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.
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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).
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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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