Method and System for low carbon thermo-metallurgical Processing and Extracting of Metals from Industrial By-Products

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No. 63/723,849, filed Nov. 22, 2024, which is herein incorporated by reference in its entirety.

FIELD

This disclosure relates to the recovery and extraction of volatile metals from industrial waste through use of thermo-metallurgical processing with indirect radiant heating and/or microwave heating.

BACKGROUND

Embodiments of the present disclosure deals with a challenge facing the global iron and steel industry—which is decarbonization of its process, reduction of carbon footprint and energy consumption, doing it more economically compared with existing thermo-metallurgical methods currently used.

Metallurgical processes, including steel processes, result in waste by-products of flue dusts. There have been attempts to recover the Zn and Pb from this dust and to obtain a metal concentrate which can be reused via existing metal refinery.

For example, the Waelz Kiln has been employed to recover Zn and Pb using a reducing roasting process. The Waelz Kiln is a directly heated counterflow type rotary kiln. The reducing roasting process comprises directly heating and roasting the iron and steel dust in the Waelz Kiln in a reducing atmosphere achieved by increased concentration of reductant carbon under selected conditions of high temperature and long retention time, thereby separating Zn and Pb through volatilization.

In practice, the reducing roasting process using the Waelz Kiln is problematic because it is extremely difficult to maintain the operation of the rotary kiln under the appropriate conditions for a long time and a retention time of more than 1 hour and temperature higher than 1250 C is generally required. Due to direct heating and high velocity of gases through the Waelz kiln there is typically a large carry over of the flue dust and iron in Waelz zinc oxide product which can cause a reduction of Zn yield in the zinc refining process. As a result, the recovery of Pb and Zn byproduct by this process is not satisfactory. As well, the carbon consumption is extremely high due to uncontrollable level of oxygen in processing atmosphere. Economic threshold of Waelz Kiln typically requires minimum 18% zinc content in processed byproduct.

SUMMARY

It is therefore desirable to have an improved process for extracting metals, such as Lead (Pb) and Zinc (Zn) from industrial waste using controlled processing atmosphere with nitrogen or nitrogen and hydrogen injection and reduction of carbon consumption.

Embodiments of the present disclosure relate to an improved thermo-metallurgical low carbon method and system for selective separation and extraction of metals and metal oxides from industrial minerals and waste materials containing zinc, lead, cadmium, arsenic, iron, mercury and selenium using an air sealed indirectly heated modular furnace with a counterflow nitrogen or nitrogen and hydrogen atmosphere and co-flow process gas recycling atmosphere. Carbon and/or hydrogen reductant is used to strip oxygen from processed material and extract metals in the form of metal oxide concentrate and residual Concentrated iron pellets (CIP).

The system is accelerated with Microwave-Assisted Reduction of Processed (MARP) materials with accelerating pre-heating/activation/metal evaporation in controlled reducing environment by using nitrogen or gas mixture containing nitrogen and hydrogen.

The controlled process produces reduced CIP reusable in steel production or in cement production.

Therefore, the disclosed methods and systems include an improved indirectly heated counterflow type furnace for extracting metals. The methods and systems offer several advantages, such as well controlled metal reduction atmosphere using lower carbon content and nitrogen and hydrogen, lower processing temperature, lower process gas flow, shorter retention time, higher metal recovery rate, with all advancements by improved low carbon processing method not achievable with currently used Waelz Kiln method.

The disclosed techniques can lead to dramatic reduction of CO₂ footprint and increase metal removal rate and its higher refined purity and improve the economic threshold of minimum zinc content in processed byproduct being lower than 18%.

As the world moves toward green steel production and green hydrogen and electricity becomes more available and affordable, this disclosed techniques can be adapted to achieve zero-emissions from a CO₂ point of view.

BRIEF DESCRIPTION OF THE DRAWINGS

In drawings which illustrate by way of example only a preferred embodiment of the disclosure,

FIG. 1 is a schematic of a process flow using a modular heating system having two heat sources, natural gas and/or electricity in accordance with an embodiment.

FIG. 2 is a schematic of an indirectly heated modular rotary furnace apparatus with three atmosphere zones in accordance with an embodiment.

FIG. 3 is a schematic of an indirectly heated modular rotary furnace apparatus with dryer in accordance with an embodiment.

