MXPA99010627A - Method for controlling a smelting reduction process - Google Patents

Abstract

Method for controlling a smelting reduction process, in particular a cyclone converter furnace process for producing pig iron, characterised in that one:measures the carbon fraction C in the off-gas in the form of CO and CO2;measures the hydrogen fraction H2 in the off-gas in the form of H2 and H2O;determines the C/H2 ratio in the off-gas;compares the C/H2 ratio thus determined in the off-gas against the C/H2 ratio prevailing for the coal being supplied, and adjusts the coal supply based on the difference found in the C/H2 ratios in the off-gas and the coal being supplied.

Description

METHOD TO CONTROL A PROCESS OF REDUCTION BY FOUNDRY DESCRIPTION OF THE INVENTION The invention relates to a method for controlling a melt reduction process, in particular, a cyclone converting furnace process for producing goa. A melt reduction process of the cyclone converter furnace process type is known, for example, from EP-A 0 690 136. The aim of the invention is to create a method for controlling a melt reduction process. With the invention, this is obtained by: measuring the fraction of C in the gas discharge in the form of CO and C02; measurement of the H2 hydrogen fraction in the gas discharge, in the form of H2 and H2O; determination of the C / H2 ratio of the carbon C fraction and the H2 hydrogen fraction in the gas discharge; - compares the proportion of C / H2 determined in this way in the gaseous discharge against the proportion of C / H2 that prevails for the coal that is supplied, and adjust the supply of coal based on the difference found in the proportions of C / H2 in the gas discharge and the coal that is supplied so that the coal slag fraction that is formed from the coal in the slag layer remains stable, the fraction is not much less than 20%. The advantage of this is that the coal slag consumption of the melt reduction process can be monitored online and that the coal supply from the smelting reduction process can be controlled automatically. Preferably, the proportion of C / H2 of the coal supplied is corrected for the carbon lost by the transport of the gas discharge, for the carbon dissolved in the goa, for carbon and / or introduced hydrogen together with the additives and for the introduced hydrogen by injecting water into the gas discharge system before the sampling point. This generates a better control of the process. Preferably, the coal supply is adjusted while the height of the lance, the ore and the oxygen supply remain the same. The advantage of this is that the process develops steadily. The invention will be illustrated for a cyclone converter oven (CCF) process with reference to the drawings. However, the invention also applies to other smelting reduction processes, such as, for example, the AISI process and the GOD process. Figure 1 shows a CCF reactor.

Figure 2 shows the equilibrium of carbon and hydrogen through the CCF reactor. In the production of the goa by the CCF process of the iron ore, often in the form of Fe203, it is previously reduced in FeO in a melting cyclone (1). A final reduction of FeO to iron (Fe) takes place in the converter vessel (2). With the CCF, the casting cyclone (1) is placed on top of a casting container (2) in the form of a converter. Coal (3) is supplied inside the casting vessel and is partially gassed by combustion in position (10) with oxygen (4) which is supplied through a lance or spears (9). The gas discharge rises towards the cyclone.

The ore (5) of cyclone iron and oxygen (6) are tangentially driven. The oxygen reacts with part of the CO and H2 present in the spent gas so they release heat. The injected ore particles are propelled through the combustion cores in the cyclone and melt instantaneously.

In position (11), the molten ore in the cyclone is previously reduced to FeO, according to the chemical reactions: 3Fe203 + C0 (H2) < - > 2Fe304 + C02 (H20) Fe304 + C0 (H2) < - > 3Fe0 + C02 (H20) The previously reduced molten ore (12) is drip-separated from the cyclone onto a layer (7) of slag in the casting vessel below. The drops of ore dissolve in the slag. In the slag layer, the final reduction to iron takes place, according to the net chemical reaction: FeO + C3olid < - > Fe1 Liquid + CO The carbon consumed in this reaction is supplemented by coal introduced into the slag layer. The volatile components in the coal are removed directly by evaporation as a consequence of the high temperature that prevails, and a carbon form, known as coal slag, remains behind in the slag. The coal slag has a triple function in the slag: 1. it is the reduction medium for the final reduction of the iron-to-iron oxides; 2. it is the fuel to supply the necessary heat for the reduction to take place and to melt the iron ore, - 3. It has a stabilizing effect on the foaming of the molten slag layer. For this, the mass fraction of coal slag in the slag should not be much less than 20%.

