Patent Application
20100043684
This disclosure generally relates to apparatus and methods for processing refuse, and more particularly to recovering energy and useful byproducts from refuse.
Handling and disposal of refuse is an ongoing problem. The volume of organic and non-organic materials that must be disposed of on a daily basis is nearing or exceeding the capacity of many existing and proposed landfills.
Various systems have been proposed to recover energy while processing refuse into a more compact size. These systems often use a rotary kiln to incinerate the refuse, thereby reducing the solids volume of the refuse while releasing gases. The temperatures inside the kiln are typically approximately 1500 degrees Fahrenheit or more. Energy recovery is generally indirect, where heat from the gases exiting the kiln is transferred to an auxiliary system such as a steam or hot water generator, and therefore is subject to losses during heat transfer. The partially-cooled exhaust gases are then vented to atmosphere, often at temperatures of approximately 400 degrees Fahrenheit or more.
Conventional refuse processing systems suffer from several drawbacks. Such systems are generally limited to use in outdoor settings due to the excessive amount of heat they radiate and the types of gases that they may exhaust or leak into the surrounding environment. Conventional systems also either exhaust potentially harmful gases into the environment or require additional fuel to run the burner at temperatures sufficient to break down the harmful gases into basic, typically less-harmful, components. Accordingly, it is desirable to provide a refuse processing system which may be used indoors, which more efficiently produces power from heat, and/or which captures a wider range of system byproducts that may be reused in the system or profitably sold for external use.
A refuse processing system includes a rotary kiln having a first end and a second end, the rotary kiln defining a volatilization chamber. A refuse inlet is coupled to the rotary kiln first end and fluidly communicates with the rotary kiln volatilization chamber, the refuse inlet including an inlet seal configured to substantially prevent gas in the volatilization chamber from exiting through the refuse inlet. A refuse loader is disposed in the refuse inlet and configured to advance refuse into the rotary kiln volatilization chamber. A burner is coupled to the rotary kiln second end, and a solids outlet fluidly communicates with the rotary kiln volatilization chamber. The solids outlet includes an outlet seal configured to substantially prevent gas from exiting the solids outlet. An exhaust gas outlet fluidly communicates with the rotary kiln volatilization chamber.
A method of processing refuse having at least refuse solids includes reducing the refuse solids to a particulate size, feeding the refuse into a rotary kiln through a refuse inlet, and volatilizing the refuse in the kiln to obtain post-volatilization solids and exhaust gas comprising a plurality of gas components. The post-volatilization solids are transferred from the rotary kiln into a solids receptacle through a solids outlet, and the exhaust gas from the rotary kiln is transferred into an organic rankine cycle unit through an exhaust gas outlet, which generates power from the exhaust gas. The exhaust gas is then transferred to a gas separator, where the exhaust gas is separated into gas components.
For a more complete understanding of the disclosed methods and apparatus, reference should be made to the embodiments illustrated in greater detail on the accompanying drawings, wherein;
It should be understood that the drawings are not necessarily to scale and the disclosed embodiments are sometimes illustrated diagrammatically in partial views. In certain instances, details which are not necessary for an understanding of the disclosed methods and apparatus, or which render other details difficult to perceive, may have been omitted. It should be understood, of course, that this disclosure is not limited to the particular embodiments illustrated herein.
Various embodiments of refuse processing systems are disclosed in which the physical size of the refuse is reduced in a volatilization chamber while the byproducts of volatilization are used to generate power and/or are recovered for further use, either inside or outside of the system. In certain embodiments, the system comprises three main stages: (1) an upstream stage during which refuse is aggregated and conditioned for volatilization; (2) a volatilization stage during which refuse is volatilized; and (3) a downstream stage during which volatilization byproducts are used to generate power and are separated for further use.
During the upstream stage, refuse solids are aggregated and certain types of refuse materials are removed. The refuse solids are then processed into a form suitable for volatilization, such as by chopping the refuse into a desired particulate size. Additional types of refuse, such as organic materials in liquid or solid form, may be added to the refuse solids prior to volatilization.
