WO2016129016A1

WO2016129016A1 - Method for inhibiting foaming of molten slag, and method for manufacturing slag product

Info

Publication number: WO2016129016A1
Application number: PCT/JP2015/001874
Authority: WO
Inventors: 田中　高太郎; 孝彦前田; 渡辺　圭児; 隆司高岡; 俊朗石毛
Original assignee: Ｊｆｅスチール株式会社
Priority date: 2015-02-10
Filing date: 2015-03-31
Publication date: 2016-08-18
Also published as: KR20170103850A; CN107208169B; JP2016148061A; CN107208169A; BR112015009830B1; BR112015009830A2; TWI585061B; JP5888445B1; KR101997377B1; TW201628992A

Abstract

Provided is a method whereby it is possible to effectively alleviate foaming of molten slag removed from a converter-type refining furnace to a molten slag storage container in an intermediate slag removal step so that the intermediate slag removal step can be performed in a short time in refining of molten iron in which two oxygen feeding refining steps and an intermediate slag removal step interposed therebetween are performed continuously using a single converter-type refining furnace. During and/or after slag removal in the intermediate slag removal step, a water jet stream 8 having a momentum per unit time of 50 kg∙m/s² or greater is jetted to slag stored in the molten slag storage container and a flow is imparted to the slag so that water droplets are drawn into the foaming slag, and foaming of the slag is thereby alleviated. The water droplets drawn into and dispersed in the slag evaporate/expand and thereby break the slag foam, and vapor contained in a foamed slag bath 6 is released to the outside of the foamed slag bath 6, and foaming of the slag is thereby alleviated.

Description

Method for calming molten slag and method for producing slag product

The present invention uses a single converter-type refining furnace, and in the refining of hot metal, in which two acid feeding refining processes are continuously performed with an intermediate intermediate refining process in between. The present invention relates to a method for calming the formation of dredged molten slag. Moreover, this invention relates to the manufacturing method of the slag product which utilized the forming sedation method of the molten slag in the intermediate | middle waste process between a desiliconization process and a dephosphorization process.

In recent years, when carrying out acid refining in which a hot metal is dephosphorized or decarburized using a converter type refining furnace, the intermediate waste process is sandwiched in the middle while holding the hot metal in one converter type refining furnace. A method of carrying out acid refining continuously in two stages has been put into practical use. For example, Patent Document 1 discloses that after the dephosphorization process, the converter is tilted while leaving the hot metal in the converter, and only the slag is discharged. Thereafter, the decarburization refining is performed in the same converter, and the decarburization refining is performed. A method is disclosed in which the later slag is reused for the subsequent dephosphorization of hot metal. Patent Document 2 discloses a hot metal pretreatment (dephosphorization) method in which a single converter-type refining furnace is used to continuously perform desiliconization treatment and dephosphorization treatment of hot metal with an intermediate waste removal step in between. Is disclosed.

In these methods, the use of a CaO-based medium solvent in the subsequent treatment is performed by discharging slag in the middle compared with a refining method in which acid refining is continued without performing intermediate waste in the middle. There is an advantage that the amount can be reduced.
In addition, after performing the first-stage acid refining, not only the slag but also the molten iron is once discharged from the furnace and transferred to the same furnace or another furnace, and then the second-stage acid refining is performed. The comparison has the following advantages.
(I) The time required for hot metal tapping and recharging can be shortened to increase the operating rate of the furnace.
(II) Heat transfer loss can be reduced because there is little transfer of hot metal.
(III) The amount of CaO-based solvent used can be reduced by leaving the slag of the second-stage acid refining in the furnace and reusing it for the first-stage acid refining of the next hot metal. .
(IV) By reducing the discharge of slag from the second-stage acid refining slag, which has a high basicity, and increasing the discharge of slag from the first-stage acid refining, which has a relatively low basicity, The use of slag can be promoted by improving the hydration expansion characteristics.

In order to enjoy these advantages, an important operational point is how quickly the target amount of slag is discharged from the furnace in the intermediate discharge process. When the amount of slag discharged in the intermediate evacuation process is small, the effect of reducing the amount of CaO-based solvent used as described above cannot be expected, and the amount of CaO-based solvent used is evacuated midway. Not much different from no method. Therefore, in Patent Document 1 and Patent Document 2, in order to efficiently perform the waste disposal in the intermediate waste disposal process, the molten slag is formed in the first-stage acid refining to increase the volume of the molten slag. Thus, it is described that when intermediate waste is discharged from the furnace port, the height of the slag bath surface from the lower end of the furnace port is increased, and the discharge efficiency due to overflow of molten slag is increased. Here, slag forming is a phenomenon in which molten slag contains bubbles and apparently expands in volume.

However, the forming of molten slag is not always easy to control to the intended level, and if the forming becomes excessive, it will overflow from the hot metal container (steaming pan) placed on the bogie under the furnace. Since the situation may hinder the operation, it was necessary to limit the discharge rate of the slag while checking the freeboard of the hot metal container, leading to the extension of the work time of intermediate waste. In general, the capacity of the hot metal container is not necessarily sufficient for the volume of the formed slag, and the slag is discharged after the forming of the hot metal container is settled. Inevitably, it was a problem in carrying out efficient intermediate evacuation.

In the method disclosed in Patent Document 2, an attempt is made to suppress excessive forming during intermediate evacuation by monitoring the slag level during refining before intermediate evacuation and controlling it to an appropriate slag level. However, a sufficient effect was not necessarily obtained for suppressing forming in the hot metal container. Further, Patent Document 2 discloses that dephosphorization slag, which requires a relatively high basicity and requires aging treatment, is suppressed, and dephosphorization slag can be obtained with good volume stability even if aging treatment is omitted. Although it is also described that slag is used by converting to slag, the unit volume mass is 1.5 kg / L or more because the slag product produced from the formed slag has a smaller unit volume mass. It is not suitable for applications such as roadbed materials that require it, and the applications are limited.

On the other hand, Patent Document 1 discloses that during the intermediate waste, the pulp cake is 35% by mass to 65% by mass in dry weight, the steelmaking slag is 20% by mass to 50% by mass, and the oil content is 3% by mass to 10% by mass. In the following, a lump forming soothing material containing water of 15% by mass or less and having a specific gravity of 1.5 g / cm ³ or more and 2.5 g / cm ³ or less is introduced into the slag pan, A method is disclosed in which slag is discharged into a drain pan while calming the forming. However, in this method, there is a possibility that foreign matters derived from the forming sedative material are mixed in the slag, which is not necessarily a preferable method in terms of quality control of the slag product.

