News

Energiron Direct Reduction Technology

• satyendra
• September 8, 2018
• 0 Comments
• DRI, EAF, Energiron, HBI, HYL process, Hytemp, natural gas, Shaft furnace, Syngas, Zero reformer,

Energiron Direct Reduction Technology

Energiron direct reduction technology is a gas based direct reduction technology. Energiron process converts iron ore pellets or lumps into metallic iron. It uses the HYL direct reduction technology developed jointly by Tenova and Danieli and is a competitive and environmentally clean solution for lowering the liquid steel production cost. It uses a simple plant configuration, has flexibility for using different sources of reducing gases and has a very efficient and flexible use of iron ores. A key factor in many of the process advantages is directly related to its pressurized operation.

Energiron is the name of the direct reduced iron (DRI) product produced by the Energiron direct reduction technology. The product is so named since it carries substantial energy with it which is realized during the steel making process.

Energiron is a highly metallized product with the carbon (C) content which is controllable in the range of 1.5 % to 5.0 %. The higher C content of Energiron generates chemical energy in the electric arc furnace (EAF) melting process. The uniquely stable characteristic of Energiron DRI makes it a product which can be safely and easily transported without briquetting, following standard IMO (International Maritime Organization) guidelines.

The process is flexible to produce three different product forms, depending on the specific requirements of each user. The three forms of Energiron DRI are cold DRI, HBI (hot briquetted iron) or hot DRI (‘Hytemp’ iron with discharge temperature greater than 700 deg C). Cold DRI discharge is normally used in an adjacent steel melt shop close to the direct reduction plant. It can also be shipped and exported. HBI is the DRI which is discharged hot, briquetted, and then cooled. It is a merchant product usually meant for overseas export. Hytemp Energiron is the hot discharged DRI, pneumatically transported from the direct reduction plant to an adjacent steel melt shop for its direct feed in the electric arc furnace (EAF).

The initial development work was done by Hylsa. In 1977, Hylsa set up a new operating division (HYL technologies) for the purpose of formally developing and commercializing the direct reduction technologies. In 2005, Techint Technologies acquired HYL technologies. Later this division was called Tenova HYL. In 2006, a strategic alliance was formed by Tenova and Danieli for the design and construction of gas-based DR plants under the new ‘Energiron’ trademark. First commercial scale

HYL ZR (zero-reformer) process plant was started in 1998. First new generation Energiron ZR plant of 2 million tons per year capacity is installed at Suez Steel and the first world largest Energiron plant in a single module of 2.5 million tons per year capacity is installed at Nucor Steel.

Energiron direct reduction process

Energiron direct reduction process uses a shaft reduction furnace to produce DRI. It is designed to convert iron pellet/lump ore into metallic iron by the use of reducing gases in a solid-gas moving bed shaft furnace. Oxygen (O2) is removed from the iron ore by chemical reactions based on hydrogen (H2) and carbon mono oxide (CO), for the production of highly metallized DRI. The process is flexible to produce three different forms of Energiron product to suit the end user. A key aspect of the process is the independent control of metallization and product carbon (C). Energiron direct reduction process is based on the ZR scheme.

Hot reducing gases are fed inside the shaft furnace at the reduction zone. Inside the furnace, these gases flow upward counter-current to the iron burden moving bed. The gas distribution is uniform and there is a high degree of direct contact between the gas and solid, without physical restrictions to the flow of solids or gases inside the unit. The exhaust gas (top gas) leaves the shaft furnace at around 400 deg C and passes through the top gas heat recuperator, where the energy of the gas is recovered to produce steam. Alternatively, the energy of the exhaust gas can be utilized to preheat the reducing gas stream, and then the exhaust gas can be cooled through the quenching/ scrubbing process by means of cooling water.

Scrubbed cooling gas passes through the cooling gas recycle compressor to be recycled to the shaft furnace, after being made-up with natural gas (NG). NG is injected as make-up to the cooling gas circuit for optimum efficiency and control of the cooling and carburization processes.

Removal of O2 from the iron ore is accomplished by the action of the hot reducing gases and then the product is carburized. A rotary valve, located at the bottom of the shaft furnace, regulates the continuous gravity flow of the charge downward through the reduction furnace. Energiron is discharged by automated mechanisms, consisting of pressurized bins and locks. Specially designed flow feeders ensure the uniform flow of solids within the shaft furnace. For cold DRI, a cooling gas is fed to the lower conical part of the furnace at around 40 deg C, flowing upward counter-current to the DRI moving bed.

