Abstract:
A pure oxygen direct combustion system using a liquid metal according to the present invention comprises: a reactor for receiving a liquid metal; a heat exchanger, connected to the bottom of the reactor, for exchanging heat for the liquid metal; a circulation pump, connected to the heat exchanger, for circulating the incoming liquid metal; a nozzle, connected to the circulation pump and disposed on the reactor; a reduction unit, connected to the circulation pump, for performing a reduction for the oxidized liquid metal; and a separation unit, connected to the reactor and the reduction unit, wherein the particles of the liquid metal injected from the nozzle are subjected to sensible heat from the gas generated from the reactor, heat-exchanged by the heat exchanger and regenerated by the reduction unit, and then supplied back to the reactor.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a pure oxygen direct combustion system using a liquid metal, and more particularly to a pure oxygen direct combustion system using a liquid metal that supplies only oxygen to a solid fuel such as coal to burn the solid fuel, and reduces the load of a heat exchanger which is a disadvantage of a conventional system and maximizes thermal efficiency by using a flow process of the liquid metal that uses a heat source of high temperature generated when the pure oxygen is burned as a layer material and a heat transfer medium. 
       BACKGROUND OF THE DISCLOSURE 
       [0002]    In general, it is known that about 54% of carbon dioxide generated in the industry is discharged in thermal power plants. Because carbon dioxide is a gas that is generally generated in the process of burning fuels, the amount of discharged carbon dioxide should be reduced at a fuel combustion time point. 
         [0003]    The existing thermal power plants use an air combustion method in which air is used as an oxidizer and burns fossil fuels such as coal, petroleum, and natural gases are burned to produce electric power. The air combustion method uses only oxygen that occupies about 21% of air as a pure oxidizer, and nitrogen that occupies about 79% of air is unnecessarily heated. 
         [0004]    Meanwhile, because a considerable amount of calories generated when air is burned is used to heat nitrogen, heat loss is caused, and because the concentration of carbon dioxide in the flue gas is as low as 20% or less, considerable costs are consumed to concentrate dioxide of low concentration in the flue gas to a high concentration. 
         [0005]    Accordingly, in recent years, a pure oxygen combustion method for burning fuels by using only oxygen instead of air as an oxidizer has been developed. Unlike the existing air combustion method, the pure oxygen combustion method reduces the heat loss of the burned gases by about 75% to 80% as it rarely burns nitrogen components, and the main component of the flue gas consists of carbon dioxide (CO 2 ) and moisture (H 2 O). 
         [0006]    If oxygen is used as an oxidizer, it is difficult to adjust flames because a rapid exothermic reaction is caused when the oxidizer makes contact with a fuel as compared with the case in which air is used as an oxidizer. That is, in general, while the pure oxygen direction combustion has a good thermal efficiency and discharges a small amount of atmospheric contaminants, it produces combustion gases of high temperature of 3000 degrees or higher so that it is difficult to apply the method to a heat exchanger. 
         [0007]    In order to solve the above-mentioned problems, Korean Patent Application Publication Nos. 10-2012-0033458 and 10-2011-0010731 relate to a measure for producing electric power by using a pure oxygen combustion boiler system, and disclose inventions related to an improved measurement for improving a thermal efficiency and an energy reducing effect through a process of exchanging heat between flue gases of high temperature, high temperature steam, and condensation heat generated in a power generation process through pure oxygen combustion and a part of the interior of a power oxygen combustion generation apparatus that is to be heated, or minimizing loss of electric power produced by a dual ignition boiler. 
         [0008]    However, the cited documents disclose only that parts of waste steam or flue gases discharged from a combustion unit are heat exchanged and supply water is preheated and vapor is reheated for heat exchange through recirculation of combustion gases, and fail to disclose a pure oxygen direct combustion apparatus that does not accompany recirculation of combustion gases. 
         [0009]    In order to solve the above-mentioned problems, the present invention provides a pure oxygen direct combustion system using a liquid metal in which sensible heat of high temperature generated in a pure oxygen combustion reaction process of a solid fuel is provided to a metal in the reactor to be used in a metal liquefying process and is circulated and supplied and heat is exchanged in a process of circulating a liquid metal of high temperature so that an overload of the reactor can be reduced in the process of supplying the liquid metal of a middle/low temperature into the reactor again. 
