阅读说明：本技术 变色火山灰的制造方法和由此获得的火山灰 (Method for producing a discolored pozzolan and pozzolan thus obtained ) 是由 吉列尔梅·马丁斯·费雷拉 路易斯·菲利佩·翁·雷纳尔·法比亚尼 路易斯·费利佩·德·皮尼奥 罗 于 2018-04-23 设计创作，主要内容包括：本发明涉及一种人工火山灰的制造方法,其最终颜色为灰色。为了以期望方式进行该方法,窑气氛应包含低氧浓度并存在还原剂。然而,由于环境影响和窑单位耗热量的增加,在窑出口处存在一氧化碳是不可取的。因此,本发明所述的方法包括以下步骤：加热(1),其由以下构成：将原料加热至100-350℃的温度直至将材料干燥至0-5％(湿基)的水分质量分数；混合(2),其由以下构成：将来自加热过程的干燥原料与根据原料中存在的赤铁矿浓度的质量分数为1％-5％的适当比例的燃料混合；煅烧(3),其由以下构成：将燃料和原料共混物加热至700-900℃的温度,氧浓度在1-5％之间,最后冷却(4),其由以下构成：快速降低火山灰温度直至600℃的初始步骤,和将火山灰温度缓慢降低直至120℃的最终步骤。(The invention relates to a method for manufacturing artificial volcanic ash, wherein the final color of the artificial volcanic ash is gray. In order to carry out the process in the desired manner, the kiln atmosphere should contain a low oxygen concentration and the presence of a reducing agent. However, the presence of carbon monoxide at the kiln exit is undesirable due to environmental effects and increased heat consumption per kiln unit. Thus, the method of the invention comprises the steps of: a heater (1) consisting of: heating the feedstock to a temperature of 100 ℃ to 350 ℃ until the material is dried to a moisture mass fraction of 0-5% (wet basis); a blend (2) consisting of: mixing the dried raw material from the heating process with a fuel in a suitable proportion of 1-5% by mass based on the concentration of hematite present in the raw material; calcination (3) consisting of: heating the fuel and feedstock blend to a temperature of 700-: an initial step of rapidly reducing the pozzolan temperature up to 600 ℃, and a final step of slowly reducing the pozzolan temperature up to 120 ℃.)

1. The manufacturing method of the color-changing volcanic ash is characterized by comprising the following steps of:

-heating (1): the device comprises the following components: heating the raw blend to a temperature of 100 ℃ to 350 ℃ until the material is dried to a moisture range of 0-5% (wet basis);

-mixing (2): the device comprises the following components: mixing the dried raw material from the heating step with a fuel in a mass fraction of 1-5% based on the hematite concentration of the raw material;

-calcination (3): the device comprises the following components: heating the blend of the fuel and the dry raw material to the temperature of 700-900 ℃, wherein the oxygen concentration is 1-5%;

-cooling (4): the device comprises the following components: an initial step of rapidly lowering the temperature up to 600 ℃ and a final step of lowering the pozzolan temperature up to 120 ℃.

2. The method according to claim 1, characterized in that the mixing step (1) precedes the heating step (2), the latter step consisting of: the blend of feedstock and solid fuel is heated to a temperature of 100 ℃ and 350 ℃ until the blend is dried to a moisture mass fraction of 0-5% (wet basis).

3. The method according to claim 1 or 2, wherein the fuel is a solid fuel and should be selected from the following: mineral coal, charcoal, petroleum coke, pulverized coal, biomass, or other carbon-rich waste.

4. The method of claim 1, 2 or 3, wherein during the mixing step (1), the solid fuel is added in an amount of about 0% for a hematite concentration in the feed composition of less than 3%; about 1.5% for a hematite concentration of 3-5% in the feed composition; about 3% for a 5-8% hematite concentration in the feed composition; and about 5% for a hematite concentration of 8-12% in the feed composition.

