Abstract:
An apparatus and method for enhancing the transfer of heat in a fluid within a reservoir. The interposition of heat exchangers between a primary heating arrangement and an auxiliary heating arrangement results in greater utilization efficiency in heat transfer to the fluid within the container. A predetermined arrangement of heat exchangers within the reservoir containing the same is also disclosed.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a method of enhancing the efficiency of heat transfer into a liquid fluid container and more particularly, the present invention relates to a method, system and apparatus for efficiently transferring heat into a fluid requiring the maintenance of a certain temperature in order to have the fluid remain effective. 
       BACKGROUND OF THE INVENTION 
       [0002]    Fluid heating arrangements have been known for many years and these permeate a wide variety of industries. One industry where the temperature maintenance of the fluid is important is in the fracturing fluid heating industry. As is known “frac” fluid requires heating in order to be effective in an oil field operation. The temperature of the frac fluid must be maintained at certain temperatures in order to prevent fallout of sand within the fracturing environment. 
         [0003]    A panoply of methods and different apparatuses to effect the method have been proposed in the prior art. An example of one such arrangement is one that which is shown and used by McAda Fluids Heating Services. The arrangement provides a truck arrangement where hot oil is used. The arrangement requires the use of fairly significant equipment that is transported to the site by a tractor trailer vehicle. In some instances, the vehicle must remain at the job site in order to provide for the necessary equipment to be available for heating the frac water. 
         [0004]    A further variation of the frac water heating systems is shown in the website of Rapid Hot Flow LLC. In the website, there is an indication that Rapid Hot Flow&#39;s heating trucks are equipped with 21 million BTU input updraft style burner that runs on propane. It is indicated that once the heater trucks arrive at the specified location, the trucks can be heating within minutes. There is a further indication that when the hoses are connected, and the trucks have started circulating water, an operator runs through a list of procedures to ensure that all the requirements have been met. In this system, it is obvious that the vehicle is an integral part of the heating system and further that there is input required by the operator. 
         [0005]    A further variation on the concept of maintaining the temperature of the frac water in the reservoir is shown on the Powerblanket website where effectively a blanket or a tank wrap is positioned around the holding tank. In the website there is an indication that the tank wrap creates a barrier of insulation to keep fluids from freezing and viscous materials flowing. 
         [0006]    Although this is generally useful, it appears to be quite cumbersome not only from a handling point of view, but also for positioning about the tank. It is well known that holding tanks or reservoirs are very large and it would be somewhat cumbersome to wrap the blanket about a large vessel. 
         [0007]    Turning to the patent art, in U.S. Pat. No. 5,983,889, issued Nov. 16, 1999, to Thomas, there is disclosed a portable water tank heating system. The reference teaches a portable system which uses a hollow continuous tubular loop containing a fluid this is circulated through the loop by convection to prevent water in the tank from freezing. The fluid in the loop flows from a reservoir and travels past a gas burner in the hot chamber for heating the fluid. The fluid flows through a heat exchanger and releases heat to the cold water in the tank before being returned into the housing through the return line. The fluid then returns to repeat the cycle. 
         [0008]    The system would appear to completely rely on the burner coil for transmitting the heat to the water body. It is well established that such arrangements have limited efficiency. 
         [0009]    In United States Patent Publication No. US 201110211818, published Sep. 1, 2011, the Applicant, Grady, teaches a fracturing tank fluid heating tank. 
         [0010]    This patent application is very broad and effectively provides a self contained tank into which is disposed in a fracturing tank fluid healing unit. In the document, the tank comprises a closed tank having an access point such as a manhole cover. The unit further includes a dimensional coil where a tube like heating unit is designed to heat the fluid once contained within the tank. 
         [0011]    As with the previous reference, this reference is confined to a relatively inefficient heating means in terms of the coil type arrangement. The inefficiency in terms of the energy is pronounced; in arrangements with the heat exchanger in the tank only, efficiency is typically 50%. 