For hot product discharge and use, the cooling circuit is eliminated and hot DRI is continuously discharged at greater than 700 deg C. For the ‘Hytemp’ pneumatic transport system, the product is transported by means of a carrier gas to the surge bins located at the steel melting shop, for a controlled feeding to the electric arc furnace. For production of HBI, hot DRI is continuously discharged at greater than 700 deg C to the hot briquetting machines arranged below. The HBI is cooled in vibrating cooling conveyors using cooling water and then discharged to the HBI transport conveyor.

One of the in-built characteristics of the Energiron process flow which has high environmental importance, is the selective elimination of the byproducts generated from the reduction process namely water (H2O) and carbon di-oxide (CO2). These byproducts are eliminated through top gas scrubbing and CO2 removal systems, respectively. The selective removal of H2O and CO2 optimizes make-up requirements. H2O produced during the reduction process is condensed and removed from the gas stream and most of the dust carried with the gas is also separated. Scrubbed gas is then passed through the process gas recycle compressor, where its pressure is increased. Compressed gas, after being sent to the CO2 removal unit, is mixed with the NG make-up, thus closing the reducing gas circuit.

The Energiron ZR scheme is characterized by (i) utilization of H2 rich reducing gases with H2 to CO ratio is around 5, (ii) high reduction temperature usually more than 1050 deg C, and (iii) high operating pressure normally in the range of 6 kg/sq cm to 8 kg/sq cm  inside the moving bed shaft furnace. The higher operating pressure allows (i) low fluidization, (ii) higher input of fines, (iii) a high productivity of around 10 tons per hour per square meters, (iv) lower consumption of iron ore, (v) low reducing gas velocities of around 2 meters per second, and (vi) lower consumption of power due to lower compression factor.  This result in smaller shaft furnaces, promotes a homogenous gas distribution through the solids bed, and minimizes dust losses (less than 1 %) through top gas carry-over because of lower dragging force. This also results into a very low standard deviation in the quality of the produced prime Energiron besides lowering of the overall iron ore consumption (around 1.4 tons of iron ore per ton of DRI with screening at 3.2 mm and no remelt). This in turn lowers the overall operating costs. Another distinct feature of this process scheme, without an integrated/external reformer, is the wider flexibility for DRI carburization.

Process automation – The Energiron process combines different and complex physico-chemical processes which are to be optimized to yield the desired set of chemical reactions and heat and mass exchanges among the variety of gaseous, liquid and solid phases. For this reason, a complete automation system is used which in turn uses the latest available technology in the field of process controllers, software diagnostics, high availability and failsafe features. The process is controlled by more than 5,500 analog and digital variables, which are automatically analyzed by the automation system. All the process variables coming from the field instruments are constantly collected by the various acquisition systems (PLCs, HMIs), providing a valuable set of information for continuously monitoring and optimizing the process. The advanced software of the Energiron process takes advantage of this huge potential by managing integrated data collection, analysis, and web reporting with powerful statistical tools to support decision-making. This finally makes it possible to further optimize the process efficiency, by detecting the optimal set points in real-time, with consequent important energy savings.

The Energiron control system is based on an architecture consisting of a traditional level 1 system for equipment control with a ‘distributed control system’ (DCS), plus a level 2 system, not only for process supervision, data tracking and creation of production reports but also for the process optimization. A ‘Process Reconstruction Model’ (PRM) has been developed. It uses instrumentation signals coming from the PLC and physical equations in order to provide a full description of the plant status. In this way it is possible to calculate many normally not measurable items such as the top gas composition and relevant red/ox ratio.

Process reactions – Three types of chemical reactions take place during the process. They are (i) reforming reactions, (ii) reduction reactions, and (iii) carburizing reactions. The following reactions take place during insitu refining.

2CH4 + O2 = 2 CO + 4 H2

CH4 + CO2 = 2CO + 2H2

CH4 + H2O = CO + 3 H2

2H2 + O2 = 2 H2O

CO2 + H2 = CO + H2O

The reactions taking place during reduction and during carburization of DRI are as follows.

Fe2O3 + 3CO = 2Fe + 3CO2

Fe2O3 + 3 H2 = 2Fe + 3H2O

3Fe + CH4 = Fe3C + 2H2

3 Fe + 2 CO = Fe3C + CO2

3 Fe + CO+ H2 = Fe3C + H2O

Flow sheet of standard Energiron process is at Fig 1.

Fig 1 Flow sheet of Energiron process

Typical energy balance of the Energiron process is shown in Fig 2.

Fig 2 Typical energy balance of Energiron process

Plant and equipment

Energiron direct reduction plant consists of mainly the following plant and equipment along with their characteristic features.