DETAILED DESCRIPTION

This disclosure includes an improved indirectly heated low carbon thermo-metallurgical processing method and apparatus for separation and recovery of metals and metal oxides from industrial minerals and waste materials containing zinc, lead, cadmium, arsenic, iron, mercury and selenium. The processing method is accelerated using microwave-assisted pre-heating/activation/metal evaporation in controlled reducing environment by using carbon and/or hydrogen and nitrogen containing atmosphere with controlled oxygen level.

While the disclosure focuses on a process for the separation and recovery applicable to zinc, lead, cadmium arsenic, mercury, selenium and antimony, it is particularly applicable to the separation and recovery of zinc and more specifically is designed and described as a method for zinc recovery contained in an Electric Arc Furnace Dust (EAF Dust) and other zinc bearing byproducts.

The EAF Dust recycling industry is an integral part of the industrial value chain. Therefore, revising its processes in order to safeguard the sector in the light of the challenges of climate change and make it fit for the future is an important goal. A direct hydrogen assisted metal reduction process is helping to achieve the climate protection goals and advancing the development of a climate neutral industrial sector.

In prior art Waelz Kiln processing, direct heating by combustion of reductant and high velocity gases containing uncontrollable CO₂ and O₂ contents, may result in unwanted particles carried over into the zinc concentrate resulting in a poor quality of zinc concentrate. For satisfactory results, the zinc may have to be processed in two stages.

With the reducing roasting process using the Waelz Kiln, there is also a fluctuation in the operating conditions due to the deposition of low melting compounds on the walls of the directly heated rotary tube. This consequently impedes the continued operation of the rotary kiln. As a result, efficiency of zinc recovery is low. It is possible to reduce the effects of this problem be adding the flux to the feed to the rotary kiln, thereby adjusting the melting point of the feed and enabling the feed to be completely melted within the rotary kiln.

Compared with the conventional Waelz Kiln, in the presently disclosed systems and methods up to 90% of directly emitted CO₂ emissions can be reduced without taking the CO₂ intensity of the additionally required electricity into account. However, the overall CO₂ footprint especially for hydrogen-based process is strongly depending on the source of green electricity due to the production of hydrogen via electrolysis.

Some prior systems include:

• • a. U.S. Pat. No. 4,525,208 attempts to avoid the above problems with the Waelz Kiln caused by the depositing of material on the walls of the rotary kiln by running the volatilization in two stages. In the first stage the material is heated and Zn and Pb are partially evaporated at a lower temperature in a rotary kiln. In the second stage, the solid material from the rotary kiln is continuously fed into the rotary smelting furnace where fluxes are added to the material to lower the melting point facilitating the evaporation of the metals from the molten stage.
  • b. In U.S. Pat. No. 3,850,613 the improvement for separating and recovering the Zn and Pb includes granulation and bricketing the dust and then volatizing the Zn and Pb by heating the briquettes.
  • c. There are also several systems for the recovery of Zn or Pb using a molten stage, including an electric arc furnace, an electrothermic smelting furnace and a slag fuming method. In U.S. Pat. No. 3,262,771, the recovery of Zn and Pb is carried out in a molten stage by using an electric arc furnace.
  • d. In U.S. Pat. No. 5,188,658, Zn and Pb are recovered from the molten stage in an electrothermic smelting furnace. The electrothermic smelting furnace described in U.S. Pat. No. 5,188,658 requires that the furnace be kept at high temperatures in order to maintain a volume ratio between CO2 and CO in the gas atmosphere in the smelting furnaces below 0.3.
  • e. In U.S. Pat. No. 3,017,261, Zn and Pb are recovered from the molten stage with a slag fuming method using a stationary furnace where metals are volatilized by melting the iron and steel dust completely and blowing air and reducing agent such as coal or coke into the molten iron. Because of higher temperature and operating conditions this processing offers great obstacles to the furnace operation.
  • f. There have also been attempts to render such industrial waste non-hazardous without recovering zinc or lead. In U.S. Pat. No. 4,840,671, using an electric arc furnace, dust, steel dust from the production of certain specialty grades of steel, is rendered less hazardous by complexing the dust in a lime kiln dust, fly ash and hydrated lime mixture and then adding an aqueous solution containing ferrous hydroxide and calcium sulfate.
  • g. In the U.S. Pat. No. 5,013,532A, zinc is recovered for electric arc furnace dust. This disclosure relates to the metallurgy of iron and particularly to the separation and recovery of metals from electric arc furnace (EAF) dusts. It discloses a process for the separation and recovery applicable to zinc, lead, cadmium and antimony contained in such EAF dusts, the disclosed techniques are particularly applicable to the separation and recovery of zinc. It describes a method using excess of hydrogen gas introduced into the heated furnace or retort at a rate sufficient to reduce the metal oxide or oxides sought to be recovered to the metallic state and to sweep the vapor of the reduced metal from the furnace or retort into a metal or metal oxide recovery section or vessel. The hydrogen used should be of 95% or higher purity. Water vapor may constitute from about 0% to about 5% of the total gas introduced to the furnace, but the preferred range is 0% to about 1.0%. Inert gases such as nitrogen, argon, neon, and the like may be present, but the total of such gases and water vapor should be as low as possible. Oxygen should be eliminated from the incoming gas stream or should be below its explosion limit in hydrogen.
  • h. In the U.S. Pat. No. 4,836,847A, zinc is recovered for electric arc furnace dust. This invention relates to the metallurgy of iron and particularly to the separation and recovery of metals from electric arc furnace (EAF) dusts. This invention describes a method to separate and recover the volatile heavy metals from the flue dust material and to convert the remaining iron into recyclable directly reduced iron pellets reduced in an inclined directly heated rotary reduction smelter vessel. Zn and Pb are recovered from the molten stage. The distilled heavy metals are reoxidized and may be selectively segregated to reduce the gangue and lead oxide contamination from the reconcentrated zinc oxide dust. The reconcentrated heavy metal oxide dust is recycled by the zinc/lead industry.
  • This disclosure includes a method for processing and extracting of metals from industrial by-products, waste materials and minerals includes the steps of mixing and agglomerating material with a reducing agent and additives to a) enhance the microwave absorption; b) improve internal gas diffusion of pellets, and c) decrease sintering temperature than drying and heating pellets using modular heating system.

