DK155438B - PROCEDURE FOR REDUCING DANGEROUS COMPONENTS IN ROEGGAS AND A PRODUCT FOR EXERCISING THE PROCEDURE - Google Patents

Description

DK 155438 B

This invention relates to a process for reducing the content of environmentally harmful flue gases and an additive for carrying out the process.

It is known that flue gas from the combustion of organic materials in the form of regular fuels and / or waste in addition to water (steam) and carbon dioxide often also contains environmentally harmful gases such as sulfur oxides such as sulfur dioxide and sulfur trioxide, chlorine-containing gases such as chlorine hydrogen. and nitrous gases in the form of nitrogen oxides in various oxidation steps.

Hydrocarbons are also considered for environmentally harmful flue gas components. Under special combustion conditions, as harmful substances as dioxins can be formed, especially in connection with waste incineration, where the fuel 20 can contain larger amounts of chlorine compounds, for example in the form of polyvinyl chloride. Many experiments are generally being carried out and theoretical models are being worked on in order to reduce atmospheric pollution with these substances in the modern technical society.

Several methods are known for reducing the content of various of the above-mentioned substances in flue gas. For example, the sulfur oxide content can be reduced, for example, by both wet and dry treatment of flue gases with calcium and / or magnesium containing products. These approaches can produce good results with a sustainable economy in large combustion plants, for example in thermal power plants.

The hydrogen chloride content - and thus the risk of dioxin formation - is often associated with 35

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2 waste incineration. It is now known that controlling the combustion so that the combustion temperature is raised drastically reduces the content of these components and that the addition of a basic material capable of binding the chlorine may be advantageous.

In recent years, it has become more and more aware that the content of nitrous gases in flue gas is not, as previously assumed, merely a fertilizer advantage; 10 but that these gases in the quantities produced in large modern combustion plants appear very environmentally damaging, for example because they strongly promote corrosion. The inventor of this invention has no knowledge of any technical method that can sufficiently and safely reduce the content of nitrous gases in the flue gas from large combustion plants, but assumes that in many countries environmental requirements for these are likely to be very soon. plants for reducing nitrogen-oxide emissions into the atmosphere.

It is therefore the object of this invention to provide a process for reducing the content of nitrous gases in flue gas, especially in flue gas from 25 major incinerators, including waste incineration plants. The new process should be applicable to other methods for reducing the content of other of the aforementioned environmentally harmful flue gas components and / or in itself producing such reduction. The object is also to provide an additive for use in the practice of the process.

According to the invention, the object is fulfilled by a method characterized in that the combustion process in addition to fuel and combustion air is supplied with a basic reactive material with high content 3.

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of hydroxide and / or oxide of alkaline earth or alkali metal with a microscopically ruptured surface structure in which a combustible oil is absorbed such that the weight ratio of the basic component to the oil component of the additive is between 1: 6 and 3: 2.

A material suitable for carrying out the process according to the invention is characterized in that it contains partly oil and partly calcium and / or magnesium in the form of hydroxide and / or oxide, the weight ratio of oil to alkaline earth metal converted to calcium hydroxide being between 1: 6 and 3: 2.

15 The peculiarities of particularly advantageous embodiments are set forth in the subclaims.

The advantage of the process according to the invention is that, by its use, the content of 20 nitrogen oxides in the flue gas from combustion plants is reduced. The reduction can be as much as one-third or less. Exercise of the process simultaneously results in a reduction of the sulfur oxides content of the flue gas in a manner similar to that known when, during combustion, basic materials in the form of calcium and / or magnesium compounds, for example magnesia, are added to a combustion process. Where the addition of basic minerals to combustion processes has hitherto been preferred to the use of magnesium-containing minerals because these do not promote the formation of digestible slag to the same extent as calcium-containing products, it is advantageous to use calcium which, during the testing of the invention, does not have shown signs of slag formation in the pre-35 combustion chamber.

It is advantageous to use an additive, 4

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which, in addition to the two essential components, contains other materials because it can thereby utilize cheaper raw materials for the production of the additive, and / or because one can choose oil-5 waste products, which disposal in itself is a problem. Another possibility is that the additive of the invention can be combined with another additive with a different or supplementary effect on the course of combustion, for example the addition of magnesia to further reduce the flue gas content of sulfur oxides. By such a combination of several additives to a material, it is possible to reduce the dosage to a single material.

15

In order to obtain an accurate dosage and insertion of the additive at a particular location in the firing zone, it is advantageous to select a powder additive and to use the blow-in technique known per se for the introduction.

In incineration of waste, it has been found that the process according to the invention can achieve an increase in the combustion temperature and thus achieve a reduction of the flue gas content of chlorine hydrogen and hydrocarbons, if the additive contains at least 25% combustible oils.

