WO2004072210A1

WO2004072210A1 - Method and plant for the conversion of solid civil and industrial waste into hydrogen

Info

Publication number: WO2004072210A1
Application number: PCT/EP2004/001411
Authority: WO
Inventors: Antonio Melloni
Original assignee: Xarox Group Limited
Priority date: 2003-02-13
Filing date: 2004-02-12
Publication date: 2004-08-26
Also published as: ITVI20030030A1; EP1597340A1

Abstract

An industrial process is described, together with the relative plant, for the thermal gasification of combustible material from waste, in the form of 'C.D.R.' or 'fluff', at zero emission into the atmosphere. The plant, which operates through a multigas plasma torch, running with oxygen-enriched air, produces hydrogen and other technical gases. The hydrogen can be used, after separation from the various gases, for the generation of electric energy through high yield systems and low harmful gas emissions, such as, for example, fuel cells or 'Turbogas', for industrial uses and/or for feeding hydrogen vehicles. The process also envisages the possibility of generating electric energy with traditional Brayton cycle gas turbines or with 'OTTO gas' groups.

Description

METHOD AND PLANT FOR THE CONVERSION OF SOLID CIVIL AND INDUSTRIAL WASTE INTO HYDROGEN

The present invention relates to a plant and the relative process for the conversion of solid civil and industrial waste into hydrogen and other technical gases, at zero emission into the atmosphere.

Processes .for the transformation of polluting or waste combustible materials into clean energy and other reusable products, have been known for some time.

The thermo-decomposition process is known, for example, of polluting combustible materials resulting from civil and industrial waste, by means of an air oxidation phase of said waste material, using the heat developing from the fumes for producing thermal and electric energy. These waste disposal techniques with energy recovery, however, have a low yield with the generation of dangerous emissions of harmful and micro-polluting substances. Various gasification methods are also known, such as, for example, those which allow the purification of raw gases produced from tar, and a method for the gasification of peat with the aim of obtaining a high gasification yield. These gasification methods, however, have also had a limited diffusion so far, due to the fact that a coherent solution has not yet been found to the problem of obtaining a high energy yield, after the elimination of the pollutants, at reasonable costs. An objective of the present invention is therefore to provide a process for the conversion of solid civil and industrial waste materials into hydrogen and other technical gases, with the highest possible efficiency and which allows a higher separation of the polluting ele- ments with respect to the known techniques, by means of an innovative dry separation technolog .

The invention therefore relates to a zero emission thermo-gasification plant, suitable for implementing the conversion process of solid civil and industrial waste into hydrogen and other technical gases mentioned above. This objective is achieved by the process for the conversion of solid civil and industrial waste into hydrogen and other technical gases according to claim 1 and a relative thermo-gasification plant according to claim 7, to which reference is made for the sake of brevity. The present invention advantageously relates specifically to a thermal gasification technology by means of a multi-gas plasma torch, operating with oxygen- enriched air, the same multi-gas plasma torch and subse- quent fume cooling system and separation of the polluting substances, with a high efficiency, until a blend of technical gases, including hydrogen, is produced.

The plant is_. capable of thermo-gasifying the C.D.R. combustible material, of the "fluff" type, deriving from solid civil and industrial waste having an overall LCP (Lower Caloric Power) in the range of 4,000-8,000 Kcal/Kg, optimal for the process .

When the above-mentioned Lower Caloric Power (LCP) is too low, the feeding material is partially dried dur- ing the grinding operations and mixed with carbonaceous material by means of a pre-mixing plant (using ground "coke", shavings of plastic or wood scraps, etc.), in order to reach the lower caloric power range,, mentioned above. The technical gases produced can be used, after separation, for industrial purposes and for the co- generation of high yield electric and thermal energy.

In this case, the objective of the process is to produce a gas having characteristics similar to "reforming gas", by maximizing, as far as is technically possible, the hydrogen H₂ fraction, to be separated downstream of the plant by means of compression and molecular ultra-filtration.

In particular, the hydrogen is separated by means of compression and molecular ultra-filtration and is partially recycled to the main flame in variable quantities according to the power to be supplied and the characteristics of the "fluff" fed; the remaining part of hydrogen (which is the majority) is used for the generation of high yield electric energy in fuel cells or in a gas turbine, for industrial use or for feeding hydrogen vehicles.

The carbon dioxide (C0₂) , produced together with hydrogen, is separated and liquefied (totally or partially) and then sold to companies operating in the field of technical gas distribution; the "fluff" type CDR fuel is obtained from solid civil and industrial waste ("SCW" and SIW") and is reduced to optimal size through grinding and sorting operations, included in a preliminary pre- treatment phase during which grinding, mechanical sieving and separation operations are effected, using currently known technologies .

If convenient and according to the plant location, the carbon monoxide (CO) can be converted to carbon diox- ide (C0₂) by adding a catalytic combustion section at 500°C, to the plant, which is obtained by injecting water vapor produced in the plant and fractionated water as combustion supporter; the carbon dioxide produced is then separated by liquefaction and sent to be reused in other industrial applications .