The system includes:

• • a. a dryer that has either both or one of conventional direct gas convection heating, radiant heating and microwave heating to evaporating the water and preheat the pellets. The dryer is used to dry the wet pellets using natural gas heat or waste heat from the kiln flue gas. The moisture in pellets is preferably reduced from about 20% H₂O content to less than about 3% H₂O residual content. The heat dryer is used for residual water content over about 3%. The microwave dryer, using energy generated by microwave magnetrons, is used to reduce the residual water content to less than about 3%.
  • b. a modular furnace, that can have both or one of an indirectly heated radiant heat and microwave energy. The furnace is used to accelerate pre-heating and activation of pellets in a controlled reducing environment by using carbon and/or hydrogen and nitrogen atmosphere with controlled oxygen level, then further heating the pellets above about 900° C., contacted with a flow of controlled gas mixture to reduce and volatilize the metals and metal oxides and separate them from the solid CIP material. The metal vapor is then oxidised, oxides are condensed and precipitated.
  • Microwave-assisted heating by the dryer and modular furnace may involve two types of energy for heating the material: microwave energy and thermal energy. This provides significant benefits to drying, preheating and further thermo-processing of pellets over conventional processes. As is best understood, each pellet becomes the heating element as the response to the microwave energy (microwave effect). The pellets are made using a dust pre-mixer. The dust pre-mixer mixes a portion of raw material dust, such as EAF dust. The dust may be mixed with carbon, water and other additives, and a pelletizer to form pellets. The pellets have a size distribution of about 1 to 12 mm, and preferably have a dimension of about 5 mm.

With radiant heating, the material's surface is first heated followed by the heat moving inward. This means that there is a temperature gradient from the surface to the inside. However, microwave heating generates heat within the material first and then heats the entire volume.

Using both radiant heat and microwave system in which the energy source can be varied without affecting a wide range of other variables is beneficial for the processing material.

Benefits from the microwave effect has been observed in which a variety of materials have been heated using both small scale radiant heat and microwave modular heating, but in each case using the same experimental system. A hybrid modular system has been used to investigate the microwave effect during the material changes.

Modular heating system is a form of indirectly heated High Temperature Metal Recovery (HTMR) processing. It has advantages, such as increased heating rate, uniform heating, reduced processing and lower capital cost compared to conventional directly heated HTMR methods. Microwave processing can improve the macroscopic mechanical performances of particles in pellets. The performances of microwave-sintered pellets on the microscopic scale are rarely investigated. The composite pellets are dried and thermo-processed by using the hybrid modular heating system, which combines the characteristics of microwave heating and radiant heating.

Microwaves can penetrate an entire matrix while offering improved process efficiency. The distribution behaviors of pore ratio and permeability in the pellets indicate that the processing is homogenously improved by hybrid modular hearting systems.

