Search

CA-3264132-C - A METHOD AND SYSTEM FOR HEATING DIRECT REDUCED IRON (DRI) BETWEEN A DRI SOURCE AND PROCESSING EQUIPMENT FOR THE DRI

CA3264132CCA 3264132 CCA3264132 CCA 3264132CCA-3264132-C

Abstract

A method of heating direct reduced iron between a direct reduced iron source and processing equipment for the direct reduced iron, comprises providing a conduit heater assembly between the direct reduced iron source and the processing equipment, wherein the conduit heater assembly receives a flow of the direct reduced iron from the direct reduced iron source and heats the direct reduced iron as the direct reduced iron flows through the conduit heater assembly and to the processing equipment.

Inventors

  • Todd Michael ASTORIA
  • JAMES LLOYD JR. LEWIS

Assignees

  • MIDREX TECHNOLOGIES, INC.

Dates

Publication Date
20260505
Application Date
20210324
Priority Date
20210323

Claims (18)

  1. What is claimed is: 1. A method of heating direct reduced iron between a direct reduced iron source and processing equipment for the direct reduced iron, comprising: providing a conduit heater assembly between the direct reduced iron source and the processing equipment, wherein the conduit heater assembly receives a flow of the direct reduced iron from the direct reduced iron source and heats the direct reduced iron as the direct reduced iron flows through the conduit heater assembly and to the processing equipment, wherein the conduit heater assembly comprises: a conduit configured to receive a flow of direct reduced iron; and a heating element comprising induction heating coils, disposed adjacent to the conduit, wherein the heating element is configured to transfer energy from a power supply in the form of heat to the conduit and heat the flow of direct reduced iron through the conduit, wherein a section of the conduit comprises a pipe and is configured to at least one of: transition to an annular shaped flow path to receive the flow of direct reduced iron and the heating element comprises a parallel set of induction heating coils, or taper out in a first portion of the section of the conduit in a transitional zone to a greater width at a second portion, which transitions to a rectangular shaped flow path, and the induction heating coils comprise rectangular pancake induction heating coils, and wherein the conduit heater assembly forms an elongated feed leg through which the direct reduced iron is heated and flows directly into processing equipment, which is one of a melter, a briquetting machine, and a hot compaction equipment to compact to a higher density.
  2. 2. The method of claim 1, wherein the pipe of the section of the conduit transitions to the annular shaped flow path to receive the flow of direct reduced iron, and the heating element comprises the parallel set of induction heating coils.-15-
  3. 3. The method of claim 1, wherein the first portion of the pipe of the section of the conduit tapers out in the transitional zone to the greater width at the second portion, which transitions to the rectangular shaped flow path, and the induction heating coils comprise the rectangular pancake induction heating coils.
  4. 4. The method of claim 1, wherein the direct reduced iron is hot direct reduced iron from a direct reduction shaft furnace or a direct reduced iron reheating furnace.
  5. 5. The method of claim 1, wherein the direct reduced iron source is at least one of a direct reduction shaft furnace, a direct reduced iron reheating furnace, a surge bin, a hot direct reduced iron feed bin, a splitter, and a rotary feeder.
  6. 6. The method of claim 1, further comprising a carburizing gas injection located downstream or upstream of the induction heating coils providing a flow of carburizing gas through the conduit.
  7. 7. The method of claim 1, wherein the direct reduced iron is heated to between about 700˚C to 750˚C.
  8. 8. The method of claim 1, wherein the direct reduced iron is heated to about 1000˚C or greater.
  9. 9. The method of claim 1, comprising heating hot direct reduced iron to about 730˚C to stabilize cementite content and minimize further decomposition.
  10. 10. A feed conduit heater assembly comprising: a conduit configured to receive a flow of direct reduced iron; and a heating element comprising induction heating coils, disposed adjacent to the conduit, wherein the heating element is configured to transfer energy from a power supply in the form of heat to the conduit and heat the flow of direct reduced iron through the conduit, wherein a section of the conduit comprises a pipe and is configured to at least one of:-16- transition to an annular shaped flow path to receive the flow of direct reduced iron and the heating element comprises a parallel set of induction heating coils, or taper out in a first portion of the section of the conduit in a transitional zone to a greater width at a second portion, which transitions to a rectangular shaped flow path, and the induction heating coils comprise rectangular pancake induction heating coils, and wherein the conduit heater assembly forms an elongated feed leg through which the direct reduced iron is heated and flows directly into processing equipment, which is one of a melter, a briquetting machine, and a hot compaction equipment to compact to a higher density.
  11. 11. The feed conduit heater of Claim 10, wherein the pipe of the section of the conduit transitions to the annular shaped flow path to receive the flow of direct reduced iron and the heating element comprises the parallel set of induction heating coils.
  12. 12. The feed conduit heater of Claim 10, wherein the first portion of the pipe of the section of the conduit tapers out in the transitional zone to the greater width at the second portion, which transitions to the rectangular shaped flow path, and the induction heating coils comprise the rectangular pancake induction heating coils. 13. The feed conduit heater assembly of Claim 10, wherein the conduit is configured to receive hot direct reduced iron from a direct reduction shaft furnace or a direct reduced iron reheating furnace.
  13. 13. The feed conduit heater assembly of Claim 10, wherein the feed conduit heater assembly is included in a system for heating direct reduced iron between a direct reduced iron source and processing equipment for the direct reduced iron, the system further comprising: a direct reduced iron source; and processing equipment for the direct reduced iron, wherein, the feed conduit heater assembly couples the direct reduced iron source and the processing equipment and is located between the direct reduced iron source and the processing equipment, the conduit heater assembly configured to receive the flow of the direct reduced iron from the direct reduced iron source and heat the direct reduced iron as the-17- direct reduced iron flows through the conduit heater assembly and to the processing equipment.
  14. 14. The feed conduit heater assembly of Claim 13, wherein the direct reduced iron source is at least one of a direct reduction shaft furnace, a direct reduced iron reheating furnace, a surge bin, a hot direct reduced iron feed bin, a splitter, and a rotary feeder.
  15. 15. The feed conduit heater assembly of Claim 10, further comprising a carburizing gas injection located downstream or upstream of the induction heating coils providing a flow of carburizing gas through the conduit.
  16. 16. The feed conduit heater assembly of Claim 10, wherein the heating element is configured to heat the direct reduced iron to between about 700˚C to 750˚C.
  17. 17. The feed conduit heater assembly of Claim 10, wherein the heating element is configured to heat the direct reduced iron to about 1000˚C or greater.
  18. 18. The feed conduit heater assembly of Claim 10, wherein the flow of direct reduced iron comprises a flow of hot direct reduced iron, and wherein the heating element is configured to heat the hot direct reduced iron to about 730˚C to stabilize cementite content and minimize further decomposition.

