Patent Application
20050211143
This invention relates to the disposal of waste and, more particularly, to a system and associated method of processing such waste into electricity in an environmentally friendly manner.
Municipal solid waste is commonly incinerated in a combustion process at high temperatures such as 1600 degrees Fahrenheit. This incineration process seeks to destroy the waste by burning it, usually at high temperatures with excess air. The ultimate purpose of the process is to burn as much waste as possible as quickly as possible. One potential problem with such incineration is the emissions of the incinerator may contain toxic and other unwanted pollutants dangerous to human health and the environment. Another potential problem with conventional incineration is that the process destructs all the municipal solid waste and does not recycle any of it. Another problem with incinerating municipal solid waste is that the resultant ash must be sent to a particular type of landfill subject to restrictive environmental regulations.
Therefore, there is a need in the industry for a process of treating municipal solid waste in an environmentally friendly manner which uses all of the residual by-products of the process.
There is also a need for a process of treating municipal solid waste in an environmentally friendly manner which is capable of generating electricity.
The method of the present invention in one embodiment comprises a method of processing solid waste in an environmentally friendly manner using waste gasification. The waste gasification process of the present invention gasifies and reduces solid waste, most often municipal solid waste. Other waste such as tires, medical waste, commercial waste, industrial waste or sewage sludge may be used in the methods and/or apparatus of the present invention. Waste gasification converts the incoming solid waste or feedstock into combustible gases such as carbon monoxide, methane and hydrogen which contain the energy originally present in the feedstock. This waste gasification process degrades the feedstock in a rotary kiln in the absence of adequate air to support full combustion. The gases generated in the rotary kiln are not burned in the kiln, but rather transported to a reduction chamber where they may be burned to generate steam for purposes of generating electricity. The temperature inside the rotary kiln is at least 800 degrees Fahrenheit and preferably between 800-1000 degrees Fahrenheit to carry out this waste gasification process.
The waste gasification process converts the feedstock waste materials such as municipal solid waste, tires, coal gob, wood construction debris and/or lawn waste into a BTU-rich gaseous fuel. This fuel may be used “on site” as a non-fossil fuel source for various industrial processes, such as the production of hot water or steam-powering internal combustion engines as examples. This process combusts the waste in a “starved air” combuster, which degrades the municipal solid waste with less oxygen, thereby improving the quality of the resultant air emissions. This process, like the incineration process, vents the flue gases to the atmosphere after they have been sufficiently cleaned.
Nothing generated by the waste gasification process of the present invention needs to be placed in a landfill. One hundred percent of the incoming waste stream is either recovered as an alternative energy source, recycled or otherwise utilized. All of the ferrous and non-ferrous metals, aluminum and glass are recovered at the end of the process. The only other product remaining is a fine, mineral residual (primarily glass containing less than five percent carbon) that is an acceptable concrete additive.
The method comprises transporting the waste to a receiving hopper where it is temporarily stored. A rotary kiln is located downstream of the receiving hopper. The municipal solid waste or other feedstock is fed into the rotary kiln via a hydraulic ram preferably. However, any other means of introducing or feeding the municipal solid waste into the rotary kiln may be used.
The rotary kiln is heated to a temperature of at least 800 degrees Fahrenheit and preferably between 800-1000 degrees Fahrenheit. A driver such as a motorized drive system rotates the rotary kiln at a rate of approximately one revolution per minute. However, the driver may rotate the rotary kiln at any desired speed.
After the kiln has been rotated for six to eight hours preferably, gases are transported to a reduction chamber. Although this document refers to this member as a reduction chamber, other terms which may be used for this apparatus may include oxidizer, air cleaner or combustion chamber. The reduction chamber functions as a destruction mechanism for the elimination or reduction of volatile organic compounds (VOCs), hydrocarbons, dioxins, furans and various other gases and compounds. The reduction chamber is heated to a temperature of at least 1800 degrees Fahrenheit before the process begins. The reduction chamber is maintained at a temperature of between 1800 and 2400 degrees Fahrenheit by at least one gas burner. However, any other means of heating the reduction chamber may be used as well without departing from the spirit of this invention.
To maintain the temperature of the gases exiting the rotary kiln and going to the reduction chamber at a temperature of 800-1200 degrees Fahrenheit, at least one of the following may be adjusted by a programable logic controller: the feed rate of the waste going into the rotary kiln; the rotation speed of the rotary kiln; and/or the amount of air flow into the interior of the rotary kiln. The gases are retained or held in the reduction chamber for at least one second.
Upon exiting the reduction chamber the gases are cooled by a spray of water in a duct to reduce the temperature of the gases to approximately 500 degrees Fahrenheit. The gases are then passed through at least one air pollution control unit in which contaminants such as SO2, NOx, hydrogen chloride, mercury, dioxins and furans, along with particulate matter are removed. In the present invention there are preferably three air pollution control units: a reduction chamber, a spray dryer absorber and a baghouse. However, there may be more or fewer air pollution control units incorporated into the system.
