WO2014183177A1

WO2014183177A1 - Method for reducing iron ore in a reactor with transient plasma torches

Info

Publication number: WO2014183177A1
Application number: PCT/BR2013/000461
Authority: WO
Inventors: Alberto Carlos PEREIRA FILHO
Original assignee: Pereira Filho Alberto Carlos
Priority date: 2013-05-14
Filing date: 2013-11-04
Publication date: 2014-11-20
Also published as: BR102013011912A2

Abstract

A method for reducing iron ore in a reactor with transient plasma torches essentially consists in using the reactor (1) with torches (2) of transient plasma technology as a catalytic converter for generating the iron ore reducing agent from natural gas or another hydrocarbon, such that reduction, synthesis gas production and enthalpy occur in a single environment.

Description

"Process for Iron Ore Reduction in Transient Regime Plasma Taps"

Short presentation

This patent application deals with the use of transient plasma technology torches in a compact reactor, which combined with the use of a hydrocarbon as fuel, preferably natural gas, generates a synthesis gas and thermal energy capable of making the reduction of pig iron in the same environment.

Application field'

Related to the ferrous and non-ferrous metal ore reduction segment, in particular but not limited to iron ore and may be applied in the reduction of other ores, metal oxides provided that the synthesis gas behaves well as a reducing agent. .

Basement

I) From metallurgy:

Iron metallurgy basically consists in the reduction of its oxides with the use of a reducing agent.

Traditionally, the transformation of iron ore into pig iron is performed in a so-called blast furnace equipment better represented by a large bowl, 50m to 100m high, which in addition to the ore also welcomes metallurgical coke and fluxes.

The basic principle of operation of a blast furnace is the removal of oxygen from the ore using mineral or vegetable coal or even the babassu coconut shell, which is thus reduced to iron. Thus, the reduction is the result of combining the carbon present in the coke with the ore oxygen, which in an exothermic reaction generates CO. Upon contact with hot air ( ^s 1000 ° C) blown through the vents, the coke comes into combustion generating heat and reducing iron ore, resulting in pig iron and slag, the temperature inside a Blast furnace can reach 1500 ° C. However, the traditional process requires some raw material preparations:

a) Coke oven - composed of a battery of coke ovens or cells where coke impurities are eliminated. The resulting product is metallurgical coke which is a porous residue composed mainly of carbon having high mechanical strength and high melting point.

b) Sintering - The preparation of iron ore for the production of pig iron is the most modern improvement of the modern blast furnace. To the ore fines are added fluxes (limestone, sand and silica fines, for example, and coke mill, as well as sinter fines). The components are deposited on a movable grate that passes through an oven that melts the mixture. This is followed by a cooling and crushing process, so that the material reaches the appropriate particle size since the finer grains are undesirable as they reduce the air permeability in combustion, compromising burning. To solve this problem, flux materials are added. This whole agglomeration process is called sintering, whose end product is the sinter with an average diameter of more than 5 cm.

II) From plasma:

Plasma can be understood as an ionized gas at elevated temperatures compared to conventional systems such as combustion, electrical resistance and others. The typical range of temperatures achieved by thermal plasmas ranges from 5,000 ° C to 10,000 ° C, although it is possible to reach higher temperatures. Plasma is generated by the use of electricity and a gas as a conductive fluid with high energy efficiency in so-called "plasma torches". Once controlled, there is a high electron temperature and less energy transfer to the heavy particles (ions and neutral particles). Under such thermodynamic conditions, some plasmas, known as transient plasmas, registered in Brazil as Rotex plasma, offer great advantages in chemical processes, with low power consumption, acting as dissociation catalysts, offering good selectivity, presenting high conversion rates. .

State of the art

A wide range of processes for reducing iron ore using coke, charcoal and other raw materials as reducing agents are known.

To overcome the problem of coke in the production of pig iron from iron ore, new processes and technologies are developed, such as RDI (Reduction Direct Irorí), including Hlsmelt®, Fastmelt, Corex, Redsmelt, Midrex. , Technored, etc.

US 4752329 - Midrex - a method of producing blast furnace iron in which the upper zone reduces iron oxide by reaction upon contact with a gaseous reducing agent represented by natural gas. Thus, synthetic gas obtained from natural gas is used as a reducing agent.

