WO2012011538A1 - 固体燃料の改質方法 - Google Patents
固体燃料の改質方法 Download PDFInfo
- Publication number
- WO2012011538A1 WO2012011538A1 PCT/JP2011/066610 JP2011066610W WO2012011538A1 WO 2012011538 A1 WO2012011538 A1 WO 2012011538A1 JP 2011066610 W JP2011066610 W JP 2011066610W WO 2012011538 A1 WO2012011538 A1 WO 2012011538A1
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- Prior art keywords
- ash
- ratio
- coal
- melt
- boiler
- Prior art date
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- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
- C10L9/00—Treating solid fuels to improve their combustion
- C10L9/08—Treating solid fuels to improve their combustion by heat treatments, e.g. calcining
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- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
- C10L10/00—Use of additives to fuels or fires for particular purposes
- C10L10/04—Use of additives to fuels or fires for particular purposes for minimising corrosion or incrustation
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- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10L—FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G, C10K; LIQUEFIED PETROLEUM GAS; ADDING MATERIALS TO FUELS OR FIRES TO REDUCE SMOKE OR UNDESIRABLE DEPOSITS OR TO FACILITATE SOOT REMOVAL; FIRELIGHTERS
- C10L9/00—Treating solid fuels to improve their combustion
- C10L9/10—Treating solid fuels to improve their combustion by using additives
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23K—FEEDING FUEL TO COMBUSTION APPARATUS
- F23K1/00—Preparation of lump or pulverulent fuel in readiness for delivery to combustion apparatus
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F23—COMBUSTION APPARATUS; COMBUSTION PROCESSES
- F23K—FEEDING FUEL TO COMBUSTION APPARATUS
- F23K2201/00—Pretreatment of solid fuel
- F23K2201/50—Blending
- F23K2201/505—Blending with additives
Definitions
- the present invention relates to a method for reforming solid fuel that is a fuel for a boiler.
- the solid fuel pulverized by the pulverizer is supplied to the boiler using the solid fuel together with the air for conveyance.
- the boiler includes a furnace that generates heat by burning supplied fuel with a burner and the like, and a heat transfer tube group that is arranged from the upper side to the downstream side of the furnace and that exchanges heat by flowing the combustion gas inside. Yes.
- Patent Document 1 discloses a solid fuel made of porous charcoal that loses pyrophoric properties and is calorie-enhanced as a whole, and a method for producing the same.
- a mixed oil containing heavy oil and solvent oil is mixed with porous charcoal to form a slurry, and this is heated to, for example, 100 to 250 ° C. to replace the moisture in the pores with the mixed oil.
- Such solid fuel can reduce heat loss even when it is used as fuel for a boiler.
- melt ratio in ash based on the slag ratio (melt ratio in ash) calculated for each solid fuel and the composition of the ash component, a plurality of types of solids are used so that the melt ratio in ash in the boiler is below the reference value.
- the fuel mixing ratio is determined.
- the reference value is preferably in the range of 50 to 60% by weight of the melt in ash.
- the mixing ratio is determined so that the melt ratio in ash (slag ratio) is below the reference value. Therefore, the melt ratio in ash is preferably sufficiently low with respect to the reference value. Furthermore, if the melt ratio of low-grade coal in ash is sufficiently low, the possibility that low-grade coal alone can be used in boilers without mixing low-grade coal with high-grade coal increases.
- An object of the present invention is to provide a solid fuel reforming method capable of suppressing the adhesion of ash to a boiler by reducing the melt ratio in ash.
- the method for reforming a solid fuel according to the present invention includes a step of mixing raw coal and raw oil, adding an additive containing at least one of a magnesium compound and an aluminum compound to form a raw slurry, and the raw material A step of heating the slurry, a step of solid-liquid separation of the raw material slurry after heating, a step of drying the solid content of the raw material slurry subjected to solid-liquid separation to obtain product charcoal, It is characterized by having.
- the melt ratio in ash means the ratio of a certain amount of solid ash that has become a melt (molten slag) at a certain temperature and atmospheric condition.
- “Slag” means a component that melts by combustion, floats on the combustion airflow in the boiler, and adheres to the furnace wall or heat transfer tube group.
- the inorganic compound added to the product coal increases, so the slag increase rate also increases.
- the addition ratio increases, the ash melt ratio in the product coal decreases, and the slag increase rate decreases.
- slag increase rate is the ratio of the amount of slag produced before and after the addition of the inorganic compound.
- the “slag generation amount” is a value obtained by multiplying the ash weight in the supplied coal and the weight of the inorganic compound to be added by the melt ratio in ash.
