JPWO2011007618A1 - Fluidized bed boiler combustion method and fluidized bed boiler - Google Patents

Abstract

In the combustion method of the CFB boiler 1 using biomass fuel, ferronickel slag is added to the biomass fuel and burned in a fluidized bed boiler. Since ferronickel slag contains magnesium oxide, generation of alkali silicate can be suppressed. Therefore, the possibility of occurrence of poor flow due to the generation of the low melting point compound is reduced, and the CFB boiler can be operated at a high temperature. As a result, it becomes easy to improve the energy recovery efficiency.

Description

  The present invention relates to a fluidized bed boiler combustion method using a fuel containing an alkali component as boiler fuel, and a fluidized bed boiler.

  Application of biomass fuel to fluidized bed boilers (also referred to as “CFB boilers”) is required. Among biomass fuels, low-grade biomass fuels such as fir shells and EFB (Empty Fruit Bunches) contain a large amount of alkali components, and these alkali components generate low melting point compounds. Since the low melting point compound may adhere to the fluidized material (also referred to as “bed material”) and cause poor flow, the furnace temperature should be set to a level that does not produce a low melting point compound, specifically 750 ° C. or less. Control such as holding is necessary (see Patent Document 1).

On the other hand, when magnesium oxide (MgO) is added to the fluidized material of a fluidized bed boiler, the production of low melting point compounds can be suppressed. However, it is not common to add magnesium oxide directly into the fluidized material, and thus magnesium carbonate (MgCO ₃ ) and magnesium hydroxide (Mg (OH) ₂ ) are usually supplied.

JP 2005-226930 A

  However, in the method described in Patent Document 1, it is necessary to keep the furnace temperature low in order to avoid poor flow, and the operating temperature of the boiler has to be lowered, which makes it difficult to improve the energy recovery efficiency. In addition, in the method of adding magnesium carbonate or magnesium hydroxide to the fluidized material, there is a concern that an endothermic reaction occurs when the magnesium oxide is decomposed into magnesium oxide, or water is generated, thereby reducing the energy recovery efficiency.

  An object of the present invention is to solve the above problems, and even when using an alkali component-containing fuel, a combustion method of a fluidized bed boiler capable of achieving both improvement in energy recovery efficiency and prevention of flow failure, and An object is to provide a fluidized bed boiler.

  Smelting slag produced by ore smelting, for example, ferronickel slag, has only been used as a roadbed material, and is usually discarded. The inventor paid attention to ferronickel slag, which is a kind of smelting slag, and contained about 30% (weight percent concentration) of magnesium oxide. The knowledge that the flow failure can be effectively prevented when added to the boiler is obtained and the present invention has been conceived.

  That is, the present invention is characterized in that in a fluidized bed boiler combustion method using an alkali component-containing fuel, smelting slag produced by ore smelting is added to the fuel and burned in the fluidized bed boiler.

  When an alkali component-containing fuel such as a biomass fuel is used as the fluidized bed boiler fuel, it is between the alkali component such as potassium (K) and sodium (Na) and the quartz particles as the fluidizing material component. An alkali silicate is formed by the chemical reaction. This alkali silicate is a low-melting-point compound that melts at about 700 ° C., and may form an adhesive layer on the surface of the particles as the fluidizing material, possibly inhibiting the fluidizing material from flowing. However, in the present invention, smelting slag is supplied to the fluidized bed boiler in addition to the alkali component-containing fuel, and since magnesium oxide is contained in the smelting slag, the production of alkali silicate is suppressed. it can. Therefore, the possibility of the occurrence of poor flow due to the generation of the low melting point compound is reduced, and the fluidized bed boiler can be operated at a high temperature. As a result, it becomes easy to improve the energy recovery efficiency. Furthermore, since smelting slag contains magnesium oxide, not magnesium carbonate or magnesium hydroxide, magnesium oxide contributes directly to the suppression of alkali silicate formation, so magnesium carbonate and magnesium hydroxide are added. Higher energy recovery efficiency can be expected compared to

  Further, it is preferable to use smelting slag as a fluidizing material for a fluidized bed boiler. Since the fluidized bed can be formed using the smelting slag, it is possible to effectively suppress the flow failure of the fluidized bed without unevenness.

  Furthermore, the fluidized bed boiler is configured to prevent a back flow from the furnace body, a separation unit that separates the fluid material in the exhaust gas discharged from the furnace body from the exhaust gas, and the fluid material separated by the separation unit. It is preferable to provide a circulation seal portion that returns to the inside of the furnace body, and supply the smelting slag to the circulation seal portion. The poor flow at the circulation seal portion can be effectively suppressed.

  In addition, the present invention is a fluidized bed boiler using a fuel containing an alkali component, and includes a furnace body that burns fuel to which smelting slag generated by ore smelting is added. According to the present invention, both improvement of energy recovery efficiency and prevention of flow failure can be achieved even when an alkali component-containing fuel is used.

  Further, it is preferable that the furnace body is filled with the smelting slag as a fluidizing material. According to this structure, since a fluidized bed can be formed using smelting slag, the fluid failure of a fluidized bed can be effectively suppressed without unevenness.

  Furthermore, a separation part that separates the fluid material in the exhaust gas discharged from the furnace body from the exhaust gas, and a circulation seal part that returns the fluid material separated in the separation part to the inside of the furnace body while preventing backflow from the furnace body; The smelting slag is preferably supplied to the circulation seal portion. According to this configuration, poor flow at the circulation seal portion can be effectively suppressed.

  ADVANTAGE OF THE INVENTION According to this invention, when using an alkali component containing fuel as a fuel of a fluidized bed boiler, improvement of energy recovery efficiency and prevention of a flow defect can be made compatible.

It is explanatory drawing which shows a fluidized bed type boiler typically. It is explanatory drawing which shows the production | generation mechanism of an agglomerate, (a) is a figure which shows a coating induction mechanism, (b) is a figure which shows a melting induction mechanism. K ₂ is a O-SiO ₂ phase diagram. Is a MgO-SiO ₂ phase diagram. It is a _{MgO-K 2 O-SiO} 2 phase diagram. It is explanatory drawing which shows typically the state in which MgO acts on the eutectic coating C. It is a figure which shows the physical property of the three samples which are ferronickel slag. It is a graph which shows the relationship between the operation time at the time of adding ferronickel slag, bet temperature, and bet differential pressure. It is a graph which shows the relationship between the operating time, bet temperature, and bet differential pressure when no ferronickel slag is added (no addition).

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of a fluidized bed boiler and a combustion method of a fluidized bed boiler according to the present invention will be described with reference to the drawings.

  As shown in FIG. 1, a fluidized bed boiler (hereinafter referred to as “CFB boiler”) 1 includes a combustion tower (furnace body) 3 that burns fuel and heats water in a sealed container to generate steam. A cyclone separator (separation unit) 5 that separates solids from combustion gas (hereinafter referred to as “exhaust gas”) G generated in the combustion tower 3, a heat recovery unit 7 that recovers heat of the exhaust gas G, and a cyclone separator 5 includes a circulation line 9 for returning fly ash separated from the exhaust gas G, that is, the fluidized material Fa (see FIG. 2) separated from the exhaust gas G to the lower part of the combustion tower 3. The heat recovery unit 7 is provided with a heat exchange tube such as a superheater.

  Biomass fuel such as fir shells and EFB (Empty Fruit Bunches) is input to the combustion tower 3. This type of biomass fuel is a low-grade fuel containing a large amount of alkaline components such as potassium and sodium. Further, ferronickel slag, which is a kind of smelting slag, is introduced into the combustion tower 3. The combustion tower 3 is supplied with a fluidized material Fa containing quartz particles as a main component. Air is supplied into the fluidized material Fa from the lower part, and the fluidized material Fa flows and is fluidized (hereinafter referred to as “bed”). ) F is formed. Formation of the bed F promotes fuel combustion. The exhaust gas G generated as a result of combustion rises in the combustion tower 3 while accompanying a part of the fluidized material Fa. In addition, although this embodiment demonstrates the aspect which adds ferronickel slag in the fluidized material Fa, it is also possible to utilize the ferronickel slag itself as the fluidized material Fa.

  The cyclone separator 5 is disposed adjacent to the combustion tower 3, receives the exhaust gas G discharged from the combustion tower 3 and the fluidized material Fa accompanying the exhaust gas G, and receives the exhaust gas G and the fluidized material Fa by centrifugal separation. The fluidized material Fa is returned to the combustion tower 3, and the exhaust gas G is sent to the heat recovery unit 7.

  A circulation line 9 is connected to the cyclone separator 5. The circulation line 9 is a pipe connected to the lower part of the combustion tower 3, and a loop seal (circulation seal part) 9 a is provided on the circulation line 9. The loop seal 9a is a facility for preventing the backflow of the exhaust gas G from the combustion tower 3. The fluid material Fa sent from the cyclone separator 5 is accumulated in the loop seal 9a, and the fluid material Fa is the loop seal 9a. Is introduced into the combustion tower 3 from a return chute portion 9b at the outlet of the gas.

  The CFB boiler 1 also includes a smelting slag supply unit 11 for supplying ferronickel slag, which is a kind of smelting slag, into the loop seal 9a. By supplying ferronickel slag into the loop seal 9a, poor flow in the loop seal 9a can be effectively suppressed.

  Next, a phenomenon that occurs when biomass fuel is charged into the CFB boiler 1 and burned will be described.

  The concept of generating bottom ash and fly ash in biomass fuel combustion will be explained. The bottom ash is formed into particles by using the sand, which is the fluidized material Fa, as seeds (seeds), and the components in the biomass fuel are condensed, melted, aggregated and adhered, or chemically reacted on the sand surface. Further, fly ash is formed by condensation, melting, and agglomeration of the components in the biomass fuel, excluding those in which part of the bottom ash formed with particles is fine.

  The main cause of the flow hindrance in the fluidized material (also referred to as “fluidized sand” or “bed material”) Fa in the combustion of biomass fuel is agglomerate X (see FIG. 2). The agglomer X is mostly composed of a melt of a low melting point compound (a melt of a substance formed by components in the biomass fuel) adhering to the surface of the fluidized material Fa, or eutectic formation on the surface of the fluidized material Fa (in the biomass fuel). Is caused by two mechanisms known as melting induction and coating induction.

  Specifically, the main cause of the production of agglomerates X when burning biomass fuel is the main component of the fluid component Fa, such as alkali components from the biomass fuel, such as potassium (K) and sodium (Na). It is specified that a chemical reaction occurs between the particles and a sticky alkali silicate layer is formed on the surface of the fluid Fa. In addition to alkaline components, phosphorus has also been confirmed to be an important factor in Agrome X.

(Mechanism of melting induction)
As shown in FIG. 2B, the agglomeration X of the melting induction mechanism is caused by a group of bottom ash particles in which the melt M of the low melting point compound (alkali silicate) adheres to the surface of the fluid Fa, The controlling factors of this mechanism are local temperature and fuel ash composition. In combustion ash containing a high concentration of alkali components and chlorine, agglomerates X tend to be formed through the melting induction mechanism.

(Coating induction mechanism)
As shown in FIG. 2 (a), the agglomeration X of the coating induction mechanism is that the bottom ash particle group in which the eutectic coating (alkali silicate phase) C is formed on the surface of the fluidized material Fa is the eutectic. The coating C is repeatedly joined and discrete, and as a result, particle aggregation starts and gradually leads to the formation of the agglomerate X that becomes a bottleneck (flow inhibiting factor). The main control factor of this mechanism is the eutectic coating thickness. (Easiness of separation and bonding), eutectic coating composition (bonding strength) and local temperature.

In addition, from the detailed analysis result of the part actually coated on the surface of the fluid Fa, it is confirmed that the coating layer is a eutectic coating (K ₂ O—SiO ₂ : alkali silicate layer) C. Yes. The eutectic coating C begins to melt at 700 ° C. as shown in FIG. It can be confirmed that at the temperature in the fluidized material Fa of the CFB boiler 1, specifically, 800 ° C to 900 ° C, the particles that are the fluidized material Fa easily adhere and aggregate. FIG. 3 is a K ₂ O—SiO ₂ phase diagram.

Next, the relationship between the formation of agglomerates X and magnesium oxide (MgO) will be described with reference to FIGS. FIG. 4 is an MgO—SiO ₂ phase diagram, and FIG. 5 is an MgO—K ₂ O—SiO ₂ phase diagram. As shown in FIG. 3, the process of becoming MgO from the state of K ₂ O-4SiO ₂ is indicated by a straight line La in FIG. 5, and the direction in which the proportion of MgO increases is indicated by an arrow Da.

As shown in FIG. 3, the first reaction state (first reaction state) occurs at a temperature as low as 700 ° C. In this first reaction state, coating or the like is performed in the form of K ₂ O-4SiO _2. Formed (see FIG. 3). Next, in the second reaction state, the reaction proceeds in the direction of the arrow Da in FIG. 5, and MgO reacts little by little with K ₂ O-4SiO ₂ formed in the first reaction state. When the MgO reaction progresses on the straight line La (see FIG. 5), the melting point increases as the first point Pb of 742 ° C. when the MgO ratio is several percent (about 4%) (third reaction state). Next, when the proportion of MgO is about 8%, it becomes the second point Pb at 1000 ° C., the melting point is increased, and a layer with less adhesion is formed (fourth reaction state).

  MgO hardly reacts above the second point Pb. This is because the melting point becomes 1000 ° C. or higher and becomes a solid, which makes it difficult to react with MgO (solid). Here, when MgO adheres, for example, it returns from the second point Pb to the first point Pb, and the melting point becomes 742 ° C., so that the adhesion easily occurs. Next, it returns to a 2nd reaction state, MgO reacts, and a 3rd reaction state and a 4th reaction state are repeated again.

As shown in FIG. 4, it is easily guessed that the reaction between MgO and SiO ₂ does not form a melt up to 1543 ° C., and as shown in FIG. 5, MgO and K ₂ O—SiO ₂ It is speculated that the melt does not form up to about 1000 ° C. in the reaction. Therefore, when burning biomass fuel containing a large amount of alkali components, the formation of a low-melting eutectic coating (K ₂ O—SiO ₂ : alkali silicate phase) C is achieved by adding magnesium oxide to the fluidized material Fa. Can be suppressed.

Here, referring to FIG. 6, the suppression of the formation of the low melting point eutectic coating C will be structurally described. FIG. 6 is an explanatory view schematically showing a state in which MgO acts on the eutectic coating C. FIG. As shown in FIG. 6, when the eutectic coating C is formed on the surface of the fluidized material Fa, a layer S of MgO—K ₂ O—SiO ₂ having a high melting point is formed and solidified on the surface, and the melting point is Go up. Further, even if the eutectic coating C is formed on the surface, a layer S of MgO—K ₂ O—SiO ₂ having a high melting point is formed and solidified to increase the melting point. As a result, even if the eutectic coating C having a low melting point is formed, a layer S of MgO—K ₂ O—SiO ₂ having a high melting point is formed on the surface of the eutectic coating C, thereby reducing the melting point. Is suppressed.

  Next, smelting slag such as ferronickel slag will be described. The smelting slag is, for example, slag generated when ferroalloy raw ore is smelted to produce ferroalloy, and various methods such as an electric furnace method and a thermite method can be applied to the smelting method. For example, in the electric furnace method, after the raw material ore is pretreated, a refining process is performed in the electric furnace, and the remaining residue obtained by extracting a desired metal in the refining process becomes a smelting slag. In this embodiment, ferronickel slag is illustrated as smelting slag.

  FIG. 7 is a diagram showing the physical properties of three samples that are ferronickel slag. For example, sample A contains 28.1% magnesium oxide (MgO) as a weight percent concentration, and sample B The sample contains 35.5% magnesium oxide (MgO), and the sample C contains about 50.0% to 55% magnesium oxide (MgO). Thus, at least 30% or more of magnesium oxide is contained in the ferronickel slag. Therefore, it is presumed that by supplying ferronickel slag into the combustion tower 3 of the CFB boiler 1, the formation of agglomerates X can be suppressed and the flow failure can be effectively suppressed.

  Next, a combustion method of the CFB boiler 1 when a low-grade biomass fuel is used as the boiler fuel will be described. In the combustion tower 3 of the CFB boiler 1, the fluid material Fa that forms the bed F has already been put. Ferronickel slag is supplied into the combustion tower 3 in addition to biomass fuel, and air is supplied from the lower part of the fluidized material Fa to form the bed F, and burned by a burner (not shown). By adding ferronickel slag to the fluidized material Fa in the combustion tower 3, magnesium oxide in the ferronickel slag contributes to suppress the formation of agglomerate X and effectively suppress the flow failure of the bed F. Can do.

  Here, with reference to FIG.8 and FIG.9, the effect at the time of adding ferronickel slag is demonstrated compared with the case where it does not add. FIG. 8 is a graph showing the relationship between the operation time when ferronickel slag is added, the bed temperature and the bed differential pressure, and FIG. 9 shows the operation when ferronickel slag is not added (no addition). It is a graph which shows the relationship between time, bet temperature, and bet differential pressure. The bet differential pressure indicates a pressure difference at the upper and lower positions in the fluidized bed F. When a flow failure occurs, the bet differential pressure rapidly decreases and finally becomes “0”. In addition, in the experimental conditions shown in FIG. 8 and FIG. 9, the potassium concentration contained in the bed F when no ferronickel slag is added is 0.6 wt% (based on ash content), whereas ferronickel slag is added. In this case, the concentration of potassium (K) contained in the bed F is as high as 2.6 wt% (ash base). Therefore, the case where ferronickel slag is added is an environment in which agglomerates X are easily formed.

  As shown in FIG. 8, when ferronickel slag is added, even if the bed temperature exceeds 800 ° C., there is no significant change in the bed differential pressure, and it can be determined that the flow is good. On the other hand, as shown in FIG. 9, when ferronickel slag is not added, the bet differential pressure rapidly decreases after a certain time has elapsed after the bet temperature exceeds 800 ° C. The growth of the agglomerates X can be inferred, and the bet differential pressure is substantially “0”, so it can be determined that the flow is poor, and as a result, an emergency stop is required. Also from these experimental results, it can be confirmed that the flow failure of the bed F can be effectively suppressed when ferronickel slag is added.

  Furthermore, in the combustion method of the CFB boiler 1 according to the present embodiment, ferronickel slag is also added into the loop seal 9 a of the circulation line 9. The fluid force of the fluid Fa at the loop seal 9a is significantly weaker than the fluid force at the bed F formed in the combustion tower 3. Therefore, the flow failure can be effectively prevented by positively adding ferronickel slag into the loop seal 9a. Furthermore, since the ferronickel slag supplied into the loop seal 9a is also circulated in the combustion tower 3, an effect of preventing the flow failure of the bed F can be obtained.

  The effect of the combustion method of the CFB boiler 1 will be described. When an alkali-containing biomass fuel is used as the fuel for the CFB boiler, a chemical reaction occurs between alkali components such as potassium (K) and sodium (Na) and quartz particles which are the main components of the fluidized material Fa. An alkali silicate is formed. This alkali silicate is a low-melting-point compound that melts at about 700 ° C., and forms an adhesive layer Fa on the particle surface as the fluidizing material Fa, possibly inhibiting the fluidizing material Fa from flowing.

Therefore, in order to enable adaptation of the alkali-containing biomass fuel in the conventional CFB boiler, it is necessary to keep the operating temperature low in order to suppress the flow failure (abrome production), or the in-furnace environment where the flow failure is unlikely to occur. In order to form a coal, processing such as co-firing with coal, addition of additives or replacement of fluidized materials and complicated control management are necessary, and CO ₂ reduction effect is not expected so much, waste of additive resources and operation This has led to an increase in cost, and furthermore, a large amount of waste (drawn waste fluidized material generated by replacement of fluidized material) is generated, which is not realistic. Therefore, when the alkali-containing biomass fuel is used as the fuel for the CFB boiler, it is very difficult to achieve both improvement in energy recovery efficiency and prevention of poor flow.

  However, in the above-described combustion method of the CFB boiler 1, ferronickel slag is supplied to the combustion tower 3 of the CFB boiler 1 in addition to the alkali-containing biomass fuel, and magnesium oxide is contained in the ferronickel slag. , Generation of alkali silicate can be suppressed. Therefore, the possibility of poor flow due to the generation of the low melting point compound is reduced, and the CFB boiler 1 can be operated at a high temperature. As a result, it has become possible to easily achieve both improvement in energy recovery efficiency and prevention of poor flow.

  Furthermore, conventionally, ferronickel slag is only used to the extent that it is used as a roadbed material, and is normally discarded, but according to this embodiment, from the viewpoint of effective use of this ferronickel slag. It is advantageous. Furthermore, since ferronickel slag contains magnesium oxide instead of magnesium carbonate or magnesium hydroxide, magnesium oxide contributes directly to the suppression of alkali silicate formation, so magnesium carbonate and magnesium hydroxide are added. Higher energy recovery efficiency can be expected compared to

  As mentioned above, although this invention was concretely demonstrated based on the embodiment, this invention is not limited to the said embodiment. For example, in the above embodiment, ferronickel slag is exemplified as the smelting slag, but other smelting slag generated by smelting ore can also be used.

It is also possible to use fluidized bed boilers that use poor quality fluid materials containing alkali components, or to use smelting slag as an alternative to fluid materials. Since the fluidized bed using the smelted slag can be formed, the fluidized bed fluidity can be effectively suppressed without unevenness.
Furthermore, with respect to the strong fouling and deposit deposition on the boiler steam superheater heat transfer tube, the removal effect and the boiler steam superheater transfer tube corrosion suppression effect can be expected.

  DESCRIPTION OF SYMBOLS 1 ... CFB boiler (fluidized bed type boiler), 3 ... Combustion tower (furnace main body), 9a ... Loop seal (circulation seal part), F ... Bed (fluidized bed), Fa ... Fluidizing material, G ... Exhaust gas.

As shown in FIG. 3, the first reaction state (first reaction state) occurs at a temperature as low as 700 ° C. In this first reaction state, coating or the like is performed in the form of K ₂ O-4SiO _2. Formed (see FIG. 3). Next, in the second reaction state, the reaction proceeds in the direction of the arrow Da in FIG. 5, and MgO reacts little by little with K ₂ O-4SiO ₂ formed in the first reaction state. When the MgO reaction progresses on the straight line La (see FIG. 5), the melting point increases as the first point Pb of 742 ° C. when the MgO ratio is several percent (about 4%) (third reaction state). Next, when the MgO ratio is about 8%, it becomes the second point Pa at 1000 ° C., the melting point is increased, and the layer becomes less adherent (fourth reaction state).

MgO hardly reacts above the second point Pa . This is because the melting point becomes 1000 ° C. or higher and becomes a solid, which makes it difficult to react with MgO (solid). Here, when K ₂ O adheres again, for example, it returns from the second point Pa to the first point Pb, and 742 ° C. becomes the melting point, and the attachment is likely to occur. Next, it returns to a 2nd reaction state, MgO reacts, and a 3rd reaction state and a 4th reaction state are repeated again.

As shown in FIG. 8, when ferronickel slag is added, even if the bed temperature exceeds 800 ° C., there is no significant change in the bed differential pressure, and it can be determined that the flow is good. On the other hand, as shown in FIG. 9, when ferronickel slag is not added, the bet differential pressure rapidly decreases after a certain time has elapsed after the bet temperature exceeds 800 ° C. The growth of the agglomerates X can be inferred, and the bet differential pressure is about “0”. Therefore, it can be determined that the flow is poor, and as a result, an emergency stop is required. Also from these experimental results, it can be confirmed that the flow failure of the bed F can be effectively suppressed when ferronickel slag is added.

Claims (6)

In the combustion method of a fluidized bed boiler using an alkali component-containing fuel,
A smelting slag produced by ore smelting is added to the fuel and burned in the fluidized bed boiler.   The method for combusting a fluidized bed boiler according to claim 1, wherein the smelting slag is used as a fluidized material of the fluidized bed boiler. The fluidized bed boiler includes a furnace body, a separation part that separates the fluid material in the exhaust gas discharged from the furnace body from the exhaust gas, and the fluid material separated by the separation part from the flow back from the furnace body. A circulation seal part for returning to the inside of the furnace body while preventing
The combustion method of a fluidized bed boiler according to claim 1 or 2, wherein the smelting slag is supplied to the circulation seal portion. A fluidized bed boiler using an alkali component-containing fuel,
A fluidized bed boiler comprising a furnace main body for burning the fuel to which smelting slag generated by ore smelting is added.   The fluidized bed boiler according to claim 4, wherein the smelting slag is introduced into the furnace body as a fluidizing material. A separation part that separates the fluid material in the exhaust gas discharged from the furnace body from the exhaust gas, and the fluid material separated by the separation part is returned to the interior of the furnace body while preventing backflow from the furnace body. A circulation seal part,
The fluidized bed boiler according to claim 4 or 5, wherein the smelting slag is supplied to the circulation seal portion.

Images