GB2196984A - Oil based additive for reduction of combustion formed nitrous gases - Google Patents

Description

1 GB2196984A 1

SPECIFICATION

Method for the reduction of environment- i nj urious components in flue gas, and a product for the execution of the method The invention relates to a method for the reduction of the content of environment-injurious gases in flue gas, and an additive for the execution of the method.

It is known that flue gas from the burning of organic materials in the form of regular fuels and/or waste often contains, in addition to water vapour and carbon dioxide, environment injurious gases such as, for example, sulphur oxides such as sulphur dioxide and sulphur trioxide, 10 and gases containing chloride such as hydrogen chloride and nitrous gases in the form of nitrogen oxides in various oxidation stages. Flue gas components which are injurious to the environment also include hydrocarbons. Under special conditions of combustion, such harmful elements as dioxins can be formed, particularly in connection with the burning of waste, where the fuel can contain large amounts of chloride compounds, for example in the form of polyvinyl chloride. Experiments and a great deal of work with theoretical models is being carried out everywhere in efforts to reduce the pollution of the atmosphere with these substances in the modern technical society.

Several methods are known for the reduction of the content of various of the above-men tioned substances in flue gas. For example, the content of sulphur oxide can be reduced with known techniques by both the wet and dry treatment of flue gases with calcium- and/or" magnesium-containing products. With large combustion plants, for example in thermic power plants, these methods can give good results with a tolerable economy.

The content of hydrogen chloride-and herewith the risk of the formation of dioxins-often arises in connection with the burning of waste. It is now known that a control of the combus- 25 tion in such a way that the combustion temperature is increased, reduces the content of these components drastically, and that an addition of a basic material which can bind the chloride can have a beneficial effect.

Over recent years, one has become more and more aware that the content of nitrous gases in flue gas is not, as was previously assumed, merely an advantage from the point of view of fertilization, but that these gases in the amounts produced in large, modern combustion plants are also very injurious to the environment, for example because they have strong corrosion promoting effects. The inventor of this invention has no knowledge of any technical method which sufficiently cheaply and safely can reduce the content of nitrous gases in flue gas from large combustion plants, but assumes that it is probable that many countries will soon be placing environmental demands on such plants concerning a reduction in the escape of nitrogen oxides into the atmosphere.

The object of this invention is therefore to present a method for the reduction of the content of nitrous gases in flue gas, particularly in flue gas from larger combustion plants, including plant for the burning of waste. The new method shall be able to be used together with other methods 40 for the reduction of the content of other of the above-mentioned, environment-injurious flue gas components and/or in itself bring about such a reduction. The object is also to present a material for use in the execution of the method.

The object is achieved according to the invention with a method which is characterized by the introduction to the combustion process, in addition to that of fuel and combustion air, of a basic 45 reacting material with a high content of hydroxide and/or oxide of alkaline earth or alkaline earth metal with a microscopically crackled surface structure, in which there is absorbed an inflamma ble oil, so that the weight relationship between the basic component and the oil component in the additive is between 1:6 and 3:2.

A material which is suitable for the execution of the method according to the invention is 50 characteristic in that it contains both oil and calcium and/or magnesium in the form of hydroxide and/or oxide, in that the weight relationship between oil and alkaline earth metal when converted to calcium hydroxide is between 1:6 and 3:2.

Characteristics of particularly advantageous embodiments will be evident from the claims.

The advantage of the method according to the invention is that its use enables a reduction to be achieved in the content of nitrogen oxides in the flue gas from combustion plants. The reduction can be as much as down to a third or less. At the same time, the execution of the method results in a reduction of the content of sulphur oxides in the flue gas, this being in a manner corresponding to that known when during combustion one adds basic materials in the form of calcium- and/or magnesium-compounds, for example magnesia for a combustion pro- 60 cess. Where by the addition of basic minerals to combustion processes it has hitherto been preferred to use magnesium-containing minerals, because these do not to the same degree as calcium-containing products promote the formation of easily fusible slag, according to the inven tion one can with advantage use calcium, which during tests of the invention has shown no sign of slag formation in the combustion chamber.

