Description:TECHNICAL FIELD OF THE INVENTION

This invention pertains to the metallurgical and materials processing industry, and particularly to the integrated process and apparatus for the production of calcined lime, calcined dolomite, soft/hard calcined bauxite and a porous, low-sulphur carbon material suitable for use in steelmaking, cement manufacturing, fused alumina and ferroalloy production.

BACKGROUND OF THE INVENTION

The steel industry is one of the largest consumers of calcined lime, calcined dolomite, and carbonaceous materials. Calcined lime (CaO) and calcined dolomite (CaO·MgO) function as essential fluxing agents in electric arc furnaces (EAF), basic oxygen furnaces (BOF), and ladle refining furnaces (LRF), where they form slag phases that absorb impurities from molten steel.

Carbonaceous materials, particularly low-sulphur, low-ash calcined petroleum coke (CPC), are injected into EAFs to promote and sustain foamy slag conditions. This enhances thermal efficiency, improves arc stability, and facilitates FeO reduction and recovery from oxidizing slag.

The calcination of limestone (CaCO₃ → CaO + CO₂) and dolomite (CaMg(CO₃)₂ → CaO·MgO + 2CO₂) is a strongly endothermic process requiring substantial thermal energy and is therefore always carried out prior to charging into steelmaking furnaces. This pre-calcination step is essential because: (i) the endothermic decomposition would otherwise absorb heat from the furnace, reducing energy efficiency; (ii) the evolution of CO₂ gas would disrupt furnace atmosphere and foamy slag stability; and (iii) the inherently slow reaction kinetics would delay metallurgical processing.

Conventional shaft kilns used for lime and dolomite calcination typically employ either natural draft configurations, or comparatively more efficient forced-draft systems, both of which utilize mixed fuel firing. However, these systems suffer from several well-recognized limitations: (i) Large feed sizes (100–200 mm) are required in natural draft kilns to maintain gas permeability, resulting in non-uniform heat penetration, unreacted cores, and over-burnt outer layers (ii) Non-uniform temperature distribution across the kiln cross-section leads to inconsistent product quality and variable reactivity, adversely impacting downstream steelmaking operations (iii) Conventional kilns are incapable of co-processing carbonaceous materials as fuel without contaminating the calcined product with sulphur, ash, and residual carbon (iv) Thermal efficiency is inherently limited due to incomplete recovery and utilization of exhaust heat (v) In oxidizing kiln atmospheres, sulphur present in fuel is converted to SO₂ and SO₃; the latter readily reacts with lime to form CaSO₄ (sulphate), an undesirable impurity in steelmaking slags.

With respect to carbon requirements in steelmaking, the industry demands:
(i) low-sulphur carbon for LRF operations, as sulphur readily dissolves into molten steel under reducing conditions; (ii) low-ash carbon for EAF/BOF applications, since ash components (e.g., silica, alumina) introduce undesirable impurities; and (iii) highly porous, high-surface-area carbon to enhance slag foaming efficiency.
At present, these materials are produced separately and charged independently, resulting in increased capital costs, higher logistics complexity, and reduced overall process efficiency.

Raw Petroleum Coke (RPC), a low-cost byproduct of petroleum refining, is typically available at less than half the cost of medium-sulphur CPC. However, its direct use in steelmaking is limited due to high volatile matter and elevated sulphur content. Conventional calcination of RPC to produce CPC is carried out in rotary kilns operating under reducing conditions without hydrogen, which do not significantly reduce sulphur content. These processes are energy-intensive and require dedicated infrastructure and capital investment.

A significant technical gap still exists in the available prior arts. There is presently no known process capable of simultaneously: (i) calcining limestone or dolomite; (ii) converting RPC into a low-sulphur, porous carbon material; and (iii) utilizing the intrinsic calorific value of RPC as the primary or sole fuel source—within a single reactor system, while maintaining a controlled reducing atmosphere that prevents sulphur absorption into the calcined lime product.

SUMMARY OF THE INVENTION

The following disclosure presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention to be presented later.

The object of present invention is to address the above mentioned limitations in an integrated, scalable, and cost-effective manner by developing a novel process and apparatus for the Production of Calcined Mineral Products and Porous Carbon Material.

Another object of present invention is to provide a novel rotating grate shaft kiln process in which limestone and/or dolomite/or bauxite are co-calcined with raw petroleum coke (RPC) within a single reactor vessel thereby enabling the simultaneous production of (i) calcined lime or dolomite or bauxite in lump form, and (ii) a porous, low-sulphur carbon product exhibiting properties comparable to calcined petroleum coke (CPC).

One aspect of present invention is to provide a process for the co-production of calcined lime and/or calcined dolomite and a porous, low-sulphur carbon material. The process comprises charging limestone and/or dolomite stones having a particle size in the range of 25–50 mm, together with raw petroleum coke (RPC) having a particle size in the range of 30–60 mm, into a vertical shaft kiln equipped with a rotating grate at its base.