- the addition ratio of at least one of the magnesium compound and the aluminum compound is such that the melt ratio in ash in the product coal is 60 wt% (wt%) or less. It is preferable to be determined as follows. According to the above configuration, the magnesium-based compound and the aluminum-based compound are added so that the melt ratio in the ash in the product charcoal is 60 wt% or less even in the vicinity of 1573 K, which is a temperature at which ash adhesion easily occurs in the boiler. Is done. Thereby, the melt ratio in ash in the product charcoal becomes equal to or less than the reference value when determining the mixing ratio of a plurality of types of solid fuel, and the ash adhesion rate decreases. By using such product charcoal for the boiler, the amount of ash adhesion to the boiler can be suppressed.
- an addition ratio of at least one of the magnesium compound and the aluminum compound is 25 wt% or more and 50 wt% or less with respect to coal ash.
- at least one of the magnesium-based compound and the aluminum-based compound is added to the mixture of raw coal and raw oil at an addition ratio of 25 wt% or more and 50 wt% or less.
- the liquid ratio can be suitably reduced.
- an average particle diameter of at least one of the magnesium compound and the aluminum compound is 5 ⁇ m or less.
- the average particle size of the magnesium-based compound and the aluminum-based compound is smaller and finer than that of ash, the effect of suppressing ash adhesion increases. Since the average particle diameter of ash is about 6.8 ⁇ m, the ash adhesion to the boiler can be suitably suppressed by setting the average particle diameter of at least one of the magnesium compound and the aluminum compound to 5 ⁇ m or less.
- the additive contains 70 wt% or more of the magnesium-based compound.
- the melt ratio in ash in product charcoal can be reduced suitably by adding the additive containing 70 wt% or more of a magnesium type compound to the mixture of raw coal and raw material oil. .
- the solid fuel reforming method of the present invention by adding at least one of a magnesium-based compound and an aluminum-based compound to a mixture of raw coal and raw oil, the shrinkage of ash is reduced and the ash is melted. It becomes difficult to become, and the melt ratio (slag ratio) in ash in the product charcoal decreases. Moreover, as the addition ratio of the magnesium-based compound and the aluminum-based compound increases, the ratio of the melt in ash in the product charcoal decreases and the slag increase rate decreases. When the melt ratio in ash decreases, the ash adhesion rate of product charcoal decreases, and the amount of ash adhesion to the boiler is suppressed by using such product charcoal for the boiler.
- low grade coal containing low melting point ash is used as raw coal, and at least one of magnesium compound and aluminum compound is added to reduce the melt ratio in ash and reduce the ash adhesion rate Charcoal is obtained. This increases the possibility that low-grade coal can be used for boilers alone without mixing low-grade coal with high-grade coal such as bituminous coal.
- the ratio of melt in ash in product coal can be reduced, and the ash adhesion rate of product coal Can be reduced.
- product charcoal for the boiler, it is possible to suppress ash from adhering to the boiler.
- the boiler 7 includes hoppers 1 and 2 that hold solid fuel, supply amount adjusting devices 3 a and 3 b that adjust the supply amount of solid fuel supplied from the hoppers 1 and 2, 2, a mixer 4 that mixes the solid fuel supplied from 2, a pulverizer 5 that pulverizes the solid fuel mixed in the mixer 4 into pulverized coal, and pulverized coal that is supplied from the pulverizer 5 together with the conveying air. And a calculator 9 for controlling the supply amount adjusting devices 3a and 3b.
- the boiler 7 collects heat by burning pulverized coal.
- the hopper 1 and the hopper 2 respectively hold solid fuels having different ash properties.
- the solid fuel includes coal, sludge carbide, biomass fuel, and the like.
- the number of hoppers is not limited to two, and may be one or two or more.
- the supply amount of the solid fuel supplied from the hopper 1 to the mixer 4 is adjusted by the supply amount adjusting device 3a, and the supply amount of the solid fuel supplied from the hopper 2 to the mixer 4 is adjusted by the supply amount adjusting device 3b. Is done.
- the boiler 7 is arranged from the upper side to the lower side of the furnace where the pulverized coal supplied from the pulverizer 5 is burned by the burner 6 and the like to generate heat, and the combustion gas is disposed inside.
- a heat transfer tube group for performing heat exchange by flowing. The combustion gas generated in the boiler 7 is discharged from the chimney.
- the heat transfer tube group includes an upper heat transfer unit including a secondary heater, a tertiary heater, a final heater, and a secondary reheater arranged in parallel at predetermined intervals above the furnace, and a rear part of the furnace.
- a rear heat transfer section including a primary heater, a primary reheater, and a economizer.
- the calculator 9 preliminarily accumulates data such as the moisture content of the solid fuel, the calorific value, the ash content, and the composition of the ash component as data.
- the computing unit 9 uses the mixing ratio of the solid fuel as a parameter, and calculates the composition of the ash component of the mixed fuel from the composition of the ash component of each solid fuel measured in advance. Further, the computing unit 9 calculates the value of the melt ratio in ash (the reference value) at which the ash adhesion ratio decreases to about 5 to 7% from the relationship between the ash melt ratio (slag ratio) and the ash adhesion ratio measured in advance. ).
