Abstract:
A system for transferring and heating fluid is disclosed comprising a fluid transfer pipe having an internal surface and an external surface, and at least one helical heating rib connected to the internal surface of the fluid transfer pipe structured and arranged to generate non-laminar flow and to heat the fluid as it flows through the fluid transfer pipe. A method of heating fluid contained in a pipe is also disclosed. The method comprises providing at least one helical heating rib connected to an internal surface of a fluid transfer pipe, and passing the fluid through the fluid transfer pipe, whereby the at least one helical heating rib generates turbulent flow of the fluid to thereby heat the fluid. The helical heating ribs may comprise hollow channels through which a heating liquid may be passed to further heat the fluid contained in the pipe.

Description:
CROSS-REFERENCE TO A RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/588,468 filed Jan. 19, 2012, which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to fluid transfer pipes, and more particularly relates to pipes having internal helical heating ribs that generate turbulent fluid flow in the pipes and are used to heat the fluid. 
       BACKGROUND INFORMATION 
       [0003]    In industries such as oil and gas production, problems can occur when water and other liquids freeze inside pipelines. For example, hydraulic fracturing (fracking) is a process for extracting oil or natural gas in which large amounts of fracking fluid are pumped into the ground to create cracks in the rock that allow the oil or gas to flow to the well for extraction. Fracking water used in hydraulic fracturing operations is transported through pipelines located on or near the ground surface. Due to extreme climate changes that can occur at oil and gas drilling installations, water transfer can be compromised due to water freezing, which creates down time that becomes extremely costly. 
         [0004]    Water can be stored on the surface in tanks or ponds, or pumped from streams. The water can be transferred over a relatively long distance to the well, where it is mixed with chemicals and pumped into the ground. During this operation, a relatively large amount of water flows through the pipes, so freezing of the water is unlikely. However, at other times the flow of water may be slow or non-existent. In cold climates, the water can freeze in the supply lines, preventing water flow or damaging the supply lines. 
         [0005]    Attempts have been made to prevent such freezing, such as by bulk heating of the liquid contained in tanks, pits, ponds, reservoirs, etc. before the liquid is transported through a pipeline. In addition, external heating of pipelines has been proposed in an attempt to prevent freezing. However, such methods are inefficient and are often not effective in preventing pipeline freezing. 
       SUMMARY OF THE INVENTION 
       [0006]    An aspect of the present invention is to provide a system for transferring and heating fluid comprising a fluid transfer pipe having an internal surface and an external surface, and at least one helical heating rib connected to the internal surface of the fluid transfer pipe structured and arranged to generate non-laminar flow and to heat the fluid as it flows through the fluid transfer pipe. 
         [0007]    Another aspect of the present invention is to provide a fluid transfer pipe section comprising an internal surface and an external surface, and a helical heating rib connected to the internal surface of the pipe section, wherein the helical heating rib has a pitch ratio L:D of greater than 3:1, and a radial height H that is less than or equal to 15 percent of an inner diameter D of the fluid transfer pipe section. 
         [0008]    A further aspect of the present invention is to provide a method of heating a fluid contained in a fluid transfer pipe, the method comprising providing at least one helical heating rib connected to an internal surface of the fluid transfer pipe, and passing the fluid through the fluid transfer pipe, whereby the at least one helical heating rib generates turbulent flow of the fluid to thereby heat the fluid. 
         [0009]    These and other aspects of the present invention will be more apparent from the following description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a partially schematic broken side view of an internally heated fluid transfer pipe in accordance with an embodiment of the present invention. 
           [0011]      FIG. 2  is a partially schematic isometric view of an internally heated fluid transfer pipe in accordance with an embodiment of the present invention. 
           [0012]      FIG. 3  is a partially schematic sectional side view of an internally heated fluid transfer pipe in accordance with an embodiment of the present invention. 
           [0013]      FIG. 4  is a cross-sectional end view of the internally heated fluid transfer pipe of  FIG. 3  taken along line  4 - 4 . 
           [0014]      FIG. 5  is a cross-sectional end view of the internally heated fluid transfer pipe of  FIG. 3  taken along line  5 - 5 . 
           [0015]      FIG. 6  is a partially schematic isometric view of an internally heated fluid transfer pipe in accordance with another embodiment of the present invention. 
           [0016]      FIG. 7  is a cross-sectional end view of the internally heated fluid transfer pipe of  FIG. 6 . 
           [0017]      FIG. 8  is a partially schematic isometric view of an internally heated fluid transfer pipe in accordance with another embodiment of the present invention. 
           [0018]      FIG. 9  is a cross-sectional end view of the internally heated fluid transfer pipe of  FIG. 8 . 
           [0019]      FIG. 10  is a schematic representation of portions of a hydraulic fracturing gas operation including an internally heated fluid transfer pipe in accordance with an embodiment of the present invention. 
           [0020]      FIG. 11  is schematic view of portions of a control system that can be used in combination with an internally heated fluid transfer pipe in accordance with an embodiment of the present invention. 
       