In functions 1 and 2 the coal slag is consumed, while in function 3 it is tried to keep the coal slag fraction in the slag as constant as possible. Functions 1, 2 and 3 can be unified with each other by maintaining a supply of coal slag equal to coal slag consumption. However, the coal slag that originates from the coal, and besides the presentation of coal slag, the volatile constituents escape from the coal as a consequence of the high temperature that prevails. On their return, the volatile constituents again make a contribution to the function (2) of the coal slag. Carbon and hydrogen often represent the major components from which the volatile constituents in coal are formed. For the casting bath process, the following is applied (see figure 2):? C coal entering "*"? C flow coming in? C gas leaving dC slag / dt + fCFe + fc powder leaving + Fc huiia rest of carbon mass? H2 coal entering + FH2 incoming water =? H2 incoming stream + FH2 gas leaving reSCO QT mass of hydrogen where: ~ Fc of incoming gas is the amount of carbon introduced into the coal, the amount of hydrogen introduced with the coal; - Gas Fc that comes out is the total carbon in CO and C02 in the gas discharge. This carbon originates from the combustion of the volatile hydrocarbons and the coal slag in the slag and the coal slag consumption for the final reduction of the iron ore and any carbon fraction in the dosed additives: - fc Fß is the amount of carbon absorbed per unit time in the newly formed iron; - fc escoi is the amount of carbon absorbed per unit of time in the newly formed slag; - Fc salt powder is the amount of carbon that leaves the CCF reactor as a fine powder; - Fc flow which is the carbon entering the CCF reactor as a consequence of the additive dosage (for example CaCO3); - fH2 gas which comes out is the total amount of hydrogen in the form of H20 and H2 from the discharge gas. This hydrogen originates from the volatile hydrocarbons in coal, from hydrogen in any additive and (possibly) introduced cooling water; - FH2 agu ent ent is the amount of hydrogen in the form of water that is used for direct (possible) cooling of the hot gas in the gas pipeline; - FH2 of fl oo that e a is the hydrogen that enters the reactor of CCF as a consequence "of the dosage of additives.

It should be noted that other sources of supply and losses for C and H2 are possible, such as, for example, air pollution and wear of the refractory lining of the metallurgical vessels. However, these are generally of minor importance. If desired, they can be taken into consideration in a similar manner. The one in figure 2 represents a sample or a measurement point.

Control of coal dosage according to the proportion C / H2.

In a melt reduction process (such as in a CCF converter), the internal conditions vary as the process is carried out because the slag / metal bath (7), (8) increases as the process progresses. These variations affect the behavior of the reactor. In addition, the bathing process has possible spill effects such as, for example, by excessive foaming of slag and by solidification of the molten slag. The essential aspects for the stable operation of a smelting reduction bath process are: a stable fraction of carbon in the metal bath; maintenance of a stable slag height, that is, excessive slag foaming is avoided, which is called "tumultuous blowing". For this, it is of essential importance to have good control over the coal slag fraction in the slag.

When enough coal scum is present, this causes small bubbles of gas to coalesce and prevents tumultuous blowing. The extreme conditions in the converter make it difficult to directly and reliably measure the internal conditions of the process such as the coal slag fraction.

Accordingly, the control of the reactor is preferably based (as much as possible) in measurable quantities externally (such as the composition of the gas discharge). The bathing process can be well controlled as soon as the coal slag fraction is under control. For this, the operator has the following control parameters available: the supply of raw material (coal, ore, additives); the oxygen flow rate; the height of the spear (= the distance between the head of the spear and the slag layer). In the following, a method is proposed with which the change in the coal slag consumption can be monitored in a simple way, and the coal dosage is controlled in such a way that the mass of coal slag remains stable in the converter . The coal consists essentially of graphite and volatile constituents (hydrocarbons). When the coal is dosed in a bathing process, the hydrocarbons are removed by direct evaporation. The high temperature causes the hydrocarbons to decompose and to be e? the gas discharge as H2, H20, CO and C02. The product (coal slag) that remains in the slag consists essentially of graphite. This coal slag is consumed by reduction reactions and direct combustion with oxygen. Both reactions produce CO and C02. The fraction of hydrogen in the gas discharge (in the form of H2 and H2O) is a consequence only of a function of the type of coal used and the amount of coal that is supplied. In addition, the carbon fraction (in the form of CO and C02) is also a function of coal slag consumption. The monitoring of the ratio between the carbon fraction and the hydrogen fraction in the gas discharge therefore provides a direct indication of the changes in the coal slag consumption of the bathing process. A stable coal slag mass is essential to carry out the bathing process. Therefore, the proportion of C / H2 in the gas discharge can serve to automatically control the coal supply. This requires reliable sampling of the gas discharge from the converter. In this case, any carbon and hydrogen fraction in the other raw materials must be taken into consideration. In addition, two phenomena must be considered which contribute to the reduction of the mass of coal slag in the converter, the loss of coal slag dust through the gas discharge pipe and the dissolution of carbon in the metal bath . At the same time, it needs to form enough coal slag, for the coal slag fraction in the newly formed amount of slag, which must be equal to the slag fraction that is already present in the converter. The phenomena can be controlled by regulating the coal supply in such a way that the proportion of C / H2 in the gas discharge is equal to the proportion of corrected C / H2.When these phenomena are not present, then the dosage of coal will be equal to the coal consumption if the proportion of C / H2 in the gas discharge is equal to that of the coal that is supplied, an example is provided for the calculation of the corrected proportion The formation of coal slag dust is determined essentially by the dust already present "in the coal that is supplied and the type of coal (decisive for the decomposition behavior during degassing) .The dust loss can reach up to 15%. However, in the CCF process, a part of the coal slag powder will be burned in the melting cyclone.