5. The method of claim 1 or 2, wherein the calcining step (3) may utilize low-oxygen recycle gas from depletion.

6. The method according to claim 1 or 2, characterized in that during the calcination step (3), the combustion of solid, liquid or gaseous fuel is carried out in a compact combustion pre-chamber according to BR PI 1000417-3.

7. The process according to claim 1 or 2, characterized in that the calcining apparatus is selected from: rotary kiln or fluidized bed or flash roaster.

8. The method according to claim 1 or 2, wherein the cooling step (4) is carried out in a cooler selected from the group consisting of: a rotary cooler or a fluidized bed or flash cooler.

9. The method according to claim 8, characterized in that the first step of the cooling process consists of: in the case of a rotary cooler or flash cooler, the outside of the drum is kept wet, or in the case of a fluidized bed, by using a water serpentine.

10. The method according to claim 1, 2 or 8, characterized in that the second step of the cooling process (4) is selected according to the concentration of hematite in the raw material.

11. The method of claim 10, wherein the second step of the cooling process comprises:

for hematite concentrations below 3%, ambient air is directly used;

for hematite concentrations of 3-6%, the recycling gas is used directly;

-for hematite concentrations of 6-10%, direct use of ambient air in combination with indirect use of water;

for hematite concentrations higher than 10%, the recycling gas is used directly in combination with the indirect use of water.

12. A pozzolan characterized in that it is manufactured according to the method of claim 1.

13. A pozzolan characterized in that it is manufactured according to the method of claim 2.

14. Pozzolan, characterized in that it is manufactured according to the method of any one of claims 3 to 11.

Technical Field

The present invention relates to a process for the manufacture of artificial pozzolans, the final colour of which is grey, characterised by a controlled atmosphere during activation of the pozzolan.

Background

The use of pozzolanic materials as a replacement for clinker in cement manufacture in the cement, concrete and grout (grout, mortar, grout) industry is of great interest for the following reasons:

the production cost of pozzolans is lower than that of clinker;

CO from volcanic ash₂The emission rate is lower than that of clinker production;

there are a large number of clay materials available for pozzolan production;

the addition of pozzolans to the cement reduces the heat of hydration of the mixture, thus reducing the expansion of the large concrete blocks and avoiding cracks.

Currently, there are many methods for producing artificial pozzolans by thermal activation of clay in a kiln. Known clay activation techniques are summarized below.

Document BRPI 1002450-6 relates to a method for manufacturing artificial pozzolans, which is activated by calcining clay in a horizontal kiln (horizontal kiln) and adding solid fuel at a temperature of 300-. There should be a reducing atmosphere in the kiln, carbon monoxide (CO) levels varying between 0.5-3% and residence times of the material varying between 40-70 minutes. The cooling process should be performed using counter-current air or at room temperature. The described methods tend to reduce or eliminate the reddish (light red) color of brown or gray pozzolans. The process occurs in a reducing atmosphere with 0.5-3% carbon monoxide, indicating that CO will be present in the kiln exhaust gas composition. There is no detailed description of the cooling process and its effect on the final color of the material. The description does not mention any control of the exact final color of the product.

Document BRPI 020453-9 relates to a method for the manufacture of artificial pozzolans, which are activated by calcining a mixture of kaolinite clay and limestone at a temperature of 600-1000 ℃. The described method does not provide information on what type of kiln or furnace is used for the clay calcination nor on the cooling process of the material. There is no description of what type of cooler is used, nor of the composition of the atmosphere required inside the cooler, nor of the necessity of any additional cooling agent. The described method does not indicate any control over the final color of the material.

