Patent Application
20120210645
The current invention is drawn to the field of Pyrolysis chambers and processes. More specifically, the invention relates to a top-loading Pyrolysis chamber for organic fuel such as wood chips, the chamber having a plurality of air plasma torches for pre-heating, steam plasma torches coupled to an enclosed annular ring distributor for uniform steam plasma application during oxidation and reduction, air plasma torches coupled to an enclosed half annular ring distributor for introduction of air plasma into outlet zone for removing ash and slag and a half annular ring collector for collection and offloading of combustible gasses.
Pyrolysis is commonly defined as the thermal decomposition of an organic fuel in an environment of less-than-stoichiometric oxygen, and devices utilizing this process are known as partial oxidation reactors. Devices utilizing organic combustion include coal-based gasification projects, which use direct and incomplete combustion of feed material to generate the necessary reaction heat. One class of prior art device heats the organic feed material only to the point of leaving a carbon-ash composite solid (known as char) as a reactor product/waste. Another class of prior art device utilizes this residual char material as an external combustion fuel to generate the required process reaction heat. In one such device, the char is burned outside the pyrolysis reactor to generate the required heat, and the resulting hot char recycled to heat the incoming feed fuel. Another prior art device uses pure oxygen or oxygen-enriched air to increase the temperature in the reactor, since standard air combustion will provide a maximum reactor temperature of only 1000-1100° C. Oxygen-enrichment can also be used to reduce the formation of undesired NOx gasses from atmospheric N2 (nitrogen) present in the chamber.
The combustion of organic material such as wood chips generates ash as a waste product. As the reaction temperature increases to 1100-1500° C., for certain compositions, the ash will melt into a viscous material known as slag. Additionally, metals which may be present in the ash will also melt into the slag when the respective metal melting point temperature is reached, which starts for many metals at temperatures above 1500° C.
In the Pyrolysis process, the ratio by volume of waste (ash and slag) to incoming fuel is 2-4% (representing a 25× to 50× reduction in fuel volume), depending upon the amount of noncombustible materials in the mixed wastes. By contrast, an efficiently-operated conventional incinerator produces a solid residue of 10% or more of the volume of refuse burned.
Prior art low temperature wood waste gasification operates in the range of 800-900° C. and yields 70-140 m3 per ton, recovering no more than 8-12% of potential heat contained in the fuel. The pryrolysis apparatus and method operates at maximum efficiency for fuel generation and waste volume reduction at increased temperatures, and as described above, these elevated temperatures may be reached using oxygen enhanced combustion air, but the use of oxygen represents an additional operational expense. It is therefore desired to provide an improved pyrolysis chamber with increased internal operating temperature and resultant efficiency without the use of oxygen enriched air.
A first object of the invention is a Pyrolysis chamber having a top-loading hopper where fuel is introduced and gravity fed into to a pre-heating zone which includes a plurality of air plasma torches directly coupling an air plasma into the chamber thereby pre-heating the fuel, after which the pre-heated fuel is gravity fed into an oxidation and reduction zone where a plurality of steam plasma torches couple high temperature steam plasma into an annular ring distributor having many apertures which uniformly couple the steam plasma into the pre-heated fuel of the oxidation and reduction zone, where the oxidizing fuel is spent and releases combustible gasses, particularly H2 and CO, and these combustible gasses are separated from the spent fuel in a gas outlet zone having a half annular ring collector with many apertures for collection and offload of the combustible gases for subsequent utilization. Opposite the half annular ring collector is a half annular ring distributor which is fed by an air plasma torch coupling an air plasma into the gas outlet zone of the enclosure. Below the gas outlet zone is a solids offloading zone having a rotating grate with apertures for collecting the waste solids and transferring them into a water trough which also provides a water seal for the pyrolysis chamber. The water trough may also provide means for the removal and disposition of ash and slag waste.
A second object of the invention is a process for pyrolysis in a chamber, the process having:
a first step of loading fuel into a pre-heating zone, the pre-heating zone heated by a plurality of air plasma torches coupling an air plasma into the chamber and thereby forming pre-heated fuel;
a second step of exposing the pre-heated fuel to an oxidation and reduction zone where a steam plasma torch generates a steam plasma which is delivered to an annular ring distributor with apertures coupled to the chamber, the annular ring distributor and apertures surrounding the pre-heated fuel and coupling the steam plasma to the pre-heated fuel, thereby releasing combustible gasses and solid waste products of ash and slag;
a third step of introducing an air plasma from an air plasma torch into the oxidized and reduced fuel (char and ash), where the air plasma is delivered to a half annular ring distributor with apertures coupled to the chamber, the half annular ring distributor and apertures delivering air plasma to the oxidized and reduced fuel, thereby gasifying the char and forming ash residue ;
a fourth step of removing the combustible gasses using a half annular ring collector for collection and offload of the combustible gases, the combustible gases moving through a plurality of apertures into the half annular ring collector and carried out of the chamber;
a fifth step of removing ash and slag waste products by exposing the oxidized and reduced fuel to a rotating grate which has apertures larger than an ash or slag grain size, the ash and slag passing through the rotating grate and transferred to the a trough.