The present disclosure provides a significantly improved method for separation and extraction of metals and metal oxides from industrial minerals and waste materials containing zinc, lead, cadmium, arsenic, iron, mercury and selenium using a modular heating system (MHS) microwave-assisted processing of material with accelerating pre-heating/activation/metal evaporation in controlled reducing environment.

The present disclosure provides a heating apparatus of a modular furnace with either one of or both radiant heat and microwave heating that is capable of integrating a radiant heating system with microwave heating system installed in a furnace chamber. The furnace is capable of improving heat efficiency and capable of improving process of heating material and shortening the drying and heating speed by effectively transmitting heat to the material.

There is provided a heating apparatus of a modular furnace that includes an indirectly heated rotary tube or conveyer installed at the furnace chamber into which a material is to be received, having an opening, a nitrogen supply inlet, for supply of nitrogen atmosphere inside the furnace chamber and a discharge opening for discharging gas with vaporized metals. The conveyor or other conveyance system may be variable to control the speed the material passes through the furnace chamber. The heating apparatus has a first heating module installed at the furnace for generating convection heat. A second heating module may also be installed for generating a radiant heat. A ventilating fan may also be installed for hot process gas flow co-currently with heated material where the exhaust is formed for circulating gas inside the heating furnace through a first cooling module and the second heating module.

The EAF Dust may be mixed and agglomerated with a reducing agent and additives to enhance the microwave absorption and internal gas diffusion of pellets and decrease sintering temperature, then dried and heated using a dryer to evaporate water and preheat the pellets. The reducing agent is preferably a carbonaceous reducing agent.

The heating is used to dry the wet pellets and may use waste heat from the furnace flue gas to reduce the moister from about 20% H₂O to less than about 3% H₂O residual content. The microwave heating module can be used with magnetrons to reduce the residual water content to less than about 3% of H₂O.

Dried pellets are pre-heated up to about 560° C., preferably up to about 450° C. The dried pellets may then be further heated in the same modular furnace to above 900° C., preferably less than 1100° C. Once heated, the pellets are contacted with a flow of controlled-reducing atmosphere to volatilize the metals and metal oxides for recovering and separation from processed material.

The heating module for generating a convection heat and the heating module for generating the radiant heat may be separately mounted.

Microwave heating provides significant benefits to drying and preheating of pellets over conventional heating alone. Each pellet becomes the heating element as the response to the microwave energy.

The modular furnace is used for further heating the pellets above about 900° C., contacted with a flow of controlled gas mixture which can contain hydrogen to reduce and volatilize the metals and metal oxides for recovering and separation from solid CIP product.

The heating module for generating a convection heat is used to further heating the pellets above about 900° C. The hot process gas is circulated in the concurrent direction of the furnace chamber as indicated in the arrows as shown in FIG. 1, heating the material.

The microwave heating may be done using a microwave heating semi-cavity comprising a wave guiding channel, a microwave heating semi-cavity sleeve and a microwave heating semi-cavity body. The microwave heating semi-cavity and said conductive heating semi-cavity can be coupled to form a microwave resonant cavity, with microwaves generated by the microwave heating unit propagated via a wave guiding channel into the microwave resonant cavity to effect on the heat-receiving pellets.

The modular heating and processing of materials is a technology that can provide the material processor a new, powerful, and significantly different tool with which to process materials that may not be amenable to conventional means of processing or to improve the performance characteristics of existing materials.

The modular heating system processing has distinct advantages over conventional processing means. The modular heating systems optimally combine microwave sources with other heat sources to balance process variables such as required energy consumption, process time savings, increased process yield, and introduce environmental benefits by using clean energy.

Accelerate kinetics of the drying and metal recovery process may represent a significant, largely untapped thermo-processing improvements enhancing of processes due to enhanced sintering, grain growth, and diffusion rates, and faster apparent kinetics of metal evaporation. Metal vaporisation and chemical reducing reactions are enhanced by reverse thermal gradients that can be achieved using microwaves. Rapid microwave heating and water evaporation during drying can reduce residual water content from about 3% to less than about 1% in pellets.

Using a microwave furnace consumes significantly lesser time than a conventional furnace for the material drying and heating. Microwave radiation uses less energy than that of conventional heating. Materials heated using hybrid systems that allowed both radiant and microwave hybrid heating benefit from this reduced time and energy usage.