In the volatilization stage, the conditioned refuse is fed into a volatilization chamber, such as a rotary kiln, where the volume of the refuse solids is reduced and exhaust gases are generated. As used herein, the terms “volatilize” and “volatilization” refer to processes in which molecular bonds are broken, resulting in molecules separating into their individual elements in vapor form and an exothermic release of energy. In the present disclosure, volatilization may occur in a “starved oxygen” environment, in which little or no oxygen is present. To the extent some oxygen is present in the chamber, a limited level of combustion may also occur. The reduced refuse solids are generally in the form of ash or clinker, which is discharged from the volatilization chamber and collected for external use, such as filler for concrete. The exhaust gases are transferred to downline equipment used in the final stage. The volatilization chamber may have a refuse inlet and a solids outlet that are substantially airtight to ensure that substantially all of the exhaust gas is directed through the exhaust gas outlet and does not leak into the surrounding environment. Additionally, an exterior heat exchanger may be provided which reduces the amount of heat radiated to the surrounding environment. Reduction of exhaust gas leakage and heat radiated from the volatilization chamber make the system more feasible for indoor use.
In the downstream stage, the exhaust gases are used to generate power and are ultimately separated for use either internally or externally. A power generator, such as an organic rankine cycle unit that may generate electrical or mechanical power, receives the heated exhaust gas from the volatilization chamber and generates power therefrom. A gas separator then receives the exhaust gas from the generator and separates it into constituent gases, such as carbon dioxide, synthetic gas, and hydrogen. The constituent gases may be reused in the volatilization chamber or may be collected for use or sale off-site.
The unconditioned refuse 22 is placed into a preliminary material separator 30, which removes specific materials from the refuse 22 that are not suitable for volatilization. For example, the separator 30 may be configured to remove batteries and glass from the unconditioned refuse 22 and discharge these materials in collection bins 30a, 30b, respectively. The separator 30 may further include a magnetic separating unit 32 which removes metals to a collection bin 30c.
The preliminarily separated refuse is then transferred to a reducing unit which processes solids in the refuse into a size suitable for volatilization. In an exemplary embodiment, the reducing unit is a chopping station 36 which cuts the refuse solids into a desired size. The desired size may be selected according to the volatilization parameters. For example, the refuse may be chopped into bundles that are approximately two inch cubes (i.e., two inches high, by two inches wide, by two inches deep), however other bundle sizes may be used without departing from the scope of this disclosure.
From the reducing unit, the chopped refuse bundles are transferred to a final materials conveyor 40 in which organic refuse may be added to the bundles. For example, sanitary sewage sludge may be deposited onto the bundles from a sludge pipe 42, while other organic materials may be added from a dump truck 44. After the optional addition of organic materials, the refuse is fully conditioned and ready for volatilization.
The volatilization stage may be performed in a volatilization chamber, such as that defined by a rotary kiln 50 as shown in
A burner assembly 62 is coupled to the kiln second end 56 and includes a fuel hopper 64 for receiving fuel for volatilization. A burner pipe 66 has a first end in fluid communication with the fuel hopper 64 and a second end disposed in the volatilization chamber 53. The burner assembly 62 may use any type of fuel, including coal fines delivered by truck 63, to generate volatilization in the chamber 53.
A solids outlet 68 for discharging post-volatilization solids to a solids receptacle 70 is also coupled to the kiln second end 56. An exhaust gas outlet 72 has a first end coupled to the kiln first end 54. The refuse inlet hopper 58 and solids outlet 68 are preferably configured to prevent exhaust gases from leaking to the exterior environment, so that substantially all of the exhaust gas exits the volatilization chamber 53 through the gas outlet 72. First and second seals 74, 76 are schematically shown in
During operation, the burner assembly 62 is operated to generate a temperature in the volatilization chamber 53 sufficient at least initiate volatilization of the refuse. The working temperatures inside the chamber 53 may be approximately 900-2,000 degrees Fahrenheit, however the actual temperature inside the chamber may fall outside this range. With the volatilization chamber 53 at its operating temperature, refuse may be introduced into the chamber 53. The burner assembly 62 supplies sufficient heat to initiate volatilization. Once volatilization of the refuse begins, exothermic energy released by the breaking of molecular bonds in the refuse should be sufficient to maintain the desired temperature inside the chamber 53, and therefore the burner assembly 62 should not be required to operate thereafter. It is possible, however, that the chamber temperature will drop below a minimum required temperature, at which time the burner assembly 62 may be operated to raise the chamber temperature.
