher than 5 mm and an internal diameter depending on the diameter of the conveying pipe  2 . 
     The anti-abrasive layer  6  is preferably made of a corrugated tube  6 . Preferably, the corrugated tube  6  is made of polyamide 12. Alternatively, the anti-abrasive layer  6  is a spiral sheath or spiral tape of appropriate dimensions to maintain the designed curve radius, preferably made of polyamide 6 or 12. E-v-en more preferably, the spiral sheath is made of polyamide 12 because it has a better chemical resistance. 
     A piping manufactured according to the structure described above is capable of reaching the objective of defrosting the aqueous urea solution in a shorter time with respect to the known pipings. 
     It is finally apparent that numerous changes can be implemented to the piping herein described and illustrated, in particular to the percentage ratio of the chemical components forming the various layers and to the relative thickness of the layers, as well as to the number of layers themselves, for example, the heat-shrink sheath may not be present, without departing from the protective scope of the present invention nevertheless. 
     It is moreover apparent that although specific reference is made to the conveying of an aqueous urea solution, a piping made according to the present invention may be advantageously used in all systems in which the fluid conveyed by the piping needs to be heated. 
     In the above description, there are apparent the advantages of a piping made according to the present invention, in particular by means of such piping it is possible to heat a liquid in a shorter time with respect to the known pipings and at the same time to have a sufficiently flexible piping and at a limited cost. 
     The invention will now be described through examples which are however non-limitative. 
     Example 1 
     Table 1 shows an example of a piping made according to the present invention, while table 2 shows an example of a comparison piping. 
     
       
         
           
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Inventive example 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Conveying pipe 2 
                 Forprene ® tube 9 × 5 mm, length 
               
               
                   
                   
                 1500 mm 
               
               
                   
                 Heating element 3 
                 Bipolar NiCr8020 wire, 6.3 
               
               
                   
                   
                 Ω, TEFLON ® insulated 
               
               
                   
                 Sealing element 4 
                 Heat-shrink polyethylene 
               
               
                   
                   
                 sheath 
               
               
                   
                 Insulating layer 5 
                 Closed cell extruded 
               
               
                   
                   
                 expanded polyurethane tube 
               
               
                   
                 Anti-abrasive layer 6 
                 Corrugated poly amide tube 12 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Comparative example 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Conveying pipe 
                 TEFLON ® tube 8 × 6 mm, 
               
               
                   
                   
                 length 1500 mm 
               
               
                   
                 Heating element 
                 Bipolar NiCr8020 wire, 
               
               
                   
                   
                 6.3 Ω, TEFLON ® insulated 
               
               
                   
                 Sealing element 
                 Heat-shrink polyethylene 
               
               
                   
                   
                 sheath 
               
               
                   
                 Anti-abrasive layer 
                 Corrugated tube 
               
               
                   
                   
               
            
           
         
       
     
     Graph 1 shows the temperature value pattern in time of a 32% aqueous urea solution contained in the piping according to the present invention whose composition is described above in table 1 and of the piping used as comparison whose composition is shown in table 2. 
     Such temperature is measured by introducing in the pipings, inside which is introduced the aqueous urea solution, into a sealed climatic cell where a temperature of −35° C. is stabilised. In such a way, the solution contained inside is frozen taking it also to a temperature of −35° C. 
     After stabilising the temperature, the electrical connections of the electrical resistor wound on the conveying pipe are connected to an electrical power supply under a voltage of 24V, and therefore a current of 3.8 A is circulated. 
     A series of thermocouples placed inside the piping allow to determine the temperature of the aqueous solution. 
     It is apparent that the use of a piping made according to the present invention allows to raise the temperature of the aqueous urea solution faster and more efficiently that in the case of the known art.