WO2021106008A1

WO2021106008A1 - A countercurrent reactor

Info

Publication number: WO2021106008A1
Application number: PCT/IN2020/050517
Authority: WO
Inventors: Narendra DHOKEY; Sameer Shinde
Original assignee: Dhokey Narendra; Sameer Shinde
Priority date: 2019-11-28
Filing date: 2020-06-11
Publication date: 2021-06-03

Abstract

A countercurrent reactor for powder metallurgy processes, said reactor comprising a rotary kiln (300) with variable angle, said rotary kiln (300) being provided on a bed (301) configured with a movable mechanism (302), at its second end (304), in order to provide said variable angle to said rotary kiln (300); thereby making flow of input powder, from its first end (306), to be gravity fed in order to achieve controlled angled flow rate for said input powder.

Description

A COUNTERCURRENT REACTOR

FIEUD OF THE INVENTION:

This invention relates to the field of metallurgy.

Particularly, this invention relates to the field of powder metallurgy.

Specifically, this invention relates to a rotary kiln based process for powder metallurgy processes.

More specifically, this invention relates to a countercurrent reactor.

BACKGROUND OF THE INVENTION:

In the field of powder metallurgy, there are two prior art processes already known: a) Pyron process b) Hoganas Process

Figure 1 illustrates a flow diagram of the Pyron process.

In the Pyron process (100), mill scale (raw material, 12) is basically obtained from steel mills which produce sheets, rods, wires, plates and pipes. The mill scale mainly consists of Fe₃ O4, and also contains oxides of tramp elements normally associated with steel, especially Si, Mn and Cr in the form of very finely dispersed oxides; which are difficult to reduce. The mill scale is cleaned (14) dried and ground up (16, 18) to a desired particle size in a continuous ball mill. Oxidation (22) of the mill scale at 870 to 980 °C converts Fe O and Fe₃ 0₄ to ferric oxide (Fe₂ 0₃). This process is essential to ensure uniform properties of Pyron-iron Powder. Reduction (24) of ferric oxide by hydrogen is done in an electric furnace (30 - 40 meter long) at 980°C . (continuous belt furnace). Hydrogen is supplied by NH₃ cracking plant and reduction is done at 980°C.

Fe₂0₃ + 3H₂ = 2Fe + 3H₂0

The reduction product is ground and mechanically densified (26, 28) to make it suitable for production of structural parts. In this process,

Fine particle size - small pores - faster sintering.

Reference numeral 32 refers to storage. Reference numeral 34 refers to a step of blending. Reference numeral 36 refers to packaged final product.

However, the Pyron process utilizes stationary bed during reduction.

In the Hoganas process, pure magnetite (Fe₃0 ) is used. Coke breeze is the carbon source used to reduce iron oxide. Some limestone is also used to react with the sulphur present in the coke. The mixture of coke and limestone (85% + 15%) is dried in a rotary kiln and crushed to uniform size. The ore and coke-limestone mixture is charged into ceramic tubes (Silicon Carbide) with care so that ore and reduction mixture are in contact with each other but not intermixed. It can be achieved by using concentric charging tubes with in the ceramic tube. Charged ceramic tubes are loaded on the Kiln cars (thirty six tubes on each) and cars are pushed into 170m long tunnel kiln where the reduction occurs. The total time a car is present in the kiln is 68h. Gas burners heat the 150m tunnel at a temperature of 1200-1260°C and remaining length is cooled by air circulation. Within the hot zone, several chemical reactions occur and metallic iron is formed in the form of sponge cake. However, the Hoganas process utilizes mixing of magnetite ore with carbon and lime, long processing time of 60 hrs plus and ceramic tubes are used to store raw material for processing.

Therefore, there is a need for a system and method which overcomes the limitations of the prior art.

OBJECTS OF THE INVENTION:

An object of the invention is to provide a ‘green’ technological process.

Another object of the invention is to improve production.

SUMMARY OF THE INVENTION:

According to this invention, there is provided a countercurrent reactor for powder metallurgy processes, said reactor comprising a rotary kiln with variable angle, said rotary kiln being provided on a bed configured with a movable mechanism, at its second end, in order to provide said variable angle to said rotary kiln; thereby making flow of input powder, from its first end, to be gravity fed in order to achieve controlled angled flow rate for said input powder.

