JPS635449B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for recovering flammable exhaust gas generated from a converter during blowing.

As is well known, the exhaust gas generated during blowing in an oxygen converter is CO2 caused by the decarburization of hot metal.
In the case of a pure oxygen bottom-blown converter, the heat content is extremely high as it also contains CO and H ₂ due to the decomposition of the hydrocarbons supplied to cool the bottom tuyere. Conventionally, converter exhaust gas has been used as an energy source.

Conventionally, two methods have been used to utilize converter exhaust gas as an energy source: one is to combust converter exhaust gas in a boiler installed in the flue above the furnace and recover heat as steam, and the other is to direct converter exhaust gas to a gas holder. A non-combustion method that recovers energy is known, but in recent years, the latter non-combustion method has become mainstream as energy prices have increased. When collecting exhaust gas using this non-combustion method, the exhaust gas is flammable and there is a risk of explosion if the mixture ratio with air reaches a certain value, so the air in the flue must be removed before collection. After completion of recovery, it is necessary to eliminate the exhaust gas in the flue. Therefore, conventionally, after the start of blowing and before transitioning to exhaust gas recovery, air is sucked into the flue from the furnace mouth and the exhaust gas is combusted, and the resulting CO ₂ , H ₂ O, and N ₂ are the main components. The air in the flue is replaced with an inert gas layer, and the same operation is performed after exhaust gas collection is completed to combust the flue gas and create an inert gas layer inside the flue. .

Fig. 1 is a graph showing the change over time in the exhaust gas flow rate due to the conventional recovery method from the start of blowing to the end of blowing, together with the change over time in the amount of combustible gas generated. The amount of gas increases from the beginning of blowing, becomes almost constant at the peak of decarburization, and then, at the end of blowing, as the carbon in the steel bath decreases, the oxygen used for decarburization decreases and the iron is oxidized. Therefore, the amount of combustible gas gradually decreases. Also,
When an auxiliary material containing solid oxygen is introduced into the steel bath during blowing, the decarburization reaction is promoted and the amount of combustible gas increases (period A in FIG. 1). On the other hand, the amount of exhaust gas is set at a predetermined flow rate by opening a damper installed in the precipitator at the same time as blowing starts and reducing the pressure at the furnace mouth, sucking in a large amount of air from outside. ) and maintain this state for a predetermined period of time. Thereafter, the damper is throttled to gradually reduce the exhaust gas flow rate and set to a predetermined flow rate (phase). In the conventional exhaust gas recovery method, an inert gas layer is formed during this period by the above-mentioned operation, but the exhaust gas flow rate control during this period, that is, the control of the amount of intake air, can be controlled depending on the properties such as hot metal components and temperature, or operating conditions. Regardless of the situation, the process is continued for a predetermined period of time, and the process is performed to generate an amount of inert gas that is 2 to 3 times the minimum amount of inert gas that is conventionally required. It is assumed that it has been replaced with . After reducing the exhaust gas flow rate to a predetermined flow rate,
The damper is adjusted to prevent blow-off from the furnace mouth and excessive intake of air (period ~), and the CO gas concentration reaches the set value, the calorific value of the recovered gas rises to the required value, and the O ₂ gas concentration explodes. Exhaust gas collection will begin when the concentration has decreased to a level that does not induce oxidation (at the end of the period). After that, exhaust gas collection was continued until the sublance was inserted into the steel melt in order to obtain data for controlling the carbon concentration at the end of blowing, and from then on, regardless of whether flammable gas was generated. First, the exhaust gas flow rate is increased to suck in air from outside, and the combustible gas is burned to generate an inert gas layer (phase).

However, the above-mentioned conventional flue gas recovery method reduces the generation of an inert gas layer at the start of blowing to an amount of inert gas that is two to three times the minimum required inert gas layer under assumed average operating conditions. This is done by uniformly inhaling a certain amount of air and burning flammable gas so as to generate an active gas layer.In other words, it depends on the properties of the hot metal, such as its composition and temperature, and the operating conditions, such as the amount of oxygen blown into it. Since the amount of intake air is not controlled according to the actual amount of combustible gas generated, which is determined by When a large amount of CO gas is generated, such as when a large amount of auxiliary raw materials (e.g. iron ore) is added, the amount of intake oxygen becomes insufficient, and exhaust gas recovery begins before an inert gas layer is formed. There was a danger of doing so. Furthermore, in the conventional exhaust gas recovery method, after inserting the sublance into the steel, exhaust gas recovery is stopped even if a large amount of flammable gas is still generated, and air is sucked in from the outside to form an inert gas layer. As a result, a large amount of recoverable combustible gas is burned. In this way, conventional exhaust gas recovery methods uniformly and continuously draw air for a certain period of time by controlling the exhaust gas flow rate when an inert gas layer is generated before and after exhaust gas recovery. Since the amount of is set to 2 to 3 times the amount that is essentially required,
A large amount of recoverable combustible gas is combusted, and the amount of exhaust gas recovered is considerably less than the amount that can be theoretically recovered.Also, depending on the carbon concentration in the hot metal, the amount of intake air may be insufficient, resulting in There was a risk that the exhaust gas would be recovered before a sufficient active gas layer was generated.

