Patent Publication Number: US-2009221865-A1

Title: Method and apparatus for injecting enriched steam

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS AND INCORPORATION BY REFERENCE 
     This application claims the benefit under 35 U.S.C. §119 of U.S. provisional application No. 61/032,387, filed Feb. 28, 2008 which is hereby incorporated by reference in its entirety. This application also hereby incorporates by reference in its entirety U.S. Pat. No. 6,471,443, issued Oct. 29, 2002. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments of the invention relate to methods of sequestering CO 2 , CO and/or NO x  into steam and injecting it into landfills, biomass reactors and the like. Specifically, the embodiments provide methods of injecting steam enriched with CO 2 , CO, NO x  and/or other gases, including exhaust gases, into a landfill or biomass reactor to accelerate the decomposition/biodegradation of organic refuse within the trash prism to increase the production of methane gas and/or CO 2 . 
     2. Description of the Related Art 
     In general, landfills are constructed using the “dry tomb” method, in which the refuse in the landfill is kept as dry as possible both during construction and when the landfill is closed and capped. This method minimizes the possibility of leachate, or liquid that drains or ‘leaches’ from a landfill, from leaking into groundwater and contaminating it. However, dry conditions are not conducive to the decomposition of the organic refuse. Instead, the organic refuse remains dormant for decades until water infiltrates the landfill in an uncontrolled and natural manner. The water infiltration may cause gas migration, which can lead to groundwater and atmosphere contamination. 
     SUMMARY OF THE INVENTION 
     Injecting enriched steam into landfills and reactors, which can include, for example CO 2 , CO, NO x  and/or other gases, including exhaust gases, according to embodiments of the invention, have several features, no single one of which is solely responsible for its desirable attributes. In addition, sequestering CO 2 , CO, NO x  and/or other gases, including exhaust gases, and other methods described herein, according to embodiments of the invention have several features, no single one of which is solely responsible for its desirable attributes. 
     Without limiting the scope, more prominent features will now be discussed briefly. The features of some embodiments of the invention provide certain advantages, which can include minimization of the amount of liquid introduced into the landfill, total moisturization and higher overall humidity of the landfill or reactor. Other benefits can include providing the above advantages without the need to apply head pressure, promotion of settlement of the landfill, thorough heating of the refuse to increase decomposition, avoidance of clogging of gas extraction collectors, the ability to distribute additional carbon in the form of CO 2  throughout the trash prism, increased methane and CO 2  production, and production of methane having higher Btu values as compared to methane produced in other landfill and/or reactor systems. In some embodiments, one goal is to heat the surface of the waste that surrounds the void spaces (about 20% by volume) in the waste prism rather than the whole waste mass. This can help keep the required Btu values manageable. 
     Some embodiments comprise a method of enhancing the decomposition of organic waste. The method can comprise providing steam, enriching the steam with gas and injecting enriched steam into organic material. The organic material, in some embodiments, can be in a landfill or a biomass reactor. The gas of some embodiments comprises CO 2 , CO and/or NO x . The method can further comprise sequestering the gas into the steam to enrich it. 
     In certain embodiments, the method can further comprise spraying water into a chamber containing the gas and creating steam by vaporizing the water. In some embodiments, the gas can be exhaust gas. The heat of the exhaust may flash the water into steam to create enriched steam. In some embodiments, waste steam can be mixed with exhaust gases to enrich the steam with CO 2 , CO and/or NO x . The enriched steam can be conveyed to the landfill or biomass reactor by negative pressure. In the different embodiments, the gas can be from different sources including industrial processes related to or unrelated to a landfill or biomass reactor. 
     Some embodiments include a method of enhancing the decomposition of organic waste. The method can comprise injecting steam enriched by CO 2  and CO into waste, the waste comprising organic refuse, heating the waste, monitoring conditions within the waste and extracting methane gas from the waste. The step of heating the waste can be heating the waste with the steam or heating the waste through other processes. The methane can also be used to create the steam. Also, the steam can be further enriched by NO x  and/or other exhaust gases. 