In the spray dryer absorber, the gases are treated to remove any remaining acids and metals that might be present. A slurry of lime and activated carbon is injected into the top of the spray dryer absorber unit for this treatment. Spent carbon and other particulate matter that may be generated at the spray dryer absorber are collected at the bottom of the spray dryer absorber and transferred via a conveyor to a fly ash bin.
From the spray dryer absorber the gases are ducted to a multi chamber baghouse for final removal of any remaining contaminates. Although the baghouse preferably has four chambers, it may contain any number of chambers in accordance with the present invention. In the baghouse, the gases pass through filters to remove particulate matter. Particulates including ash generated in the baghouse are collected and transported on a conveyor belt to the fly ash bin.
From the baghouse the gases are discharged into the atmosphere and continuous emission monitors record the air quality of the emissions.
In an alternative embodiment of the present invention, additional apparatus is added onto the existing apparatus to generate electricity. More specifically, a second reduction chamber, boiler steam turbine and generator are added along with two dampers or valves and additional lines or conduits. The dampers may be adjusted so that the power option may be turned off or on, depending upon the desired operation.
In the event, the method of the present invention is intended to generate power, in particular electricity, gases from the rotary kiln are transported to a second reduction chamber and then to a steam boiler before entering a duct entering the spray dryer absorber. From the spray dryer absorber, the gases pass through air pollution control units as described herein.
When the apparatus is in this power generation mode, heat from the gases exiting the reduction chamber heat water passing through the boiler, changing it to steam which is passed on to a turbine. The steam acts on the turbine blades to rotate them and thereby rotate an output shaft which through a speed reducer operates a generator to create electricity.
Thus, with the present invention all of the solid waste is used or recycled in an environmentally-friendly manner and electricity may be generated. These and other objects and advantages of the present invention will be evident from the following detailed description and the drawings.
Referring to the drawings, and particularly to
Preferably, the building 16 is large enough (100 feet by 70 feet) to accommodate approximately 800 tons of municipal solid waste so that if a need arises to store a large quantity of waste, the facility will be able to handle it. Inside the building 16, the municipal solid waste 12 is preferably transferred from the trucks 14 via one or more conveyors (not shown) to the receiving hopper 18. The building 16 preferably has a reinforced concrete floor. Although the conveyor and receiving hopper 18 are preferably enclosed to keep the municipal solid waste 12 from getting wet from precipitation, they need not necessarily be so covered.
The receiving hopper 18 is positioned directly above a feeder 20 in the form of a hydraulic ram which pushes the municipal solid waste into a rotary kiln 22, shown in greater detail in
As best shown in
As best shown in
Each end 30, 32 of the rotary kiln 22 has a double seal system 25 which comprises a plurality of spring steel overlapping leafs (not shown) attached to a stationary hood (not shown). The purpose of the overlapping leaf seal is to keep any air entrained particulate (dust) from escaping the rotary kiln. The second component of each double seal 25 is a high temperature fabric belt (not shown) that keeps outside air from entering the interior of the rotary kiln 22. This fabric belt is secured to the stationary hood and fits tightly against a wear band (not shown) attached to the outer shell 24 of the rotary kiln 22.
The rotary kiln 22 is driven by a drive means 3 including a motor 4 which rotates a drive shaft 5 which turns a first gear 6. The first gear 6 engages a second gear 7. Rotation of the first gear 6 causes the second gear 7, which extends around the shell 24 of the rotary kiln 24, to rotate. The second gear 7 is preferably welded to the shell 24 of the rotary kiln 22 but may be secured any other way. The rotary kiln 22 preferably rotates at a rate of one revolution per minute, but may rotate at any desired speed. Any other drive means may be used to rotate the kiln 22.
The rotary kiln 22 is heated by a heating system 35 including burners 37 located at the feed and exit ends 30, 32 of the kiln 22 and fuel lines 38 leading from one or more natural fuel supplies 39 to burners 37. Although natural gas is the fuel of choice, any other fuel other than natural gas such as propane may be used in accordance with the present invention. Although the burners 37, fuel lines 38 and fuel supply 39 are illustrated in certain locations, they may be located elsewhere without departing from the present invention. The burners 37 may be any type of burners. However, one burner known to work in accordance with the present invention is manufactured by Maxon Corporation (www.maxoncorp.com), generates 18 million BTUs and sold as a model 18 M Maxon KINEDIZER®.
