Nitrogen in Energiron Direct Reduction Technology

Energiron Direct Reduction Technology

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

Energiron is the name given to the Direct Reduced Iron (DRI) product produced by Energiron's direct reduction technology. The product is so named because it carries a large amount of energy that is realized in the steelmaking process.

Energiron is a highly metallized product with a controlled carbon (C) content between 1.5% and 5.0%.Energiron's high carbon content generates chemical energy during the electric arc furnace (EAF) melting process.Energiron DRI's unique stabilization properties make it a product that can be safely and easily transported without briquetting， in compliance with standard IMO ( International Maritime Organization (IMO) guidelines.

The process has the flexibility to produce three different product forms， depending on the specific requirements of each user. three forms of Energiron DRI are cold DRI， HBI (hot briquetted iron) or hot DRI ('Hytemp' iron with discharge temperatures above 700 degrees C). Cold DRI discharge is typically used in adjacent steel smelters near direct reduction plants. It can also be shipped and exported. HBI is hot discharged DRI that has been briquetted and then cooled. It is a commercial product and is typically used for overseas export. Hytemp Energiron is hot discharged DRI that is pneumatically transported from the direct reduction plant to an adjacent steel melt shop and directly into the electric arc furnace (EAF).

The initial development work was done by Hylsa. in 1977， Hylsa formed a new operating division (HYL technologies) for the purpose of formally developing and commercializing direct reduction technology. in 2005， Techint Technologies acquired HYL technologies. this division later became known as Tenova HYL. In 2006， Tenova and Danieli formed a strategic alliance to design and build a gas-based direct reduction plant under the new "Energiron" trademark. First commercial scale

HYL ZR (Zero Reformer) process plant was launched in 1998. The first new generation Energiron ZR plant with a capacity of 2 million tons per year was installed at Suez Steel， and the world's first single module Energiron plant with a capacity of 2.5 million tons per year was installed at Nucor Steel.

Energiron Direct Reduction Process

The Energiron Direct Reduction process uses a shaft furnace reduction method to produce DRI. it is designed to convert iron pellet/bulk ore into metallic iron by using reducing gas in a solid gas moving bed shaft furnace. Oxygen (O2) is removed from the iron ore through a chemical reaction based on hydrogen (H2) and carbon monoxide (CO) to produce a highly metallized DRI. the process is flexible and can produce three different forms of Energiron products to suit the needs of the end user. A key aspect of the process is the independent control of metallization and product carbon (C).The Energiron direct reduction process is based on the ZR scheme.

Hot reduction gases are fed in a vertical furnace in the reduction zone. Inside the furnace， these gases flow upwards against the moving bed of the iron charge. The gases are uniformly distributed， there is a high degree of direct contact between the gases and the solids， and there are no physical restrictions on the flow of solids or gases within the unit. The exhaust gas (top gas) leaves the shaft furnace at a temperature of approximately 400 degrees Celsius and passes through the top gas heat exchanger where the energy of the gas is recovered to produce steam. Alternatively， the energy of the exhaust gas can be used to preheat the reduction gas stream， which is then cooled by a quenching/scrubbing process with cooling water.

The scrubbed cooling gas is passed through a cooling gas recirculation compressor and circulated to the shaft furnace after being mixed with natural gas (NG). NG is injected into the cooling gas circuit as a supplement for optimum efficiency and to control the cooling and carburizing process.

In the presence of hot reducing gas， O2 is removed from the iron ore and the product is then carburized. A rotary valve located at the bottom of the shaft furnace regulates the continuous downward flow of the charge by gravity through the reduction furnace. energiron is discharged by an automated mechanism including pressurized bins and locks. A specially designed flow feeder ensures a uniform flow of solids through the shaft furnace. For cold DRI， at a temperature of about 40 degrees Celsius， the cooling gas is conveyed to the lower conical section of the furnace， flowing upwards against the flow to the DRI moving bed.