The process requires a synthesis gas production unit (H ₂ and CO), obtained from the partial combustion of natural gas, which is directed to the ore reduction unit. US4439233 anticipates a method for the production of synthesis gas, in which natural gas and Water vapor passes through a steam reformer to form the reducing gas at elevated temperature.

A drawback of the above process is the high cost of implantation, and the iron produced, not liquefied due to the low temperature achieved, is of inferior quality, popularly known as "sponge iron".

The Fastmelt process uses natural gas, oil and pulverized coal as reducing agents, but does not employ plasma but a burner. The reactor is of the rotary type, different from the one proposed in this claim, in addition the ore receives a carbon-enriched sintering preparation.

Purpose of the invention

Technology for the production of pig iron based on the use of natural gas or any other hydrocarbon, liquid or gaseous or even heavy oil, as a reducing agent, combined with electrical energy applied to transient plasma torches, with no need for materials raw materials undergo the primary coke oven / sintering processes and also the plant for the production of synthesis gas, thus being injected directly into the reactor in the natural state characterizing an RDI (Reduction Direct Iron) process.

The process is made possible by the different characteristics of the reactor containing transient plasma torches whose quantity is determined by the desired production capacity, torch channels through which the plasma flows and the bowl where a plasma zone and a zone are configured. through which they pour liquid metal and slag, in an operating regime very similar to that of a blast furnace leak, but without the use of coke or charcoal, which depending on the procedural advantage can also be used. Thus, part of the energy contained in the synthesis gas is used for preheating and reducing the ore load. In turn, the differential in the fusion zone is the atmosphere with strong presence of the synthesis gas, which prevents reoxidation. Residual reduction of iron oxides present and dengue and ash scorification occur in the liquid state in the lower vat.

In the process, the natural gas or hydrocarbon is injected into the transient plasma torch with the addition of compressed air in an appropriate equivalence ratio for the formation of the synthesis gas and heat production, according to the reaction below:

Basic reaction of methane gas in synthesis gas

CH ₄ + ½ 0 ₂ + plasma → CO + 2H ₂

Then the fresh ore is injected, which in contact with the gas and the temperature undergoes the reduction process according to the reactions below, which may occur in different ways:

Hematite to Magnetite

3 Fe ₂ 0 ₃ + CO = C0 ₂ + 2 Fe ₃ 0 ₄ starts at 850 ° F

3 Fe ₂ 0 ₃ + H ₂ = H ₂ 0 + 2 Fe ₃ 0 ₄

Magnetite in Wustite - Iron Oxide

Fe ₃ 0 ₄ + CO = C _{2 2} + 3 FeO starts at 1,100 ° F

Fe ₃ 0 ₄ + H ₂ = H ₂ 0 + 3 FeO

Wustite - Iron Iron Oxide

FeO + CO = Fe + C0 ₂ starts at 1300 ° F

FeO + H ₂ = Fe + H ₂ 0 In the melting zone, inside the reactor, the liquid and agitated material remains in constant interaction with the synthesis gas, increasing the residence time of the process and, consequently, the rate of conversion of iron ore to pig iron. For separation of impurities, agents such as limestone, dolomite or the like are added to the ore according to their chemical need by the action of these agents. Iron in the liquid state and in the bottom of the reactor is continuously poured at a rate defined by the function of its feed rate and synthesis gas consumption. Supernatant slag is expelled through a passage in the middle of the reactor. For process optimization, the remaining gases make their way to the thermal reserve unit positioned at the upper reactor inlet. In this unit the first ore reductions occur, as shown in the above equations. Afterwards, the exhaust gases pass through a set of filters, cleaning and burning the residual fuel, to finally be thrown into the atmosphere. Depending on the composition of exhaust gases, they can be reused in energy production.

Major changes to the process

The replacement of coke or charcoal by natural gas, or another hydrocarbon, which provides thermal energy and at the same time part of it is converted into synthesis gas thanks to transient plasma torches.