    
    
       [0021]    It is noted that certain features shown in the various figures are not drawn to scale in order to more clearly illustrate various aspects of the present invention. 
       DETAILED DESCRIPTION 
       [0022]    The present invention provides pipes that heat a fluid as it passes through the pipe. Helical heating ribs in the form of solid or hollow tubes, channels or other structures are provided inside the pipes to induce non-laminar or turbulent flow of the fluid, which reduces or prevents freezing of process fluids, such as water-containing liquids, in the pipes. In one embodiment, a first pipe (also referred to as an outer pipe or host pipe) has an interior passage including a helical rib structure within the first pipe that is configured to cause a turbulent or helical flow of the process fluid, at least when the process fluid is flowing within a predetermined range of flow rates. The helical rib structure can include an internal channel for passage of a heating liquid. The heating liquid in the helical rib can be used to interiorly heat the pipe and the process fluid. 
         [0023]    In one embodiment, the helical heating rib comprises at least one coiled heating tube positioned inside the pipe. The coiled heating tube can be used to transport a heating liquid that heats the pipe wall and can also provide heat to the process fluid. In certain embodiments, the coiled heating tube can have an internal channel having a substantially circular or non-circular cross-sectional shape. 
         [0024]    A smooth inner wall having a circular cross-section would generally cause a laminar flow of a fluid in the pipe. However, the helical rib structure of the present invention creates a turbulent flow pattern, e.g., a helical or swirling flow of the process fluid. The turbulent flow generates frictional heating of the process fluid and can also reduce the pressure drop of the process fluid along the axial direction of the pipe. The helical or swirling flow can also have a higher velocity than a laminar flow in a pipe of comparable size. This higher velocity and/or turbulence caused by the helical structure can lower the probability of the process fluid freezing. 
         [0025]    Referring to the drawings,  FIG. 1  is a partially schematic side view of a heated pipeline  10  in accordance with an embodiment of the invention. The pipeline  10  includes at least one heated pipe section  12  having an outer pipe  14  and an internal helical heating rib in the form of a heating tube  16  therein. A single helical heating rib  16  is shown in the embodiment of  FIG. 1 . However, two or three helical heating ribs may possibly be used in each heated pipe section  12 . The heating tube  16  includes an inlet  18  and an outlet  20  forming passageways extending radially through the sidewall of the pipe  14 . In addition to the heated pipe section(s)  12 , the pipeline  10  may also include standard or non-heated pipe sections  22 . In certain embodiments, the heated pipe sections  12  may comprise less than 50 percent, or less than 25 percent, of the overall length of the pipeline  10 . The pipeline  10  may be used in many different applications, including transportation of fracking water and other liquids in the oil and gas industry, as well as for the transportation of fluids in many other industries. 
         [0026]      FIG. 2  is a partially schematic isometric view of a heated pipe section  12  in accordance with an embodiment of the present invention. The heated pipe section includes an outer pipe  14  having the shape of a right circular cylinder which serves as a fluid transfer pipe, and a helical heating rib in the form of an internal heating tube  16  is connected to an internal surface of the pipe  14  in a helical pattern. The internal heating tube  16  communicates with the inlet  18  and the outlet  20 , which extend radially through the sidewall of the outer pipe  14 . Liquid may pass through the inlet  18  of the internal heating tube  16  to the outlet  20 , as shown by the arrows in  FIG. 2 . In the embodiment shown, both the inlet  18  and outlet  20  pass radially through the sidewall of the outer pipe  14  near opposite ends of the pipe. However, any other suitable configuration may be used, e.g., one or both of the inlet  18  and outlet  20  may be moved to any other desired location along the length of the outer tube  14 . Furthermore, the inlet  18  and/or outlet  20  may extend radially between the exterior and interior of the outer pipe  14  at or adjacent to the ends of the pipe, e.g., by passing radially through a coupling or sleeve connected to one or both ends of the outer pipe  14 . In such configurations, the inlet and outlet are considered to extend radially through the sidewall of the fluid transfer pipe. 
         [0027]      FIG. 3  is a partially schematic longitudinal sectional view of the heated pipe section  12  containing the internal heating tube  16 . The heated pipe section  12  can have a length LP of any desired dimension, for example, from 1 foot or less to 10,000 feet or more. For many applications, pipe sections of from 10 to 100 feet may be desirable. As shown in  FIG. 3 , the outer pipe  14  of heated pipe section  12  has an outer diameter OD and an inner diameter D having any desired dimensions. For example, the OD and D may each range from 1 inch or less to 10 feet or more. The wall thickness of the outer pipe  14  may be selected as desired, for example, from 0.01 inch or less to 1 foot or more. In certain embodiments, the length LP of the heated pipe section  12  may be from 1 to 100 feet, the outer diameter OD may be from 1 inch to 10 feet, the inner diameter D may be from 1 inch to 10 feet, and the wall thickness may be from 0.05 to 10 inches. 
