Hot Briquetted Iron (HBI)
Hot Briquetted Iron (HBI) is a premium form of Direct Reduced Iron (DRI)* that has been compacted at a temperature greater than 650° C at time of compaction and has a density greater than 5000 kilograms per cubic meter (5000 kg/m3).
*DRI is a metallic material produced from iron oxide fines or iron oxide pellets and/or lump ores that have been reduced (oxygen removed) without reaching the melting point of iron.
Listed by IMO as: Direct Reduced Iron (A) Briquettes, hot-moulded
International Maritime Solid Bulk Cargoes (IMSBC) Code, which on 1 January 2011 supersedes the Code of Safe Practice for Solid Bulk Cargoes (BC Code), 1994 Edition Description of HBI:
HBI is a premium quality, high density steel industry raw material containing 90-94% total iron (Fe) in a nearly pure form, which is used in Electric Arc Furnace (EAF) and Basic Oxygen Furnace (BOF) steelmaking, Blast Furnace (BF) ironmaking, and foundry applications.
Hot Briquetted Iron (HBI) Advantages:
● High bulk density of 2500-3300 kg/m3 (156-206 lbs/ft3).
● Known, consistent chemistry certified by the producer.
● Minimal (trace) amounts of undesirable chemical elements (Cu, Ni, Cr, Mo, Sn, Pb, and V).
● High thermal and electrical conductivity
● Low reactivity with fresh and saltwater (reoxidation).
Typical Chemistry of Hot Briquetted Iron (HBI)
Apparent Density: > 5000 kg/m3 (> 312 lbs/ft3)
Bulk Density: 2500-330 kg m3 (156-206 lbs/ft3)
Length: 50-140 mm (1.97-5.5 in)
Width: 40-100 mm (1.6-3.9 in)
Thickness: 20-50 mm (0.79-1.97 in)
Fines: (under 6.35 mm) not to exceed 5%
* Grangue is oxides not in metallic form (i.e., SiO2, Al2O3, CaO, MgO, MnO) that remain in the HBI and are removed in the iron or steelmaking process
** Residuals are undesirable chemical elements for steelmaking (i.e., Cu, Ni, Cr, Mo, Sn, Pb, V)
How HBI Is Made
The majority of the direct reduction processes are gas-based; therefore, we will focus on them today.
The iron ore feed is either fines in fluid beds or pellets and lump in the other reduction furnaces. The feedstock is prepared to adjust the size to that required in the reduction furnace. This may require screening for separation or grinding to adjust the particle size downward.
The process gas is formed by different methods to generate H2and CO to remove the oxygen from the ore. Coal is also added in some processes to the process gas to actuate in the reduction. Natural gas enters the reduction furnaces and is heated to the required temperature for reduction of the oxide feed. We will look at the reduction furnaces in more detail in the following two slides.
Once reduced, the product is either briquetted while hot as HBI (hot briquetted iron) or cooled and discharged as DRI. In the hot briquetting process, the HBI must be cooled prior to storage in piles.
Gas-Based Processes – Lump and Pellet Feed
The principal shaft-based furnace operations are those of Midrex and Tenova/HYL, which together account for 98% of the gas-based processes. In these furnaces, the mixture of ump ore and pellets is introduced for reduction by different systems that we will clarify later. The ore flows by gravity downwards and is contacted by upflowing reducing gas. The ore is reduced and heated during the downward flow.
The hot reducing gas enters the shaft around the exterior diameter and flows upwards. In the upwards flow, the reduction of the Fe2O3occurs. By the time the gas exits the reducing zone, it has been partially cooled by the heating of the incoming ore feed. The shaft furnace can provide either hot product for briquetting or cooled final product.
Gas-Based Processes – Fines Feed
The principal fines reactor based furnace operation is that of FINMET, which is the only fines-based process in service at present. In the FINMET Process, the reactor layout is different from another fines-based process, CIRCORED, as we will see later. In all cases, the fines are maintained in a fluidized condition by upwards flowing reducing gas. In the FIOR and FINMET Processes, a total of four fluid bedsare used. In the CIRCORED Process, two fluid beds of different conditions are used. Between reactors, the ore flows by gravity downwards and is contacted in each by upflowing reducing gas. The ore is reduced and heated during the downward flow.
The hot reducing gas enters the reactors through fluid bed grids from the reactor bottom and flows upwards. By the time the gas exits the top, it has been partially cooled by the heating and reduction of the incoming ore feed. The fines-based processes must briquette the final product.
Iron oxide, in pellet or lump form, is introduced through a proportioning hopper at the top of the shaft furnace. At VENPRECAR in Venezuela, the feed mix is 65% pellets, 32% lump ore, and the rest is recycled remet.