The calcination of bauxite is carried out under regulated temperature and atmospheric conditions, enabling improved control over the degree of calcination as compared to conventional calcination systems, thereby yielding calcined bauxite with enhanced and consistent material properties.

The kiln is operated to maintain a temperature of approximately 1000 to 1200°C in the belly zone by controlled injection of CO₂ and O₂ through the grate.

Steam is injected into a central zone of the kiln to promote the water–gas reaction, thereby facilitating sulphur removal from the carbonaceous material, while simultaneously preventing hydration of calcined lime by maintaining appropriate temperature profiles in the lower zones.

The process further comprises recovering, from an ash discharge zone, calcined lime or dolomite lumps along with a burnt porous carbon product, wherein lime or dolomite oxide particles are entrapped within the pores of the carbon matrix.

In an embodiment of present invention, the flue gases are treated through an air pollution control device (APCD).

Another aspect of present invention is a rotating grate shaft kiln apparatus comprising a vertical shaft body, a rotating grate at the base, tuyere-level injection ports configured for introduction of CO₂, O₂, and steam, an ash discharge pan for product removal, and an off-gas outlet operatively connected to an air pollution control device (APCD).

In a third aspect, the invention provides a porous carbon product produced by the above process, characterized by a high-porosity carbon matrix with lime and/or dolomite oxide particles entrapped within its pore structure, low sulphur content, and suitability for use as a combined carbon injector and lime carrier in electric arc furnace (EAF) and ladle refining furnace (LRF) steelmaking operations.

In a fourth aspect, the invention provides an alternate process wherein hot exhaust gas from a lime calcination kiln, rich in CO₂, is directed into a separate raw petroleum coke (RPC) gasification unit. The CO₂ acts as the primary gasifying agent via the Boudouard reaction (C + CO₂ → 2CO), thereby enhancing carbon conversion efficiency, increasing usable carbon yield, and contributing to sulphur reduction in the resulting calcined carbon product.

In this process, the thermal decomposition of carbonate feedstock, controlled calcination of bauxite—tailored to achieve either soft or hard calcination depending on application requirements—and the regulated calcination of raw petroleum coke (RPC), may occur concurrently under optimized temperature and atmospheric conditions. This integrated approach enhances overall energy efficiency and improves material utilization.

The present invention provides significant advantages in the calcination of bauxite too, when carried out in a rotating grate shaft kiln, as compared to conventional calcination systems such as rotary kilns and fluidized bed reactors. These advantages include, but are not limited to: (i) The packed bed configuration enables efficient counter-current heat exchange between process gases and descending bauxite, resulting in improved heat utilization and reduced specific energy consumption during calcination (ii) The process allows precise control over temperature and permeability, enabling selective production of: Soft calcined bauxite with higher porosity and reactivity, or Hard calcined bauxite with higher density and mechanical strength, depending on end-use requirements such as refractory or metallurgical applications (iii) The rotating grate ensures uniform material movement and temperature distribution, minimizing localized overheating or under-calcination, thereby achieving consistent phase transformation of alumina-bearing minerals (iv) The low gas velocity within the kiln minimizes entrainment of fine bauxite particles, resulting in higher product recovery and reduced need for dust handling systems (v) The controlled heating profile minimizes thermal stresses within bauxite particles, reducing cracking, spalling, and structural degradation compared to rapid heating in conventional kilns.

Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The above and other aspects, features and advantages of the embodiments of the present disclosure will be more apparent in the following description taken in conjunction with the accompanying drawings, in which:

Figure 1: illustrates a schematic diagram of a system with proper dimensions of a mix feed vertical shaft kiln / gasifier according to present invention.

Figure 2: A schematic representation of exemplary reactor (1) configurations for processing carbonaceous carbonate/alumina feed stocks under thermal conditions; a single, continuous reactor system (02) using a multi-zone vertical shaft gasifier (02) integrating drying (08), pyrolysis (09), oxidation (10), and secondary reduction zone (11) for producing porous low-sulphur calcined petroleum coke (CPC) from high-sulphur RPC according to present invention.

Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity and clarity and may not have been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve understanding of various exemplary embodiments of the present disclosure. Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of various embodiments of the present disclosure as defined by the claims and their equivalents. It includes various specific details to assist in that understanding, but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the various embodiments described herein can be made without departing from the scope and spirit of the present disclosure. In addition, descriptions of well-known functions and constructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the present disclosure. Accordingly, it should be apparent to those skilled in the art that the following description of various embodiments of the present disclosure is provided for illustration purpose only and not for the purpose of limiting the present disclosure as defined by the appended claims and their equivalents.

It is to be understood that the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, a reference to "a component surface" includes a reference to one or more of such surfaces.

All terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which various embodiments belong. Further, the meaning of terms or words used in the specification and the claims should not be limited to the literal or commonly employed sense but should be construed in accordance with the spirit of the disclosure to most properly describe the present disclosure.

The terminology used herein is for the purpose of describing particular various embodiments only and is not intended to be limiting of various embodiments. As used herein, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising" used herein specify the presence of stated features, integers, steps, operations, members, components, and/or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, members, components, and/or groups thereof. Also, expressions such as "at least one of," when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list.

The present disclosure will now be described more fully with reference to the accompanying drawings, in which various embodiments of the present disclosure are shown. The present disclosure may, however, be embodied in many different forms and should not be construed as being limited to the various embodiments set forth herein, rather, these various embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the present disclosure. Furthermore, a detailed description of other parts will not be provided not to make the present disclosure unclear. Like reference numerals in the drawings refer to like elements throughout.

The following terms and abbreviations are used throughout this specification and shall have the meanings assigned to them below, unless the context otherwise requires:
(a) RPC refers to Raw Petroleum Coke, being an uncalcined carbonaceous byproduct obtained from crude oil refining processes, typically containing volatile matter, moisture, sulphur, and ash.
(b) CPC refers to a porous, low-sulphur carbon Calcined Petroleum Coke, being RPC that has been subjected to high-temperature thermal treatment to substantially remove volatile matter and reduce impurities, including sulphur.
(c) VM refers to Volatile Matter, comprising hydrocarbons and other thermally decomposable compounds released from carbonaceous materials upon heating.
(d) EAF refers to Electric Arc Furnace, a steelmaking furnace in which heat is generated primarily by electric arc between electrodes and the charge material.
(e) LRF refers to Ladle Refining Furnace, a secondary metallurgical processing unit used for refining, alloying, and temperature adjustment of molten steel.
(f) BOF refers to Basic Oxygen Furnace, a steelmaking vessel in which oxygen is blown into molten iron to remove impurities through oxidation reactions.
(g) BST refers to Blast Surface Temperature, a process control parameter representing the effective thermal and chemical conditions at the tuyere injection zone of the kiln, governed by the composition and ratio of injected gases including CO₂, O₂, and/or steam.
(h) APCD refers to Air Pollution Control Device, comprising equipment configured to capture, treat, and/or neutralize gaseous and particulate emissions from process exhaust streams.
(i) Foamy Slag refers to a slag phase formed in EAF and/or BOF operations, characterized by a gas-entrained, porous structure generated primarily by reactions between carbon and oxidized slag constituents (including FeO), which enhances thermal efficiency, arc stability, and metal recovery.

Co-Production of Calcined Lime/Dolomite and Porous Low-Sulphur Carbon

Step 1: Feed Preparation and Charging: Limestone (CaCO₃) and/or dolomite (CaMg(CO₃)₂) stones of size 25–50 mm are prepared by crushing and screening. Raw petroleum coke (RPC) of size 30–60 mm is used as the co-feed and primary fuel source. The feed size ranges may be adjusted during commissioning to optimize permeability and heat transfer. In a preferred embodiment, the feed proportions are selected such that approximately 40–60% of the carbon input from RPC exits the kiln as an unburnt porous carbon product.

Both materials are preferably charged as a mixed feed into the top of a vertical shaft kiln. The quantity of RPC charged is determined based on calorific requirements, such that it provides a gross heat input of at least 3000 kcal per kg of calcined lime/dolomite produced. Approximately 900–1100 kcal/kg is consumed by the endothermic calcination reactions, while the remaining heat is managed through controlled partial oxidation and gasification to ensure partial retention of carbon in the discharged product.

Step 2: Rotating Grate Operation: The kiln is equipped with a rotating grate at its base. The rotational speed is adjustable and is selected to control bed permeability, and discharge rate. Rotation of the grate continuously redistributes gas flow paths through the packed bed, thereby: (i) preventing gas channelling (ii) ensuring uniform temperature distribution (iii) improving heat transfer efficiency.

This enables the use of smaller stone sizes (25–50 mm), in contrast to conventional shaft kilns requiring 100–200 mm feed sizes. Unlike fixed-grate systems, which develop preferential gas pathways leading to non-uniform calcination, the rotating grate ensures that all material experiences substantially uniform thermal exposure over its travel time.

The upper partial calcination zone (4), maintained at a temperature of approximately 600 °C, is configured to facilitate stepwise thermal decomposition of carbonate materials, particularly dolomite, and to ensure completion of partially initiated reactions. Within this zone, dolomite (CaCO₃·MgCO₃) undergoes a first-stage decomposition wherein the magnesium carbonate component preferentially decomposes to magnesium oxide (MgO) with the release of carbon dioxide, leaving calcium carbonate (CaCO₃) as an intermediate product. Concurrently or subsequently, partial decomposition of calcium carbonate to calcium oxide (CaO) and carbon dioxide may be initiated depending on local thermal and gas-phase conditions. The upper partial calcination zone (4) thereby functions as a transitional region between the lower preheating zone (6) and the intermediate high-temperature calcination zone (5), enabling controlled and gradual decomposition of the feed material, promoting internal pore development, and preventing abrupt structural degradation or collapse of the solids as they progress into higher temperature regions.