The gasification technology uses a burner which operates with a multi-gas plasma torch, in oxygen-enriched air, running at a high temperature (about 3, 000-6, 000°C in the flame) ; the burner exploits the ionization of a minor gas flow (plasma) , which is blended with a carrier gas (usually air) for triggering a mixture of combustible gases (usually consisting of natural gas, methane, LPG, bio-gas or hydrogen in oxygen-enriched air or pure oxygen) , whereas the plasma torch is capable of sustaining the thermal cracking reactions of the materials charged into the oven (CDR or "fluff") with a final production (as a result of the reaction chamber turbulence and high temperature of about 1,600°C) of simple technical gases (H₂, CO, H₂0 and gaseous hydrocarbons) . Oxygen is used for enriching the air as combustion supporter, produced on the spot by means of a "package" compression and air separation equipment with molecular membranes, whereas the use of air for generating plasma allows a considerable oxygen saving with respect to other technologies. Pure methane is also injected into the oven, of the static type and having a vertical, cylindrical shape, with an inlet for the products at the top and outlet of the gases at the bottom (so that the movement of the gases is directed downwards with a helicoidal motion maintained by the flames diversely distributed along the height of the oven) , for the carburetion and enrichment of the reactions.

The non-condensed residual gases deriving from the separation of the carbon dioxide and hydrogen still containing traces of carbon monoxide, residual hydrocarbons and nitrogen, can be re-injected into the gasifying oven to enrich the reactions or used as such directly in "OTTO gas" groups for the production of electric energy, or sent back to a torch.

Should the total recovery of the carbon dioxide be envisaged together with the injection of the residual gases from the separation of the carbon dioxide and hydrogen into the gasifying oven, it is possible to design the gasification plant without any stack and consequently entirely without gaseous discharges into the atmosphere (zero emission) .

When the poor gas is used in "OTTO gas" groups, for a further production of electric energy and heat in order to maximize the overall yield, there is a centralized discharge, channel of the motors characterized however by more or less zero emissions (as the gas has been purified by the high efficiency purification process) .

Finally, the quantity of electric energy produced by 5 the plant at regime is much higher than that absorbed by the plant itself, and consequently the plant, which is activated by means of methane gas, is self-sufficient from the point of view of energy; it is thus possible to transfer the excess electric energy to the local distri-

10 bution networks.

The hydrogen produced is partly recycled to the main flame (multigas plasma torch) in a quantity varying according to the power to be supplied and characteristics of the fluff being fed.

15 The final result of the process is the transformation of the C.D.R. or fluff into thermal and electric energy and into technical gases of a high commercial value, depending- on the. quantities used and. specified below.

Further objectives and advantages of the present in-

20. vention will appear evident from the following description and enclosed drawings (figures 1-4), provided for purely illustrative.and non-limiting purposes, which, represent an overall flow scheme of the process and plant for the conversion of solid civil and industrial waste

25 into technical gases., according to the present invention. With reference to the above figures, these illustrate a series of process phases as follows: storage of the material to be fed, grinding and separation; - actual gasification and refining of the gas; energy recovery by means of thermal exchange; forced dry purification of the gases; catalytic combustion of the carbon monoxide into carbon dioxide; - separation of the carbon dioxide and H₂; thermo-electric cogeneration; extraction, collection and recycling of the slag. The accessory plants are indicated only for informative purposes on the enclosed flow schemes, as they are produced in package units with technologies already existing in the state of the art; we would simply like to point out that it is possible to introduce enhancing technological variations (not determinant for the functioning of the technology) , which can be specified each time, after indicating the exact technological and chemical composition of the waste materials at the inlet.

In general, the waste products which can be adopted in the plant, whose composition must be known, can be: - solid urban waste (SUW) or similar; - solid industrial waste (SIW) of a varying nature; - wood scraps (shavings, broken panels, etc.);

- plastic scraps;

- agro-zootechnical liquid manure;

- mineral or vegetable oils, fats, etc. (in specific tanks) ;

- rubbers, polyurethanes, etc.

The basic plant described in the present invention is dimensioned, it being unadvisable to have too small a size, for treating 120 t per day approximately of C.D.R. of the fluff type with a project humidity at the inlet of the oven equal to 10% by weight; the C.D.R. or fluff is obtained from SUW or SIW having an initial weight relative humidity referring to the waste matter as such varying from 20% to 40% by weight (with an average value equal to 30%) .

The initial humidity of the waste matter at the inlet is partly reduced naturally during the subsequent grinding and separation operations, and partly when charging into the oven, by means of microwave sources, so that the humidity value of the fluff at the inlet of the gasifier is brought to 10% by weight (project value) .

