JP2023092562A - Cement clinker, method of producing cement clinker, and cement composition - Google Patents

Abstract

To provide a cement composition and the like produced using biomass ash as a part of raw materials, which have strength development properties equal to or higher than those of ordinary Portland cement.SOLUTION: A cement clinker of this invention has a belite content of 28-45 mass%, a pore phase content of 3-25 mass%, and an alkali content of 0.65-2.5% mass%. A method for producing the cement clinker includes burning a cement clinker raw material that partially contains a raw material with a biomass ash replacement ratio of 25% or more to coal ash. A cement composition of this invention comprises at least 1 to 6 pts.mass of gypsum in SO3 equivalent based on 100 pts.mass of the cement clinker.SELECTED DRAWING: None

Description

Application for application of Article 30, Paragraph 2 of the Patent Act (1) The Cement Association of Japan, 75th Cement Technical Conference Abstract 2021, pp. 110-111, date of issue: April 30, 2021

TECHNICAL FIELD The present invention relates to a cement clinker manufactured using wastes containing a large amount of alkali metals as a raw material, a method for manufacturing the cement clinker, and a cement composition manufactured using the cement clinker.

Coal ash, which is obtained by burning coal in coal-fired power plants, has been used as a clay substitute in the cement industry for many years because its chemical composition is similar to clay, which is the raw material of cement. However, as a countermeasure against global warming, which is becoming more serious year by year, in recent years, coal-fired power plants, which emit a large amount of carbon dioxide, have decreased their power generation ratio and reduced the amount of coal ash produced. In addition, carbon neutrality is being advocated in Japan to reduce greenhouse gas emissions to zero as a whole, and it is believed that biomass power generation will increase and the amount of biomass ash generated will increase with the aim of realizing a decarbonized society.
However, as shown in Table 3 below, biomass ash has a high alkali metal content of about three times that of coal ash. In addition to this, there is a concern that the long-term strength of cement with an age of 28 days will decrease.
For example, Non-Patent Document 1 describes the compressive strength of mixed cement mortar in which cement and wood ash (unburned ash) are substituted at various ratios. As can be seen from the description, the higher the substitution rate of biomass ash, the smaller the strength ratio (activity index) of mixed cement mortar/base cement mortar, so biomass ash reduces the strength of mortar. In addition to biomass ash, alternative raw materials for coal ash include construction soil, volcanic ash and other volcanic materials, sewage sludge and its incinerated ash, and purified water sludge and its incinerated ash. High metal content.
In addition, Non-Patent Documents 2 to 4 can be cited as documents showing the high content of alkali metals in woody biomass ash and documents related to the properties of mortar containing woody biomass ash.

Sagawa et al., “Application of woody biomass incineration ash to cement mixture”, 70th Cement Technology Conference Abstract 2016, pp100-101 Takahashi et al., “Safety evaluation and effective use of woody biomass incineration ash”, 19th Research Report Meeting of Japan Society of Waste Management 2008, pp65-67 Sato et al., “Fundamental research on safety related to recycling of woody biomass incineration ash”, 29th Annual Meeting of the Japan Society of Material Cycles and Waste Management 2018, pp219-220 Maekawa et al., “Fundamental research on various characteristics of hardened mortar mixed with woody biomass incineration ash”, 29th Annual Meeting of the Japan Society of Material Cycles and Waste Management 2018, pp209-210

Accordingly, the present invention provides a cement clinker manufactured using biomass ash as a part of the raw material, and a cement composition containing the cement clinker, which has a strength development property equal to or higher than that of ordinary Portland cement. intended to provide

MEANS TO SOLVE THE PROBLEM As a result of earnestly examining in order to achieve the said subject, this inventor discovered that the cement clinker etc. which have the following structures can achieve the said subject, and completed this invention.