The intermediate high-temperature calcination zone (5), maintained at a temperature in the range of about 800 °C to 1200 °C, constitutes the primary calcination and reaction region of the reactor (1), wherein the majority of carbonate decomposition occurs. Said zone is characterized by a gas atmosphere predominantly comprising carbon dioxide (CO₂) and water vapor (H₂O), generated from in-situ decomposition reactions and optionally supplemented by externally introduced or recycled gas streams. Within this zone, limestone (CaCO₃) undergoes thermal decomposition to calcium oxide (CaO) with the release of carbon dioxide, and magnesium carbonate (MgCO₃) decomposes to magnesium oxide (MgO) with the release of carbon dioxide. The decomposition reactions are endothermic in nature and require sustained elevated temperatures to proceed effectively. The rate and extent of calcination within the intermediate high-temperature calcination zone (5) are governed by process parameters including temperature, the partial pressure of carbon dioxide, and physical characteristics of the feed material such as particle size and porosity, thereby enabling controlled and efficient conversion of carbonate feedstock into corresponding oxide products.

CaCO₃ → CaO + CO₂ (ΔH = +178 kJ/mol, endothermic)
CaMg(CO₃)₂ → CaO·MgO + 2CO₂ (ΔH = +330 kJ/mol, endothermic)

The heat required for the endothermic calcination and decomposition reactions is supplied in situ by partial combustion and gasification of raw petroleum coke (RPC) within the same reaction bed. Carbon dioxide released during the calcination of carbonate materials is advantageously utilized within the reactor by participating in the Boudouard reaction with adjacent carbonaceous material.

C + CO₂ → 2CO (Boudouard reaction)

This interaction increases the yield of carbon monoxide in the product gas stream and enhances the overall calorific value of the off-gas. Additionally, the consumption of carbon through gasification promotes the development of internal pore structure within the residual coke, thereby increasing its porosity and reactivity for subsequent reactions or applications.

A controlled mixture of carbon dioxide (CO₂) and oxygen (O₂) is injected through tuyeres positioned at or proximate to the grate level of the reactor. The ratio of CO₂ to O₂ is regulated so as to maintain a bed temperature in the range of about 800–1200°C within the belly region, corresponding to the intermediate high-temperature calcination zone (5), while ensuring sub-stoichiometric oxygen availability. By maintaining the oxygen supply below the stoichiometric requirement relative to the total carbon input from raw petroleum coke (RPC), a predominantly reducing atmosphere is established within the calcination zone. Such a reducing environment facilitates controlled partial combustion for in situ heat generation, while simultaneously promoting gasification reactions of C with CO₂ and other gaseous species.

In the presence of steam and hydrogen generated via water–gas reactions (C + H₂O → CO + H₂), sulphur contained in the RPC is preferentially converted to hydrogen sulphide (H₂S) rather than oxidized sulphur species such as sulphur dioxide (SO₂) or sulphur trioxide (SO₃). This suppresses the formation of sulphate (CaSO₄) and thereby minimizes sulphur fixation in the calcined lime or dolomite product.

The principal reactions governing the process include
C + O₂ → CO₂ (Partial oxidation & heat generation)
C + CO₂ → 2CO (Boudouard reaction)
C + H₂O → CO + H₂ (Steam gasification)
S + H₂ → H₂S (In presence of hydrogen)

In this process, the thermal decomposition of carbonate feedstock, the controlled calcination of bauxite, and the regulated calcination of raw petroleum coke (RPC) are carried out concurrently within integrated or coordinated reaction zones under optimized temperature and atmospheric conditions. The calcination of bauxite is selectively tailored to achieve either soft calcination or hard calcination depending on downstream application requirements, wherein soft calcination preserves higher reactivity and surface area, while hard calcination produces a denser and more thermally stable phase. This integrated multi-feed processing approach enables efficient utilization of heat and reactive gases, reduces overall energy consumption, and improves material conversion efficiency across all feedstocks.