- the calculator 9 determines the mixing ratio of each solid fuel by thermodynamic equilibrium calculation so that it may become the ash composition from which the melt ratio in ash becomes below the determined reference value.
- the supply amount of the solid fuel as the fuel is determined so that the amount of heat input to the boiler becomes constant.
- the computing unit 9 controls the supply amount adjusting devices 3a and 3b based on the determined mixing ratio of the solid fuels. Thereby, the supply amount of the solid fuel from the hoppers 1 and 2 to the boiler 7 is adjusted.
- the melt ratio in ash which is an evaluation index of the ash adhesion characteristics used in the present embodiment, is a melt (molten slag) in a certain amount of solid ash at a certain temperature and atmospheric condition.
- Means the percentage of “Slag” means a component that melts by combustion, floats on the combustion airflow in the boiler, and adheres to the furnace wall or heat transfer tube group.
- the ash melt ratio is calculated according to each solid fuel and the mixing conditions of each solid fuel.
- the melt ratio in ash is the state in which the ash of each solid fuel measured in advance is thermodynamically most stable under a certain condition (temperature, atmospheric gas composition), that is, Gibbs free energy ( ⁇ ).
- the composition and phase (gas phase, solid phase, liquid phase) in a state where G) is close to zero are obtained by calculating by thermodynamic equilibrium calculation.
- the ash composition at this time is an ash composition after mixing several kinds of coal at a certain ratio.
- thermodynamic equilibrium calculation the ambient temperature in the vicinity of the burner where the ash adhesion to the boiler wall is noticeably generated and the ambient gas composition are used.
- the thermodynamic equilibrium calculation may be performed based on the atmospheric temperature and the atmospheric gas composition of a desired portion such as a heat transfer tube group in which ash is likely to adhere, without being limited to the atmospheric temperature and the atmospheric gas composition near the burner.
- the melt ratio in ash in the ash in each part inside the boiler can be obtained appropriately, and an appropriate mixing ratio of a plurality of types of solid fuels can be calculated.
- the thermodynamic equilibrium calculation may be performed using the maximum ambient gas temperature in boiler design and the ambient gas composition at the site, without being limited to the above-described embodiment.
- the atmosphere gas composition having the highest degree of reduction (the highest concentration of the reducing gas such as CO or H 2 ) and the temperature of the part may be used in boiler design.
- the mixing ratio can be determined without depending on the combustion temperature in the furnace of the boiler.
- the calculation of the melt ratio in ash is not limited to the above-described form, and the ash melt ratio in ash may be calculated based on the ash melt ratio measured in advance at each temperature and atmospheric gas composition. Thereby, the melt ratio in ash according to the actual situation of the boiler can be obtained.
- the melt ratio in ash may be calculated from the actual shrinkage of coal ash using a thermomechanical analyzer (TMA (Thermo Mechanical Mechanical) apparatus).
- TMA thermomechanical analyzer
- the ash adhesion rate is the ratio of the amount of ash adhering to the ash adhesion probe to the amount of ash adhering to the ash adhesion probe inserted into the furnace of the boiler, and means the ease of ash adhesion. It is represented by The “impact ash amount to the ash adhesion probe” is the total amount of ash that collides with the projected area of the ash adhesion probe, and is determined by the supply amount of solid fuel, the ash content rate, and the furnace shape of the boiler.
- the calculation of the ash adhesion rate may be performed using a combustion test furnace or an actual can boiler instead of the boiler 7.
- raw coal such as low-grade coal and raw oil are supplied to the mixing unit 11 and mixed.
- An additive containing MgO, which is a magnesium compound (inorganic compound), is supplied to the mixing unit 11 and added to the mixture in the mixing unit 11, thereby forming a raw material slurry.
- the additive contains 70 wt% or more, preferably 90 wt% or more of MgO.
- the average particle diameter of MgO is 5 ⁇ m or less, preferably about 0.2 ⁇ m.
- the addition ratio of MgO to the inorganic component of the solid fuel is 25 wt% or more and 50 wt% or less.
- the magnesium compound is not limited to MgO that is an oxide, and may be MgCO 3 or Mg (OH) 2 .
- the heated raw material slurry is supplied to the solid-liquid separation unit 13 and separated into solid and liquid by any means such as sedimentation, centrifugation, filtration, and pressing.
- the separated liquid moisture is discharged, and the oil is recycled as raw material oil in the mixing unit 11.
- the separated solid component is sent to the molding unit 14 and dried to be taken out as product charcoal.
- the extracted product charcoal is used in the boiler 7 (see FIG. 1) as a solid fuel.