With fluff having a high caloric power, such as that, for example, deriving from plastic waste scraps, it is possible to operate with a higher humidity at the in- let, with a consequent saving of electric energy and oxy- gen.

The fluff or C.D.R. obtained from the waste matter can be enriched with carbonaceous combustible fractions to increase the PCI caloric power and make it correspond exactly to the plant project data and for this purpose there is a dosage and pre-mixing plant of organic- carbonaceous fractions.

The material at the inlet is brought to the ideal size for correct charging into the oven, said size corre- sponding to a particle size of 0-30 mm, by means of two- step grinding operations and subsequent sorting; furthermore, coal, wood scraps and/or scraps of a plastic nature can be added to the fluff.

The process pretreatment plant according to the in- vention is schematically illustrated in figure 1, which indicates with 1 a storage warehouse with a multi- compartment pit.

It should be noted that the capacity of the machinery is exuberant as the pretreatment plant operates for one daily shift only, storing the excess product awaiting gasification, for the other two shifts; the machines of this section, moreover, must have a considerable dimensional margin to be able to function without mechanical problems . The means, generically indicated with 4, for trans- porting and transferring the waste material as such have access to the multi-compartment storage pit 1, which is divided into compartments by means of various double- inlet access tunnels, to prevent odours being released during the discharge phases.

The jack 2 lifts the waste material according to necessity and feeds it to the hopper 3 of the twin-step grinding system generically indicated with 5.

The first grinder 5A is of the rotating knife type, whereas the second grinder 5B can he of the knife or hammer type, depending on the type of waste matter being fed and according to the detail data to be verified each time.

After the grinding phase, the material passes on a series of conveyor belts 7 equipped with magnetic belt separators 6 of the iron parts (2%-3% by weight) and induced current separators 8 for aluminous and non-ferrous conductor metal materials; the ferrous and aluminous materials separated are then removed by secondary transver- sal conveyor belts 7A and loaded into the relative containers which are periodically sent to the recovery plants.

The rest of the product (separated from, the iron and aluminum) is dropped onto the belt 9 of the ballistic separator 8A of the heavy parts (glass and non-gasifiable inert materials) ; the heavy parts are dropped onto the conveyor belt 7B, which sends them to the recovery container of inert products.

The remaining material falls into the feeding hopper 9A of the vibrating screen 10, which separates the fine fluff fraction from the large fraction, which is recycled to the head of the grinders 5A, 5B; the appropriately sized material is removed by a vibrating conveyor belt (vibro-extractor) 7C, which collects and doses the sieved material and feeds the pneumatic loading system 11 of the storage silo.

The sieved material pneumatically transported, is separated by means of a separator cyclone 12 and loaded into the daily storage silo 21; a screw or "redler" con- veyor can be used instead of the pneumatic system, depending on the type and specific weight of the material to be loaded.

The large/dry fraction is recycled upstream of the grinding system by means of secondary conveyor belts 7D and undergoes a further grinding process.

The silo 21 has the function of daily accumulation and is suitable for feeding the gasifier for 1 day. The uniformly sized material is extracted from the silo 21 at a constant flow-rate, by means of the silo extraction system, which comprises an extractor with a rotating bot- torn 15 and a vibro-extractor 13, whose belt feeds the feeding hopper of the plough mixer 16 for loading the rotating mixing drum 14.

The rotating mixer 14 discharges the mixed and ho- mogenized product into the feeding hopper of the Archimedean screw 23 which lifts the product to the gasifying oven; the screw 23 has microwave lamps along its development for pre-drying the product on-line.

The coal and wood and plastic scraps (for the possi- ble enrichment of the fluff) are stored in the relative compartments of the accumulation pit or pits 1, which are situated in the same multi-storage building.

The bucket-shaped jack 2 of the "multi-compartment" storage pit 1 intermittently lifts the coal or various materials of a carbonaceous nature from the relative holds and loads the feeding hoppers 28 (figure 2) , equipped with a level control and vibro-extractors at the bottom, with an extraction screw 28A, with plastic material, wood shavings or coal, respectively. The flow-rate of the extraction screws 23, 28A can be adjusted, by varying the revs, controlled by the pulverizer regulation system of the carbonaceous products, indicated with 29 in figure 2; the screws 23, 28A load the various carbonaceous materials in the right quantity onto a series of conveyor belts which feed the feeding hopper 29A of the pulverization system of the carbonaceous materials 29, equipped with a level control, driven by a computerized control system, such as a PLC.

The pulverized carbonaceous material falls onto the feeding belt 30, which feeds the suction inlet of the pneumatic conveyor ventilator 31; the powder is then conveyed upwards by means of the pneumatic conveying duct and is then separated by means of the separator cyclone 12A and discharged into the vertical loading chamber of the reactor, into which it enters through two stellar feeding valves N positioned in series.