A gas mixture containing hydrogen is introduced into the indirectly heated modular heating system (MHS) at a rate sufficient to reduce the metal oxide or oxides sought to be recovered to the metallic state and to precipitate the vapor of the reduced metal from the furnace in the metal collection section.

The 4% by volume, lower explosive limit (LEL) of hydrogen in air is the minimum concentration of hydrogen used in the gas mixture. Inert gases such as nitrogen, argon, neon, and the like may be present. Oxygen level in the mixture should be below about 8%, preferably below about 0.5%.

The reduction of residual water content to less than about 3% in pellets is beneficially used to extract residual water prior to exposing the pellets to the high temperature furnace to prevent compromising the mechanical integrity of pellets. It can be used for a range of applications where the required residual moisture content has to be lower than 1%. Microwave drying is quicker and more energy efficient below about 10% of moisture in the pellets than traditional drying methods, such as convection ovens.

Described methods may be used for the recovery of Zn, Pb, Cd, As, Fe, Hg and Se and for separating and recovering metals and metal oxides from industrial waste material containing Zn, Pb, Cd, As, Fe, Hg and Se comprising the following steps:

• • a. mixing and processing the industrial waste material comprising metals and metal oxides with microwave absorption material which enhance the microwave absorption properties and a carbon based reducing agent to form a solid agglomerated material. Microwave absorption material examples include graphite, graphene, carbon nanotubes (CNTs) and carbon fibers, oxides such as Fe₂O₃, Fe₃O₄, ZnO and carbides such as SiC.
  • b. drying and preheating pellets to a temperature below about 300° C., preferably about 170° C. by a dryer heating using a microwave heater to form a preheated pellets;
  • c. heating the solid agglomerated material using convectional drying combine with microwave-assisted reduction of processed material with accelerating pre-heating/activation in controlled reducing environment (containing nitrogen mixed with hydrogen), then heated material above about 900° C., reduction of metals using a nitrogen atmosphere which can contain hydrogen until a zinc, lead and other volatile metals in the preheat pellets vaporize to form a metal vapor and residual pellets;
  • d. contacting the material in oxidizing zone with a recycled process gas and/or nitrogen and oxygen atmosphere comprising of controlled oxygen concentration wherein the concentration of N₂ is preferably more than about 90% and O₂ concentration less than about 10% by volume;
  • e. volatilizing the metals and oxidizing it in oxidizing zone to produce metal oxides; and,
  • f. separately recovering solid zinc concentrate using process gas cooling system and metal oxide dust collector.

The method may volatize the metals and metal oxides of Zn, Pb, Cd, As, Se and Hg. The residual solid CIP can be composed of iron, calcium, aluminum, silicon, or other inorganic materials suitable for further processing in steel, cement and iron alloy manufacturing or fill in the construction industry.

In an embodiment, the O₂ volume may be less than about 10%, preferably less than about 5%. The counterflow gas may comprise an inert gas such as nitrogen or a reducing gas such as CO, hydrogen or methane in an amount of about 5% by volume.

Additives such as microwave absorption material and carbon based reducing agent are used to increase pellets porosity, its inner surface, area to increase gas diffusion of pellet, increase microwave absorption and reduce processing temperature.

With reference to FIG. 1, an embodiment of the process of the disclosure in which, in the pre-treatment step, iron or steel dust 100 containing Zn, Cd and Pb is first mixed together with additives 105, such as carbon and/or reducing agents and water 110 to form pellets at a pelletizer 115. It is believed that the additives carry out the following functions: increasing the surface area and porosity of pellets, increase gas diffusion of pellet, increase microwave absorption and reduce sintering temperature, which is beneficial to reduce residual water content in pellets to less than 1% and for more effective release of the volatile metals from pellets matrix.

The mixture is pelletized using conventional methods 115. In a preferred embodiment, a liquid such as water 110 or wastewater is added to the mixture which is pelletized. The wet pellets 120 are heated using a dryer 125, such as a heat dryer and/or microwave dryer to evaporating the water and preheat/activate the pellets to temperature up to about 300° C. The dried and preheated pellets 130 are fed into a modular heating system 135.

The reducing agents 105 comprise about 5-20% by weight of the dried pellets, and preferably about 13% by weight of the dried pellets. In particular, the reducing agents are preferably in the form of carbon dust form. It is believed that the reagents carry out the following functions: release the volatile metals from hard to reduce complexes; reduce the oxides to metals; react with CO₂, HCl and SO₂ during the reduction of oxides to metals; and produce residual by-product (iron, calcium, aluminum, silicon or other inorganic materials) with composition suitable for further applications.

