EP1866059A1

EP1866059A1 - Use of an ammonia-releasing residue

Info

Publication number: EP1866059A1
Application number: EP06710535A
Authority: EP
Inventors: Werner Kepplinger; Bernd Hollauf
Original assignee: Montanuniversitaet Leoben
Current assignee: Montanuniversitaet Leoben
Priority date: 2005-03-11
Filing date: 2006-03-10
Publication date: 2007-12-19
Also published as: AT500744A4; AT500744B1; AT500744B8; WO2006095261A1

Abstract

The invention relates to the use of an ammonia-releasing residue from a desulphurisation method for the denitrification of combustion exhaust gases and a method for production of cements, whereby said residues are used to denitrify the combustion exhaust gases. The ammonia-releasing residue is preferably obtained from a desulphurisation method in mineral oil processing and is used in a method for production of cement.

Description

Use of an ammonia-releasing residue

The present invention relates to the use of an ammonia-releasing residue for denitrification of combustion gases according to the preamble of patent claim 1 and a method for producing cement according to the preamble of claim 11.

It is known to apply two principle principles in the secondary measures for the removal of nitrogen oxides from exhaust gases:

A distinction is made between non-catalytic and catalytic reduction. Nitrogen oxides (NO _x ) are reduced to molecular nitrogen, NH _{3 is} generally used as a reducing agent for oxygen uptake. The denitrification mechanism can be described for both process principles by the following reaction equations:

4 NO + O ₂ + 4 NH ₃ → 4N ₂ + 6H ₂ O 2 NO ₂ + O ₂ + 4 NH ₃ → 3N ₂ + 6H ₂ O

For large combustion plants, selective catalytic reduction (SCR) is the most commonly used method of reducing nitrogen oxide emissions. In this case, there is a separation of the NO _x in the gas phase, as described by the above reaction equations, by catalytic reduction in nitrogen and water vapor. For denitrification, the flue gas is passed over ceramic fixed bed catalysts based on titanium oxide with additions of vanadium pentoxide, tungsten and other metals and added to the reduction of ammonia. The catalyst causes the reduction, which normally proceeds optimally in the temperature range of 900-HOO ⁰ C, to proceed even at lower temperatures (preferably 300-400 ° C).

In the alternative method of selective non-catalytic reduction (SNCR), urea solution or ammonia water are usually added at temperatures of 900-1100 ° C the hot flue gases injected. The water in the solution evaporates, and the reducing agent reacts with the nitrogen oxides to form water vapor and nitrogen, as in the SCR.

From EP 0 622 108 Bl a method for denitrification of the resulting in the production of cement exhaust gases is known in which the exhaust gases after leaving the rotary kiln at a temperature of 750-950 ° C ammonia is added, and in which the exhaust gases in a Temperature of 300 to 400 ° C is brought into contact with a pulverulent introduced into the exhaust gas stream catalyst consisting of iron sulfate or a mixture of iron sulfate and manganese sulfate. The process operates with a degree of denitration of 75-95% and prevents the NH ₃ slip reliable.

From DE 100 11 327 Al a method and apparatus for the catalytic treatment of sulfur and nitrogen oxides containing dust and oxygen-containing exhaust gases of a cement rotary kiln are known. As a reducing agent, pure ammonium sulfate can be used inter alia. For cost reasons, pure ammonium sulfate, which is much more expensive than urea for example, is not used in cement production. Taking into account that urea contains about 46% nitrogen and ammonium sulfate about 21% nitrogen, the effective price difference per kg nitrogen still remains more clear.

In DE 43 09 510 Al a process for the production of sulfuric acid is described. This document presents a possibility of utilization of ammonium sulphate from flue gas cleaning.