         [0028]    As shown in  FIG. 3 , the internal helical heating rib, such as the heating tube  16 , has a helical shape in which each 360° turn of the helix corresponds to a length L measured in a direction parallel to the axis of the helix. The helix has a pitch ratio L:D corresponding to the length L divided by the inner diameter D of the outer pipe  14 . The pitch ratio of L:D may be greater than 1:1, or greater than 2:1, or greater than 3:1. In certain embodiments, the pitch ratio may be from 4:1 to 20:1, for example, from 5:1 to 10:1. The pitch ratio L:D typically remains constant along the length LP of the heated pipe section, but it could be varied in certain embodiments. In certain embodiments, for an outer pipe having an inner diameter D of about 12 inches, the length L may range from 3 feet to 50 feet, typically from 4 feet to 20 feet, for example, from 5 feet to 7 feet. The pitch ratio may be optimized to account for the viscosity, density and velocity of the process fluid to be transported by the pipe. 
         [0029]      FIG. 4  is a cross-sectional view of the heated pipe section  12  of  FIG. 3 , taken along line  4 - 4 . The internal heating tube  16  is connected to an inner surface  24  of the outer pipe  14 , and includes an inlet end  18  extending through the sidewall of the outer pipe  14 . As shown in  FIGS. 2 and 3 , the internal heating tube  16  also includes an outlet end  20  extending through the sidewall of the outer pipe  14 . 
         [0030]      FIG. 5  is a cross-sectional view of the pipe section  12  of  FIG. 3  taken along line  5 - 5 . In this view, the heating tube  16  is shown to have a circular cross-sectional shape. In this embodiment, the heating tube is connected to the internal surface  24  of the outer pipe  14  to attach the components together, and to prevent the flow of process fluid between the heating tube  16  and the internal surface  24  of the outer pipe  14 . This connection can be made, for example, by bonding or fusing the heating tube to the internal surface of the pipe, using for example, adhesive, welding, or any other suitable method that permanently bonds the internal surface of the pipe and the heating tube together. The bonding method may vary depending on wall thickness, pipe size, pressure requirements, and the type of fluid to be transported. In the embodiment shown, the heating tube  16  has an internal channel  26  for passage of the heating liquid. In this embodiment, the channel has a circular cross-sectional shape. However, the channel can have other cross-sectional shapes. The outer diameter and pitch of the heating tube  16  can be selected to produce the desired helical flow of the process fluid. 
         [0031]    As shown in  FIGS. 4 and 5 , the internal helical heating rib, in the form of the tube  16 , has a height H measured radially from the inner surface  24  of the outer pipe  14 . The rib height H may be in a range of from 0.1 inch to 10 inches or more, depending upon the dimensions of the pipe sections in which they are installed. For example, the height H may range from 1 to 15 percent of the inner diameter D of the outer pipe  14 . In certain embodiments, the height H may range from 5 to 14 percent of the inner diameter D of the outer pipe  14 , for example, from 6 to 12 percent. 
         [0032]    By providing the internal helical heating rib structure, such as the helical arrangements shown in  FIGS. 1-5 , the ribs cause a non-laminar or turbulent flow of the process fluid, e.g., a helical or swirling pattern, as it is transported through the heated pipe section  12 . Such a turbulent flow generates heat within the process fluid, e.g., by frictional heating, and may provide increased heat transfer between the heating liquid and the process fluid. 
         [0033]    In accordance with embodiments of the invention, the internal heating tube  16  is connected to the internal surface of the outer pipe  14 , e.g., by welding or adhesive, to secure the heating tube to the internal surface of the outer pipe. Alternatively, the outer pipe  14  and internal heating tube  16  may be integrally formed, e.g., by co-extrusion. In certain embodiments, the internal heating tube  16 , or other type of helical heating rib, is permanently bonded, welded, adhered, integrally formed or otherwise attached to the internal surface of the outer pipe, as opposed to being removable. 
         [0034]    The outer pipe  14  and internal heating tube  16  can be constructed of materials that are selected based on the characteristics of the fluid to be transported and the expected operating parameters of the fluid transport system. For example, the outer pipe  14  and internal heating tube  16  may be made of polymeric materials such as thermosets, thermoplastics, polyethylene, polypropylene, and the like, or metals such as iron, steel, and the like. The material used for the host pipe and the inner coil may be the same or different, e.g., a polymer such as polyethylene, polyurethane, or the like. In certain embodiments, the outer pipe  14  may be made of a material having a relatively low thermal conductivity and high thermal insulation in order to provide a degree of thermal insulation that helps retain heat within the outer pipe  14 . For example, the outer pipe  14  may be made of a polymer such as polyethylene or the like having a thermal conductivity k of less than 0.5, wherein k represents cal/cm·sec·K for a material at a temperature of 300K. In certain embodiments, the thermal conductivity k may be less than 0.4, or less than 0.2, or less than 0.1. The internal heating tube  16  may have the same or different thermal conductivity as the outer pipe  14 . In certain embodiments, the internal heating tube  16  and outer pipe  14  may have the same or similar coefficients of thermal expansion. 
         [0035]    Table 1 shows several examples of pipes that can be used for the outer pipe  14  and the internal helical tube  16 . In each example, the helical tube  16  has a pitch ratio of about 6:1, that is, there is one turn of the helix for every six feet measured along the central axis of the host pipe. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 OD 
                   
