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Thursday, January 16, 2014

#167 - Using the Energiron Process with SynGas for DRI Production

The following article appeared back in January 2007 in the technical section of Acero magazine. This concept combines two industrial processes that are of interest to us at Nova.
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Using the Energiron Process with SynGas for DRI Production

The standard Energiron process does not require major changes to operate with SynGas from a wide variety of sources.

The possibility of successfully coupling a DRI plant with a coal gasifier system will provide new perspectives in ironmaking. New possibilities are thus opened to introduce gas-based direct reduction technology in markets (like India, China or Europe) where there is low availability of natural gas at competitive prices, but high availability of coal.

In this respect, due to the specific characteristics of the process scheme, the technology offered by the Energiron alliance presents the most adequate configuration for this application, in terms of proven technology and investment/operating costs.

Increasing prices for energy, mainly for coke and natural gas, and environmental restrictions related to CO, emissions have led to new considerations for using available energies and materials. Additionally, continuing rising prices of metallics and prevailing market fluctuations make it necessary to analyze the alternatives for processing metalling units on site, for advantages in cost and availability. Energiron, the innovative Direct Reduction Technology, jointly developed by Tenova and Danieli, is offering an approach based on coal or other carbonaceous fuels as a source of reducing gas to a standard DR module for DRI production in locations lacking availability and/or low price of natural gas. By using synthesis gas (SynGas) from a gasifier as source of reducing agents, the amount, quality, and conditions of the gases required for the reduction process are the most important parameters defining the most adequate gasifier-DR scheme.

Alternative Energy Use - Coal Gasification

One of the main advantages of the Energiron process is the configuration based on independent reducing gas generation and reduction sections. Under these conditions the only requirement for the reduction process is the supply of the required amount of hydrogen and carbon monoxide: the process scheme remains unchanged. For the Energiron process there is a wide flexibility
for using alternative sources of reducing gases:
  • Hydrogen.
  • Conventional reformed gas.
  • Gases from coal gasification processes.
  • Coke oven gas.
  • Gases from hydrocarbon gasification.
  • Gases from smelter gasifiers.
  • Others.

In case the reducing gas (SynGas) comes from a coal gasifier, it is possible to adjust its characteristics by conditioning it to enhance its H2 content.

Figure 1
DRI plant with gasifier: general arrangement


Coal Gasification: General background

Gasification refers to the partial oxidation of a fossil fuel, forming SynGas, which consists primarily of hydrogen (H2) and carbon monoxide (CO). The Energiron process is characterized by the use of H2-enriched gas. Most gasifiers produce SynGas with suitable analysis for use in the DR process. Gasification or partial oxidation consists of converting low-grade fuel that is often dirty. (such as coal, refinery residues and biomass). The partial oxidation reaction for carbon is:

C + 1/2 O2 = CO

This reaction is exothermic and thus, water is introduced into the gasifier in the form of steam or liquid water to moderate the temperature of the reaction by the endothermic reaction:

C + H2O = H2 + CO

Other reactions that occur within a gasifier are the shift reaction:

CO + H2O = H2 + CO2

and the hydro-gasification reaction:

C + 2H2 = CH4

For any DR process, carbon from the reducing gases make-up (either in the form of CO or CH4) must be eliminated from the DR plant. Typically, for other DR process, this carbon is purged from the system via tail gas, which is used as fuel in reforming/heating equipment. In the Energiron process, due to selective carbon elimination through CO, removal, the purge is minimized and recycling/reuse of reductants is maximized, thus optimizing reducing make-up requirements.

Energiron - Gasifier Scheme

As presented in Figure 2, the treated, H2-enriched SynGas from the gasifier is fed to the standard Energiron DR plant. The mixture of SynGas make-up and recycle gas is preheated in a direct gas heater up to 930°C and fed to the reactor. After reduction of iron ores in the DR reactor, top exhaust gas is passed through a scrubbing unit for dust removal and cooling. Then, the gas is recycled by the compressor and CO2 is selectively removed. To further decrease energy consumption, a top gas heat recuperator can be incorporated. Specific requirements of SynGas per tonne of DRI basically correspond to the typical makeup of the conventional Energiron gas scheme (about 685 Nm3/t DRI).

Figure 2
Energiron plant with syngas from gasifier, including HYTEMP system


In case a steel mill is present downstream, pneumatic transport of hot DRI (HYTEMP) to the Electric Arc Furnace can be incorporated as part of the basic plant arrangement. By comparing the scheme based on SynGas with the conventional Energiron DR scheme, the similarity of reducing gases entering the DR reactor can be noted; hence, no technological risk is foreseen for this application. Based on the analysis of treated SynGas (typically from a conventional gasifier), expected DRI characteristics for coal-SynGas are 93% metallization and up to 2% carbon.

Depending on particular applications, optional schemes, which can be incorporated, are: 
  • In plant electrical generation. This can be achieved by installing a turbo expander in the treated SynGas stream before it is fed to the DR module. This allows potential power savings of about 20-40 kWh/tonne of DRI (depending on gasifier technology), taking advantage of the gasifier high operating pressure. 
  • Carbon dioxide (CO2) recovery. For sale as by-product.

Most Suitable DR Technology for using SynGas from coal gasification

When comparing the basic Energiron Process scheme to the one required for SynGas from coal gasification, the following main aspects related to the Energiron Process application can be easily noticed: 
  • General process scheme. No major changes and innovations are required in the basic process scheme. The reduction section is incorporated as it is in typical Energiron plants. 
  • H2-rich gases use in DR plants. SynGas is conditioned through shifting and CO2 removal to produce the H2-rich gases, which characterize the Energiron process. 
  • Optimization of process SynGas consumption. Recycling of reducing gases through CO2 removal, minimizes SynGas make-up. 
  • HYTEMP iron use.

Potential incorporation of the HYTEMP system for delivering hot DRI to the EAF leads to important economic benefits related to power savings and productivity increase. The HYTEMP iron presents a unique option as an alternative product for integrated steelmaking facilities, based on the use of SynGas from coal gasifiers.

Overall plant performance

As compared to other existing and emerging coal-based DR technologies, this scheme offers the possibility of installing a DR plant of any size up to 1.7 million tonnes/year of DRI in a single module. This approach is based on the incorporation of proven technologies: Gasifier unit and Energiron DR plant.

A similar scheme, based on coal gasification, is being implemented by Danieli in India for a Jindal project to produce 1.7 million tons of DRI.

Conclusions

The possibility of successfully coupling a DRI plant with a coal gasifier system will provide new perspectives in iron making.

New possibilities are thus opened to introduce gas-based direct reduction technology in markets (like India, China or Europe) where there is low availability of natural gas at competitive price, but high availability of coal.

In this respect, due to the specific characteristics of the process scheme, the technology offered by the Energiron alliance presents the most adequate configuration for this application, in terms of proven technology and investment/operating costs.

Original article can be found on the Tenova website here.

Other links to HYL and Energiron:
http://www.tenovagroup.com/companies_hyl.php?id_company=2
http://www.energiron.com/

HYTEMP® is registered trademark of Tenova HYL

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