         [0012]    Chandler, in United States Patent Publication No. US2010/0000508, published Jan. 7, 2010, teaches an oil fired frac water heater. The document teaches a portable system for heating treatment fluids at a remove worksite. The arrangement has a firebox, heat exchanger within the firebox, a fluid supply system including a fluid supply pump connected to an inlet of a tubular coil associated with the heat exchanger and a plurality of burner assemblies in the firebox. The arrangement further provides for a primary air system for supplying pressurized air flow to each of the burners and a secondary air system for supplying a second pressurized air flow to the firebox. The secondary pressurized air flow increases the convective heat transfer of thermal energy from the combustion flow to the treatment fluid. The arrangement is fairly complex and does not indicate any thermal energy augmenting system which would elevate the efficiency of the unit. 
         [0013]    In U.S. Pat. No. 6,516,754, issued Feb. 11, 2003, Chadwick, teaches a convective heating system for liquid storage tanks. The arrangement incorporates a heating chamber with an inlet and an outlet for convective fluid flow past a flameless heater. Heated liquid is circulated through the upper outlet of the tank from the heating chamber and back into the tank. It is indicated that the heated liquid reenters the tank through a floating discharge flexibly connected to the upper section of the tank to remain dynamically in contact with the liquid at all times. This is said to avoid airlocks which interrupt the convective flow of liquid through the heating system. 
         [0014]    Hefley, in United States Patent Publication No. US2010/0294494, published Nov. 5, 2010, teaches a water heating apparatus for continuous heated water flow and method for use in hydraulic fracturing. Essentially, the publication includes a discussion regarding mixing device for ensuring that the frac fluid is maintained at the proper temperature during operation. 
         [0015]    Other references which are generally relevant to the area of technology of the instant application include U.S. Pat. Nos. 2,067,063; 3,933,205; 3,512,239; 3,937,275; 4,318,549; 5,115,491; 6,662,861; 7,793,707; and United States Patent Publication Nos. US 2006/0196958; US 2007/0000453; US 2008/0217420; US 2008/0236275; US 2008/0206699; US 2010/010156; and US 2010/0193155. 
         [0016]    Despite the comprehensive prior art and numerous methods that have been set forth in the fracturing frac fluid heating methods, there still exists the need to improve on the existing systems and operation where heat transfer can be maximized using a portable system and further where there is not any requirement that the vehicle be present at all times for operation. 
         [0017]    The present invention has successfully unified various technologies in a unique manner to result in an elegant solution for maximizing heat energy in a frac fluid environment. It will be appreciated by those skilled that the fluid referred as frac fluid could be any fluid, drilling water, acid, inter alia. 
       SUMMARY OF THE INVENTION 
       [0018]    One object of the present invention is to provide an improved method, system and apparatus for augmenting the heat enthalpy available for transfer into a frac fluid or other fluid in an efficient manner. 
         [0019]    A further object embodiment of embodiment of the present invention is to provide a method of enhancing the rate of heat exchange in a fluid retained in a reservoir, comprising: providing a heater circuit having a primary heater for heating a reservoir heat exchanger disposed within the reservoir; providing an auxiliary heater; and interposing a secondary heat exchanger in fluid communication between the primary heater. The auxiliary heater and the reservoir heat exchanger is present to augment heat content of cool fluid returning from the reservoir heat exchanger with heat from the primary heater and the auxiliary heater. 
         [0020]    Conveniently, the use of the secondary heat exchanger within the environment of the other components which are high efficiency, results in significant operational efficiency for heating the frac fluid. Any of the suitable heat exchangers may be used such as those manufactured by the Dry Air Corporation, the Alfa Laval Corporation. The Alfa Laval unit is referred to as a brazed plate heat exchanger (CB Series). Of particular convenience is the fact that the heat exchanger arrangement can be incorporated without significant increase in mass or footprint to the overall heating arrangement. In one of embodiment, the entire heating arrangement can be configured and loaded onto a single skid and easily transported to a worksite and left at the worksite to therefore free the use of the transporting vehicle for other purposes. Further, the unit can be remotely controlled to avoid significant operator input and repetitive visits to the worksite with replacement heating units which would result in heavy traffic flow at the worksite. As noted supra, the utilization efficiency of existing arrangements is typically 50%; by incorporating the instant technology, utilization efficiency can reach 100%. This represents a significant advance in the art. 
         [0021]    It has been found that by incorporating an auxiliary heater together with the secondary heating exchanger, the overall utilization efficiency of the system can be significantly increased. The result is that the secondary auxiliary heater functions to warm, cool fluid within the heat exchanger system leaving the frac fluid reservoir. In this manner, there is effectively a dual heating process taking place, namely one from the auxiliary heater and the second from the heater circuit from the primary heater. By the introduction of the heat exchanger, the method may be optimized in terms of output utilization efficiency. 