2 GB 2 196 984A 2 It is an advantage to use an additive which, in addition to the two necessary main components, contains other materials, because one can thus utilize cheaper raw materials in the production of the additive material, and/or because for this purpose one can choose oil-waste products, the removal of which is a problem in itself. Another possibility is that one can combine the additive material according to the invention with a second additive material with another or supplementary effect on the course of combustion, for example the adding of magnesia out of regard for a further reduction of the flue gases' content of sulphur oxides. By such a combination of several additives for a material, it is possible to reduce the dosage to comprise a single material.

Out of regard for obtaining a precise dosage and an introduction of the additive at a certain place in the combustion zone, it is of advantage to choose an additive in powder form and to use known injection techniques for its introduction.

When burning refuse, it has proved that with the method according to the invention one can achieve an increase in the combustion temperature, and hereby obtain a reduction in the con- tents of hydrogen chloride and hydrocarbons in the flue gas, this being on the condition that the additive material contains at least 25% inflammable oil.

It is economically advantageous to hold the dosage of additive materials at as low a level as technically possible. In the burning of normal household refuse, a dosage of additive materials which introduce up to 2 kilos of calcium hydroxide or a corresponding amount of other alkaline earth compounds per 100 kilos of refuse is sufficient to reduce the flue gas content of nitrogen 20 oxides to about a third or less, while at the same time achieving a very significant reduction in the content of other flue gas components which are injurious to the environment.

The invention is not based on nor does it formulate any scientific theory, and its chemical reasons can not be given. However, it is assumed that the special structure of the additive material, which under microscopic examination has proved to contain hydroxides and/or oxides 25 of alkaline earth metals with microscopic cracks, and on this large surface an absorbed film of oil, is of decisive significance. It is assumed that hydroxides and oxides of alkali metal salts, which chemically can react correspondingly advantageously with the environment-polluting flue gas components, can be brought into the same oil-activated form as the tested hydroxides and oxides of the alkali earth metals, and also give rise to corresponding reductions of at least the 30 nitrous flue gas components.

The method according to the invention and its execution during the use of calcium hydroxide as basic mineral, has in a surprising manner functioned without giving rise to the formation of slag during the tests carried out. As a technical hypothesis, it can thus be assumed that the burning of the oil film on the granulated mineral with the microscopic cracks is so intense that it 35 results in an evaporation or extraordinary great comminution of the mineral grains, which results in the metal ions being able to react to an hitherto unknown degree with the nitrous gases, remove these from the flue gas and at the same time prevent the formation of slag which normally arises with the use of calcium mineral. Whether this hypothesis may prove to be correct, or whether there are other reasons for the method in this embodiment showing the described results, the embodiment is advantageous in connection with the burning of refuse.

The additive material according to the invention is advantageous because it enables the execution of the method. The embodiments which are presented in the claims are advantageous because they each enable the execution of a corresponding, advantageous embodiment for the method according to the invention. Concerning that embodiment for the additive material which 45 is based on waste oil, it should be noted that a more or less identical material is known from Germany. In the periodical "Markt und Betrieb" no. 32, November 1980, there is described a material of this kind, and it states that this material has been used for road construction by the company ''Meissner Grundbau". The advantages of the material are reported to be that it offers a solution to the disposal of oil waste from the refineries, while at the same time being a 50 favourably inexpensive material for the chosen purpose of road building.

In the following, the invention will be further illustrated by means of a detailed description of an example of an advantageous embodiment.

Example of additive for the execution of the method according to the invention.