Description

A METHOD AND SYSTEM FOR HEATING DIRECT REDUCED IRON (DRI) BETWEEN A DRI SOURCE AND PROCESSING EQUIPMENT FOR THE DRI CROSS-REFERENCE TO RELATED APPLICATION [0001] The present non-provisional patent application claims the benefit of priority of U.S. Provisional Patent Application No. 62/993,836, filed on March 24, 2020, and entitled “MIDREX HOT DRI REHEATING”. TECHNICAL FIELD [0002] The present invention relates generally to the direct reduced iron (DRI) and steelmaking fields. More specifically, the present invention relates generally to a direct reduction process utilizing electric heating means to add or recover heat to the DRI prior to metallic iron processing following the reduction process. BACKGROUND [0003] Hot Direct Reduced iron (HDRI) is distributed at about 700-750°C via insulated steel conduits or feed legs from a DRI furnace to, among other processes, briquetting machines to form hot briquetted iron (HBI), which must be formed at a temperature of no less than 650°C. Other processes may include hot transport as a means for charging melt furnaces, alternately, containment vessels, conveyors, or gravity-flow conduits, other hot compaction methods, or additional chemical conversion processes such as carburization. [0004] At the melting operation employing, preferably, an electric arc furnace (EAF), but possibly other melting furnaces, HDRI may have cooled to as low as about 550-600°C. HDRI is charged to a surge bin to contain the material and retain its heat as much as possible, and then to feed the melter as needed. Overcoming the heat losses between the high point of about 700-750°C and the feed point to the melter, about 550-600°C is an opportunity to improve quality and energy efficiency. Adding heat to the DRI prior to melting is an opportunity to improve melting furnace efficiency and throughput. -1-[0005] DRI quality can be deleteriously affected by HDRI cooling in the feed legs, with compaction density and strength decreasing, and, secondarily, cementite content, which is needed for metal quality, decreasing. HDRI may cool as much as about 50°C in the feed legs depending on several factors which may or may not be within the control of the plant operations. It is optimal to briquette at about 680° to 720°C, but no less than 650°C, to make briquette densities above 5.0 g/cm3 and to improve tumble index values by as much as 3% without continued operation above about 720°C. Briquettes formed at about 715°C generally are superior quality briquettes, exhibiting greater weathering resistance and lower breakage as measured by metallization loss and fines generation. While briquetting at higher temperatures can make higher quality HBI, continued operation above about 720°C results in unacceptably high maintenance on briquetting machinery such as briquette machine feed screws. [0006] Additionally, there is published research which points to an optimal cementite (iron carbide) retention at about 750 °C. Cementite stability is highest in the 730 to 750 °C range, with decomposition occurring more rapidly outside that range. Cementite isthe most desirable form of carbon content in HBI for steelmaking. Optimizing the HDRI temperature near this range helps avoid decomposition of cementite into graphitic carbon. BRIEF SUMMARY OF THE INVENTION [0007] Therefore, a primary aim of embodiments of the present invention is to arrest and maintain HDRI temperature at or near 715-720 °C through the use of an induction heating means arranged on the feed legs either as, e.g., a supplemental design, or as a replacement feed leg design. Problems advantageously solved include: 1) overcoming heat losses in feed legs prior to briquetters; and 2) help achieve and/or retain the desired level of carbon in HBI. [0008] Another primary aim of embodiments of this invention is to reheat or preheat HDRI prior to melter charging, using a new design for the HDRI surge bin discharge. Further problems advantageously solved include how to: 1) reheat HDRI prior to melter (bring HDRI back to about 700°-750°C); and 2) preheat material to a higher level (e.g., about 1000°C) for melter charging. -2-[0009] Thus, in various exemplary embodiments, the present invention provides a method of heating direct reduced iron between a direct reduced iron source and processing equipment for the direct reduced iron. The method comprises providing a conduit heater assembly between the direct reduced iron source and the processing equipment, wherein the conduit heater assembly receives a flow of the direct reduced iron from the direct reduced iron source and heats the direct reduced iron as the direct reduced iron flows through the conduit heater assembly and to the processing equipment. The direct reduced iron can be hot direct reduced iron from a direct reduction shaft furnace or a direct reduced iron reheating furnace. The direct reduced iron source can be at least one of a direct reduction shaft furnace, a direct reduced iron reheating furnace, a surge bi