Abstract:
A flameless boiler comprising generator means for generating heat in fluid circulated therethrough by shearing of the fluid; a prime mover drivingly connected to the generator means for shearing of the fluid; a supply reservoir for the fluid; a first pump for circulating the fluid from the supply reservoir to the generator means; and a pressure vessel in fluid communication with the generator means for receiving heated fluid therefrom, the pressure vessel having an outlet for drawing steam therefrom.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a flameless system for boiling water and, more particularly to a flameless boiler in which heat for heating the water comes primarily from the energy produced by a prime mover which may be the engine of the tractor transporting the boiler.  
       BACKGROUND OF THE INVENTION  
       [0002]     In a drilling operation, steam is required throughout the drilling process and in maintenance operations after drilling has finished. Present systems generally use a conventional boiler housed in a boiler building to generate and supply the steam. Because conventional boilers use an open combustion process, the boiler building must be located at least 26 metres from the wellhead. This presents the disadvantage that the footprint of the lease site must be enlarged accordingly and more tubing is required to bring the steam to the well bore with attendant thermal losses.  
         [0003]     Open combustion boilers have a number of additional disadvantages. The open flame is less controlled compared to the use of a flameless system which derives heat from the energy produced by an internal combustion engine. Exhaust gases are often hotter in an open combustion system and if they are not monitored these systems can flood and expel flame. The temperatures in these systems can reach instantaneous temperatures greater than the kindling temperature of natural gas. This means that if there were a natural gas leak, the danger of explosive combustion is present. A diesel or propane leak in the vicinity of the burner can also be ignited.  
         [0004]     Further, the combustion process in an open flame system is not as complete as in enclosed systems, which can produce free radicals that escape into the atmosphere. Closed combustion systems have compression ratios commonly many times greater than open combustion burners. This lack of compression negatively affects the reactiveness of oxygen. Hydrocarbon/oxygen reactions are exothermic which provides the heat energy used by the boiler. Provided that the combustion is given enough oxygen, heat and time to complete the process, carbon dioxide and water are produced which are more benign byproducts. However, nitrogen gas is also present during combustion and if the reaction is not ideal, some molecules of nitrogen attach themselves to oxygen to produce the poisonous gas NO. This gas is referred to as a free radical. Other byproducts include carbon monoxide (CO), volatile organic compounds (VOC), and particulate matter (PM). All of these produces are well recognized as being harmful to the environment.  
         [0005]     Some open flame systems also require more fuel than a flameless system. Fuel is burned less efficiently in these systems, sometimes requiring a greater amount of fuel to produce an equivalent amount of heat compared to a flameless system.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention seeks to overcome the above disadvantages by providing a flameless boiler in which heat can be derived from an engine, which engine might also be the same engine used for other purposes, and transferred to the water to produce steam. In the present invention, heat is transferred from the engine using heat exchangers to transfer heat from the engine coolant to the water. An exhaust heat exchanger can be used to transfer heat from the engine exhaust to the heat exchange fluid. This allows the present system to recover more heat from the engine. The engine is preferably but not necessarily the engine from the truck or tractor which transports the boiler.  
         [0007]     To make use of available excess horsepower, one or more water brakes are provided to load the engine, thereby producing more heat from the engine. Further, the shearing of the fluid in the water brake produces heat on its own. Water is used to load the water brake, and the shearing heat is thereby transferred to the water.  
         [0008]     The water brake of the present invention provides a further advantage that it can run empty when no additional loading of the engine is required or steam generation is unnecessary. This removes the requirement for the usual gear box that disengages the water brake, saving weight and costs for this system.  
