PRODUCTIVITY AND RATIONAL ENERGY USE IN THE STEEL MANUFACTURING PROCESS AT ACINDAR

THE COMPANY

Acindar is the largest steel manufacturing company in Argentina engaged in the business of manufacturing non-flat steels.  It is a domestically owned company, and since the very beginning it has been a leader in the continuous inclusion of new technologies for improving the quality of its products and decreasing its costs.

Acindar’s first industrial plant was set up at the city of Rosario, which began producing round iron rods for construction in April, 1942.  In 1951 a new plant was installed on the banks of the Paraná river at the town of Villa Constitución, Province of Santa Fe.  This plant was vertically integrated in 1978 when it began producing its own steel from iron ore.  The “semi-finished products area” as it is called, consists of the following:

From this area, the steel is then transported to the “finished products area”, which basically consists of two continuous Rolling Mills Plants from which high and low carbon wire, bars and strapping are obtained, which are used as the raw materials for other later processes for producing a wide range of related steel products such as wire, tubing, mesh, nails, etc.

THE PROCESS

The semi-finished products area at Acindar has two stages: direct reduction process and electric arc furnace meltshop. The Direct Reduction Plant is where the first stage of transforming iron into steel is carried out.  The resulting product is Sponge Iron or Pre-Reduced Iron, which is the raw material to be loaded into the electric arc furnaces during the melting process. The Direct Reduction Plant, using a Midrex design, is a continuous process consisting of:

Raw materials required in the process are: high grade iron oxide ( lump and pellet ) and natural gas, which generates catalytic reformed gases that are mostly composed of hydrogen and carbon monoxide.  When these hot gases are sent into the reduction furnace, they react with the iron oxide that is present, and remove the combined oxygen from it to produce controlled quality metallic iron in a solid state (94.5% metallization and 1.9% carbon).

The cooled product is sent to the Steel Mill where it is used as the metallic load for the electric arc furnaces after mixing with scrap iron.  It is melted down there by a high power electric arc to remove along with the slag, the non-metallic components that are contained in the sponge iron (gangue), thus enabling the grades of steel required for different applications to be sorted out through the use of additives and an appropriate refining process.

The following page shows the flowchart for the direct reduction process with modifications to it, which will be explained later.

Flowchart for the Direct Reduction Process

THE PROJECT

Growing market demand has made it necessary for these facilities in general and the Direct Reduction Plant in particular, to undergo successive modifications in a continuous effort to maximize their capabilities and efficiency due to their limited status for steel production, with special attention on the area of energy consumption, due to its significant involvement in the total cost of steel which amounts to approximately 25%.

The achievements that have been made at the Direct Reduction Plant during the ‘90s as a result of the development and application of a schedule of activities for decreasing specific energy consumption, may be seen by looking at conditions at the start and the conditions under which it is now operating.  These conditions have enabled it to be considered as one of the most efficient plants.

This becomes more evident when considering the final cost of liquid steel as a priority, during the 91/92 fiscal year, the quality of sponge iron produced was improved.  This increase in metallic content of over one point caused a specific consumption increase of 5.8% for natural gas and 12.4% for electric power, which was generously compensated for by the savings achieved at the steel production stage, which were not only due to decreases in the consumption of electricity and other inputs, but to increases in steelmaking capacity without having to modify facilities.

STRATEGY APPLIED

The strategy used at the Direct Reduction Plant considers two issues:

1.- Technological Innovation

2.- Continuous Improvement

1.- Technological innovation is carried out through different projects, each one of which takes into account the following stages:

Specific consumption data for the 91/92 period after product quality had been improved, were used as a reference for looking at how specific consumption had been evolving, which are: 323.4 m³ per product metric tonne for natural gas and 124.5 KWh per product metric tonne for electric power.

Implementation of actions for maximizing energy consumption efficiency started in July of 1993 when a heat exchanger was installed for preheating natural gas going into the catalytic reforming process.  The heat exchanger uses as a heating source, the flue gas coming from the combustion chamber.  Along with this, the cooling gas distributor at the bottom of the furnace was also redesigned.

A lime coating of the iron ore charge was implemented in November, 1994 to decrease clustering of material due to softening under high temperatures.  As a result of it in May, 1996 oxygen injection into the reactor was developed and implemented to increase the reduction temperature.

Expansion of the Direct Reduction Module’s production capacity was developed and put in place during the 96/97 period.

2.- Continuous improvement (Kaizen) is being used throughout the entire company since 1993 and includes the following issues:

Educational and Training Activities:

Operational Activities:

Maintenance Activities:

Process Activities:

RESULTS

The result from installing the heat exchanger that was completed in July, 1993 was that natural gas became preheated from 15°C to 370°C, which produced a savings of 2,985,200 Kcal/h of fuel and a decrease in electric power consumption.  The modifications made to the furnace and the installation of a bleed line enabled, the thermal profile at the reduction area to be optimized, average furnace temperature to be increased and quality variations to be minimized.  This increase in the efficiency of the cracking furnace lowered electric power consumption in related equipment.  As a result of both of these modifications, specific consumption decreases of 2.4% for natural gas and 8.6% for electric power were reached in the 93/94 period.