[1] A cement clinker having a belite content of 28 to 45% by mass, an interstitial phase content of 3 to 25% by mass, and an alkali metal content of 0.65 to 2.5% by mass.
Here, the interstitial phase content is the total content of aluminate phase and ferrite phase in cement clinker. The alkali metal content (R ₂ O) is the content of equivalent Na ₂ O calculated using the following formula (1) based on the content of Na ₂ O and K ₂ O in the cement clinker. .
R ₂ O=Na ₂ O+0.658×K ₂ O (1)
However, the unit of the chemical formula in formula (1) is % by mass.
[2] The cement clinker according to [1] above, which has a silicic acid ratio (SM) of 2.7 to 15.0.
Incidentally, the silicic acid ratio is calculated using the following formula (2).
_SM = _SiO2 /( _Al2O3 + _Fe2O3 ) ( ₂ )
However, the unit of the chemical formula in formula (2) is % by mass.
[3] Cement clinker, wherein the cement clinker according to [1] or [2] is produced by calcining a cement clinker raw material that partially contains a raw material having a biomass ash replacement rate for coal ash of 25% or more. manufacturing method.
Here, the replacement ratio of biomass ash to coal ash of 25% or more means that 25 parts by mass or more of coal ash out of 100 parts by mass of coal ash is replaced with 25 parts by mass or more of biomass ash. In the replaced state, "the replacement rate of biomass ash with respect to coal ash is 25% or more" is synonymous with "the total of coal ash and biomass ash is 100% by mass, and the content of biomass ash is 25% by mass or more". is.
[4] The method for producing cement clinker according to [3] above, wherein the biomass ash has an alkali metal content of 2.5% by mass or more.
[5] A cement composition containing at least 1 to 6 parts by mass of gypsum in terms of _SO3 per 100 parts by mass of the cement clinker described in [1] or [2] above.
[6] The cement composition according to [5] above, which further contains 0.001 to 0.1 parts by mass of alkanolamine with respect to 100 parts by mass of the cement clinker according to [1] or [2] above.
[7] The cement composition according to [5] or [6] above, which has a Blaine specific surface area of 3000 to 5000 cm ² /g.
[8] 0 to 10 parts by mass of one or more selected from limestone, fly ash, and blast furnace slag in addition to 100 parts by mass of the cement clinker according to [1] or [2], [5] to [5] to [ 7], the cement composition according to any one of the above.

A cement composition produced using the cement clinker of the present invention has a strength development property equal to or greater than that of ordinary Portland cement, particularly a long-term strength development property. Therefore, the present invention can utilize a large amount of biomass ash in the production of cement.

The present invention, as described above, is a cement clinker or the like having a specific range of belite content, interstitial phase content, and alkali metal content.
Hereinafter, the present invention will be described in detail by dividing into a cement clinker, a method for producing a cement clinker, a cement composition, and the like.

1. Cement Clinker The cement clinker of the present invention is a cement having a belite content of 28 to 45% by mass, an interstitial phase content of 3 to 25% by mass, and an alkali metal content of 0.65 to 2.5% by mass. It is clinker. When the belite content, the interstitial phase content, and the alkali metal content are within the above ranges, the cement composition produced using the cement clinker exhibits high strength development, particularly long-term strength development.

The belite content is preferably 30 to 43% by mass, more preferably 33 to 41% by mass, and still more preferably 36 to 40% by mass. Also, the interstitial phase content is preferably 4 to 23% by mass, more preferably 10 to 21% by mass, still more preferably 13 to 20% by mass. Also, the alkali metal content is preferably 0.76 to 2.2% by mass, more preferably 0.85 to 2.0% by mass, still more preferably 1.0 to 1.5% by mass.

Also, the silicic acid ratio (SM) of the cement clinker of the present invention is preferably 2.7 to 15.0. When the silicic acid ratio is in the range of 2.7 to 15.0, the cement composition containing the cement clinker has high long-term strength development. The silicic acid ratio is more preferably 2.8 to 10.0, still more preferably 2.9 to 5.0, and most preferably 3.0 to 3.5.

The cement clinker of the present invention preferably has an iron fraction (IM) of 1.5 to 2.5 and an Al ₂ O ₃ content of 1.5 to 6.0% by mass.
Incidentally, the iron content is calculated using the following formula (3).
IM=Al ₂ O ₃ /Fe ₂ O ₃ (3)
However, the unit of the chemical formula in formula (3) is % by mass.
In addition, the content of free lime (free lime) in the cement clinker of the present invention is preferably 1.0% by mass or less, more preferably 0.2 to 0.8% by mass, in order to improve strength development. be.