The mechanism of bauxite calcination involves the progressive thermal transformation of hydrated aluminum-bearing minerals, primarily gibbsite (Al(OH)₃), boehmite (AlO(OH)), and diaspore (AlO(OH)), into transition alumina phases through dehydration and dehydroxylation reactions. At temperatures typically ranging from about 300 °C to 600 °C, gibbsite undergoes dehydroxylation to form amorphous or poorly crystalline alumina with the release of water vapor. At higher temperatures, generally between about 500°C and 800°C, boehmite and diaspore decompose to form γ-alumina and other transition alumina phases. This process may occur and complete in the upper partial calcination zone (4) and intermediate high-temperature calcination zone (5). In soft calcination, the process is controlled to limit sintering, thereby retaining high porosity and surface area. In hard calcination, higher temperatures, typically above 950°C, promote phase transformation toward α-alumina with increased crystallinity and reduced surface area. The extent and pathway of transformation are governed by temperature, travel time, particle size, and partial pressure of water vapor, thereby enabling precise control over the physical and chemical properties of the calcined bauxite product.

As volatile matter (VM) is released from raw petroleum coke (RPC) at elevated temperatures, and concurrent partial combustion and gasification reactions proceed, an interconnected pore network is generated within the residual carbon matrix. Simultaneously, carbonate feed materials such as limestone and/or dolomite undergo calcination, producing finely divided calcium oxide (CaO) and/or calcium–magnesium oxide (CaO·MgO). Due to intimate contact within the packed bed and continuous gas–solid interactions, a portion of these fine oxide particles becomes mechanically entrained and physically accommodated within the pore structure of the carbon matrix, rather than merely adhering to external surfaces.

The resulting product is a composite porous carbon material characterized by: (a) High porosity and enhanced surface area resulting from volatile matter release and gasification reactions; (b) Physical incorporation and retention of CaO and/or CaO·MgO particles within the internal pore network of the carbon matrix; (c) Reduced sulphur content due to operation under a predominantly reducing atmosphere, promoting conversion of sulphur to gaseous hydrogen sulphide (H₂S); and (d) An apparent increase in ash content during proximate analysis, wherein said ash fraction comprises predominantly calcium- and magnesium-based oxides entrapped within the carbon structure, rather than conventional mineral impurities such as silica, alumina, or metal oxides.

Step 3: Product Discharge and Separation

The calcined lime and/or dolomite lumps/or bauxite lumps and the porous carbon product are discharged together from the ash collection zone at the base of the rotating grate. Depending on end-use requirements, the discharged material may be utilized directly as a combined co-injection product or subjected to downstream separation. Separation, where required, may be carried out by one or more of the following methods:

(a) Optical sorting (colour-based separation): exploiting the visual contrast between light-coloured calcined lime/dolomite (white to grey) and dark carbonaceous material using sensor-based sorting systems;
(b) Screening/classification by particle size: based on differences in size distribution arising from differential degradation behaviour, wherein calcined mineral phases may exhibit higher friability compared to the relatively stronger carbon matrix, or vice versa depending on operating conditions;
(c) Density-based separation: including air classification, fluidized separation, or gravity-based techniques, utilizing the difference in apparent density between calcined minerals (typically ~3.0–3.9 g/cm³) and porous carbon (typically lower apparent density, depending on porosity), noting that effective separation depends on particle size and pore structure rather than true density alone.
Fines generated during discharge and handling, typically below about 1 mm in size, are collected separately. Such fines may comprise a mixture of calcium oxide, magnesium oxide, and carbonaceous particles, and may be advantageously utilized in downstream applications, including gas scrubbing, desulphurization, or as reactive fines in other process units.

Step 4: Flue Gas Treatment
The off-gas from the kiln comprises primarily carbon monoxide (CO), carbon dioxide (CO₂), and hydrogen sulphide (H₂S), along with minor constituents depending on operating conditions, and is directed to an air pollution control device (APCD) for treatment. In a preferred embodiment, the flue gas is subjected to wet scrubbing, wherein H₂S is absorbed into an aqueous scrubbing medium. The absorbed hydrogen sulphide forms a weak acidic solution (hydrosulphuric acid) and, in the presence of dissolved oxygen or oxidizing conditions, may be further converted to sulphurous and/or sulphuric species.

This flue gas treatment step is described as a preferred embodiment for environmental management and resource utilization and does not form a limiting or essential part of the claimed invention, being based on known industrial gas treatment practices.

EXAMPLES: Experimental Data — Laboratory Scale Test Run

A laboratory-scale test was conducted to demonstrate the feasibility of the disclosed process using a bench-scale vertical shaft reactor equipped with a simulated rotating grate discharge mechanism. The reactor was operated to maintain a belly zone temperature of approximately 1000-1200°C, corresponding to the intermediate high-temperature calcination zone (5) of the reactor (1). The feed materials comprised sized limestone (25–50 mm) and raw petroleum coke (RPC) (30–60 mm), introduced in a fixed ratio. The principal input and output parameters recorded during the test run are summarized below.