       SUMMARY OF THE INVENTION 
       [0010]    In accordance with an aspect of the present invention, there is provided a pure oxygen direct combustion system using a liquid metal, the pure oxygen direct combustion system including: a reactor  10  in which a liquid metal  11  is fullfilled; a heat exchanger  20  connected to a lower portion of the reactor  10  such that heat is exchanged between the liquid metal  11  and the heat exchanger  20 ; a circulation pump  25  connected to the heat exchanger  20  to circulate the introduced liquid metal  11 ; and a nozzle  32  connected to the circulation pump  20  and situated on the reactor  10 , wherein particles of the liquid metal  11  injected from the nozzle  32  is resupplied to the reactor  10  after receiving sensible heat from a gas generated in the reactor  10  and passing through the heat exchanger  20 . 
         [0011]    Preferably, the pure oxygen direct combustion system further include: a reduction unit  40  connected to the circulation pump  25  to perform a reduction operation on the oxidized liquid metal  11 ; and a separation unit  50  connected to the reactor  10  and the reduction unit  40 , and the particles of the liquid metal  11  injected from the nozzle  32  is resupplied to the reactor  10  after receiving sensible heat from a gas generated in the reactor  10  and being reproduced through the reduction unit  40 . 
         [0012]    Preferably, the pure oxygen direct combustion system further includes a water flow pipe  18  disposed in the reactor  10 , and heat is transferred from any one of the particles of the liquid metal  11  and the gas generated by the reactor  10  to water in the water flow pipe  18  such that the water in the water flow pipe  18  is evaporated. 
         [0013]    Preferably, a part of the oxidized liquid metal separated from the separation unit  50  is introduced into the reduction unit  40  through an oxidized metal discharge pipe passage  52 , or is resupplied to the reactor  10  through an oxidized metal supply pipe passage  54 . 
         [0014]    Preferably, the pure oxygen direct combustion system further includes a slag discharge hole  17  coupled to the reactor  10 , and slag melted by the liquid metal  11  in the reactor  10  is discharged to the outside of the reactor  10  through the slag discharge hole  17 . 
         [0015]    Preferably, the liquid metal is any one of a group consisting of Sn, Bi, a mixture of Sn and Bi, and a metal that satisfies an operation condition. 
         [0016]    Preferably, the gas generated by the reactor is an exhaust gas containing a sulfur composite. 
         [0017]    Preferably, the pure oxygen direct combustion system further includes a buffer tank  30  disposed at an upper portion of the reactor  10  to receive the liquid metal  11  from the circulation pump  25 , and the nozzle  32  is detachably mounted to the buffer tank  30  so that the nozzle is selectively coupled to the buffer tank  30  according to the size of the injection hole of the nozzle  32 . 
         [0018]    In accordance with another aspect of the present invention, there is provided a pure oxygen direct combustion system using a liquid metal, the pure oxygen direct combustion system including: a reactor  10  in which a liquid metal  11  is fullfilled; a first heat exchanger  20  connected to a lower portion of the reactor  10 ′ such that heat is exchanged between the liquid metal  11  and the heat exchanger  20 ; a circulation pump  25  connected to the first heat exchanger  20  to circulate the introduced liquid metal  11 ; and a buffer tank  30  connected to the circulation pump  20  and situated on an upper surface of the reactor  10 ′, wherein particles of the liquid metal  11  injected from the buffer tank  30  is resupplied to the reactor  10 ′ after receiving sensible heat from a gas generated in the reactor  10  and passing through the first heat exchanger  20 . 
         [0019]    Preferably, the pure oxygen direct combustion system further includes: a reduction unit  40  connected to the circulation pump  25  to perform a reduction operation on the oxidized liquid metal  11 ; and a separation unit  50  connected to the reactor  10 ′ and the reduction unit  40 , and particles of the liquid metal  11  injected from the buffer tank  30  is resupplied to the reactor  10 ′ after receiving sensible heat from a gas generated in the reactor  10 ′ and being reproduced through the reduction unit  40 . 
         [0020]    Preferably, a water flow pipe  18 ′ disposed in the reactor  10 ′ makes contact with the liquid metal  11 . 
         [0021]    As described above, in the pure oxygen direct combustion system using a liquid metal according to the present invention, because sensible heat of high temperature generated in a pure oxygen combustion reaction process of a solid fuel is provided to a metal in the reactor to be used in a metal liquefying process and is circulated and supplied and heat is exchanged in a process of circulating a liquid metal of high temperature, an overload of the reactor can be reduced in the process of supplying the liquid metal of a middle/low temperature into the reactor again. 
         [0022]    According to the present invention, an effect of reducing a load of a purification facility disposed at a rear side of the system through a process of separating impurities and unburned powder contained in the gases from the gases by injecting the liquid metal to the gases using nozzles. 
         [0023]    According to the present invention, an effect of eliminating impurities contained in gases by injecting the liquid metal to the gases using nozzles. 