From DE 41 23 155 Al a method is known which recovers unreacted ammonia and ammonium sulfate formed from the flue gas with the aid of a wet scrubber. In a reaction crystallization step, ammonium sulfate is converted to gypsum and ammonia by adding quicklime. The recovered ammonia is used again for denitrification and desulfurization. In this process SO ₂ is thus initially bound in the form of ammonium sulfate and finally discharged from the process in the form of gypsum. DE 197 52 600 A1 describes a process for the production of Portland cement, Portlandkompositzen and blast furnace cements in a rotary kiln, in which a designated Oxiton residue, which is obtained from the processing of salt slag from the aluminum production, for NO _x reduction with the hot meal on the exhaust gas side Rotary kiln end is abandoned. The residue, referred to as oxitone, is 67% alumina, which according to this document is an ammonia carrier. Although the detailed analysis of an oxitrone published in DE 197 52 600 A1 does not list any nitrogen content, it is stated that a value of 5 g NH ₄ per kg aluminum oxide was determined by calculation. The teaching of DE 197 52 600 Al can be clearly seen that an Oxitron addition in the low temperature range of below 500 ⁰ C leads to harmful ammonia emissions and the desired non-catalytic NOχ reduction only by adding to the exhaust side furnace end at temperatures of 800 to 1200 ⁰ C is reached. It is described that an emission reduction of 0.2 to 0.3 g (NO ₂ ) per cubic meter was determined in preliminary tests. Since the ammonia content of oxone is very low and since oxitron addition to the denitrification is limited by the negative effects of an increasing proportion of Al carriers in the raw meal, a controlled use of Oxitron for denitrification in a plant for cement production is only very selectively possible. DE 197 52 600 Al already discloses that at levels of more than 3 wt .-% Al carriers in the raw meal losses in ultimate strength, so that in raw meals with a sufficient aluminum content of the negative influence of Oxitron residue on the Clinker composition would not allow the addition of an amount effective for denitrification. ,

In order to achieve sufficient denitrification must in the application of the method of DE 197 52 600 Al in many cases - as well as in the conventional method for denitrification of exhaust gases - usually pure substances are purchased as denitrogenization, which has a negative effect on the cost of the process ,

In contrast, the present invention sets itself the task of a cost-effective and ecologically advantageous uses of ammonia-releasing residues and a To provide cost effective and ecologically advantageous method of cement production.

This object is achieved with the use according to the invention of a residue originating from a desulphurisation residue and discharging ammonia for denitrification of combustion exhaust gases according to patent claim 1 and the process for cement production according to patent claim 11.

Preferred embodiments of the invention will be explained in more detail with reference to the following description, examples and figures. Show it:

1 shows the result of the thermogravimetric analysis of an ammonia-releasing residue from a desulfurization process,

Figure 2 comparatively to the analysis according to Figure 1, the result of the thermogravimetric analysis of pure ammonium sulfate, and

FIG. 3 shows a diagram of a combustion plant for cement production in which the ammonia-releasing residue according to an embodiment of the invention is used.

The invention is based on the finding that residues from desulfurization processes, in particular from flue gas desulphurization processes (such as the Walther process or similar processes), which hitherto usually had to be disposed of in a complicated manner, are used as denitrogenizers in conventional processes for denitrifying exhaust gases can be used. Desulfurization processes in the context of the present invention should also be understood as meaning sulfur decomposition processes in which ammonium sulfate or a mixture of ammonium sulfate and ammonium hydrogen sulfate is obtained as residue. As an example, the production of pesticides may be mentioned in which arise as by-product Ammonsulfatlösungen. From copper vitriol [CuSO ₄ .5H ₂ O] tribasic copper sulphate [CuSO ₄ .3Cu (OH) ₂ ] is added by addition of ammonia [NH ₃ ] manufactured, which represents the active ingredient in the pesticide. The ammonia reacts with a portion of the sulfur from the copper vitriol to ammonium sulfate [(NH ₄ ) 2SO ₄ ], since the copper vitriol must be desulfurized in order to produce tribasic copper sulfate can. It falls while a 10-15% ammonium sulfate solution, which can be used according to the invention alternatively as a reducing agent for nitrogen oxides in eg cement plants as an alternative to the fertilizer industry.

The residue from flue gas desulphurisation plants, which is used according to preferred embodiments of the present invention, mainly comprises ammonium sulphate or a mixture of ammonium sulphate and ammonium hydrogen sulphate. Typical contents of ammonia in this residue are from 12 to 24% by weight. At elevated temperatures, ammonia is liberated from this residue.

For - in particular ammonium sulphate - containing residues from the flue gas desulphurization, which are contaminated with toxic water-soluble heavy metals, there is so far mostly no recovery option.

This residue is classified as hazardous waste and must therefore be disposed of consuming. Only if a costly removal of fly ash is carried out in the desulfurization, the correspondingly cleaner residue may optionally be used as fertilizer.

In countries where it is - such. In Austria - there are no landfills for hazardous waste, the waste owner is thus forced to export. At present desulphurisation residues are e.g. deposited in Germany in expensive to operate underground storage areas. The transport and disposal costs for this residue amount to several hundred euros per tonne.

Numerous advantages can now be achieved by the use of this residue according to the invention as a denitrification agent and by the process according to the invention for cement production. For purer residues (for example from desulphurization processes in which flyash removal is carried out), apart from use as a fertilizer, an alternative now results Possibility of use in denitrification of combustion gases or in cement production. For residues that are not exempt from fly ash, not only the economic and environmental disadvantages of disposal of these problematic residues can be avoided, but it can also be on the side of the operator of the denitrification cost savings, as this residue is far more cost-effective than For example, pure ammonium sulfate or can be used better than the known from DE 197 52 600 Al residue.