The side wall 52 of the kiln 50 may be rotated (such as by external gear 51), to advance the refuse from the first end 54 to the second end 56 of the kiln 50. The kiln 50 may be rotated so that the refuse remains in the volatilization chamber 53 for a desired residence period. The residence period may be inversely proportional to the chamber temperature, and may also take other factors into consideration such as refuse content and physical size. During volatilization, the volume of the refuse is substantially reduced and constituent gases are released. Any remaining post-volatilization solids are discharged through the solids outlet 68, typically in the form of ash and/or clinker, which may be used as a filler for concrete. Heat from the exiting ash/clinker may be returned to the volatilization chamber 53 to improve efficiency of the system. Meanwhile, the exhaust gas is directed through the gas outlet 72 for use in the downstream stage.
The rotary kiln 50 may further include an external heat exchanger to recover heat from an exterior of the kiln while reducing the amount of heat radiated to the surrounding environment. In the illustrated embodiment, a thermal exchange blanket 80 is disposed around an exterior surface 82 of the kiln 50. The blanket 80 defines an annular chamber 84 that retains a substantial portion of the heat radiating from the kiln 50. Inlet and outlet pipes 86a, 86b fluidly communicate with the annular chamber 84 and carry a heat transfer fluid, such as thermal oil, to direct the recovered heat as desired.
In the downstream stage, exhaust gas from the rotary kiln 50 is used to generate power and is ultimately separated into constituent gases for use either internally within the system or externally outside the system. In the illustrated embodiment, a power generator, such as an organic rankine cycle unit 88, receives the hot exhaust gas from the volatilization chamber 53 via the gas outlet 72. The organic rankine cycle unit 88 comprises a series of cascading closed loop heat exchangers having a heat exchange medium, such as propane, disposed therein. Heat from the exhaust gas is used to vaporize the heat exchange medium which is then expanded in multiple expansion turbines to generate useful mechanical or electrical power. In the illustrated embodiment, electrical power is delivered to outlet 91. As the exhaust gas is partially cooked in the organic rankine cycle unit 88, byproducts of nitrates, sulfates, and phosphates may be collected in respective containers 90a, 90b, and 90c. The collected byproducts may have value in other uses, such as in fertilizer. The partially cooled exhaust gas is then discharged from the organic rankine cycle unit 88 through an outlet 92. Additional details of specific embodiments of the organic rankine cycle unit 88 are provided in U.S. Pat. Nos. 6,857,268 and 7,096,665, both to Stinger et al., which are incorporated herein by reference.
A gas separator 94 has an inlet 96 in fluid communication with the outlet 92 of the organic rankine cycle unit 88. The gas separator 94 may remove one or more toxins from the exhaust gas. For example, the gas separator 94 may remove sulfur, gold, palladium, platinum, and zinc and collect these materials in receptacles 96a-e. The collected materials may then be used in other processes or sold. Additionally, the gas separator 94 may separate the exhaust gas into its constituent gases. For example, the gas separator may separate one or more substantially pure streams of carbon dioxide, synthetic gas (a carbon monoxide and hydrogen mixture), and hydrogen and discharge the constituent gases through respective outlet conduits 98a-c. Again, these constituent gases may be reused in the refuse processing system, used in other on-site processes, or sold. Residual gases not previously separated and collected are exhausted to atmosphere through outlet 99. In general, the residual gases should have a temperature no greater than approximately 200 degrees Fahrenheit, and preferably no greater than approximately 40 degrees Fahrenheit above the current ambient temperature.
From the foregoing, it will be appreciated that the system safely processes refuse to have a smaller solids volume while recovering several useful and/or valuable byproducts. The byproducts that are recovered include not only solids, but gases, which may be used in the refuse processing system itself or in other processes. Additionally, heat from the refuse processing system may be used to generate power. The sealed kiln prevents harmful gases from escaping to the surrounding environment, and the thermal blanket reduces the amount of heat radiated from the kiln, thereby facilitating use of the system indoors.
A conveyor 264 is disposed inside the inlet conduit intermediate segment 258. As best shown in
A similar auger and conveyor arrangement may be provided at the solids outlet end of the kiln 250. As shown in
While only certain embodiments have been set forth, alternatives and modifications will be apparent from the above description to those skilled in the art. These and other alternatives are considered equivalents and within the scope of this disclosure and the appended claims.