         [0022]    In accordance with a further object of one embodiment of the present invention, there is provided a system for enhancing the rate of heat exchange in a fluid retained in a reservoir comprising: a heater circuit having a primary heater for heating a reservoir heat exchanger disposed within the reservoir; an auxiliary heater and a secondary heat exchanger interposed and in fluid communication between the primary heater, the auxiliary heater and the reservoir heat exchanger to augment heat content of cool fluid returning from the reservoir heat exchanger with heat from the primary heater and the auxiliary heater. 
         [0023]    The system incorporates a highly efficient reservoir heat exchanger. It has been found that by making use of a dimpled closed heat exchanger of planar configuration, in combination with the secondary heat exchanger and heater circuit, as well as auxiliary heater, results in a very effective compact modular system. The dimpling effect of the heat exchanger within the reservoir significantly increases the available surface area for heat transfer. The exchanger, as noted above, is closed and uses for example, propylene glycol as the heating fluid for transferring the heat enthalpy sensed by the fluid. 
         [0024]    In accordance with a further object of one embodiment of the present invention, there is provided an apparatus for enhancing the rate of heat exchange in a fluid retained in a reservoir having a heater circuit having a primary heater for heating a reservoir heat exchanger disposed within the reservoir. The improvement comprises an auxiliary heater; and a secondary heat exchanger interposed and a fluid communication between the primary heater, the auxiliary heater and the reservoir heat exchanger to augment heat content of cool fluid returning from the reservoir heat exchanger with heat from the primary heater and the auxiliary heater. 
         [0025]    Having thus generally described the invention, reference will now be made to the accompanying documents illustrating preferred embodiments. 
         [0026]    Copious advantages flow from the practice of the methodology and use of the apparatus. These include:
       i) the lack of moving parts;   ii) the portability of the arrangement due to the reduced size;   iii) lighter weight for certain embodiments;   iv) reduced capital cost;   v) no fluid mixing of fluid to be heated with the heat exchanger fluid;   vi) expedited assembly of the apparatus;   vii) the ability to use the main generator; and   viii) no extraction of the fluids in the tanks, therefore avoiding fluid leaks from the tank.       
 
       INDUSTRIAL APPLICABILITY 
       [0035]    The invention has utility in the head transfer art, 
         [0036]    Having thus generally described the invention, reference will now be made to the accompanying drawings, illustrating preferred embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0037]      FIG. 1  is a schematic illustration of the apparatus employed to effect the method according to one embodiment; 
           [0038]      FIG. 2  is a schematic illustration of the heat exchange system according to one embodiment; 
           [0039]      FIG. 2A  is a further variation of  FIG. 2 ; 
           [0040]      FIG. 3A  is a schematic illustration of the reservoir heat exchanger according to one embodiment; 
           [0041]      FIG. 3B  is a side view of  FIG. 3A ; 
           [0042]      FIG. 4  is a plan view of the heat exchanger in  FIG. 3A ; 
           [0043]      FIG. 5  is a section along line  5 - 5  of  FIG. 4 ; 
           [0044]      FIG. 6  is a top view of the reservoir illustrating the positioning of the heat exchangers; and 
           [0045]      FIG. 7  is a top view of an alternate embodiment. 
       
    
    
       [0046]    Similar numerals used in the Figures denote similar elements, 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0047]    Referring now to  FIG. 1 , schematically depicted is the overall apparatus employed as an example. The overall arrangement is denoted by numeral  10 . A reservoir  12  retains a fluid, one example of which is fracturing fluid, commonly referred to as “frac” fluid. Such vessels typically include a liner  14  which secured to the reservoir by, for example, clamps or other suitable fasteners  16  (not shown). As is well known to those skilled in the art, frac fluid needs to be maintained at an elevated temperature in order to be useful. This requires the injection of heat into the fluid. 