• A reduction shaft furnace which holds the moving bed. This shaft furnace has a system for charging iron burden and a product discharge system.
• A reducing gas circuit, consisting of a process gas heater, top gas heat recuperator, top gas quenching/scrubbing unit, reducing gas recycle compressor, humidification tower and knock out drums.
• Operation of the furnace is carried out with minimum NG and water consumption, as well as O2 injection.
• The product discharge system can have (i) a cooler for the cold DRI production, (ii) hot briquetting machine for the production of HBI, and/or (iii) Hytemp pneumatic transport system to transfer hot DRI directly from the shaft furnace to the electric arc furnace (EAF).
• An external cooling gas circuit, consisting of a quenching/scrubbing unit and cooling gas recycle compressor.
• An adsorption system, based on PSA (pressure swing adsorption), for carbon dioxide (CO2) removal from the reducing gas stream.
• Iron ore handling equipment including iron ore surge bin, transfer conveyors, screening station, pellets coating system, feeding conveyor, along with sampling and weighing units.
• DRI handling system consisting of conveyors and related equipment for the transport of cold DRI.
• Cooling tower along with filtering equipment and pumps.
• Process cooling water system, based on closed circuit to minimize water consumption, with clarifier and settling ponds.
• A process control and instrumentation system, using microprocessor-based distributed control.
• Electrical substation, electric motors and lighting.
• Inert gas system normally based on nitrogen (N2) gas.
• An air compressor

Operating parameters and specific consumption

The typical characteristics of the product of the Energiron ZR process are given in Tab 1.

The typical operating parameters and the specific consumptions for the Energiron ZR process are given in Tab 2.

The typical emissions from the Energiron ZR process are given in Tab 3.

Features of Energiron ZR process

Energiron ZR process has decreased the size and improved the efficiency of the direct reduction plants. Reducing gases are generated in-situ reforming of the hydrocarbons of the natural gas within the reduction shaft furnace, by feeding NG as make-up to the reducing gas circuit and injection of the O2 at the shaft furnace inlet. In the process, optimum reduction efficiency is achieved, since the reducing gases are generated in the reduction section. Because of this, an external reducing gas reformer is not required. Normally, the overall energy efficiency of the Energiron ZR process is more than 80 %, which is optimized by the in-situ reforming inside the shaft furnace. The product takes most of the energy supplied to the process, with minimum energy losses to the atmosphere.

The impact on plant size of eliminating the external gas reformer is significant. For a capacity of 1 million tons per year, the area requirement reduces by around 60 %. This also facilitates locating the DR plant adjacent to the steel melting shop.

Additional advantage of the Energiron ZR process is the flexibility for the carburization of DRI, which allows attaining of C levels up to 5 %. This is because of the improved carburizing potential of the gases inside the shaft, which allow for the production primarily of Fe3C. DRI with a high content of Fe3C has a much lower reactivity than the normal DRI since higher heat of dissociation is needed for Fe3C.

The operating conditions which are existing in the Energiron direct reduction process are characterized by high temperature (higher than 1050 deg C), presence of H2O and CO2 as oxidants produced by partial combustion of the reducing gas with O2 injection. These conditions promote the in-situ reforming of the hydrocarbons. Once H2 and CO are generated, simultaneous reduction of the iron ore and subsequent carburization of the DRI, take place inside the reactor, making this process scheme a very efficient in terms of energy utilization and overall energy consumption.

The basic Energiron ZR scheme allows the direct use of NG. Plants using Energiron process for direct reduction can also use conventional steam-NG reforming equipment as an external source of reducing gases, which has long characterized the gas-based direct reduction process. In place of NG, other gases such as H2, syngas produced from coal gasification systems, pet coke and similar fossil fuels, and coke-oven gas (COG), among others, can also be used as the potential sources of reducing gas, depending on the particular situation and availability. In any case, the same basic process scheme is used regardless of the reducing gas source.

A unique feature of the Energiron ZR technology is its ability to produce controlled high carbon levels in the DRI in the form of iron carbide (Fe3C) (usually greater than 90 %). DRI carbon levels up to 5 % can be obtained, due to the conditions existing in the reduction zone of the reactor. These conditions consist of high methane (CH4) concentration (around 20 %) along with the H2 and CO, and the high temperature of the bed. These conditions favour the diffusion of C into the iron matrix and the precipitation of Fe3C. The DRI with a high content of Fe3C shows a much lower reactivity than the normal DRI.