On the other hand, in Patent Document 3, after the slag after desiliconization / dephosphorization treatment of hot metal or slag after decarburization treatment is discharged to a waste pan, forming is performed by spraying mist-like water on the slag surface. A method of suppression is disclosed. In this method, it is said that the forming is subdued by the action of degassing and solidifying the surface of the slag surface, but with low basicity hot metal pretreatment slag such as desiliconized slag, due to the action by cooling from the surface, etc. It takes a long time to calm down the forming of the entire slag in the slag pan. In addition, when watering while discharging slag into the sewage pan, a sufficient sedation effect was not obtained, so it was not effective in reducing the work time for intermediate sewage.

Further, in Patent Document 4, when hot metal is received in a kneading car together with a cast floor desiliconizing agent, water having a high flow rate of 20 m / s or more is sprayed on the desiliconizing slag forming in the kneading car. Thus, a method for suppressing forming is disclosed. In the hot metal received by the kneading vehicle together with the cast iron desiliconizing agent, the iron oxide is melted by winding the iron oxide constituting the desiliconizing agent or the slag containing this iron oxide into the hot metal by the falling flow of the hot metal. The desiliconization reaction proceeds by reacting with the silicon inside. However, the hot metal temperature at this time is as high as about 1500 ° C., and this temperature is a condition in which the decarburization reaction due to the reaction between iron oxide and carbon in the hot metal proceeds predominately. CO gas is generated at a high production rate from the produced iron oxide or iron oxide-containing slag. The CO gas generated from the hot metal easily accumulates at the interface between the hot metal and the slag because of the interfacial tension, and relatively coarse bubbles are formed at the interface between the hot metal and the slag. When the CO gas bubbles pass through the slag layer, the slag is formed when the bubble generation speed is high or the rising speed is low. In the method of Patent Document 4, a slag layer is formed by tearing the slag layer with high-speed water to remove (escape) the CO gas, and the CO gas accumulated at the interface between the hot metal and the slag is removed to form the slag. It is going to suppress. At this time, the high flow rate of water reaches the hot metal surface, reacts with the hot metal and causes a small steam explosion, and the slag layer is broken by the force of the explosion.

However, slag forming, which is a problem in the hot metal storage container (slagging pan), in the intermediate smelting of acid refining using a converter-type smelting furnace, The generation mechanism including the generation form of CO gas is completely different from the forming. Therefore, the method of Patent Document 4 cannot suppress the slag forming in the hot metal container of the intermediate waste. That is, in the intermediate waste of the acid feeding refining using the converter type refining furnace, the slag already formed in the converter refining furnace is discharged into the hot metal container. At this time, since the temperature of the slag and hot metal is relatively low at about 1350 ° C., the viscosity of the slag is relatively high. In addition, in converter-type refining furnaces with large in-furnace freeboards, a large amount of microbubbles are dispersed in the slag because the acid feed rate and the stirring power density are orders of magnitude greater than those in a chaotic car. It stays in high viscosity slag. For this reason, the slag is maintained in the forming state. In the molten slag in the hot metal container, C in the molten iron dispersed and present in the slag reacts with the iron oxide component in the slag to generate CO gas. This reaction is an endothermic reaction, and as the reaction proceeds, the temperature is further lowered and the viscosity of the slag is increased. Therefore, a large amount of CO gas is not continuously generated. Compared with the CO gas produced in the hot metal received in the kneading vehicle in the method of Patent Document 4, the production rate is remarkably low. In addition, there is only a small amount of hot metal inevitably mixed in the slag in the hot metal storage container of the intermediate waste, and in addition, iron oxide or Since the iron oxide-containing slag is not continuously entrained in the hot metal bath with a large heat capacity, a large amount of CO gas is generated in the hot metal bath below the slag layer, and this accumulates at the interface between the hot metal and slag. There is no such thing. As described above, the slag forming in the hot metal container of the intermediate waste is fundamentally different from the slag forming situation assumed by the method of Patent Document 4, and therefore the method of Patent Document 4 cannot be applied. That is, a large amount of minute bubbles are dispersed and staying in the highly viscous slag, like the slag forming in the hot metal container in the intermediate waste of the acid refining using the converter type refining furnace In this case, in order to promote the destruction and detachment of the bubbles, it is not effective to partially cut the slag layer with water having a high flow rate as in the method of Patent Document 4 to partially make a gas escape passage.

JP 2008-255446 A International Publication No. 2014/115526 JP-A-8-325619 Japanese Patent Laid-Open No. 3-291321

Therefore, the object of the present invention is to solve the above-mentioned problems of the prior art, and in a converter-type refining furnace, two acid feed refining processes are performed continuously with an intermediate intermediate discharge process in between. In refining, in order to enable intermediate waste to be carried out in a short time, the formation of molten slag discharged from the converter-type refining furnace to the hot metal container in the intermediate waste process can be effectively calmed down. It is in providing the forming sedation method of molten slag. In addition, another object of the present invention is to use the forming sedation method in an intermediate evacuation process between the desiliconization process and the dephosphorization process. It is providing the manufacturing method of the slag product which can be manufactured stably.

In order to solve the above-mentioned problems, the present inventors have repeated experiments and studies on a method for calming slag forming in a hot metal container in which molten slag has been discharged in intermediate waste. As a result, the present inventors injected a water jet having a predetermined momentum into the molten slag accommodated in the hot metal storage container during or after the intermediate waste, and the water droplets were formed by giving a flow to the molten slag. By entraining in the slag, the water droplets entrained and dispersed in the molten slag evaporates and expands to break bubbles in the forming slag, resulting in effective slag forming. I found out that I was sedated.
In addition, by spraying the water jet as described above on the desiliconized slag discharged in the intermediate discharging process between the desiliconization process and the dephosphorization process, the slag forming is only calmed down. However, it was found that the slag after cooling and solidification was densified, and a high-quality slag product having a large unit volume mass was obtained.