Between the two stellar valves N there is an inter- chamber 32 which is inertized by the flushing of carbon dioxide (C0₂) . The carbonaceous powder having a suitable particle size, charged into the reaction chamber contributes both to completing the chemical reactions which produce hydrogen and also to a pre-purification of the polluting substances which are absorbed by the surface layer of the powder itself, which is subsequently withheld by the filtration devices .

The loading system of the gasifying oven 34 comprises a slanting Archimedean screw for lifting the ground product, with a microwave drying system, an upper feeding hopper, a push loading system for feeding the loading pit, a loading pit with an inert interchamber and servo-activated double clapet valve, a lower feeding hopper of the loading screw, a loading screw of the oven, cooled with water. In particular the slanting screw 23, used for lifting the ground product to the gasifier 34, is equipped with various microwave emitting devices 27, distributed along the length, for the on-line drying of the product, if necessary, until reaching the project humidity rate; in addition, in order to facilitate the drying, a certain quantity of hot air is circulated inside the screw 23.

The above screw 23 loads, with a constant flow-rate, the upper hopper 33A of the push feeding loader 33 of the oven, which is positioned above and causes the product to advance with an alternating cycle, pushing the material into the vertical feeding pit 33B of the oven 34, equipped with two clapet valves 33C for air sealing against the inlet.

The intermediate chamber of the pit 33B, situated between the two clapet valves 33C, is further flushed with carbon dioxide (C0₂) , which is heavier than air.

The valves 33C open and close one after another, immediately after the pushing cycle of the loader 33 is completed, in order to prevent the inlet of external air. The loaded fluff drops into the intermediate chamber of the loading pit 33B of the oven, situated directly above the feeding screw 33D of the gasifying oven 34, cooled with water, in order to prevent excessive heating and the pre-melting of the material during the loading phase; the level of the hopper of the screw is regulated by means of level regulators with rotating flaps .

The material is charged at a constant flow-rate and falls by gravity onto a rotating distributor 33F, also water-cooled, which distributes the product inside the gasification chamber of the oven 34.

At the nominal loading rate of the screw 33D, the gasifying oven 34 has a continuous effective thermo- destruction capacity of fluff equal to 4000 Kg/h referring to dry solid water matter (including the carbona- ceous material possibly added) .

A vertical cylindrical oven 34 is preferably used, static and adiabatic, perfectly insulated and internally coated with refractory material with the multi-layer technique, suitable dimensioned according to the effec- tive thermo-destruction capacity.

The material, charged from above in a suitable size, falls by gravity and passes through the jets of a first row of hydrogen-air-oxygen or methane-air-oxygen plasma flames, at a high rate, which are arranged tangentially in the vertical gasification chamber of the oven 34. The material is therefore enveloped by the rapid stream of high temperature gases (about 1600 °C) produced by the plasma torches, which are situated at various levels and are divided into several regulation areas, and acquires a vortical helicoidal downward movement, consequently there is a very high contact time inside the chamber.

Pure methane gas which acts as fuel for the chemical reactions, is also injected into the upper head of the oven 34, by means of special nozzles and in several points; the quantity of enriching pure methane gas can vary according to the composition of the waste material being fed and, in some cases, can also be reduced to zero

(high caloric power fluff) . Fractionated water is also injected at different heights, in specific quantities, which is necessary for sustaining the endothermic gasification chemical reactions; the injection of water is effected by means of special fractionation spears, inserted through refractory blocks, with sealing connections.

The oven is maintained by the regulation system under conditions of slight overpressure, regulated in continuous and automatically, in order to prevent any entrance of external air and, at the same time, to avoid putting the chamber under pressure, which in any case is capable of tolerating the project overpressures. The endothermic reactions cause cooling of the gas which passes from 1600°C to about 1200°C at the outlet of the oven 34. The heat power necessary for feeding the endothermic reactions is obviously supplied by the plasma torches situated at various levels and subdivided in different temperature regulation zones.

In this way, the fluff is thus transformed into gas. The vitrified infusible scraps fall onto the bottom 34A of the oven 34, which is basin-shaped (filled with water and with hydraulic sealing) and are extracted by means of a rake 34B (of the "Redler" type) and discharged into the scrap recovery container 45, situated on the outer side of the gasifying oven 34, which is periodically substi- tuted.

The gases leave the gasifier at 1200°C, along the line 36A, and are sucked through a post-heat exchanger 36, whereas the scraps are conveyed to a scrap treatment plant where they are subjected to further crushing by means of a hammer mill, separated according to the particle size and put on sale as inert material.

The gas leaving the gasifier has a similar composition to a water gas, containing H₂, CO, H₂0, as well as residual N₂, deriving from the air and various polluting gases; furthermore, in the outgoing gas there* are also traces of secondary hydrocarbons among which methane (CH₄) .

The pollutants mainly consist of acid gases (HC1, HF, S0₂) , as well as NO_x and various metallic oxides, in the form of powder in suspension.

At the outlet of the gasifying oven 34, the gas enters tangentially (line 36A) into a vertical adiabatic reactor 35 for refining the ^• reactions, perfectly insulated and internally coated with refractory material, in which it moves upwards with a helicoidal movement.