One important characteristic of the Energiron direct reduction plant is the possibility to design the process for a zero make-up water requirement. This is possible mainly because water is a by-product of the reduction reaction since it is condensed and removed from the gas stream. As a consequence, with the adoption of a closed-circuit water system based on the use of water heat exchangers instead of conventional cooling towers, there is no need for fresh make-up water and actually a small stream of water is left available at battery limit.

Emissions from Energiron direct reduction plant

Energiron plant emissions are in accordance with the most stringent environmental regulations. This is achieved mainly due to the nature of the process itself. Energiron technology is efficient by design because of its process configuration. Hence, while achieving high overall thermal efficiency in the plant, there is no significant need for preheating the combustion air to high temperatures in the reformer (when used) or in the heater, thus eliminating the possibility of high NOx generation. The NOx emission can be additionally reduced by adopting ultra-low NOx burners. A further improvement can be obtained with the application of SCR (selective catalytic reduction) technology.

Energiron is a very clean direct reduction technology available. Depending on the configuration, an Energiron plant can remove from 60 % to 90 % of total CO2 emissions. CO2 emissions can be considerably different between the two technologies employed for the production of DRI. Irrespective of whether using NG, syngas, or COG, the make-up of reducing gases to the direct reduction plant contain C, either in the form of hydrocarbons and/or carbonaceous compounds (CO, CO2). Also, irrespective of the direct reduction process configuration, only 15 % to 40 % (depending on the C content in the DRI) leaves the process as combined C in the DRI, the remainder leaves as CO2.

Since the DRI produced from the Energiron ZR process contains higher percentage of C, lesser amount of C is removed in the form of CO2. The difference in the CO2 gas generation can be noticed when it is compared with the CO2 gas generation in a direct reduction configuration with an external catalytic reformer integrated to a direct reduction shaft furnace is used as the reducing gas make-up source. In the case of generation in a direct reduction configuration with an external catalytic reformer integrated to a direct reduction shaft furnace, out of the total process NG makeup containing 140 kg of C per ton of DRI, around 25 kg of C per ton of DRI (17 %) leaves the process as part of the DRI and the balance is released as flue gas from the reformer. These figures compare with 110 kg of C per ton of DRI, from which 40 kg of C per ton of DRI (36 %) is in the DRI produced in case of the Energiron ZR process. In addition, of the remaining 70 kg of C per ton of DRI, 65 kg of C is selectively removed as pure CO2, which can be used for other applications or sequestrated. The elimination of both by-products generated from the reduction process H2O and CO2, improves the gas utilization in the process to more than 95 %. In short, the Energiron process provides in-built selective elimination of around 65 % of total C input as CO2 (around 240 kg of CO2 per ton of DRI).

Energiron plants offer the unique option of selective recovery of CO2. The CO2 absorption system not only captures the CO2, but also the sulphur, whenever present in the process gas stream, reducing the overall SO2 emission from the plant by around 99%.

H2 as reducing gas

In the iron and steel plants, H2 is expected to replace C as energy source for the iron ore reduction process in the near future. In the case of gas-based direct reduction processes, H2 is going to replace NG. The Energiron ZR process is already prepared to use any amount of H2 in replacement of NG with no major equipment adjustments. In fact, in the Energiron ZR process scheme, the use of H2 will be reflected in a more smooth operation and increase in productivity since the requirement of the in-situ reforming of NG gas is going to be lower.

Use of H2 concentrations as high as 70 % at the inlet of reduction shaft is already well proven in the existing Energiron direct reduction plants, which involves a steam reformer to produce the reducing gases (H2 and CO).

However, with the use of H2 as a replacement of NG as energy input, there is going to be a decrease of % C in the DRI Since it will dilute the CH4 concentration in the reducing gas, but because of the flexible process configuration of the Energiron ZR scheme in terms of make-up distribution to the reduction circuit and to fuel utilization, it is possible to achieve 3.5 %C even at 35 % energy input as H2 (or around 64 % as volume – N cum per ton of DRI). For 70 % H2 as energy (around 88 % as volume – N cum per ton of DRI), the expected C in DRI will be less than 2.0 %.

Alliance with NSENGI

In 2014, Tenova HYL and Danieli, have entered into an agreement with Nippon Steel & Sumikin Engineering Co., Ltd. (NSENGI) to combine and commercialize their Energiron direct reduction technology with an optimized blast furnace technology, as well as syngas technology (high efficiency coal gasification and steelworks by-product gas utilization technology) developed and owned by NSENGI. The aim of new alliance is to combine research and development activities with their respective expertise in Energiron DR, blast furnace and syngas technologies, with the ultimate objective of developing a new iron making technology which will reduce CO2 emissions and operating costs, while increasing productivity and/or decreasing capital expenditures for integrated steelmaking facilities.