The present invention has been made on the basis of such knowledge and has the following gist.
[1] A primary acid refining process (A) in which a single converter-type refining furnace (x) is used to oxidize and refine hot metal discharged from a blast furnace to perform a pretreatment, and the primary acid refining process (A ), The molten slag generated in the primary acid refining step (A) is left in the converter refining furnace (x) while the molten slag is left in the converter refining furnace (x) from the converter refining furnace (x). (B) an intermediate slagging process (B), and a secondary acid refining process (B) for dephosphorizing and / or decarburizing the molten iron remaining in the converter-type smelting furnace (x) ( C) and the refining of hot metal performed in this order, in the intermediate waste process (B), the method of calming the formation of molten slag in the hot metal storage container (y), the intermediate waste During and / or after evacuation in the step (B), a water jet is supplied to the molten slag contained in the hot metal container (y). A molten slag forming sedation method, wherein the molten slag forming is sedated by jetting such that the momentum of the water jet per hour is 50 kg · m / s ² or more.

[2] A primary acid refining step (a) for desiliconizing hot metal discharged from a blast furnace using one converter-type refining furnace (x), and the primary acid refining step (a) The desiliconized slag produced in the primary acid refining step (a) while the hot metal remains in the converter type refining furnace (x) is transferred from the converter type refining furnace (x) to the hot metal container (y). An intermediate waste discharging step (b) for discharging the molten iron, a secondary acid feeding refining step (c) for dephosphorizing the hot metal remaining in the converter type refining furnace (x), and the secondary acid feeding The hot metal process that has passed through the refining process (c) is performed in this order from the hot water discharge process (d) in which the hot metal is discharged from the converter-type refining furnace (x), and desiliconization that has been discharged in the intermediate exhaust process (b). A method for producing a slag product using slag as a raw material, which is accommodated in the hot metal container (y) during and / or after the waste in the intermediate waste process (b). After the slag forming is subdued by spraying the water jet on the desiliconized slag so that the momentum of the water jet per unit time is 50 kg · m / s ² or more, from the hot metal container (y) A method for producing a slag product, comprising discharging the desiliconized slag, solidifying the desiliconized slag, and processing the slag product.

[3] After the tapping step (d), without discharging the slag in the converter-type refining furnace (x), the molten iron of the next charge is charged, the primary acid refining step (a), the intermediate discharge The method for producing a slag product according to [2], wherein the dredging step (b), the secondary acid refining step (c), and the tapping step (d) are performed in this order.
[4] Slag product production according to [2] or [3], wherein the solidified desiliconized slag is pulverized and classified to obtain a slag product having a unit volume mass of 1.5 kg / L or more. Method.

According to the molten slag forming sedation method according to the present invention, in the refining of hot metal, the two acid feeding refining processes are continuously performed with the intermediate waste process interposed between them while holding the hot metal in the converter type refining furnace. Therefore, the formation of molten slag discharged from the converter-type smelting furnace into the molten iron storage container in the intermediate smelting process can be effectively subdued, so that the target amount of molten slag can be quickly discharged out of the furnace. The intermediate excretion can be completed in a short time. As a result, the operating rate of the converter-type refining furnace can be increased and the productivity can be improved, so that the ratio of the charge for the hot metal pretreatment can be increased, and the amount of CaO-based solvent used in the entire refining process Can be reduced. Or since the slag discharge | emission amount in an intermediate waste can be increased, the usage-amount of the CaO type | system | group solvent solvent in a secondary acid refining process can be reduced. Therefore, it can also contribute to reduction of energy consumption required for the production of the CaO-based medium solvent.
Moreover, according to the manufacturing method of the slag product according to the present invention, the above-described slag forming sedation method is used in an intermediate evacuation process between the desiliconization process and the dephosphorization process, so that the intermediate evacuated desiliconization is performed. A high-quality slag product having a large unit volume mass can be stably produced from the slag. For this reason, the use of the slag product by desiliconization slag can be expanded.

It is explanatory drawing which shows an example of the refinement | purification form in this invention method in process order. It is explanatory drawing which shows typically the implementation condition which injects a water jet to the slag accommodated in the hot metal storage container y in the intermediate | middle waste process of this invention method. It is the photograph which image | photographed the implementation condition which injects the water jet to the slag accommodated in the hot metal container y in the intermediate | middle waste process of this invention method from diagonally upward. In the intermediate waste removal process, the converter type refining is performed in the desiliconization process when water jets with different momentum per unit time are injected into the slag in the hot metal container y and when water jets are not injected. It is a graph which shows the relationship between the Si density | concentration of the hot metal charged into the furnace x, and intermediate waste time. 1 shows an embodiment of equipment for injecting a water jet into a slag in a hot metal container y in the intermediate waste process of the present invention and its usage, and a converter type refining furnace for waste It is a front view shown in the state where x was tilted. FIG. 6 is a plan view showing the converter type refining furnace x tilted for waste in the embodiment of FIG. 5. It is explanatory drawing which shows the converter type refining furnace x used by this invention method.

Hereinafter, an example of the forming and calming method for molten slag according to the present invention will be described.
The molten slag forming and calming method uses a single converter type refining furnace x, a primary acid refining process (A) in which the hot metal discharged from the blast furnace is subjected to oxidation refining and pretreated, and this primary acid refining process. Molten slag generated in the primary acid refining step (A) is discharged from the converter type refining furnace x to the hot metal containing container y while the hot metal after the refining step (A) remains in the converter type refining furnace x. In the refining of hot metal, the intermediate waste process (B) and the secondary acid refining process (C) of dephosphorizing and / or decarburizing the hot metal remaining in the converter-type refining furnace x are performed in this order. In addition, during and / or after evacuation in the intermediate evacuation step (B), a water jet is applied to the molten slag contained in the hot metal container y, and the momentum of the water jet per unit time is 50 kg · m. / S2 Forming of slag is calmed down by spraying to become ² or more Is.

The hot metal refining process which is the premise of the present invention can take various forms, for example, the following forms.
(I) Form in which primary acid refining step (A) is desiliconization treatment and secondary acid refining step (C) is dephosphorization treatment (ii) primary acid refining step (A) is desiliconization treatment, secondary Form in which the acid feeding refining process (C) is dephosphorization / decarburization treatment (iii) The primary acid sending refining process (A) is desiliconization / dephosphorization treatment, and the secondary acid sending refining process (C) is decarburization treatment Form (iv) Form in which the primary acid refining process (A) is a dephosphorization process and the secondary acid refining process (C) is a decarburization process. Of these, the object of the present invention is mainly (i ) And (iii).
FIG. 1 shows the refining forms of (i) above in the order of processes, where the desiliconization treatment (desiliconization blowing) is the primary acid refining step (A), and the dephosphorization treatment (dephosphorus P blowing) is the secondary. This corresponds to the acid refining step (C).

In FIG. 1, a cold iron source 3 such as iron scrap is first charged in a converter-type refining furnace x, and then hot metal 1 is charged from a charging pot 4 that has transported the blast furnace hot metal, and then primary. A desiliconization process (deSi blowing) is performed as the acid refining step (A). This desiliconization process is performed by supplying an oxygen source into the furnace and, if necessary, supplying a combustion heat source such as a CaO-based solvent or a silicon source. In this desiliconization treatment, in order to enhance the slag evacuation performance in the intermediate evacuation in the next process, the execution conditions are controlled so that the slag is appropriately formed. Details of the conditions for carrying out this silicon removal treatment will be described later. After the desiliconization process is completed, at least a part of the slag 2 (desiliconization slag) generated by the desiliconization process is discharged into the hot metal container y (removal pan) as an intermediate waste removal process (B). . The amount of slag discharged at the time of intermediate waste is half the amount of slag 2 in the converter type refining furnace x in order to effectively reduce the amount of CaO-based solvent used in the next acid refining process (C). It is desirable to set it to about or more. Therefore, in order to efficiently discharge slag without discharging hot metal from the furnace port, intermediate slag is performed with the surface level of the slag layer increased by forming the slag, but details such as the implementation conditions Will be described later. Subsequently, a dephosphorization process (de-P blowing) is performed as a secondary acid refining process (C). This dephosphorization process is performed by supplying a CaO-based medium solvent and an oxygen source, and details such as implementation conditions will be described later. After this dephosphorization treatment, the hot metal 1 is discharged and sent to the next step (decarburization treatment). In this case, the slag 9 (dephosphorization slag) generated by the dephosphorization process may be left as it is and used for the desiliconization process of the next charge.

In the method of the present invention, using one converter-type refining furnace x as described above, two acid feeding refining steps (A) and (C) are sandwiched between them and an intermediate waste discharging step (B) is sandwiched between them. In the hot metal refining performed continuously, a predetermined amount is applied to the molten slag (foamed slag bath) accommodated in the hot metal storage container y during and / or after the intermediate waste process (B). A jet of momentum is injected, and the molten slag is flowed so that water droplets are entrained in the formed slag, thereby reducing the slag forming.
FIG. 2 schematically shows the state of implementation. Reference numeral 5 denotes a slag flow discharged from the converter-type refining furnace x to the hot metal container y, and reference numeral 6 denotes the hot metal container y. A slag bath in a forming state, numeral 7 is a water jet nozzle, and numeral 8 is a water jet formed by jetting water from the water jet nozzle. As shown in FIG. 2, a water jet 8 is injected from the water injection nozzle 7 disposed above the hot metal container y into the slag (forming slag bath 6) in the hot metal container y. Two (two) or more of these water jets 8 may be jetted from a plurality of water jet nozzles 7 or from different jet ports of the single water jet nozzle 7.

In the method of the present invention, the mechanism by which molten slag forming is subsided will be described. When a water jet 8 having a sufficient momentum is injected into the formed slag (forming slag bath 6) in the hot metal container y, The water droplets of the water jet 8 are entrained in the formed slag due to the flow, and the fine water droplets are dispersed in the slag. The water droplets dispersed in the slag evaporate and expand to break up a large amount of microbubbles present in the slag in the forming state, and the gas contained in the slag bath 6 in the forming state (mainly CO gas) ) Is released to the outside of the slag bath 6 in the forming state, and it is considered that the slag forming is calmed down.

FIG. 3 is a photograph of the situation in which a water jet is jetted from the jet nozzle onto the slag in the hot metal container (steaming pan) after drainage, taken obliquely from above, and the water jet flows along the arrow, You can see how water is caught in the forming slag bath. At the location where the water jet collides with the slag bath surface, slag flow is induced and the surface is renewed, so a hot hot spot is formed, and the surface temperature of the surrounding slag bath surface decreases due to radiation cooling. This is a very different aspect. At the high temperature part (hot spot) on the surface of this slag bath, water in the water jet is entrained in the slag and dispersed as fine droplets, then evaporates and expands, generating a large amount of water vapor in the slag bath It is considered that the flow in the slag bath is further accelerated by the buoyancy generated thereby. Here, since the liquid water entrained in the molten slag has a lower interfacial tension with the molten slag than the interfacial tension with the gas, it easily enters the liquid film between the bubbles in the molten slag. It is considered that the bubble breakage proceeds effectively by evaporating and expanding in the liquid film between the bubbles.

In the method of the present invention, the momentum per unit time of the water jet 8 injected to the molten slag in the hot metal container y is set to 50 kg · m / s ² or more. Here, in the case where there are a plurality of water jets 8, the momentum per unit time is the total amount, but there is one place when there are a plurality of high temperature portions (hot spots) on the surface of the slag bath where the water jet collides. The total amount per unit. In general, the amount of exercise is a vector amount, and the total amount means the absolute value of the amount of exercise added in vector.
In the present invention, a sufficient amount of momentum of the water jet 8 is injected into the molten slag in the forming state so that the slag is flowed so that the water droplets are entrained in the slag, and the water droplets dispersed in the slag in the forming state evaporate and Although it expands the minute bubbles existing in the formed slag by expanding, if the momentum per unit time of the water jet 8 is small, the molten slag is more cooled and more sufficient for the slag. Since it cannot give a flow, it becomes difficult to properly entrain water droplets in the slag, and the forming suppression effect of the molten slag cannot be sufficiently obtained. Further, since the flow becomes difficult to be transmitted to the slag bath as the injection direction of the water jet 8 approaches the horizontal direction, the vertical component of the momentum per unit time of the water jet 8 is set to 40 kg · m / s ² or more. More preferably, the jet 8 is jetted.

The upper limit of the momentum per unit time of the water jet 8 is not particularly limited. However, since the amount of molten slag scattered tends to increase as the momentum increases, the upper limit is preferably about 200 kg · m / s ² . The water jet 8 is injected during and / or after the discharge, but if the volume of the slag in the forming state discharged by the intermediate discharge is larger than the capacity of the hot metal container y, the water jet 8 is discharged. It is preferable to reduce the working time of intermediate waste by injecting it into the soot to calm down the slag forming. At this time, the water jet 8 is injected from the converter-type refining furnace x without overflowing the slag from the hot metal container y while referring to the surface level of the slag bath in the hot metal container y during the intermediate waste. What is necessary is just to implement suitably so that it can discharge efficiently. When the capacity of the hot metal storage container y is sufficiently large, the water jet 8 may be injected after the discharge to make the slag dense.

There is no particular restriction on the position (place) of the slag surface that injects the water jet 8, but at the time of evacuation as shown in FIG. It is preferable to inject so that it may hit. In the case of evacuation, a solidified layer develops on the surface of the slag bath for a long time after the end of evacuation, so that the water jet 8 is less likely to be caught in the slag bath. It is desirable to start the water jet 8 in as short a time as possible.
The position of the slag surface for injecting the water jet 8 is usually sufficient to calm the forming if there is only one central portion of the slag surface in the hot metal container y, but the hot metal container y is large and the slag bath When the ratio of the area of the hot spot occupying the surface is small, the position of the slag surface for injecting the water jet is moved so as to move the hot spot, or the injection positions are provided so as to provide a plurality of hot spots. Thus, the forming can be calmed down in a shorter time, which is effective.

Moreover, although the one where the flow volume of the water jet 8 is large can calm down forming in a short time, there exists a tendency for the scattering amount of a molten slag droplet to increase. Therefore, the flow rate of water may be adjusted so as to increase the flow rate so as to allow the working time, and the flow rate of water may be decreased so as to allow the slag scattering, which is about 100 to 300 L / min. It is desirable to adjust the flow rate of water within the range. The jetting time of the water jet 8 may be adjusted so as to be appropriately shortened within a range in which the sedation effect is sufficiently obtained by visually confirming the sedation state of forming after jetting. However, if the flow rate of water is increased in order to calm down the forming in a short time, there is a problem that slag scattering increases. Therefore, it is desirable to adjust the injection time in the range of about 3 to 15 minutes.
Since the momentum is generally preserved, it is not necessary to consider that the flow velocity of the water jet 8 is attenuated before reaching the slag surface from the water jet nozzle 7, and the momentum per unit time of the water jet 8 is not necessary. In calculating (kg · m / s ² ), the flow velocity (m / s) at the outlet of the water injection nozzle may be multiplied by the mass flow rate (kg / s). However, since the attenuation due to air entrainment cannot be ignored when the nozzle inner diameter becomes smaller, the inner diameter of the nozzle (equivalent diameter calculated by dividing the cross-sectional area by four times the circumference if the section is not circular) is It is desirable that it is 5 mm or more.

FIG. 4 shows a case where water jets 8 having different momentum per unit time are injected into intermediate waste with respect to the slag 2 (molten slag) in the hot metal container y in the equipment shown in FIGS. In the case where the water jet was not injected, the silicon concentration of the hot metal charged in the converter type refining furnace x and the time required from the start of discharge to the end of discharge during intermediate discharge in the desiliconization process ( This shows the relationship with the intermediate elimination time. The jet of the water jet 8 starts when the surface level of the slag bath in the hot metal container y becomes about half of the height in the hot metal container y, and includes the slag including when the exhaust gas is suspended. The bath was continuously carried out so that the surface level of the bath was at a level appropriate for receiving the discharged slag. Regardless of whether water jet is injected or not, if the surface level of the slag bath in the hot metal container y rises and there is concern about slag overflow, adjust the tilt angle of the converter-type refining furnace x to adjust the slag. Decrease the discharge speed or stop the discharge. For this reason, in the conventional intermediate waste which does not inject a water jet, the frequency which requires a long time to discharge | emit the target slag mass was high.
According to FIG. 4, by charging the water jet 8, the particularly long charge of the intermediate evacuation time is greatly reduced. In particular, the momentum per unit time of the water jet 8 is 78 kg · m / s ² . In this case, since the charge with a longer intermediate evacuation time is reduced compared to the case of 26 kg · m / s ² , it turns out that it is effective by suppressing slag forming, and the water jet is not injected. Compared to the average value, it is possible to shorten the intermediate elimination time by about 3 minutes.

FIGS. 5 and 6 show an embodiment of equipment for injecting a water jet to the slag in the hot metal container y (a waste pan) in the intermediate waste, and the use state thereof. FIG. A front view showing a state in which the converter type refining furnace x (converter) is tilted for dredging, FIG. 6 is also a plan view.
A water injection nozzle 7 is installed on the side of the converter-type refining furnace x (converter) and above the hot metal container y (slagging pan) stopped at the rejecting position. During and / or after the discharge of the process, a water jet 8 having a predetermined momentum is jetted from the water jet nozzle 7 to the molten slag in the hot metal container y, and the molten slag is flowed to form water droplets. In the slag.
Water is supplied to the water injection nozzle 7 from a water supply pipe 11, and the water supply mechanism including the water supply pipe 11 is protected by the heat shield wall 10 from heat at the time of discharge. In addition, as shown by the broken lines in FIGS. 5 and 6, the water injection nozzle 7 is desirably provided with a mechanism capable of adjusting the injection direction in the horizontal direction and the vertical direction so that the arrival position of the water jet can be adjusted. . Thereby, it is possible to follow the position of the hot metal container y adjusted in accordance with the tilt angle of the converter-type refining furnace x, and it is also possible to adjust the arrival position of the water jet 8 on the slag surface in the hot metal container y.

According to the present invention, in other refining forms, it is possible to calm down the slag forming in the molten iron storage container y at the time of intermediate waste, thereby reducing the time required for intermediate waste. Productivity can be improved. For example, in the refining forms (i) to (iv) mentioned above, the primary acid refining process (A) is desiliconization, and the secondary acid refining process (C) is dephosphorization / decarburization. The refining form (ii) is carried out when the silicon content of the hot metal is particularly high, when a large amount of scrap is melted by adding silicon as a combustion heat source, or when the desulfurization reaction proceeds simultaneously with the desiliconization process. However, it is necessary to reduce the amount of residual slag, especially after intermediate waste, from the viewpoints of slag composition control in dephosphorization / decarburization treatment and prevention of slag from slag. For this reason, usually, a method of discharging almost all of the in-furnace slag after pouring hot metal once is often used.

The refining form of (iii), in which the primary acid refining process (A) is desiliconization / dephosphorization, and the secondary acid refining process (C) is decarburization, is the same as the refining form of (i). Although often used, in the primary acid refining step (A), since dephosphorization is performed, the basicity of the slag is adjusted to be higher than in the refining form of (i). However, it is the same as the refined form (i) in that the slag is formed so that it can be easily discharged by intermediate waste, and the basicity of the slag is 1.2, which is relatively low as the dephosphorization treatment of hot metal. While adjusting to a range of about ~ 1.8, the iron oxide concentration in the slag is increased to promote slag forming. Therefore, at the time of intermediate evacuation, as in the case of the refinement form (i), there is a problem that the intermediate evacuation time is likely to be extended, and it is effective to apply the molten slag forming sedation method according to the present invention. is there.
The refining mode (iv) in which the primary acid refining process (A) is dephosphorization and the secondary acid refining process (C) is decarburization is intended for hot metal previously desiliconized. However, in order to efficiently perform the intermediate waste, it is necessary to add a large amount of silicon oxide source in the dephosphorization process. For this reason, usually, a method of discharging almost all of the in-furnace slag after pouring hot metal once is often used.

Next, the manufacturing method of the slag product which concerns on this invention is demonstrated.
This slag product manufacturing method uses a single converter-type refining furnace x, a primary acid refining process (a) in which the molten iron discharged from the blast furnace is desiliconized, and this primary acid refining process (a). The intermediate waste that discharges the desiliconized slag generated in the primary acid feed refining step (a) from the converter type refining furnace x to the hot metal container y while the hot metal having passed through the furnace remains in the converter type refining furnace x Step (b), secondary acid refining step (c) for dephosphorizing the hot metal remaining in the converter type refining furnace x, and the hot metal after the secondary acid refining step (c) A method for producing a slag product in which the hot water discharge step (d) discharged from the mold refining furnace x is performed in this order, and the desiliconized slag discharged in the intermediate waste discharge step (b) is solidified and then processed into a slag product. The water jet is applied to the desiliconized slag contained in the hot metal container y during and / or after the waste in the intermediate waste process (b). , Slag forming is subdued by jetting so that the momentum of the water jet per unit time is 50 kg · m / s ² or more, and then desiliconized slag is discharged from the hot metal container y and solidified. It is.

FIG. 1 also shows an example of a refining mode (in order of steps) in the method for producing a slag product according to the present invention, in which the desiliconization treatment (deSi blowing) is the primary acid refining step (a), and the dephosphorization treatment The form in which (de-P blowing) is the secondary acid refining step (c) corresponds to the above example. The contents of each step shown in FIG. 1 are as described above. Details of the conditions for performing each step will be described later.
In the method of the present invention, using one converter-type refining furnace x as described above, an acid-feeding refining step (a) for performing desiliconization treatment and an acid-feeding refining step (c) for carrying out dephosphorization treatment are performed in the middle. In the refining of hot metal performed continuously with the hot metal step (b) in between, desiliconized slag (forming state) accommodated in the hot metal container y during and / or after the hot metal removal in the intermediate waste step (b) After spraying a water jet with a predetermined momentum on the slag bath) and applying flow to the desiliconized slag, water droplets are entrained in the formed slag, and the slag foaming is subdued. The desiliconized slag is discharged from the storage container y and solidified. Then, this desiliconized slag is processed (usually pulverized and classified) to obtain a slag product.

Regarding the injection of water jet to this desiliconized slag, the implementation status, the effect of shortening the fluent time by water jet injection, the equipment used for water jet injection, etc. are based on FIG. As explained.
In the method of the present invention, the slag forming is calmed by spraying the water jet as described above to the desiliconized slag discharged in the intermediate waste process between the desiliconization process and the dephosphorization process. In addition, the slag after cooling and solidification becomes dense, and a high-quality slag product with a large unit volume mass is obtained.

In the present invention method, in order to increase the unit volume mass of the slag product by densifying the slag after cooling and solidification, a water jet is applied to the desiliconized slag in the hot metal container y in the intermediate waste disposal step (b). In the injection, water jet is injected so that the bulk specific gravity of the desiliconized slag is 0.7 kg / L or more to calm down the forming of the slag, and then the desiliconized slag in the hot metal container y is slag yarded. It is preferable that the product is discharged and allowed to cool and solidify. As the solidification progresses, the air bubbles are further defoamed and the pores in the slag are reduced, but the forming is subdued so that the bulk specific gravity is 0.7 kg / L or more in the hot metal storage container y, and then discharged into the slag yard. Thereby, the unit volume mass of a slag product can be stably made into 1.5 kg / L or more.
From the same viewpoint as described above, it is preferable that the total amount of water jet of the water jet injected into the desiliconized slag is 30 to 150 L / desiliconized slag-t (tons). If the amount of jet water is small, defoaming may be insufficient and the unit volume mass of the slag product may be small. Further, even if the amount of jet water is increased, the effect is saturated, and when the amount of jet water is further increased, solidification partially progresses during jetting, and conversely, the porosity in the solidified slag may increase.

The desiliconized slag cooled and solidified after being discharged in the intermediate waste process (b) is usually pulverized and classified into a slag product. As described above, the desiliconized slag after cooling and solidification is used in the method of the present invention. Since the slag is densified, a slag product satisfying a unit volume mass of 1.5 kg / L or more required for upper layer roadbed materials can be easily obtained. Slag products obtained without jetting water jets are porous (and therefore have low strength), and because of their small unit volume mass, products of upper-layer roadbed materials as defined in Japanese Industrial Standards JIS A 5015: 2013 Does not meet standards. In addition, since the slag particles are porous and low in strength, there is a possibility that other characteristics such as supporting force may be adversely affected, and such desiliconized slag is not suitable for roadbed materials. On the other hand, the slag product obtained by jetting a water jet according to the method of the present invention is densified and has a large unit volume mass and satisfies the above product standards.

Since dephosphorization slag generally has a higher basicity than desiliconization slag, its use in civil engineering materials is often restricted due to characteristics such as hydration expansion. Therefore, in order to reduce the amount of dephosphorization slag as much as possible and convert dephosphorization slag to desiliconization slag with less application restrictions, the pre-charge dephosphorization process was completed and the hot metal in the furnace was discharged. After that, it is preferable not to discharge the dephosphorization slag in the furnace, but to charge new hot metal while leaving the pre-charge dephosphorization slag in the furnace and repeat the refining process of the present invention. That is, the slag in the converter-type smelting furnace x is discharged after the hot water discharge process (d) in which the hot metal that has undergone the secondary acid refining process (c) for dephosphorizing the hot metal is discharged from the converter-type smelting furnace x. Instead, the first charge acid refining step (a), the intermediate discharge step (b), the second acid refining step (c) and the tapping step (d) are performed in this order by charging the molten iron of the next charge. To do. In this method, the amount of CaO-based solvent used during the desiliconization process can be reduced.

Further, among the slag products obtained in the present invention, in particular, (mass% CaO) / (mass% SiO ₂ ) is set to 0.8 to 1.5, and “after the hot water step (d), the converter type refining The slag product obtained by the method of repeating the refining process of the present invention by charging the molten iron of the next charge without discharging the slag in the furnace x is not only dense and large in unit volume mass but also low in volume. It has the characteristic that it is alkali and has a small amount of expansion, and can be said to be particularly suitable for roadbed material applications.

Next, the details of the configuration of the converter type refining furnace x used in the present invention and the implementation conditions (execution conditions other than those already described) of the desiliconization treatment, intermediate waste removal, and dephosphorization treatment performed in the present invention will be described. .
FIG. 7 shows an example (schematic cross section) of the converter type refining furnace x used in the present invention. This converter-type refining furnace x is a converter capable of blowing an upper bottom, and includes an up-and-down raising and lowering acid lance 12 (upper blowing lance), and a bottom blowing for gas bottom blowing at the bottom of the furnace body. A nozzle 13 (bottom blowing tuyere) is provided, and a hot water outlet 14 is provided on the side of the furnace body upper side.
From the acid delivery lance 12, oxygen gas (industrial pure oxygen gas) or oxygen-containing gas (oxygen-enriched air, air, mixed gas of oxygen gas and inert gas, etc.) is supplied to the hot metal as a gaseous oxygen source. . From the bottom blowing nozzle 13, a bottom blowing gas for stirring (inert gas such as argon gas and nitrogen gas, gas containing oxygen, etc.) is blown into the hot metal in the furnace. Further, a medium solvent or the like may be blown using the bottom blowing gas as a carrier gas.

In the present invention, the desiliconization treatment performed as the primary acid refining step (A) or the primary acid refining step (a) is performed by supplying a gaseous oxygen source as an oxygen source to the hot metal in the converter type refining furnace x, Further, a solid oxygen source such as iron oxide is supplied as necessary. Silicon contained in the hot metal reacts with oxygen in the oxygen source (Si + 2O → SiO ₂ ), and desiliconization proceeds. The hot metal temperature rises due to the oxidation heat of silicon by this desiliconization reaction, and the melting of the cold iron source in the hot metal is promoted.
The gaseous oxygen source is supplied through the acid lance 12 and, if necessary, a solid oxygen source such as iron oxide and a medium solvent for adjusting the basicity of the generated slag (CaO-based solvent, MgO-based solvent) Etc.) and a combustion heat source such as a silicon source. Further, by blowing the stirring gas from the bottom blowing nozzle 13 into the hot metal, the hot metal stirring is strengthened and the melting of the cold iron source is promoted.
As a method for supplying solids such as a solid oxygen source and a medium solvent, granular and lump-shaped ones are usually charged from a hopper on the furnace, and powdery ones are fed through an acid feed lance 12 and a bottom blowing nozzle 13.

In addition, in order to improve the slag dischargeability in the intermediate slagging process, the slag is formed in the converter-type refining furnace x. For this purpose, the iron oxide in the slag and the slag are entrained as droplets. It is necessary to increase the generation rate of CO gas generated by the reaction with carbon contained in the molten iron. For this reason, it is effective to increase the iron oxide concentration in the slag, and forming can be promoted by methods such as increasing the acid feed rate, adding a solid oxygen source, increasing the lance height, and reducing the bottom blowing gas flow rate. It is. On the other hand, if slag forming becomes excessive during refining, there may be a problem that the slag overflows from the furnace port and the refining is interrupted, resulting in an increase in processing time. Therefore, it is desirable to control the above operating factors within an appropriate range with reference to the results of the surface level of the slag layer in the forming state.

In the intermediate waste process (B) or the intermediate waste process (b), the converter-type refining furnace x is tilted to the side opposite to the side where the outlet 14 is provided, and the slag in the furnace is caused to flow out of the furnace mouth. Then, the molten metal is discharged into a hot metal container y (a waste pan) waiting in the downward direction. This intermediate evacuation is performed with the slag formed, but usually a part of the slag remains in the furnace.
In the present invention, in this intermediate evacuation step, the water jet is jetted onto the slag in the hot metal container y as described above.

In the present invention, the dephosphorization treatment performed as the secondary acid refining process (C) or as the secondary acid refining process (c) is performed on the hot metal left in the converter refining furnace x after the intermediate waste process. It is performed by supplying a CaO-based medium solvent and an oxygen source. The oxygen source supplied by the dephosphorization treatment is mainly composed of a gaseous oxygen source from the acid delivery lance 12 as in the desiliconization treatment, but a solid oxygen source such as iron oxide may be used in combination. .
As a method for supplying solids such as a solid oxygen source and a medium solvent, granular and lump-shaped ones are usually charged from a hopper on the furnace, and powdery ones are fed through an acid feed lance 12 and a bottom blowing nozzle 13.

Phosphorus in the hot metal is oxidized to oxygen in the supplied oxygen source to become phosphor oxide (P ₂ O ₅ ), and this phosphor oxide is produced by the incubation of the CaO-based solvent and functions as a dephosphorizing refining agent. It is taken in as a stable compound of 3CaO · P ₂ O ₅ and the hot metal dephosphorization reaction proceeds. After the dephosphorization treatment, dephosphorization slag containing a phosphorus oxide is generated.
After the dephosphorization process is completed, the converter type refining furnace x is tilted to the side where the tap hole 14 is installed, and the hot metal in the converter type refining furnace x is discharged from the tap port 14 (hot water process). After the hot water discharge process, the dephosphorization slag in the furnace may not be discharged, and hot metal may be charged into the converter-type refining furnace x to start the next charge desiliconization process.

