EP0135784A2 - Coal or coke briquet and process for manufacturing same - Google Patents

Abstract

Coal or coke briquettes which burn without smoke and soot and have a high mechanical stability during loading, weathering and in a fire, are produced by adding 1 to 3 % by weight of molasses and 0.3 to 2% by weight of a fully saponified polyvinyl alcohol having a viscosity of 40 to 100 mPas as a binder, especially in aqueous solution, and pressing the homogenised mixture to form briquettes, with efficient removal of fumes.

Description

The common binders for hard coal briquettes are pitch and bitumen. Because briquettes with these binders do not burn without smoke and soot and break down too quickly due to softening of the binder, so that unburned coal falls through the grate, there has been no lack of attempts to improve hard coal briquettes by choosing other binders. A new briquette that meets the requirements of the domestic fire market from a comfort fuel must have good loading, weather resistance and fire resistance, it should burn free of smoke and soot and the combustion gases must be free of pollutants.

Loading strength means that the briquettes are so strong about 20 minutes after being pressed that they can withstand the mechanical stresses when loading them into wagons, buckets, trucks and the like. have grown without breaking. This strength in the cold state (cold strength) should increase with a greater time interval from the pressing, but in no case should it drop noticeably again, in order to ensure that briquettes are resistant to trade and consumers.

The weather resistance indicates whether and to what extent the briquette strength can decrease due to the influence of air humidity and precipitation when stored outdoors. If it also increases again due to drying, for example due to solar radiation, it should not, however, fall below a point pressure resistance according to DIN 23081 of 50 kg.

The stability of the briquettes in the fire is ultimately the goal of any briquetting. Since fine-grained material, such as washed anthracite fine coal, fine coke of any kind and similar fine-grained fuels, cannot be burned in domestic furnaces, they are made into pieces by pressing with a binder and are therefore usable like nut coal. It would make no sense for the briquettes to fall apart at the start of the combustion and to pass through the grate into the ash pan as unburned material.

The smoke-free and soot-free combustion as well as the freedom from pollutants in the combustion exhaust gases has meanwhile become a requirement of environmental protection. Emission values of briquettes are expected which do not significantly exceed those of anthracite nut coal and crushed coke.

A new binder should be easy to work with and should not cause any nuisance to the workforce or the surroundings of the briquette factory. If a briquette factory with a conventional procedure already exists, the new binder should not require extensive renovation or even the new construction of the briquette factory for market and cost reasons.

Numerous organic and inorganic binders have been known for decades (see Jünemann, Brikett-Industrie p.140-147). However, they could not be introduced in practice because the briquettes could no longer be produced with the usual devices, but instead required difficult processing techniques, which made the briquettes' production costs too high. In many cases, the briquette qualities also proved to be inadequate. The disadvantage of all inorganic binders is that they increase the ash content of the briquettes quite a bit.

Molasses have also been proposed as an organic binder. But it turned out because of its water dissolving! and long solidification time for modern briquette processes as unusable and could not be introduced in the past due to the poor weather resistance. In order to improve the resistance to weathering, it is also known, the molasses sulfuric acid or substances which form in their Verset- _i Zung sulfuric acid to mix, but what is ruled out today because of the increase in the sulfur dioxide content in the exhaust gas.

More recently, experiments with adhesive plastics, such as latex-like aqueous plastic preparations, thermoplastics and polyurethanes, have been carried out, but they also did not meet practical requirements (see Glückauf Research Books 36 (1975) pp. 156-61). The same applies to specially selected, namely cationic, polyurethanes which, according to DE-OS 30 17 599, were used with up to 19% of a natural or synthetic binder, in particular on a bitumen basis. DE-OS 31 14 141 also suggests using polyvinyl alcohol as a binder in combination with the cationic polyurethane. However, tests by the applicant have shown that this does not result in a satisfactory loading strength, since the setting takes place very late and the weather resistance is also insufficient.

It has now surprisingly been found that certain types of polyvinyl alcohol in combination with molasses, with special incorporation, enable the production of coal or coke briquettes, in particular hard coal briquettes, which meet the conditions mentioned above and, above all, have good stability in fire.