For the discharge and use of hot products， the cooling circuit is eliminated and the hot DRI is continuously discharged at temperatures above 700 degrees Celsius. For the "Hytemp" pneumatic transport system， the product is transported by carrier air to a surge bin located in the steel melting shop for controlled feeding into the electric arc furnace. To produce HBI， hot DRI is continuously discharged at temperatures above 700 degrees C into the hot briquetter below. HBI is cooled in a vibratory cooling conveyor using cooling water and then discharged onto the HBI transport conveyor.

One of the inherent features of the Energiron process is the selective elimination of by-products from the reduction process， namely water (H2O) and carbon dioxide (CO2)， which are of great environmental importance. These by-products are eliminated by means of top gas scrubbing and CO2 removal systems， respectively. The selective removal of H2O and CO2 optimizes the recharge requirements. The 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. The purified gas then passes through the process gas recirculation compressor， where its pressure is increased. After being sent to the CO2 removal unit， the compressed gas is mixed with the NG make-up gas， thus closing the reducing gas circuit.

The Energiron ZR scheme is characterized by (i) the utilization of H2-rich reducing gas with an H2 to CO ratio of about 5， (ii) high reducing temperatures， typically exceeding 1050 degrees C， and (iii) high operating pressures， typically between 6 kg/cm2 and 8 kg/cm2 in a moving bed shaft furnace. The higher operating pressure allows (i) lower fluidization， (ii) higher fines input， (iii) higher productivity of about 10 t/h per m2 ， (iv) lower iron ore consumption， (v) lower reducing gas velocity of about 2 m/s， and (vi) lower power consumption due to the lower compression factor. This results in a smaller shaft furnace， promotes a uniform gas distribution through the solid bed and minimizes dust losses (less than 1%) carried by the gas through the top due to lower drag forces. This also results in a very low standard deviation of the quality Energiron produced and a reduction in overall iron ore consumption (approximately 1.4 tons of iron ore per ton of DRI with 3.2 mm screening and no remelt). This， in turn， reduces the overall operating costs. Another distinctive feature of the process solution is the absence of an integrated/external reformer and the greater flexibility of DRI carburization.

Process Automation - The Energiron process combines different， complex physicochemical processes that will be optimized to produce the required range of chemical reactions and heat and mass exchange between the various gaseous， liquid and solid phases. For this purpose， a complete automation system is used， which in turn uses the latest available technologies in the field of process controllers， software diagnostics， high availability and fail-safe functions. The process is controlled by more than 5，500 analog and digital variables that are automatically analyzed by the automation system. All process variables from the field instruments are continuously collected by various acquisition systems (PLC， HMI)， providing a valuable set of information for continuous monitoring and optimization of the process.The Energiron process' advanced software harnesses this enormous potential by managing integrated data collection， analysis and network reporting with powerful statistical tools to support decision making. This ultimately makes it possible to further optimize process efficiency by detecting optimal set points in real time， thereby achieving important energy savings.

The Energiron control system is based on an architecture consisting of a traditional primary system， the "Distributed Control System" (DCS) for plant control， plus a secondary system for not only process supervision， data tracking and production report creation， but also for process optimization. A "Process Reconstruction Model" (PRM) has been developed. It uses instrumentation signals from the PLC and physical equations to provide a comprehensive description of the plant state. In this way， many items can be calculated that are not normally measured， such as top gas composition and associated red/oxygen ratios.

Process Reactions - There are three types of chemical reactions that occur in the process. They are (i) reforming reactions， (ii) reduction reactions， and (iii) carburization reactions. The following reactions occur during the in situ refining process.

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 that occur during the reduction and 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

The flow chart of the standard Energiron process is shown in Figure 1.

Figure 1 Flow diagram of the Energiron process

A typical energy balance diagram for the Energiron process is shown in Figure 2.

Figure 2 Typical energy balance of the Energiron process

Plant and Equipment

The Energiron direct reduction plant consists mainly of the following plants and equipment， and their characteristics.

A reduction shaft furnace housing a moving bed. This shaft furnace has a system for charging the iron charge and a product discharge system.

A reducing gas circuit， including a process gas heater， top gas heat exchanger， top gas quench/scrub unit， reducing gas recovery compressor， humidification tower and elimination drum.

• The furnace is operated with minimal NG and water consumption and O2 injection.