     Additional embodiments can comprise a method of accelerating decomposition of organic refuse. Certain methods comprise combusting a fuel and thereby creating exhaust gas, providing steam, sequestering CO 2  from the exhaust gas into the steam to create enriched steam and injecting the enriched steam into organic refuse. The method may further comprise extracting methane gas from the organic refuse. The method can further comprise spraying water into the exhaust gas to create steam. In some embodiments, the steam can be exhaust steam. The exhaust steam can be from a source such as a power plant. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Certain embodiments of this invention, illustrating its features, will now be presented. Among other features, these embodiments depict a novel and non-obvious method of injecting steam, enriched with CO 2  and/or other gases into landfills or biomass reactors as shown in the accompanying drawings, which are for illustrative purposes only. These drawings include the following figures, in which like numerals indicate like parts: 
         FIG. 1  is a schematic top view of an apparatus for performing one embodiment of the present method; 
         FIG. 2  is a schematic side view of the apparatus of  FIG. 1 ; 
         FIG. 3  is a schematic top view of an apparatus for performing another embodiment of the present method; 
         FIG. 4  is a schematic of an apparatus useful in some embodiments; 
         FIG. 5  is a schematic of another apparatus useful in some embodiments; and 
         FIG. 6  is a schematic of another apparatus useful in some embodiments. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As discussed above, landfills constructed using the “dry tomb” method are not conducive to the decomposition of the organic refuse. Instead, the organic refuse remains dormant for decades until water infiltrates the landfill in an uncontrolled and natural manner. The water infiltration may cause gas migration, which can lead to groundwater contamination. 
     The slow decomposition of the organic refuse under dry conditions also slows the settling of the landfill and hinders the production of methane gas, which is a natural by-product of anaerobic (oxygen-starved) decomposition of organic material. 
     Moisture accelerates decomposition of organic refuse, but does not accelerate the decomposition of the non-organic refuse. Thus, the addition of moisture to the trash prism increases the purity of methane extracted from the landfill, because the proportion of decomposing organic refuse to decomposing inorganic refuse is higher as compared to a dry trash prism. The extracted methane is thus more useful because it has a higher Btu value. If the refuse is flooded with water, however, the gas becomes bound up in the liquid and is difficult to recover. Further, introducing water into a landfill cools the refuse which can decrease decomposition, as decomposition proceeds best at a temperature around 100 to 120 degrees F. Therefore, a method of introducing moisture into a trash prism that does not flood the trash prism or cool the trash prism would be of great benefit to the landfill-management industry. The same effect occurs with a biomass reactor. 
     Methane is primarily known as the main component of natural gas. Methane, with the molecular formula CH 4  is the simplest alkane, meaning that of chemical compounds made up of only carbon and hydrogen, it has the most basic chemical structure with only one carbon atom and four hydrogen atoms. Methane has bond angles of 109.5 degrees. The burning of methane, in the presence of oxygen, produces carbon dioxide and water. The relative abundance of methane, as a natural resource, and its clean burning process make it a very attractive fuel. 
     Methane can be produced by methanogens. Methanogens are single-celled microorganisms that produce methane as a metabolic byproduct in low oxygen conditions. This process of producing methane is called biomethanation. Methanogens are common in wetlands and animals, where they produce marsh gas and the methane content of animal waste. Methanogens can also be found in other environments as well. In marine sediments, biomethanation is generally confined to where sulfates are depleted, below the top layers. In extreme conditions, such as hot springs, submarine hydrothermal vents and in the “solid” rock of the earth&#39;s crust, methanogens are also known to reside. 
     Methanogens are usually coccoid or rod shaped. There are over 50 described species of methanogens, which do not form a monophyletic group, although all methanogens belong to Euryarchaeota, in the taxonomy of microorganisms. 