         [0048]    Heat injection in the example is achieved by making use of a modular heating station, generally denoted by numeral  18 . With the instant technology, the station  18 , is particularly effective since it is retained on a skid  20  which may be easily transported to a worksite and disengaged from a truck for use. This has the advantage of preventing the invasiveness of several trucks at the site for prolonged periods and avoiding the concomitant costs and environmental impact. The skid and ancillary equipment is thus independent of a vehicle in use and therefore is self-contained. The skid  20  includes a plurality of heaters  22 , generator  24 , storage tank  26  for a heat transfer liquid, such as propylene glycol, fuel tank  30 , inter alia. The heaters  22  each include secondary heat exchangers  32  which will be discussed in greater detail herein after. A plurality of fluid lines  34  fluidly communicate with reservoir  12  and more particularly with reservoir heat exchangers  36  which will now be discussed with respect to  FIG. 2 . 
         [0049]      FIG. 2  is a schematic representation of the overall layout in accordance with one example. Reservoir heat exchangers  36 , shown as two such units in the example for purposes of explanation, are planar elements and will described in detail later in the specification. The units  36  fluidly communicate with the water heaters  22  by lines  34  supra and  38 . Conventionally, the water heaters  22  would simply run heating fluid, such as glycol, through heating units positioned in the tank  12  to heat the fluid retained in the reservoir. In the present system, by making use of ancillary heaters and interposition of secondary heat exchangers, utilization efficiency has been greatly improved with a complementary small portable system. 
         [0050]    The secondary heat exchangers  32  are interposed in fluid communication with the heaters  22  and reservoir heat exchangers  36  as well as auxiliary heater  40 . In operation, cool water from the reservoir heat exchangers  36  denoted by A on line  34  enters a respective secondary heat exchanger  32 . 
         [0051]    From the respective exchanger  32  cool fluid exits each exchanger  32  as stream B and with passive enthalpy transfer at C. Stream C then enters auxiliary water heater  40  where it is heated exiting as stream D for introduction back into the individual exchangers  32  as separate streams E. Streams E exit the respective exchangers  32  as warmed streams F for introduction into the heaters  22  for upgrade heating to hotter streams exiting the respective heaters  22  as stream G. The latter are then introduced into the reservoir heat exchangers  36 . In this manner of operation, the utilization efficiency of the system is significantly boosted while avoiding the use of vehicle based power, heavy equipment and costly human intervention. 
         [0052]    Referring now to  FIG. 2A , shown is a further embodiment of the method. In this embodiment, hot fluid exists primary heater  22  via stream G and travels through heat exchanger  36  exiting cold via stream A. Cold fluid enters heat exchanger  32  receiving heat via passive transfer from auxiliary heater  40  and particularly by stream D and exits heat exchanger  32  wam  1  via stream F returning to primary heater  22 . This is generally the primary circuit. Subsequently, hot fluid exists auxiliary heater  40  via stream D and travels through heat exchanger  32  (or heat exchangers in applications where one auxiliary unit is used to boost more than one primary circuit) transferring heat passively to primary stream F, returning cool to auxiliary heater  40  via stream C. This is referred generally as the second circuit. 
         [0053]    Of particular advantage is the fact that the method and apparatus related to  FIG. 2A  allows the second circuit component (auxiliary heater  40  and heat exchanger  32  and related connections) to be removed from the primary circuit, once the desired temperature has been reached in the tank. The secondary circuit could then be transported to another tank to elevate the utilization efficiency and heat the contents of the tank. In this manner, for the arrangements of  FIG. 2A  the secondary circuit functions as an optimization module. 
         [0054]    Returning now to the reservoir heat exchangers  36 ,  FIGS. 3A ,  38 ,  4  and  5  illustrate the structure in more detail. The arrangement as noted above is planar and generally rectangular in the example. The exchanger  26  includes an inlet connection  40  and an outlet connection  42  in a sealed body. For enhanced efficiency, the entire surface area of the exchanger  26  is dimpled, the dimples being denoted by numeral  44 . This is more clearly illustrated in  FIGS. 4 and 5  where the exchanger is shown in plan view. As shown, the dimples  44  extend over the Whole area of exchanger  26 . A cross section of the exchanger  26  is shown in  FIG. 5 . The heating fluid, using glycol as the example, flows through the channels  46  which are in alternation with the dimples  44 . As will be appreciated by those skilled, this arrangement provides enormous surface area for heat transfer to the reservoir  12 . 
         [0055]    In order to further augment the efficiency of the arrangement, the exchangers  26  provide supports  48  for positioning the exchangers onto the bottom  50  of the reservoir  26  as shown in  FIG. 6 . 