2. Method for Producing Cement Clinker In the method for producing cement clinker of the present invention, preferably, a cement clinker raw material partially containing a raw material having a biomass ash replacement ratio for coal ash of 25% or more is calcined to produce the cement clinker. It is a method of manufacturing.
The raw material of the cement clinker used in the present invention is one or more selected from industrial waste, general waste, and construction soil as a _SiO2 source, and one selected from limestone, quicklime, slaked lime, and shells as a CaO source. The above can be used.
Here, in addition to coal ash, the industrial waste includes biomass ash, sewage sludge, purified water sludge, construction sludge, steelmaking sludge, boring waste soil, foundry sand, rock wool, waste glass, construction waste materials, ready-mixed concrete sludge, Concrete waste materials, blast furnace secondary ash, and the like can be mentioned. In addition, examples of the general waste include municipal refuse incineration ash, sewage sludge dry powder, shells, sewage sludge incineration ash, and volcanic ash. Further, examples of the construction-generated soil include soil generated from construction sites, construction sites, and the like, surplus soil, waste soil, and the like.
Among these raw materials, the cement clinker raw material used in the present invention preferably partially contains a mixed raw material of coal ash and biomass ash in which the replacement ratio of biomass ash to coal ash is 25% or more. is.
In addition, if it is difficult to prepare the mineral composition of the fired product within the above range using only the waste, natural raw materials such as calcium raw materials, silicon raw materials, aluminum raw materials, and iron raw materials may be supplemented. good. Here, calcium raw materials include limestone, quicklime, slaked lime, steelmaking slag, and the like, silicon raw materials include silica stone and clay, and aluminum raw materials include clay and the like, and iron raw materials include iron slag and An iron cake etc. are mentioned.

Cement clinker raw materials (prepared raw materials) are prepared based on the chemical compositions of the various raw materials and using the formulas (1) to (3) above so that the various raw materials have the desired chemical composition. In addition, in order to improve the mixability, the various raw materials may be pulverized and then blended.
In addition, in the cement clinker raw material, the higher the alkali metal content, the higher the belite content, based on the CaO/SiO ₂ molar ratio or the hydraulic modulus (HM). In addition, in the cement clinker raw material, the higher the alkali metal content, the higher the belite content, using the silicic acid ratio as a guideline. Depending on the alkali metal content, the cement clinker of the present invention can be obtained by reducing the hydraulic rate by about 0.05 to 0.1 and increasing the silicic acid rate by about 0.2 to 0.8 compared to ordinary Portland cement. can be obtained. The hydraulic ratio is preferably 1.9 to 2.3, more preferably 1.95 to 2.1, and the iron ratio is preferably 1.5 to 2.5 as described above.

For this reason, when biomass ash or construction soil is used as the SiO ₂ source, it is easy to obtain a cement clinker raw material with a high silicic acid content.
The silicic acid ratio of biomass ash and construction soil is preferably 3 to 20, more preferably 4 to 18, still more preferably 5 to 16, and the content of Al ₂ O ₃ is preferably 1 to 13. % by mass, more preferably 1.5 to 8% by mass, more preferably 2 to 5% by mass, and the alkali metal content is preferably 2 to 10% by mass, more preferably 3 to 8% by mass. be.

The biomass ash is not limited as long as it is biomass incineration ash, and examples thereof include incineration ash of plants and bamboo, and incineration ash of food residues. As the biomass ash, either mono-combustion ash obtained by burning biomass alone or co-combustion ash obtained by mixing and burning biomass and coal can be used. When the biomass ash is co-combustion ash, the biomass ash is preferably ash obtained by burning fuel having a biomass content of 50% by mass or more.
Moreover, the biomass ash is preferably palm shell ash obtained from a thermal power plant using palm shell as a part or all of the fuel. Palm kernel shells are a by-product of palm oil production and are primarily used in the natural biomass energy industry. Palm coconut shell is a yellow-brown fibrous substance with a low ash content, and its particle size is about 5 to 40 mm, and the calorific value is about 4000 Kcal/kg. In recent years, husks have been increasingly used as a fuel for biomass power generation.

Combustion furnaces for biomass power generation using palm shells as fuel include stoker and fluidized bed types. In the cement clinker production method of the present invention, biomass ash generated in a fluidized bed type circulating fluidized bed combustion furnace or a pressurized fluidized bed combustion furnace can be used.

As for the particle size of the biomass ash obtained from the fluidized bed combustion furnace, the median diameter (D50) is preferably 200 μm or less, more preferably 150 μm or less, still more preferably 90 μm or less. A laser diffraction/scattering particle size distribution analyzer can be used to measure the particle size of biomass ash. For example, using MW3300EXII manufactured by Microtrac Bell, ethanol is used as a dispersion medium, and measurement is performed after ultrasonic dispersion for 1 minute. do it. The D50 means the particle size at 50% cumulative volume-based particle size distribution.