A Pyrolysis chamber has, in succession, a fuel loading zone, a fuel pre-heating zone, a steam plasma oxidizing and reduction zone, a gas outlet zone including a combustible gas outlet, and a solids offloading zone for removing ash and slag. The fuel pre-heating zone has a plurality of air plasma torches which couple a 1200-1500° C. air plasma into the chamber and heat the fuel to a pre-heat temperature of approximately 1200-1500° C., after which the pre-heated fuel is exposed to a steam plasma of approximately 1500° C. which is generated by a plurality of steam plasma torches which first couple the steam plasma into an annular ring distributor within the walls of the chamber, the annular ring distributor containing a plurality of apertures into an oxidation and reduction zone of the chamber, whereby the steam plasma and pre-heated fuel oxidize and reduce to generate combustible gasses and waste solids. The combustible gasses and solid waste are thereafter directed towards a gas outlet zone which is formed by the half annular ring distributor and the half annular ring collector. The half annular ring distributor is pressurized by a plurality of air plasma torches coupling an air plasma into the half annular ring distributor within the chamber walls, the half annular ring distributor having a plurality of apertures conducting the air plasma into the gas outlet zone. The half annular ring collector contains a plurality of apertures coupled to the chamber for drawing the combustible gasses out of the chamber and to external equipment such as a steam turbine or internal or external combustion engine for energy extraction. Below the gas outlet zone is a solids offloading zone with a rotating grate for removal of slag and ash, the rotating grate having apertures for solids removal and in contact with a water trough for aggregation of solids and slag removal.
In another embodiment of the invention, a process for pyrolysis in a chamber has a first step of loading fuel into a pre-heating zone, the pre-heating zone heated by a plurality of air plasma torches coupling air plasma into the chamber and thereby forming pre-heated fuel;
a second step of exposing pre-heated fuel to a steam plasma generated by a steam plasma torch coupling the steam plasma into an annular ring distributor in the chamber and surrounding the pre-heated fuel, coupling the steam plasma in the annular ring distributor to the pre-heated fuel using a plurality of apertures, thereby oxidizing and reducing the pre-heated fuel and generating combustible gasses and waste products of ash and slag; a third step of gasification of the ash residual carbon by injecting an air plasma into the oxidized and reduced fuel with a half annular ring distributor having a plurality of apertures directing the air plasma into the outlet zone;
a fourth step of removing the combustible gasses by means of a half annular ring collector having a plurality of apertures coupling the chamber with the half annular ring collector and directing the combustible gases to the combustible gas outlet for energy extraction;
a fifth step of removing ash and slag waste products by exposing the oxidized and reduced fuel to a rotating grate having apertures for removing ash and slag solids which have a grain size smaller than the apertures of the rotating grate, ash and slag solids which pass through the rotating grate thereafter coupled to a waste accumulation reservoir.
The present invention describes an apparatus and method for pyrolytic waste recovery which can extract energy in the form of combustible gases from a wide variety of heterogeneous organic materials including municipal refuse, biomass, agriculture wastes, wood and forest product processing wastes, hazardous wastes, petroleum coke, coal or oil shale, individually or as mixtures. Depending on the nature of the input fuel, the resultant combustible gas is suitable use as a fuel for electric power generation, for conversion to synthetic hydrocarbons, hydrogen, or other valuable chemicals. In one embodiment of the invention, the combustible gas includes H2 and CO and a steam plasma is injected in the oxidation and reduction zone which generates these gasses, the steam plasma containing sufficient energy to compensate for the endothermic heat required to generate these combustible gasses. In another embodiment of the invention, the fuel is wood chips or other biomass fuel. The instant process operates with a volume reduction on the order of 20× of input fuel volume and a weight reduction on the order of 10× in fuel with respect to the waste ash and slag.
In one prior art system described in U.S. Pat. No. 7,452,392, oxygen is removed from a combustible gas stream by oxidizing a portion of the fuel with less than the stoichiometric amount of oxygen, typically as close to 50% as possible. Steam is also added to the combusted gases in deliberately controlled quantity. This process reaction, known as gaseous partial oxidation, is quick, complete (in terms of oxygen removal extent), and generates significant heat as it is highly exothermic.