• The product discharge system can have (i) a cooler for cold DRI production， (ii) a hot briquetter for HBI production， and/or (iii) a Hytemp pneumatic transport system to transfer the hot DRI directly from the shaft furnace to the electric arc furnace (EAF).

• An external cooling gas circuit， consisting of a quench/scrub unit and a cooling gas circulation compressor.

• A PSA (variable pressure adsorption) based adsorption system for carbon dioxide (CO2) removal from the reduction gas stream

• Iron ore processing equipment， including iron ore sand silos， conveyors， screening stations， pellet coating systems， feed conveyors， and sampling and weighing units.

• DRI processing system， including conveyors and associated equipment for transporting cold DRI.

• Cooling towers， and filtration equipment and pumps.

• A process cooling water system， based on a closed loop to minimize water consumption， with clarifiers and settling tanks.

• A process control and instrumentation system， using distributed microprocessor-based controls.

• Substation， motors and lighting.

• An inert gas system usually based on nitrogen (N2).

• An air compressor

Operating parameters and specific consumption

The typical characteristics of Energiron ZR process products are given in Table 1.

Features of the Energiron ZR process

The Energiron ZR process reduces the size and increases the efficiency of the direct reduction plant. The reducing gas is produced by in situ conversion of hydrocarbons from natural gas in the reducing shaft furnace by feeding NG as make-up gas into the reducing gas circuit and injecting O2 at the shaft furnace inlet. in this process， optimal reduction efficiency is achieved because the reducing gas is produced in the reducing section. Because of this， an external reducing gas reformer is not required. Typically， the overall energy efficiency of the Energiron ZR process exceeds 80%， which is optimized by the in-situ reforming within the shaft furnace. The product takes up most of the energy supplied to the process， with minimal energy loss to the atmosphere.

The impact of eliminating the external gas reformer on plant size is significant. For a capacity of 1 million tons per year， the area required is reduced by about 60%. This also facilitates the placement of the DR plant near the steel melting plant.

Another advantage of the Energiron ZR process is the flexibility of DRI carburizing， which allows to reach C levels of 5%. This is due to the increased carburizing potential of the in-shaft gas， which allows for the production of mainly Fe3C. DRI with high Fe3C content is much less reactive than normal DRI due to the higher heat of dissociation required for Fe3C.

The operating conditions present in the Energiron direct reduction process are characterized by high temperatures (above 1050 degrees C) and the presence of H2O and CO2 as oxidants， which are produced by partial combustion of the reducing gas injected with O2. These conditions promote the in situ conversion of hydrocarbons. Once H2 and CO are produced， simultaneous reduction of the iron ore and subsequent carburization of the DRI takes place in the reactor， making the process scheme very efficient in terms of energy utilization and overall energy consumption.

The basic Energiron ZR scheme allows for the direct use of natural gas. Plants using the Energiron process for direct reduction can also use conventional steam-NG reformers as an external source of reduction gas， which has long been a feature of gas-based direct reduction processes. Other gases that replace NG， such as H2， syngas from coal gasification systems， petroleum coke and similar fossil fuels， as well as coke oven gas (COG)， can also be potential sources of reduction gas， depending on the particular circumstances and availability. In any case， the same basic process scheme is used regardless of the source of the reducing gas.

A unique feature of Energiron ZR technology is its ability to produce a controlled high carbon content (typically greater than 90%) in DRI in the form of iron carbide (Fe3C). Due to the conditions present in the reduction zone of the reactor， DRI carbon contents of up to 5% can be obtained. These conditions include high concentrations of methane (CH4) (~20%) as well as H2 and CO， and the high temperature of the bed. These conditions favor the diffusion of C into the iron matrix and the precipitation of Fe3C. DRI with high Fe3C content shows much lower reactivity than normal DRI.

An important feature of the Energiron direct reduction plant is that the process can be designed to have zero make-up water requirements. This is possible mainly because water is a by-product of the reduction reaction， as it is condensed and removed from the gas stream. Therefore， because a closed circuit water system based on a water heat exchanger is used instead of a conventional cooling tower， there is no need for fresh make-up water and in fact a small stream of water is available at the cell limit.