Further, in the fluidized bed combustion furnace, sand containing quartz as a main component is charged as a fluidizing medium for incineration. Thus, biomass ash from such incinerators contains relatively coarse-grained melt-solidified or agglomerated glass- and sand-derived materials, and relatively fine-grained limestone-derived materials and volatilized alkali metal salts. Biomass ash may have a maximum chlorine content of 1% by mass, and generally has a higher chlorine content than coal ash.
Therefore, the chlorine content can be efficiently removed by extracting the coarse-grained fraction between the fine-grained mountain with a high chlorine content and the coarse-grained mountain with a low chlorine content in the biomass ash as a classification point. Furthermore, the coarse fraction of biomass ash also has the advantage of having a higher silicic acid content than the fine fraction.
From the viewpoint of chlorine removal, the classification point is preferably 20 μm to 100 μm, more preferably 30 μm to 90 μm, still more preferably 38 μm to 75 μm.

The device used for classifying the biomass ash is not particularly limited as long as it can classify the biomass ash at the μm-order classification point as described above. Type classifiers and the like can be mentioned, and cyclone air separators, vortex-type centrifugal classifiers, sieving devices, and the like are particularly preferable because of their high classification accuracy. In addition, when the classification is carried out by a wet method, chlorine dissolves in water, and even the fine particles contain almost no chlorine. In addition, the fluidized bed incinerator is equipped with a boiler, air preheater, equipment for collecting incinerated ash that has settled in the high-temperature gas flow path, equipment for collecting incinerated ash using a cyclone, equipment for collecting incinerated ash using a bag filter, etc. Sometimes. Since the particle sizes of the incinerated ash recovered by these recovery facilities are different, when these facilities are used for sorting and recovery, they can be used as a classifier instead.

Next, for reference, the particle size distribution and chemical composition of the classified biomass ash are shown in Tables 1 and 2, respectively. The biomass ash B was obtained as a sieve residue by sieving the biomass ash A (raw powder) through a sieve with an opening of 45 μm (spin air sieve: SAR-75/200 manufactured by Seishin Enterprise Co., Ltd.). In addition, the particle size distribution of the biomass ash before and after classification was measured using a laser diffraction particle size distribution analyzer (MT3300EX-II manufactured by Microtrack Bell).

Also, the biomass ash is preferably water-washed ash. As shown in Table 3 below, biomass ash contains more alkali metals, especially potassium and chloride, than coal ash, and most of the chlorine is present as water-soluble potassium chloride. can remove chlorine. If water washing is carried out in the present invention, it is not necessary to heat the biomass ash to remove the alkali metal, or add a chlorine source in the baking process to volatilize the alkali metal.

In the production method of the present invention, the cement clinker of the present invention is obtained by calcining the cement clinker raw material at a temperature of preferably 1000 to 1450°C, more preferably 1150 to 1400°C. Biomass ash has a high CaO content, so the amount of limestone used is less than Portland cement, and the increase in alkali metal and belite content reduces the firing temperature, so the amount of carbon dioxide emitted during production is low. .
In addition, when a cement clinker raw material having a high alkali metal content is charged from the front of a rotary kiln into a cement kiln or the like at a temperature of 1000 ° C. or higher and fired, the alkali metal is incorporated into the cement clinker, so the amount of alkali metal scattered. is reduced, which in turn reduces cyclone clogging and coating due to alkali metal salts.

3. Cement Composition The cement composition of the present invention is a composition containing at least 1 to 6 parts by mass of gypsum in terms of SO ₃ per 100 parts by mass of the cement clinker. If the amount of gypsum is less than 1 part by mass in terms of _SO3 , the fluidity of concrete, etc., produced using the cement composition may decrease, and the pot life may not be ensured. There is a risk of expansion due to the formation of ettringite.
The gypsum is not particularly limited, and may be one or more selected from natural gypsum, flue gas desulfurization gypsum, phosphate gypsum, titanium gypsum, hydrofluoric gypsum, and the like. The forms of gypsum include dihydrate gypsum, hemihydrate gypsum, and anhydrous gypsum.

In addition, the cement composition of the present invention further contains 0 to 10 parts by mass of one or more selected from limestone, fly ash, and blast furnace slag with respect to 100 parts by mass of the cement clinker in order to adjust strength and fluidity. It's okay. When the content is 10 parts by mass or less, the strength development of the cement composition can be maintained.