Many different fuels may be used in the present device, including those listed in the table below:
The preheat zone 140 provides for introduced fuel 122 to be heated to approximately 1200-1500° C. through the rapid introduction of air plasma at a temperature of 2000-4000° C. through air plasma torches 110 and 112, where air 114, 118 is forced through the plasma torches 110 and 112, respectively, which air plasma 116, 120, respectively, exits directly into the chamber pre-heated fuel 122, is gravity packed with a fuel/air volume ratio preferably on the order of 1:1 and a fuel density range of 180-800 kg/m3, with 400 kg/m3 being a typical density. The pre-heated fuel 122 is then subjected to a steam plasma which is generated by steam 124 injected into plasma torch 126, and the resultant steam plasma which is at a temperature of approximately 1500 degrees C. is then directed through an annular ring distributor 128 formed in chamber 109, then through a plurality of apertures 202 (shown in
C+CO2→2CO (Eq 1)
C+H2O→CO+H2−31.2Kcal/mole of C (Eq 2)
CO+H2O→CO2+H2 (Eq 3)
Equation 1 is known as Bouduart reaction, equation 2 is known as the water gas shift reaction, and equation 3 is known as the hydrogen shift equation. Equations 1 and 2 are endothermal, and the use of a steam plasma 128 at 1500° C. or more in this stage introduces sufficient external energy to offset the endothermic heat loss during combustible gas (CO and H2) generation. The combustible gasses 123 and 125 migrate to the gas outlet zone 143, via the apertures 304 (described later for
The high speed pyrolysis of the current system has several advantages over a prior art pyrolysis system, including a greater conversion fraction of the incoming waste to combustible gas. Thermal or normal pyrolysis promotes liquefaction giving only 45-50% conversion to pyrolysis gases, while rapid pyrolysis of the present invention has gas yields of greater than 65%.
Many methods for extraction of energy from the combustible gasses 137 using the gas outlet port 139 are possible. With the efficiency of gas turbine-combined cycle systems approaching 60%, the present method of waste-to-energy conversion provides an effective alternative to standard waste incinerators. Under favorable conditions, the incinerator-steam generator systems achieve 15-20% efficiency in the conversion of the potential energy contained in the waste to usable electric energy. In one example system, 1 Kg of incoming waste generates 14-15 MJ of chemical energy at the combustible gas outlet port, and 2-3 MJ of electrical energy is consumed in the generation of the various plasmas which feed the chamber.
The specific gravity of slag will be on the order of 2.0-2.5 which will allow it to adequately gravity feed through the apertures of the grate. The solid vitrified waste products produced in accordance with the present invention when the oxidation and reduction temperatures are sufficiently high may be used in a variety of applications. The vitrified slag waste may be crushed and incorporated into asphalt for use in roads and the like. Alternatively, the vitrified slag may be utilized to replace cinder in cinder or building blocks, thereby minimizing absorption of water within the block. Further, the vitrified slag may be solidified to a final form which exhibits substantial volume reduction over prior art vitrification products. The solidified form is suitable for disposal without health risks or risks to the environment.
Pre-heating plasma torches (110,112), steam plasma torch (126) and air plasma torch (134) gasifying the ash residual carbon can be realized using any prior art long arc torch configuration, and operative on 4-12 KV with an arc length greater than 0.3 m. Although specific numbers of plasma torches are shown for clarity, any number of torches may be used in each respective pre-heat zone (torch 110, 112), oxidation and reduction zone (torch 126), and gas outlet zone (torch 134). Many different prior art embodiments of the plasma torch can be utilized in the present invention. In one embodiment, each torch is a long arc forming plasma torch of the type described in U.S. Pat. No. 3,818,174 for a single phase excitation, or as described in U.S. Pat. No 7411,353 by Routberg et al. for polyphase excitation. Long arc column plasma torches have become well known in the art as having the capability of sustaining stabilized plasma arcs on the order of one meter in length. In contrast, conventional short arc plasma torches generally sustain arcs of less than 0.2 meter and typical non-plasma electric arc devices have no stabilizing character and produce relatively short arcs. The apparatus and method of the invention recognize and utilize features of the long arc torch which makes its stabilized, electrically conducting gas column especially suited for use with gasification of coal as a source of radiant heat and particularly when used in multiple and arranged as described with the “long arc” being at least 0.3 meter in length.
One advantage of long plasma arc torches such as those described above is the conversion of electrical energy to heat with an efficiency of approximately 90% as compared with an efficiency of 30-50% for conventional short arc torches. Further, it is recognized that the capability of the long arc torch in combination with the annular ring distribution is that the torches are now placed outside of the furnace wall and away from the intense furnace heat produced during gasification. This advantage reduces the wear on the torch and increases the thermal efficiency of the process. Also, the invention recognizes that the long arc torch requires significantly less current than a conventional torch thereby reducing the cost of electrical conductors and reducing the complexity of the electrical power connections.
Chamber 109 including annular ring plasma distributors 128 and 135 and half annular ring collector 136 may be formed using any material which provides resistance to surface degradation from exposure to the high temperature plasma and pyrolysis process. Suitable materials include brick with a refractory brick (fire brick) lining with a typical maximum temperature of 1650° C., or steel treated with an insulating material. In another embodiment, a chamber for 100 kg/hr wood waste has an inside dimension of 0.6 m and a preheat zone, oxidation and reduction zone, gas outlet zone, and solids offloading zone with 1.9 m overall vertical extent, with the chamber constructed of heatproof steel with the high temperature areas insulated with aluminum oxide.
Many different embodiments of the present invention are possible, and those shown are for clarity in understanding the invention, and do not limit the invention, which is understood as set forth in the claims below.