         [0056]    The supports  48  include a vertical component  52  and a horizontal component  54 . The connection of the vertical component  52  is such that the body of the exchanger is angularly disposed relative to the horizontal. It has been found that this angular disposition has ramifications in terms of heat transfer to the fluid in the reservoir. The effective range for the disposition is from 0.1 degrees to 90 degrees relative to the horizontal. As a preferred range, the angle may be between 15 degrees and 20 degrees. The vertical component  52  spaces the exchanger from the bottom  50  ( FIG. 6 ) of the reservoir  12  to facilitate effective heat transfer. A suitable elevation has been found to be, for example 6 centimeters. This will largely depend on the reservoir volume and other specific individual requirements. As an option, the elevation and angle may be changed using suitable linkages and motors (both not shown) in order to provide the highest de gee of flexibility for the operator. 
         [0057]    Perhaps one of the most advantageous features of the arrangement set forth herein relates to the fact that there is no need for supplementary pumps or other forms of drivers to have effective heat transfer within the reservoir. This has posed a problem in the prior art; typically existing systems required pumping either extraneously or internally of the reservoir to enable uniform heat distribution. This was necessary to avoid thermoclines or temperature stratification within the reservoir which inherently would cause regular cycling of the heating elements to maintain a uniform temperature. The present invention has discovered a method to avoid the need for pumps or other distribution means for the heat. 
         [0058]    It has been found that natural convection can be achieved in the arrangement by arrangement of the exchangers  26  on the bottom surface  50  of the reservoir  12 . Returning to  FIG. 6 , the Figure illustrates D1 D2, D3 and D4 in a counter clockwise array. By varying the distance in an increasing amount from D1 through with progressive additions to D4, natural convection has been observed thus obviating the need for extraneous energy input to induce a homogeneous temperature. In terms of the useful range between D1 through D4 a ratio 1:1 to 1:7 has been found effective. The result is very pronounced in light of the previously described heat exchanger and the secondary heat exchangers. These elements work in concert to result in an environmentally effective, small footprint and easily deployable arrangement with the possibility for remote operation. 
         [0059]    Although four heat exchangers are shown in  FIG. 6 , it will be understood that any number of such units may be included in the reservoir  12 . This will, of course, depend on the size of the reservoir  12  and ambient temperature conditions, etc. 
         [0060]    As illustrated in  FIG. 6  by dashed line numeral  52 , a cover layer partially covering the top surface of the reservoir  12  is depicted. This cover may consist of a suitable buoyant cover that prevents or significantly reduces evaporation of the fluid from the reservoir  12 , as well as providing an insulating factor to prevent any temperature drop of the fluid. Suitable materials include, for example, Styrofoam®, polyethylene, metalized plastic, etc. It will be readily apparent to those skilled in the art which other suitable materials may be used. 
         [0061]    In respect of numeral  54 , this represents an evaporation prevention layer which, may comprise, a suitable oil material. An example of a suitable material would be canola oil as canola oil is useful for purposes of insulation and preventing evaporation. Further, the canola oil is useful in that it does not interfere with the composition of the frac fluid where frac fluid is the fluid stored in the reservoir  12 . Other fluid possibilities have been mentioned. Provided the liquid cover material does not interfere with the composition of the frac fluid, any suitable material achieving the insulation and liquid surface coverage features could be used and is envisioned for a possibility. Another example could be a sealed air blanket, suitable foam, etc. 
         [0062]    Turning to  FIG. 7 , shown is a further possible variation of the arrangement that could be used in the practicing of the instant methodology. In this embodiment, numeral  56  shown in dashed line indicates a further series of heat exchangers  26  which are vertically elevated from the existing heat exchangers  26  positioned on the bottom of the reservoir  12  as discussed herein previously. 
         [0063]    In the arrangement shown, the additional heat exchangers  26  are not only vertically elevated from the existing heat exchangers  26  but also staggered radially therefrom such that a respective vertically disposed heat exchanger  26  is from a relative distance point of view adjacent to heat exchangers  26  on the bottom of the reservoir, in this manner, the entire volume of the reservoir  12  benefits from the heat exchangers in the vertically disposed position. Simple connectors  56  may be employed to connect the vertically disposed heat exchangers  26  into the reservoir  12  as shown by the dotted line represented by numeral  56 .