Coal powder (or powder of other carbonaceous materials) produced in situ by means of a pulverization plant, is injected, if necessary, into the reactor 35; as an alternative to powder, pulverized wood scraps obtained from wood scraps or shavings, can be used if available. The coal powder or pulverized wood material, having an adequate particle size, falls downwards into the reactor 35 in countercurrent with respect to the gas, which flows upwards, and reacts with the overheated vapour, present in the gas itself, and with fractionated water which is injected, at a temperature of about 1200°C, producing additional carbon dioxide (C0₂) and hydrogen according to the typical water gas reactions which take place spontaneously over 1000°C (enrichment phase of the hydrogen fraction) . The fractionated water injected into the reactor can be supplied to the plant in the form of lurid water or polluted aqueous solutions, or it can be taken from the recovery tank of condensed products. The gas, thus further enriched with hydrogen, leaves the upper part of the reactor 35.

Downstream of the reactor 35, there is an energy recovery section, consisting of a post-heat exchanger, a high efficiency multicyclone and a boiler for producing overheated vapour.

The post-heat exchanger 36 is an exchanger of the concentric radiant type and consists of two large concentric cylinders made of Nickel-Chromium alloy, having an adequate thickness. The gas leaving the enrichment reactor 35 is sent downwards through the internal cylinder of the post-heat exchanger 36; the gas already purified (line 36B) which comes from the tail of the plant and which must be preheated at the outlet from room temperature to 180°C in order to enter the catalytic reconversion step of carbon monoxide to carbon dioxide, passes, in countercurrent (therefore upwards) , in the air space between the two cylinders .

The purpose of the post-heat exchanger 36 is to brusquely cool the gases from about 1050°C (outgoing tem- perature from the enrichment reactor 35) to about 900°C (optimal ingoing temperature to the boiler) .

Before being immersed in the boiler, the gases leaving the post-heat exchanger 36, cooled to about 900°C, pass into a multicyclone 38, consisting of two vertical parallel cyclones internally coated with anti-acid refractory material and running under heat, where they are subjected to a strong vortical movement to deposit the larger particles which are entrained into the reactor 35. The large-sized powder withheld by the multicyclone

38 forms about 50÷60% by weight of the particulate in suspension.

The atomization chamber (situated in a widening of the pipe) of the first additive (in the gas inlet zone) , is positioned at the inlet of the multicyclone; the additive is stored in aqueous solution in the tank 38A and is pumped by a specific pump at the service of the injection spear.

The additive is injected in the form of a spray, at a flow-rate accurately dosed by means of a potenziometric regulation system, for the reduction of the nitrogen oxides, allowing it to come into close contact with the polluting substances, due to mixing with the gases, effected by means of static mixers 37; the gas then enters the multicyclone 38, where it undergoes a first depul- verization.

Two air-tight stellar valves (for each cyclone) 88, 89, are situated below the multicyclone 38, in the cold area, and operate in series for discharging the powders. The inter-chamber 90, situated between the stellar valves 88, 89, is inertized with gaseous carbon dioxide produced by the plant.

The gases leaving the multicyclone 38 and post-heat exchanger 36 (lines 38B and 38C, respectively) enter the "membrane-walled" boiler 43 for the production of overheated vapour at 42 bar and 420°C (figure 3) .

The heater 43 has an empty rectangular section, with a double passage for the gases inside, an inlet from above and U-run (first downwards and then upwards) , in order to favour the depositing of the powders in the bottom hoppers 43A, served by the "Redler" 55, with a liquid seal, which discharges the powders into a metallic container 55A.

The gases leave the top and pass into an overheater 43B, from which they leave at about 450°C and enter the economizer (Tailend) of the boiler 43, from which they exit at a temperature of about 250°C.

The walls are equipped with an automatic "hammer" shaker system to favour the detachment of the powders from the walls causing them to fall into the lower col- lection hoppers 43A.

The boiler 43 produces overheated vapour which is only partly used for the production of secondary electric energy, by means of the two-step turbine 52 for over- heated vapour; a part of the vapour is extracted from the first conversion step of carbon monoxide to carbon dioxide, for the initial saturation of the gas.

The sensitive heat recovered from 900°C to about 200°C is equal to about 1,900,000 Kcal/h and is suffi- cient for the production of 2.4 t/h of overheated vapour at 42 bar and 420°C, which is partly used, as already mentioned, for the production of additional electric energy (about 400 electric Kw at the terminals) , by means of the turbine 52, and partly (about 400 Kg/h of vapour extracted from the first step) for increasing the H₂0/CO ratio at the inlet of the carbon monoxide conversion steps.

