JP2005114261A - Combustion method of biomass-based fuel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a combustion method of biomass-based fuel, capable of performing a combustion while suppressing generation of NOx more than in pulverized coal firing of coal, burning biomass at a high mixed-fuel ratio, and suppressing corrosion of a heat transfer tube or the like by a halogen-containing gas or generation of an unburnt component or dioxins. <P>SOLUTION: A pulverized powder obtained by pulverizing at least one kind of carbonates of biomass selected from ligneous biomass, a plant-based residue generated in a plantation and the like with a pulverized coal such as coal are mixed and burnt, whereby NOx contained in combustion exhaust gas is reduced. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for burning biomass fuel, and more particularly, a biomass fuel that can suppress NOx generation when biomass fuel is mixed and burned with coal using a thermal power generation facility and can reduce environmental burden. It relates to a combustion method.

In order to prevent global warming, suppression of atmospheric emission of carbon dioxide (CO ₂ ), which is a greenhouse gas, is demanded. In particular, a large amount of combustion exhaust gas such as coal, petroleum, and LNG is generated in a thermal power plant, but these exhaust gases contain 1 to 40 vol% of CO ₂ and further contain NOx and SOx. Reduction of exhaust gas components is essential.

However, if biomass such as plants, agricultural waste, waste wood, livestock excrement, and sewage sludge is used as an energy source, it will help prevent global warming. For example, even if the CO ₂ burning plants were released into the atmosphere, the CO ₂ is for those taken from the atmosphere at the plant growth process, CO ₂ concentration in the atmosphere does not change. Therefore, research on various types of biomass energy such as solid waste such as municipal waste and wood has been actively conducted. However, since biomass fuel is supplied in different seasons, mixed combustion with coal (hereinafter sometimes referred to as “mixed combustion”) is considered desirable to obtain a certain amount of power generation. . However, since some biomass contains a large amount of moisture, in the case where biomass and coal are actually co-fired, 5 to 10% is the limit in order to secure a calorific value.

  Regarding co-firing with coal, Japanese Patent Laid-Open No. 11-108324 discloses that solid waste fuel (RDF) is pulverized and put into a furnace such as a coal fired boiler and floated together with main fuel such as pulverized coal. A waste co-firing method for combusting is proposed (see Patent Document 1). In this method, waste is introduced into the boiler furnace from a port different from the main fuel burner, thereby avoiding an air shortage caused by combustible waste burning prior to the main fuel. In addition, the combustibility of the main fuel is prevented from being reduced to prevent the generation of dioxins.

  Japanese Patent Application Laid-Open No. 2002-349821 discloses a combustion apparatus suitable for mixed combustion of solid fuel containing chlorine-based compounds, such as solid waste such as municipal waste, and biomass such as wood and wood scrap, and coal. And a combustion method has been proposed, in which a solid fuel comprising at least one of solid waste and biomass is fluidized bed combusted, and pulverized coal is combusted using the combustion gas of the fluidized bed combustion step. It has a powder combustion process (refer patent document 2).

  However, in the former, when fluidized bed combustion is used for co-firing with coal in order to desalinate chlorine compounds contained in solid waste, the temperature of the combustion gas is as low as about 800 ° C., so that the thermal efficiency cannot be increased. It solves the problem. In the latter, when solid fuel and coal are co-fired by the powder combustion (floating combustion) method used in normal coal combustion, the combustion gas temperature can be raised to 1200 ° C or higher, so the thermal efficiency increases, but it is included in solid waste and biomass In order to solve the problem of corroding the heat transfer tube due to the halogen element being released from the halogenated substance into the gas, it also burns to suppress the generation of unburned components and dioxins due to a decrease in combustion temperature It is an improvement of the method. Only wood chips, wood, fir shells, etc. are disclosed as biomass.

  Japanese Patent Laid-Open No. 2002-243108 discloses that even when biomass fuel is burned with coal at a mixed combustion rate of 40% or more, stable combustion with suppressed generation of CO and NOx can be maintained. There has been proposed a combustion apparatus equipped with a burner that reduces ash adhesion to the surface (see Patent Document 3). However, the biomass fuel used has a low volatile content of 70% or more, a calorific value as low as about 4000 kcal, and a moisture content of 10% or more. To increase.

JP-A-11-108324 (paragraph numbers 0018 to 0019, etc.) JP 2002-349821 A (paragraph number 0020, etc.) JP-A-2002-243108 (paragraph number 0005, etc.)

  The present invention has been made in view of the above-described conventional problems, and combustion capable of suppressing generation of NOx is possible as compared with the case where coal is pulverized, and biomass can be burned at a high co-firing ratio. Further, it is an object of the present invention to provide a method for burning a biomass fuel that can suppress corrosion of a heat transfer tube or the like by a halogen-containing gas, generation of unburned components, and dioxins.

  In order to solve the above-mentioned problems, the present inventors diligently studied. As a result, the calorific value is high by mixing the carbonized biomass of biomass with pulverized coal under the conventional pulverized coal-fired condition, compared with the case where each is calcined. It has been found that NOx is reduced, and the present invention has been completed.

  That is, the biomass fuel combustion method of the present invention is characterized in that biomass carbide and coal are mixed and burned.

  Further, in the biomass fuel combustion method of the present invention, the biomass carbide and coal are preferably finely pulverized, and by pulverizing the biomass fuel, a thermal power generation facility such as a conventional pulverized coal fired boiler It becomes possible to burn the fuel using the.

  Further, in the biomass fuel combustion method of the present invention, the biomass carbide and coal may be fed into the combustion furnace from the same burner.

  In the biomass fuel combustion method of the present invention, the biomass is preferably at least one selected from woody biomass and plant residue.

  In general, NOx generation during combustion includes fuel NOx due to nitrogen contained in fuel and thermal NOx due to nitrogen contained in combustion air and furnace temperature. Therefore, if the nitrogen content of the biomass carbide used as fuel is less than that of coal, the higher the biomass co-firing ratio, the less nitrogen content in the fuel and the fuel NOx will be reduced, but the biomass carbide according to the present invention was co-fired. In this case, even when the nitrogen content of the carbide of biomass is larger than that of coal, the amount of NOx generated is reduced by co-firing as compared with the case where each of them is exclusively fired. Although the cause of NOx reduction due to co-firing of biomass carbide and coal is not clear, it is presumed to be the effect of thermal NOx, not the effect of fuel NOx. In other words, when two types of fuels with different combustion states are put into the furnace at the same time, the temperature distribution occurs in the furnace because the flames are burned differently, and pulverized coal with a lower calorific value than that of biomass is reduced. Can be burned in a state. In combustion in the reduced state, nitrogen oxides are reduced to nitrogen, so the amount of NOx at the outlet of the combustion apparatus is considered to be reduced.

As described above, according to the biomass fuel combustion method of the present invention, it is possible to significantly reduce CO ₂ emissions compared to coal-fired, and it is possible to reduce NOx, thereby reducing the environmental load. Is done. Moreover, since the calorific value of the biomass of the biomass is high, the combustion efficiency can be further improved as compared with the coal-fired combustion, and the combustion efficiency can be increased even when coal having a high fuel ratio is used. Furthermore, corrosion of heat transfer tubes and the like due to halogen-containing gas generated by combustion of biomass fuel and generation of dioxins can be prevented.

  Moreover, according to the biomass fuel combustion method of the present invention, biomass can be burned in an existing pulverized coal combustion furnace (coal-fired boiler), so that the addition of equipment can be minimized and economically achieved. Also excellent.

  The biomass fuel combustion method of the present invention is a method in which biomass carbide and coal are mixed and burned, and the biomass carbide is obtained by carbonization of biomass.