     Methanogens are anaerobic, meaning they do not need oxygen to grow or survive. In fact, methanogens cannot function under aerobic conditions, though they can sustain oxygen stresses for prolonged times. An exception is  Methanosarcina barkeri,  which contains a superoxide dismutase (SOD) enzyme and may survive longer. Some methanogens, called hydrogenotrophic, use carbon dioxide (CO 2 ) as a source of carbon, and hydrogen as a reducing agent. Some of the CO 2  is reacted with the hydrogen to produce methane, which produces an electrochemical gradient across a membrane, used to generate ATP through chemiosmosis. In contrast, plants and algae use water as their reducing agent. It is known that in decomposition, the basic conversion of organic carbon, such as waste in a landfill, will convert to 50% methane and 50% CO 2  However, higher levels of methane over CO 2  levels are often indicated at landfill gas (LFG) collectors. The readings will usually indicate a mass balance such as 60% CH 4  and 40% CO 2  totaling 100% in a closed system, unless air has intruded into the gas stream, changing the ratios. The way this change in ratios can occur is that the carbon in the CO 2  is converted into methane by the methanogens. 
     It has been observed at landfills that if the extraction process is slowed, the level of methane increases and the level of CO 2  decreases over time. Conversely if the gas is extracted too fast, the concentration of methane will decrease to 50% and if the well is overdrawn then the methane will drop below 50% and oxygen and nitrogen will be indicated in the readings. 
     Therefore, it can be assumed that if the landfill gas is allowed to stay inside the landfill longer and if there is excess moisture (hydrogen), the methanogens will take the carbon from the CO 2  and convert it to methane. This whole process is water/moisture driven. Therefore injecting CO 2  enriched steam into an organic waste mass can provide the methanogens with additional carbon for methane conversion. 
     Biogas generally includes CO 2  and not 100% methane. As carbon is removed from a CO 2  molecule, it releases the two oxygen molecules. These oxygen molecules attach to another carbon molecule in a process called oxidation creating another CO 2  molecule so there will always be CO 2  in biogas. The benefit of this oxidation process is that another molecule of carbon is converted from the waste, converted to CO 2  and removed from the landfill or reactor. 
     The majority of the world&#39;s CO 2  is absorbed by the oceans and is converted into various types of food and energy for the many life forms living within it. CO 2  is readily absorbed into water which changes its condition or density and allows it to remain in a vapor phase longer. It also increases its expansion pressure. Thus steam can readily absorb CO 2  to create enriched steam. Steam can also be enriched with other gases. 
     Some embodiments of the present invention relate to methods of sequestering CO 2 , CO, NO x  and/or other gases, including exhaust gases, into steam and injecting it into organic and other matter such as found in landfills, biomass reactors and the like. A method of injecting steam enriched with CO 2 , CO, NO x  and/or other gases, into a landfill or biomass reactor can accelerate the decomposition/biodegradation of organic refuse within the trash prism. This can also increase the production of methane gas and CO 2 . 
     The organic waste in a landfill, reactor or the like, can be used as a scaffold to support anaerobic microbes, which can convert organic carbon into biogas and can also convert the carbon in CO 2  and CO into additional biogas. Further, the anaerobic microbes can convert NO x  into acid in the steam, as it does when it rains. Enriching steam with NO x  can change the pH of the steam. 
     Some embodiments can increase the production of additional methane. For example, this can be done by separating the CO 2  produced in the first application of steam from the methane component of the landfill gas and then re-introducing it into the steam system. The enriched steam can then be conveyed into the landfill waste prism or reactor to be converted to methane. In some embodiments this separated CO 2  is for example, sent to algae tanks to make alternative fuels, sent to greenhouses, or made into food grade dry ice. 
     Exhaust can also be mixed into the steam system and returned to the landfill or reactor site. Preferably, exhaust from flares, power plants and other landfill gas (LFG) conversion processes, since it is contaminated with other volatile organic compounds (VOC), is mixed into the steam system and returned to the landfill or biomass reactor. This reduces the carbon emissions from the landfill or reactor site allowing more power plants and other LFG conversion technologies to operate at these sites without air quality restrictions. LFG typically consists of 50% methane and 50% CO 2  when organic waste decomposes naturally. With enriched steam injection, the LFG can consist of 80% methane and 20% CO 2  with an increase in volume in relation to the amount of enriched steam injected. Various embodiments of the inventions address the CO 2  portion of landfill gas and the exhaust from combustion engines and flares. 
