DE3530421A1 - METHOD FOR TREATING SOLID MATERIALS CONTAINING THE CALCIUM SALTS OF SULFUR OXOAIC ACID AND PROCESS FOR PURIFYING EXHAUST GAS USING THIS METHOD - Google Patents

Description

Process for the treatment of solids which contain the calcium salt of a Schujefel oxo acid and the process for Purify exhaust gas using this method

The invention relates to a dry process for the treatment of solids containing the calcium salt of a Contain schuefel oxo acid, such as plaster of paris, and on one Process for cleaning exhaust gases from boilers, waste incinerators and other fireplaces using this process for the effective removal of harmful acidic constituents from the exhaust gas.

There has already been a dry method of cleaning exhaust gas from boilers, waste incinerators, or the like Fireplaces suggested in the case of particles of a Ca-based absorbent (such as quick lime, slaked Lime, limestone, dolomite or the like.) Are dispersed directly into the interior of the furnace or the flue, so that the absorbent particles are harmful acidic substances, how to absorb sulfur oxides (SO). In this process, the absorbent particles are through the Reaction with the sulfur oxides partly in gypsum (CaSO) converted and together with other solid particles than Soot and dust collected in a dust collector. In addition to gypsum, the soot and dust obtained contain fly ash and unreacted absorbent components and he can therefore not for the production of plasterboard or gypsum cement which are the preferred uses for plaster of paris. If the fireplace is big, you can Soot and dust, which are produced in large quantities, are not released directly into the atmosphere because this does so significant problems arise.

A method has also already been proposed with which gypsum is calcined in a furnace in the presence of a lack of air quick lime and a gas containing sulfur dioxide

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obtained and from the sulfur dioxide to produce sulfuric acid. Another method is to place plaster of paris in a furnace with limited air supply in a reducing atmosphere converted into calcium sulfide, from which after crushing an aqueous slurry is made through which carbon dioxide is passed to recover shoe oxygen.

The conventional processes not only require equipment large scale, but also require non-uniform heating by the furnace to produce the resulting fired Lime or the calcium sulfide through accelerated crystallization make them less reactive / and they cause problems in the subsequent treatment. In addition, these methods have a high energy consumption.

The invention is based on the object of creating a method with which the above problems of the known methods to be overcome.

According to the invention, this object is achieved by the characteristics of claim 1 specified process steps solved.

The inventive method is not limited to Treatment of gypsum, which arises from the cleaning of exhaust gases, but can also be used for solids containing the calcium salt contain a sulfur oxo acid, which by Reduction gives off calcium sulfide.

Examples according to which calcium salts of sulfur oxo acids are except calcium sulfate) calcium sulfite (
and calcium polythionate (CaS

Gypsum (calcium sulfate) calcium sulfite (CaSO,), calcium thiosulfate

The invention also relates to a method for cleaning an exhaust gas containing sulfur oxides, in which dry particles a Ca-based absorbent having a predetermined mean grain size is introduced into the exhaust gas

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to absorb the sulfur oxides by the absorbent _; and then the absorbent particles are collected together with other particles contained in the exhaust gas in a dust collector. According to the invention, this method is expanded by the features specified in the characterizing part of claim 7.

The Ca-based absorbents used in this process are limestone (CaCO,), slaked lime (Ca (OH) ₂ ), fitzkalk (CaO), dolomite (CaCO ₃₁ MgCO ₃ ), slaked dolomite (Ca (OH ) _2. Mg (OH) ₂ or Ca (OH) ₃₁ IVIgO), calcined dolomite (CaO.MgO or CaCO.,. MgO) and any other material that contains CaO or forms CaO at a high temperature. So, the Ca-based absorbent originally contains CaO or it generates CaO due to the following reactions at a high temperature:

Ca (OH) ₂ -ν- CaO + H ₃ O (1)

CaCO ³ -V- CaO + CO ₃ (2)

CaO absorbs sulfur oxides (SO) from the exhaust gas following reactions ":

CaO + SO ₄ + ^ O ₂ - *. CaSO ₄ (3)

CaO + SO ₃ - * - CaSO ₄ (4)

The CaS0 ₄ shells formed on the surfaces of the absorbent particles by the reactions {'S) and ( d ) have a compact structure and prevent harmful acidic constituents such as SO from diffusing into the particles, thereby increasing the reactivity of the absorbent is reduced. However, the method according to the invention converts the CaS0 ₄ shells into calcium carbonate (CaCO), as a result of which the absorbent particles are regenerated. The regenerated absorbent can be reintroduced into the exhaust gas, which significantly reduces the amount of fresh absorbent required.