  The biomass used in the present invention includes biomass from grass such as rice straw, straw, bagasse; wood, thinned wood, felled trees, pruned branches, sawdust, bark, chips, mill ends, driftwood, bamboo, firewood, Woody biomass such as woody building waste; Biomass from cellulose products such as waste paper; Plant waste such as plants and fir shells; And so on.

  The carbonization treatment of biomass may be performed according to a conventionally known carbonization method or a method equivalent thereto, and a conventionally known biomass carbide such as charcoal can also be used. Carbonization is broadly divided into internal combustion and external combustion. Internal combustion burns part of the raw material in the furnace and maintains the carbonization temperature by the heat. Combustion of tar and combustible gas generated during carbonization. This includes the self-combustion type. The external combustion type is an indirect type in which the outside of the furnace is heated with a kerosene burner or the like. Carbonization is usually performed in an inert gas that limits or shuts off the air supply.

  A conventionally known carbonization furnace may be used for the carbonization treatment. Carbonization furnaces are broadly divided into batch and continuous types. The batch type is an open type such as a simple type or a flat furnace type, the closed type is a charcoal kiln type, a trolley type, or a stirring type. There are rotary types such as a vertical type, vertical types such as a fluidized bed type and a multistage stirring type, and horizontal types such as a stirring type and a screw type.

  The carbonization treatment conditions are not particularly limited because they vary depending on the type of biomass, the type of carbonization furnace, and the like. In the case of wood, carbonization is generally performed at 400 to 500 ° C. to obtain carbonized carbon, open hearth coal, etc., black carbon is obtained by carbonizing at 600 to 700 ° C., and white coal is carbonized at about 1000 ° C. (Ubmegashi white charcoal is called “Bincho charcoal”). In the case of biomass other than wood, carbides carbonized at about 400 to 600 ° C. are usually used. When the carbonization temperature is high, the degree of carbonization proceeds, but the yield of the carbide is low, or it is not preferable when using the carbide as a fuel, such as being difficult to burn because the volatile matter is removed. The range of 400-600 ° C is preferred.

  Furthermore, in addition to the carbonization method described above, biomass carbide obtained by hydrothermal liquefaction in which biomass is thermally decomposed in hot water at high temperature and high pressure can be used. Specifically, biomass is reformed in the presence of water at a pressure equal to or higher than the saturated vapor pressure to reform the biomass, and the reformed reactant obtained in the reforming process is converted into a solid component and a liquid component. The thing obtained by the process to isolate | separate etc. can be mentioned. In this case, the amount of water added to the biomass raw material varies depending on the amount of water originally contained in the cellulosic biomass raw material, but is preferably about 1 to 20 times the mass (dry base) of the biomass raw material, More preferably, it is about 3 to 15 times.

  The treatment temperature in the reforming step is preferably 250 to 380 ° C, and more preferably 270 to 350 ° C. The operating pressure is preferably 0.5 to 5 MPa higher than the saturated vapor pressure of water, and more preferably 1 to 3 MPa higher. The treatment time in the reforming step is not particularly limited, but is preferably 5 minutes to 120 minutes, and more preferably 10 minutes to 60 minutes. The processing time is a trade-off with the processing time. If the processing time is high, the processing time may be short, and if the processing temperature is low, the processing time may be long. The reforming step may be a batch process using an autoclave or the like, or may be a continuous reaction apparatus composed of one or two or more reaction zones.

  The reforming reaction product obtained by the reforming step is separated into a solid component and a liquid component in the separation step. In the separation step, the solid component is separated from the liquid component, and when the amount of water is large, it is heat-dried as necessary. By the separation step, biomass carbide is obtained as a solid component.

  Each of the above-mentioned biomass carbides may be used alone or in combination of two or more. Among these, wood, thinned wood, felled trees, pruned branches, sawdust, bark, chips, edgewood, driftwood, bamboo, firewood, wood construction waste, etc. At least one kind of biomass carbide selected from carbides of plant-based residues generated in plantations, such as carbonized carbides of plant biomass and palm shells of oil palm (raw material of palm oil), is preferably used.