     Some embodiments of the present method comprise injecting steam and CO 2  into a landfill or biomass reactor and collecting the methane produced by the decomposition/biodegradation of the organic component of the trash prism. The steam accelerates the decomposition of the organic refuse, thereby enhancing methane gas production and increasing the purity of the methane. For example, the CO 2  component of the steam can provide more carbon for the conversion process into methane. The reduced decomposition time advantageously reduces the impact of the landfill on the environment. With increased production of methane of a higher purity, what is normally waste gas can instead be converted into fuel. 
     The steam can be derived from a source such as a boiler, heat exchanger or waste steam from a power plant. In some embodiments of the invention, steam is produced by injecting water into the hot exhaust from flares, internal combustion engines, boilers or other gas conversion devices thereby sequestering the CO 2  into the steam stream. By spraying water into the exhaust system of the power generator or other engine on site, the water will flash into steam and capture the exhaust components into the steam. In some embodiments, this enriched steam can then be injected into the landfill or reactor through an array of steam injection wells or ports respectively. Additional CO 2  separated from the LFG and not cleaned to food grade may also be introduced to this steam stream. 
     The CO 2  Sequester Process 
     Keeping the natural processes described above in mind, it should be possible to enhance this process by using steam injected into the waste prism. Enriching the steam stream with CO 2 , CO and/or NO x  by sequestration can also enhance the process further. The sequester can contain a chamber mounted downstream of a burner or exhaust of an internal combustion (IC) engine. The chamber of some embodiments contains spray nozzles to apply water into the chamber and into the hot exhaust of the burner or IC engine. This can cause the water to flash into steam and absorb the exhaust gases into the steam. In some embodiments, a second nozzle is located near the burner to insure that the temperature remains below 1,100° F. to prevent the water from breaking down to hydrogen and oxygen. Some embodiments may allow the temperature to exceed 1,100° F. to allow the creation of the hydrogen and oxygen to increase the Btu value of the biogas. If the methanogens do not convert the raw hydrogen into methane then it will be used as fuel as part of the biogas. In another embodiment, waste steam, instead of, or in addition to water, can be sprayed into the sequester chamber where the exhaust gases are sequestered. 
     In a preferred method, steam enriched with CO 2 , CO and NO x  is injected into a landfill  10 . The steam promotes the anaerobic biodegradation of the organic refuse in the landfill  10 , which in turn increases methane gas generation and increases the rate of settlement of the landfill  10 . The carbon in the CO 2  and CO sequestered in the steam will be digested by the methanogens in the waste prism of the landfill  10  and produce additional methane and CO 2 . 
       FIG. 1  schematically illustrates an apparatus for performing an embodiment of the present invention in a landfill  10 . Several lines of steam and CO 2  injection wells  12  and several lines of gas extraction collectors  14  are positioned within a landfill  10 . The arrangement depicted in  FIG. 1  is merely exemplary. The ideal location for the injection wells  12  and gas collectors  14  is preferably determined prior to installing the steam injection apparatus, and may differ significantly from the arrangement of  FIG. 1 . 
     One method of determining the ideal location for the steam and CO 2  injection wells  12  and gas collectors  14  is to perform a piezo-penetrometer test (PPT) profile on the landfill  10 . The PPT profile can be performed with a cone-shaped instrument having sensors that measure several parameters as the cone is hydraulically pushed into the landfill  10 . The PPT profile provides information about the in-situ conditions of the landfill  10 . A PPT rig may also be used to install the steam injection wells  12  and gas extraction collectors  14  following the PPT profiling. More information concerning PPT profiling and monitoring with PPT profiling can be found in U.S. Pat. No. 6,471,443 to Renaud, which is herein incorporated by reference in its entirety. 
     After installation of the steam injection wells  12  and gas extraction collectors  14 , steam injection can commence through the injection wells  12 . Low pressure centers are preferably created at the gas extraction collectors  14 , as by attaching a header and blower system to the collectors  14 , for example. The low pressure centers create currents within the trash prism that distribute the steam throughout the trash prism. Adjustment of the relative positions of the injectors  12  and collectors  14  enables the enriched steam currents to be altered in case particular areas of the trash prism are not receiving sufficient enriched steam. 