Furthermore, the cement composition of the present invention can further contain 0.001 to 0.1 part by mass of alkanolamine with respect to 100 parts by mass of the cement clinker in order to enhance strength development, particularly long-term strength development. . The alkanolamine is added to the cement composition as a grinding aid or admixture. The alkanolamine content in the cement composition of the present invention is preferably 0.1 to 1.0 parts by mass, more preferably 0.15 to 0.5 parts by mass.
The alkanolamine includes one or more selected from monoalkanolamine, dialkanolamine, and trialkanolamine. Among these, one or more selected from triisopanolamine, triethanolamine, and methyldiethanolamine are preferable because they are readily available.

The Blaine specific surface area of the cement composition of the present invention is preferably 3000 to ⁵⁰⁰⁰ cm ² /g. If it exceeds ² /g, the grinding cost increases. The Blaine specific surface area is more preferably 3500 to 4800 cm ² /g, still more preferably 3800 to 4600 cm ² /g.

Further, mixed cement can be produced by mixing the cement composition of the present invention with mixed materials such as blast furnace slag and fly ash. Further, by mixing various admixtures, additives, etc., solidifying materials, premixed cement, and premixed mortar products can be produced. In the hardened cement described later, if there is concern about alkali-aggregate reaction, it is preferable to mix at least one selected from blast furnace slag and fly ash.

4. Production of Hardened Cement Body The cement composition of the present invention and water are mixed at a water/cement composition mass ratio of preferably 0.3 to 1.0, more preferably 0.4 to 0.7 to obtain mortar. , or hardened cement such as concrete can be produced.

Common aggregates can be used as the aggregates contained in the hardened cement. The fine aggregate includes one or more selected from river sand, mountain sand, land sand, sea sand, crushed sand, silica sand, slag, lightweight fine aggregate, recycled aggregate, and artificial calcined aggregate. , river gravel, mountain gravel, land gravel, crushed stone, slag, lightweight coarse aggregate, recycled aggregate, and artificial calcined aggregate.
Moreover, when alkali-aggregate reaction is a concern, it is preferable to use one or more selected from limestone aggregates, basaltic aggregates, gabbros aggregates, lightweight aggregates, and heavy aggregates.

When the hardened cement contains coarse aggregate, the fine aggregate ratio is preferably 5 to 60%. If the fine aggregate ratio is within the above range, the workability of the kneaded product and the ease of molding are improved.
The amount of aggregate (the total amount when fine aggregate and coarse aggregate are used together) is preferably 200 to 700 parts by mass, more preferably 200 to 600 parts by mass, with respect to 100 parts by mass of the cement composition. be.
The coarse particle ratio when fine aggregate and coarse aggregate are combined is preferably 1.0 to 7.0, more preferably 1.5 to 6.5.
In addition, the cement hardened body may contain additives such as water reducing agents, antifoaming agents, and shrinkage reducing agents, fly ash, silica fume, granulated blast furnace slag, and fine limestone powder, etc., depending on the required properties and applications. of admixtures.

EXAMPLES The present invention will be described below with reference to Examples, but the present invention is not limited to these Examples.
1. Materials used (1) Coal ash (abbreviation: CA)
The chemical composition is shown in Table 3.
(2) Biomass ash A (abbreviation: BA)
It is palm shell ash obtained from a circulating fluidized bed incinerator of a thermal power plant using palm shell as a part or all of the fuel, and its chemical composition is shown in Table 3.

(3) calcium carbonate, silicon dioxide, aluminum oxide, ferric oxide, sodium carbonate, potassium carbonate, magnesium oxide, gypsum dihydrate, titanium oxide, calcium hydrogen phosphate dihydrate, diethylene glycol (abbreviation: DEG), and triisopropanolamine (abbreviation: TIPA) are all special grade reagents (manufactured by Kanto Kagaku Co., Ltd.).

2. Manufacture of cement clinker Coal ash and biomass ash, calcium carbonate, silicon dioxide, aluminum oxide, ferric oxide, sodium carbonate, potassium carbonate, magnesium oxide, gypsum dihydrate, titanium oxide, and calcium hydrogen phosphate dibasic The hydrates were mixed at the ratios shown in Table 4, pulverized with a vibrating disk mill, and the pulverized product was molded into a cylindrical shape to prepare a raw material for cement clinker.
Next, the cement clinker raw material was calcined at 1000° C. for 30 minutes using an electric furnace, then heated to 1450° C. at 10° C./min and held for 30 minutes to obtain a fired product. Furthermore, the fired product was cooled in the atmosphere to produce cement clinker. Table 5 shows the belite content, interstitial phase content, alkali metal content, etc. in the cement clinker. The mineral composition of Reference Example is the same as that of ordinary Portland cement clinker.