- FIG. 3 shows the relationship between the melt ratio in ash and the ash adhesion rate of various coal blends at 1573 K, which is a temperature at which ash adhesion easily occurs in the boiler. From FIG. 3, it can be seen that when the melt ratio in ash exceeds 60 wt% at the atmospheric temperature and the atmospheric gas composition in the furnace, the ash adhesion rate increases rapidly. In other words, the ash adhesion rate can be lowered by setting the melt ratio in ash to 60 wt% or less.
- the reference value that is the value of the melt ratio in ash at which the ash adhesion rate becomes low is 50 to 60 wt%.
- the computing unit 9 determines the mixing ratio of each solid fuel by thermodynamic equilibrium calculation so that the ash composition is such that the melt ratio in ash is equal to or less than the determined reference value.
- FIG. 4 is a calculation result of calculating the melt ratio in ash by the above method.
- FIG. 5 shows the result of the ash shrinkage obtained by thermomechanical analysis (TMA, Thermo Mechanical Analysis) in which the deformation of the material is measured by applying a load while changing the temperature of the ash sample.
- TMA thermomechanical analysis
- As the ash sample low grade coal (here, ash of modified lignite) (a) to which MgO is not added and ash (b) of modified lignite to which 25 wt% of MgO is added are used.
- the higher the shrinkage rate of ash the more the ash sample is converted from a solid to a melt (molten slag).
- FIG. 6 is a calculation result showing the relationship between the addition ratio of the inorganic compound and the slag increase rate when various inorganic compounds are added to the coal ash.
- the slag at 1573 K which is a temperature at which ash adhesion easily occurs in the boiler.
- the rate of increase is shown.
- the “slag increase rate” is the ratio of the amount of slag produced before and after addition of the inorganic compound, and is represented by the following formula.
- the slag generation amount is obtained by multiplying the ash weight in the supplied coal and the weight of the inorganic compound to be added by the melt ratio in the ash. Specifically, the slag generation amount ([kg / hr]) before the addition of the inorganic compound is (melt ratio in ash [wt%] ⁇ coal supply amount [kg-dry base / hr] ⁇ ash content [%] ]). Further, the slag generation amount ([kg / hr]) after addition of the inorganic compound is (melt ratio in ash [wt%] ⁇ (coal supply amount [kg-dry base / hr] ⁇ ash content [%]) + Inorganic compound addition amount [kg / hr])).
- the slag increase rate 100% shown in FIG. 6 is the slag generation amount (calculated value) of the low melting point ash under the condition where no inorganic compound is added.
- slag increase rate is less than 100%, slag generation is suppressed.
- the inorganic substance contained in coal increases, so that the addition rate of the inorganic compound in coal ash increases, slag increase rate also becomes high.
- MgO and Al 2 O 3 are inorganic compounds having an effect of suppressing ash adhesion as the addition ratio increases.
- FIG. 7 shows the relationship between the ratio of magnesium-based compound and aluminum-based compound added to coal ash and the ratio of melt in ash.
- FIG. 7 shows the melt ratio (calculated value) in ash when the addition ratio of MgO and Al 2 O 3 is changed at 1573 K, which is a temperature at which ash adhesion easily occurs in the boiler.
- the addition ratio of MgO at which the melt ratio in ash is 60 wt% or less is 15 wt% or more.
- the addition ratio of MgO added to the mixture in the mixing unit 11 in FIG. 2 is 25 wt% or more and 50 wt% or less with respect to the inorganic component (coal ash) of the solid fuel.
- FIG. 8 shows the relationship between the MgO content in the additive and the ash melt ratio.
- the MgO content is 70 wt% or more. Therefore, if the additive contains 70 wt% or more, preferably 90 wt% or more of MgO, the melt ratio in ash becomes 60 wt% or less, and the ash adhesion rate can be lowered.
- an additive containing 70 wt% or more, preferably 90 wt% or more of MgO is added to the mixture in the mixing section 11 in FIG. 2 to form a raw material slurry.
- FIG. 9 shows the relationship between the MgO content in the additive added at a rate of 25 wt% with respect to the coal ash, the melt ratio in ash, and the ash adhesion amount.
- the melt ratio in ash is 60 wt% or less at 1573 K, which is a temperature at which ash adhesion easily occurs in the boiler.
- FIG. 9 shows that the amount of ash adhesion decreases as the MgO content in the additive increases.
- the raw material slurry is formed by adding an additive containing 70 wt% or more, preferably 90 wt% or more of MgO to the mixture in the mixing section 11 in FIG.
- FIG. 10 shows the particle size distribution of the coal ash used in this embodiment.
- the average particle diameter of the coal ash used in this embodiment (particle diameter when the integrated weight is 50% (median diameter)) is 6.8 ⁇ m.
- the average particle diameter of MgO added to the mixture in the mixing part 11 in FIG. 2 is 5 ⁇ m or less, preferably about 0.2 ⁇ m.
- the ash adhesion probe is inserted into a furnace having a gas atmosphere temperature of 1573 K below the burner and held for 100 minutes. And the adhesion amount (weight) of the ash adhering to the surface of an ash adhesion probe is measured.
- FIG. 11 shows the result.
- FIG. 11 shows the relationship between the addition ratio of the MgO sample to the coal ash and the ash adhesion amount.
- the ash adhesion amount is 4.4 g-ash / 100 min.
- the weight is less than that, there is an ash adhesion suppression effect.
- the ash adhesion suppressing effect is recognized by adding an MgO sample having an average particle size of 5 ⁇ m or less. That is, it can be seen that the effect of suppressing ash adhesion can be obtained by adding a MgO sample having an average particle size smaller than that of ash.
- the amount of ash adhesion is lower in the MgO sample having an average particle diameter of 0.2 ⁇ m than in the MgO sample having an average particle diameter of 5 ⁇ m. From this, it can be seen that the smaller the average particle size of the MgO sample to be added, the greater the effect of suppressing ash adhesion.
- the average particle diameter of MgO added to the mixture in the mixing section 11 in FIG. 2 is 5 ⁇ m or less, preferably about 0.2 ⁇ m, which is smaller than the average particle diameter of coal ash, 6.8 ⁇ m. .
- the addition ratio of the MgO sample is preferably 50 wt% or less.
- the addition ratio of MgO added to the mixture in the mixing unit 11 in FIG. 2 is 25 wt% or more and 50 wt% or less with respect to the inorganic component of the solid fuel.
- the product coal which reduced the melt ratio in ash and reduced the ash adhesion rate is obtained by adding a magnesium-type compound by using low grade coal containing low melting point ash as raw coal. . Accordingly, there is a high possibility that the low-grade coal can be used for the boiler alone without mixing the low-grade coal with the high-grade coal such as bituminous coal.
- the ratio of melt in ash in the product coal can be reduced, and the ash adhesion rate of the product coal is reduced. Therefore, it can suppress that ash adheres to a boiler by utilizing such product charcoal for a boiler.
- the magnesium-based compound is added so that the melt ratio in the ash in the product charcoal is 60 wt% or less, particularly in the vicinity of 1573 K where the ash adhesion is likely to occur in the boiler.
- the melt ratio in ash in product charcoal becomes below the standard value at the time of determining the mixture ratio of a plurality of kinds of solid fuel, and the ash adhesion rate falls. Therefore, the ash adhesion amount to a boiler can be suppressed by using such product charcoal for a boiler.
- the melt ratio in ash in the product coal can be suitably reduced.
- the average particle size of the magnesium-based compound is smaller and finer than that of ash, the effect of suppressing ash adhesion increases. Since the average particle diameter of ash is about 6.8 ⁇ m, the ash adhesion to the boiler can be suitably suppressed by setting the average particle diameter of the magnesium-based compound to 5 ⁇ m or less.
- the melt ratio in ash in the product coal can be suitably reduced.
- the second embodiment differs from the first embodiment in that when reforming the raw coal to produce product coal, Al 2 O which is an aluminum compound (inorganic compound) is added to the mixture of raw coal and raw oil. This is the point at which an additive containing 3 is added.
- the average particle diameter of Al 2 O 3 is 5 ⁇ m or less, preferably about 0.2 ⁇ m, and the addition ratio of Al 2 O 3 to the inorganic component of the solid fuel is 25 wt% or more and 50 wt% or less.
- the aluminum compound is not limited to an oxide such as Al 2 O 3 , and may be a carbonate or hydroxide.
- FIG. 12 shows a calculation result of adding the Al 2 O 3 and calculating the melt ratio in ash by the above method.
- FIG. 13 shows the result of the ash shrinkage obtained by thermomechanical analysis (TMA) in which the load is applied and the deformation of the material is measured while changing the temperature of the ash sample.
- TMA thermomechanical analysis
- the higher the shrinkage rate of ash the more the ash sample becomes a melt from solid, and the higher the temperature, the higher the melt ratio in ash and the shrinkage rate of ash.
- both the melt ratio in ash calculated by thermodynamic equilibrium calculation and the shrinkage ratio of the measured ash are drastically reduced.
- the shrinkage rate of the ash is reduced and the ash is less likely to become a melt, and the melt ratio in the ash is reduced.
- the ash melt ratio in the vicinity of 1573K where ash adhesion in the boiler is likely to occur decreases to about 60 wt% when 25 wt% of Al 2 O 3 is added to the ash of the modified lignite.
- FIG. 6 is a calculation result showing the relationship between the addition ratio of the inorganic compound and the slag increase rate when various inorganic compounds are added to the coal ash.
- FIG. 6 shows the slag increase rate at 1573 K, which is a temperature at which ash adhesion easily occurs particularly in the boiler.
- slag increase rate also becomes high.
- FIG. 6 as the addition ratio of MgO and Al 2 O 3 increases, the ash melt ratio decreases and the slag increase ratio decreases. Therefore, these MgO and Al 2 O 3 can be said to be inorganic compounds having an effect of suppressing ash adhesion as the addition ratio increases.
- FIG. 7 shows the relationship between the ratio of magnesium-based compound and aluminum-based compound added to coal ash and the ratio of melt in ash.
- FIG. 7 shows the melt ratio (calculated value) in ash when the addition ratio of MgO and Al 2 O 3 is changed at 1573 K, which is a temperature at which ash adhesion easily occurs in the boiler.
- the ratio of Al 2 O 3 to be added is 25 wt% or more.
- the addition ratio of Al 2 O 3 added to the mixture in the mixing unit 11 in FIG. 2 is 25 wt% or more and 50 wt% or less with respect to the inorganic component (coal ash) of the solid fuel.
- FIG. 11 which shows the test result of an ash adhesion characteristic test shows that there is an ash adhesion inhibitory effect when an inorganic compound having an average particle size smaller than that of ash is added. Moreover, it turns out that an ash adhesion inhibitory effect is so large that the average particle diameter of the inorganic compound to add is fine.
- the average particle diameter of Al 2 O 3 added to the mixture in the mixing section 11 in FIG. 2 is 5 ⁇ m or less, preferably 0.2 ⁇ m, which is smaller than the average particle diameter of coal ash, 6.8 ⁇ m. Degree.
- the inorganic compound added to the product coal increases, so the slag increase rate also increases.
- the melt ratio in ash in the product coal decreases, and the slag increase rate decreases.
- the melt ratio in ash in the product coal can be reduced, and the ash adhesion rate of the product coal is reduced. Therefore, it can suppress that ash adheres to a boiler by utilizing such product charcoal for a boiler.
- the aluminum-based compound is added so that the melt ratio in the ash in the product charcoal is 60 wt% or less, particularly in the vicinity of 1573 K, which is a temperature at which ash adhesion easily occurs in the boiler.
- the melt ratio in ash in product charcoal becomes below the standard value at the time of determining the mixture ratio of a plurality of kinds of solid fuel, and the ash adhesion rate falls. Therefore, the ash adhesion amount to a boiler can be suppressed by using such product charcoal for a boiler.
- the melt ratio in ash in the product coal can be suitably reduced.