At the outlet of the Tailend of the boiler 43, the gases enter the "dry" purification system. The gas purification is effected with a completely "dry" technology, following the steps of a dry reaction chamber or reactor, or a filtration system, a suction ventilator of the gases and a series of active carbon filters. The reaction chamber 44 consists of a vertical, in- sulated stainless steel tank having a volume which is such as to guarantee the residence of the gases for a time exceeding 2 seconds; the gases enter from above with a tangential inlet and move downwards with a helicoidal movement, subsequently effecting a U inversion and rise upwards through the central cylinder, leaving from the upper part.

Two reagents in powder form, such as bicarbonate and activated carbon, are injected into the gas inlet area; the bicarbonate is stored in silos 541 and is ground in situ using a mill 54, and is subsequently injected by means of the relative blow fan 545 and injection micro- screw, whereas the activated carbon is stored in sacks, discharged by means of a vibrating sack discharger and injected directly by means of respective blow fan (pneumatic transport) and injection micro-screw.

On the bottom of the chamber 44 there is a conical hopper 52 for collecting the powders and two air-tight stellar valves 56, 57, placed in series, for discharging the powders.

The filtration system operates according to a "dry" process and envisages the use of a high efficiency filter 45 with sleeves 45A.

The sleeve filter 45 is, in particular, of the pulse-jet type and the cleaning of the sleeves 45A is therefore effected by means of pulses (shots) of compressed gas (inert) injected into the sleeves 45A in countercurrent with the gases; the sleeves 45A, as a result of the shots, swell at pre-selected time intervals causing the detachment of the mat of powder deposited, which falls into the underlying hoppers 63.

The inert gas necessary for the pulses (shots) is sucked in derivation, using a small gas compressor, from the carrier pipe of the purified gas, in a point down- stream of the purification system, after leaving the activated carbons .

In this way, the gas used for the shots is already completely purified.

The filtration degree is extremely high and the out- going powders are practically equal to zero.

The gases leave the depulverization filter 45 at about 150°-180°C, as they are cooled naturally starting from 200°C, due to the heat dispersions through the non- insulated pipes and the structures of the filter (only partly insulated) .

Immediately after being discharged from the sleeve filter 45, the gas undergoes a first intermediate cooling from 180°C to the project temperature of 30°C through the vertical tube-bundle heat exchanger 93, by means of icy water containing glycol at 5%. The exchanger 93 is protected from particles of dirt as it is situated downstream of the filtration system and uses icy water generated by a first external freezing tation 93A, whereas the freezing gas used is preferably Freon R13 (in a closed circuit) .

After cooling to 30°C, the gases are sucked through activated carbon filters 47A, 47B which have the function of withholding the residual traces, mainly NO_x and S0₂, which have passed through the purification system and conversion system, to provide the required purification degree.

At the same time, other residual pollutants present in a smaller concentration are also absorbed.

The two filters 47A, 47B, of the activated carbon type, the same and situated in parallel (one of which is therefore always in stand-by) consist of two air-tight inox sheet tanks having a parallelepiped shape, in which there are vertical cartridges (plugs) , made of inox sheet, perforated and filled with activated carbon having a suitable size; the system allows the exhausted cartridges of one filter to be substituted when the other is functioning.

The duration of the cartridges is extremely high, thanks to the fact that the filters 47A, 47B are situated downstream of the dry purification system, which has al- ready effected the first purification.

At the outlet of each activated carbon filter (47A, 47B, there is the relative pocket filter to prevent en- trainment of the fine carbon powder. The gases, completely filtered and purified, are then sucked (after the action of the activated carbon filters 47A, 47B, which operate in depression and at a temperature close to room temperature) by the tail ventilator 55, with a high prevalence and at the theoretical temperature of 30°C (in any case close to room temperature, following the various natural cooling steps in the pipe) , and are sent to the post-heat exchanger 45A, from which they leave at 180°C to be sent to the catalytic conversion system consisting of columns of catalysts 49, 50, 51.

The flow-rate of the suction ventilator 46 is regulated in continuous by a motorized valve which keeps the pressure conditions constant inside the gasifier 34.

The gases, in the inlet zone of the first catalytic conversion step, are saturated by means of overheated vapour injection produced by the boiler 43; the temperature of the gases can therefore rise to 280°C (project temperature at the inlet of the first catalytic conversion step) and is mitigated by means of the fractionated water injection system, in order to regulate the H₂O/CO ratio for entering the catalytic conversion system. If the catalytic conversion system of carbon monoxide to carbon dioxide is not envisaged, the gas is sent directly to the final cooling step. After pre-saturation, effected with overheated vapour, the gas is blown through the conversion system of carbon monoxide to carbon dioxide, which is situated on the supply pipe of the blow ventilator 55 and which consists of various vertical towers situated in series: - a first conversion tower 49 on catalysts of copper oxide and ferric oxide (CuO-Fe₂0₃) , with inlet of the' gases at 380°C and outlet at 450°C approximately;

- a first quench tower 50 with cooling to 180°C;

- a second tower 49 of Copper-Zinc-Alumina catalysts with heating from 180°C to 250°C;

- a second quench tower 50 with intermediate cooling to 180°C;

- a third tower 49 of Copper-Zinc-Alumina catalysts with final heating of the gas from 180°C to 290°C; - a third dry-bottomed quench tower 50 with final cooling of the gas to 180°C.