These modifications imply a series of differentials in relation to conventional processes, involving equipment, raw materials, procedures, and mainly technology.

a) Equipment: The main difference from the blast furnace or even the conventional RDI process is the transient plasma torches installed in the reactor;

Power source for plasma torches;

Compressed air generator unit for plasma torches; Natural gas or other hydrocarbon network for synthesis gas generation;

s Mineral load feeder to the reactor;

Thermal reserve unit for preheating and reduction of iron ore in its oxide phases.

b) Raw materials:

Liquid or gaseous hydrocarbon, in particular natural gas, but may also be used, heavy oil, diesel oil, gasoline, ethanol and even pulverized coal;

Compressed air;

Fresh iron ore ore fines, without preparation (sintering in the case of the blast furnace);

Cooling water;

Loads - according to the needs of slag separation chemistry and metal cleaning in the process.

c) Procedures and technology:

Synthesis gas production, ore reduction and enthalpy generation are performed in the same environment, ie in the reactor with a more favorable kinetics due to the high temperature achieved with the torches.

Description of the figure Figure 1: Schematic view of the main components of the invented process.

Detailed Description

The "PROCESS FOR REDUCING IRON ORE IN TRANSIENT PLASMA TORCH REACTOR" object of this patent application consists essentially of the use of torch reactor (2) with transient plasma technology as catalytic converter in the generation of the iron ore reducing agent from natural gas or another hydrocarbon, so that the reduction, synthesis gas production and enthalpy occur in the same environment.

More particularly, the claimed process does not require the blast furnace figure as it uses transient plasma technology, ie in an intermediate range between cold plasma and thermal plasma effected by compact torches (2) strategically located in the area. of plasma (3) from an equally compact reactor (1), thus acting as a catalytic converter in the generation of the synthesis gas via natural gas or another hydrocarbon. Catalysis is explained by the combination of the high inherent plasma temperature and the high density of high energy electrons above 2eV of cold plasma. Torches (2) are connected to an external plasma source (4), natural gas or other hydrocarbon network (not shown) and a compressed air source (not shown). A mineral feeder (5) containing ore fines and or in natura iron ore with the fillers provides this material to the reactor (1), in a ratio proportional to the required pig iron flow rate and the synthesis gas, not without it must first pass a thermal reserve unit (6) using the hot gas return from the melting zone (7) located above the plasma zone (3). In unit (6) Preheating takes place favoring the first reductions of ore oxides, especially hematite and magnetite, due to the presence of the countercurrent hydrogen and carbon monoxide reducing gases at a temperature of 450 ° C to 850 ° C, suitable for this stage. Thus, the preheated mineral charge is carried to the melting zone (7) where it is subjected to the action of plasma from the torches (2) blowing high temperature synthesis gas to the central reactor bowl in the melting zone. (7) itself. In this phase, already in liquid form and in a state of agitation, the ore remains in contact with the synthesis gas, interacting with it and increasing the reduction period. To further increase the residence time and the interaction between the reducing agent and the ore, the synthesis gas makes up a vortex helical path. After performing the vortex trajectory, the gas is forced out of a central opening (8) directed to the thermal reserve unit (6), and thereafter to the filter assembly (9) where it is treated through a duct. When faced with a fork (10), the gases are directed to a flare chimney (11) in which the residual fuel is burned to finally be thrown into the atmosphere. Depending on the composition, exhaust gases can be reused in energy production (12). Thus, the highest density material, ie pig iron, is deposited on the underside of the reactor and drained through a passage (13) towards a crucible (14). On the other hand, the lower density material, the slag, remains in the supernatant and is leaked through a lateral passage (5) and from there to another crucible (16).

In addition to natural gas, other hydrocarbons such as gasoline, diesel and ethanol can be used by adjusting the fuel supply system and adjusting the air / fuel mixture inside the torch (2). The reactor (1) is designed to operate at elevated temperatures in the range 1500 ° C to 1600 ° C, and is coated with refractory cement and insulating material.

Transient plasma source (4) is an alternating or direct current electro-electronic equipment with variable power according to the appropriate reduction ratio. The source (4) has a current and power control system, electrical resistors, circuit breakers, special wiring, high voltage fuses and other components necessary for its operation.

Non-equilibrium transient plasma torches (2) bring together the benefits of good energy density thermal (high temperature) plasma with the advantages of "corona", "glow", and cold plasma discharges. which have high selectivity of radicals and energetic electrons. Typical electron temperatures in these plasmas range from 11,000 ° K (~ 1 eV) to over 23,000 ° K (~ 2eV), which is sufficient to break the bonds of the gas and oxidizer molecules and is sufficient to produce free radicals. The fluid is cracked into smaller radicals, energized in excited states or transformed into free radicals, which contribute to the formation of the process synthesis gas. Thus, it is possible to obtain a high rate in the production of energetic electrons, which enables the dissociation of molecules in favor of synthesis gas formation and the generation of enthalpy in the process.