  When co-firing biomass carbides, it is preferable to use a finely pulverized one to increase combustion efficiency. As the finely pulverized product, one having a passing rate of 200 mesh (74 μm) sieve is preferably 70 to 80%.

  In the present invention, coal such as anthracite, bituminous coal, subbituminous coal, lignite, etc. is used as fuel to be co-fired with biomass carbide. What is used as carbonaceous energy sources, such as obtained carbon black, can also be used. Coal or the like may be used alone, but two or more kinds may be appropriately combined. As the fuel such as coal, it is preferable to use pulverized coal obtained by fine pulverization as in the case of a conventional pulverized coal fuel furnace. As the pulverized coal, those having a 200 mesh (74 μm) sieve passage ratio of 70 to 80% are preferable.

In the present invention, the co-firing ratio of biomass carbide (A) and coal (B) is not limited, but is preferably (A) / (B) = 1/99/50/50, more preferably by mass ratio. It is good to set it as 10 / 90-30 / 70. When the ratio of the carbide of biomass is too low, the CO ₂ reduction effect and the NOx reduction effect are insufficient. On the other hand, when the ratio of the carbide of biomass is too high, it becomes difficult to obtain a certain amount of power generation depending on the procurement status of the biomass, and it becomes difficult to obtain an NOx reduction effect commensurate with the amount of addition.

  In the present invention, when the finely pulverized biomass carbide and pulverized coal are co-fired, the method of charging into the combustion furnace is not particularly limited, and both may be charged into the combustion furnace through separate charging ports. May be charged into the combustion furnace from the same charging port. Or you may mix both and throw in in a combustion furnace. When both are introduced into the combustion furnace from the same charging port, it is assumed that it becomes easier to create a temperature distribution of the flame by injecting different types of fuel at once, and therefore it is preferable to input from the same burner into the combustion furnace. . In the case of charging from the same burner, the finely pulverized biomass carbide and pulverized coal may be supplied separately to the same burner or may be supplied in advance. Alternatively, biomass carbide and coal may be mixed at the time of pulverization to prepare a mixture of biomass carbide fine powder and pulverized coal.

  When preparing a mixture of carbonized carbide (A) and coal (B) (mixed coal), the mixing ratio is not limited. However, for the same reason as described above, the mixing ratio is preferably (A ) / (B) = 1/99/50/50, more preferably 10/90 to 30/70. The calorific value of the mixed coal is desirably as high as possible, but the calorific value of the solid component is preferably 6,000 kcal / kg or more, and more preferably 6,400 kcal / kg or more.

  In the present invention, the combustion furnace to be used is not particularly limited, but it is possible to use a pulverized coal combustion furnace (coal-fired boiler) because existing facilities can be used and the addition of facilities can be minimized. preferable. The combustion conditions are not particularly limited, and may be performed according to normal pulverized coal combustion conditions. As a combustion temperature, 1200-1500 degreeC is preferable, and it becomes possible further to aim at reduction of NOx, improving combustion efficiency by making it co-fire in the said temperature range.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to only the following Examples.

(Example 1)
The fine powder (200 mesh under) obtained by finely pulverizing the carbides of various biomass shown in Table 1 and the pulverized coal (200 mesh under) obtained by finely pulverizing coal (A charcoal) were mixed at a ratio shown in Table 2. A fuel was prepared. This fuel is filled in the fuel hopper 4 shown in FIG. 1, and is sent to the vertical combustion furnace drop tube furnace (Drop Tube Furnace) 6 together with the primary air via the fuel supply machine 5, and from the combustion burner (pulverized coal burner) 7. It was injected into the combustion furnace. At the same time, combustion air that has been pressurized by the pushing fan 1 and heated through the air preheater 2a and the air preheater 2b is introduced into the burner and the combustion furnace via the air lines 3a and 3b, and the combustion temperature is about 1300. The fuel was burned at ˜1350 ° C. The exhaust gas at the combustion furnace outlet 8 is sampled, and the O ₂ , NOx, SO ₂ , CO, CO _2, and CH ₄ concentrations in the exhaust gas are measured with an exhaust gas analyzer (NSA-308, manufactured by Shimadzu Corporation, measurement principle: non-dispersive infrared) Absorption method). On the other hand, the combustion exhaust gas was passed through the cyclone 11 and the bag filter 12 while being sucked by the suction fan 13 through the exhaust gas line 10, treated with the water scrubber 14, and then discharged from the chimney 15 into the atmosphere.