         [0009]     The present invention therefore provides a flameless boiler comprising generator means for generating heat in fluid circulated there through by shearing of said fluid; a prime mover drivingly connected to said generator means for shearing of said fluid; a supply reservoir for said fluid; a first pump for circulating said fluid from said supply reservoir to said generator means; and a pressure vessel in fluid communication with said generator means for receiving heated fluid therefrom, said pressure vessel having an outlet for drawing steam therefrom. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     Preferred embodiments of the present invention will now be described in greater detail and will be better understood when read in conjunction with the following drawings in which:  
         [0011]      FIG. 1  is a schematic flow diagram of the flameless shear boiler;  
         [0012]      FIG. 2  is a top plan partially schematical view of a flameless shear boiler unit;  
         [0013]      FIG. 3  is a side elevational partially schematical view of a flameless shear boiler;  
         [0014]      FIG. 4  is a front side elevational partially schematical view of a flameless shear boiler;  
         [0015]      FIG. 5  is a schematic flow diagram of another embodiment of the flameless boiler; and  
         [0016]      FIG. 6  is a pictorial representation of a water brake forming part of the present boiler.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]     Reference will now be made to  FIG. 1  for a more detailed description of a flameless boiler unit  10 . Flameless boiler unit  10  is preferably capable of producing 2.5 million BTU/hr and captures this heat from three sources: engine coolant; exhaust gases; and the use of excess engine horsepower to provide shear heat in the heat transfer fluid, which in this application will normally be water boiled to produce steam.  
         [0018]     Heat from engine  70  is transferred to the engine&#39;s cooling system in which the coolant will be water, glycol or a mixture of the two. The heated coolant flows through line  5  to a heat exchanger  16 , such as a shell and tube heat exchanger well known in the art, and returns to the engine via line  6 . Both lines  5  and  6  can be valved to control the flow of coolant from the engine through exchanger  16 .  
         [0019]     Cold water for the present system is stored in a storage tank  12 . A pump  14  pumps water from storage tank  12  through engine coolant heat exchanger  16 . Since the heat energy rejected to the engine cooling system cannot be used to generate steam since the temperatures of the coolant are normally too low for boiling water, heat exchanger  16  is used primarily to preheat the water from tank  12  that is being pumped into a reservoir  18 .  
         [0020]     Pump  14  is a positive displacement pump and is used to add water to reservoir  18  when the water level falls below a predetermined level. Signals from a level indicator sensor  20  are used by a controller  9  to start and stop pump  14  when required.  
         [0021]     Water from reservoir  18  is pumped from a location below the water line through a valve  22  by centrifugal pump  24 . The water is then pumped through a filter  26  and, if valve  28  is open, into a shear heat generator  30 . Generator  30  is typically a water brake or dynamometer mechanically coupled to engine  70 .  
         [0022]     Shear heat generator  30  results in heat being added to the water in two ways. First, while the tractor&#39;s engine is providing power to pump fluids and to operate the usual parasitic loads such as the alternator and coolant pumps, this consumes only a fraction of its available output, leaving excess capacity. Mechanically coupling the tractor&#39;s engine to generator  30  loads the engine and draws horsepower, which increases the amount of heat rejected to the engine coolant circulated through heat exchanger  16 . Second, generator  30  itself converts the engine&#39;s mechanical energy into thermal energy in the water circulated through the generator sourced from reservoir  18 . The water brake is set up to generate enough heat to boil the water and convert it into steam. Approximately 2546 BTU/hr is generated in a preferred shear heat generator of the present invention for each horsepower of load on the engine.  
         [0023]     The mechanical coupling between engine  70  and generator  30  is conventional and numerous means of coupling them operationally together will occur to those skilled in the art. For example, as is known in the art, the truck&#39;s gearbox (not shown) will have one or more auxiliary power take-offs. One of these take-offs can be coupled to generator  30  such as by means of a shaft, belt or chain. Or the engine&#39;s power take-off can be drivingly coupled to a gearbox which in turn can be directly coupled to the water brake. As will be described below, one of the preferred aspects of the present invention is that adaptations to the generator allow it to run empty, which obviates the need for a gearbox, which saves considerable weight and expense.  
         [0024]     Generally, generator  30  is a water brake which comprises a sealed chamber that is normally kept full of heat transfer fluid. A plurality of radially extending, shaft mounted blades, impellers or rotor/stators are disposed to rotate within the chamber against the shear resistance of the heat transfer fluid. The shaft is rotated by the engine being loaded through the mechanical coupling described above. The mechanical energy from the spinning rotors is converted to heat energy in the heat transfer fluid which is continuously circulated through the chamber to cool the water brake and its seals and to produce heated heat transfer fluid. In the present system, wherein the heat transfer fluid is water, the intent is to heat the water to the boiling point for the creation of steam.  
         [0025]     Pump  24  further allows water to be pumped through shear heat generator  30  into exhaust heat exchanger  32 . Heat exchanger  32  takes advantage of engine inefficiencies. Specifically, most engine inefficiencies are from the loss to the atmosphere of escaping exhaust gases. In a typical 400 hp engine, the engine may reject up to 2.8 million BTU/hr from the exhaust system alone.  