The invention accordingly relates to coal or coke briquettes which contain 1 to 3, preferably 1.5 to 2.5% by weight of molasses and 0.3 to 2, preferably 0.5 to 1.5% by weight of a fully hydrolyzed polyvinyl alcohol with a Viscosity of 40 to 100, preferably 50 to 70 mPas, each based on the dry matter of coal or coke. "Fully hydrolyzed" polyvinyl alcohols are those with a degree of saponification or hydrolysis of the underlying solvolysed polyvinyl acetate of over 97 mole percent, in particular 98 to 100 mole percent. In this area the crystallinity of the polyvinyl alcohol rises sharply and this leads to drastic differences in the property profile compared to other, for example, only partially saponified polyvinyl alcohols. The fully saponified polyvinyl alcohols with high viscosities suitable for the purposes of the invention are commercially available, for example, as MOVIOL ^R types 56-98 and 66-100 (HOECHST).

The invention further relates to a process for the production of coal or coke briquettes, in which the fine-grained fuel heated to a temperature of 100 + 20 ° C. is heated with an aqueous binder solution which is 70 to 100 ° C., in particular 80 to 95 ° C. Molasses and the polyvinyl alcohol sprayed, the mixture of fuel and binder solution, optionally with additional heat, homogenized and pressed with good dewatering to briquettes.

In the production of briquettes made of anthracite coal with an aqueous binder solution which, however, contained only the specially selected fully saponified polyvinyl alcohol but did not contain molasses, briquettes with a fairly good loading resistance and very good ones have already been produced Ultimate strength achieved. The stability in water was sufficient immediately after production, but improved noticeably after 24 hours. The heat resistance, i.e. the stability of the briquettes in the fire, can still be used for domestic furnaces without too much unburned coal falling through the grate in the ash pan during combustion, but appears to be in need of improvement, especially for use in heating boilers, so that these smokeless briquettes also very low emission value can also be used there.

Regardless of the bad experiences that have been made in the past with molasses as a binder, it has surprisingly been found that the combination of the special polyvinyl alcohol in combination with molasses achieves a very significant improvement in the heat resistance while maintaining the good briquette properties mentioned. With the method according to the invention, which fits well into the usual briquette production, low-smoke hard coal briquettes can thus be produced which fully meet the conditions of a comfort fuel mentioned at the beginning.

Tubular or beet molasses are useful for the purposes of the invention. Beet molasses is obtained with a dry substance of 85 to 89%, with tubular molasses the water content is usually somewhat higher. Molasses has a high content of carbohydrates, especially sugar, as well as non-sugar substances, especially amino acids and nitrogen-free carboxylic acids, in the order of about 40%. There is also an ash content of 10 to 16% on average, which mainly consists of potassium, sodium, calcium and magnesium salts.

For a homogeneous distribution of the aqueous binder solution with the fine-grained fuel, on the one hand it is necessary that this solution is not too viscous, but on the other hand no more water should be introduced than is absolutely necessary. For this reason, the polyvinyl alcohol and / or the molasses are added in the most concentrated aqueous solution possible.

To prepare the binder solution to be used according to the invention, the fully saponified polyvinyl alcohol of the required viscosity range is expediently first dissolved in hot water and then mixed with the generally undiluted molasses. This gives an aqueous solution with 15 to 30% dry matter, which is sprayed hot on the coal and then in a suitable mixing unit, e.g. a double mixing screw, well mixed with the coal.

The heat resistance can be further improved by adding up to 2% by weight of powdered calcium carbonate, based on the dry matter of coal or coke. Part of the molasses can also be replaced by calcium carbonate. In order to be fully effective in the mixture, the calcium carbonate should be as fine as possible and should have a grain size of less than 100 µm.

Calcium carbonate can be used in its finely powdered, pure natural or synthetic forms. Only for the purposes of the invention, cheaper products such as ground limestones, such as lime slate, marble, marl, chalk, stalactites or limestone tuff, are preferred for reasons of cost. The limestones can also contain a certain percentage of dolomite.

Precipitated calcium carbonates are also usable for the purposes of the invention, which accumulate in chemical processes as a waste product and do not even dry need to be, because even with the incorporation of a slurry in the mixing units, sufficient homogenization can still be achieved with the fine-grained fuel and because the use of the aqueous binder solution according to the invention requires dewatering anyway.

The weather resistance of the briquettes can be increased by spraying the freshly pressed briquettes with a high-percentage, in particular saturated sodium carbonate solution or briefly immersing them in them.

Various fine-grained fuels such as e.g. Anthracite coal, fine coke, flame coal, fat and lean coal, eating coal, lignite and charcoal are used.

