DE2416291A1 - PROCESS FOR MANUFACTURING LOW CARBON, WHITE RIPPING ASH FOR BUILDING PURPOSES - Google Patents

Description

Refratechnik Albert GmbH, 34 Göttingen, Rudolf-Winkel-Strasse 1

Process for producing low-carbon, whiter ones Rice husk ash for building

The invention relates to a method for producing carbon poor, white ice trays, for the production of building materials, especially refractory building materials,

Rice is a staple food in Asia, particularly India and Japan, and is used in significant quantities also grown in various countries in America and Europe. Because of the strong population increase in particular in the Asian countries there is a further increase in the future, which is currently around 400 million tonnes per year lying world rice production to be expected. When peeling the rice grains fall, depending on the Type of ice cream, around 14 to 35% rice husks as waste product at, a lot that is due to the low weight of the rubble

411

Bremen office:
D-? 800 Bremen 1 P.O. Box 786, Fddstraße

© Tclefoii
telex

! 0421 "!" 7 4044 2-lt? 3-Sr.o;: aid )) iai.ry; in), E; a

509843/043 2

Ko.iteii Bremen:
Brew; · "Bank, iircinen
(BLZ 25080010) 10014 W

PSchA Hai.ihurg

(BLZ 2M)! 0020} 126OHK-Mi

Munich office: D-8000 Munich 90 Schlotthauer Straße 3

Telephone: (0ii9) 6523?] Telegr.: Telepatent, Munich

Husks of around 100 kg / nr a space requirement of 560 to Ί400 million m ^ required.

The chemical analysis of the rice husks shows the following typical ones Composition (based on substance free from ignition loss)

Water 9 %

! Protein 3.5%

Fats 0.5 %

Cellulose 30 to 42%

Pentosan 1.4 to 18%

mineral ash 14 to 30 %

The composition of the mineral ash is as follows Limits:

SiO ₂ 92 to 97 %

Al ₂ O 0.75 to 3 %

Ee ₂ O ₅ 0.17 to 2%

CaO 0.56 to 3%

HgO 0.32 to 1.5%

In addition, depending on the degree and type of "combustion" of the organic constituents, carbon proportions of up to 30 % are found before the analysis.

Because of the composition of rice husks, a number of proposals have been made to use them on a large scale Scale to use agriculturally or industrially. These suggestions include immediate use in the uncrushed or in the crushed state, the chemical-technological decomposition of the rice husks with the extraction of organic-chemical Raw materials, incineration for heat recovery and the use of the mineral ash recovery

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stands. In detail "include these possible applications the use of bowls as animal feed, for loosening the soil, for pressing fruit or the like, for the production of building materials, such as panels or the like, as filler, packaging material, or else as (^ absorbent. In industrial technology, "ice trays provide a raw material for the production of Furfurol, for the saccharification of wood, as well as for the extraction of acetic acid and other organic raw materials. Ice bowls are still used as abrasives, as heat carriers for steam or electricity generation, also for the production of ferrosilicon, silicon carbide, silicon nitride, lignin and nitrogen-lignin compounds, Sodium silicate, silicon tetrachloride and the like.

In particular, Keisshell ash is used in the glass industry, the ceramic industry, the cement industry and above all in the refractory industry because it has the property of a porous silica raw material. Was Vie already mentioned, Eeisschalenasche 92 to 97% siop and therefore has a melting point of over 1600 ⁰ C. For this reason, it is a silica support as! Raw material for the production of heat insulating refractory and heat-resistant materials, such as

refractory, chemically bonded or fired bricks

■ f and Hassen, as well as for the production of calcium silicate hydra-bound Lightweight building materials (tobermorite synthesis) especially well suited. For the production of such building materials, ashes are required, which are defined on the one hand by a Mark the carbon content, on the other hand, point to a certain structural formation. So is E.g. for the tobermorite synthesis an ice-cream shell ash suitable, the silicic acid content of which is in an "amorphous" vitreous and therefore very reactive form. For refractory purposes, however, is

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it because of the required volume stability "at high Temperatures are desirable that the silica is in a crystalline form, for example the quartz form, the cristobalite form or the tridymite form.