     The source of steam  16  can be, for example, a gas-fired boiler, or a heat exchanger on the gas flare (see  FIG. 5 ). Preferably, however, the source of steam  16  is exhaust steam from a power plant, which may be more economical to harness as compared to steam specially produced for the landfill  10 . Different embodiments can have combinations of the steam sources or other steam sources could be used in place of the above devices or in conjunction with them. The process of steam generation of another preferred embodiment is to make steam by injecting water into the exhaust stream of flares or IC engines for generators sequestering the CO 2 , CO and/or NO x  into the steam stream (see  FIGS. 4 &amp; 5 ). Additional CO 2  separated from the landfill gas can also be introduced to this steam stream or the steam stream of other embodiments. 
     The steam enriched with CO 2 , CO and/or NO x  can then be injected into the landfill  10 , raising the moisture content and the level of carbon in the landfill  10 . Moisture promotes the rapid decomposition of the organic portion of the trash prism, while at the same time raising the amount of methane gas produced during decomposition. The rapid decomposition of the organic refuse causes the rapid settling of the landfill  10 , which shortens the amount of time that the landfill  10  is required to be active. Once the landfill  10  has settled a sufficient amount, it is capped, and the land may thereafter be used for other purposes. 
     Injecting enriched steam into the landfill  10  can be more advantageous than injecting water for a variety of reasons. First, water expands to approximately 1,600 times its original volume upon boiling. Thus, injecting enriched steam allows total coverage of the trash prism using only a small fraction of the water that would otherwise be needed. Using less water minimizes the potential for liquid to migrate to the bottom of the landfill  10  and into the groundwater, which could cause contamination. 
     Second, enriched steam containing CO 2 , which is a vapor, is under steam expansion pressure as well as CO 2  pressure. Thus, it requires no head pressure, as water does, to move it through the trash prism. Steam also moves naturally across temperature differentials, from hot to cold areas. Total coverage of the landfill  10  can thus be achieved with minimal work input to the system. The more effective expansion of steam also creates better moisture distribution and higher overall humidity as compared to water. Water tends to flow down to the bottom of the landfill  10  and stay there causing the lower portion of the landfill  10  to be more humid, while the upper portions, which contain the freshest refuse, remain dry. Because methane production within the landfill  10  increases with humidity, it is advantageous to maximize the humidity throughout the trash prism, rather than raising the humidity only near the bottom of the trash prism. 
     Third, enriched steam, as a gas, is compressible while water is not. Water thus occupies free space in the landfill  10 , inhibiting settlement. As stated above, the landfill  10  desirably settles rapidly. The use of enriched steam promotes more rapid settlement of the landfill  10  than does liquid water. Airspace recovery, associated from water occupying the free space in the landfill, can make active landfills remain open for longer periods of time, delaying closure. 
     Fourth, enriched steam, which is at a higher temperature than liquid water under the same pressure, will tend to increase, rather than reduce, the overall temperature of the waste in the landfill  10 . Decomposition proceeds best at about 100 to 120 degree F. Enriched steam can thus tend to promote better decomposition by maintaining a higher temperature within the landfill  10 . 
     Fifth, liquids carry suspended solids and calcium carbonate, which tend to clog the gas extraction collectors  14  and bottom drains of landfills. Enriched steam does not generally carry suspended solids or calcium carbonates, and so will not lead to clogging. 
     To achieve these and other advantages, a first preferred method of injecting enriched steam into a landfill  10  can comprise several lines of steam injection wells  12  and several lines of gas extraction collectors  14 , as in  FIG. 1 . The injection wells and extraction collectors  14  are preferably 2″ steel push-in screens and risers, but could be any diameter to suit a particular application, and could be constructed from sturdy materials other than steel. The collectors  14  preferably include sensors for measuring certain parameters, such as flow rates, methane concentrations, and Btu values, in order to monitor the effectiveness of the enriched steam injection method. 