Parameter Input Output
Limestone (25–50 mm), kg 100 –
Raw Petroleum Coke (30–60 mm), kg 43 –
Calcined Lime (CaO), kg – 51.2
Porous Carbon Product (CPC-type), kg – 20.8
Fines (<1 mm), kg – 4.6
Calorific Value of RPC (kcal/kg) ~7800 –
Estimated Heat Consumption (kcal/kg product) – ~980
Kiln Belly Temperature (°C) ~1000-1200 –
Fixed Carbon in Porous Product (%) – ~82
Sulphur in Porous Carbon (%) – ~0.8-1
Ash in Porous Carbon (%) – ~9*
CO₂ in Flue Gas (%) – ~68
H₂S in Flue Gas (%) – ~2.1
*Ash includes calcium oxide (CaO) entrapped within the carbon matrix.

The above data represents a single representative test conducted at laboratory scale, with all material balances expressed on a per-100 kg limestone feed basis. The sulphur content of the RPC feedstock was approximately 7.2 wt%. The substantial reduction in sulphur content in the resulting porous carbon product (~0.8-1.0 wt%) indicates effective conversion of sulphur to gaseous species, primarily hydrogen sulphide (H₂S), under the maintained reducing and hydrogen-containing atmosphere. This confirms that sulphur retention within the solid carbon matrix is significantly suppressed under the disclosed operating conditions.

The measured ash content of approximately 9 wt% in the porous carbon product is attributed predominantly to calcium oxide (CaO) entrapped within the pore structure of the carbon matrix, rather than conventional mineral impurities. This observation supports the proposed mechanism of in situ incorporation of lime into the carbon structure during simultaneous calcination and carbonization.

The flue gas composition, characterized by high CO₂ (~68%) and measurable H₂S (~2.1%), is consistent with the occurrence of calcination and sulphur conversion reactions under controlled sub-stoichiometric conditions.

It is noted that the above results are subject to variation depending on feedstock characteristics, reactor configuration, and operating parameters. Further optimization and validation are expected during pilot-scale and industrial-scale implementation.

CO₂ Recycle from Lime Calcination to RPC Gasifier

The inventive step in this embodiment is the deliberate use of CO₂ generated in situ from the endothermic calcination of carbonates as the primary gasifying agent in an adjacent RPC gasifier — a connection not disclosed in prior art — resulting in simultaneous improvement of lime kiln efficiency (CO₂ is otherwise wasted) and CPC yield improvement in the RPC gasifier.

Thus, the present invention addresses persistent technical limitations associated with the desulfurization and calcination of high-sulphur raw petroleum coke (RPC), including inadequate sulfur removal efficiency, excessive energy consumption, degradation of fixed carbon, and poor scalability of existing processes. Conventional techniques fail to achieve uniform removal of both inorganic and complex organic sulfur species, particularly under continuous operating conditions, while also suffering from inefficient heat utilization and limited gas–solid mass transfer. Additionally, known methods relying on chemical reagents generate undesirable effluents and introduce operational complexity, whereas static or poorly controlled reactor systems exhibit non-uniform gradients, localized overheating, and incomplete reaction control. These deficiencies are further compounded by the lack of integrated systems capable of simultaneously recovering sulfur values, utilizing process gases, and enabling by-product valorization, thereby necessitating the development of a compact, continuous, and thermally integrated process architecture.

Accordingly, the present invention provides a technically robust, energy-efficient, and environmentally sustainable process for producing low-sulphur calcined petroleum coke (CPC) from high-sulphur RPC within a single, continuous reactor system (02) using a multi-zone vertical shaft gasifier(02) that unifies drying (08), pyrolysis and reduction zone (09), oxidation and firing zone (10), and secondary reduction zone (11) under counter-current gas–solid flow wherein calcination is carried out at 1000-1600oC (Normally calcination of CPC is done <1000oC in reducing atmosphere). In this process, RPC feed, blended with catalytic additives (optional) such as manganese ore, iron ore, mill scale etc. may be introduced from the top of the reactor, while a controlled mixture of CnHm, H2, CO with air, with or without oxygen (O₂) from side of the gasifier follows CH4, CO2, steam with or without air from a lower region of said gasifier to establish counter-current. The invention further aims to enable in-situ sulfur removal and recovery, wherein sulfur present in the RPC feedstock is thermally and catalytically converted into gaseous species including SO₂, SO₃, and H₂S within controlled oxidizing and firing (10) and reducing zones (09,11) of the same system (02), followed by downstream conversion into recoverable products such as sulfuric acid (H₂SO₄) or elemental sulfur.

Another objective is to achieve a CPC product having a fixed carbon content exceeding 95 wt.% with substantial sulfur reduction, while preserving the structural integrity and physical properties of the carbon matrix through controlled thermal gradients and redox conditions that prevent over-oxidation and carbon loss. The integrated system achieves high fixed carbon recovery (95–99 wt%), deep sulfur removal below 2.5 wt% (50-99% Sulphur reduction from input).