- the average particle size of the aluminum-based compound is smaller and finer than that of ash, the effect of suppressing ash adhesion increases. Since the average particle diameter of ash is about 6.8 ⁇ m, the ash adhesion to the boiler can be suitably suppressed by setting the average particle diameter of the aluminum-based compound to 5 ⁇ m or less.
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Abstract
Description
を有することを特徴とする。
(ボイラの構成)
本実施形態による改質方法で形成される製品炭は、固体燃料としてボイラに利用される。図1に示すように、ボイラ7は、固体燃料を保持するホッパ1,2と、ホッパ1,2から供給される固体燃料の供給量を調整する供給量調整装置3a,3bと、ホッパ1,2から供給された固体燃料を混合する混合機4と、混合機4で混合された固体燃料を粉砕して微粉炭にする粉砕機5と、粉砕機5から搬送用空気と共に供給された微粉炭を燃料として燃焼させるバーナ6と、供給量調整装置3a,3bを制御する演算器9と、を有している。ボイラ7は、微粉炭を燃焼させて熱を回収する。
次に、上記の構成のボイラに利用される固体燃料としての原料炭の改質方法について説明する。
次に、灰中融液割合と灰付着率との関係について説明する。図3は、特にボイラ内で灰付着が起こりやすい温度である1573Kにおける、様々な混合炭の灰中融液割合と灰付着率との関係を示している。図3より、火炉内の雰囲気温度及び雰囲気ガス組成において、灰中融液割合が60wt%を越えると、灰付着率が急激に増大することがわかる。言い換えれば、灰中融液割合を60wt%以下にすることで、灰付着率を下げることができる。本実施形態において、灰付着率が低くなる灰中融液割合の値である基準値は、50~60wt%である。図1において、演算器9は、灰中融液割合が決定された基準値以下となるような灰組成になるように、熱力学平衡計算によって各固体燃料の混合比率を決定している。
次に、温度と灰中融液割合との関係、および、温度と灰の収縮率との関係について説明する。図4は、上記の方法で灰中融液割合を算出した計算結果である。図5は、灰サンプルの温度を変化させながら、荷重を加えてその物質の変形を測定する熱機械分析(TMA,Thermo Mechanical Analysis)により灰の収縮率を求めた結果である。灰サンプルとして、MgOが添加されない低品位炭(ここでは、改質褐炭の灰)(a)と、MgOが25wt%添加された改質褐炭の灰(b)と、が用いられる。ここで、灰の収縮率が高いほど、灰サンプルが固体から融液(溶融スラグ)になることを意味しており、温度が高くなるほど灰中融液割合および灰の収縮率は高くなる。
図6は、様々な無機化合物を石炭灰に添加したときの無機化合物の添加割合とスラグ増加率との関係を示す計算結果であり、特にボイラ内で灰付着が起こりやすい温度である1573Kにおけるスラグ増加率を示している。ここで、「スラグ増加率」は、無機化合物添加前後のスラグ生成量の比であり、次式で表わされる。
図7は、石炭灰に対するマグネシウム系化合物およびアルミニウム系化合物の添加割合と灰中融液割合との関係を示す。図7は、特にボイラ内で灰付着が起こりやすい温度である1573Kにおいて、MgOおよびAl2O3の添加割合をそれぞれ変化させたときの灰中融液割合(計算値)を示している。図3に示されるように、灰中融液割合が60wt%以上になると、灰付着率が劇的に増大する。ここで、図7に示されるように、灰中融液割合が60wt%以下になるMgOの添加割合は、15wt%以上である。本実施形態において、図2における混合部11内の混合物に添加されるMgOの添加割合は、固体燃料の無機成分(石炭灰)に対して、25wt%以上50wt%以下である。
図8は、添加物中のMgO含有率と灰中融液割合との関係を示している。灰中融液割合が60wt%以下になるとき、MgO含有率は70wt%以上である。よって、添加物がMgOを70wt%以上、好ましくは90wt%以上含有していれば、灰中融液割合が60wt%以下になり、灰付着率を下げることができる。本実施形態においては、MgOを70wt%以上、好ましくは90wt%以上含有する添加物を、図2における混合部11内の混合物に添加して、原料スラリーを形成している。
図9は、石炭灰に対して25wt%の割合で添加される添加物中のMgO含有率と、灰中融液割合および灰付着量と、の関係を示している。添加物中のMgO含有率が70wt%以上であれば、特にボイラ内で灰付着が起こりやすい温度である1573Kにおいて、灰中融液割合が60wt%以下になる。また、図9から、添加物中のMgO含有率が高くなるほど、灰付着量が低減することがわかる。よって、添加物中のMgO含有率を70wt%以上、好ましくは90wt%以上にすることで、ボイラへの灰付着を抑制することができる。本実施形態においては、MgOを70wt%以上、好ましくは90wt%以上含有する添加物を、図2における混合部11内の混合物に添加することによって、原料スラリーが形成される。
図10は、本実施形態で用いた石炭灰の粒子径分布を示している。本実施形態で用いた石炭灰の平均粒子径(積算重量が50%時の粒子径(メディアン径))は、6.8μmである。これに対して、本実施形態において、図2における混合部11内の混合物に添加されるMgOの平均粒径は、5μm以下、好ましくは0.2μm程度である。