Activation of the heating system 35 allows the operating temperature of the interior 21 of the rotary kiln 22 to be at least 800 degrees Fahrenheit and preferably between 800-1000 degrees Fahrenheit. Once the appropriate temperature has been reached in the interior 21 of the rotary kiln 22, the flame will be extinguished in the burners 37, and the municipal solid waste 12 inside the interior 21 of the rotary kiln 22 is able to sustain the temperature during the rest of the processing time. The high temperature inside the rotary kiln 22 vaporizes all moisture that is part of the municipal solid waste 12. After the burners 37 are turned off, the municipal solid waste 12 serves as its own fuel source inside the interior 21 of the rotary kiln 22.
As seen in
The combustion control system 2, shown in
The reduction chamber (“R.C.”) 40 is placed on a reinforced concrete pad (not shown) and receives gases from the rotary kiln 22. The reduction chamber 40 is preferably cylindrical in configuration having a length of 45 feet and a diameter of 11 feet. Inside the reduction chamber 40 are three ceramic baffles 41, each in the shape of a semi-circle. Each baffle 41 is constructed of firebrick and covers approximately half of the interior of the reduction chamber 40. The baffles 41 are offset from one another to increase the retention time of the gases inside the reduction chamber 40. The baffles 41, once heated, retain heat and help ensure complete combustion of all volatile organic compounds (VOCs), hydrocarbons, and other pollutants. Although three baffles are illustrated and described, any number of baffles of any configuration may be incorporated into the reduction chamber. Any other configuration or size of reduction chamber may be used in accordance with the present invention.
The gases passing through the duct 36 to the reduction chamber 40 from the rotary kiln 22 and measured at temperature probe 42 are preferably at 800 degrees Fahrenheit. A heating system 49 including a start-up burner 50, a fuel supply (“FS”) 8 which is preferably natural gas and a gas supply line 52 extending from the fuel supply to the start-up burner 50 is located at the first end 48 of the reduction chamber 40. The burner 50 may be any type of burner. However, one burner known to work in accordance with the present invention is manufactured by Maxon Corporation (www.maxoncorp.com), generates 9 million BTUs and sold as a model 9 M Maxon KINEDIZER®. The temperature in the reduction chamber 40 is maintained at a minimum of 1800 degrees Fahrenheit and preferably between 1800 to 2400 degrees Fahrenheit. Therefore, the gases exiting the reduction chamber are preferably at least at 1800 degrees Fahrenheit. Once the gases brought to the reduction chamber 40 via duct 36 are self-sustaining, the start-up burner 50 may be shut off with the gases able to maintain the temperature. The gases are retained in the reduction chamber 40 for at least one second.
Duct 56 extends from a second or exit end 58 of the reduction chamber 40 to air pollution control equipment which includes two units: a spray dryer absorber 60 and a baghouse 62. The duct 56 is preferably circular in cross section having a diameter of five feet. However, any other size or configuration of duct may be used in accordance with the present invention. The duct 56 has a series of misting nozzles 64 and a series of temperature probes 66 to control and monitor the temperature of the gases going from the reduction chamber 40 to the spray dryer absorber 60. The temperature of gases going into the spray dryer absorber 60 is approximately 500° F.
The spray dryer absorber (“SDA”) 60 receives the gases from the reduction chamber 40. The purpose of the spray dryer absorber 60 is to treat the gases for any remaining metals and acids that may be present. An eighty ton lime silo (not shown) and a thirty ton carbon silo (not shown) are installed on site. Any other size or storage means may be used to store those items. A holding tank 68 contains a lime slurry 70 stirred by a power driven stirrer 72. The lime slurry 70 is pumped via pump 74 through a line 76 to a head tank 78. Carbon is introduced into the top of the head tank 78 in the direction of arrow 80 to create a mixed slurry 82 in the head tank 78. An overflow line 84 extends from the head tank 78 to another holding tank 86. The mixed slurry 82 is stirred by a power driven stirrer 83 and is pumped via pump 88 through a line 90 to the head tank 78. The mixed slurry 82 is passed through a line 91 and sprayed into an upper portion 92 of the spray dryer absorber 60. The mixed slurry 82 reduces the temperature of the gases and removes SO2, NOx and certain metals from the gases. The spray dryer absorber 60 has a lower portion 94 having an exit 96 through which passes spent carbon and other particulate matter generated in the spray dryer absorber 60. The spent carbon and other particulate matter generated in the spray dryer absorber 60 after having passed through the exit 96 are carried via an endless conveyor 98 to a fly ash bin 100.
The fly ash bin 100 has an exit 101 through which the fly ash passes. The fly ash then is carried via endless conveyors 102, 103 to a final ash bin 104. Ash in the final ash bin may be used in concrete as filler.
