Patent Application
20070081930
Not Applicable
Not Applicable
The present invention relates to an apparatus and method for thermolizing industrial, residential, and medical waste for the purposes of sterilization, energy or oil recovery, molecular decomposition, and volumetric reduction of waste.
While there are alternative systems to process waste through incineration, autoclaving and gasification, they pale in comparison with regards to making the waste safe for disposal. In waste processing, if the process does not provide complete molecular decomposition into basic elements, it is incomplete, unsafe and does not meet the needs of the twenty-first century.
One would have to conclude that if the condensed steam from autoclaving medical waste contains mercury so does the processed waste. And yet, with the existing laws, autoclaved medical waste is shredded and taken to municipal landfills to leak its dangerous chemical contents such as mercury into the groundwater. In fact, traces of chemo and heart medication has now found its way into our lakes and rivers.
Furthermore, natural decaying, as in backyard composts, septic tanks, or municipal landfills, are also not a viable options because they are extremely slow and produce heat, VOC's, CO, CO2 same as incomplete combustion even though the process is seemingly safe and anaerobic. In natural decaying the oxygen is supplied from atmospheric moisture and groundwater.
On the other hand, burning waste as in incineration, forms and releases toxic chemical compounds into the air and spreads the contamination over a wider area. There are also so many variations of incineration under the heading of pyrolysis. It seems any combustion system with controlled oxidation is mistakenly classified under the heading of “pyrolysis.” Thus the term “thermolysis” is used herein to differentiate this process from pyrolysis.
Used tires also present a unique disposal problem due to their bulky shape and size. While shredding improves the disposal problem, it is an expensive alternative and does not recover any of the renewable resources from the used tire.
Many prior attempts to recycle tires through pyrolysis have not proven successful. In dealing with tires, mere carbonization is not the primary issue, but the efficiency and maximizing oil production is. Ability to maintain process temperature with accuracy is also an essential component in the producing good quality oil. Furthermore, tires do not lend themselves to pyrolysis by hot metal contact due to their size and shape. Only a small portion of the tire can be contacted with the hot metal, therefore processed.
While high temperature steam systems are better suited for handling the shape and size but necessitate high-pressure vessels to handle the temperatures and pressures involved, making the system unnecessarily dangerous, inefficient and expensive. Microwave technology has also proven unsuccessful for this application.
Prior art by the same inventor (application Ser. No. 10,217,386 Art Unit 1764) depicts an apparatus and method most suitable for processing bulk medical waste, but not suitable for intact tires. Furthermore, the optimum operating temperature of the inferenced apparatus being 1500° F. is too high for optimum oil production. Higher temperature is more suited for vaporizing into gaseous product with higher molecular fragmentation. The optimum processing temperature for oil production from used tires is 1216° F.
Two distinct systems are provided for thermolizing: a batch unit, which processes a batch of waste at a time, and a continuous system requiring continuous feed to support a continuous thermolysis process. Both systems however utilize the same concept of controlled incremental immersion of waste into a molten salt bath solution and a secondary means of superheating of gasses for complete molecular decomposition. Both systems also utilize a sealed containment for collecting, treating and partially or fully oxidizing the vaporized gasses to maintain process temperature.
The continuous system consists of a liquid salt bath configured within a sealed containment with interlocked double sealed entry gates, internal conveyors and heating system. The benefit of using liquid salt for heat transfer is that it lowers the required process temperature while affording fast process time. Furthermore, the set point process temperature can be maintained more precisely owing to the high heat content of sodium/potassium solution, making the medium behave more like a heat storage.
In both cases, a salt bath is utilized which is preheated by means of electrical resistance, propane or natural gas. The switch over to manufactured gas is automatic, based on the amount of manufactured gas available. Since neither the quantity (CFM) nor the quality (Btu/CF) of the manufactured gas is known with any certainty, the combustion stoichiometry is maintained by controlling the combustion air to match the manufactured gas available by means of monitoring the O2 in the exhaust stream.
The process temperature is controlled independently by means of controlling the BTU/SF content by adding propane or natural gas to the manufactured gas to increase the process temperature or by pumping waste rinse water through a tube inside the salt bath to lower the process temperature. If excess heat is a constant as in medical waste, this can be harnessed for other uses. Best way to accomplish this is to circulate the liquid salt through a heat exchanger.
The continuous system utilizes a conveyor with protruding spikes or treads to engage with tires or waste for the purposes of regulating the immersion speed of the waste into the salt bath. The intent of P.I.D. (proportional integral derivative) controlled immersion is to produce steady controllable vaporization pressure within the sealed chamber. The stoichiometry of the combustion air to fuel ratio is regulated by a butterfly valve slaved to the exhaust O2 sensor. As usual standard practice 10% excess air is used for the cleanest combustion. This tends to provide a hot flame temperature suitable for molecular fragmentation within the heat exchanger.
The remaining residue consists of metals and carbon black. Carbon being lighter than liquid sodium floats on the surface. The discharge conveyor collects and discharges all solids floating carbon and metallic parts into the rinse tank.