                 Min. Wall 
                 Operating 
               
               
                   
                 (inch) 
                 D (inch) 
                 Thickness (inch) 
                 Pressure (psi) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Outer Pipe 
                   
                   
                   
                   
               
               
                 12″ SDR 11 
                 12.75 
                 10.29 
                 1.159 
                 160 
               
               
                 12″ SDR 13.5 
                 12.75 
                 10.74 
                 0.994 
                 125 
               
               
                 12″ SDR 17 
                 12.75 
                 11.16 
                 0.750 
                 100 
               
               
                 Helical Heating 
               
               
                 Tube 
               
               
                 1.25″ SDR 11 
                 1.66 
                 1.358 
                 0.151 
                 160 
               
               
                 1.25″ SDR 13.5 
                 1.66 
                 1.414 
                 0.123 
                 125 
               
               
                 1.25″ SDR 17 
                 1.66 
                 1.464 
                 0.098 
                 100 
               
               
                   
               
             
          
         
       
     
         [0036]      FIG. 6  is a partially schematic isometric view of a heated pipe in accordance with another embodiment of the present invention.  FIG. 7  is a cross-sectional view of the pipe of  FIG. 6 . In this embodiment, an outer pipe  30  contains an internal helical heating rib  32  that comprises a protrusion from the internal surface  34  of the outer pipe. The portion of the internal helical heating rib  32  contacting the internal surface  34  of the outer pipe  30  may have substantially the same cross-sectional radius of curvature as the internal surface  34  in order to maximize the surface contact area therebetween. The helical rib  32  has a channel  36  for passage of the heating liquid. In this embodiment, the channel has a circular cross-sectional shape. However, the channel can have other cross-sectional shapes. The height H and pitch ratio L:D of the helical rib  32  can be selected as described above to produce the desired turbulent flow of the process fluid. It is recognized that the optimal height H may depend on the expected flow rate, or range of flow rates, of the process fluid, as well as the characteristics of the process fluid. 
         [0037]      FIG. 8  is a partially schematic isometric view of a heated pipe in accordance with another embodiment of the present invention.  FIG. 9  is a cross-sectional view of the pipe of  FIG. 8 . In this embodiment, an outer pipe  40  encloses an internal helical heating rib  42  that comprises a protrusion provided on the internal surface  44  of the pipe. The portion of the internal helical heating rib  42  contacting the internal surface  44  of the outer pipe  40  may have substantially the same cross-sectional radius of curvature as the internal surface  44  in order to maximize the surface contact area therebetween. The helical rib  42  has a channel  46  for passage of the heating fluid. In this embodiment, the channel has a circular cross-sectional shape. However, the channel can have other cross-sectional shapes. The height H and pitch ratio L:D of the helical rib  42  can be selected as described above to produce the desired turbulent flow of the process fluid. 
         [0038]    The outer pipes  30  and  40 , and the internal helical heating ribs  32  and  42 , in the embodiments shown in  FIGS. 6-9  may be made of similar types of materials having similar characteristics as the embodiments of  FIGS. 2-4 . 
         [0039]    The heating liquid contained in and transported through the internal channels of the helical ribs may be any suitable liquid such as water, hydraulic fluid, antifreeze and the like. The rate of flow of the heating liquid through the internal helical structure may be adjusted to achieve the desired heat transfer, e.g., at a rate sufficient to prevent freezing of the process fluid that is held and/or transported through the heated pipe sections  12 , as well as any additional non-heated pipe sections  20 . The temperature of the heating liquid passing through the helical channel is typically above 0° C., for example, above 10 or 20° C. In certain embodiments, the heating fluid may have a temperature of greater than 50° C., 100° C., 200° C., or higher. 