Of the aforementioned Ca-based absorbents dolomite, slaked dolomite and burnt dolomite have a large pore volume and therefore the advantage that the harmful acidic substances can diffuse more easily into the particles. Since the foreign components like WqO does not participate directly in the regeneration reactions, the change in these components is not explained in more detail to simplify the description.

Exhaust gases, especially those from coal-fired boilers and waste incinerators, in general Large particle size fly ash in addition to harmful acidic substances. In this case it is desirable the particles collected by the first dust separator in a first proportion of coarse, predominantly Particles containing fly ash and a second, fine one Particles and predominantly absorbent particles with a predetermined maximum size containing fraction separate and then regenerate only the second part. In the case of burners operated with oil, the proportion of fly ash is less than the proportion of absorbent particles, see above that the classification step is not always necessary.

The invention is explained in detail below with reference to the drawings.

Fig. 1 is a flow diagram of a process for treatment of solids containing the calcium salt of a sulfur

Contain oxo acid, and
Fig. 2 is a flow diagram of a process? for the purification of exhaust gases using the method according to FIG. 1.

In Fig. 1, 1 denotes a silo, the fine particles of used absorbent based on Ca (partly gypsum) or solids containing the calcium salt of a sulfur oxo acid, such as high purity gypsum. That

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fine particulate matter is removed from the silo 1 through an ejector 2, which serves as an example of a dispersion nozzle, added to a carrier gas stream and introduced with this into a reduction reactor 3. To the reduction reactor 3, a reduction gas generator 4 is connected, in which a hydrocarbon, for example asphalt, incompletely burned with oxygen and water vapor is used to generate a reducing gas having a high temperature and carbon monoxide and hydrogen contains. In the reduction reactor 3, the CaSO. Component of the solid particles is therefore corresponding to following equation reduced to calcium sulfide (CaS).

CaSO ₄ + 4H ₂ - »- CaS - (5) CaSO + 4CO - ^ - CaS j (B) Y 4H ₂ O Y 4CO ₂

Downstream of the reactor 3 is a carbonation reactor 5 with a cooler 6 (which is a heat exchanger or a device for evaporating or spraying water can be arranged). The gas flow from the reduction reactor 3 is cooled in the carbonation reactor 5, the CaS being converted into carbonate and hydrogen sulfide in the process emits according to the following equation:

CaS + H ₂ O + CO ₂ - »·? CaCO ₃ + H ₂ S (7)

The gas flow emerging from the reactor 5, the fine carbonate particles and H "S contains, then the dust collector 7 supplied, in which the fine solid particles, which mainly consist of fine carbonate particles are collected in a calcium carbonate silo 8.

The gas flow to the dust collector 7 is passed to a hydrogen sulfide separator 9 supplied, in which the HpS deposited will. The H-S can be converted into elemental sulfur by the Claus process or by a wet process in sulfuric acid converted or as a material for chemical synthesis

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be used. The gas stream freed from the H ^ S contains Hydrogen, carbon monoxide and carbon dioxide as not reacted components, so that it is advantageous to this gas flow through a return line 10 with a compressor 11 to be used as a carrier gas for feeding the fine particles from the silo 1 to the reduction reactor 3. When the carrier gas Contains impurities (mainly nitrogen) in an impermissibly high concentration, reactors 3, 5 with greater capacity can be used and the formation of calcium carbonate is also adversely affected. The carrier gas is therefore partly blown off, for example through a blow-off line 12.

The smaller the fine ones passed through reactors 3 and 5 Particles are, the better the result, since the reduction in particle size results in a uniform diffusion of the Heat and 'of the reactants in the particles are guaranteed, which shortens the required reaction time and Reactors 3, 5 of reduced size can be used. Due to the improved noise transfer efficiency the reduction reactor 3 ensures uniform heating in order to prevent the crystallization of CaS, while a uniform carbonate formation takes place in the reactor 5, creating highly reactive calcium carbonate is produced. In view of the energy required for shredding, it should consist of fine particles Material has an average grain size of not more than 10 XJm, preferably 1 to 3 yum.