It has now been shown that for the production of refractory building materials or the like only white, so essentially Carbon-free or at least low-carbon rice husk ash can be used, because namely black Rice husk ash, which has a high carbon content, is hydrophobic because of the remaining carbon and thus because of the poor wetting of the rice husk ash particles with aqueous binder solutions, the binding the stones and the achievement of a mechanically strong structure made more difficult. In the synthesis of tobermorite there is presence of carbon also disruptive, since it hinders the formation of tobermorite or at least has a disruptive effect. In the Manufacture of ceramic products, an undefined carbon content can lead to undesirable reduction phenomena lead in shards. In other uses of the rice husk ash, such as filler, filter material or the like Also, because of a uniform color of the rice husk ash, it becomes a controlled carbon content and a defined structure is required.

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It has now been found that white, low-carbon rice husk ash with open kilns or "Detachment" of rice husks in heaps occurs, a process which is used in the Rice-growing areas are mostly carried out in the open air. Here, the rice husks glimmer from a previously created one Embers through central from the inside to the outside in the event of subsequent stacking. This process that largely runs without flame development, lasts about 3 his 6 months. This creates aromatic vapors and gases that cause extensive and intense odor nuisance to lead. The silica-rich ash particles blown into the area by the wind pose a further hazard of humans and animals as silicosis pathogens. The burnt out rice husk heap, which is now made of rice husk ash exists, also shows in terms of its color, its chemical composition, its crystal structure as well as their degree of crystallization no uniformity, because the "roasting" takes place under uncontrolled conditions, so that the color of the ashes within a mountain of ash changes between pink, white, gray and black. One Separation of the individual zones, which also differ chemically, mineralogically and physically, is only possible to a limited extent. so that such rice husk ashes meet the conditions that apply in particular when used as a refractory component Building materials must be provided, not met. It is particularly important to consider that the specific weight "amorphous" and crystalline ash is inconsistent. Amorphous rice husk ashes were found to have values of 2.12, while in the case of crystalline, cristobalite-containing ashes, values of 2.28 were determined. From the uniform crystal structure, namely both the crystal modification and the degree of crystallinity, of the SiOp of the rice husk ash but depends in particular on the thermal

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see expansion coefficients the quality of the finished Building materials.

Because of the high calorific value of the hot bowls from 34-30 to 3995 kcal / kg, the so-called "roasting" of the hot bowls takes place automatically in the open healing process, but it is an energetically unfavorable process that, as already mentioned, also takes about 3 to 6 months takes, so that this method, in particular because of the environmental problems described, not can be used on an industrial scale for the production of white shell ash, and of particular The significance of the fact is that by means of this process there is no hot-shell ash with a uniform crystal structure and uniformly low carbon content can be obtained.

On the other hand, during incineration in industrial plants for heat generation, eg for steam generation, the ice-cream ashes are obtained as black, highly carbon-containing residues, the carbon content of such "black ashes" generally being between 10 and 25 % . For the reasons mentioned, hot dishes with such a high carbon content are unsuitable for many purposes, but in particular for the production of refractory building materials. This inertia of the carbon in the present special case is likely to be due to the fact that after the crystallization of the silica, the carbon is no longer sufficiently accessible for the attack of the oxygen.

All attempts to "burn" rice husks like that control that a low-carbon or carbon-free Ashes emerge were unsuccessful. On the other hand, it has been shown that a subsequent annealing black

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• V

Rice husk ash is uneconomical because the carbon is in a very inert form. V / pus table below shows 4- that seihst at high temperatures such as 1000 ⁰ C is not obtained white ash even after one and a half hours of treatment.

It is therefore up to now no method known which works under conditions in which the same time Organic constituents converted into. Energy or separable degradation products and a low-carbon white Ash produced for the manufacture of building materials can be produced.