The mixture of gases produced leaves the catalytic conversion system at 280°-290°C and then passes into the vertical final cooling column 51, where it is subjected to a cooling and separation process; this process co - prises the following phases:

- cooling of the stream of gas to a temperature of 10- 15°C, below the dew point of the gas, to effect the forced extraction of the condensed water, which is en- tirely recovered by means of the drain-piping system 51A of the plant and sent to the collection tank of the condensed products 74;

- compression and separation of the hydrogen at 6 absolute bar and molecular ultrafiltration (the hydrogen is separated by molecular ultrafiltration and is then sent to the storage tanks 84, of the nickel iodide filled type, at a pressure of 6 absolute bar, figure 4) ;

- forced cooling of the residual gas (at 6 absolute bar) to -40°C to effect the liquefaction and recovery of the pressurized carbon dioxide, which is subsequently sent to the liquid storage tank (maintained at a low pressure) .

The freezing power necessary for the two cooling steps indicated above is supplied by two external freezing stations, connected to the exchangers situated inside the cooling tower 77 (figure 4) , which operates with Freon R13 or R14.

A first zone of the freezing station effects a first cooling phase of the gas from 280-290°C to about 10-15°C, with an installed freezing power of 1,400,000 Fr/h; this station is connected to a vertical tube-bundle exchanger made of austenitic steel with icy water circulation (external freezing fluid) , and has an overall installed electric power of 600 Kw.

A second zone of the freezing station has a freezing power lower than 200,000 Fr/h, at the maximum; the cooling is obtained by passing the compressed gas at 6 absolute bar into a heat exchanger of the concentric coil type with closed circuit circulation of liquid carbon dioxide (external freezing fluid) , taken from an atmos- pheric carbon dioxide storage tank 79.

The carbon dioxide is maintained in circulation by the circulation pump system and is cooled in a closed circuit by a third Freon (R13 or R14) freezing station, which has an installed electric power of 200 Kw and a nominal freezing power of 571,000 Fr./h, whereas the absorbed electric power is equal to 130 Kw, including the circulation pumps.

The only consumption consists of the electric energy consumption necessary for the compression, which is sup- plied by the electric station of the plant. The residual gas, containing traces of carbon monoxide and various light hydrocarbons, in addition to residual N₂ of the feeding air, is stripped at the top of the cooling tower 77 by means of a secondary compressor and sent to the torch. The final result of the process, if applied integrally, consequently consists in the separation of the H₂ (by means of the fractionation block 80) and C0₂ (which is drawn, by means of the valve 82, from the tank 81 to be sent to the recovery devices 83) , one being destined for the production of electric energy and the other for industrial application.

The first zone of the cooling tower 77 has the function of cooling the fumes from 290°C to a temperature of about 10-15°C.

The heat is subtracted from the gas by means of a concentric coil heat exchanger 93 made of inox pipe and the circulating icy water cools it from 8 to 4°C.

The installed freezing power is such as to allow a wide cooling margin of the gases from 290°C (maximum temperature at the outlet of the conversion system) to a temperature of 10-15°C, below the dew point, and consequently almost all the water content of the gases is condensed; the condensed product is recovered by means of a piping system in the plant collector 69.

The characteristics of the process and plant for the conversion of solid civil and industrial waste into hydrogen and other technical gases, object of the present invention, are evident from the above description, as also the advantages. Finally, numerous other variants can obviously be applied to the process and plant in question, without being excluded from the novelty principles of the inventive concept. It is also implicit that, in the practical embodiment of the invention, the materials, forms and dimensions of the details illustrated can vary according to the demands and can be substituted with other technical equivalents.

Claims

1. A process for the conversion of solid civil and industrial waste into hydrogen and other technical gases, characterized in that it comprises the following phases: - storage of the material to be fed, grinding and separation; gasification of said matter and refining of the gas; energy recovery by means of thermal exchange; forced dry purification of the gases; - thermo-electric cogeneration; extraction, collection and recycling of the slag.

2. The conversion process according to claim 1, characterized in that it further comprises a catalytic combustion phase of carbon monoxide into carbon dioxide for the separation of carbon dioxide and hydrogen, wherein the hydrogen is separated by means of compression and ultrafiltration and is partly recycled to the gasification phase.

3. The conversion process according to claim 2, charac- terized in that part of the hydrogen is used directly in fuel cells for the production of high performance electric energy or in a gas turbine.

4. The conversion process according to claim 1, characterized in that the material being fed can be partially dried during the grinding operations and subjected to mixing with carbonaceous material by means of a premixing plant, should it have a lower caloric power less than a pre-established quantity.