The ejector 2, which serves as a dispersion nozzle and with the Carrier gas interacts through 'the return line 10 is supplied under pressure, causes the pre-crushed particulate material from the silo 1 uniformly into the reducing Gas is dispersed within the reactor 3, the CaSO. Component having a high reactivity be reduced. Instead of the fine particles

standing material that has been finely divided can contain solids, which contain the calcium salt of sulfur oxoic acids, be pulverized separately by a jet mill or the like before they are fed to the dispersion nozzle 2 »

Normally, the CaSO, component contains water of crystallization and sie.verliert the water at a temperature of 100 to 200 ⁰ C. When this dehydrogenation reaction takes place at the location of the dispersion nozzle, which is exposed to a high temperature, it may occur that the nozzle 2 becomes clogged or that particles agglomerate (in order to achieve a reduced reactivity), which leads to a poor efficiency. Accordingly, it is desirable to calcine the particulate material to make the CaSO, anhydrous before it is fed to the nozzle 2.

To regenerate the CaSO, component to CaCO-, it is advantageous to that the concentration of the reducing gas in the reactor 3 and the liiasserdampf concentration as well the carbon dioxide concentration in the reactor 5 can be kept at a high level. To do this, be more focused Oxygen with a concentration of at least 95 ° instead of air, which contains large amounts of nitrogen and other impurities, preferably as an oxygen source for the partial combustion of a hydrocarbon used in the reducing gas generator 4.

The reduction reactions of Equations (5) and (6) take place at a temperature of at least 700 ⁰ C. While these reactions progress from the surface of the particles inward, the rate of reaction is dependent on the rate of diffusion of H- or CO from the surface of the particles into the interior, so that the reaction is accelerated as the particle size becomes smaller. Since the diffusion rate is the determining factor, the increase is the

Reaction temperature above 90G ⁰ C is not very effective for the reduction of CaSD, to CaS. In addition, temperatures above 1100 ⁰ C support the crystallization of the CaS generated, whereby the diffusion won H _? or CO is suppressed in the particles and the subsequent carbonate formation is adversely affected. Accordingly, it is advantageous that the temperature in the reduction reactor 3 at 700 to 900 ⁰ C is set.

The carbonation reaction according to equation (7) is an equilibrium reaction, and it is necessary to keep the temperature at a level of up to 500 ° C for a complete reaction. However, this carbonation reaction proceeds at a slow rate. Accordingly, it is necessary to maintain the reaction temperature at the highest possible value within the range ⁰ to 500 C to promote reaction um'die. Although it was not certain whether the carbonation reaction can be carried out within a practically useful reaction time (particle residence time), it has been found that the required reactivity can be achieved with a reaction time of about 3 to 20 seconds when particles of reduced mean grain size (especially 1 to 3 ym) at a reaction temperature of 300 to 500 ⁰ C can be used.

The following are examples that are used for illustrative purposes the benefits of the treatment method described above.

Example I.

Hollow cylindrical refractory bricks with an inner diameter of 20 cm were placed on top of one another to form a column 12 m high, corresponding to an experimental reaction column the combined reactors 3 and 5 of FIG. A combustion chamber (corresponding to

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the reduction gas generator 4) made of refractory bricks. A dispersion nozzle (corresponding to ejector 2) was placed on the column below the combustion chamber. A water spray nozzle (corresponding to the cooler 6) was on attached to the column 1.5 m below the nozzle »On a Place 0.5 m below the dispersion nozzle and at one Temperature measuring points were located 6 m below the water spray nozzle Thermocouples inserted into the reaction column. The section of the reaction column above the.Ulassersprühdüse was surrounded on the outside with an electric radiator, the outside with heat-insulating Bricks and an iron pipe was protected. This unit was also covered with elm insulation. The other part of the column was only protected by an iron pipe. The liquid spray nozzle used was a supersonic nozzle, which is able to produce very fine water droplets to create. The outlet of the reaction column was connected to a dust collector in the form of a high-performance cyclone Mistake.