As the ore descends through the furnace by gravity flow, it is heated and the oxygen is removed from the iron (reduced) by counter flowing gases, which have a high H2 and CO content. In the VENPRECAR plant, the process gas is 60% H2 and 35% CO on a dry basis. These gases react with the Fe2O3in the iron ore and convert it to metallic iron, leaving H2O and CO2.
For production of cold DRI, the reduced iron is cooled and carburized by counter flowing cooling gases in the lower portion of the shaft furnace. The DRI also can be discharged hot and fed to a briquetting machine for production of HBI, or fed hot, as HDRI, directly to an EAF using the HOTLINK Systemor insulated transfer vessels.
To maximize the efficiency of reforming, off-gas from the shaft furnace is recycled and blended with fresh natural gas. This gas is fed to the reformer, a refractory-lined furnace containing alloy tubes filled with catalyst. The gas is heated and reformed as it passes through the tubes. The newly reformed gas, containing 90-92 % H2and CO, is then fed hot directly to the shaft furnace as reducing gas. At VENPRECAR, the gas temperature exiting the reformer is 940° C and is cooled to 850° C to enter the shaft furnace.
The thermal efficiency of the MIDREX Reformer is greatly enhanced by the heat recovery system. Sensible heat is recovered from the reformer flue gas to preheat the feed gas mixture, the burner combustion air, and the natural gas feed. In addition, depending on the economics,the fuel gas also may be preheated.
HBI – Industrial Production
Figure 1 represents the hot briquetting process for the production of HBI. The direct reduced iron is discharged hot form the reduction process. With a screw this hot feed is pushed into the nip between two counter rotating rollers. Pockets in the synchronously rotating rollers form the briquettes. This process occurs at high temperatures (typically approx. 700 °C) and high pressing forces (e.g. 120 kN per cm active roller width). The continuous string of briquettes leaving the rollers is guided by a heavy chute and is separated into mostly singles for example by a rotor with impact bars. Briquettes from fine material, produced in fluidized bed processes, may also be separated in a rotating tumbling drum.
HBI is produced in the form of briquettes at high temperature and pressure with roller presses. Alternative briquette sizes and shapes have been tested in several plants. The typical volume of industrially manufactured briquettes is in the range of approx. 100 cm³. So far, this is independent of the method used in the preceding direct reduction process.
The key component in hot briquetting is a specially designed roller press. Figures 2 and 3 show the assembly bay of Maschinenfabrik KÖPPERN featuring modern machines for the production of HBI.
The entire plant for the hot briquetting of sponge iron typically consists of (Figs. 4 and 5):
– Briquetting press with screw feeder and material supply
– Briquette string separator (impact separator or tumbling dru
– Hot screen for the elimination of fines which occur during briquetting and separation
– Product cooler
– Bucket elevator for the recirculation of fines to the briquetting press
– Chutes and accessories
For hot briquetting of the total production of a direct reduction facility several of the above described “briquetting lines” are used. The layout of the briquetting plant is designed such that during the necessary scheduled maintenance on the machines and the system the overall availability of the plant is guaranteed.
In addition to the above mentioned industrially proven features, optimizations and new developments take place. For example, alternative concepts for briquette cooling are presently under consideration and larger machines are being designed to handle more effectively the higher output of future direct reduction plants.
HBI – From Various DR Processes
Hot briquetting is applied both for products from pellets and lump ore (shaft furnaces) and from fine ore (fluid bed reactors). Particularly in the case of fine DRI from fluidized bed processes, in addition to passivation, it isa major task of hot briquetting to eliminate the inherent handling problems of this material. Both direct reduction technologies are based on gaseous reductants.
More recent investigations, including operation of a pilot plant, have shown that products from coal based processes (rotary hearth furnace) can be also briquetted hot at suitable conditions.
The mechanism of briquetting as well as the briquette structure and, consequently, details of the equipment used in the particular system, depend on the characteristics of the material to be briquetted.
The deformed pellets and lump ore pieces originating from a gas based shaft furnace technology are still visible in the briquette structure, while a more uniformly briquette results from the fine particles of a fluidized bed process.
The knowledge of briquette structure that depends on the properties of the particular feed from different reduction processes helpsin optimizing the briquetting process (e.g. material feed systems, pressing tools, etc.)
“How HBI Is Made” can be found here.
1 Introduction to HBI – International Iron Metallics Association, May 2012.
3 DRI HBI Process – International Iron Metallics Association (HBIA), 2008.
4 How HBI Is Made (Based on the Direct Reduction Fundamentals and Applications short course by Roy Whipp, President of Whipp Technology, Inc./IIMA Special Member).
5 Direct Reduction Fundamental and Applications – Short Course ( Direct Reduction Systems and Products – Roy Whipp, President of Whipp Technology, Inc./IIMA Special Member).