The batch system uses a wire basket with a lid to contain and immerse the waste incrementally into the salt solution. A quick water rinse cycle follows the thermolyzation cycle to wash off and collect any salt remaining on metallic parts within the basket. Depending on the mesh size of the wire basket, the carbon may be collected within the basket or by the screen over the rinse water holding tank. The rinse water from the holding tank is then used in the next cycle to cool the process temperature or to maintain the steam-laden atmosphere necessary for the process.
Sodium/potassium solution also facilitates the capturing and neutralizing of hydrochloric acids released during thermolysis of chlorinated plastics. Sodium carbonate is added as additive to compensate for losses.
While thermolysis is best achieved by subjecting the waste to high heat in an anaerobic, steam-laden environment, total fragmentation is not desirable when dealing with used tires. So, the process temperature is case specific depending on the type of waste and level of molecular fragmentation desired. With tires, if oil is the desired byproduct the initial process temperature should not exceed 1216° F.
Five years of test data however shows that, regardless of the set process temperature, the initial step of the vaporization never produces 100% decomposition. This is because the very nature of vaporization from solid or liquid to gaseous product requires high thermal energy causing a local cooling effect thus, impeding the decomposition of fragmentation process. The vaporized gasses, also insulate the waste from the heat source during vaporization, further impeding the process. This is why a three-step process is utilized in this apparatus, first step is to vaporize the waste, the second step is to distill in the case of tires or filter by adsorption in the case of medical waste, and a third to defragment molecules by higher heat just before the gasses are oxidized.
Thermolysis however, does not treat nor break down heavy metals. This is because heavy metals like mercury, and lead are already natural elements. In this case, if required, adsorbers are used to capture the heavy metals into activated charcoal and lignite in-line filter.
Two independent conveyors are fitted within the anaerobic chamber (14). The charge conveyor (18) is designed to engage with the waste using spikes (30) attached to the conveyor belt to control the immersion rate of vaporization. The discharge conveyor (17) is designed to capture and remove byproducts, namely carbon black (21) and wires and metallic parts (31) from the salt bath. The fire tube (19) is submerged and extends across the salt bath and back with sufficient diameter to accommodate the flame and length to transfer the heat from the combustion to the molten salt.
The discharge from the byproduct conveyor (17) is gravity fed into the water rinse bath (20), which also acts as a seal against manufactured gasses escaping from the sealed containment (14). Surface of the rinse bath water exposed to the hot side is minimized to limit the heat transfer into the rinse water.
If desired, the vaporized gasses can be partially condensed and extracted as oil. A condensing coil with a condensate discharge valve is fitted in-line between the anaerobic chamber (14) and the superheater (33) to facilitate the removal of oil. The cooling water (22) for the condensing coil can be re-circulating through a heat exchanger or evaporative water tower to maintain the water temperature close to ambient as possible. The condensing tube (23) is sized to accommodate the flow rate with sufficient length to condense the oil (29) at near ambient pressure.
The condensate separator (24) is designed to discharge liquid volatiles and or oil including water but capture gasses. It utilizes a float to sense the presence of liquids to open the discharge gate for the liquids. The function of the superheater (25) is to fragment the manufactured synthesis gas through high heat within steam laden atmosphere to achieve the cleanest possible combustion. The burner (34) premixes the gas with combustion air. The amount of air required is determined by the O2 sensor (26) in the exhaust, which drives the air mixture control valve (28).
Spray mist nozzles (28) directed at the second interlocked entry gate is to (a) lower the gate and bulkhead temperature sufficiently to utilize silicone or Viton® seals and (b) to maintain positive pressure within the vestibule to prevent the backflow of gasses while the inner gate is open.
The burner assembly (125) including the ends of the fire tubes (104) are positioned outside the sealed containment (101). The number of burners can be singular or multiple, depending upon the total Btu requirement. Each burner is equipped with an airflow regulator valve (116), gas flow regulator (115), and an exhaust fan (112) to draw the proper mixture of natural gas, manufactured synthesis gas, and air into the heating tube for true stoichiometric combustion. The amount of air for combustion is regulated by valve slaved to the O2 sensor (113) located at the exhaust end of the fire tube.
The solenoid valve (123) is activated to spray water through the nozzles (107) when the basket (109) is in the rinse cycle. The salt bath (103) is fitted with an insulated lid (105) to keep the splash from the rinse spray from cooling the molten liquid medium (119).
The vaporized gasses from the containment vessel (101) are directed through the pipe (102). An activated charcoal/lignite adsorber (111) is installed in line, if the waste to be processed contains heavy metals. The adsorber canister is fitted with a condensate float valve (122) to return the condensate from the adsorber canister back to the liquid holding tank (106) via the return line (121). The condensate along with the waste rinse water is injected by pump (117) through piping (120) and vaporized in the following cycle to generate the steam-laden atmosphere.
The superheater (120) is sized to ensure complete molecular fragmentation before the gasses reach the burner (125). The burner is equipped with a gas flow control valve (115) to blend in natural gas or propane should the Btu content of the manufactured synthesis gas fall below what would be required to maintain process temperature.
This application claims the benefit of Provisional application Ser. No. 60/724,097, filed Oct. 6, 2005.
| Number | Date | Country | |
|---|---|---|---|
| 60724097 | Oct 2005 | US |