The lime coating applied to iron ore since November, 1994 represents a gain of 5,124,500 Kcal/h.  Since the speed of the reaction increases as the temperature goes up, a production increase of around 7% was obtained, which also means a significant additional decrease in specific electric power consumption items.  This process change and the benefits gained from the continuous improvement program begun in 1993, made it possible for decreases in energy consumption items amounting to 4.6% for natural gas and 10.4% for electric power to be shown with respect to the reference period (91/92).

The 96/97 period shows a decrease in specific consumption compared to 91/92, amounting to 7.8% for natural gas and 18.4% for electric power.  This decrease has been brought about by oxygen injection into the reactor, which enabled the temperature of reducing gas to be raised from 905ºC to 980ºC, thus gaining benefits similar to those gained by the lime coating.

The design for expanding production capacity at the Direct Reduction Module completed between 1996 and 1997 ended up providing a 30% production increase in August, 1997.  This project considered not only an increase in production capacity, but also a redesign of the recovery system in order to optimize use of residual energy in gases that were going out the stack.  By raising the temperature of the gas being fed into the hardening furnace from 410 to 520/540 ºC and of combustion air going to the burners from 600 to 650 ºC, this generated a total savings of 10,398,000 Kcal/h, which is equal to 9.41 NCM of natural gas per tonne of sponge iron produced, and a consequent decrease in specific electricity consumption.  The 97/98 fiscal year is closing out with specific consumption levels of 291.3 SCM/Ton of natural gas and 92.5 KWh/Ton of electric power, representing decreases of 9.9% and 25.7% with respect to the reference fiscal year (91/92).

During the 98/99 and 99/February 2000 periods, specific consumption rates for the 97/98 fiscal year were maintained, despite a decrease in required production and the utilization of a lower quality load mix due to reasons of cost.

Following is a table showing progress in specific energy consumption at the Direct Reduction Plant during the study period.

Progress in Specific Energy Consumption in Sponge Iron Production at the Direct Reduction Plant

(*) Reference Fiscal Year                                    

(**) Cumulative up to April, 2000.

(***) Standard Cubic Meters (gas status, pressure 1 atmosphere and temperature 15º C).

FINANCIAL BENEFITS

The financial benefits in this case should be attributed to the fact that during the 93/00 period, the decrease in energy consumption was from 30.7 SCM/Ton (9.5%) for natural gas and 31.8 KWh/Ton (25.5%) for electric power.  If only the portion of natural gas consumed that is used for power generation (52%) is considered, then savings go up to 18.6%.  According to the savings mentioned for natural gas and electric power, this cost decrease amounts to somewhere on the order of $3,325,000 per year.

However, if the expansion for the year 1997 is not considered, which has a significant production component within its justification, the rest of the innovations generated annual benefits of U.S.$2,546,000, which are much higher than the investments made which amounted to U.S.$690,000.

Overall during this period of time, a reduction was achieved in the generation and emission into the atmosphere of 112,075 SCM per day of CO₂, a compound that is responsible for 49% of the causes of the greenhouse effect.  This represents a savings of 13 million standard cubic meters (SCMs) of natural gas or 11,500 tons of coal required for the generation of electric power at thermoelectric plants.

CONCLUSIONS

The objective of the program carried out at the Semi-Finished Products Area at Acindar within the framework of Integrated Management, was rational energy use.  The results achieved over six years are showing that productivity and financial profitability can go hand in hand with a concern for care and preservation of the environment through efficient use of natural resources, which are the basic pillars of Ecoefficiency.

FUTURE OUTLOOK

This program of Technological Innovation and Continuous Improvement is not over yet.  Numerous possibilities for improvement have been found which have not yet been implemented at the Semi-Finished Products Area, including:

As progress continues to be made in achieving the goals set forth, the degree of success attained depends on a firm purpose in carrying forth established programs.  Consideration also needs to be given to involving all the company’s personnel in a teamwork effort based on the philosophy and tools of Continuous Improvement, by starting off activities with awareness and training for all personnel, and an analysis of the initial situation and a search for improvement opportunities in all areas and sectors, processes, procedures, equipment and operations.

GLOSSARY

Bleed Line: Gas blowing line (going out of the system to produce a change in direction in internal system flows).
VWF: speed regulator
NCM: Normal gas conditions (0°C and 1 atmosphere)

CONTACT

Rafael D. Leone
Techology Manager – ACINDAR S.A.
Plant Nº  2 – Ruta 21 – Km 247 – Villa Constitución – Santa Fe (C.P. 2919)
Tel: (03400) 47 8328
Fax.: (03400) 478211
E-mail: rleone@acindar.com.ar