In a converter-type refining furnace having a hot metal capacity of 330 t as shown in FIG. 7, the desiliconization treatment (desiliconization blowing) and dephosphorization treatment (dephosphorization P blowing) of hot metal discharged from the blast furnace are sandwiched between the intermediate waste removal processes. In the intermediate evacuation process, a water jet is injected into the desiliconized slag contained in the hot metal container to calm down the formation of the desiliconized slag. (Comparative Examples 1 to 4 and Invention Examples 1 to 4). In the intermediate waste removal process, the equipment as shown in FIGS. 5 and 6 is used, and after the surface of the slag bath in the hot metal storage container reaches a predetermined level during waste discharge, it is stored in the hot metal storage container. Water jet injection was started against desiliconized slag (forming slag bath). During the intermediate slag, water jet injection is continued, and if the slag bath surface level in the hot metal container rises and slag overflow is a concern, adjust the tilt angle of the converter smelting furnace. Water jet was continued by reducing the slag discharge speed or interrupting the slag. When the surface of the slag bath in the hot metal storage container is higher than a predetermined level corresponding to a bulk specific gravity of 0.7 kg / L after the end of the slag, water is used so that the surface of the slag bath is below a predetermined level. The jet of water jet was continued within a jet time of about 10 minutes or less.

In the converter-type refining furnace, a cold iron source (iron scrap) was charged in advance, and blast furnace hot metal was charged from the charging pot into the furnace, followed by desiliconization treatment. In this desiliconization treatment, oxygen gas was supplied from the acid feed lance and stirring gas was blown into the hot metal from the bottom blowing nozzle. Moreover, a solid oxygen source (iron oxide), a medium solvent (CaO-based medium solvent, etc.), and a silicon source (ferrosilicon) were charged as necessary. In this desiliconization treatment, the basicity of the slag is adjusted in the range of 0.8 to 1.3, and the acid feed rate and lance height are adjusted in order to improve the slag evacuation performance in the intermediate evacuation process. As a result, the slag was formed under operating conditions such that the iron oxide content in the slag after desiliconization was 10 to 30% by mass.

In the intermediate slagging process, the converter-type smelting furnace was tilted to the side opposite to the side provided with the tapping port, the slag in the furnace was allowed to flow out of the furnace port, and discharged to the hot metal storage container waiting below. Under the present circumstances, the water jet was injected with respect to the slag (forming slag bath) in a hot metal storage container on the conditions shown in Table 1. This water jet is jetted so as to be jetted toward the center of the slag bath surface in the hot metal container using one or two jet nozzles provided at the tip of one water supply pipe. The direction was adjusted. In the case of using two injection nozzles, the center position of the water jet was about 0.7 m away at the surface level of the slag bath, but the hot spot on the surface of the slag bath became one place so as to merge. . After the forming of the slag in the hot metal container was subdued, the hot metal container was transported to the slag yard, and the desiliconized slag was discharged from the hot metal container to the slag yard and allowed to cool and solidify. The solidified desiliconized slag was roughly crushed with a heavy machine, further cooled, and then pulverized and classified to obtain a slag product for an upper roadbed material that passed through all sieves having an aperture of 26.5 mm.

In each operation (Invention Examples 1 to 4 and Comparative Examples 1 to 4), a hot metal pretreatment of about 50 charges was performed. Table 1 shows the intermediate evacuation time in the intermediate evacuation process and the average value of the unit volume mass of the obtained slag product together with the injection conditions of the water jet in the intermediate evacuation process.

In any operation, the Si concentration in the hot metal before desiliconization was stable in the range of 0.25 to 0.45 mass%, and the average discharge of slag at the intermediate waste was about 10 t / charge. It was. According to Table 1, in the example of the present invention, intermediate waste was completed in a short time, and a high-quality slag product having a large unit volume mass was obtained from the desiliconized slag that was intermediately discharged.

x Converter type refining furnace y Hot metal container 1 Hot metal 2 Slag (desiliconized slag)
3 Cold Iron Source 4 Charging Pan 5 Slag Flow 6 Forming Slag Bath 7 Water Injection Nozzle 8 Water Jet 9 Slag (Dephosphorization Slag)
DESCRIPTION OF SYMBOLS 10 Heat insulation wall 11 Water supply pipe 12 Acid feed lance 13 Bottom blowing nozzle 14 Hot water outlet

Claims

A primary acid refining step (A) in which a single converter-type refining furnace (x) is used for pretreatment by oxidizing and refining the hot metal discharged from the blast furnace, and the primary acid refining step (A) The molten slag generated in the primary acid refining step (A) with the hot metal remaining in the converter type refining furnace (x) is transferred from the converter type refining furnace (x) to the hot metal storage container (y). An intermediate slagging step (B) for evacuating to the furnace, and a secondary acid feeding smelting step (C) for dephosphorizing and / or decarburizing the hot metal remaining in the converter type smelting furnace (x) Among the refining of hot metal that is performed in this order, in the intermediate waste process (B), the method of calming the forming of molten slag in the hot metal container (y),
During and / or after evacuation in the intermediate evacuation step (B), a water jet is applied to the molten slag contained in the hot metal container (y), and the momentum of the water jet per unit time is 50 kg. A molten slag forming sedation method, wherein the molten slag forming is sedated by spraying so as to be m / s 2 or more.
A primary acid refining step (a) for desiliconizing hot metal discharged from a blast furnace using one converter-type refining furnace (x), and the hot metal that has undergone the primary acid refining step (a) The desiliconized slag generated in the primary acid refining step (a) while remaining in the converter type refining furnace (x) is discharged from the converter type refining furnace (x) to the hot metal container (y). Intermediate refining process (b), a secondary acid refining process (c) for dephosphorizing the hot metal remaining in the converter type refining furnace (x), and a secondary acid refining process ( c), the hot metal step (d) for discharging the hot metal from the converter type refining furnace (x) is performed in this order, and the desiliconized slag discharged in the intermediate waste step (b) is used as a raw material. A method for producing a slag product,
During and / or after evacuation in the intermediate evacuation step (b), a water jet is applied to the desiliconized slag contained in the hot metal container (y), and the momentum of the water jet per unit time is 50 kg. -After calming down slag forming by spraying to m / s 2 or more, desiliconized slag is discharged from the hot metal container (y),
A method for producing a slag product, wherein the desiliconized slag is solidified and processed into the slag product.
After the tapping step (d), without discharging the slag in the converter type refining furnace (x), the hot metal of the next charge is charged, and the primary acid feeding refining step (a), intermediate waste step ( The method for producing a slag product according to claim 2, wherein b), secondary acid refining step (c) and tapping step (d) are performed in this order.
The method for producing a slag product according to claim 2 or 3, wherein the solidified desiliconized slag is pulverized and classified to obtain a slag product having a unit volume mass of 1.5 kg / L or more.