2. Production of Cement Composition For 100 parts by mass of cement clinker of Examples 1 to 13, Comparative Examples 1 to 3, and Reference Example, flue gas desulfurization gypsum produced at a domestic thermal power plant was added to 1.0 in terms of SO ₃ . 6 parts by mass, 4.0 parts by mass of limestone fine powder obtained by pulverizing limestone produced in domestic mines, and the grinding aid shown in Table 6 (DEG is an abbreviation for diethylene glycol and TIPA is an abbreviation for triisopropanolamine. ) was added in the amount shown in Table 6 and pulverized in a ball mill to produce a cement composition having a Blaine specific surface area shown in Table 6.
The Blaine specific surface area was measured according to JIS R 5201 "Physical test method for cement". The cement composition OPC is a composition imitating ordinary Portland cement.

3. Measurement of compressive strength of mortar using cement composition
Using the cement composition, a mortar was prepared according to JIS R 5201 "Physical test method for cement", and the compressive strength of the mortar was measured. Table 6 shows the results.

4. Test Results From the above test results, the following can be said.
(1) Regarding Compressive Strength at 28 Days of Material Age (Long Term) As shown in Table 6, the compressive strength at 28 days of material age was obtained using the cement clinker of Examples 1 to 13 for cement compositions A to For mortars of I, L, and N to P, it was as high as 54.9 N/mm ² (cement composition A) to 63.5 N/mm ² (cement composition I), which indicates the compression of mortars of cement composition OPC. It is equivalent to the strength (57.2 N/mm ² ).
On the other hand, the mortars of cement compositions J, K, and M produced using the cement clinker of Comparative Examples 1 to 3 had compressive strengths of 53.3 N/mm 2 and 53.3 N/mm ² at the age of 28 days, respectively. 8 N/mm ² and as low as 51.3 N/mm ² .

(2) About Compressive Strength at 7 Days of Material Age (Mid-term) As shown in Table 6, the compressive strength at 7 days of material age was 39 for mortars of cement compositions A to I, L, and N to P. It is as high as 0.5 N/mm ² (cement composition P) to 53.6 N/mm ² (cement composition H), whereas it is as low as 35.4 N/mm ² for cement composition OPC. Therefore, it can be said that the cement composition of the present invention has higher medium-term strength development than ordinary Portland cement.

(3) Grinding Aid Triisopropanolamine was used as a grinding aid with the same replacement rate of biomass ash for quicklime, belite replacement rate, interstitial content, alkali metal content, and Blaine specific surface area. Comparing the strength development properties of cement composition H and cement composition D using diethylene glycol, cement composition H is higher than cement composition D at all ages, and particularly has significantly higher long-term strength.

As described above, the cement composition of the present invention has a strength development property equal to or higher than that of ordinary Portland cement. Therefore, the present invention can contribute to the effective use of biomass ash having a high alkali metal content, which is expected to increase in the future, in the production of cement.

Claims (8)

Cement clinker with a belite content of 28-45% by weight, an interstitial phase content of 3-25% by weight and an alkali metal content of 0.65-2.5% by weight. Cement clinker according to claim 1, having a silicic acid content (SM) of 2.7 to 15.0. 3. A method for producing a cement clinker, comprising firing a cement clinker raw material partly containing a raw material having a biomass ash substitution rate with respect to coal ash of 25% or more to produce the cement clinker according to claim 1 or 2. The method for producing cement clinker according to claim 3, wherein the biomass ash has an alkali metal content of 2.5% by mass or more. A cement composition containing at least 1 to 6 parts by mass of gypsum in terms of SO ₃ per 100 parts by mass of the cement clinker according to claim 1 or 2. 6. The cement composition according to claim 5, further comprising 0.001 to 0.1 parts by mass of alkanolamine with respect to 100 parts by mass of the cement clinker according to claim 1 or 2. The cement composition according to claim 5 or 6, having a Blaine specific surface area of 3000 to 5000 cm ² /g. 8. The cement clinker according to any one of claims 5 to 7, further comprising 0 to 10 parts by mass of one or more selected from limestone, fly ash, and blast furnace slag with respect to 100 parts by mass of the cement clinker according to claim 1 or 2. cement composition.