The dried and preheated pellets 130 are fed into modular heating system 135. The furnace 135 is an air sealed reactor with one cooling zone 150 and two processing zones 140, 145 which are heated indirectly to a temperature higher than about 900° C. and preferably in the range of about 1000-1150° C. The heat may be obtained by conventional radiant heat combined with microwave heat. The counter flow gas may also be heated and used as an energy source.

The heated material in the reactor is contacted with gas comprising an inert gas such as nitrogen 155 and/or a reducing gas such as CO, hydrogen, methane or combinations thereof. The oxygen concentration should be lower than about 10% by volume and preferably less than about 1% by volume depending on whether the metals in the gas stream are to be oxidized to metal oxides in oxidizing zone. Preferably, the total of CO₂, CO and H₂ concentrations is more than about 5% by gas volume to reduce and vaporize the desired metals and/or metal oxides and to vaporize alkali metal salts.

The vaporized and precipitated metal concentrate comprises mostly Zn, Cd and Pb oxides and is cooled and separated from the gas stream in process gas cooling system 160 and collected in dust filter, cyclone or by electrostatic precipitation and stored in a product silo. A water/air cooling system may be used. Water or air may be injected into the incoming process gas from the furnace so that the process gas containing vapours causes metal oxides to precipitate and accumulate in the form of dust. Generally, the concentration of impurities like Fe, Mn, Ca are very low, and the alkali metal salts can be separated from the metal concentrate by washing with water or by thermal processing before the concentrate is shipped for further refining. The process gas 165 is partially recycled back into the process.

The solid residual product is then removed from the reactor and cooled. The solid residual product preferably has less than 10,000 ppm of Zn, Cd or Pb. The solid residual product can be recycled to a steel, cement and metal alloy making process.

The heating system of a modular heating furnace may further include ventilating fans and the first and the second module for guiding process gas flow through the furnace. In the heating apparatus of a modular heating furnace of the present disclosure, both ends of furnace are air sealed.

With reference to FIG. 2, an embodiment of a modular heating furnace 200 having two heating rotary tube zones 205, 210 and one cooling zone 215 is schematically represented. Radiant heat or microwave heat (using magnetrons 207) or a combination of both heat sources is used. In the first heating rotary tube zone 210 an oxidizing atmosphere is used and in the second heating rotary tube zone 205, a reducing atmosphere is used. The processed gases 220 that flow counterflow to the pellets are captured in a gas cooler 225 and processed as described above at [0059]. Residual CIP pellets 230 that exit the cooling zone 215 are primarily concentrated iron. Flue gases may be discharged, or cooled and used to dry the pellets.

With reference to FIG. 3, an embodiment of a modular heating system furnace system 300 having two heating rotary tube apparatuses 305, 310 is schematically represented. An indirectly heated rotary furnace 310 uses radiant heat and/or microwave dryers (using magnetrons 315). A rotary heating dryer 305 uses furnaces with radiant (using burners 330) and microwave heat source (using magnetrons 320). The processed gases 325 that flow counterflow to the pellets are captured in a gas cooler 350 and processed as described above at [0059]. Residual CIP pellets 335 exit the furnace system 300 and may pass through a cooling zone (not illustrated). Air filter 340 processes the flue gas and may collect zinc oxide product.

A modular furnace that uses indirectly heated radiant heat and/or microwave furnace accelerate pre-heating and activation of pellets in controlled reducing environment. Microwave-assisted heating of the modular furnace involves two types of energy for heating the material; microwave energy and thermal energy from the external sources which provides significant benefits to drying, preheating and further thermo-processing of pellets over the prior art processes. Each pellet becomes the heating element as the response to the microwave energy (microwave effect).

When the radiant heat and the convection heat are simultaneously supplied into the apparatus, the temperature of the pellets typically goes up quickly, so that the processing speed can be increased.

The heater generating the radiant heat and the heater generating the convection heat are inserted in the furnace which is installed either in two modular or in one modular chamber. The installation space is considerably reduced in one modular chamber. Accordingly, the system can be compact, and accordingly as the number of components is reduced, its fabrication cost can be reduced. Secondly, the heat efficiency can be improved. In addition, since the heat is uniformly transmitted to the pellets, a processing can be improved and retention time can be shortened.

As the present embodiments may be in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its scope as defined in the appended claims, and therefore all changes and modifications that fall within the meets and bounds of the claims, or equivalence of such meets and bounds are therefore intended to be embraced by the appended claims.