Patent Publication Number: US-2011073048-A1

Title: Pressure gain combustion heat generator

Description:
RELATED APPLICATIONS 
     This application claims priority benefit of U.S. Provisional Application 61/245,963, filed Sep. 25, 2009 and incorporated herein by reference. 
    
    
     BACKGROUND OF THE DISCLOSURE 
     a) Field of the Invention 
     The invention is in the field of heat generation; more specifically it deals with heat generation using pressure gain combustion, such as for example the pulse detonation system which is described in U.S. patent application Ser. No. 12/560,674, filed Sep. 16, 2009 and incorporated herein by reference. 
     Pressure gain combustion utilizing detonation based combustion is a high speed combustion process where the reaction zone is coupled to a shock wave traveling at supersonic speeds. The result is a higher pressure gain compared with subsonic or near constant pressure combustion. Detonation based combustion is thermodynamically more efficient because it approximates a near constant volume (pressure gain) condition to produce higher pressure and temperatures. 
     One method of initiating detonation waves in the combustor is to accelerate the flame through turbulence using obstacles along the flow path. A turbulence-enhancing device known as Schelkin spirals installed along the entire length of the combustion tube is such a device. The spirals increase deflagrative flame speeds through increased turbulence and flame mixing and produce ‘hot-spots’ that in turn result in micro-explosions which then coalesce to form a stable detonation front. 
     Presented here is the use of detonation based pressure gain combustion utilizing Schelkin spirals which are constructed from hollow tubes. The tubes forming the Schelkin spirals also contain fluid which is heated by the combustion process to increase boiler efficiency. 
     SUMMARY OF THE DISCLOSURE 
     An efficient heat generation device is introduced where fuel is burnt in a pressure gain combustion process. The heat generating system has an inner combustion chamber that is housed in heat exchangers. The combustion chamber walls are covered with fluid conduits. While different fluids could be utilized, water is most common and the term water herein is intended to define water and all functional equivalents. The water conduits (tubes) may be multi-pass longitudinal, parallel to the combustor axis or they may be winded around the combustion chamber in a spiral fashion. The combustion products exiting the combustion chamber enter the outer liner where water tube bundles extract the heat of the combustion. There is also an air preheating stage further downstream. Heated water and steam generated in the heat exchanger stages wrapped around the combustor enters the final heating stage where it passes through the flame accelerators in the combustion chamber. The flame accelerators are in the hottest region in the combustor and therefore exchanging heat at high temperatures increases the efficiency of the steam generation cycle. It also increases the produced steam quality. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a highly schematic view of a sample embodiment of the pressure gain combustion steam generator; 
         FIG. 2  is a highly schematic view of a second sample embodiment of the Pulse detonation steam generator; and 
         FIG. 3  is a highly schematic view of a third sample embodiment of the pulse detonation steam generator. 
     
    
    