To avoid the possible reduction of the coal slag fraction in the slag through dust losses, the calculation of the corrected C / H2 ratio is better based on the maximum dust loss. During the process cycle, when there is a smaller dust loss, there is a slight increase in the coal slag in the converter (see example). However, the slag fraction of coal in the slag will remain relatively unchanged due to the growth of the slag layer. In order to correct any excessive fraction of high coal slag in the slag remaining after a (partial) drain of metal and slag, it is possible to adjust the coal supply for some time downward and allow the coal slag to be removed by burned. The coal slag fraction is then lowered sufficiently to allow progress with control of the coal supply, "according to the proportion of C / H2.The amount of C in the goa can be determined by regularly taking a sample of the goa produced (casting) and determine the carbon content in it.An additional correction to the desired proportion of C / H2 is also necessary when introducing dosed additives (for example CaCO3) and possibly water injection where carbon is added. and / or additional hydrogen in the gas discharge (see example).

Example Calculation of the C / H2 ratio This example provides the calculation of the corrected C / H2 ratio. The calculation is based on (RY = goa): - an installation of 0.7 million tons of RY / year; a production rate of 90 tonnes RY / hour, with laundry every hour; a coal consumption of 600 kg / ton of RY, of medium volatile coal; a maximum coal slag dust loss of 15% of the measured coal mass; carbonization of the goa bath up to a mass fraction of 4.5%.

Analysis of average volatile coal (mass fractions): volatile constituents 29% fixed carbon (graphite) 70% minerals 5% - humidity 5% Dry ash-free analysis (90% of the total mass) carbon 90% hydrogen 5% - rest 5% Calculation of the desired ratio of C / H2 in the gas discharge H2 as hydrocarbon in 600 kg of coal = 0.9 x 0.05 x 600 - 27 kg H2 = 13.5 kmol H2 H2 additional from moisture in 600 kg = 0.05 x 600 = 30 kgH20 = 1.7 kmol H2 H2 total in 600 kg of coal - 15.2 kmol of total H2 of C in 600 kg of coal = 0.9 x 0.9 x 600 = 486 kg C = 40.5 kmol "C C / H2 in metered coal = 40.5 / 15.2 = 2.66 maximum dust loss per 600 kg of coal = 0.15 x 600 = 90 kg of coal slag = 7.5 kmol C carbonization of the goa per ton = 0.045 x 1000 = 45 kg C = 3. 75 kmol C corrected proportion of C / H2 for control, according to the gas discharge converter C / H2 = (40.5 - 7.5 - 3.75) /15.2 = 1.92 dosage of calcium carbonate in the cyclone = 170 kg / ton of RY = 1.7 kmol of C corrected proportion of C / H2 to control according to the cyclone gas discharge: C / H2 = (40.5 - 7.5 - 3.75 + 1.7) /15.2 = 2.04

Claims (6)

1. A method for controlling a smelting reduction process, in particular a cyclone converting furnace process for producing goa, wherein iron oxide, coal and oxygen material is provided, characterized in that one: measurement of the carbon C fraction in the gaseous discharge in the form of CO and C02; measurement of the H2 hydrogen fraction in the gas discharge, in the form of H2 and H2O; determination of the C / H2 proportion in the gas discharge; compare the proportion of C / H2 determined in this way in the gas discharge against the proportion of C / H2 that prevails for the coal that is supplied, and adjust the supply of coal in base in the difference found in the proportions of C / H2 in the gas discharge and coal that is supplied in such a way that the coal slag fraction that is formed from the coal in the slag layer remains stable, the fraction is not much smaller than twenty%.

2. The method according to claim 1, characterized in that the proportion of C / H2 of the coal supplied is corrected for the carbon losses due to the entrainment of the gas discharge.

3. The method according to claim 1 or 2, characterized in that the proportion of C / H2 of the coal supplied is corrected for the carbon dissolved in the goa.

4. The method according to one of claims 1 to 3, characterized in that the proportion of C / H2 of the coal supplied is corrected for the carbon and / or hydrogen introduced together with the additives.

5. The method according to one of claims 1 to 4, characterized in that the proportion of C / H2 of the coal supplied is corrected for the hydrogen introduced by injection of water into the gas discharge system before the sampling point.

6. The method according to one of claims 1 to 5, characterized in that the coal supply is adjusted while the spear height, the ore and the oxygen supply remain the same.