         [0026]     Heat exchanger  32  attempts to recover approximately two-thirds of the heat loss in escaping exhaust gases. This is accomplished by using an air to liquid heat exchanger. Due to the constraints of heat exchangers, however, the remaining one-third of heat is lost to the air. Obviously, improvements to exchanger design can be expected to recover a grater proportion of exhaust heat.  
         [0027]     Steam and boiling water from exhaust heat exchanger  32  are then forced by pressure through a valve  34  into reservoir  18 .  
         [0028]     Reservoir  18  is connected to a steam tank  36  and gravity is used to separate the steam from the water. A pressure sensor  40  is used to sense the pressure of steam in tank  36  and when this pressure falls below a predetermined value, controller  9  starts or accelerates centrifugal pump  24  to increase the flow of water to generator  30  to provide additional steam to reservoir  18  and tank  36 .  
         [0029]     Tank  36  includes a safety valve  42  in case excessive pressure is achieved to prevent rupture.  
         [0030]     Pump  24  is also used to provide water to cool seals and bearings in shear heat generator  30 . Reduced diameter (eg. one-quarter inch) supply lines  52  provide water from pump  24 . These small lines fluidly connect with one-eighth inch orifices inside generator  30  as shown in  FIG. 6  that divert water against the generator&#39;s seals and/or bearings for times when the generator runs empty as will be described below in greater detail. Supply lines  52  bypass valve  28 , and thus even if valve  28  is closed, water is still supplied to the generator for cooling purposes.  
         [0031]     As indicated above, shear heat generator  30  can at times be allowed to run empty. This occurs when steam generation is not required. In conventional systems, a gear box would be required to disengage the generator from the engine. These gear boxes are however are heavy and expensive. To avoid this, the present shear heat generator has been adapted to run empty. Normally, this would cause the generator and its seals to burn out.  
         [0032]     In the present system, the brakes&#39; housing is 4140 HTSR (Heat Treated Stress Relieved) steel. Aluminum hardened to 85 rockwell is another alternative. Supply lines  52  continuously deliver a small amount of water to one-eighth inch orifices which internally direct water against the seals and/or bearings. When valve  28  is closed to stop delivery of water to shear heat generator  30 , steam is allowed to flow through line  60 , through restrictive orifice  62  and into shear heat generator  30  to allow any water remaining in generator  30  to drain into line  64 , through valve  66  and into reservoir  18 .  
         [0033]     Without water in it, generator  30  simply spins without loading the engine. The additional hardening of the shear heat generator&#39;s housing and the continuous flow of water against the seals of the generator prevents erosion and pitting of the generator&#39;s walls and burnout, respectively. These adaptations to generator  30  provide additional advantages over conventional system water brakes which cannot be run empty.  
         [0034]     The present system therefore derives heat from an engine coolant heat exchanger, an exhaust gas heat exchanger, and from one or more shear heat generators  30  to heat the water above boiling, which in turn provides steam to steam tank  36 .  
         [0035]     Tank  36  in a preferred embodiment will be connected to a manifold  45  on the truck bed or on the cargo box housing the boiler. This manifold will be used to fix lines to run steam to desired locations.  
         [0036]     Another advantage of the present invention is that as pressure in tank  36  is reduced due to consumption, the boiling temperature of the water in reservoir  18  decreases, causing the water in the reservoir to boil more aggressively to maintain a full head of steam in tank  36 . This effect allows the system to kick in shear heat generator  30  and exhaust heat exchanger  32  to bring the pressure in the tanks back to a set pressure which gives the users of the present boiler unit steam on demand.  
         [0037]     Reference is now made to FIGS.  2  to  4 . All of the above described elements can be mounted on a truck for transport and mobility. A sample layout of the elements is shown in FIGS.  2  to  4 . Water tank  12  is located behind a truck engine  70 . The location of exhaust heat exchanger  16 , steam tank  36 , reservoir  18 , shear heat generator  30 , fuel tank  72 , gear box  74 , control panel  9 , and centrifugal pump  24  are shown in these figures.  
         [0038]     Reference is now made to  FIG. 5  which is a flow diagram for a modified flameless boiler in which like numerals have been used to identify like elements.  