A waste oil product containing 56% oil, of which more than 10% were fractions with distillation temperatures of more than 1 10'C, a water content of 16% by weight and the remainder diverse mineral impurities, among other things sulphur, originating from an oil tank at an oil refinery, was used after intensive stirring with a worm in a worm conveyor, and in an amount of 1000 kg., for the slaking of 615 kg of burnt calcium with a CaO content of 96.5%, in that the pulverized burnt calcium was added to the water-mixed oil during the stirring. During 60 the slaking of the calcium, extra water was added in an amount sufficient partly to ensure the completion of the conversion of calcium oxide to calcium hydroxide, and partly to replace the evaporated water. The treatment was controlled in such a way that the temperature was allowed to increase from the storage temperature of the raw materials (5- 10'C) to the boiling point of the water, and was held at this 100'C during the slaking process. During the slaking 3 GB2196984A 3 and the continuous stirring, the mixture changed character from being a liquid to a dry, brownish powder. An analysis of this powder showed an oil content of 34% by weight, and a calcium content which when converted to calcium hydroxide corresponded to 48% by weight. The residual contents of the brownish powder were mineral impurities, stemming mainly from the waste oil used, and insignificant amounts from impurities in the calcium. From other waste oil products with the same type of oil but with varying amounts of impurities, corresponding powders were produced with between 50 and 65% oil content and with between 30 and 50% content of calcium hydroxide. The water dosage was based each time on a smaller test slaking, thus enabling it to be ensured that the dosing was precisely sufficient to effect the slaking, and to cover the incalculable loss by evaporation. The product can be defined as oil-activated calcium. A sample was taken from the mixing of materials from several productions, and the part-amounts were chosen so that the total sample had a calcium hydroxide content of 40%. This sample was used as additive material in the burning of refuse. The test is described in more detail in the following.

In a plant for the burning of normal town refuse, injection equipment was installed for the introduction of pulverized additive material to different places in the combustion zone. The refuse disposal plant constantly burned approximately 4000 kg of refuse per hour. During normal operation, i.e. without any introduction of additive material for the regulation of the chemical composition of the flue gas, an analysis of the flue gas proved to be as that shown in column 1 in the table.

During a first burning test, oil-activated calcium of the type described above was injected into the foremost part of the combustion zone, i.e. into the place where the refuse is ignited for the reason that the temperature has risen to above the ignition temperature of the fuel. The amount of additive material introduced was 100 kg per hour, which corresponds to an introduction of

40 kg calcium hydroxide per hour, which again is 1 % of the amount of 4000 kg refuse burned per hour. The analysis of the flue gas from this test is as shown in column 2 in the table.

A second burning test was carried out in the same plant and with the same fuel introduced in the same amount. In this second test a dosage of 150 kg oil-activated calcium was used, this having the same analysis as that used in the first test, and all other control parameters were the same for both tests. The results of the analysis from test 2 are as shown in column 3 in the 30 table.

The results of the emission measurements are analyses of the flue gas from a refuse disposal plant of the "Bruun & Scirensen- type, in that the flue-gas samples are taken after the installed FILS electrofilter. The rate of combustion was 4000 kg refuse per hour.

It will be seen clearly from the example that the method according to the invention is in a conclusive manner able to reduce the content of nitrous gases from a refuse disposal plant. This reduction has occurred at the same time that there has been achieved a reduction in the contents of sulphur oxide, hydrogen chloride and of hydrocarbons. The method according to the invention thus also produces a particularly desirable effect on the content of these components.

4 GB2196984A 4 TABLE

Measurement no. 2 3 5 Gas channel mm 0 930 930 930 Gas speed m/S 22.7 22.6 20.3 Gas temperature 0 C 254 252 239 Gas amount M 3 /h 55.510 55.330 49.530 10 H 2 0 content Vol% 3 15.1 15.6 15.9 15 H 2 0 amount kg/m n 0.143 0.149 0.153 Dust emission kg/h 0.83 0.67 0.54 20 0 2 content vol% in dry gas 15.5 15.0 14.0 CO 2 content vol% in dry gas 5.4 5.9 6.9 25 CO content ppm in dry gas 40 20 0 SO 2 rate kg SO 2 /h 3 3.13 1.52 1.90 30 so 2 conc. mg SO 2 /m n dry, 0 0 C, 1013 mbar 166 74 86 35 HCl rate kg HCl/h 10.4 6.8 6.9 HCl conc. mg HCl/m 3 n dry, 0 0 C, 1013 mbar 554 329 312 N oxides NO + NO 2_ rate kg NO + NO 2 /h 3.17 2.12 1.17 NO + NO 2_ conc. mg NO+NO 2 /m 3 n 45 dry, 0 0 C, 1013 mbar 168 103 53 50 CH n -rate kg CH n /h 5.9 < 1.6 < 1.7 CH n -conc. mg CH n /m n dry 0 0 C, 1013 mbar 308 < 77 < 77 55 GB2196984A T 45 It should be noted that when examined under a microscope, the oil- activated calcium of the type described above proved to contain small crystals of calcium hydoxide, the surface of which had microscopic cracks, and that these cracks were filled to a wide extent with absorbed oil, which also covered the regular crystal surfaces. A material with corresponding structure and completely the same effect has been produced on the basis of ordinary fuel oil with 30% water added, and thereafter during the addition of burnt calcium used for slaking, during which the stoichiometric excess amount of water evaporated. The additive material is therefore not limited to a material produced from waste oil from oil tanks at refineries.

