DE102018108934A1 - Use of polythionate-coated trass for emission control - Google Patents

Abstract

The present invention relates to the use of polythionate-coated trass for the removal of substances from fluids, in particular from exhaust gases of combustion plants. The invention further relates to a process for the preparation of the polythionate-coated trass.

Description

The present invention relates to the use of polythionate-coated trass for the removal of substances from fluids, in particular from exhaust gases of combustion plants.

For energy production, as well as for the disposal of waste or for the conversion or purification of substances, especially ores, currently fossil fuels, such as gas, oil and coal are used. Due to rising demand for electricity and the simultaneous planned exit from nuclear power in countries such as Germany and Japan, the use of coal, which is also present in the industrialized countries and can be mined there, is gaining new importance.

In the combustion of fossil fuels, especially in coal, in addition to carbon dioxide even more pollutants are released, such as sulfur dioxide, nitrogen oxides, hydrocarbons, hydrochloric acid, dioxins, furans, fly ash, soot and highly toxic heavy metals, such as mercury. This pollutant problem generally occurs in combustion plants and especially in waste incineration plants, in which an inhomogeneous mixture of a variety of disused articles is burned, and the materials originally contained in the materials or produced by the combustion of pollutants are emitted into the environment.

Firing systems must therefore no longer be operated worldwide without elaborate exhaust gas purification, in which the most complete removal of pollutants from the combustion gases should be achieved. Despite all the measures taken, however, an increase of mercury in the area is currently being recorded, for which mainly the increasing coal combustion is held responsible. According to the United Nations Environment Program (UNEP), a total of about 498 tonnes of mercury (Hg) were emitted into the air in 2005, of which 6 tonnes were from German, about 50 tonnes from US and more than 100 tonnes from Chinese power plants. In the EU, Germany leads the way with 10 tons Hg in 2015 followed by Poland and Greece.

The exhaust gases emitted by combustion plants, such as coal-fired power plants, waste incineration plants, sewage sludge incinerators, lime and cement works, crematoria or ore roasting plants, contain gaseous as well as liquid and solid components. For the removal of the solid components in the exhaust gas dedusting methods are generally used, such as by using surface filters, electrostatic precipitators, scrubbers and centrifugal separators, while for gaseous and liquid substances essentially the processes of thermal afterburning, catalytic conversion, absorption and adsorption are used become. From an economic point of view, the focus in the purification of exhaust gases is on the last-mentioned methods of absorption, and in particular of adsorption, by means of which an effective reduction of the pollutants in the exhaust gases can be achieved at low cost.

Absorption can be carried out in the most cost-effective case simply by passing the exhaust gases through water, which was optionally supplemented by chemical additives or absorbents.

In the adsorption, the gases or liquids are passed over or through a substance that can absorb the substances contained therein on its surface. The adsorbent itself can then be freed from the adsorbent in an often thermally carried out regeneration and then reused.

Activated carbon has proved to be a good adsorbent due to its large active surface area of about 300 - 1000 m ² / g, the use of which is associated with some significant disadvantages. Thus, due to its inherent combustible properties, activated carbon can not be used at higher flue gas temperatures for safety reasons. There is also a problem with conventional thermal desorption, since the temperatures must not be set too high, which in turn does not always sufficiently ensure the desired complete desorption.

To avoid the problems listed above proposes the DE-P 10 2012 012 367 the use of modified or activated trass whose active and pollutant-accessible surface has been increased by treatment with acids and / or water / surfactant mixtures to a BET value above 40 m ² / g. Trass can be exposed as rock material to high temperatures which allows its use in or near the hearth and also allows complete desorption of the adsorbed hazardous material from the material for its reuse. Although good results here adsorption of mercury in particular could be achieved, this material also has the disadvantage that the adsorbed hazardous material must be desorbed under strictly monitored conditions.

The DE 10 2014 113 620 further discloses the use of pozzolans with a proportion of leachable components, such as silicon and aluminum compounds for exhaust gas purification. The envisaged pozzolans can be injected directly into the offgas stream without pretreatment and provide excellent adsorption of mercury. As in the case of activated carbon and trass with an extended surface, the absorbed mercury is also adsorbed in the pozzolans disclosed here and must be carefully caught again during desorption as a hazardous substance.

An object of the present invention is to provide a further simple, inexpensive and effective means for the purification of fluids, in particular exhaust gases from furnaces, on the one hand a good cleaning of the flue gases of particular mercury is made possible, on the other hand, the danger of aftertreatment of Capture material is reduced in terms of trapped toxins.

It has now surprisingly been found that conventional trass which has been coated with polythionates gives excellent results in trapping pollutants, especially mercury, from flue gases, at the same time converting the toxic mercury into insoluble mercury sulphide which is separated from the trass in a subsequent treatment step can easily be removed. Since mercury sulfide is insoluble, the danger level in the regeneration step of the trass is greatly reduced.

The invention therefore relates to the use of polythionates coated trass for cleaning or removal of pollutants, especially mercury from fluids such as exhaust gases in furnaces, waste incinerators, lime and cement works, crematoria and power plants or liquids such as water, ethanol, etc ..

As used herein, the term mercury is intended to include any mercury bond from which insoluble mercury sulfide forms with the polythionates used, ie, elemental mercury, but also organic and inorganic mercury compounds, such as its salts, eg, HgCl ₂ , HgBr ₂ , HgJ, or HgJ ₂ .

The terms "polythionate" and "polythionate", respectively, are used interchangeably and, in the light of the present disclosure, are intended to denote sulfur compounds of the general formula - S _n SO 3 ^- _m X -, where n is an integer from 2 to 15, m is 1 or 2 and X is a positive charge counterion. n is preferably an integer from 3 to 10, more preferably from 3 to 7, even more preferably from 3 to 5, ie 3, 4 or 5. m is preferably 2. The counterion can be either H ⁺ or Na ⁺ , K ⁺ , Ca ²⁺ or Mg ²⁺ , preferably Na ⁺ . It is clear that the polythionate used is not limited to a specific compound, but rather mixtures of different polythionates are explicitly included within the scope of the invention. Thus, in particular polythionates of different chain length ("n") can be used and / or with one or two sulfite end groups ("m").

The polythionate used to coat the trass can be, for example, in the form of a polythionate itself prepared as a solution or suspension, with the proviso that the sulfur compound (s) correspond to or correspond to the formula given above. This can be done by passing hydrogen sulphide into a solution of sulfur dioxide (sulphurous acid) to give a solution known as "Wackenroder's liquid" comprising mainly tetrathionic acid H2S4O6 and pentathionic acid H2S5O6. Polythionates are also commercially available, such as a 25.5% Polythionatlösung sold under the trade name Netfloc ^® by the company. New Environmental Technologies, Mannheim, Germany. Further polythionates can be obtained from the Chemieportal, Göttingen, Germany.

The polythionate used to coat the trass may also be provided in acid form or in basic form, i. e.g. in the form of a solution having a pH in the range of about 3 to 13. A particularly advantageous for the adhesion has proven to be a basic polythionate solution having a pH in the range from about 10 to about 13, preferably from about 12 to 13. 13th

The trass used for coating with the polythionate (s) can be any known trass, such as Bavarian trass, Rhineland trass, etc., which has been produced worldwide by volcanic activity or meteorite impact. For the purposes of the invention, the trass is present as granules or in powder form and has a particle size (average diameter) in the range of approximately <5 mm, preferably <2 mm, more preferably <1 mm, more preferably <500 μm, even more preferably <200 μm, and more preferably <100 μm or even more preferably <50 μm.

To coat the tress with the polythionate, the two starting materials described above are brought into contact under conditions suitable for allowing adhesion of the polythionate to the surface of the trass. This can be done by immersing the trass material in a polythionate solution or suspension, or alternatively by spraying the trass material with a polythionate solution or suspension. The temperatures for contacting are in the range of ambient temperatures, i. from about 15 ° C to about 35 ° C, preferably at room temperature in the range of about 20-25 ° C. The time for contacting is from about a few seconds to several minutes, e.g. 5 to about 10 minutes, taking into account the concentration of polythionates in the solution or suspension. That the higher the concentration of the polythionates in the starting material, the shorter the period of contacting to deposit a sufficient amount of polythionate on the trass material.

The material produced in this way can optionally be dried before use, or even stored in a dried state.

The thus coated native trass has surprisingly been found to be an excellent mercury scavenger, with the observed results far exceeding those expected from the adsorptive ability of the material. Also, the expected results of the polythionate alone were exceeded. Even more surprising was the fact that the coated native trass, with its low BET of about 24.5 m ² / g, achieved better deposition values than activated trass coated with polythionates, which had a significantly higher BET surface area for adsorption.

Since trass itself is not flammable as rock material, it can be introduced close to or even already into the combustion chamber in order to adsorb the pollutants formed there or to bring the polythionate into contact with the toxic substances already at the beginning of pollutant formation.

The material described here can be used directly and alone in power plants as such, which in the purification of power plant exhaust gases or - flue gases due to the much lower cost compared to activated carbon saving for Kaftwerkbetreiber brings with itself, or in a mixture with other known Means, such as the known activated carbon. A preferred mixture is the trass coated according to the invention together with carbon and / or lime variants, such as, for example, a mixture of the trass coated according to the invention with calcium carbonate and / or activated carbon.

A particular advantage of the trass coated according to the invention is the fact that this mercury is substantially completely removed from the flue gases, but unlike activated carbon it is not flammable. It can therefore be introduced directly into it without technically complex cooling of the exhaust gas or flue gas stream of the combustion plants and be used safely even at temperatures above 200 ° C. Even temperatures of 800 ° C do not change the trass structure, so that alternatively a direct introduction into the furnace is possible, wherein the coated according to the invention trass is then deposited together with the exhaust gas flow to the fabric or electrostatic precipitators and throughout the path with the exhaust gases can react. In contrast to activated carbon, trass, as a bloated granite, is very resistant to abrasion with little fine dust formation.

The polythionates applied to the trass react with the mercury present in the exhaust gas stream to form insoluble mercury sulphide. This is much less toxic due to its insolubility to the environment, so the regeneration of the trass, i. the replacement of the HgS from the rock proceeds more safely and requires less precautionary measures compared to a desorption of elemental mercury from the trass.

The coated according to the invention trass can also be used for the purification of liquids, such as water, especially drinking water. The previously used for this purpose activated carbon was not recyclable due to the biological materials contained in the water to be purified, such as bacteria, such as cyanobacteria or algae, since a regeneration of the activated carbon by burning the biological materials at the same time also brought the activated carbon itself to burning.

Since trass can be ground or ground according to conventional methods to any desired particle size, ie as a powder or as granules, this is also in the fly-stream process as a substitute for activated carbon used directly in power plants, here in a particle size of about <100 microns, preferably <50 microns. It can be injected in a known manner in the exhaust stream and swirled in this, wherein the solids are then deposited on a downstream, usually used in furnaces fabric filter or in an electrostatic precipitator. Alternatively, the trass according to the invention can also be used in a fixed bed.

The following examples illustrate the invention without limiting it.

Examples

Example 1: Preparation of the materials

trass

The tests used Rhenian trass (obtained from Tubag, Kruft, Germany), which had the following composition according to type analysis: Type analysis (only components> 1%) SiO ₂ 56.9% Al ₂ O ₃ 18.5% CaO 5.2% Fe ₂ O ₃ 6.3% MgO 2.2% SO ₃ 0.2% Na2O 3.5% K2O 5.7% TiO2 1.1% Physical data Bulk density about 08-1.0 g / L Specific surface 5000 - 8000 Blaine

The trass had an average particle diameter of 0.06 mm. The active surface of the trass was according to DIN ISO 9277: 2003-05 determined at 24.5 m ² / g.

Production of trass with enlarged surface

For the production of trass with an enlarged surface, 50 g of the Rhenish trass listed under point (A) were transferred into 100 ml of a mixture of 50 ml of 10% hydrochloric acid (manufacturer Merck) and 20% sulfuric acid (manufacturer Merck) , supplemented with 50 ml of distilled water for 1 hour at reflux.

The liquid was then decanted off and the residual trass powder was stirred 3 times with in each case 100 ml of distilled water for 1 hour. After the third wash, the wash water was decanted off, new water added, shaken and the pH measured. This was 7.3. The liquid was decanted off again and the powder dried at 250 ° C for two hours in an oven.

The active surface of the trass powder thus obtained was according to DIN ISO 9277: 2003-05 determined at 118 m ² / g.

Polythionate coated activated trass

For the preparation of the material 50 g of the activated trass prepared in section (B) in 100 ml of a 25.5% aqueous solution were Polythionatlösung; added (Netfloc ^® New Environmental Technologies, Mannheim, Germany). The solution had a basic pH of 12.5. The suspension was stirred for 3 minutes at room temperature, the solid material allowed to settle and the supernatant decanted off. The material was then dried at 50 ° C under reduced pressure.

Natural pozzolan

As pozzolan vulcanite 500 Fa. Hauri, Germany; active surface according to BET approx. 7 m ² / g; Blaine value about 14,000; used directly without pretreatment.

Polythionatlösung

As Polythionatlösung the product Netfloc ^® by the company was. New Environmental Technologies, Mannheim, Germany, 25.5% owned Polythionatlösung used.

Preparation of polythionate-coated trass

For the preparation of the material, the procedure was as under point (C), with the proviso that 50 g of the trass specified under point (A) was used.

Example 2: Use of materials in gas purification

30 l of a gas with the predetermined composition: - Nitrogen 90 vol.% - oxygen 10 vol.% - HCL 19.0 mg / l - humidity 0.20 g / l - Hg (as HgCl ₂ ) 4,500 μg were passed at 180 ° C through 300 mg of the above-listed materials (A) to (D) and (F) (dry, granules / powder) and the residual amount of mercury found in the gas stream was determined. In Example 1 (E), 150 ml of the polythionate solution was placed in a sealed flask (inner diameter 2 cm) with an inlet tube leading to the bottom of the flask and with an outlet opening at the top, and the gas passed through the solution as bubbles rose from the bottom area through the solution. The gas flowing out of the outlet port was recovered to determine the residual amount of mercury.

The following table shows the mercury recovered from the various materials in the residual gas, as well as the calculated percentage purification. table (A) (B) (C) (D) (E) (F) trass activated trass Activated Trass & Polythionate pozzolans Polythionate solution Trass & polythionate 3.965 μg 0.396 μg 0.314 μg 0.995 μg 0.867 0.041 μg 11.9% 91.2% 93.02% 78.1% 80.73% 99.1%

As can be seen from the above table, despite the low active surface of native trass, Trass & polythionate exhibits a surprisingly high absorption of mercury that was superior to all other systems.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE P102012012367 [0009]
• DE 102014113620 [0010]

Cited non-patent literature

• DIN ISO 9277: 2003-05 [0030, 0033]

Claims (10)

Use of polythionate-coated trass for the purification of fluids. Use after Claim 1 , where the trass is selected from Bavarian trass and Rhenish trass. Use after Claim 1 or 2 in which the coated trass is mixed with hearth furnace cokes, activated carbon and / or basic substances and / or acidic substances. Use according to one of the preceding claims, wherein the fluid is selected from flue gases from combustion plants and liquids, Use after Claim 4 , wherein the liquid is water. Use according to any one of the preceding claims, wherein the purification comprises removal of sulfur dioxide, nitrogen oxides, hydrocarbons, hydrochloric acid, dioxins, furans, flyash, soot, highly toxic heavy metals, mercury and / or mercury compounds from the fluids. A process for producing polythionate-coated trass which comprises contacting trass with polythionates under conditions which allow the polythionates to adhere to the surface of the trass. Method according to Claim 7 wherein the polythionate is in the form of an aqueous solution. Method according to Claim 8 wherein the solution has a basic or acidic pH. Method according to Claim 9 , wherein the basic pH is in a range of between 10 and 13.