This invention was made in view of the above circumstances, and aims to generate an inert gas layer in just the right amount, improve the exhaust gas recovery rate, and eliminate the risk of explosion due to air being mixed in the recovered gas. The purpose of this invention is to provide a method for recovering exhaust gas that can be used.

In other words, this invention calculates the decarburization oxygen efficiency in advance based on data such as the composition and temperature of hot metal, and also calculates flammability based on the decarburization oxygen efficiency and operating conditions such as the amount of blown oxygen and the amount of solid oxygen. The amount of gas generated is calculated in advance, and the amount of air necessary to burn a part of the calculated flammable gas is sucked into the flue in order to generate an inert gas layer before and after collecting the exhaust gas. This is an exhaust gas recovery method that performs so-called advance control of the intake oxygen amount.

The method of the present invention will be explained in more detail below.
In addition, in a converter with a bottom tuyere, hydrocarbons are used to cool the bottom tuyere, so _H2 in the exhaust gas is
The concentration is higher than that of the exhaust gas of the LD converter, so in such cases it is necessary to consider the combustion of H ₂ when creating an inert gas layer, but normally CO gas is Since it can be considered as the main component of exhaust gas, the following explanation will be given using exhaust gas consisting only of CO gas as an example.

First, the decarburization oxygen efficiency η _c (%) is defined as η _c ≡Amount of oxygen consumed for decarburization/(Amount of blowing oxygen + Amount of solid oxygen)×100.

On the other hand, since carbon in hot metal reacts as C + O ₂ → 2CO, Q _cp = (V _p2 + S _p2 ) x η _c /100 x 2 (1). Here, Q _cp is the amount of CO gas generated in the furnace (N
m ³ /min), V _p2 is the blowing oxygen amount (Nm ³ /min), S _p2
is the amount of solid oxygen (Nm ³ /min) converted into gas. Since both V _p2 and S _p2 in equation (1) can be known from the operating conditions, Q _cp can be calculated if η _c is known. By the way, η _c is the temperature (T) of the charged hot metal, the components (especially Si, Mn, etc.), and the hot metal ratio (HR).
It is a function such as, and is expressed by equation (2).

η _c = η _c (T, Si , Mn , HR,...) ...(2) In the formula (2), Si is the Si concentration in the hot metal, and Mn is the Mn in the hot metal.
It is concentration.

Therefore, the change over time in the decarburization oxygen efficiency η _c can be easily determined by analyzing actual operation data. Figure 2 uses Si as a parameter, and Si is
Decarburization oxygen efficiency η _c at 0.15%, 0.30%, 0.50%
It is a graph showing a change over time.

By the way, the amount of intake air Q _air required to completely burn the gas generated in the furnace is 1/2 Q _cp , which is the amount of oxygen required to completely burn the amount of CO gas generated in the furnace in the amount of Q _cp above. Since the oxygen concentration in the air is 20%, Q _air = 5/2Q _cp (Nm ³ /min) ...(3), and therefore the amount of N ₂ in the exhaust gas after combustion,
The amount of CO ₂ is 2Q _cp and Q _cp (Nm ³ /min), respectively.
As a result, the exhaust gas flow rate Q _WG is Q _WG = 2Q _cp + Q _cp = 3Q _cp (Nm ³ /min), so by substituting equations (1) and (2) into this equation, we get becomes.

As mentioned above, it is possible to calculate the change over time in the decarburization oxygen efficiency η _c based on the properties such as the composition and temperature of the hot metal before the start of blowing, or the operating conditions. It is possible to calculate the amount of exhaust gas, that is, the amount of inert gas produced when gas is completely combusted. Therefore, if the exhaust gas flow rate is controlled according to equation (4), that is, the intake air amount is controlled so that the amount of inert gas is the amount necessary to replace the air in the flue, there will be no excess or deficiency of flammable gas. The required amount of inert gas layer can be generated by combustion without any waste.