         [0024]    Further, because the liquid metal used in the present invention is melted at an operation range to maintain a liquid state and has a high boiling point, loss due to evaporation thereof can be prevented. 
         [0025]    Further, because the liquid metal used in the present invention has a high thermal capacity as compared with air and water mainly used for the existing heat exchange, the heat transfer efficiency is high so that heat can be effectively exchanged and the liquid metal can be moved conveniently due to its low viscosity. 
         [0026]    Further, the liquid metal used in the present invention makes direct contact with gases, which are to be heated, to exchange heat, and can easily control heat exchange efficiency through changing a spray condition of the liquid metal. 
         [0027]    Further, according to the present invention, because the liquid metal that circulates heat has a specific gravity that is greatly different from various impurities (gray ashes, unburned fuels, and moisture) that may be generated when the liquid metal makes direct contact with gases. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]      FIG. 1  is a concept view illustrating a pure oxygen direct combustion system using a liquid metal according to a first embodiment of the present invention as a whole. 
           [0029]      FIG. 2  is a concept view illustrating a pure oxygen direct combustion system using a liquid metal according to a second embodiment of the present invention as a whole. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0030]    In the present invention, a “fuel” may be a concept that includes all of a solid state fuel including coal, a liquid fuel, and a gas fuel. 
         [0031]    In the present invention, a “gas” is defined as a concept that includes a combustion gas or a synthetic gas discharged from a combustion furnace or a heat engine such as a gasification system. The “gas” is defined as a concept that includes a combustion gas including CO 2  and H 2 O. 
         [0032]    The elements constituting the pure oxygen direct combustion system  100  using a liquid metal according to the present invention may be integrally used or separately used according to occasions. Further, some elements may be omitted according to the usage of the pure oxygen direct combustion system. 
         [0033]    Preferred embodiments of the pure oxygen direct combustion system  100  using a liquid metal according to the present invention will be described with reference to  FIG. 1 . It should be noted that the drawings are not to precise scale and may be exaggerated in thickness of lines or size of components for descriptive convenience and clarity. In addition, terms used herein are defined by taking functions of the present invention into account and can be changed according to user or operator custom or intention. Therefore, definition of the terms should be made according to the overall disclosure set forth herein. 
         [0034]    Description of Pure Oxygen Direct Combustion System  100   
         [0035]    Hereinafter, a configuration of the pure oxygen direct combustion system  100  using a liquid metal according to a first embodiment of the present invention will be described with reference to  FIG. 1 . 
         [0036]    The pure oxygen direct combustion system  100  according to the present invention includes a reactor  10  to which an oxidizer and a fuel are supplied such that a combustion process is performed, a first heat exchanger  20  connected to a lower portion of the reactor  10  such that heat is exchanged between a liquid metal  11  and the first heat exchanger  20 , a circulation pump  25  connected to a rear end of the heat exchanger  20  to circulate the liquid metal  11 , a buffer tank  30  connected to the circulation pump  20  and situated on the upper surface of the reactor  10 , a plurality of nozzles  32  coupled to the lower surface of the buffer tank  30  and having a plurality of injection holes through which the liquid metal  11  of the buffer tank  30  is injected into the reactor  10 , a reduction unit  40  connected to the circulation pump  25  such that the oxidized liquid metal is reduced, and a separation unit  50  connected to the reactor  10  and the reduction unit  40 . 
         [0037]    The reactor  10  is a site where the liquid metal  11  in a melted state and the combustion gas  12 , which is to be purified, and the liquid metal  11  is maintained in a melted state by using a supplied oxidizer and sensible heat generated in the combustion process of the fuel and the gas  12  generated when the liquid metal  11  is injected through the nozzle  32  is purified. 
         [0038]    The liquid metal  11  and the gas  12  in the reactor  10  are vertically separated due to the difference between the specific gravities thereof In detail, the liquid metal  11  is situated at a lower portion of the interior of the reactor  10 , and the gas  12  is situated above the liquid metal  11 . 
         [0039]    Nozzles  32  are situated at an upper portion of the reactor  10 . The liquid metal  11  is injected in the form of liquid metal particles  13  between combustion gases by the nozzles  32 . The liquid metal particles  13  injected into the gas  12  melt foreign substances such as H2S contained in the gas  12  into the liquid metal particles  13 . The injected liquid metal particles  13  and the foreign substances drop to a lower portion of the reactor  10  while being coupled to each other, and are collected together with the liquid metal  11  situated at a lower portion of the reactor  10 . 
         [0040]    The liquid metal  11 , to which the sensible heat is transferred in the combustion process of the reactor  10 , is fed to the first heat exchanger  20 , and the first heat exchanger  20  recycles waste heat from the liquid metal  11  of high temperature through a separate heat exchange medium. 
