Plasma method for disposing of waste material, and apparatus therefor

Abstract

A method and an apparatus based on a reactor vessel ( 201 ) that is brought to a predetermined vacuum degree, in particular said vacuum degree set between 2 and 6 absolute millibar, an to a high temperature. A waste material is continuously introduced in the vessel ( 202 ), in particular a solid waste material ( 5 ) is introduced in such a way that a vacuum loss from the vessel ( 201 ) is prevented. Owing to the high temperature, waste material ( 5 ) forms a plasma that undergoes a molecular rearrangement, which gives origin to a substantially liquid residue that is collected in a bottom portion ( 204 ) of reactor ( 201 ), and to a gas ( 11 ). The gas ( 11 ), which mainly comprises carbon monoxide, hydrogen, carbon dioxide and steam, i.e. a typical syngas composition, is continuously taken away from the vessel ( 201 ) through a duct ( 12 ), and is sent to subsequent treatments to obtain a gas fuel that can be burnt by devices such as a gas turbine, a motor or a boiler. The high temperature in reactor ( 201 ) is maintained due to a current in the form of electric discharges ( 20 ) that is established between two electrodes ( 21,22 ) below the liquid head ( 7 ). The substantially liquid residue is periodically discharged to maintain a liquid head height ( 7 ) not exceeding a reference height value H*, in such a way that air inlet into vacuum loss from the vessel ( 201 ) is prevented.

1 . A method for transforming a waste material, said method comprising the steps of:
 prearranging a vessel, said vessel having a bottom part, an inlet duct that is associated to an inlet port, and an outlet port;   heating said vessel to a prefixed conversion temperature;   depressurizing said vessel to a prefixed vacuum degree, and maintaining said prefixed vacuum degree, by suction downstream of said outlet port;   feeding said waste material into said vessel through said inlet duct, said waste material being thus heated to said conversion temperature, said conversion temperature being such that said waste material turns into a ionized gas, in particular a plasma, and into a substantially liquid residue, in particular a lava, said liquid residue forming a predetermined liquid head with respect to said bottom part,   maintaining said conversion temperature by causing electric discharges to occur in said vessel, in particular below said head through said substantially liquid residue,   extracting said gas from said vessel through said outlet port,   extracting a part of said liquid residue through said outlet port, such that said liquid head is maintained between prefixed minimum and maximum levels,   
       wherein:
 said steps of feeding said waste material and extracting said gas are continuous, 
 said step of maintaining said prefixed vacuum degree is obtained by said step of extracting said gas, and 
 said step of feeding said waste material into said vessel through said inlet duct is carried out under vacuum conditions within said vessel. 
 
     
     
         2 . A method according to  claim 1 , wherein said prefixed vacuum degree is comprised between one and ten absolute millibar, preferably between three and six absolute millibar. 
     
     
         3 . A method according to  claim 1 , wherein said step of feeding said waste material under vacuum conditions is selected from the group comprised of:
 feeding a loose and substantially solid waste material, forming a gas-tight plug within said duct by compressing said waste material, said plug protruding into said conversion vessel through said inlet port,   feeding a waste material packaged into rigid capsules, said capsules forming a gas-tight engagement with said inlet duct while they are pushed towards said inlet port,   feeding a liquid or a gas, or a combination thereof, under said head of liquid residues.   
     
     
         4 . A method according to  claim 1 , wherein a step of determining the level of said head is provided by ultrasonic analysis. 
     
     
         5 . A method according to  claim 1 , wherein said step of extracting a part of said liquid residue is carried out through an outlet hole of said vessel through said bottom part, a step being provided of eliminating a plug that is formed by a hardened amount of said liquid residue at said outlet hole, in particular, said plug is eliminated by withdrawing it to a prefixed extent into said vessel such that it melts and opens said outlet hole, said plug restored when said liquid head decreases down to a prefixed minimum level. 
     
     
         6 . A method according to  claim 1 , wherein said electric discharges take place in a discharge region below said head close to a plurality of conductive elements, in particular two electrodes, a prefixed voltage being established and maintained between a pair of said elements, wherein said discharges are produced with an intensity and/or a frequency responsive to said voltage. 
     
     
         7 . A method according to  claim 6 , wherein said voltage is adjusted responsive to an inlet throughput of said waste material into said vessel. 
     