Further, the invention is directed to maximizing thermal efficiency and process sustainability through in-situ heat recovery, closed-loop gas utilization, and integration of by-product streams into a circular process framework. Process gases generated during operation are recycled for fuel or reduction purposes, thereby minimizing external energy requirements and enabling co-production of low-carbon metals using the same or similar reactor configurations. The system is designed to be modular and scalable, allowing adjustment of throughput and temperature profiles to meet varying industrial demands while maintaining continuous operation and synchronized reaction control. Overall, the invention provides an integrated, continuous, and environmentally compliant process that produces high-grade CPC, recovers valuable sulfur and metallic by-products too according to the requirement (which is optional), reduces emissions, and meets stringent global standards for sulphur and particulate control in metallurgical and allied industries.

The integrated system enables the direct utilization of CO₂ generated from carbonate calcination as a primary gasifying agent, thereby transforming an otherwise waste emission into a reactive intermediate and improving overall process efficiency. The coupling of calcined mineral productions and petroleum coke upgrading to porous low sulphur carbon material within a unified process architecture provides enhanced CPC yield, reduced sulphur content, improved fuel efficiency through syngas recycling, and minimized external energy requirements, while maintaining independent control of calcination and gasification environments to ensure product quality and operational stability.

ADVANTAGES OF THE INVENTION

1) The process achieves a substantially reduced net external fuel requirement by utilizing partial combustion and controlled gasification of raw petroleum coke (RPC) within the reactor to supply the endothermic heat demand of calcination. The residual unreacted carbon is recovered as a value-added calcined porous low sulphur petroleum coke (CPC) product, thereby offsetting fuel consumption. Owing to the lower cost of RPC relative to conventional calcined fuels, and the internal heat integration within the system, the effective calcination energy cost is significantly minimized, approaching near-zero net fuel input under optimized operating conditions.

2) The use of a rotating grate shaft kiln configuration enables uniform gas–solid contact and improved permeability across the burden, allowing the processing of smaller particle sizes in the range of approximately 25–50 mm as compared to 100–200 mm in conventional shaft kilns. The reduced particle size enhances heat and mass transfer rates, accelerates calcination kinetics, and improves overall process throughput and conversion uniformity without compromising operational stability.

3) The process maintains a controlled reducing atmosphere within the reaction zones, thereby facilitating the evolution of sulphur predominantly in the form of gaseous species such as H₂S rather than promoting fixation as sulphates (e.g., CaSO₄) within the calcined lime matrix. This results in the production of a substantially sulphur-free lime product with improved chemical purity and suitability for downstream metallurgical and chemical applications.

4) The process generates a novel porous carbonaceous co-product comprising a structured carbon matrix with entrapped or associated lime phases, formed as a result of in-situ gasification and mineral interaction. This engineered material exhibits enhanced reactivity and is directly utilizable in electric arc furnace (EAF) and ladle refining furnace (LRF) operations for simultaneous carbon and flux injection, thereby eliminating the need for separate handling and dosing of carbon and lime inputs.
In an alternate embodiment incorporating CO₂ recycling, the CO₂-rich exhaust gas generated from carbonate calcination is introduced into a separate RPC gasifier, thereby enhancing the extent of carbon conversion via gasification reactions and improving the yield of low-sulphur CPC from high-sulphur RPC feedstock. This integration increases process efficiency and economic returns by simultaneously improving coke quality and utilizing process-derived CO₂ as a reactive gasifying medium.

5) The apparatus demonstrates operational versatility, wherein a single rotating grate shaft kiln system can be selectively operated to produce calcined lime, calcined dolomite, calcined low sulphur porous carbon depending on feed composition, temperature profile, and gas atmosphere control. This adaptability enables flexible deployment across multiple industrial applications without significant modification to the core reactor design.

6) the process incorporates an integrated environmental control system, wherein flue gases are treated through an air pollution control device (APCD), and sulphur-containing gases, particularly H₂S, are captured in a scrubbing system. , Claims:WE CLAIM:

1. An integrated process for the simultaneous production of calcined mineral products and a porous, low-sulphur carbon material, the process comprising:
charging a mixed feed of mineral stones and raw petroleum coke (RPC) into a vertical shaft kiln;
subjecting the mixed feed to a controlled temperature of 800°C to 1200°C in a high-temperature calcination zone of the kiln;
injecting a regulated mixture of air or oxygen (O2), carbon dioxide (CO2), and steam through a rotating grate at the base of the kiln to establish a sub-stoichiometric, reducing atmosphere;
utilizing the in-situ calorific value of the RPC as the primary fuel source to supply heat for the endothermic calcination of the mineral stones;
promoting a water–gas reaction via steam injection to convert sulfur in the RPC into gaseous hydrogen sulfide (H2S); and
discharging a combined product comprising calcined mineral lumps and a porous, low-sulfur carbon product.