It is economically advantageous to keep the dosage of 30 additives as low as technically possible. A dosage of additive supplying up to 2 kg of calcium hydroxide or equivalent amount of other alkaline earth compound per 100 kg of waste is sufficient to burn off the flue gas content of nitrogen oxides to about one-third or less while combustion of the usual waste gas. significant

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5 reduction in the content of other environmentally harmful flue gas components.

The invention is not based on or formulates any scientific theory and its chemical rationale cannot be given. However, it is believed that the particular structure of the additive, which by microscopic examination has been found to contain hydroxides and / or oxides of alkaline earth metals with microscopic cracks 10 and an oil film absorbed on this large surface, is of crucial importance. It is believed that hydroxides and oxides of alkali metal salts, which can chemically react similarly advantageously to the environmentally polluting flue gas components, can be put in the same oil-activated form as the tested hydroxides and oxides of the alkaline earth metals and also induce corresponding reductions of at least the nitrous flue gas. .

The process of the invention and practiced using calcium hydroxide as a basic mineral has surprisingly worked without giving rise to slag formation during the experiments performed. As a technical hypothesis, it can be assumed that the burning of the oil film on the mineral grains with the microscopic cracks is so intense that it results in evaporation or extraordinarily large comminution of the mineral grains, which causes the metal ions to react to the nitrous to an unknown extent. gases, removing them from the flue gas and at the same time preventing the slag formation usually occurring with the use of calcium mineral. Whether this hypothesis turns out to be true or if there are other reasons why the method in this embodiment has shown the results described, embodiment 35 is advantageous in connection with waste incineration.

The additive according to the invention is advantageous.

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6 because it allows the practice to be carried out.

Regarding the embodiment of the additive based on waste oil, it should be noted that an approximately identical material is known from Germany. In the journal "Markt und Betrieb" no. 32, November 1980, a material of this kind is described and it is stated that this material by the company "Meissner Grundbau" has been used for road construction. The advantages of the material are stated to be that, at one time, 10 provides a solution for depositing oil waste from refineries and is an advantageously inexpensive material for the selected road construction purpose.

The invention will be further illustrated below by a detailed description of an exemplary advantageous embodiment.

Example of the additive for carrying out the process according to the invention.

20

A waste oil product containing 56% oil, of which more than 10% was fractions with distillation temperature of more than 110 ° C, a water content of 16% by weight and the remainder various mineral impurities including 25 other sulfur originating from an oil tank at an oil refinery, after intensive stirring with a snail in a snail conveying plant in an amount of 1000 kg used for grinding 615 kg of burnt lime with a content of 96.5% CaO, the powdered burnt lime being added to the water-mixed oil with stirring. During the leaching of the lime, additional water was added, sufficient to partly complete the conversion of calcium oxide to calcium hydroxide, and partly to replace evaporated water. The treatment was controlled so that the temperature was allowed to rise from the storage temperature of the raw materials (5 - 10 ° C) to the boiling point of the water and kept at these 100 ° C.

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7 the healing process. During the slurry, the mixture, under constant stirring, changed from being a liquid to becoming a dry, brownish powder. An analysis of this powder showed an oil content of 34% by weight and a content of calcium converted to calcium hydroxide corresponding to 48% by weight. The residual content of the brownish powder was mineral impurities, mainly derived from the waste oil used, and insignificant amounts of impurities in the lime. Other waste oil products with the same type of oil, but with varying amounts of impurities, produced similar powders with between 50 and 65% oil content and between 30 and 50% calcium hydroxide content. The dosing of water was each time based on a minor sample loss so that it could be ensured that just enough was dosed for the completion of the slurry and to cover the undesirable evaporation loss. The product may be referred to as oil-activated lime. A sample was sampled at 20 blends of material from several productions and the aliquots were selected so that the total sample had a calcium hydroxide content of 40%. This sample was used as an additive in waste incineration. The experiment is described in more detail below.

25 In a waste incineration plant for incineration of ordinary urban refurbishment, blowers were installed for blowing powdery additives at various locations in the combustion zone. The incinerator constantly burned approximately 4000 kg of waste per hour. In normal operation, that is, without any addition of additives to regulate the chemical composition of the flue gas, the flue gas analysis was that shown in column 1 of the table.

During an initial combustion test,

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8 the front part of the zone, that is, at the place where the waste is ignited because the temperature has risen above the ignition temperature of the fuel, oil activated lime of the type described above is blown. The amount of feed additive was 100 kg per hour, which corresponds to the addition of 40 kg of calcium hydroxide per hour, which in turn is 1% of the burnt waste volume of 4000 kg per hour. The flue gas analysis from this experiment is listed in column 2 of the table.

Another combustion test was carried out at the same plant and with the same fuel supplied in the same amount.

In this second experiment 150 kg of oil-15 activated lime were dosed per day. hour with the same analysis as that used in the first experiment, all other control parameters were similar in the two experiments. The analysis results from Experiment 2 are listed in column 3 of the table.