     DETAILED DESCRIPTION 
     The detonation based Pressure Gain Heat Generator (PGHG) is composed of an inner combustion chamber, where the air-fuel mixing and combustion takes place. The combustion chamber is composed of an inlet section where air is introduced through radial inlets and a fuel inlet injecting the fuel axially towards the air jet. The mixed air-fuel travel down the combustion chamber and, in one form, passes through a divergent nozzle and a porous plate for stratification. At a specific time, when the air-fuel mixture has filled the required volume of the combustor an ignition system is triggered and the air and fuel mixture is ignited. The flame front propagates in the combustion chamber and accelerates by the turbulence generated in the combustor. 
     One feature used in pressure gain combustors is a spiral shaped obstruction in the combustion chamber that generates turbulence and increases the flame velocity. This feature is generally called a flame accelerator, and in one form these flame accelerators are in a particular arrangement called a Schelkin spiral. The flame accelerators are located in the combustion chamber and are typically the hottest region in the combustor. Therefore, heat extraction in the accelerators will be at high temperatures and therefore highly efficient. The idea in this disclosure is to build the flame accelerators as hollow tubes, where the operating fluid is passed through the spiral for heat extraction. The heat transfer at the flame accelerators will be at high temperature and therefore in the final stages of heating the fluid. This heat is a portion of the heat generated by the detonation process. Therefore, the outlet of the PDC is passed through a set of heat exchangers that extract further heat from the combustion products. The heat exchangers utilized for this purpose may have various designs such as tubular, shell and tube or plate heat exchangers. Sample embodiments are explained here. In the first concept  20 ,  FIG. 1 , the combustion chamber  22  is covered in a concentric tubular heat exchanger  24  design; the inner tube being the combustion chamber  22  with the detonation section and flame accelerators  26  such as for example Schelkin spirals. The outer section is a three way heat exchanger. In this chamber, combustion air entering inlet  28  is entered in a counter-current direction and is heated by the heat transferred through the walls of the combustion chamber  22 . Also, water pipes  30  are situated in this chamber that heat the feed water  32  and generate steam which exits through a heated fluid (steam) discharge  34 . Therefore, in this tubular heat exchanger the heat transferred through the combustion walls is transferred to the water in the tubes and also preheats the combustion air. 
     Air (exhaust  36 ) exited from the combustion chamber  22  is then rerouted 180 degrees and passes through another liner  38  that houses the aforementioned tubular heat exchanger  24  and functions as a muffler. Therefore, further heat is transferred to the tubular air preheater-water heater section through the outer walls of the tubular heat exchanger  24 . The outer liner is equipped with baffles and water tubes to extract heat from the combustion products. This section operates as a recuperator for the steam generation process. At the discharge  40  of the outer liner  38 , the combustion products are exhausted. 
     The overall design of the steam generator explained above is a counter-current flow. The circuit of different streams is explained here: water  32  enters the system at the recuperator heat exchanger. Water is passed through tubes and preheated by the combustion products. Preheated water enters the water tubes located in the tubular heat exchanger and heats up further. At the final stage, water (or steam) is passed through the flame accelerators  26  which are the highest temperature component in the system and extract further heat at high temperature. The outlet of the flame accelerators  26  (saturated or superheated steam) is the output  34  of the steam generation device. 
     Air  28  enters the system at the air pre-heater tubular heat exchanger and once heated, it is passed to the mixing chamber where the air is mixed with fuel  41  and then the combustion chamber  22  where it is detonated. In one form, a ignition source  44 , such as a spark plug or laser is utilized to initiate detonation. The detonated mixture travels through the detonation section and is partially cooled by the heat dissipated to the flame accelerators  26  and combustor walls  22 . After this stage air passes through the heat exchanger  24  in the outer liner  38  and heats the water in the tubes  30  and then exhausted  36 . 
     Another design that can utilize the high efficiency detonation heat energy is depicted in  FIG. 2 . In this embodiment, similar elements to those shown in  FIG. 1  are designated with a numeral  1  prefix. In this design, the inner combustion chamber  122  is similar to the combustion chamber  22  in the first embodiment explained above. The mixing chamber where air  128  and fuel  142  are injected and mixed, the ignition and detonation chamber are as explained in the first embodiment. The preferred orientation in this design is vertical such that the detonation wave travels through the combustion chamber in vertical direction, upwards. The walls of this combustion chamber  122  are covered with water pipes  130  extending along the combustion chamber, parallel to the combustion chamber axis. The water pipes may be single pass or multiple U-passes. Heat generated in the combustion chamber is transferred through the combustion chamber walls and the tube walls to feed water  132  and heats the feed water. Heated water or steam generated in the pipes is then passed through the flame accelerators  126  such as for example Schelkin spirals to gain further energy. The outlets of the flame accelerators is saturated or superheat steam  134  and is discharged from the steam generator. 
     Combustion products exiting the combustion chamber  122  are then passed through the outer liner  138 , in one form comprising a recuperator for further heat extraction. An air preheater  150  is also utilized to heat the combustion air  154  by the flue gas  152  before it&#39;s exhausted. 
     The path of water/steam through the steam generator is as follows: water  132  enters the pipes in the outer liner  130  (recuperator) where it&#39;s heated by the combustion products. Water is heated as it flows in the pipes towards the center of the heat generator where pipes are attached to the outer walls of the combustion chamber  122 , where it is further heated and then passes through the flame accelerators  126  for final stage heating. The heated fluid  134  exiting the flame accelerators is discharged from the steam generator  120  and may be used for steam applications. 
     A third embodiment is depicted in  FIG. 3 . In this concept, the combustion chamber is covered by a water/steam drum  260 . In this embodiment, similar elements to those shown in FIGS.  1 / 2  are designated with a numeral  2  prefix. The drum diameter and mechanical design is selected such that it can tolerate high pressure steam. Water boils in the water drum and steam rises in the drum resulting in a steam volume  258  up in the drum and boiling water  256  in the bottom portion. The steam generated in the drum is passed through the super-heater flame accelerators  226  for further heating and then discharged  234  from the steam generator  220 . In this design, the walls of the combustion chamber  222  are in continuous conductive contact with a chamber of water  256  resulting in more efficient and direct heat transfer from the combustion chamber  222  to the operating fluid  256 . 
     Similar to the previous embodiments, feed water  232  enters the heat exchanger  230  passes of the recuperator  238  and preheats before entering the water drum  260 . Water from the recuperator enters the water drum  260  from the bottom and get further heated by the combustor  222  walls. The rise in temperature pushes the heated water upwards due to buoyancy. Once water  256  starts boiling, steam bubble start rising to the water surface and join the steam volume  258  on the top of the drum  260 . The saturated steam generated on top of the drum will go through the flame accelerators  226  and then discharge  234  from the system. 
     If saturated steam is required in the outlet, the flame accelerators may be linked to the water  256  in the drum  260  rather than the steam section  258 . In this design, the heat transferred to the flame accelerators will be transferred to water and saturated steam is produced. 
     While the present invention is illustrated by description of several embodiments and while the illustrative embodiments are described in detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications within the scope of the appended claims will readily appear to those sufficed in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicants&#39; general concept.