Since in the burning of fossil fuels in heating plants and power stations there are formed nitrous gases of completely the same kind as in the burning of refuse, and since it is also 10 possible in such plants to execute the method according to the invention, so that one introduces the oil-activated additive material and brings this to reaction in the combustion process under corresponding conditions, it is assumed that the method according to the invention can also be shown to provide advantageous results in such plants.

The invention is therefore not limited to use in connection with the burning of refuse, as 15 described in the example, but as defined in the patent claims also covers the burning of other fuels, also in plants other than refuse disposal plants.

Claims (10)

1. Method for the reduction of the nitrous gases formed by the combustion in refuse disposal 20 plants, characterized in that in addition to fuel and combustion air, to the combustion process is added a basic reacting material which contains hydroxide and/or oxide of alkali earth and or alkali metal with a microscopically crackled surface structure, in which there is absorbed an inflammable oil in such a manner that the weight relationship beteen the basic component and the oil component in the additive material is between 1:6 and 3:2.

2. Method according to claim 1, characterized in that the material used as additive material contains a reaction product brought about by the slaking of burnt calcium (CaO) in a mixture of an oil product and water, so that the reaction product becomes a powdered material with an oil content of from 10 to 40 percentage by weight, and a content of Ca(OH), from 30 ot 70 percentage by weight, up to approximately 15% water and the rest impurities introduced with the raw materials and/or other admixed combustion additive agents.

3. Method according to claim 1 or 2, characterized in that a powdered additive material is chosen, and that this is introduced to the combustion process by injection into the combustion zone of the refuse disposal plant.

4. Method according to one of the above claims and executed in a plant during the burning 35 of refuse, characterized in that additive material is used in such an amount that there is introduced up to 2 kg of calcium hydroxide or therewith the equivalent amount of other earth alkali or alkali compound per 100 kg of refuse.

5. Additive material for the execution of the method according to one of the above claims, characterized in that its contents are partly oil and partly hydroxide and/or oxide of earth alkali 40 and or an alkali metal in the form of crystals with microscopic cracks, in which there is absorbed oil, and that the weight relationship between the oil and alkali earth metal when converted to calcium hydroxide equivalents is between 1:6 and 3:2.

6. Additive material according to claim 5, characterized in that it is in powdered form and contains at least 10 percent by weight of oil, at least 30 percent by weight of calcium- or magnesium hydroxide, and possibly also other inflammable and/or non- inflammable components.

7. Additive material according to claim 6, characterized in that the other inflammable and non-inflammable components are are at least partly sludge particles or other products which are typically to be found in waste oil from refineries and tankers, and which can comprise particles of sulphur, or in used lubricating oil such as used engine oil which normally contains particles of 50 metal and metal oxides.

8. Additive material according to claims 5, 6 or 7 and intended for use in connection with the burning of refuse, characterized in that the content of oil is greater than 25 percent by weight, so that the additive material in itself has a calorific value which is sufficient to raise the combustion temperature of the combustion process.

9. Method for the reduction of the nitrous gases formed by the combustion in refuse disposal plants, substantially as hereinbefore described with reference to the foregoing example.

10. Additive material for the reduction of the nitrous gases formed by the combustion in refuse disposal plants substantially as hereinbefore described with reference to the foregoing example.

Published 1988 at The Patent Office, State House, 66/71 High Holborn, London WC 1 R 4TP. Further copies may be obtained from The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Burgess & Son (Abingdon) Ltd. Con. 1/87.