         [0040]      FIG. 10  is a schematic representation of portions of a hydraulic fracturing or fracking gas operation  50  including a heated pipeline  52  including sections of heated pipe  54  in accordance with an embodiment of the present invention.  FIG. 10  shows a source of fracking fluid in the form of a pond  56 . A pump  58  extracts water from the pond and pumps it into a pipeline  52 . The pipeline includes one or more heated pipe sections  54 . The pipeline delivers the water to fracking tanks  60 . After the water is used in the fracking operation, at least a portion of the water may be returned to the pond or otherwise handled. The heated pipeline  52  may comprise an open or discontinuous system in which the process fluid does not flow in a continuous closed loop, i.e., some or all of the process fluid flowing through the heated pipeline  52  may not be recirculated through the pipeline. During various aspect of the fracking operation, the water may flow at a high rate through the internally heated pipe  54 , of for example, greater than 100 gallons per minute, often greater than 200, 300 or 400 gallons per minute. At other times, the water may flow at a low rate, or it may be stagnant. During these times, if the pipeline is exposed to a low ambient temperature, the water in the pipeline can freeze. To prevent freezing, a boiler  62  is provided to heat the heating liquid that is passed through the internal helical structure in the heated pipe sections. 
         [0041]    In certain embodiments, the heated pipes are provided in 30 to 500 ft sections, e.g., 40 ft sections. The pipes may be fused together to the desired length and the heated sections may be placed approximately every 100 to 200 feet apart, e.g., 120 feet apart. Another area where the internal helical structure can be used is the manifold. Freezing may result from lack of movement of the process fluid or low flow during fracking. A heating tube can also be placed in the manifold as well as the pipe sections. 
         [0042]      FIG. 11  is schematic block diagram of portions of a control system  70  that can be used in combination with a heated pipe  12  in accordance with an embodiment of the present invention. The control system includes a computer or other signal processing device  72  that receives signals from various sensors  74 ,  76 ,  78 ,  80  that provide signals representative of various parameters such as ambient temperature, process fluid temperature, process fluid flow rate, process fluid pressure, heating liquid temperature, heating liquid flow rate, heating fluid pressure, outer pipe temperature, inner pipe temperature, etc. The processing device can then be used to control the operation of the boiler  82  to provide heating fluid at a desired temperature and/or flow rate. 
         [0043]    The turbulent or helical flow produced by the internal helical structure provides numerous advantages. For example, the heat transfer between the pipe wall and the process fluid is improved. Turbulent or helical flow reduces the probability of precipitate accumulation on the internal surface of the pipe, and may also promote mixing of the process fluid. In addition, pressure losses and energy losses can be reduced. Furthermore, the velocity profile of the flow across the pipe may be more uniform than with laminar flow in a conventional pipe, which can allow the process fluid to clean the pipe. 
         [0044]    In various applications, the pipes described herein can be used for the transportation of various fluids, such as fracking water, potable water, waste water, sewage, slurries, powders, food or beverage products, or any single phase or multiphase fluids. The use of an internal heating fluid channel inside of the pipe and/or manifolds provides a cost-effective approach. The apparatus and methods of the present invention have applications inside and outside of the oil and gas industry where freezing is a problem. 
         [0045]    Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention.