NL1007310C2 - Processing residue from scrubbers used to treat flue gases from e.g. aluminium recycling plants or waste incinerators - Google Patents

Abstract

Residue from a flue gas scrubber is heated to at least 700 deg C in the presence of an aluminium oxide source. A method for processing flue gas scrubbing residue comprises heating the residue to a temperature of at least 700 deg C in the presence of an aluminium oxide source. Independent claims are also included for (a) the use of the end product for making cement, especially calcium (sulpho)aluminate cement, and (b) the product obtained by this process.

Description

VO 1145

Title: Method for processing flue gas cleaning residue and the use of the product obtained from this method

The invention relates to a method for processing flue gas cleaning residue. In addition, the invention relates to the use of the product obtained in carrying out this process in the preparation of cements.

Flue gas cleaning residue is created when cleaning waste gases that are formed in thermal processes. Examples of such thermal processes are waste combustion methods and aluminum recycling methods. In more detail, off-gases generated by such processes, prior to release to the atmosphere, are usually subjected to one or more chemical reactions and a filtration step in order to minimize the emission of environmental pollutants. This filtration step can be performed dry or semi-dry as well as wet.

In a dry filtration, the off-gases are treated with a dry or powdered absorbent and / or adsorbent and / or reactive additive which can react with components of the off-gases prior to the actual filtration step. In semi-dry filtration, the additive is not added in dry form, but as an aqueous slurry to the waste gases to be cleaned. This addition is made such that all water has evaporated before the off-gases are subjected to the filtration step; in a wet filtration, the waste gases are passed through a washing liquid consisting of a solution or dispersion of absorbent and / or adsorbent and / or reactive compounds. The additive which serves for reaction, absorption or adsorption of compounds to be captured generally comprises calcium compounds, such as calcium oxide, calcium carbonate or calcium hydroxide, in dry or powder form or in the form of milk of lime. In addition to these calcium compounds, other reactive, absorbent and / or adsorbent compounds such as activated carbon can be used.

Over time, the saturated or unsaturated additive is separated in a filtration step along with any reaction products and other filtered components and replaced with fresh additive. The separated mixture forms the so-called flue gas cleaning residue, which product is also referred to as the flue gas cleaning salt. This residue is obtained in dry form or in the form of a filter cake (with wet filtration).

Usually at least some of the following compounds are present in flue gas cleaning residue: Ca (OH) 2, CaO, CaSO 4, CaCO 3, CaCl 2, NaCl, KCl, CaF 2, Al 2 O 3 3 × 2 O, SiO 2, MgO, oxides of heavy metals and meta loids , polychlorinated biphenyl compounds (PCBs), polyaromatic hydrocarbons (PAHs), dioxins, carbon black and (active) carbon. However, depending on the composition of the waste gas and the way in which the waste gas is cleaned (wet filtration, dry filtration), the composition of flue gas cleaning residue will vary.

For example, flue gas cleaning residue from waste gases from aluminum recycling processes has a low sulfate content and a high calcium hydroxide content, while flue gas cleaning residue from waste incineration plants has a high sulfate content and a low calcium hydroxide content. In addition, flue gas cleaning residue consisting of filter cakes from wet filtrations contains virtually no salt, while the salt content of dry or powder-shaped flue gas cleaning residue, as is the result of (semi-) dry filtration, is relatively high.

Flue gas cleaning residue has been designated as "hazardous substance" in the Designation Decree 35 Hazardous Waste (BAGA) issued by the Dutch government. Hazardous substances are classified on the basis of their leaching behavior 10073 1 0 3, which categories determine, among other things, the way in which the waste is to be processed: category C2, C3 or C4 waste. Category C2 prescribes the most strict regime. Waste in this category may only be deposited under strict conditions.

In untreated form, flue gas cleaning residue falls under category C2.

In order to process flue gas cleaning residues in the most environmentally friendly manner possible, it is essential that the leaching behavior of this residue is adjusted in such a way that less pollutants are released into the environment.

One option to achieve this objective is to immobilize flue gas cleaning residues, in particular flue gas cleaning residues from waste gases from waste incineration plants, with cement. All types of cement can be used for this. Preferably, however, calcium aluminate cements are used instead of the usually most commonly used calcium silicate cements.

Calcium aluminate cements react with sulfate and chloride anions which are usually present in the flue gas cleaning residue, whereby ettringite and Friedels salt are formed, among other things. In addition to the aforementioned anions, ettringite also contains heavy metal cations. The immobilization of flue gas cleaning residues with cements, and preferably with cements which form ettringite after reaction with flue gas cleaning residues, in which salts components of flue gas cleaning residues are incorporated, ensures that at least a part of the harmful pollutants do not leach out or to a considerably lesser extent. A disadvantage of immobilizing with cement, however, is the much higher weight of any material to be dumped.

According to the invention it has now been found that considerable advantages are obtained when flue gas cleaning residue is heated at a high temperature in the presence of an alumina source.

More particularly, the invention relates to a process for processing flue gas cleaning residue, wherein the residue is subjected to a heating step at a temperature of at least 700 ° C in the presence of an alumina source.

By heating, for example annealing or sintering, a flue gas cleaning residue in the presence of an alumina source, a reaction occurs between the alumina component from the alumina source and components from the flue gas cleaning residue, which, as mentioned above, usually contain calcium compounds. Solids, including crystals containing calcium and aluminum ions, are formed in this reaction. Some of the contaminants from the flue gas cleaning residue are included in the forming solids. In addition, a number of components of the flue gas cleaning residue are oxidatively degraded into harmless or less harmful compounds, while in addition a number of components of the flue gas cleaning residue volatilize and can subsequently be captured. The leaching behavior of the residual product is thus considerably improved; considerably less unwanted compounds leached. In addition, this method of immobilization, compared to the known forms of cement immobilization, results in a significant weight reduction.

The source of alumina used in the process of the invention preferably includes aluminum oxides and / or hydroxides, a composition containing such compounds or a composition containing aluminum compounds required at the operating conditions for the heating step of the process according to the invention are converted into such compounds.

In a preferred embodiment, waste compounds containing aluminum compounds are used as the alumina source 10073105. The oxide fraction resulting from the recycling of salt slags from the aluminum recycling industry can very suitably be used. Also ball waste dust that is produced during the grinding and sieving of aluminum slag, and which consists of that part of the slag that cannot be economically processed in order to recover aluminum metal, while it is still usual for 5-30 wt.% Metallic aluminum is a very useful aluminum (hydr) oxide source. The same applies to other difficult-to-recycle aluminum-containing material, such as aluminum powder, grinding chips and fine turning and milling chips, which material also forms a suitable raw material for the method according to the invention. Metallic aluminum also has the advantage of burning during the annealing and sintering process of the invention, releasing energy that contributes to the efficiency of the entire process.

Incidentally, not only metallic aluminum, such as the above-mentioned aluminum powder and aluminum chips, but also other compounds which are introduced into the heating device in which the heating step according to the invention is carried out, such as carbon black and (active) carbon, as well as organic compounds, can become thermal which benefits the efficiency of the process. Any impurities that are present in the aluminum source, such as oil, paint residues and plastics, do not need to be removed. Namely, in the heating step according to the invention, these impurities are mainly thermally utilized, so that their presence is usually preferred. This can be optimized and adjusted by the expert without any problem, depending on the flue gas cleaning residue and the aluminum compound.

The method according to the invention can be operated batch-wise or continuously in a continuous process. Suitably, flue gas cleaning residue can be introduced into a tube or drum furnace, while fluid bed furnaces are also suitable for use. Incidentally, the method according to the invention is not limited to certain types of furnaces. Preferably the oven is fired with an oxygen-5 burner. The heating device used usually contains a provision for introducing additional amounts of air or oxygen. Namely, it has proven to be very advantageous to carry out the method according to the invention to create and maintain an oxidative atmosphere by supplying sufficient air or oxygen during the heating step. Certainly when the aluminum oxide source used does not comprise fully oxidized aluminum compounds or when the flue gas cleaning residue or the aluminum oxide source comprises other incompletely burnt components, for instance when metallic aluminum is present in the aluminum oxide source, it is advantageous to supply additional air or oxygen.

The aluminum oxides formed from the aluminum oxide source react with at least the calcium constituents, and, for example, any sulphates present, from the flue gas cleaning residue to solids such as calcium aluminates and calcium sulpho aluminates. In the forming solids, ions from pollutants, for example heavy metal cations, are also incorporated. This shows the importance of the presence of calcium compounds that can react with the aluminum oxide source in the flue gas cleaning residue. Such calcium compounds, which are referred to below as calcium oxides, do not include gypsum (CaSOJ because gypsum does not react with the source of alumina). A calcium (hydr) oxide source is also necessary for the formation of calcium sulphoaluminates in addition to an alumina source. that in the end product 35 calcium oxides and alumina are present in a molar ratio between 3: 1 and 1: 3, and more preferably between 2: 1 and 1007 310 7 1: 1. From analyzes of the flue gas cleaning residue to be treated and the alumina source, an expert can easily deduce how much calcium oxides and alumina are needed to obtain a suitable end product For an industrially applicable process it is desirable that the end product contains at least 10 wt%, and more preferably 20 wt% calcium oxide, based on the total weight of the flue gas cleaning residue Preferably, at lower levels of calcium oxides, a calcium oxide compound is used thing, for example in the form of calcium hydroxide or calcium carbonate, added to the flue gas cleaning residue. Aluminum oxide is suitably added in an amount of at least 10 wt% and more preferably at least 20 wt% up to more than 100 wt% based on the weight of the flue gas cleaning residue.

By optimizing the amount of oxygen, alumina source, flue gas cleaning residue and possibly other thermally utilizable compounds, it is possible to arrive at a process which only requires external energy before start-up, but which then proceeds without further energy supply.

The reaction between the calcium-containing flue gas cleaning residue and the aluminum oxide source in the process according to the invention is carried out in an oven at temperatures of at least 700 ° C. Preferably, the temperature at which the heating step is performed is at least 800 ° C, suitably between 800 ° C and 1400 ° C. Depending on the presence of organic impurities, such as PCBs, PAHs and dioxins, the temperature and time in the process can be adjusted within the limits of the invention to destroy these impurities. Although organic compounds present at temperatures higher than 1400 ° C are also converted, no additional advantages are obtained, while the costs of and the requirements for the required installation, fuels, etc. increase, resulting in 10 073 1 0 8 from from an economic point of view it is not attractive to work at these higher temperatures.

Depending on the composition of the flue gas cleaning residue and the aluminum oxide source, the residence time of the reactants in the oven is usually between 10 minutes and 5 hours. The person skilled in the art can easily determine what are suitable and optimal residence times in the reactor by analyzing the product produced in the process.

At the temperatures used in the method according to the invention, chloride salts evaporate or volatilize, while a number of heavy metals also volatilize, in particular cadmium and zinc. These impurities can be collected from the gases and vapors that form during the heating step. To this end, the gases and vapors are usually sent to a conventional gas washing installation. Many gas scrubbers used are so-called wet scrubbers. In the gas scrubber, the chloride salts are removed from the gas stream obtained according to the invention in ways generally known to the skilled worker. The volatilized heavy metal-containing compounds, in particular zinc and cadmium compounds, can be collected according to known techniques and can be separated separately, so that such compounds dissolve in a gas washing liquid with an acidic pH and can be precipitated therefrom, for instance by periodically adjusting the pH to a value of about 8.5-9, and may thus end up in the salt crystals to be separated from the scrubber. The products recovered from the gas scrubber can be processed in conventional ways.

Preferably, the gases and vapors formed are rapidly cooled in or before the gas scrubber to a temperature of less than 250 ° C, and more preferably to less than 150 ° C, so that dioxins or other impurities of organic impurities from the carbonaceous compounds present do not re-emerge 073 1 0 9 nature. A common device for this purpose is a washing tower in which large amounts of water are circulated.

When a flue gas cleaning residue naturally has a low salt content, such as a flue gas cleaning residue obtained by wet filtration, or when the salt content, in particular the chloride content, is lowered before carrying out the method according to the invention, the temperature in the heating step according to the The invention will be relatively low and will preferably be between 800 and 1100 ° C. Such a temperature is considerably lower than the temperatures conventionally used in the preparation of calcium aluminates. Flue gas cleaning residue with a high salt content usually requires a higher temperature in the range of 950-1400 ° C in order to remove chloride salts and to give a leaching behavior comparable residue as a flue gas cleaning residue with a lower salt content. In a preferred embodiment, flue gas cleaning residue with a high salt content is therefore first subjected to a step in which salts, in particular chlorides, are removed, preferably in a washing step with water, before being heated according to the invention.

The method according to the invention results in a flue gas cleaning residue that leaches out to a much lesser extent than the untreated flue gas cleaning residue.

Moreover, oxidative degradation of organic impurities and volatilization and capture of chlorides and heavy metal impurities and subsequent processing separately reduce the weight of the waste to be processed.

The method according to the invention is in particular very suitable for use in the treatment of flue gas cleaning residues which are formed during the recycling of aluminum and in secondary aluminum melting. First, waste products generated during the recycling of the 10 073 1 Q 1 10 or melting can act as an aluminum source. In addition, salt crystals separated from the scrubber can be reused in the aluminum industry, incorporating heavy metal contaminants such as cadmium and zinc into aluminum, thus eliminating the need for disposal and processing.

As already mentioned, the final product obtained has a considerably better leaching behavior from an environmental point of view. Not only can it generally be dumped under a less strict regime, but moreover the volume and weight relative to the flue gas cleaning residue usually decreases to a significant extent.

Many of the products obtained from the method according to the invention, after being ground, have cement properties. More particularly, the obtained annealing or sintering products generally consist of some of the following major phases, which are referred to in conventional cement chemistry notations: calcium aluminates such as C3A, C12A7, CA, CA2, and calcium sulfo-aluminates as C4ASIT, and side phases such as C2S and C3S.

Thus, the sinter product obtained from flue gas cleaning residue from aluminum recycling plants, which flue gas cleaning residue has a low sulfate content, contains a relatively high percentage of calcium aluminate cement. As stated in the introduction, this calcium aluminate cement can be used, inter alia, for the immobilization of other hazardous waste materials, in particular metal sludge and flue gas cleaning residue from 30 incineration plants.

Flue gas cleaning residue from waste incineration plants contains a relatively high calcium sulfate content. When this flue gas cleaning residue is subjected to the sintering process according to the invention, C4A3! 3 is formed, which phase forms ettringite in the cement reaction.

1007310 11

In a preferred embodiment of the invention, the sintered product obtained from the process is therefore used as a raw material for the cement industry, and in particular for the preparation of calcium aluminate and / or calcium sulfoaluminate cement.

The properties of the cement to be obtained can be influenced by mixing different types of flue gas cleaning residues. This offers the possibility, for example, of preparing cement with a higher or lower content of ettrinite formers, depending on the sulfate content of the waste materials to be immobilized, such as metal sludge. High sulphate contents in the waste to be immobilized require a cement without C4A3S, whereby ettringite is still formed by the CaSO4 present.

The invention will now be further elucidated by means of the following non-limiting example

EXAMPLE

20 1 part by weight of flue gas cleaning residue from an aluminum recycling plant was rinsed with water. 0.5 part by weight of a mixture of aluminum oxides and hydroxides was added from the washed flue gas cleaning residue. This oxide mixture contained 7% metallic aluminum.

The whole was sintered for 1 hour in an oxidative atmosphere. After sintering, 0.9 part by weight of sinter product remained. 70% of this product consisted of compounds C12A17.

Both the flue gas cleaning residue and the sintered product obtained therefrom were subjected to a column test according to NEN 7343, at an L / S ratio of 1.

1007310 12

Accumulation leaching

Flue gas cleaning Sinter product residue 5

Copper Cu 0.200 mg / kg <0.002 mg / kg

Lead Pb 200 mg / kg 0.01 mg / kg

Zinc Zn 70 mg / kg 0.05 mg / kg

Barium Ba 2 0 mg / kg 2 0 mg / kg 10 Molybdenum Mo 0.04 mg / kg 0.02 mg / kg

Cadmium Cd 1 mg / kg <0.002 mg / kg

Selenium Se 50 mg / kg <0.002 mg / kg

Sulphate SO 2 2000 mg / kg 0.30 mg / kg

Chloride Cl 15000 mg / kg 500 mg / kg 15 Bromine Br 700 mg / kg <0.10 mg / kg 10 0731 0

Claims (11)

A process for processing flue gas cleaning residue, wherein the residue is subjected to a heating step at a temperature of at least 700 ° C in the presence of an alumina source. The method according to claim 1, wherein the aluminum oxide source is an aluminum oxide or aluminum hydroxide, or a composition comprising such compounds or aluminum compounds which are converted therein in the heating step. The method according to claim 1 or 2, wherein the aluminum oxide source is an oxide fraction that is generated during the recycling of salt slags from aluminum recycling or ball mill dust that is generated during the grinding and sieving of aluminum slags. Method according to claim 1 or 2, wherein as aluminum oxide source a composition containing metallic aluminum is used. A method according to any one of the preceding claims, wherein the flue gas cleaning residue is subjected to the heating step in the presence of a calcium oxide compound in an amount such that at least 10% by weight of calcium oxide is present in the final product. 6. A method according to any one of the preceding claims, wherein the heating step is carried out in the presence of an amount of the alumina source corresponding to at least 10% by weight, based on the total weight of the final product, alumina. 7. A method according to any one of the preceding claims, wherein the heating step is carried out at a temperature between 800 and 1400 ° C. A method according to any preceding claim, wherein the flue gas cleaning residue is subjected to a step of removing chloride 1007310 ions before heating, preferably a washing step with water. 9. A method according to any one of the preceding claims, wherein in the final product calcium oxides and aluminum oxides are present in a molar ratio between 3: 1 and 1: 3. Use of the product obtained according to the method according to one or more of Claims 1 to 9, for the preparation of cement, in particular calcium aluminate and / or calcium sulphoaluminate cement. 11. Product obtainable by the method according to one or more of claims 1-9. 1007310 COOPERATION TREATY (PCT) REPORT ON NEWS RESEARCH OF INTERNATIONAL TYPE LOENTlFlKATlE OF OE NATIONAL ACQUISITION Characteristic of the applicant ol van üe gemacnugae | Nw 1145 j Neananose ad va 9e nr 1 na leongsaatum 1007310 October 17, 1997 -: -'-— I Claimed priority date I Applicant (Name) j VAN WIJK, Gijsbert Willem Meindert ji Danjm from just Verzec * for an one nen of mtemaoonaai type By oe Insanoe for International Unquestioning (ISA) to wet request for an unquestioning from interna do na all type oeoenenfl nr SN 30576 NL. '' '' 1 I. CLASSIFICATION OF THE SUBJECT (in case of oeoassmg of different oe classifications, indicate all egg-assurance symbols) J According to Oe Inemaooraie classification (IPC) j Int.Cl.6: C 04 B 7/32, C 04 B / 724 II. FIELDS OF TECHNIQUE RESEARCHED _____ Unclassified minimum Documentation____ I Classification system 1 Classifications vmoolen_ ~ _I i Int.Cl.6: I C 04 B I I Onoerzccn: e anoere cocumenaoe o an αβ minimum öocumenaoee insofar as they are included in the onl | I I I. * i j i * _ I I lil. i NO RESEARCH EQUAL FOR CERTAIN CONCLUSIONS (reviews on sanvutimgsplaPï 1 I _ _________ '_ I _! (V.' LACK OF UNIT OF INVENTION (comments on additional incs) £ zc: ~ pZ ~ .'SA. "1 a 'Ci" 99 ~ ΙΊ