2. The process as claimed in claim 1, wherein the mineral stones have a particle size of 25–50 mm and the RPC has a particle size of 30–60 mm.

3. The process as claimed in claim 1, wherein the mineral stones are selected from the group consisting of limestone, dolomite, bauxite, or combinations thereof.

4. The process as claimed in claim 1, wherein approximately 40–60% of the carbon input from the RPC is recovered as an unburnt porous carbon product characterized by having lime or dolomite oxide particles entrapped within its internal pore structure.

5. The process as claimed in claim 1, wherein the rotating grate is operated at an adjustable speed to continuously redistribute gas flow paths, thereby preventing gas channeling and ensuring uniform temperature distribution throughout the mixed feed.

6. The process as claimed in claim 1, further comprising separating the discharged calcined mineral lumps from the porous carbon product using a method selected from optical sorting, size-based screening, or density-based separation.

7. The process as claimed in claim 1, wherein said catalytic additives are selected from manganese ore, iron ore, mill scale or combination thereof.

8. An integrated process for the simultaneous production of calcined mineral products and a porous, low-sulphur carbon material, the process comprising:
charging a mixed feed of mineral stones and raw petroleum coke (RPC) into a vertical shaft kiln;
subjecting the mixed feed to a controlled temperature of 800°C to 1200°C in a high-temperature calcination zone of the kiln;
injecting a regulated mixture of air or oxygen (O2), carbon dioxide (CO2), and steam through a rotating grate at the base of the kiln to establish a sub-stoichiometric, reducing atmosphere;
utilizing the in-situ calorific value of the RPC as the primary fuel source to supply heat for the endothermic calcination of the mineral stones;
promoting a water–gas reaction via steam injection to convert sulfur in the RPC into gaseous hydrogen sulfide (H2S);
diverting CO2-rich hot exhaust gas from the kiln into an adjacent raw petroleum coke gasification unit to act as a primary gasifying agent via the Boudouard reaction (C + CO2→ 2CO); wherein RPC feed, optionally blended with catalytic additives is introduced from the top of the gasification unit, and a controlled mixture of CnHm, H2, CO with air, with or without oxygen (O₂) are introduced from side of the gasification unit following CH4, CO2, steam with or without air from a lower region of said gasification unit to establish counter-current thereby
removing and recovering sulfur present in the RPC in-situ in the gasification unit; wherein sulfur present in the RPC feedstock is thermally and catalytically converted into gaseous species including SO₂, SO₃, and H₂S within controlled oxidizing and firing and reducing zones of the gasification unit, followed by downstream conversion into recoverable products such as sulfuric acid (H₂SO₄) or elemental sulfur; and
discharging a combined product comprising calcined mineral lumps and a porous, low-sulfur carbon product.

9. A continuous reactor system for an integrated production of calcined minerals and porous carbon material, comprising:
a vertical shaft kiln comprising an upper partial calcination zone, an intermediate high-temperature calcination zone, and a lower cooling zone;
a rotating grate positioned at the base of the shaft body configured to regulate bed permeability and material discharge;
a plurality of tuyere-level injection ports located proximate to the rotating grate configured for the controlled introduction of O2, CO2 and steam into the shaft body;
an ash discharge pan for the removal of calcined products and carbon material; and
an off-gas outlet operatively connected to an air pollution control device (APCD) configured to capture and treat gaseous H2S and CO.

10. A continuous reactor system for an integrated production of calcined minerals and porous carbon material, comprising:
a vertical shaft kiln comprising an upper partial calcination zone, an intermediate high-temperature calcination zone, and a lower cooling zone;
a rotating grate positioned at the base of the shaft body configured to regulate bed permeability and material discharge;
a plurality of tuyere-level injection ports located proximate to the rotating grate configured for the controlled introduction of O2, CO2 and steam into the shaft body;
an ash discharge pan for the removal of calcined products and carbon material; and
an off-gas outlet operatively connected to an air pollution control device (APCD) configured to capture and treat gaseous H2S and CO; and
an adjacent raw petroleum coke gasification unit fluidly connected to the off-gas outlet of the vertical shaft kiln, comprising a multi-zone vertical shaft gasifier comprising drying, pyrolysis and reduction zone, oxidation and firing zone, and secondary reduction zone under counter-current gas–solid flow, configured to in-situ removal and recovery sulfur present in the RPC; wherein calcination is carried out at 1000-1600oC.

11. The system as claimed in claim 9 or 10, wherein the high-temperature calcination zone of the vertical shaft kiln is configured to maintain a temperature between 800°C and 1200°C.

12. A porous carbon product produced by the process as claimed in claim 1 or 8, comprising:
a high-porosity carbon matrix derived from raw petroleum coke;
calcined mineral oxide particles, including at least one of calcium oxide or magnesium oxide, physically entrapped within the internal pore structure of the carbon matrix; and
a sulphur content of less than 1.0 wt%.