Regarding the decarburization oxygen efficiency and exhaust gas flow rate mentioned above,
A specific example using the Si concentration in hot metal as a parameter is as follows. First, the change over time in the decarburization oxygen efficiency η _c from the start of blowing until 100 seconds has passed is shown in Figure 2 above, and similar changes over time were analyzed for many heats. If three points at 2 seconds, 50 seconds, and 100 seconds after the start of blowing are taken as representative points, the decarburization oxygen efficiency η ² _c , η ⁵⁰ _c , η ¹⁰⁰ _c at each time is E−(1) to (3 ) expression.

Regression formula Contribution rate η ² _c = 39.37−42.63 Si (%) ρ = 0.7215
...E-(1) η ⁵⁰ _c = 75.57-65.56 Si (%) ρ = 0.7695
...E-(2) η ¹⁰⁰ _c = 86.38-69.19 Si (%) ρ = 0.6771
……E-(3) By approximating the temporal change of η _c with a quadratic curve based on the regression equation at these three points, equation E-(4) is obtained, and η _c
can be expressed as a function of Si and time t.

At t = 0 to 100 seconds, η _c = (-5.01×10 ^-3 +3.86×10 ^-3 Si ) t ² + (0.967-0.652 Si ) t + (39.7-42.6 Si ) (%)...E -(4) Figure 3 shows the exhaust gas flow rate pattern obtained in E-(4) when Si = 0.25%. The shaded area in Figure 3 indicates the inert gas area, where the inert gas is CO<12.5%, H ₂ <4.0%, CO+H ₂ <11.0.
%, O ₂ <5.5%. Therefore, if the flow rate is controlled so that the exhaust gas flow rate falls within the shaded range in Figure 3, (CO > 12.5%, H ₂ > 4% due to insufficient intake air amount)
_Inert gas can be obtained by controlling the flow rate so that the following formula is satisfied: If the intake of air from the outside is stopped when the total amount of inert gas becomes sufficient to replace the air in the flue, the inert gas layer can be generated in just the right amount.

Next, to explain the formation of an inert gas layer at the final stage of blowing, first, the decarburization rate d _c /d _p2 is a function of the carbon concentration in the steel C at that point, the molten steel weight W _ST , the parameter α, etc. .

−d _c /d _p2 = f ( C , W _ST , α, …) ...(5) Here, α was determined by regression using the carbon concentration in steel C _SL measured by sublance measurement, the molten steel temperature T _SL, etc. as factors. It is a parameter. The value of -d _c /d _p2 over time is calculated using C _SL as the initial value of C , for example, estimate C after 2 seconds, and use this C to calculate -d _c /d _p2 . It can be obtained by repeating the process of estimating C after 2 seconds.

In addition, decarburization oxygen efficiency η' _c is expressed as a function of decarburization rate and molten steel weight, and the unit of d _c /d _p2 is (%C/
Nm ³ ) and the unit of W _ST is (ton). Since C + 1/2O ₂ →CO, η′ _c = (W _ST +10 ⁶ ×ΔC/100/12×0.0224/2/
ΔO ₂ ) × 100 (%) = 933W _ST・ΔC／ΔO ₂ (%) = −933W _ST d _c /d _p2 (%) ……(6) Therefore, the decarburization oxygen efficiency η′ _c over time changes can be calculated. Therefore, the amount of exhaust gas Q′ _WG after completely burning the combustible gas is (6)
It can be calculated using equation (7) based on the decarburization oxygen efficiency η′ _c found from the equation.

Q' _WG = 3 × (V _p2 + S _p2 ) × η' _c /100 × 2... (7) Therefore, at the final stage of blowing, decomposition is Since the carbon-oxygen efficiency η′ _c can be calculated,
Based on the calculation result, it is possible to calculate the exhaust gas flow rate, that is, the amount of inert gas generated when the gas generated in the furnace is completely combusted. Therefore, if the exhaust gas flow rate is controlled according to equation (7), that is, the amount of intake air is controlled so that the flue is filled with the amount of inert gas, the combustible gas can be burned in just the right amount and the necessary amount can be achieved. An active gas layer can be generated.

Figure 4 shows the carbon concentration C in steel measured by sublance measurements.
is 0.2%, the oxygen flow rate is 670Nm ³ /min, and the weight of molten steel is 230 tons. Changes in decarburization oxygen efficiency η′ _c over time and the flow rate of exhaust gas that becomes inert gas at the final stage of blowing.
This is a graph showing a specific example with Q′ _WG . Therefore, inert gas can be obtained by controlling the flow rate so that the exhaust gas flow rate falls within the inert gas region shown with diagonal lines in Fig. By setting the time to start air intake so that the total amount of inert gas generated up to the time of stopping is sufficient to fill the flue, it is possible to generate just the right amount of inert gas layer.