     
         8 . An apparatus for transforming a waste material, said apparatus comprising:
 a vessel having a bottom part and an inlet duct that is associated to an inlet port,   a heating means for heating said vessel to a prefixed conversion temperature, and maintaining said vessel at said conversion temperature;   a depressurizing means for depressurizing said vessel to a prefixed vacuum degree, and maintaining said prefixed vacuum degree;   a waste feeding means for feeding said waste material into said vessel through said inlet duct, said waste material being thus heated to said conversion temperature, said conversion temperature being such that said waste material turns into a ionized gas or a plasma, and into a substantially liquid residue, in particular a lava, said liquid residue forming a liquid head with respect to said bottom part,   a gas extracting means for extracting said gas from said vessel   a liquid extracting means for extracting a part of said liquid residue such that said head of said liquid residue is maintained between prefixed minimum and maximum levels,   
       characterized in that said depressurizing means is adapted to maintain in use said prefixed vacuum degree within said vessel during said gas extracting, and that said waste feeding means is adapted to continually feed in use said waste material into said vessel and to create a gas-tight seal against air leakage together with said waste material. 
     
     
         9 . An apparatus according to  claim 8 , wherein said waste feeding means is selected from the group comprised of
 a loose solid waste feeding means for feeding a loose and substantially solid waste material, said material forming a gas-tight plug within said duct by compressing said waste material, said plug protruding into said conversion vessel through said inlet port,   a packed waste feeding means for feeding rigid capsules containing a waste material, in particular a solid waste material, said capsules forming a gas-tight engagement with said inlet duct while being pushed towards said inlet port,   a liquid/gas waste feeding means for feeding a liquid or a gas, or a combination thereof, below said head of liquid residues.   
     
     
         10 . An apparatus according to  claim 9 , wherein
 said loose solid waste feeding means comprises a screw having a profile that is suitable for engaging said inlet duct in such a way that said loose solid material is compressed forming said gas-tight plug when it is fed into said vessel through said inlet duct.   said liquid/gas waste feeding means comprises a duct that protrudes inside said vessel and is arranged at a level below said head.   
     
     
         11 . An apparatus according to  claim 8 , wherein said liquid extracting means comprises:
 an outlet hole of said vessel,   a plug breaking means for breaking a plug that is formed by a hardened amount of said liquid residue at said outlet hole, said means selected from the group comprised of
 a drilling means that is associated with breaking detection means, 
 a screw that is arranged inside an extraction duct, said outlet duct being arranged through a wall of said vessel, said screw being kept in a first position within said outlet duct by a plug that is formed by a solidified amount of said residue, said screw adapted to assist said extraction by rotating towards the inside of the vessel. 
   
     
     
         12 . An apparatus according to  claim 8 , wherein said vessel comprises:
 a plurality of conductive elements, in particular two electrodes,   a voltage maintaining means for maintaining a prefixed voltage between a pair of said elements of said plurality of elements, in order to generate said discharges in a region that in use is submerged by said substantially liquid residue, said discharges having an intensity and a frequency, said intensity and frequency responsive to said voltage.   
     
     
         13 . An apparatus according to  claim 12 , comprising:
 an inlet throughput detecting means for detecting an inlet throughput of said waste material in said vessel   a voltage adjustment means for arranging said voltage responsive to said throughput   
       such that a heat input associated with such discharges can be adjusted responsive to said throughput by adjusting said voltage. 
     
     
         14 . An apparatus according to  claim 12 , wherein said conductive elements are consumable electrodes, each of said consumable electrodes formed by a plurality of substantially linear elements, each of said elements having ends, in particular screwed ends that are adapted to engage with another adjacent element, wherein an electrode restoring means is provided for restoring a consumed part of said electrode, said electrode restoring means comprising:
 a positioning seat, for positioning an electrode element close to an electrode end, said extremity protruding out of said vessel   an electrode joining means for joining an end of said element to said end of said electrode,   an actuator for pushing said electrode through said wall of said vessel,   a gas-tight seal such that during said progression air leakages into said vessel are hindered.   
     
     
         15 . An apparatus according to  claim 8 , wherein a purification means is provided to remove hydrogen sulphide from said extracted gas, in particular a means for contacting said gas with a solution of ferrous oxides and/or salts.