         [0039]     As in the previous embodiment, heat from engine  70 &#39;s cooling system is captured by heat exchanger  16  to pre-heat water from tank  12 . Pump  14  draws water from the tank for circulation to exchanger  16 , the water being discharged through line  17  where the flow is split between line  19  which diverts some water directly to reservoir  18 , and line  23  which directs the remaining flow to centrifugal pump  24 .  
         [0040]     From pump  24 , the water is delivered through line  27  and the flow is again split, with a portion of the water being diverted into line  29  for flow through exhaust gas heat exchanger  32  and then into reservoir  18 , and the remaining flow continuing through line  27  to generator  30 . As in the previous embodiment, reduced diameter lines  52  connect with one-eighth inch orifices inside the generator that direct water against the generator&#39;s seals and/or bearings for times when the generator runs empty.  
         [0041]     The main flow of water to generator  30  is controlled by an actuatable valve  31  connected to a main settable pressure cutout sensor  33  mounted on reservoir  18  as will be described in more detail below. Obviously, when valve  31  is closed, all of the flow from pump  24  is directed to exhaust heat exchanger  32  with the exception of the small amounts that continue to flow into reduced diameter lines  52 . This trickle can drain back into tank  12  through lines  59  or it can drain to atmosphere. Heated water and steam produced in generator  30  return to reservoir  18  either directly through line  37  and/or through exhaust heat exchanger  32  by intersecting lines  29  and  37  (now shown).  
         [0042]     As will be appreciated, this embodiment uses reservoir  18  for both heated water and steam collection.  
         [0043]     The water level in reservoir  18  is maintained by lower and upper level switches  57  and  58 , respectively, connected hydrostatically to the reservoir. In the event that the water level falls below a predetermined lower level, switch  57  actuates an audible and/or visual alarm  75 . Switch  58  actuates pump  14  to keep the water level topped up to a predetermined level. A one way check valve  15  prevents the reverse flow of heated water from reservoir  18  into tank  12 . Steam pressure is monitored by settable pressure cutout  33 . Steam pressure will normally be settable within a range from approximately 10 psi to 150 psi and a normal operating range might be 80-90 psi. Cut out  33  actuates generator on/off valve  31  to maintain steam pressure within the selected range. As a safety backup in the event that cutout  33  fails, backup pressure cutout  39  is permanently set at a maximum pressure and will shut off the flame to generator  30  off if that pressure is ever reached and can also be wired to activate alarm  75 .  
         [0044]     As yet another safety backup, reservoir  18  includes a safety relief valve and over pressure switch  42 . The bottom of the tank is provided with a blow down valve  43  for periodic draining to minimize the buildup of mineral deposits on the tank&#39;s inner walls. It will be appreciated however that unlike conventional boilers in which kettle cake undesirably insulates the water in the boiler from the heat source, the cake will actually insulate reservoir  18  against heat loss, which can be advantageous, provided of course that the build up does not significantly diminish the tank&#39;s capacity.  
         [0045]     In this embodiment, there is also provided a steam return line  65  for those applications in which steam is used in a closed loop system and is therefore recoverable either as steam or as condensed water.  
         [0046]     One skilled in the art will realize that the present system can also be mounted in a building or elsewhere and does not need to be mobile. In that case, the engine could be used for other purposes or it could be dedicated to flameless shear boiler unit  10 . The boiler could be used in any application requiring steam.  
         [0047]     The use of an internal combustion engine provides advantages over a flamed boiler. Regulatory bodies have set stringent controls for diesel engines for example. This includes lower allowable emissions set by the Environmental Protection Agency in the U.S.  
         [0048]     There is also a fine line of control that is needed to balance the reduction of nitrogen oxides and particulate matter. Internal combustion engines are electronically controlled and can react fast enough to control emissions within each stroke of the engine. This is contrary to open flame systems in which no such controls exist.  
         [0049]     The present invention can be retrofit using existing engines on rigs to produce steam required by the rig. Shear heat generators could be used to load the engines to make exhaust systems produce heat for steam production. When the engine is loaded up with normal rig operations, the shear heat generator can be unloaded to allow maximum power to be available to the rig.  
         [0050]     The above described embodiments of the present invention are meant to be illustrative of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications, which would be readily apparent to one skilled in the art, are intended to be within the scope of the present invention. The only limitations to the scope of the present invention are set out in the following claims.  
         [0051]     The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: