Description:The present invention shall now be described in detail with the help of drawings and flow diagrams. It is to be understood that several variations are possible around the inventive concept of the present invention and the detailed description of the preferred embodiment should not be construed to limit this invention in any way.
The present invention stems from the industrial need to have a process invention of economic significance and technical advance w.r.t management of spent pot lining, hereinafter abbreviated as SPL (130), a hazardous waste. Figure 4 shows a first step of painstakingly breaking SPL (130) to removable size of 400 to 500 mm long pieces. The present invention aims at producing carbonaceous fuel therefrom, for industrial furnace while at the same time attempting to cautiously treat the corresponding hazardous industrial waste and reduce adverse impact on environment besides humans. The utilization process involves safe transportation, storage and processing, improving upon basic guidelines of Central Pollution Control Board (CPCB). It is to be understood that the challenge lies in economics of the process while making sure that the extraction of hazardous part form SPL (130) is consistent and as much cleaner as possible within industrial challenge and beyond statute!
The present invention exploits ground information of India that SPL (130) samples from Indian industry exhibit the following contents:

Normally, in context of aluminum smelting, "1st cut" and "2nd cut" refer to two main fractions of spent pot lining (SPL), a hazardous waste product. The 1st cut is the carbon-rich fraction, primarily consisting of graphitized cathode blocks and sidewall blocks, while the 2nd cut is the refractory fraction containing aluminosilicate bricks and other materials.
1st Cut (Carbonaceous):
Composition: Primarily graphite, with some silicon carbide and other carbonaceous materials
2nd Cut (Refractory):
Composition: Mainly aluminosilicate refractories, insulating bricks, and other non-carbonaceous materials.
Origin: From the lower part of the pot lining and other refractory materials used in the electrolysis cell.
In the present invention, both SAMPLE-1 and SAMPLE-2 in the table above are samples from SPL block of the first cut.
SAMPLE-3 is broken powder of SPL, while SAMPLE-4 is mixture of all the above.
Therefore, the 1st and the 2nd samples are pertinent for the present inventive process, while 3rd and 4th samples are illustrative of ideal sampling; as presently, the industrial process may not be worthy of value generation.
Cyanide and fluoride as found in SPL (130) make it hazardous and need to be converted into safe chemical compounds in the most economical manner.
Figure 3A-3B lays an economical process details of the present invention and includes key processing time for blending and thermal reaction in thermolyzer for a typical 1000kg input of SPL. The description here below explains Figure 3A in particular comprising an economical simultaneous reaction set-up (100) wherein at least five chemical reactions take place within a narrow range of temperature between 200 degrees C and 350 degrees C. The simultaneous reaction set-up (100) carries out the steps of :
- Reducing of SPL (130) in particle size less than or equal to 10mm
- Homogeneous mixing of constituents in a high viscosity form
- Consistent reaction of complete volume of reactants
- “No-moisture” or moisture-less discharge of non-hazardous exhaust and flue gases
in an economical manner.
The spent pot lining materials is transported in covered transport vehicle and stored in covered shed (110) with concrete floor and with heighted side walls in conformance to CPCB guidelines.
Figure 3B lays steps of handling pollutants as outcome of the inventive process, as per CPCB guidelines as known and is therefore not explained in details.
Figure 1, 2, the set-up (100) comprises a blender (111) and a thermolyzer (101) combination fed by a serial arrangement of crusher (121) followed by a pulverizer (125) in a loop arrangement with a vibro screener (127). The vibro screener (127) is a vibrating sieving arrangement that prevents shifting and crossing over of particles bigger than a prescribed sieve size, which is 10mm in the present set-up (100). Such bigger particles undergo pulverizing process again. The thermolyzer (101) comprises a securely closed chamber equipped with a plurality of heating burners and precise temperature control all around its inside. A spill-proof trolley (107) moves in and out of the thermolyzer (101) on a track (108).
A pre-processing step reduces input SPL (130) received in size widely varying from 200-500 mm linear dimensions to below 10 mm in a closed condition. Such reduced size SPL (130) is termed here as pulverized SPL (130).
In a preparation step, the pulverized SPL (130) is transferred to the blender (111) wherein additives such as lime (140), dolomite and clay in powder form are added to the pulverized SPL (130) for a subsequent plurality of chemical reactions in the thermolyzer (101). To facilitate a uniform chemical reaction, it is important that requisite amount of lime (140) is present around each pulverized SPL (130) granule in a stationary manner so that participation of reactants in the chemical reaction gets requisite surface area as well as time to complete the reaction. This is inventively achieved by “wetting” the pulverized-lime mixture with atomized water, produced by extra-fine spray nozzles used for pressurized water, and particularly by avoiding use of rotary kiln, which would have thrown away the lime particles due to centrifugal force of rotation. A minimum volume of water fragmented into maximum number of water particles which are as small as molecularly possible to add to active surface area of the reactants injected in the blender (111). Effect of this step can be visualized by Figure 5 wherein lime (140) is seen temporarily clinging to the pulverized SPL (130) consequent to adhesion of atomized water to pulverized SPL (130). As can be understood from weights of reactants/inputs shown in Figure 3A, less than 0.8% water by weight, with respect to weight of inputted SPL (130), is required to achieve this prudent and inventive effect. Prudent mobility imparted to lime-SPL particles by virtue of viscosity ensures exposure of maximum active area for maximum time.

Such prepared SPL (130)-lime mix is then laid with a maximum exposed surface area in the spill-proof trolley (107). Towards this objective, the spill-proof trolley (107) is mechanically fabricated in multi-tier form, step form, or laid with lesser material in order to ensure complete chemical reaction involving most volume of the pulverized SPL (130)-lime mixture. The spill-proof trolley (107) is then temporarily parked in the thermolyzer (101) for a prescribed time.
In a heat treatment step, the closed chamber of the thermolyzer (101) is pre-heated to a temperature of 200 degrees C when the spill-proof trolly (107) enters the chamber. The temperature is increased and adjusted till an equilibrium temperature of 350 degrees C is achieved.
At 200 degrees C, cyanide ions, comprising largely of sodium cyanide, besides other group IA and IIA metals of the periodic table, including Lithium, Potassium, Magnesium, start breaking down and produce carbon dioxide and nitrogen dioxide as per the following generic chemical equation:
CN- + (1+0.5x)O2 → CO2 + NOx

Ions of CN in presence of oxygen produce oxides of nitrogen, represented by NOx, specifically, nitric oxide (NO) and potentially nitrogen dioxide (NO2). This process is an important aspect of the present invention to be cautious formation of NOx, a group of air pollutants
Following understanding is also key to the present invention:
● Fuel-bound NOx:
When a fuel containing nitrogen (like coal, oil, or natural gas) burns, it can lead to the formation of intermediate substances like HCN and CN. These intermediates then react with oxygen (O2) to produce nitric oxide (NO).
● NOx Formation:
The reaction between CN and O2 (and other similar intermediates) produces nitric oxide (NO), which is a component of NOx. NO can further react with oxygen in the air to form nitrogen dioxide (NO2), another component of NOx.
● Importance of CN:
CN is one of the intermediates involved in the fuel-bound NOx formation process.
● Other Sources of NOx:
Besides fuel-bound NOx, NOx can also be formed by direct combination of atmospheric nitrogen and oxygen in high-temperature combustion zones, a process known as "prompt NOx".
In summary, reaction of CN (or similar nitrogen-containing compounds) with oxygen (O2) during such processes is a significant contributor to the formation of NOx, particularly nitric oxide (NO) (according to the European Environment Agency) and other nitrogen oxides. Thus such unwanted products of chemical reactions involved need to be handled simultaneously as per CPCB guidelines.

As the temperature rises to 300 degree C, lime breaks down leachable fluoride from Sodium fluoride, besides other group IA and IIA metals of the periodic table, including Lithium, Potassium, Magnesium, to form stable and non-leachable Calcium fluoride as per the following major chemical reaction:
CaO + 2NaF → CaF2 + Na2O
Simultaneously, following beneficial reactions also take place
6NaF + Al → 3Na + Na3AlF6
6NaF + 3SiO2 + 2Al2O3 → 3NaAlSiO4 + Na3AlF6
6NaF + 9SiO2 + 2Al2O3 → 3NaAlSi3O8 + Na3AlF6
Thus, aluminum, silica as well as alumina present in the hazardous waste of pulverized SPL (130) participate in breaking down leachable Sodium fluoride. Particularly, participation of aluminum, alumina and silica is due to smaller size of SPL (130) granules of 10 mm resulting in finer pulverization and consequent surface area exposure.
Most products of above chemical reactions are exited as flue gases which are treated by known pollution control units (151), including wet scrubbers, as per CPCB guidelines, while hazard-free carbon mineral fuel (150) stays in the spill-proof trolley (107) which exits from the close chamber of thermolyzer (101).
The thus produced carbon mineral fuel (150) as allowed to cool down to a handle-able temperature and transported to cement and other pertinent industry.
Important to note that the present invention does NOT use water as part of the chemical reaction, as prevalent in the known methods, wherein a much larger volume of water, of the order of 30% or more of the weight of the inputted SPL (130), is necessarily deployed! Not only avoidance of such higher water consumption a non-obvious major technical advance and economic significance of the present invention, there is minimal probability of hazardous water getting released in the atmosphere along with flue gases exiting from the pollution control units (151) as yet another non-obvious technical advance/economic significance of the present invention.
Figure 6,7, as a variation, and to save on cooling time, fuel consumption in the thermolyzer (101), overall cycle time and consequently running cost furthermore, an optional quenching process is introduced following the heat treatment step, wherein the same spill-proof trolley (107) next enters a quenching cabinet (105). The quenching cabinet (105) is mechanically similar as the securely closed chamber, however without thermal insulation and fuel nozzle, which is replaced by nozzle for sprinkling a minimum volume of water as atomized water or water mist (128).This process of the simultaneous reaction set-up (100) for spent pot lining (SPL) (130), of a plurality of chemical reactions within a range of temperature between 200o Centigrade and 350o Centigrade around out the key steps of reducing of SPL (130) in particle size less than or equal to 10 mm, blending of SPL (130)-lime mixture in a viscous form, executing a plurality of simultaneous chemical reactions of viscous SPL (130)-lime mixture in a thermolyzer (101), and discharging a “moisture-less” non-hazardous exhaust and flue gases,
resultantly producing a non-hazardous carbon mineral fuel (150); as lime clings around each pulverized SPL (130) granule due to a non-rotating reaction base, reactants having enlarged surface area to complete the plurality of chemical reactions in the thermolyzer (101), can have several minor variations towards implementing this inventive concept.
, Claims:We claim:
1. A simultaneous reaction set-up (100) for spent pot lining (SPL) (130)), wherein a plurality of chemical reactions take place within a range of temperature between 200o Centigrade and 350o Centigrade, the simultaneous reaction set-up (100) carries out the steps of :
o reducing of SPL (130) in particle size less than or equal to 10 mm,
o blending of SPL (130)-lime mixture in a viscous form,
o executing a plurality of simultaneous chemical reactions of viscous SPL (130)-lime mixture in a thermolyzer (101), and
o discharging a “moisture-less” non-hazardous exhaust and flue gases,
resultantly producing a non-hazardous carbon mineral fuel (150); lime clings around each pulverized SPL (130) granule due to a non-rotating reaction base, reactants having enlarged surface area to complete the plurality of chemical reactions in the thermolyzer (101).
2. The simultaneous reaction set-up (100) of claim 1, wherein the simultaneous reaction set-up (100) comprises a blender (111) and a thermolyzer (101) combination fed by a serial arrangement of crusher (121) followed by a pulverizer (125) in a loop arrangement with a vibro screener (127).

3. The simultaneous reaction set-up (100) of claim 1, wherein the vibro screener (127) comprises a vibrating sieving arrangement that prevents shifting and crossing over of particles bigger than a prescribed sieve size, which is 10mm in the present set-up (100), wherein the such bigger particles undergo pulverizing process again.
4. The simultaneous reaction set-up (100) of claim 1, wherein the thermolyzer (101) comprises a securely closed chamber equipped with a plurality of heating burners and precise temperature control in its inside, a spill-proof trolley (107) moves in and out of the thermolyzer (101) on a track (108).
5. The simultaneous reaction set-up (100) of claim 1, wherein the SPL (130)-lime mixture in the viscous form comprises less than 0.8% water by weight with respect to a weight of inputted SPL (130).
6. The simultaneous reaction set-up (100) of claim 1, wherein the simultaneous reaction comprises:
- breaking down of leachable fluoride from Sodium fluoride, group IA and IIA metal-fluorides of periodic table including Lithium, Potassium, Magnesium, to form stable and non-leachable Calcium fluoride,
- breaking down of cyanide ions of sodium cyanide, group IA and IIA metal-cyanides of periodic table including Lithium, Potassium, Magnesium, to form carbon dioxide and nitrogen dioxide, and
- breaking down of Sodium Cyanide by aluminum, silica as well as alumina present in the hazardous waste of pulverized SPL (130).
7. The simultaneous reaction set-up (100) of claim 1, further comprising the step of quenching the non-hazardous carbon mineral fuel (150) in a quenching cabinet (105) comprising a securely closed chamber having a nozzle for sprinkling atomized water or water mist (128), the spill-proof trolley (107) further moves in and out of the thermolyzer (101) on the track (108).