  As is clear from Table 1, the biomass carbide according to the present invention had a large fuel ratio (fixed carbon / volatile content) and a calorific value sufficient for use as fuel. Moreover, although nitrogen content differed with the kind of biomass, the thing with little sulfur content was obtained compared with coal.

And mixing ratio of the carbide and coal biomass, the measurement results of the NOx concentration and SO ₂ concentration in the combustion exhaust gas when burned Each mixture fuel shown in Table 2, Table 3.

As is clear from Table 2, the amount of NOx in the exhaust gas increases as the amount of nitrogen contained in the fuel increases. However, when coal and biomass carbides are co-fired, NOx is reduced as compared with the case where each is co-fired. You can see that Further, as apparent from Table 3, it can be seen that SO ₂ is reduced as compared with the case where coal is exclusively burned because the sulfur content of the biomass carbide is small.

(Example 2)
Fine powder (200 mesh under) obtained by finely pulverizing sludge carbide shown in Table 4 and pulverized coal (200 mesh under) obtained by finely pulverizing coal (B charcoal and C charcoal) are mixed at a ratio shown in Table 5. A fuel was prepared. Using this fuel, a combustion test was conducted in the same manner as in Example 1, and the composition of the exhaust gas at the outlet of the combustion furnace was analyzed. The measurement results of the NOx concentration and SO ₂ concentration in flue gas shown in Table 5.

  As is clear from Table 5, it can be seen that when coal and biomass carbides are co-fired, NOx is significantly reduced compared to when coal is exclusively fired.

(Example 3)
Fine powder (200 mesh under) obtained by finely pulverizing sludge carbide shown in Table 4 and pulverized coal (200 mesh under) obtained by finely pulverizing coal (B charcoal and C charcoal) were mixed at a ratio shown in Table 6. A fuel was prepared. Using this fuel, a combustion test was conducted according to Example 1, and the composition of the exhaust gas at the outlet of the combustion furnace was analyzed. In this example, a combustion test was performed by blowing a part of combustion air as tertiary air (Over Fire Air) to the subsequent stage of the flame. The measurement results of the NOx concentration and SO ₂ concentration in flue gas shown in Table 6.

The OFA (Over Fire Air) factor is obtained by the equation (1).
OFA blowing position = (OFA blowing position / effective furnace length) x (OFA air volume / total air volume) x 100 (1)

  As is apparent from Table 6, it can be seen that when coal and biomass carbides are co-fired, NOx is greatly reduced compared to when coal is exclusively fired.

BRIEF DESCRIPTION OF THE DRAWINGS It is a whole schematic block diagram which shows an example of the form which implements this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Push-in fan 2a, 2b ... Air preheater 3a, 3b ... Air line 4 ... Fuel hopper 5 ... Fuel supply machine 6 ... Combustion furnace 7 ... Burner 8 ... Combustion furnace exit 10 ... Exhaust gas line 11 ... Cyclone 12 ... Bag filter 13 ... Suction fan 14 ... Water scrubber

Claims (4)

A biomass-based fuel combustion method comprising mixing and burning biomass carbide and coal. The method for burning biomass fuel according to claim 1, wherein finely pulverized biomass carbide and coal are mixed and burned. The biomass fuel combustion method according to claim 1 or 2, wherein the biomass carbide and coal are charged into the combustion furnace from the same burner. The method for burning biomass fuel according to any one of claims 1 to 3, wherein the biomass is at least one selected from woody biomass and plant residue.

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