20 The results of emission measurements are analyzes of the flue gas from waste incinerators of type "Bruun & Sørensen", as the smoke samples were taken after the installed FLS electro filter. The incineration rate was 4000 kg of waste per hour.

25

It is clearly seen. For example, the process according to the invention is capable of substantially reducing the content of nitrous gases in the flue gas from an incinerator. The reduction occurred simultaneously with a reduction of the sulfur oxide content, of the chlorine hydrogen content and of the hydrocarbon content. Thus, the process of the invention also produces a highly desired effect on the content of these components.

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9

TABLE

Measurement no. 123 Smoke channel mm ø 930 930 930 5 Smoke speed m / s 22.7 22.6 20.3 Smoke temperature ° C 254 252 239 Smoke volume m3 / h 55.510 55.330 49.530 H20 content vol% 15.1 15.6 15, 9 10 H2 O amount kg / m3n 0.143 0.149 0.153

Dust emission kg / h 0.83 0.67 0.54 O2 content vol% in dry smoke 15.5 15.0 14.0 15 CO 2 content vol% in dry smoke 5.4 5.9 6.9 CO content ppm in dry smoke 40 20 0 SO2 rate kg SO2 / h 3.13 1.52 1.90 SO2 conc. mg SO2 / m3n dry, 20 0 ° C, 1013 mbar 166 74 86 HCl rate kg HCl / h 10.4 6.8 6.9 HCl conc. mg HCl / m3n dry 0 ° C, 1013 mbar 554 329 312 25 N-oxides, NO + NO2 rate kg NO + NOz / h 3.17 2.12 1.17 NO + NO2 conc mg NO0 + NO2 / m3n dry, 0 ° C, 30 1013 mbar 168 103 53 CHn rate kg CHn / h 5.9 <1.6 <1.7 CHn conc. mg CHn / m3n dry 0 ° C, 1013 mbar 308 <77 <77 10 DK 1 55438 Β

It should be noted that the oil-activated lime of the type described above, when examined under a microscope, was found to contain small crystals of calcium hydroxide, the surface of which had microscopic crevices, and that these crevices were largely filled with aspirated oil. which also covered regular crystal surfaces. A material of similar structure and quite the same effect has been prepared on the basis of ordinary fuel oil added to 30% water and then added with powdered, burnt lime used for grinding, during which the stoichiometric excess amount of water evaporated. Therefore, the additive is not limited to a material made from waste oil from refineries.

15

Since in the combustion of fossil fuels in heating plants and power plants, nitrous gases of the same kind as in the combustion of waste are formed, and since it is also possible in such plants to carry out the process according to the invention to supply the oil-activated additive, and bringing this to reaction in the combustion process under similar conditions, it is believed that the process of the invention can also be shown to give advantageous results in such plants.

The invention is therefore not limited to use in connection with the incineration of waste, as described in the example, but covers, as defined in the claims 30, also incineration of other fuels, also in plants other than waste incineration plants.

Claims (5)

A process for reducing the nitrous gases produced by combustion in combustion plants, characterized in that the combustion process, in addition to fuel and combustion air, is supplied with a basic reacting material containing hydroxide and / or oxide of alkaline earth and / or alkali metal with a microscopically fractured surface structure in which a combustible oil is absorbed such that the weight ratio of the basic component to the oil component of the additive is between 1: 6 and 3: 2. Process according to claim 1, characterized in that, as an additive, a material containing a reaction product produced by crushing burnt lime (CaO) in a mixture of an oil product and water is used so that the reaction product has become a reaction product. powdered material having an oil content of from 10 to 40% by weight and a Ca (OH) 2 content of from 30 to 70% by weight, up to about 15% water and the remainder impurities introduced with the raw materials and / or blended, other combustion additives. Method according to claim 1 or 2, characterized in that a powdery additive is selected and this is added to the combustion process by blowing into the combustion plant's burning zone. Process according to one of the preceding claims and carried out on a waste incineration plant, characterized in that it is used for setting material in such an amount that up to 2 kg of calcium hydroxide or equivalent equivalent of other soil alkali is applied. or alkali compound per 100 kg of waste. An additive for use in the practice of one of the preceding claims, and in particular for use in the combustion of waste and containing, partly, oil and partly hydroxide and / or oxide of an alkaline earth and or an alkali metal in the form of crystals with microscopic cracks. wherein 10 is absorbed oil and the weight ratio of oil to alkaline earth metal converted to calcium hydroxide equivalents is between 1: 6 and 3: 2, has a powder form and contains at least 30% by weight of calcium or magnesium hydroxide and contains other combustibles and / or non-combustible components which are at least partially sludge particles or other products typically found in refinery and tanker waste oil and which may include sulfur particles, or in spent lubricating oil such as used engine oil, which usually contains metal particles and metal oxides, characterized in that the oil content is greater than 25% by weight, so that the additive itself itself has a calorific value sufficient to raise the combustion temperature of the combustion process 25.