FIG. 5 is a graph showing the exhaust gas flow rate according to the recovery method of the present invention together with the amount of combustible gas generated,
At the start of blowing, the damper installed in the precipitator is opened and the exhaust gas flow rate is set to the flow rate determined by equation (4). As a result, air is drawn into the flue from the outside and the flammable gas is combusted, making it inert. gas and draw air in until the total amount of inert gas is sufficient to displace the air in the flue, i.e. to create an inert gas layer in the flue (period '). After that, the exhaust gas flow rate is controlled by restricting the damper so that air is not sucked in from the furnace mouth and flammable gas is not spewed out, and wait until the CO gas concentration and O ₂ gas concentration reach the predetermined values (' period), then exhaust gas collection will begin. After measuring with the sublance, the exhaust gas flow rate is calculated using equation (7) using the data obtained from the sublance measurement.
In order to create a sufficient amount of Q' _WG to form an inert gas layer, the damper is opened for a predetermined period (' period) before the end of blowing to suck in air and generate an inert gas layer. Therefore, exhaust gas recovery will be carried out between periods '' and '' in FIG.

However, according to the above-mentioned blowing method, the exhaust gas flow rate for burning the flammable gas generated from the converter into inert gas is calculated and known in advance, and the amount of inert gas is required. Since the flow rate is controlled to create a sufficient amount of inert gas layer,
In periods '' and '' in Figure 5, recoverable combustible gas is not burned excessively;
Therefore, the amount of recovered gas can be increased more than ever before.

Note that the above explanation deals with the case where only CO gas is generated as a combustible gas, but when hydrocarbons are injected to cool the bottom tuyeres, _H2 gas is included in the converter exhaust gas. However,
The amount can be easily calculated depending on the type of hydrocarbon used and the amount of injection. Therefore, even when hydrocarbons are injected to cool the bottom tuyere, an inert gas layer is required. By calculating the flow rate of exhaust gas to be generated, it is possible to generate an inert gas layer with just the right amount.

As is clear from the above explanation, according to the converter exhaust gas recovery method of the present invention, air is introduced from the outside in an amount corresponding to the amount of combustible gas generated when an inert gas layer is generated before and after exhaust gas recovery. Since it generates a necessary and sufficient amount of inert gas layer, the recoverable combustible gas is not burned unnecessarily, and in other words, the amount of recovered exhaust gas is reduced to the total amount of flammable gas. Since the amount of air can be increased to about 90% of the amount of flammable gas generated from the outside and the amount of air is sucked in from the outside according to the amount of flammable gas generated, an auxiliary material containing solid oxygen is added to the hot metal before the start of blowing. Even when a large amount of flammable gas is generated, such as when the collected gas is injected into the tank, a sufficient inert gas layer can be generated to reliably prevent dangers such as explosions of recovered gas. Can be done.

[Brief explanation of the drawing]

Figure 1 is a graph showing the change in exhaust gas flow rate over time due to the conventional exhaust gas recovery method along with the change in combustible gas generation amount over time, Figure 2 is a graph showing the change in decarburization oxygen efficiency over time, and Figure 3 is a graph showing the change in the amount of combustible gas generated over time. A graph showing the change in decarburization oxygen efficiency over time and the flow rate of inert exhaust gas when the concentration is 0.25%. Figure 4 shows the change in decarburization oxygen efficiency over time when the carbon concentration in steel is 0.2% by sublance measurement. FIG. 5 is a graph similar to FIG. 1 showing the change over time in the flow rate of exhaust gas according to an example of the exhaust gas recovery method of the present invention together with the change over time in the amount of combustible gas generated.

Claims (1)

[Claims] 1 Changes in decarburization oxygen efficiency over time in a converter exhaust gas recovery method in which an inert gas layer is generated in the flue by sucking air from the outside into the flue and burning the converter exhaust gas before and after recovering the converter exhaust gas. is calculated in advance based on data about hot metal, and the amount of combustible gas generated from the converter is calculated in advance based on the calculated decarburization oxygen efficiency and blowing operating conditions, and the amount of flammable gas generated from the converter is calculated before and after recovering the converter exhaust gas A converter exhaust gas recovery method comprising sucking into a flue an amount of air necessary to combust the calculated amount of combustible gas to generate the inert gas layer.