WO2009126052A1

WO2009126052A1 - Electric arc-resistance furnace in particular for manufacturing of concentrated silicon alloys using the method of silicon dioxide and iron oxides reduction with carbon

Info

Publication number: WO2009126052A1
Application number: PCT/PL2009/000024
Authority: WO
Inventors: Jerzy Tomeczek; Tadeusz Wisniewski; Wojciech Bialik
Original assignee: European Silicon Sp . Z O.O.
Priority date: 2008-04-11
Filing date: 2009-03-17
Publication date: 2009-10-15

Abstract

An electric arc-resistance furnace, in particular for manufacturing of concentrated silicon alloys using the method of silicon dioxide and iron oxides reduction with carbon, which has a furnace tank filled with a charge blend and a gas capture hood situated above it, in which space the post-reaction gases - products of reduction processes proceeding in the furnace tank - are subject to post combustion, connected via a system of flues with a filtration system, consists in the fact that it is equipped with air nozzles supplying in a controlled way the combustion air to the space between the charge surface and the gas capture hood, where the air nozzles are situated in the hood roof (1), in components of electrode column equipment (2), and at the ends of charging pipes (3) situated under the roof, while in the space under the hood and in flues discharging the gases after post- combustion to the filtration system sets of heat exchangers (4) are installed, flushed by hot exhaust gases, through which hot compressed air flows receiving physical heat from hot gases and, once heated, inflows to the expansion gas turbine (5), where mechanical power is generated, converted in the generator into electric energy.

Description

Electric arc-resistance furnace in particular for manufacturing of concentrated silicon alloys using the method of silicon dioxide and iron oxides reduction with carbon

The invention concerns an electric arc-resistance furnace, in particular for manufacturing of concentrated silicon alloys using the method of silicon dioxide reduction with carbon, which uses the chemical and physical energy of post-reaction gases to generate electric energy using a expansion gas turbine.

The solution using the post-reaction gases energy to generate electric energy using

Clausius-Rankine water cycle and a steam turbine is well-known [Kolbeinsen L., Linstad T., Tveit H., Bruno M., Nygaard L. - Energy recovery in the Norwegian Ferro Alloy

Industry. The Norwegian Ferroalloy Research Organization, SINTEF, Trondheim 1999,

165-177]. In this solution the post-reaction gases are burned only in the air sucked in to the hood from the surroundings through partly open process ports. This results in lengthy combustion of post-reaction gases and partial flushing of heating surfaces in the hood by the flame. This manifests itself in an intensive dust deposition on low-temperature heating surfaces and is a source of pipes corrosion. This solution is also expensive in terms of capital expenditure.

The Mannesmann Demag Metallgewinnug solution [Reichelt Dr., Rath Dr., Hajduk

W., Fettweis W. - Energy Recovery on Submerged Arc Furnaces, Document Mannesmann Demag Metallgewinnug, Duisburg] using a steam boiler for electric energy generation is also known. In this solution post-reaction gases are burned in the hood only in the stream of air sucked in from the surroundings through partly open process ports in side walls. The Elkem solution [Aase E. - Electric reduction furnaces for high grade ferro- silicon and silicon metal with energy recovery systems. Paper presented at exhibition Elektro - 82 in Moscow, July 26, 1982] using Clausius-Rankine water cycle and a condensing or backpressure steam turbine is also known. In this solution low-temperature water surfaces are also installed in the hood, on which dusts are intensively deposited, making stable plant's operation difficult. Gases combustion occurs in the stream of air sucked in from the surroundings, what does not create conditions for rapid combustion of post-reaction gases.

In the present invention post-reaction gases are burned in the furnace hood in a stream of combustion air supplied by nozzles situated in the hood roof, in components of electrical column equipment and at ends of charging pipes situated under the hood roof. The temperature control of exhaust gases from the hood is carried out by means of controlled opening of closed process ports allowing the air sucked in from the furnace hood surroundings. The heat released in the process of post-reaction gases combustion is used to heat the compressed air flowing by a set of heat exchangers in the hood and in flues discharging the exhaust gases from the hood to the filtration system. The heated compressed air flows then to the expansion gas turbine, where it generates mechanical power converted in the generator into electric energy.

The solution proposed will be definitely cheaper than the known solutions. Moreover, replacement of water in pipes with compressed air will eliminate the effect of arduous dusts deposition on low-temperature heating surfaces in the hood and in the flue. The introduction of combustion air into the hood interior through a system of three groups of nozzles forms very favourable conditions for post-reaction gases combustion. It is particularly important when using coal as a reductant, because the hydrocarbons released during the coal carbonisation feature lengthy combustion.

An electric arc-resistance furnace, in particular for manufacturing of concentrated silicon alloys using the method of silicon dioxide reduction with carbon, is shown as an example in the figure presenting the schematic diagram of the furnace. It consists of a tank and located above it hood to capture post-reaction gases, in which electrode columns equipped with water coolers are installed. Post-reaction gases released from the top surface of the charge are subject to post combustion in the air supplied, in the stoichiometric amount necessary for complete and perfect gases combustion, through a system of three groups of nozzles: in the hood roof 1 directing the air downwards, countercurrent to post- reaction gases flow, in water coolers of electrodes equipment 2 directing the air horizontally and at the ends of charging pipes 3 situated in the hood roof 1 directing the air downwards. The temperature in the hood is controlled by means of stream of air sucked in to the hood interior through partly open process holes. The thermal energy obtained from post-reaction gases combustion is used to heat the compressed air in heat exchangers 4 situated in the hood and in the flue discharging the exhaust gases to the filtration system. Heated high-temperature compressed air flows to a expansion gas turbine 5, where during expansion performs mechanical work, which is used to drive the compressor and the electric generator. In the compressed air system, upstream the expansion gas turbine 5, a natural gas combustion chamber 6 is installed, which operation stabilises inlet parameters of the gaseous medium to the gas turbine and hence the amount of electric energy generated in the generator. These parameters stabilisation during individual process stages occurring in the arc-resistance furnace is an important element to obtain appropriate quality of electric energy.

Claims

1. An electric arc-resistance furnace, in particular for manufacturing of concentrated silicon alloys using the method of silicon dioxide and iron oxides reduction with carbon, which has a furnace tank filled with a charge blend and a gas capture hood situated above it, in which space the post-reaction gases - products of reduction processes proceeding in the furnace tank — are subject to post combustion, connected via a system of flues with a filtration system, characterised in that it is equipped with air nozzles supplying in a controlled way the combustion air to the space between the charge surface and the gas capture hood, where the air nozzles are situated in the hood roof (1), in components of electrode column equipment (2), and at the ends of charging pipes (3) situated under the roof, while in the space under the hood and in flues discharging the gases after post- combustion to the filtration system sets of heat exchangers (4) are installed, flushed by hot exhaust gases, through which hot compressed air flows receiving physical heat from hot gases and, once heated, inflows to the expansion gas turbine (5), where mechanical power is generated, converted in the generator into electric energy.

2. The electric furnace according, to claim 1, wherein in the compressed air system, upstream the expansion gas turbine (5), a natural gas combustion chamber (6) is installed, which operation stabilises the thermal energy of the air flow upstream the turbine and hence the amount of electric energy generated in the generator.