         [0041]    The liquid metal  11 , the temperature of which is lowered to a middle/low temperature of 500 degrees or less in the first heat exchanger, is circulated to the reactor  10  by using the circulation pump  25 . 
         [0042]    The buffer tank  30  injects the moved liquid metal  11  between the gases  12  situated at an upper portion of the reactor  10  through the nozzles  32  in the form of liquid metal particles  13  while being connected to the circulation pump  25 . 
         [0043]    A plurality of nozzles  32  may be disposed in a row at a lower end of the buffer tank  30 , and the injection holes formed in the nozzles  32  may be radially formed such that the liquid metal  11  may be finely injected between the gases  12  situated at an upper portion of the reactor  10 . 
         [0044]    It may be preferable that the liquid metal circulated in this way is introduced from an upper end of the reactor  10 . In this way, an insulation effect may be achieved by introducing the liquid metal into the reactor  10  through the nozzles  32  or introducing the liquid metal along a wall surface in the interior of the reactor  10 . 
         [0045]    The above-mentioned nozzle injection method may achieve a combustion gas purifying effect as the liquid metal is atomized to be lowered, and contacts with a combustion gas that is generated by a pure oxygen combustion reaction to flow to a downstream side. Further, overheating of a water cooling pipe, which is a conventional disadvantage, can be prevented and slagging of the wall surface of the water cooling pipe can be prevented by injecting the liquid metal onto a water flow pipe  18  in the interior of the reactor  10 . 
         [0046]    Meanwhile, CO2 and H2O, which are combustion gases generated by the reactor  10 , are fed to a separate heat exchanger disposed outside the reactor  10  such that heat is exchanged, and CO2 is stored in a separate storage through the carbon capture &amp; storage (CCS) technology and the condensate is discharged. 
         [0047]    Meanwhile, the combustion gas  12  in the interior of the reactor  10  is moved to a dust collector  72  after being discharged from the reactor  10  together with oxidants of the liquid metal  11  and passing through the second heat exchanger  70 . Thereafter, the oxidants is collected by the dust collector  72 , and the gas is discharged to a post process. The oxidants collected by the dust collector  72  are directly introduced into the reactor  10  through an oxidant storage vessel  74 , or is introduced into the reduction unit  40 . 
         [0048]    The liquid metal  11  in the reactor  10  may be discharged to a discharge vessel  60  according to situations and conditions. The liquid metal  11  discharged to the discharge vessel  60  may be preserved in the storage vessel  62  through a milling or cutting process, and may be reintroduced into the reactor  10 . 
         [0049]    A fuel injection port  14  through which a solid fuel and an oxidizer are injected after being mixed, and a water flow pipe  18  through which water is introduced to be evaporated by heat from the liquid metal of high temperature are disposed in the reactor  10 . The combustion gas  12  generated in the interior of the reactor  10  may be purified through the reactor  10 , and may be discharged to the outside. That is, because the injected liquid metal is moved into the gas such that heat is exchanged, the temperature of the discharged gas is reduced. Because the temperature of the flames generated due to the combustion of the solid fuel and the oxidizer is a high temperature, it is preferable that the fuel injection port  14  is disposed between the water flow pipe  18  and the liquid metal in the reactor  10 . 
         [0050]    Meanwhile, the water introduced into the water flow pipe  18  is evaporated due to the heat transferred from the liquid metal particles  13  injected from the nozzles  32  and the combustion gas  12 , and accordingly, may be used for a steam turbine or as heating water. The water flow pipe  18  can prevent overheating and slagging due to the liquid metal particles  13 . 
         [0051]    The reactor  10  may further include a slag discharge pipe passage  17  through which slags are discharged to the outside. The slags, which are impurities melted in the liquid metal particles  13  while the liquid metal particles  13  pass through the gas  12  float on the surface of the liquid metal  11  due to the difference of gravities of the liquid metal  11  while the liquid metal  11  stays at a lower portion of the reactor  10 . Accordingly, the slag discharge pipe passage  17  may be situated in the vicinity of an upper end of the liquid metal  11  and may discharge the slags to the outside. Then, the discharged slags are discharged while being mixed with the oxidized metal particles. 
         [0052]    The circulation pump  25  is connected to the first heat exchanger  20  and the buffer tank  30  such that the liquid metal  11  is circulated in the pure oxygen direct combustion system  100 . The circulation pump  25  may be connected to a lower portion of the reactor  10  to circulate the liquid metal  11  that contains a small amount of slags. That is, because slags of low specific gravity floats in the reactor  10 , a relatively small amount of impurities are left at a lower layer of the liquid metal  11 . 
