Corex
The Corex process is a method for producing liquid pig iron . In contrast to the blast furnace process , no blast furnace coke is required, which makes special demands on the coal used.
history
The basis of today's Corex process is the KR (coal reduction) process, which was developed by Ralph Weber in Brazil in the 1970s. The corresponding patent was bought in 1978 by Willy Korf , who invited what was then VOEST-Alpine to develop the Corex process with him until it was ready for industrial use. After the bankruptcy of Korf Stahl AG, all rights were transferred to VOEST-Alpine and, after its division, to VAI . The first industrial Corex plant was built in 1989 at ISCOR in South Africa (capacity approx. 300,000 t / a). In the meantime, a Corex plant at POSCO in South Korea with 600,000 t / a, a plant near Saldanha (South Africa) and two plants at Jindal Steel in India have successfully started up. Two more Corex plants were ordered by Hanbo Steel in Korea in 1994, but never went into operation due to the bankruptcy of Hanbo Steel. These two Corex systems have since been bought by Essar Steel and are to be rebuilt in India. In November 2007, the world's largest Corex plant to date was put into operation at Baosteel , Shanghai , with an annual capacity of 1.5 million tons. Another Corex system of this size was then ordered by Baosteel and went into operation at the end of March 2011.
Process description
The Corex process is a two-stage smelting reduction process, in which pig iron can be produced on the basis of non-coked coal and iron ores . The aim of the smelting reduction process is to combine the smelting process, coal gasification and direct reduction to produce liquid iron, the quality of which corresponds to that of blast furnace pig iron. Smelting reduction combines the process of direct reduction (pre-reduction of iron oxide to sponge iron ) with a melting process (final reduction). The process therefore runs in two stages in separate units. First, the ores are reduced to sponge iron, in the second step the final reduction, melting and carburization to pig iron takes place. The energy required for the melting process is provided by the gasification of coal (smoldering coke, char). Large amounts of carbon monoxide and hydrogen are produced as exhaust gas, which is used as a reducing gas.
Basic principle
Lump ores, sinter, pellets or their mixtures are metallized to approx. 90% in a reduction shaft in countercurrent with the process own reducing gas and conveyed via discharge screws into the melter gasifier arranged below. In addition to the residual reduction and the melting of the sponge iron, the necessary metallurgical metal and slag reactions take place here. Pig iron and slag are tapped like in a blast furnace. Investigations on the Corex slag did not show any fundamental differences to HO slag.
The furnace gas of the reduction shaft - top gas - can be used after cleaning and cooling in a scrubber as so-called export gas for energetic and metallurgical purposes. The Corex export gas is characterized by an average calorific value (Hu = 7,500–8,000 kJ / m³ (iN) ) and high purity (dust 5–10 mg / m³ (iN) ).
Coal is fed into the top of the melter gasifier. After the coal has been dewatered and degassed, a fixed bed of char is formed in the melter gasifier. In the hearth of the melter gasifier, the smoldering coke is gasified with oxygen. In the upper part of the fixed bed, further gas is formed by the pyrolysis of the coal. The resulting hot process gas (approx. 1,000 ° C) consists primarily of CO, H 2 and is laden with fine dust. After cooling and dedusting (hot cyclone), this raw gas is fed to the reduction shaft as a reducing gas. The separated dust from the cyclone is returned to the melter gasifier and gasified there with oxygen to generate additional gas.
Advantages and disadvantages compared to the blast furnace process
- The use of non-coked coal replaces the coking plant and thus one of the main emission sources of a steelworks.
- At the high gasification temperatures of coal in the meltdown reactor (T> 1,000 ° C), organic compounds are completely broken down into their basic gaseous components (CO, CO 2 , H 2 ) and organic sulfur compounds are broken down into gases containing carbon and hydrogen (COS, H 2 S) transformed. In the subsequent process in the melter gasifier, these foul-smelling and highly toxic compounds are almost quantitatively bound in the sponge iron, in the aggregates and in the slag and thus immobilized.
- The higher flexibility with regard to the heterogeneity of the loading allows a stable process control even with strongly varying raw material quality. In addition, the Corex process enables more cost-efficient control of the process due to the tolerance to fluctuations in the loading capacity and the advantages of easier start-up and shutdown of the system.
- The main disadvantage of the process is the enormous amount of corex gas that arises, which has to be recycled in order to be able to operate the process economically. Since the gas is difficult to integrate as a fuel into a grown iron and steel works during the running process , it is mainly sold on to energy suppliers or to heavy industry as heating and combustion gas .
Use of residues and waste
As in the blast furnace process, metallurgical residues and waste from smelting works can be used in the Corex process. These include oxidic , metallic and carbon-containing materials. For example, fine dust and mill scale are briquetted cold with binding materials and then fed to the reduction shaft. Sludge from waste gas cleaning (e.g. furnace gas sludge) is pelletized and fed into the melter gasifier together with coal dust. Process sludge can also be returned in this way. 10% of the pellets are discharged with direct return in order to avoid an accumulation of heavy metals. Residues heavily contaminated with alkalis or zinc (e.g. steel mill dust) cannot be introduced into the Corex process, as they would restrict the functionality of the system. This applies in analogy to the blast furnace process.
swell
- ^ Hermann Druckenthaner, Angelika Klinger, Kurt Wieder, Ulrike Aichhorn, Johann Wurm, Joseph Stockinger: Optimization of the COREX Process Through the Application of Advanced Process Models AISE, Pittsburgh, 1999 ( Memento of the original from October 10, 2007 in the Internet Archive ) Info : The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ RT Jones Iron and Steel ( Memento of the original from March 23, 2006 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Essar to buy two Korean steel units ( Memento of the original from September 1, 2006 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Siemens press release I&S 1107.6735 d November 16, 2007 ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.
- ↑ Siemens press release IIS201104997e April 8, 2011
Patents
AT373970 Process and device for the production of liquid pig iron or steel precursors
AT382390 Process for the production of liquid pig iron or steel precursors