Document BRPI 1004045-5 relates to a method of controlling clay calcination in a rotary horizontal kiln under a reducing atmosphere, with or without the addition of solid fuel. The cooling process may be carried out with or without direct application of water. Depending on the chosen process, the final product may have three different colors: (1) rose if no solid fuel is added during the clay calcination and no water is injected during the refrigeration; (2) light gray if a small amount of solid fuel is added during the clay calcination and no water is used during the refrigeration process; (3) dark gray if a large amount of solid fuel is added during the clay calcination and water is injected during the refrigeration process. The described method produces a light grey pozzolan only when solid fuel is added to the calcination stage, which means that carbon monoxide will be in the kiln exhaust gas composition. Furthermore, the refrigeration stage uses water directly on the material.

Document WO 2012/126696 relates to a method of manufacturing a clinker substitute in cement production that can replace 10-40% of the clinker in a cement composition. The mentioned materials are made of clays with an iron mass fraction higher than 1.5% (wet basis) and a kaolinite mass fraction lower than 40% (wet basis). The clay calcination should be carried out in a fluidized bed kiln or rotary kiln or in an upward calciner (upware) or in a cyclone tower (cyclone tower) under a reducing atmosphere using an exhaust gas and at a temperature of 600 ℃. The cooling process should be carried out until the temperature is below 300 ℃, and a liquid fuel (usually oil) is added, which vaporizes and produces carbon monoxide (CO) during contact with the hot material, helping to maintain a reducing atmosphere. The final material should contain more than 90% of magnetite-Fe₃O₄-mass fraction (wet basis), CaO mass fraction of more than 0.1% and no hematite-Fe₂O₃. The final color of the material should be gray. The described method uses a liquid fuel (oil) on the hot material to maintain a reducing atmosphere during cooling. This solution results in a more complex system (tanks, pumps, valves) and, due to the higher price of the fuel oil, generally results in more expensive operations.

Document US 2012/0160135 relates to the manufacture of artificial pozzolans by heat treatment of raw alumina. The resulting material appears light gray or white. The heating process should be carried out in a rotary kiln or a rising calciner, and the liquid fuel (oil) is added at the clay activation temperature (700-. The cooling process should be carried out under a reducing atmosphere, adding liquid fuel (oil) or water spray on the hot material until the pozzolan color stabilization temperature (between 180 ℃ C. and 400 ℃ C.) is reached. A certain amount of the resulting synthetic pozzolan is recycled back to the heating process in the rotary kiln or calciner. The described method allows for the addition of liquid fuel during cooling and the use of water directly on the hot material.

Document US 2016/0304395 relates to the manufacture of pozzolanic materials for use as a substitute for clinker in cementitious compositions. The process is based on the calcination of a mixture containing clay and solid fuel (coal) or a mixture of clay and ash (ash). The heating process should be carried out in a rotary kiln or a fluidized bed kiln or a heating tower or a pneumatic suspension heat exchanger (heat exchanger). The heating temperature should preferably be between 700 ℃ and 900 ℃. The cooling of the hot material should take place in a rotary cooler or grate cooler (grate cooler) or fluidized bed cooler or vertical cooler (vertical cooler) or screw cooler. The described method does not provide details about the cooling process.

An important point must be emphasized with respect to the presence of carbon monoxide (CO) at the outlet of the chemical process. Carbon monoxide is a toxic pollutant gas, and prolonged inhalation of carbon monoxide can result in death of the human being. For this reason, environmental agencies require emission control of CO in all industrial processes, especially processes that burn fossil fuels, where such gases are more likely to be present.

The use of water to directly cool the active pozzolan (e.g. using water sprays on hot materials) has the negative effect of increasing the heat consumption of the process. Moisture is generated inside the cooler and drawn into the kiln, thereby increasing the kiln exhaust gas flow and, as a result, the heat loss of the process. This is a characteristic of increased heat consumption in the kiln.

In addition to the inefficiencies of existing pozzolan manufacturing methods, its large-scale use still faces resistance from the market due to the reddish color of pozzolans with high iron content.

Although color has no effect on pozzolan resistance, reddish cements are not widely accepted in the civil construction market because redness is associated with the addition of soil to the cement, which results in low quality materials. Currently, there is still no technology to activate high iron content clays economically and energetically efficiently, resulting in a light grey superior pozzolan.

Disclosure of Invention

Object of the Invention

A first object of the present invention is an improved method for manufacturing pozzolan-based cements.

A second object of the present invention is an innovative manufacturing process of pozzolans, which allows controlled variation of the colour of the final product.

A third object of the present invention is an improved environmentally friendly method for manufacturing pozzolan based cement, in the absence of carbon monoxide (CO) at the kiln exit.

Other objects of the invention will be set forth in the brief summary and description of the preferred mode of carrying out the invention.

Drawings

The present invention will be better understood from the detailed description of a preferred, but not exclusive, mode of carrying out the invention, which makes use of the attached drawings, which should not be taken in a limiting sense.

Figure 1 contains a diagram of the pozzolan manufacturing step according to the invention, with the addition of solid fuel after the heating step.

Figure 2 contains a diagram of the pozzolan manufacturing step according to the invention, with the addition of solid fuel before the heating step.

Figure 3 contains the separation from hematite (Fe) according to the amount of solid fuel blended with the material₂O₃) To magnetite (Fe)₃O₄) Diagram of the reduction reaction of (a).

FIG. 4 contains a Boudouard reaction (Boudouard reaction) diagram.

Detailed Description

The method described in the present invention aims at obtaining a light grey active pozzolan which can partially replace the cement component, enhancing or maintaining the cement resistance, without altering the original cement colour, eventually maintaining the commercial value of the cement. Furthermore, the process of the present invention is particularly important from an environmental point of view, since it eliminates carbon monoxide from the kiln exhaust gases.

Carbon monoxide (CO) emitted to the atmosphere through the exhaust gas after the clay activation process is unacceptable. Some clay activation processes are described in the prior art section, which present 0.5-3% (5000-. The inventions from documents BRPI 1004045, WO 2012/126696 and US 2012/0160135 all use additional fuel (igniters, such as fuel oil) to maintain a reducing atmosphere during cooling, except that no estimate is made of the CO fraction in the kiln or in the cooler or in the stack.

The environmental authorities are responsible for defining the maximum allowable emissions of carbon monoxide for industrial processes. For example, the brazilian national environmental Commission (CONAMA) describes an "air quality standard" in resolution 03/90 that specifies concentrations of air pollutants that may affect the health, safety, and well-being of local populations and cause damage to animals, plants, materials, and the general environment. This resolution stipulates that for carbon monoxide the average concentration of 10000 mug (9ppm) per cubic meter of air in 8 hours must not exceed once a year. The resolution also states that the average concentration of 40000 mug (35ppm) per cubic meter of air in 1 hour must not exceed one time per year. Another resolution of CONAMA is 264/99, which refers to the approval of a clinker rotary kiln to co-process the residue. It indicates a maximum carbon monoxide emission of 100ppmv at 7% oxygen. Processes that allow carbon monoxide emissions between 5000-. Thus, in order to make the clay activation process environmentally safe, carbon monoxide should be removed from the exhaust gas composition.

In the industry, the most common way to mitigate CO in flue gas is to burn it in the presence of air. This burnout results in an increase in gas temperature due to the energy released by the combustion process. The increase in the temperature of the exhaust gas represents a waste of energy and leads to an increase in the specific heat consumption (heat rate) of the kiln. That is, one cannot say that the pozzolan manufacturing method of eliminating carbon monoxide by increasing the flue gas temperature is the most effective. Thus, the presence of carbon monoxide (CO) at the kiln exit is undesirable, both due to environmental influences and due to an increase in the specific heat consumption of the kiln.

The method of the invention comprises the following steps: 1) heating; 2) mixing; 3) calcination and 4) cooling.

In "step 1", the kiln is fed with a feedstock containing 0-50% moisture. These materials are heated in a kiln. The heating process may be performed slowly when it occurs in a rotary kiln, where the residence time is about one hour, or it may be performed in a rapid manner when it occurs in a fluidized bed or flash furnace, where the residence time is only a few seconds. The heating process was continued until the temperature reached 100 ℃ to 350 ℃ to dry the material to 0-5% moisture. During this step, the oxygen concentration is still not of concern because oxidation of the material is not significant in this temperature range.

In "step 2", the hot feed is mixed with a solid fuel in a proportion of 1-5% fuel (weight fraction), depending on the content (level) of hematite in the feed composition. When charged, showed high content of hematite (Fe)₂O₃) They appear red, which is enhanced during calcination because high temperatures promote iron oxidation reactions. The particle size of the mixed fuel should be close to the feedstock particle size. Solid starting materials which can be used in this case are: coal, charcoal (charcoal), petroleum coke, biomass or other rich materialsCarbon waste. Solid fuels are necessary because the iron oxides contained in the feedstock require the presence of carbon to reduce to magnetite. This chemical reduction occurs when the mixture of clay and solid fuel reaches a temperature of about 600 ℃. Below this temperature, by the Bowden mechanism (C + CO)₂->2CO) to achieve a minimum kinetic rate of triggering the process. FIG. 3 contains a graph derived from hematite (Fe) as a function of the amount of solid fuel blended with the material₂O₃) To magnetite (Fe)₃O₄) Diagram of the reduction reaction of (a). FIG. 4 contains a Bowden reaction scheme. The figure shows that almost no carbon monoxide is formed up to a temperature of 500 c. The generation of CO is more obvious after 600 ℃, which is beneficial to the reduction process of hematite.

In "step 3", activation of the feedstock occurs. Water is released from the crystal structure of the raw material and the reduction of hematite results in a change in the pozzolan colour. The water release results in an amorphous structure of the activated feedstock. Clay activation occurs between 700-900 ℃ and when the water of crystallization is removed, it results in a breakdown of the crystal structure of the material, rendering the pozzolan hydraulically active. (hydraulic activity is the reactivity of the aluminium or silicon oxides contained in the pozzolan with the calcium oxide from the clinker or lime). Thus, the temperature at which the clay is calcined may vary between 700 ℃ and 900 ℃ depending on its mineral composition. Still in this step, it undergoes a color change of the raw material, from reddish to light grey. Hematite (Fe) contained in clay₂O₃) Conversion to magnetite (Fe) by reaction with a reducing atmosphere, preferably with carbon monoxide₃O₄) In the process, carbon dioxide (CO) is released₂). Magnetite is brown or light gray. The simplified reaction that occurs is shown below:

3Fe₂O₃+CO→2Fe₃O₄+CO₂

if "step 1" and "step 3" are performed in separate equipment (e.g., in a rotary kiln or flash dryer (flash dryer), respectively), the solid fuel should be blended with the clay immediately after heating and drying, as shown in fig. 1. The amount of solid fuel added to the blend varies between 1-5% (weight fraction) depending on the content of hematite contained in the raw material. Table I shows the necessary amount of solid fuel added to the blend as a function of the hematite concentration in the clay.

TABLE I-solid fuels added according to hematite content

Hematite (Fe) in the raw material2O3) Content (wt.)	Mass fraction of solid fuel in blend
		﹤3％	Not applicable to
3-5％	1,5％
		5-8％	3,0％
8-12％	5,0％

Using these values for the reference fuel, parameter (% C)_{fix (fixed)}90% of volatiles); using the parameters (% C) of the reference fuel and the actual fuel_fix+% volatiles) to correct the amount of fuel blended with the clay.

In case the "heating" and "calcining" steps are performed in the same equipment, the solid fuel should be added before "step 1" in order to heat and dry simultaneously with the raw material. This process is illustrated in fig. 2.

In order to maximize the color change result, the internal atmosphere of the kiln should be kept at a very low oxygen concentration (between 1-5%). One way to achieve such a reducing atmosphere is to burn off the solid, liquid or gaseous fuel (which is fed in "step 2") with very little excess air.

An apparatus capable of promoting the proper combustion of many types of fuel (both solid and liquid), particularly under the critical conditions identified in the present invention, is a compact combustion pre-chamber, as described in the document BRPI 1000417-3, which is incorporated by reference. The apparatus is capable of combusting both solid and liquid fuels under low excess air conditions (oxygen content between 1-5%). However, the results of the present invention can be achieved using other similar devices.

The mean temperature of the pozzolan should not exceed 900 ℃, which is the temperature at which mullite is formed, a stable crystal structure that does not have the activating properties of pozzolans. To maintain a suitable temperature range for the process, the gas temperature should be limited. Without dilution with air (which means maintaining low oxygen concentrations), one approach is through recirculation of the system exhaust. In other words, combustion is performed with a small excess of oxygen, and the temperature control of the process is also performed with low oxygen gas (instead of normal fresh air). In this way, the entire process within the kiln is performed with low oxygen availability, which contributes to an efficient change of the product color.

In a subsequent step ("step 4"), the volcanic ash produced in the kiln and having a changed color will now enter the cooling process. The invention can be applied to different types of coolers: a rotary cooler, a fluidized bed cooler or a flash cooler (flash cooler).

During the cooling process, special attention should be paid to: the color change that occurs within the kiln is not restored or the product color may change back to reddish.

For the reasons explained above, a mandatory feature of the invention is that the cooling process should be carried out in two steps: an initial step of rapidly lowering the pozzolan temperature to 600 ℃ and a final step of lowering the pozzolan temperature to 120 ℃. The invention proposes that the first cooling step can be increased by indirectly using water (for example, by keeping the outside of the drum (drum) wet in a rotary or flash cooler, or by using a water serpentine in a fluidized bed cooler). On the other hand, the second cooling step should be performed using air or a low oxygen stream (from the recycle gas). The need to use water and a low oxygen gas stream depends on the hematite content found in the feed. The inventors have determined the scope of application of each cooling method (direct use of ambient air; indirect use of water; direct use of recirculated hypoxic gas). Table II relates to the cooling method applied according to the hematite concentration in the feed. It can be confirmed from the table that as the hematite concentration of the raw material increases, the complexity of the cooling process also increases. This is because the higher the hematite concentration of the thermal pozzolan and the oxygen concentration during cooling, the faster and more intense the reversion.

Table II-refrigeration conditions according to the hematite concentration in the feed.

Hematite concentration (Fe) in the raw material2O3)	Cooling technique
		<3％	Direct use of ambient air
3-6％	Direct use of recycle gas
		6-10％	Direct use of ambient air and indirect use of water
>10％	Direct use of recycle gas and indirect use of water

The artificial pozzolan produced by the method described herein meets the following criteria:

NBR 5736 pozzolana Portland cement

NBR 5737 sulfate-resistant Portland cement

-NBR 12653 pozzolanic material

NBR 5751 pozzolanic Material-determination of pozzolanic Activity-pozzolanic Activity index with lime

NBR 5752 pozzolanic Material-determination of the pozzolanic Activity of Cement

NBR 5753 Portland Cement-pozzolana Portland Cement test for pozzolanic Activity

The techniques known to date for producing artificial active pozzolans have five important differences from the techniques developed by Dynamis:

(1) applying liquid fuel directly on the hot material during the cooling process to allow for the desired color change; and/or

(2) Using a solid fuel during the "calcination" step to maintain a reducing atmosphere within the kiln, allowing carbon monoxide to be emitted with the process off-gas; and/or

(3) Applying water directly onto the hot material during the cooling process; and/or

(4) No light grey pozzolan is produced; and/or

(5) The final color of the pozzolan cannot be controlled.