Town gas was burned in the combustion chamber in order to heat the reaction column to a certain temperature. An experiment was then carried out for two hours under the following conditions:
First of all, the town gas was replaced by carbon monoxide and hydrogen. Carbon monoxide was added to the combustion chamber in an amount of 14 IMm / h (IM is the standard state), hydrogen in an amount of B Nm / h and air in an amount of 34.8 Nm / h for partial combustion (to maintain a predetermined Reaction temperature) supplied. On the other hand, dehydrated gypsum (purity 99%) pulverized to an average particle size of 3 μm was used as the calcium salt of a sulfur-oxo acid-containing solid in an amount of 13.6 kg / h from the dispersion nozzle at the top of the column

supplied, namely in a carrier gas, which consisted of 50% carbon monoxide and 50% hydrogen and was supplied in an amount uon 24.2 Nm / h, the finely divided gypsum were dispersed in the hot combustion gas from the combustion chamber and the carrier gas through the nozzle was accelerated to a flow velocity of 200 m / s. Finely divided water was supplied in an amount of 21.2 kg / h through the water spray nozzle. At this time, the portion of the reduction reactor located above the water nozzle had a temperature uon 820 ⁰ C, while the Karbonationsreaktorabschnitt above the die was at 340 C uon.

Dust and particles were separated from the cyclone in an amount of 9.5 kg / h. The analysis showed that the dust and the particles contained 92.4% CaCO ₁₃ , 3.5% GaS, 2.7% CaSO ₄ and 1.4% other components. On the other hand, a gas stream having a temperature of 340 ° C and a content of 2.4% HS was discharged from an upper portion of the cyclone.

Example II

The procedure of Example I was repeated with the following modifications:

Solids containing a calcium salt of a sulfur oxo acid:

Used Ca-based absorbent (anhydrous gypsum content -43.756)

Average particle size: * 2 pi

Amount of particles fed in: 20 kg / h

Amount of carrier gas: 25 Nm / h speed of the carrier gas from the

Dispersion nozzle: '. 300 rn / sec

Amount of the supplied finely divided

Water: 20.0 kg / h

Temperature of the reduction reaction: 81O ⁰ C

Carbonation reaction temperature: 335 C

Dust and particles were separated from the cyclone in an amount of 21.1 kg / h. The analysis showed that the dust and the particles contained 67.7 _{% CaCO 3} , 0.7% CaS, 0.4% CaSO ₄ and 31.2% other components. A gas stream with 1> 5% H ^ S and a temperature of 335 ° C. was discharged from the upper area of the cyclone.

FIG. 2 shows an exhaust gas cleaning system including the system shown in FIG. This system is an example of how it is used for a thermoelectric power plant of the 1000 MhJ class, which is specially set up for burning coal and an air heater 15, which generates an exhaust gas containing fly ash and harmful acidic substances, fine particles of a Ca-based absorbent such as finely divided limestone (CaCO ₃ ) having an average grain size of 1 to 3 µm introduced through a supply line 16 into the upper end of the boiler. 13 the particulate absorbent is held for a period of about 2 to about 3 seconds at a temperature of 900 to 1100 ⁰ C, wherein CaCO is immediately thermally decomposed to highly reactive CaO according to the The CaO continues to undergo the reactions of Equations (3) and (4), absorbing sulfur oxides and forms calcium sulfate (CaSO.) on the surface of the absorbent particles. The reactivity of CaO is about 40 to about 50%, and unreacted CaO remains as it is inside the particles. The heat released during the reactions is used in the boiler 13.

The exhaust gas from the boiler 13 is through a Denitriereinhe.it 17, which removes nitrogen oxides from the gas .. About the air heater 15, the gas then enters a dust separation unit 18, in which the consumed absorbent

tel particles, the soot and the dust from fly ash from the gas stream to be deposited. The exhaust gas cleaned in this way is then released into the atmosphere through a chimney 19.

According to the invention, the desulfurization is carried out at a high temperature of 900 to 1100 ° C. so that the exhaust gas has a reduced acid dew point temperature. As a result, the exhaust gas emerging from the chimney 19 has a temperature of about 100 ^° C. compared to the normal temperature level of 140 to 150 ^° C. This means that a larger amount of heat can be used usefully in the boiler 13. Before the absorbent particles reach the dust separation unit 18, they absorb hydrogen fluoride (HF) and hydrochloric acid (HC1) in addition to the sulfur oxides from the exhaust gas. However, since the CaF and CaCl ₂ which are formed do not take part in the subsequent treatment of the absorbent, these halogens are not described further.

The soot, the dust and particles collected by the unit 18 are fed via a hopper 20 to a Windklassierer 21, in which it is in a proportion of coarse <■ particles of primarily of fly ash having an average grain size of 12 to 15 jum »and are separated into a second fraction of fine particles, which primarily contains the used absorbent. The fraction containing the coarse particles is stored in a container 22. The fraction containing the fine particles is introduced into a regeneration cycle via a silo 1. The regeneration cycle shown in FIG. 2 corresponds to that of FIG. 1 and has an ejector 2, a reduction reactor 3, a reduction gas generator 4, a carbonation reactor 5 with a cooler 6 in the form of a heat exchanger, a dust separation unit 7, a calcium carbonate silo 8, a Hydrogen sulfide separator 9 »has a return line 10 with a compressor 11 and a blow-off line 12. The Staubabscheideednheit 7 contains a

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Zyklon 23 in combination with a bag filter 24. The hydrogen sulfide separator 9 contains a cooler 25 with a cooling water circulation pump 26, a hydrogen sulfide absorption column 27 and a stripper 28. The stripper 28 is with a Hydrogen sulfide container 29 connected,

The CaSO. Component that is in the spent absorbent is contained, which is fed through the ejector 2 to the reduction reactor 3, is determined by the reactions of equations (5) and (6) in the hot reducing gas from generator 4 to CaS reduced. The CaS further reacts in the carbonation reactor 5 with carbon dioxide and water vapor according to the equation (7), whereby CaCO., Is formed. Now is the absorbent regenerated, producing hydrogen sulfide (H „S). While During the carbonation reaction, the unreacted component (CaO) within the absorbent particles undergoes the following reaction and it is converted into a carbon:

CaO + CO - &> CaCO, (8)

2 y

The reduction reaction and the carbonation reaction described above are both exothermic and the heat of reaction is recovered through the heat exchanger B.

The gas stream flowing out of the carbonation reactor 5, which contains the regenerated absorbent, H "S and other unreacted gas components, is subjected to a separation between solids and gas in the dust separation unit 7. The separated absorbent particles are conveyed back to the boiler 13 via the calcium carbonate silo 8, the rotary valve 30, the ejector 31 and the return line 16. Since, in the classification by the air separator 21, a portion is lost to the absorbent particles is in the supply of fresh absorption agent not always CaCO, shall include, but CaO or Ca (OH) may contain _{7 4} of an absorbent-supplying means 32 via pin silo 32, a rotary valve 34 and an ejector 35 introduced to make up for the loss. At 36 a compressor is

which is connected to the feed line 16.

The gas flow emerging from the dust separation unit 7 is cooled by the cooler 25 to about 40 C and then in the absorption column 2? and the stripper 28 of an amine wash subjected, whereby only H ^ S is excreted. The HpS will stored in the container 29 and, for example, occasionally treated according to the Claus process. That through the Claus process Accumulating water and the elemental sulfur are discharged through lines 37 and 38.

The gas stream emerging from the hydrogen sulfide separator is fed to the reduction reactor 3 through the compressor 11 supplied again via the return line 10. Part of the The gas stream can be discharged to the outside via the discharge line 12 will.

If v / is requested, the amount of absorbent particles, that are lost through the air classifier 21, so contains the particulate material that the absorption regeneration circuit downstream of the same is supplied, an increased amount of impurities (fly ash, etc.), whereby the regeneration cycle is heavily loaded, - accordingly, the separation ratio that is achieved by the air classifier 21, be adjusted so that a balance between the lost absorbent and the load on the regeneration circuit is achieved.

The exhaust gas cleaning system according to Fig. 2 has the following advantages:

a) Because the absorbent used. On a Ca basis after regeneration recycled for reuse »the exhaust gas can be effectively made using a smaller amount of absorbent can be cleaned without the difficult problem of by-products.

b) Reuse won absorbent, once pulverized is, helps to reduce the energy required for pulverizing »

c) From desulfurization with the absorbent to regeneration of the absorbent (the series of process steps up to the dust separation unit 7) becomes the process carried out continuously in the dry state and therefore has only low heat losses »In addition, the heat generated during desulphurisation and regeneration is effective exploited in the boiler 13 and in the heat exchanger B, so that there is an improved energy efficiency. The proposed Process has no problems in terms of the treatment of wastewater with wet or semi-wet processes occur or cause secondary pollution.

d) The boiler 13 and the dust separation unit 15, which also serve as desulphurisation units make the system compact.

e) Since the desulfurization with the absorbent is carried out at a high temperature of 900 to 1100 ^° C., SO- ,, which is more toxic than SO- and which is difficult to remove at low temperatures (SO, suspended in the exhaust gas in the form stable tiny crystals at low temperatures) can be removed effectively.

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Claims (10)

Claims Method of treating solids, such as the calcium salt contain a sulfur oxo acid, characterized in that that - A reduction reactor, a reducing gas stream containing hydrogen and / or carbon monoxide, the one has the first predetermined temperature, and dry particles, which contain the calcium salt of Schuefel oxo acid and have a predetermined mean grain size around the calcium salt to reduce calcium sulfide, be fed that then the gas flow from the reduction reactor in a carbonation reactor is cooled to a second temperature. to get out of the calcium sulfide with carbon dioxide and UIa sser steam f Generate calcium carbonate and hydrogen sulfide, - That the resulting gas flow won the carbonization reactor is passed into a dust collector to remove solid particles to deposit - and finally the hydrogen sulfide from that from that Dust separator escaping gas stream separated, is ^ Bank details: Hypobank Gauting account no. 3 750123 448 (bank code 700 260 01) BATH 2. V / experience according to claim 1, characterized in that the calcium salt of the sulfur oxo acid is calcium sulfate, calcium sulfite, calcium thiosulfate and / or calcium polythionate individually or in any combination. 3. The method according to claim 1, characterized in that the first temperature is 700 to 900 ° C. 4. The method according to claim 1, characterized in that the second temperature is 300 to 500 C. 5. The method according to claim 1, characterized in that the reducing gas flow through partial combustion of a hydrocarbon is generated with water vapor and concentrated oxygen. 6. The method according to claim 1, characterized in that the Gas after removal of the hydrogen sulfide as a carrier gas for the dry particles is returned to the reduction reactor. 7. A method for purifying an exhaust gas containing sulfur oxides by blowing in dry particles of a Ca-based absorbent with a predetermined mean grain size in the exhaust gas to remove the sulfur oxides through the absorbent to absorb, and then collecting the Absorbent particles along with others in the exhaust gas contained particles in a dust separator, characterized in that that the used absorbent particles collected in the dust collector and a reducing, Hydrogen and / or carbon monoxide-containing gas stream which has a first predetermined temperature to in to reduce calcium sulfate contained in the absorbent particles to calcium sulfide, fed to a reduction reactor that then the gas stream passed the reduction reactor in a carbonation reactor to a second temperature is cooled to remove the calcium sulfide with carbon BATH ORIGINAL dioxide and water vapor calcium carbonate and hydrogen sulfide to generate, then the resulting gas flow from the carbonation reactor into a second dust collector is passed to separate solid particles, and close Lich the solid particles as regenerated absorbent particles be reintroduced into the exhaust gas. 8. The method according to claim 7, characterized in that the hydrogen sulfide from the second dust collector exiting gas stream is separated and the residual gas is then returned to the reduction reactor as a carrier gas. 9. The method according to claim 7, characterized in that the Particles collected in the first dust separator are converted into a first fraction of coarse, predominantly fly ash Particles and a 'second portion of fine particles, which consists mainly of used absorbent particles exists below a certain maximum size, are separated and that-only the second fraction in the reduction reactor is returned. 10. The method according to claim 7, characterized in that as Absorbent limestone, slaked lime, dolomite, slaked dolomite and / or calcined dolomite individually or is used in any combination.