Energiron Direct Reduction Plant Emissions

Emissions from the Energiron plant comply with the most stringent environmental regulations. This is achieved primarily due to the nature of the process itself. Due to its process configuration， Energiron technology is designed to be highly efficient. As a result， while achieving high overall plant thermal efficiency， there is no need to preheat the combustion air to high temperatures in the reformer (when used) or in the heater， thus eliminating the possibility of high NOx generation. NOx emissions can also be further reduced by using ultra-low NOx burners. Further improvements can be obtained by applying SCR (Selective Catalytic Reduction) technology.

Energiron is one of the available very clean direct reduction technologies. Depending on the configuration， Energiron plants can eliminate between 60 and 90 percent of total CO2 emissions. CO2 emissions can vary significantly between the two technologies used to produce DRI. Whether natural gas， syngas or COG is used， the reducing gas entering the direct reduction plant contains C， in the form of hydrocarbons and/or carbonaceous compounds (CO， CO2). In addition， regardless of the configuration of the direct reduction process， only 15% to 40% (depending on the C content in the DRI) leaves the process as combined C in the DRI， and the rest leaves as CO2.

Since the Energiron ZR process produces DRI with a higher percentage of C， the amount of C removed as CO2 is lower. The difference in CO2 gas production can be noted when comparing it to the CO2 gas production in the direct reduction configuration， which integrates an external catalytic converter into the direct reduction shaft furnace as a supplemental source of reduction gas. In the direct reduction configuration that integrates the external catalytic converter with the direct reduction shaft furnace， out of a total process NG supplement containing 140 kg C per ton of DRI， about 25 kg C per ton of DRI (17%) leaves the process as part of the DRI and the rest is released from the converter as flue gas. These figures compare to 110 kg C per ton of DRI， of which 40 kg C per ton of DRI (36%) is DRI produced in the Energiron ZR process. in addition， 65 kg of the remaining 70 kg of carbon per ton of DRI is selectively removed as pure carbon dioxide， which can be used for other purposes or sequestered. The elimination of H2O and CO2， two by-products of the reduction process， increases the gas utilization in the process to over 95%. In short， the Energiron process provides built-in selective elimination of approximately 65% of the total CO2 input (approximately 240 kg of CO2 per ton of DRI).

The Energiron plant offers the unique option of selectively recovering CO2. The CO2 absorption system captures not only CO2， but also sulfur from the process gas stream， resulting in a reduction of approximately 99% of the plant's total SO2 emissions.

H2 as a reducing gas

In steel plants， H2 is expected to replace C as an energy source for iron ore reduction processes in the near future. In gas-based direct reduction processes， H2 will replace NG. The Energiron ZR process is ready to use any amount of H2 to replace NG without major equipment modifications. In fact， the use of H2 in the Energiron ZR process scenario will be reflected in smoother operations and increased productivity， as the requirement for in-situ conversion of NG gas will be reduced.

The use of H2 concentrations up to 70% at the reduction shaft inlet has been well demonstrated in existing Energiron direct reduction plants， which involve a steam reformer to generate the reduction gases (H2 and CO).

However， using H2 instead of NG as the energy input， the % C in the DRI will drop because it will dilute the CH4 concentration in the reducing gas， but due to the flexible process configuration of the Energiron ZR scheme in terms of reduction loop and fuel utilization， it is possible to achieve 3.5% even at 35% H2 energy input (or about 64% by volume - N cum per ton of DRI). C. For 70% H2 energy (or about 88% volume-per-ton Num of DRI)， the expected C in DRI would be less than 2.0 %.

Alliance with NSENGI

In 2014， Tenova HYL and Danieli entered into an agreement with Nippon Steel & Sumikin Engineering Co. (NSENGI) reached an agreement to combine and commercialize their Energiron direct reduction technology with optimized blast furnace technology developed and owned by NSENGI， as well as syngas technology (high efficiency coal gasification and steel mill by-product gas utilization technology). The purpose of the new alliance is to combine R&D activities with their respective expertise in Energiron DR， blast furnace and syngas technologies with the ultimate goal of developing a new ironmaking technology that will reduce CO2 emissions and operating costs while increasing productivity and/or reducing capital expenditures for integrated steelmaking facilities.