The gases are ducted from the spray dryer absorber 60 via duct 106 to the baghouse 62. The baghouse 62 has four chambers 107, each chamber 107 having a filter 108. A temperature probe 109 is inserted into the duct 106 to monitor the temperature of the gases going to the baghouse 62. The temperature of the gases exiting the spray dryer absorber before going to the baghouse 62 is preferably 290 degrees Fahrenheit. If this temperature reaches 350 degrees Fahrenheit, the combustion control system 2 may shut down the operation of the facility 10. Exits 110 are located at the bottom of the baghouse 62. Ash generated in the baghouse 62 passes through these exits 110 onto an endless conveyor 112 which carries it to the fly ash bin 100.
From the baghouse 62, gases are pulled by an induced draft (“ID”) fan 126 through a duct 112. After the gases pass through the fan 126 they are released to the atmosphere through an exit stack 114. Gases exiting the exit stack 114 are preferably at 260 degrees Fahrenheit but may be at any other desired temperature.
The combustion control system 2 is operational such that if any of the temperature probes detect a temperature above/below a predetermined value, the operation of the facility 10 will be terminated or shut down. For example, no waste will be introduced into the rotary kiln 22 until the temperature in the kiln 22 is at least 800 degrees Fahrenheit. If the gases entering the baghouse 62 are above 350 degrees Fahrenheit, the combustion control system will cut off or shut down the facility 10. In addition, if an operator observes deviations from the operating standards, the operator may manually shut down the operation of the facility 10.
Referring to
In use, the method of processing municipal solid waste using the facility 10 described above includes heating the interior 21 of the rotary kiln 22 to a temperature of at least 800 degrees Fahrenheit and heating the reduction chamber to a temperature of at least 1,800 degrees Fahrenheit. Untreated municipal solid waste is fed into the rotary kiln 22 via the feed ram 20. The kiln 22 is rotated at approximately one revolution per minute by the drive means 3.
After the waste has been in the interior 21 of the rotary kiln 22 for a predetermined time period, preferably six to eight hours, the processed municipal solid waste, residual byproduct, or residual solids are removed from the interior 21 of the rotary kiln 22 via discharge or exit chute 34. These residual byproducts are transported to a holding hopper 116 for a time before being transported via a conveyor 120 to the inclined vibrating screen 122. The residual byproducts are then separated into components; the ash passing through the vibrating screen 122 and the other residual byproducts passing along on top of the vibrating screen 122 to another conveyor 124. The metals are then separated from the non-metals as the residual byproducts pass along endless conveyor 124. The metals are recycled. The non-metals are pulverized and used as filler in concrete.
The gases generated in the interior 21 of the rotary kiln 22 are transported to the reduction chamber 40. In the reduction chamber 40 these gases are held for at least one second while they are burned. This process may be used to generate hot water or steam which may be used to generate power.
The gases exiting the reduction chamber 40 are cooled in duct 56 with water sprayed from misting nozzles 64 while being transported to the spray dryer absorber 60. Other means of cooling these gases may used as desired such as a heat exchanger. The gases are treated to remove contaminants in the spray dryer absorber 60 by exposing them to a lime and carbon water mist. Particulate generated in the spray dryer absorber 60 is passed via a conveyor 98 to an ashbin 100 where it is collected for disposal. The gases are then passed from the spray dryer absorber 60 to the baghouse 62 via duct 106. In the baghouse 62 the gases are further treated to remove any remaining contaminants. Particulate generated in the baghouse 62 is passed via an endless conveyor 112 to ashbin 100 where it is collected for disposal. The gases are then discharged to the atmosphere via a stack 114.
Referring to
In the event the power generation system 120 is used, valves or dampers 122, 124 will be opened to their positions shown in solid lines in
Alternatively, when the dampers 122, 124 are in their second or open positions illustrated in dashed lines in
In the event one desires to generate electricity, the dampers 122, 124 are moved to their blocking positions shown in solid lines in
Duct 56 extends from the boiler 130 to air pollution control equipment which includes two units: a spray dryer absorber 60 and a baghouse 62 (See
Steam generated in the boiler 130 passes through duct or pipe 134 to a steam turbine 136. As is conventional and known in the art, the steam is used to turn the turbine blades to rotate an output shaft 138 which powers a generator 140 for generating electricity.
While we have described two preferred embodiments of the present invention, those skilled in the art will appreciate changes and modifications which may be made to the present invention without departing from the scope of the present invention. For example, the baghouse may have more or less than four chambers or more than one screen may be used to separate the solids generated in the rotary kiln. Therefore, we intend to be limited only by the scope of the following claims.
This application is a continuation-in-part application of pending U.S. patent application Ser. No. 10/654,673 filed Sep. 4, 2003 entitled “System and Method of Processing Solid Waste”, which is fully incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10654673 | Sep 2003 | US |
| Child | 11130523 | May 2005 | US |