         [0053]    The reduction unit  40  allows recycling the oxidized liquid metal introduced through an introduction pipe  42  from the circulation pump  25  by using reductant, and the reduced liquid metal flows to the circulation pump  25  again through the discharge pipe  44 . Here, the reductant for the oxidized liquid metal includes char, H 2 , and CH 4 , and CO, CO 2 , H 2 , and H 2 O are discharged from the reduction unit  40  through a reduction reaction. The liquid metal reduction reaction and the heat exchange may be performed at the same time by using the reduction medium as the fluid of the first heat exchanger  20 . 
         [0054]    The separation unit  50  performs a process of separating slags and the liquid metal discharged through the slag discharge pipe passage  17 . A centrifugal separator using a density difference may be suitable for the separation unit  50 . The oxidized liquid metal separated from the separation unit  50  is introduced into the reduction unit  40  through an oxidized metal discharge pipe passage  52 , or is directly resupplied to the reactor  10  through an oxidized metal supply pipe passage  54 . 
         [0055]    According to the present invention, because the liquid metal  11  that circulates heat has a high thermal capacity as compared with air and water that have been mainly used in the conventional heat exchange, its heat transfer efficiency is high so that it is suitable for an effective heat exchange when a suitable process design is accompanied, and it has a low viscosity as compared with other liquid metals so that it can be moved conveniently and is suitable for the process. 
         [0056]    Further, according to the present invention, liquid metal  11  is effective for separation by a filter and difference of specific gravity. Because the liquid metal  11  that circulates heat has a specific gravity that is greatly different from various impurities (gray ashes, unburned fuels, and moisture) that may be generated when the liquid metal  11  makes direct contact with gases. 
         [0057]    Further, according to the present invention, it is preferable that the liquid metal  11  that circulates heat is formed by melting any one of tin (Sn), bismuth (Bi), or a mixture of tin (Sn) and bismuth (Bi), and any metal that satisfies the operation conditions is possible. The liquid metal  11  consisting of tin (Sn), bismuth (Bi), or a mixture of tin (Sn) and bismuth (Bi) can be melted to maintain a liquid state according to an operation of a gas purifying apparatus  100  according to the present invention, and has a high boiling point so that it is not lost due to evaporation thereof during an operation of the gas purifying apparatus  100  according to the present invention. 
         [0058]    Hereinafter, a configuration of the pure oxygen direct combustion system  100  using a liquid metal according to a second embodiment of the present invention will be described with reference to  FIG. 2 . 
         [0059]    In the second embodiment  100 ′, the same parts as the first embodiment  100  will be omitted and different technical parts will be mainly described. 
         [0060]    The pure oxygen direct combustion system  100 ′ is configured such that a liquid metal  11  surrounds a space in which a combustion gas  12  in a reactor  10 ′ is generated. The liquid metal  11  may be supplied through an upper portion of the reactor  10 ′ from a buffer tank  30  without using a separate nozzle while the nozzles  32  in the first embodiment  100  are removed. The water flow pipe  18 ′ is disposed on a wall surface of the reactor  10 ′ and makes contact with the liquid metal  11  that flows down along the wall surface. Through the above-mentioned structure, overheating and slagging of the water flow pipe  18 ′ can be prevented. Through this, a high temperature area can be prevented from being generated in a specific area of a water flow pipe of an actual reactor. 
         [0061]    As described above, in the pure oxygen direct combustion system using a liquid metal according to the present invention, because sensible heat of high temperature generated in a pure oxygen combustion reaction process of a solid fuel is provided to a metal in the reactor to be used in a metal liquefying process and is circulated and supplied and heat is exchanged in a process of circulating a liquid metal of high temperature, an overload of the reactor can be reduced in the process of supplying the liquid metal of a middle/low temperature into the reactor again. 
         [0062]    That is, according to the present invention, because a heat source of high temperature, which is generated when a solid fuel such as coals is burned into pure oxygen by the pure oxygen direct combustion system, is processed by using the metal liquefying and heat exchange characteristics, the load of the heat exchanger, which has been a problem of an existing system, can be reduced and thermal efficiency can be maximized. Through this, because combustion gas of a high temperature of 3000 degrees or higher can be generated in the conventional pure oxygen direct combustion process, a disadvantage of hardly applying the combustion gas to a heat exchanger can be overcome, thermal efficiency can be increased, and the amount of discharged atmospheric contaminants can be reduced. 
         [0063]    Although the preferred embodiments of the present invention have been described, it will be understood by those skilled in the art that the present invention can be variously corrected and modified without departing from the spirit and scope of the present invention claimed in the claims.