• Die Kaltfestigkeit wird geprüft, indem jeweils 10 bis 50 Briketts wahllos aus der Produktion genommen werden. Jedes Brikett wird nach DIN 23081 zwischen zwei Stempeln von mindestens 15 mm Durchmesser mit einem Stempelvorschub von mindestems 8 mm/min bis zum Bruch belastet. Die Bruchlast in kg wird als Kaltfestigkeit angegeben, wobei das Mittel aus den Einzelwerten gebildet wird.

The following procedures are used to check the quality characteristics of the briquettes described at the beginning:

• The cold strength is checked by randomly removing 10 to 50 briquettes from production. Each briquette is loaded according to DIN 23081 between two stamps of at least 15 mm diameter with a stamp feed of at least 8 mm / min until it breaks. The breaking load in kg is given as the cold strength, the mean being calculated from the individual values.

The stability of the briquettes in water is checked as a measure of the weather resistance. Immediately after pressing and then at certain intervals, 10 briquettes are placed in a water bath. After a dwell time of 15 minutes, they are removed and their strength is immediately tested using the cold strength method. The start of water bathing is the time of the water resistance.

The heat resistance of the briquettes is examined to determine their stability in the fire. 5 briquettes are placed in a muffle furnace heated to 600 ° C and removed after certain time intervals. Then they are loaded on the test press immediately after the cold strength process until they break.

As a measure of this fire resistance, combustion tests are carried out in the house furnace in accordance with the test regulations of DIN 18 890. The ash content is determined on the basis of the grate diarrhea. The soot-tar number is also identified as an indication of the emission. The pollutants in the exhaust gases are measured using the method described by Ahland / Merten in VDI report No. 358/1980.

example 1

1 kg of a fully hydrolyzed polyvinyl alcohol with a degree of hydrolysis of 98.4 mol% and a viscosity of 56 mPas (commercial product MOVIOL 56-98) is dissolved in 10 l of water at 95 ° C. and then in each case as much molasses with a dry substance content of 80% is stirred in that the finished briquette has the molasses content (in percent by weight) given in Table 1.

The aqueous binder solution is sprayed in a quantity of 10 1/100 kg coal at a temperature of 80 to 95 ° C onto washed anthracite coal, which in turn is heated to 100 ° C + 20 ° C. For the various tests, up to 3% molasses, based on the dry matter, was stirred into this binder solution. There are approximately 10 minutes between metering and pressing on conventional briquette presses, in which the briquette material is homogenized in a mixing unit and at the same time ensures that the water can escape easily becomes. The briquettes are then processed into egg briquettes in conventional double-roll presses. The various strengths, emission values and the analysis of the exhaust gases were then carried out as described above.

The increase in the strength of the briquettes with a constant polyvinyl alcohol content of 1% and increasing proportions of 1 to 3% molasses, both based on the dry substance, are shown in Table 1. The percentage increase in strength was given in brackets behind the strength values.

The loading strength, 20 minutes after pressing, was 415 N, well above the minimum value of 300 N to be demanded.

The final strength was excellent at 950 N.

With a soot-tar number of 18, the emission value when burning the briquettes fell well below the upper limit of low-smoke fuels of 200.

The stability in water was 350 N, but the values were already over 24 hours after pressing

500 N much better.

Table 1

Claims (7)

1. coal or coke briquettes containing 1 to 3% by weight of molasses and 0.3 to 2% by weight of a fully saponified polyvinyl alcohol having a viscosity of 40 to 100 mPas, in each case based on the dry substance of coal or coke. 2. Briquettes according to claim 1, containing 1.5 to 2.5% by weight of molasses and 0.5 to 1.5% by weight of the polyvinyl alcohol. 3. Briquettes according to claim 1 or 2, characterized in that the fully saponified polyvinyl alcohol has a viscosity of 50 to 70 mPas. 4. briquettes according to any one of claims 1 to 3, characterized by the addition of up to 2 wt .-% powdered calcium carbonate, based on the dry matter of coal or coke. 5. A process for the production of coal or coke briquettes according to one or more of claims 1 to 4, characterized in that the fine-grained fuel heated to a temperature of 100 ^t 20 ° C with an aqueous, 70-100 ° C, in particular 80 -95 ° C, spray the molasses and the binder solution containing polyvinyl alcohol, homogenize the mixture of fuel and binder solution, possibly with additional heat, and press it into briquettes with good dewatering. 6. The method according to claim 5, characterized in that the polyvinyl alcohol and / or the molasses are added in the most concentrated aqueous solution possible. 7. The method according to claim 5 or 6, characterized in that the freshly pressed briquettes are sprayed with a high-percentage, in particular saturated sodium carbonate solution or briefly immersed therein.