     Methane can be withdrawn from the system when it is in an anaerobic phase. Steam injectors  12  can also be installed around gas collectors  14  that are already in place in the landfill  10 .  FIG. 3  illustrates a schematic of according to certain embodiments of a system.  FIG. 3  shows a blower  26  that can force enriched steam into the landfill  10 . U.S. Pat. No. 6,471,443, incorporated by reference above, provides further details concerning the anaerobic phase. 
     Now referring to  FIG. 2 , the illustrated moisture sensors  20  monitor the amount of liquid accumulating on a dense layer  18  below the injection wells  12 . If liquid is detected, the amount of enriched steam injected into the landfill  10  can be reduced. The temperature sensors  22  can be used to monitor the movement of the enriched steam through the waste in a landfill or reactor. These sensors  22  can provide better monitoring of the conditions inside the landfill  10  than the moisture sensors  20 . This is because the temperature sensors  22  can be used to determine not only if enriched steam is reaching the sensor  22  but also how well the enriched steam is penetrating throughout the entire system. The information that the temperature sensors  22  provide about the landfill  10  conditions can also be used to adjust the amount of enriched steam injected into the system in order to prevent liquid from accumulating on the dense layer  18 , rather than adjusting the enriched steam injection after liquid is detected. 
       FIG. 4  shows an embodiment of a system with the use of an internal combustion (IC) engine  29 . The system can be useful to flash water into steam using the heat inside an exhaust system  32  of the IC engine  29 . Water can be sprayed through water jets  28  from a water supply  36  into the exhaust system  32  of the IC engine  29  to produce enriched steam. As illustrated, the enriched steam can be forced from the exhaust system  32  into a landfill, biomass reactor, etc. by a blower  26 . The steam can be enriched by the gases present in the exhaust. These gases can include, for example, CO 2 , CO, NO x  and/or other gases, including exhaust gases. 
     In the embodiment of  FIG. 5 , landfill gas (LFG) can flow through a pipe  34  into a burner  31  of a flare or boiler. In the burner  31 , the LFG are combusted to produce heated exhaust gases. The heated exhaust gases from combustion of the LFG can be sprayed with water from spray nozzles  28  to flash the water into steam. At the same time, the steam can mix with the exhaust gas in the sequester chamber  27  to create enriched steam. The enriched steam can then injected into the landfill via blower  26 ′. Some of the landfill gas may be drawn off of pipeline  34  by pipeline  37  and converted into usable fuel or for other purposes. 
     Another embodiment of the invention, shown in  FIG. 6 , is the injection of enriched steam into a biomass reactor  30  instead of a landfill  10 . A biomass reactor  30  can be a substantially airtight vessel sized to contain any type of organic material to be converted into biogas. The conversion takes place from enriched steam which is injected into the vessel/reactor  30 . The enriched steam can come from the sequester chamber  27  and is piped to the bottom, top or both of the biomass reator. If the distance from the sequester to the landfill is too great to be drawn by the collectors  14  in the landfill, then a blower  26 ′ can be used to boost the steam to the steam injector  12 . Once the enriched steam is converted inside the landfill into landfill gas, another blower  26  is used to remove the landfill gas from the waste prism via the gas collectors  14 . In some embodiments, the sequester can be used in place of a flare, though a flare may be used. The sequester can contain a burner  31  that can combust biogas/landfill gas or any combustible fuel. The exhaust from the combustion can enter the chamber  27  with spray nozzles  28 , which apply the water to the exhaust. In some embodiments the exhaust is heated. When the exhaust is heated, it can flash the water into steam, sequestering the exhaust gases into the steam. In some embodiments, the water is preheated by waste heat, or otherwise, prior to being sprayed into the chamber  27  to retain more heat in the exhaust and produce hotter steam. In some embodiments, some of the biogas may be used to fire the sequester to make enriched steam to be introduced into the waste prism while the majority of the bio gas will be extracted by, for example, a pipeline  37  and used as alternative fuel and other products. 
     Though embodiments of the invention have been set forth above, they are susceptible to modifications and alternate constructions which are fully equivalent. Consequently, it is not the intention to limit this invention to the particular embodiments disclosed. On the contrary, the intention is to cover all modifications and alternate constructions coming within the spirit and scope of the invention.