5. The conversion process according to claim 2, charac- terized in that the carbon dioxide produced is, at least partly, separated and liquefied, and sold to companies operating in the technical gas field.

6. The conversion process according to claim 2, characterized in that the residual gases deriving from the separation of carbon dioxide and hydrogen still containing traces of carbon monoxide, non-condensable residual hydrocarbons and nitrogen are additionally used during the gasification phase, in order to enrich the reactions or used as such directly in "OTTO gas" groups for the production of electric energy or sent to a torch.

7. A plant for the conversion of solid civil and industrial waste, of the type comprising:

- at least one storage warehouse (1) ,

- means (4) for transporting and delivering the waste; - means (2) for moving and feeding the waste material to a loading hopper (3) of a grinding system (5) ; first separating means (6) of the ferrous and aluminous parts; first conveying means (7, 7A) of said ferrous and aluminous parts to recovery containers; - second separating means (8A) of heavy parts;

- second conveying means (7B) of said heavy parts to recovery containers;

- further separating means (9A, 10) of the fine and large fractions of the remaining material;

- collection and loading means (7C, 11) of the material into a collection silo (21) ;

- extracting means (13, 15) , which feed a mixing hopper (16) ; and - loading means (23, 27, 33, 33A, 33D, 33F) of a gasifying oven (34) , characterized in that said gasifying oven (34) comprises at least one burner, which uses at least one multigas plasma torch in oxygen-enriched air, functioning at a high temperature.

8. The conversion plant according to claim 7, characterized in that said burner exploits the ionization of a plasma, which is mixed with a carrier gas for activating a mixture of combustion supporting gases, said plasma torch being capable of sustaining the thermal reactions of the material charged into the oven (34) .

9. The conversion plant according to claim 7, characterized in that said gasifying oven (34) is of the vertical cylindrical type, static and adiabatic, perfectly in- sulated and internally coated with refractory material with the multi-layer technique.

10. The conversion plant according to claim 7, characterized in that said plasma torches are arranged tangen- tially inside a vertical gasification chamber of the oven (34) , on different levels and divided into various regulation areas.

11. The conversion plant according to claim 7, characterized in that pure methane gas, which acts as a fuel for the chemical reactions, is injected., in several points, inside said gasification oven (34) , maintained under slight overpressure, together with fractionated water, necessary for sustaining the endothermic chemical reactions for transforming the material fed into gas .

12. The conversion plant according to claim 7, charac- terized in that it comprises, downstream of the gasifying oven (34), at least one adiabatic reactor (35) for refining the reactions, in order to obtain an enrichment of the hydrogen fraction in the gas, and an energy recovery section, consisting of a high efficiency post-heat ex- changer (36) for the brusquely cooling of the gases, a high efficiency multicyclone (38) for the depositing of the larger particles and a boiler (43) for the production of overheated vapour.

13. The conversion plant according to claim 12, charac- terized in that said boiler (43) is of the rectangular section type, empty, with a double passage of the gases inside, inlet rom above and U-run, in order to favour the depositing of the powders in the discharge hoppers (43A) of the powders deposited.

14. The conversion plant according to claim 12, characterized in that said boiler (43) produces overheated vapour, which is partly used for the production of secondary electric energy, by means of a two-step turbine (52) for overheated vapour, part of said overheated vapour be- ing further drawn from a first conversion step of carbon monoxide to carbon dioxide, for the initial saturation of the gas.

15. The conversion plant according to claim 12, characterized in that downstream of said boiler (43), there is a gas purification step comprising a dry reaction chamber (44) , a filtration system (45, 45A) , a series of activated carbon filters (47A, 47B) , a suction ventilator (55) of the gases and suitable means for sending the filtered gases to a post-heat exchanger (45A) and to a final cooling and separation step (51) .

16. The conversion plant according to claim 15, characterized in that said gases, when leaving the post-heat exchanger (45A) , are sent to a catalytic conversion system comprising a series of catalyst columns (49, 50, 51), in order to convert the carbon monoxide into carbon diox- ide.

17. The conversion plant according to claim 15, characterized in that said final cooling step (51) comprises first means for cooling the stream of gas below the gas dew point, in order to effect a forced extraction of condensed water, which is entirely recovered by means of a - drain-piping system (51A) of the plant, means for the compression and separation of the hydrogen and means for the molecular filtration of the hydrogen, second means for the forced cooling of the residual gas, for effecting the liquefaction and recovery of the pressurized carbon dioxide, which is then sent to a storage tank.

18. The conversion plant according to claim 17, characterized in that it also comprises compressors for the stripping of the residual gas, containing traces of carbon monoxide and various light hydrocarbons, at the top of a cooling tower (77) and means for sending said residual gas to said plasma torches.

19. A process and plant for the conversion of solid civil and industrial waste into hydrogen and other technical gases as substantially described and illustrated in the enclosed drawings and for the purposes specified herein.