Typically, said movable mechanism is selected from a group of mechanisms consisting of a hydraulically movable mechanism, pneumatically movable mechanism, and mechanically movable mechanism.

Typically, said reactor comprises an input for flow of gases at said first end. Typically, said reactor comprising an input for flow of gases at said first end, in that, said gas being selected from a group of gases consisting of Hydrogen gas, Nitrogen gas, Argon gas, and Oxygen gas.

Typically, said reactor is an angularly displaceable reactor.

Typically, said reactor comprises baffles located inside a chamber of said reactor so that input powder does not slide, instead travels through a reaction zone, configured by said chamber, by tumbling; thereby avoiding agglomerated sliding.

Typically, said rotary kiln comprises insulation at its either end.

In at least one embodiment, two separate rotary kilns are placed in series, spaced apart by a conveyor belt, there between, so that after oxidation, reduction can be carried out.

In at least one embodiment, two separate rotary kilns are placed in series, spaced apart by a conveyor belt, there between, characterised in that, a first rotary kiln being configured to provide a first step of oxidation, of said input powder in order to obtain oxidized powder, and a second rotary kiln, in series with the first rotary kiln, being configured to provide a second step of reduction on received oxidized powder from said first rotary kiln in order to obtain a reduced powder.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:

Figure 1 illustrates a flow diagram of the Pyron process. The invention will now be described in relation to the accompanying drawings, in which:

Figure 2 illustrates a process of a countercurrent reactor of this invention;

Figure 3 illustrates a setup of a countercurrent reactor of this invention; and Figure 4 illustrates a graph according to a non-limiting exemplary embodiment of the countercurrent reactor of this invention.

DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS:

According to this invention, there is provided a countercurrent reactor for powder metallurgy processes.

Figure 2 illustrates a process (200) of this invention.

Figure 3 illustrates a setup (300) of this invention.

In at least an embodiment, there is provided a rotary kiln (300) with variable angle. Rotary kiln angle can be changed as per requirement.

A bed (301) is provided on which the rotary kiln (300) is placed. This bed is supported by a hydraulic / pneumatic / mechanical arrangement (302) at its one end in order to provide this variable angle.

This makes the flow of input powder to be gravity fed. Apart from being gravity fed, the angle is pre-determined to the effect that:

- pre-defmed / optimized oxidization is obtained because of controlled angled flow rate; and

- pre-defmed / optimized reduction is obtained because of controlled angled flow rate. Therefore, angle controls flow rate, oxidation rate, and reduction rate; as per user requirement.

Input is provided at one end (304) and flow of gases is provided at the other end (306). For oxidation, this flow of gas is Oxygen gas. For reduction, this flow of gas is Hydrogen / Nitrogen gas.

In at least an embodiment, the rotary kiln is angularly displaceable (308). This is provided so that all the internal particles, being subject to oxidation and / or reduction, rotates / angularly displaces; thereby, allowing opportunity for each particle from all sides to interact with gases. Furthermore, it provides enhanced particle - gas interaction, hence improved productivity.

In at least an embodiment, the rotary kiln comprises baffles (310) located inside the chamber so that so that powder does not slide; this avoids agglomerated sliding

In at least an embodiment, the rotary kiln comprises insulation (312) at its either end.

Using this rotary kiln, with variable angle, a rotary kiln process is devised in which charge is fed from one end and reactive gases entered from opposite end. Firstly, oxidation reaction is carried out in rotary kiln process in which Fe20₃ is obtained with more than 95% purity and, secondly, reduction is carried out by hydrogen with nitrogen as carrier gas. This gives rise to iron powder purity more than 98%. Either both the stages can be carried out in the rotary kiln process or it can be decentralized wherein oxidation in performed in a first kiln and reduction is performed in a second kiln. Both these kilns can be kept in series.

Thus, the same rotary kiln process can be used for oxidation and then for reduction. In both these cases, process completes either in one step or both processes can be carried out in separate rotary kilns and the same can be placed in series, by placing a conveyor belt (318), there between, so that after oxidation, reduction can be carried out.