Used with natural gas and air, in an appropriate equivalence ratio, an average conversion factor in synthesis gas production of 80% is reached. The conversion factor is the ratio of the amount of synthesis gas produced by the quantity of natural gas, ie:

a = [H ₂ ] [CO] / 3 [CH ₄ + ...] For the transient plasma torch, α = 0,65 to 0,80, ie for 1 m ³ of natural gas around 1,95 to 2,4 m ³ of synthesis gas (CO + H2). The process temperature is controlled from 1500 ° C to 2400 ° C.

Constructively, the transient plasma torch is basically composed of two electrodes - cathode and anode, between which an electric arc is maintained. The passage of a gas (any gas can in principle be used), initially at room temperature, through the electric arc causes collisions between the electric arc electrons and the molecules or atoms (in the case of inert gases) of the gas. These collisions transfer some of the electron kinetic energy to the gas, dissociating it and ionizing it directly or by thermal ionization.

The transient plasma torch is a device based on a cylindrical geometry, generating a plasma in a continuous volumetric flow, providing a uniform flow for discharge and application in the process. The flow is of the reverse vortex type very similar to a tornado that develops inside the torch. When high voltage is applied, the arc begins at the small gap between the electrodes. Due to the strong effect of vortex flow, the arc is forced to lengthen on one of the electrodes inside the cylinder. To lengthen the arc, a greater demand for power is required. As the arc stretches, the voltage increases and the current decreases; consequently, the electric field and the electron temperature increase, but the gas temperature decreases. Therefore, plasma intensifies its non-equilibrium state. Plasma zone reactive species are trapped within the reactor. Recirculation is critical for catalytic reactions via plasma. All gas passes through the discharge zone and may be pure or a mixture of various types of gases or liquids such as air and ethanol, air and methane, air and pulverized coal, air and butane, pure methane, air pure etc.

Claims

1) "PROCESS FOR REDUCING IRON ORE IN TRANSIENT PLASMA TORCHES", characterized by the use of a transient plasma in an intermediate range between cold plasma and thermal plasma, effected by a compact torch (2) installed in the plasma zone (3) of a compact reactor (1), thus acting as a catalytic converter to generate a synthesis gas as a reducing agent from natural gas or another liquid or gaseous hydrocarbon with enthalpy required to maintain the temperature in the melting zone between 1500 ° and 1600 ° C.

2) "PROCESS FOR REDUCING IRON ORE IN TRANSIENT REGIME PLASMA TORCHES" according to claim 1, characterized in that the reduction, synthesis gas production and enthalpy occur in the same environment.

3) "PROCESS FOR REDUCING IRON ORE IN TRANSIENT PLASMA TORCHES" according to claim 1, characterized by the use of hydrocarbons such as gasoline, diesel and ethanol by simply adjusting the fuel supply system and an air / fuel mixture adjustment inside the torch (2). (4) "PROCESS FOR REDUCING IRON ORE IN TRANSIENT PLASMA TORCHES" according to claim 1, characterized in that control of the torch temperature makes it possible to reduce other ferrous and non-ferrous metal ores.

5) "PROCESS FOR REDUCING IRON ORE IN TRANSIENT PLASMA TORCHES" according to claim 1, characterized in that the torch (2) in the plasma region (3) of the reactor (1) is connected to an external source (4), the natural gas network or other hydrocarbon to a source of compressed air.

(6) "PROCESS FOR REDUCING IRON ORE IN TRANSIENT PLASMA REACTOR TORCHES" according to Claim 1, characterized by a mineral filler (5) containing ore fines and / or fresh iron ore with loads, make this material available to reactor (1), not without first passing through a thermal reserve unit (6) using the hot zone gas of the melting zone (7) located above the plasma zone (3) where it is subjected to plasma action from the torches (2); gas is forced out of a central opening (8) directed to the thermal reserve unit (6), and thereafter into the filter assembly (9); at a fork (10), the gases are directed to a flare chimney (11) in which it is burned and depending on the composition, exhaust gases can be reused in energy production (12); the higher density material, the pig iron is deposited in the bottom of the reactor and drained through a passage (13) towards a crucible (14); the lower density material, the slag, remains in the supernatant and is leaked through a lateral passage (15) and thence to another crucible (16).