次に、MgOの灰付着抑制効果を実証するために、石炭燃焼炉(炉内径400mm、炉内有効高さ3650mm)を用いて、石炭および加熱用都市ガスの投入熱量が149kWで一定である条件下で、灰付着特性試験を行なった。ここでは、石炭灰に対してそれぞれ25wt%、50wt%のMgO試料を添加した。石炭に添加するMgO試料としては、平均粒径が10μm、5μm、0.2μmの3種類の試料が用いられる。石炭は微粉炭であり、燃焼空気とともに炉頂に設けたバーナで燃焼される。このとき、バーナの下方においてガス雰囲気温度が1573Kになる炉内に灰付着プローブが挿入され、100分間保持される。そして、灰付着プローブの表面に付着する灰の付着量(重量)が測定される。図11はその結果を示す。
以上のように、灰の収縮率が高いほど灰は固体から融液になるが、原料炭と原料油との混合物にマグネシウム系化合物を添加すると、灰の収縮率が低下して灰が融液になりにくくなり、製品炭における灰中融液割合が低下する。
次に、本発明の第2実施形態について説明する。第2実施形態が第1実施形態と異なる点は、原料炭を改質して製品炭とする際に、原料炭と原料油との混合物に、アルミニウム系化合物(無機化合物)であるAl2O3を含有する添加物を添加する点である。Al2O3の平均粒径は5μm以下、好ましくは0.2μm程度であり、固体燃料の無機成分に対するAl2O3の添加割合は、25wt%以上50wt%以下である。なお、アルミニウム系化合物は、Al2O3のような酸化物に限定されず、炭酸化物や水酸化物であってもよい。
図12は、Al2O3を添加すると共に、上記の方法で灰中融液割合を算出した計算結果である。図13は、灰サンプルの温度を変化させながら、荷重を加えてその物質の変形を測定する熱機械分析(TMA)により、灰の収縮率を求めた結果である。灰サンプルとして、Al2O3が添加されない低品位炭(ここでは改質褐炭の灰)(c)と、Al2O3が25wt%添加された改質褐炭の灰(d)と、Al2O3が50wt%添加された改質褐炭の灰(e)と、が用いられる。ここで、灰の収縮率が高いほど灰サンプルは固体から融液になり、温度が高くなるほど灰中融液割合および灰の収縮率は高くなる。
図6は、様々な無機化合物を石炭灰に添加したときの無機化合物の添加割合とスラグ増加率との関係を示す計算結果である。図6は、特にボイラ内で灰付着が起こりやすい温度である1573Kにおけるスラグ増加率を示している。一般に、石炭灰における無機化合物の添加割合が増えるほど、石炭中に含まれる無機物質が増加するため、スラグ増加率も高くなる。しかし、図6に示されるように、MgOおよびAl2O3の添加割合が増加するほど、灰中融液割合が低下して、スラグ増加率が低下している。したがって、これらMgOおよびAl2O3は、添加割合が増加するほど灰付着抑制効果がある無機化合物と言える。
図7は、石炭灰に対するマグネシウム系化合物およびアルミニウム系化合物の添加割合と灰中融液割合との関係を示す。図7は、特にボイラ内で灰付着が起こりやすい温度である1573Kにおいて、MgOおよびAl2O3の添加割合を変化させたときの灰中融液割合(計算値)を示している。ここで、図3に示されるように、灰中融液割合が60wt%以上になると、灰付着率が劇的に増大するが、図7に示されるように、灰中融液割合が60wt%以下になるAl2O3の添加割合は、25wt%以上である。本実施形態において、図2における混合部11内の混合物に添加されるAl2O3の添加割合は、固体燃料の無機成分(石炭灰)に対して、25wt%以上50wt%以下である。
また、灰付着特性試験の試験結果を示す図11から、灰よりも小さな平均粒径の無機化合物を添加すると、灰付着抑制効果があることがわかる。また、添加する無機化合物の平均粒径が細かいほど、灰付着抑制効果が大きいことがわかる。本実施形態において、図2における混合部11内の混合物に添加されるAl2O3の平均粒径は、石炭灰の平均粒子径である6.8μmよりも小さい5μm以下、好ましくは0.2μm程度である。
以上のように、灰の収縮率が高いほど灰は固体から融液(溶融スラグ)になるが、原料炭と原料油との混合物にアルミニウム系化合物を添加すると、灰の収縮率が低下して灰が融液になりにくくなる。これにより、製品炭における灰中融液割合(スラグ割合)が低下する。
以上、本発明の実施形態を説明したが、上記実施形態は、具体例の例示に過ぎず、特に本発明を限定するものではなく、具体的構成などは特許請求の範囲に記載した限りにおいて適宜設計変更可能である。また、発明の実施の形態に記載された、作用及び効果は、本発明から生じる最も好適な作用及び効果を列挙したに過ぎず、本発明による作用及び効果は、本発明の実施の形態に記載されたものに限定されるものではない。原料スラリーは、マグネシウム系加合物とアルミニウム系加合物の両方を含有する添加物を添加して形成されてもよい。
3a,3b 供給量調整装置
4 混合機
5 粉砕機
6 バーナ
7 ボイラ
9 演算器
11 混合部
12 加熱部
13 固液分離部
14 成形部
Claims (5)
- 原料炭と原料油とを混合し、マグネシウム系化合物およびアルミニウム系化合物の少なくとも一方を含有する添加物を添加して原料スラリーを形成するステップと、
前記原料スラリーを加熱するステップと、
加熱後の前記原料スラリーを固液分離するステップと、
固液分離された前記原料スラリーのうち、固体分を乾燥して製品炭とするステップと、
を有することを特徴とする固体燃料の改質方法。 - 前記マグネシウム系化合物および前記アルミニウム系化合物の少なくとも一方の添加割合は、前記製品炭における灰中融液割合が60重量%以下になるように決定されることを特徴とする請求項1に記載の固体燃料の改質方法。
- 前記マグネシウム系化合物および前記アルミニウム系化合物の少なくとも一方の添加割合が、石炭灰に対して25重量%以上50重量%以下であることを特徴とする請求項1に記載の固体燃料の改質方法。
- 前記マグネシウム系化合物および前記アルミニウム系化合物の少なくとも一方の平均粒径が5μm以下であることを特徴とする請求項1に記載の固体燃料の改質方法。
- 前記添加物が、前記マグネシウム系化合物を70重量%以上含有していることを特徴とする請求項1に記載の固体燃料の改質方法。
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