In a first step (202), mill scale is milled to powder size of 100 micron.

In a second step (204), the powdered output is oxidized, in a first kiln of the rotary kiln (50), at a temperature of 1100°C.

In a third step (206), the oxidized output is reduced, in a second kiln of the rotary kiln (50) at a temperature of 875°C.

The resultant powder can be compacted to pellets and then it can be melted to make ingots.

In the Pyron process, input is Fe₃0₄, whereas in the current invention, input is Fe₂0₃ which is actually an intermittent product obtain at the end of 1 ^t step.

In the Hoganas project, Carbon is used, whereas in the current invention, Hydrogen is used.

No lime, no carbon, but only hydrogen are used. So process categorized as Green technology.

Two-directional input is provided (one input being material and one input being gas) In at least a non-limiting exemplary embodiment, the countercurrent reactor of this invention for Mill scale was used for the processes of oxidation and reduction.

Figure 4 illustrates a graph according to this non-limiting exemplary embodiment, in which the following was observed:

A) Reduced Iron powder. XRD shows strong peaks of metallic iron when subjected to reduction in 50%H₂-50%N₂ (1:1) at 875+5 °C.

B) The metallic purity of reduced iron powder obtained is 98.91% and above.

The TECHNICAL ADVANCEMENT of this invention lies in the provisioning of a rotary kiln with variable angle. The rotary kiln comprises at least two kilns for series-processing or simultaneous-processing. This same rotary kiln process can be used for oxidation and then for reduction. In both these cases, process completes in one step. Or both processes can be carried out in separate rotary kiln and same can be placed in series, so that after oxidation, reduction can be carried out. This is a green technology and no use of carbon. Purity of Fe203 is more than 95 % as intermediate product. Purity of reduced iron powder gives purity of more than 98% depending upon the origin of mill scale.

While this detailed description has disclosed certain specific embodiments for illustrative purposes, various modifications will be apparent to those skilled in the art which do not constitute departures from the spirit and scope of the invention as defined in the following claims, and it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation.

Claims

CLAIMS,

1. A countercurrent reactor for powder metallurgy processes, said reactor comprising a rotary kiln (300) with variable angle, said rotary kiln (300) being provided on a bed (301) configured with a movable mechanism (302), at its second end (304), in order to provide said variable angle to said rotary kiln (300); thereby making flow of input powder, from its first end (306), to be gravity fed in order to achieve controlled angled flow rate for said input powder.

2. The countercurrent reactor as claimed in claim 1 wherein, said movable mechanism (302) is selected from a group of mechanisms consisting of a hydraulically movable mechanism, pneumatically movable mechanism, and mechanically movable mechanism.

3. The countercurrent reactor as claimed in claim 1 wherein, said reactor comprising an input for flow of gases at said first end (306).

4. The countercurrent reactor as claimed in claim 1 wherein, said reactor comprising an input for flow of gases at said first end (306), in that, said gas being selected from a group of gases consisting of Hydrogen gas, Nitrogen gas, Argon gas, and Oxygen gas.

5. The countercurrent reactor as claimed in claim 1 wherein, said reactor is an angularly displaceable (308) reactor.

6. The countercurrent reactor as claimed in claim 1 wherein, said reactor comprising baffles (310) located inside a chamber of said reactor so that input powder does not slide, instead travels through a reaction zone, configured by said chamber, by tumbling; thereby avoiding agglomerated sliding.

7. The countercurrent reactor as claimed in claim 1 wherein, said rotary kiln (300) comprises insulation (312) at its either end.

8. The countercurrent reactor as claimed in claim 1 wherein, two separate rotary kilns being placed in series, spaced apart by a conveyor belt (318), there between, so that after oxidation, reduction can be carried out.

9. The countercurrent reactor as claimed in claim 1 wherein, two separate rotary kilns being placed in series, spaced apart by a conveyor belt (318), there between, characterised in that, a first rotary kiln being configured to provide a first step of oxidation, of said input powder in order to obtain oxidized powder, and a second rotary kiln, in series with the first rotary kiln, being configured to provide a second step of reduction on received oxidized powder from said first rotary kiln in order to obtain a reduced powder.