The invention is therefore based on the object of providing an industrially feasible process for the production of white, to create low-carbon rice husk ash, which is energetically favorable and economical to run and the production of homogeneous, white rice husk ash with a uniformly low carbon content as well as continuously defined SiOp crystal modification and homogeneous SiOp degree of crystallization permitted.

According to the invention, this object is achieved in a method of the type mentioned at the outset in that the rice husks are first heated to a first, relatively low temperature below the ignition temperature of the rice husks in order to separate off the post-combustible volatile constituents without the supply of air; that then the rice husks to oxidize the fixed carbon

509843/0432

with the addition of a reactant to one above the separation temperature, but below the crystallization temperature of the SiOo of the rice husks, the second temperature be heated; and that the rice husk ash obtained in this way is then used to produce a uniform SiC ^ - The crystal structure is annealed at a third temperature above the crystallization temperature of the SiÜ2 will.

A preferred embodiment of the method is characterized in that the separation of the volatile components takes place at a temperature in the range from 200 ⁰ C to 4-5O ⁰ C temperature; and that the oxidation of the fixed carbon is carried out at a temperature between 450 ⁰ C and 70O ⁰ C, it can further be provided that the rice husks are initially heated at a heating rate of 10 to 40 ° C / min, from a feed temperature of <L1OO G brought to a separation temperature of 200 to 250 C; that is then heated with the same heating under access of the reagent to a Oxydationstemperar-ur from 450 to 55O ⁰ C; and that thereupon the rice husk ash obtained in this way with the same Aufheizgeschwindigkf
will.

to a temperature between 70O ⁰ C and 80O ⁰ C heated

The heating rate is preferably 25 ° C./min. Another embodiment of the method provides that as a reactant for the oxidation of the fixed carbon in the second process step, combustion air with an air ratio of η = 4.0 - 6.0 is supplied, alternatively it can also be provided that steam is supplied as the reactant.

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Λ.

In other words, the real inventive idea lies in that the rice husks are incinerated in a three-stage process, initially in a first step the Rice husks are freed from the volatile constituents in the absence of air, whereupon at "a higher temperature the oxidation of the fixed carbon takes place and finally to adjust the degree of crystallization, moreover also the crystal modification, the SiOo annealing even higher temperature takes place. Those involved in the separation of the volatile components as well as in the gasification of the fixed The combustible gases produced by carbon are burned afterwards, with the energy obtained not only being used for the entire process is used, but also recovered useful energy under particularly favorable conditions in terms of energy v / can earth.

The method according to the invention makes it possible to obtain a white rice husk ash under industrial conditions To produce carbon content e.3 and defined composition and structure, with the separated organic Components can be volatilized and used for thermal energy. Compared to the organic components recoverable The heat content of the rice husks can be used for the incineration process itself and / or, as already stated, for used for other purposes. Of course, there is also the possibility of using the organic thermal decomposition products of the rice husks in a manner known per se according to the to further process various synthesis methods, for example to furfural, wood vinegar, methanol or the like, whereby of course there is also the possibility of already in an upstream process stage for furfural production to incinerate rice husks treated in a known manner by the specified method according to the invention.

509843/0432

The method according to the invention thus enables the large-scale production of white rice husk ash with a defined composition and structure in an energetically justifiable manner, such as that obtained from black ash from combustion processes through subsequent annealing. known type could not be produced due to lack of economic efficiency, namely because additional energy and time would have to be expended for this. The invention is based on the surprising finding that an optimally low carbon content can not be obtained for example by an arbitrarily high combustion temperature of the rice hulls, but rather showed an operation performed between 100 and 1000 ⁰ C series of experiments that optimal white Eeisschaienasche Achmann in which £ ' unpredictable Ueise, at. Temperatures of about 4-50 to 55O ° C is obtained, while at lower and higher üxydationemperaturen black bsw. gray, unusable ashes result. This observation applies to both continuous heating and temperature shock treatment in the specified temperature range.

In addition, provision can also be made for the rice husks to be comminuted prior to the heat treatment in order to increase the weight of the debris. The resulting increase in bulk density to approx. 0.5 t / m ^J enables the energy yield of the process according to the invention and the throughput to be increased considerably.

Further features and advantages of the invention emerge from the claims and from the following description, in which the invention is explained in detail using an exemplary embodiment and test results.

example

Ice trays in non-pretreated and in purpurol production pretreated i'orm σ; own following composition and features:

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description Rice bowls Rice bowls off
Italy from the from Italy lurfurol process ash 14.4% 20.7% Flammable components 85.6 % 79.3 % Volatiles 69.7% 53.9 % Lower calorific value 3430 kcal / kg 3995 kcal / kg Ignition point (air) / w 250 ⁰ C / -25O ⁰ G C. 39.6 % 43.0% H 5.4% ■ 4.5 ^l / o S. traces - E " 0.32 ^c / o 0.44% O 40.28% 31.36%

The investigation by means of differential thermal analysis (DTA)
and differential thermogravimetry (DTG) shows the following decomposition reactions in a nitrogen atmosphere and in the presence of air:

( ⁰ C)

Rice bowls N2 atmosphere

Bowls of rice

without air exclusion

100 ° C endothermic reaction: destruction of pentosan with formation of volatile components; . Formation of tar

27O C exothermic reaction: "Destruction of the cellulose with the formation of volatile components (GO) 360 ° C exothermic reaction: Destruction of the lignin with the formation of volatile components (GO, GHJ

23O-5OO C exothermic reaction : Destruction of the cellulose and "oxidation of the free carbon

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700 700-80O ⁰ C exothermic reaction 700-800 ⁰ C exothermic retention: action:

Crystallization of the SiO2 Crystallization of the SiOo and whereabouts of fixed C

Black rice bowl ash White rice bowl ash

From the above table it follows that the thermal separation of the volatiles is at its maximum at about 36O ⁰ C and largely completed at about 450 ⁰ G, the proportion of fixed carbon is left in nitrogen atmosphere in the rice hull ash, while in the presence of it of air in the range of 500 to 55O ⁰ G can be optimally removed oxidatively, exactly according to the inventive method.

Structural investigations of the silica content of the rice husks have shown that this is apparently mainly present in oxidative bonds in the "amorphous" state in the form of strongly disordered cristobalite. Depending on the temperature used, this remains either X-ray amorphous or crystallizes out. Without the addition of mineralizers, the crystallization begins at 70O ⁰ C with clear oscillation of the rice husk ash. With the addition of mineralizing agents crystallization starts already at 300 ⁰ C. Particularly effective Mineralizers the attempts alkali halides (FaF, UACL, KCl) have been found. For this purpose, it is sufficient, for example, to wet the rice husk with 0.2 η aqueous NaCl solution. On the other hand, it has been found that the crystallization of the silica can be delayed if the rice husks are wetted with HCl before the thermal decomposition. In this way, highly reactive white rice husk ash can get even -Be at 700 ⁰ C. It continued to be

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found that the removal of the fixed carbon from the rice husk ash is ^{accelerated by the addition of mineralizers such as NaIi 1} ', NaCl, KCl etc.

Systematic incineration tests of a semi-technical nature in the presence of still air have shown that a white ash in the temperature range from about 450 to 550 C. is obtained, as can be seen from Table 1 below:

Weight loss

29.8% black 66.8% gra · « 77, ^% White ! ! 7 ^l ^ 7% Gray 69.4 % black 73.5 % black 75.8% black

300 ⁰ C 400 ⁰ C 500 ⁰ C 600 ⁰ C 700 ⁰ C 800 ⁰ C 1000 ° C

Panel 1; Loss of weight during the thermal decomposition of rice husks and color of the ashes when they are spontaneously heated to temperature. Hold time 1 hour. Still air.

As can also be seen from Table 1, the organic constituents of the rice husks are only insufficiently decomposed below the temperature range from 450 to 550 C. Above 55O C spontaneous heating results in a black, unsuitable, carbon-containing ash. A temperature increase far beyond 1000 ⁰ C, that too

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has been studied, brings compared to decomposition in said Breich of 450 to 55O ⁰ C no improve-. the rate of decomposition and the purity of the inorganic end product. Table 1 shows that the greatest weight loss occurs during spontaneous heating at around 500 ^{° C.} The end product is white, while on ^{both sides of 500 0} G the quality of the ash product deteriorates continuously.

With regard to the speed with which the rice husks v brought to the temperature of 450 to 55O ⁰ C must ground / was / min determined as optimum a heating rate of 25 C as well, the following Table 2 is based on:

Weight loss

37.1% black 72.1 % Gray 77.5 % White 76.9 % White 78.0 % White 76.1% White 78.6 % White

20 - 300 ⁰ C 20 - 400 ⁰ C 20 - 500 ⁰ C 20 - 600 ⁰ C 20 - 700 ° C 20 - 800 ° C 20 - 1000 ⁰ C

Table 2: Weight loss during continuous heating of rice husks to temperature. 25 ° C / min. Still air.

From Table 2 it can be seen that when the temperature is gradually increased from room temperature at 25 ° C./min from 50O ⁰ C, white ashes are obtained. It has been shown that the upper and lower limits for the heating rate at which

509843/0432

Rice husk ash with a sufficient "degree of whiteness" (C <ζ 2%) can be obtained, 10 ° C / min and 40 ° C / min can be specified.

The following table 3 shows the time course of the weight loss at the optimal temperature of 500 C:

Time Weight loss fcolor

O % gold-yellow

.1.7% black 45.6% black 4-9.2 % black

56.0% black

76.1%. Gray

78.8% white

0 Min. 1 Min. 3 Min. 5 Min. 10 Min. 30th Min. 60 Min. Table 3:

Loss of weight in the thermal decomposition of rice husks with spontaneous heating to 500 ^° C. as a function of time. Still air.

As Table 3 shows, 41.7% of the combustible components of the rice husks are removed after just 1 minute. Between 10 and 30 minutes is the total amount of volatiles expelled. At the same time, the gasification of the fixed carbon content begins after 60 minutes is practically removed.

The following table 4 shows the loss of weight at ox # dative post-treatment of black rice husk ash from high temperature incineration:

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temperature

Weight loss / min.

colour

60

120

180

300 ⁰ C 400 ⁰ C 500 ⁰ C 600 ⁰ C 700 ⁰ C 800 ⁰ C

1000 ⁰ C

2.4% 2.61% 2.6% 2.9% black 8.93% 8.98% 9.05% 9.06% black 24.26% 24.47% 24.68% 24.90% Gray 24.60% 24.87% 24.95% 24.96% Gray 24.00% 24.01% 24.05% 24.07% Gray 24.41% 24.50% 24.55% 24.54% Gray 24.45% 24.83% 24.81% - 24.90% Gray

Table 4: Weight loss with ox / dative aftertreatment of black beet-shell ash from high-temperature incineration.

Table 4 shows that the oxidative removal of the Carbon in black rice husk ashes also contribute 500 ° C takes place. An increase in temperature or time no longer has an effective effect.

Overall, that white Eeisschalenasche with desirably low ^ carbon content (C <C 2% or at least ^. 3%) results from the discussion of the test results described above in Tables 1 to 4, and defined structure can be generated when proposed according to the invention in the The volatile constituents are separated off at temperatures preferably below 450 ° C., while the gasification of the fixed carbon is carried out between preferably 45 ° and 55O ° C. by oxidation, water gas reaction or the like.

If necessary, the addition of additives is recommended, which the gaseous separation of the fixed carbon in the

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second process step "accelerate, for example of NaCl. The distillation products formed in the process according to the invention can be used in syntheses known per se for the production of heat or for the production of organic raw materials. In order to produce a white ash, in which the silica should be maintained in reactive state, the maximum process temperature must (Tobermoritsynthese) below the crystallization temperature of the SiO ₂ remain the Eeisschale, ie in the region below 700 ⁰ C. Optionally, in this particular case kriställisationshemmende additives can be added, such as, for example, HCl.

To produce a white ash in which the silica has crystallized out, as is particularly recommended when using rice husk ash for the production of refractory building materials, the ash must, according to the invention, be tempered in the range of preferably 700 to 800 ° C. after the organic components have been separated off. In addition or presence of mineralizers such as Kacl, NaF or KCl, crystallization takes place at temperatures between 300 and 800 ⁰ C.

The process according to the invention can be carried out in one or more stages in apparatuses known per se, such as rotary kilns, shaft furnaces, Retort furnace, sintering belts or the like can be carried out. Within the inventive concept, which is in particular relates to the production of rice husk ash suitable for use in refractory building materials Of course, modifications of the inventive concept described above and defined in the claims, which are familiar to the person skilled in the art, are possible.

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^; '"■■'" ■■ 241629

• ff

Of course, the method according to the invention is also suitable for treating other suitable cereal husks such as wheat, oat or barley husks or the like.

The features of the invention disclosed in the above description and in the following claims can both individually and in any combination for the implementation of the invention in its various Embodiments are reasonable.

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Claims (10)

New claims 1 Ms 10 1. Process for making low carbon whiter Rice husk ash for the production of building materials, especially refractory building materials, in which the rice husks are used to separate the volatile components and to convert the fixed carbon into a gaseous compound at a temperature below the crystallization temperature of the SiOp of the rice husks lying temperature, whereupon the rice husk ash obtained in this way to produce a uniform SiOp crystal structure is annealed at a temperature above the crystallization temperature of the SiOp, thereby characterized that the rice husks initially exclusively to separate the post-combustible volatile constituents without supplying air to a first, relatively low separation temperature are heated; and that the volatile components are then removed Rice husks to convert the fixed carbon into a gas phase before tempering at the above Crystallization temperature of the SiOp lying tempering temperature with the addition of a reagent to the Gasification temperature lying below the stated crystallization temperature are heated. 2. The method according to claim 1, characterized in that the volatile constituents are separated off at a temperature in the range from 200 G to 450 C; and that the transfer is carried out of the fixed carbon in a gaseous compound at a temperature between 450 ⁰ C and 7oC ⁰ C. 3 · Method according to claim 2, characterized in that 509843/0432 The rice husks are min, first brought at a heating rate of 10 to 40 ° G / from an object temperature of <C1OO ° C to a separation temperature of 200 to 25O ⁰ O; that is then heated with the same heating under access of Beaktionsmittels a Yergasungstemperatur from 45O to 55O ⁰ G; and that thereupon the HeisschaXen ash obtained in this way with the same heating rate to e:
is heated. dability to a tempe: temperature between 70O ⁰ G and 800 ⁰ G 4. The method according to claim 3, characterized in that the heating rate is 25 C / min. 5. Method according to one of Claims 2 to 4, characterized in that that as a means of realization for the transfer of the fixed carbon in the second process step combustion air with an air * aM of η = 4.0 - 6.0 will. 6. The method according to any one of claims 1 to 4, characterized in that that supplied as a reaction agent water vapor will. 7. The method according to any one of the preceding claims, characterized by adding the transfer of the fixed Carbon in a gaseous compound in the second process step accelerating additives, such as EaCl or similar. 8. The method according to any one of the preceding claims, characterized by adding mineralizers, such as NaCl, NaF or KCl, to facilitate the crystallization of the during annealing. 9. The method according to any one of the preceding claims, 509843/0432
- 2 - BOFHMERT & BGEHMERT _o . characterized by the addition of the crystallization of the SiOP in Vergasüngsäelix'itt nenmienden _t additives such as HCl or the like. 10. Yerfahren according to one of the preceding claims, characterized in that the Eeissclialen before the Warm handling is broken down into the bulk weight will", 50SS43 / 0432