Particularly preferably, the residue used according to the invention is derived from a desulphurization process within the scope of mineral oil processing.

Such residuals contain - especially if no fly ash removal is carried out - larger amounts of vanadium, which is known from the literature as a catalyst for denitrification reactions. Table 1 below gives an example of such a residue from a desulfurization process which is successfully used in the denitrification of combustion exhaust gases, in particular in cement production.

Table 1: Composition of a residue

The removal of ammonia relevant for the nitrogen oxide reduction from the residue according to Table 1, also referred to below as desulfurization residue, is subsequently quantified and explained on the basis of a laboratory example.

Laboratory Example:

130 mg of desulphurisation residue are first weighed into a sample container and placed in the oven. Subsequently, the sample is heated in the test facility at a heating rate of 20 ° C / min up to 1000 ⁰ C. During the heating program, the mass decrease of the sample is recorded continuously. The resulting exhaust gas is sucked in succession over two washing bottles filled with dilute sulfuric acid in order to detect the ammonia liberated during the thermal decomposition. The ammonia concentration in the wash solution is then determined photometrically.

It can be seen from FIG. 1 that the thermal decomposition takes place between 300 and 600 ° C., with a total weight loss of 90.65% in the temperature range investigated.

By means of the photometric determination of the ammonium concentration in the washing solution, the release of ammonia can be detected and thus the suitability as a nitrogen oxide reducing agent can be confirmed. It can be concluded from the DTA signal in FIG. 1 that the major part of the weight loss results from the decomposition of the ammonium sulfate contained in the desulfurization residue. FIG. 2 comparatively shows the result of the thermogravimetric analysis of pure ammonium sulfate.

To bring the ammonia-releasing residue according to the present invention, in particular a residue from a desulfurization in the context of mineral oil processing, as disclosed in a preferred embodiment in Table 1, in that temperature zone of the combustion furnace, in which the flue gases has a temperature of 250 -400 ⁰ C, so the relatively high vanadium content of the residue acts as a catalyst for denitrification. The reason for this is the oxidation of the Vanadium compounds in this temperature range in the presence of oxygen to vanadium pentoxide. Preferably, the vanadium content of these residues is between 0.1 and 9 wt .-%, more preferably it is around 2 wt .-%. Furthermore advantageous is that the vanadium is emitted as a low volatile oxide not via the exhaust path, but embedded in the dust and can be deposited and, for example, incorporated into the cement as part of a cement production process.

Even with the introduction of this vanadium-containing residue in the temperature zone at 750-HOO ⁰ C V ₂ Os is formed, which in turn can be effective in the temperature zone at 250-400 ° C downstream as a catalyst for the denitrification reaction.

Advantageously, a carbon content of between 0.5 and 10% by weight, preferably between 3 and 6% by weight, of the residue used according to the invention also has an effect. The carbon contained on the one hand brings energy into the system through combustion to CO or later to CO ₂ , and on the other hand, the resulting CO also acts as a reducing agent for nitrogen oxides.

The ammonia-releasing residue used according to the invention may be in the form of an aqueous solution, as a suspension or as a solid, e.g. be used in the form of pellets.

In a further preferred embodiment of the present invention, a first ammonia-releasing residue is mixed with another ammonia donor, e.g. Urea or photo-water used. This further, ammonia-donating substance may preferably again be a residue, for example as described above from agrochemistry, from the chemical industry or metallurgical industry or a freshly purchased denitrification agent.

The residue used according to the invention is preferably used for denitrification of combustion exhaust gases from caloric combustion plants or firing plants of the building materials industry, in particular a plant for the production of cement. The ammonia-releasing residue can be injected in a manner known per se in the form of an aqueous solution, a suspension or as a solid, and optionally in admixture with other denitrification, in the 750-HOO ⁰ C hot flue gases.

At these temperatures, the ammonium sulphate contained in the residue decompose, whereby NH ₃ and SO ₂ are released. The resulting NH ₃ reduces the nitrogen oxides.

Bringing the residue in this way, for example, in the calcination zone in the cement production, so at the present temperatures in this zone, the nitrogen oxides are reduced. The liberated SO ₂ reacts with the deacidified limestone, which is abundant in this zone, to CaSO ₄ and is incorporated into the cement.

CaSO ₄ is usually added to all standard cements for solidification control in an amount adjusted to the fineness. As a result of the addition of ammonium sulfate resulting from the use of the ammonia according to the invention, it is now also possible to reduce the amount of natural gypsum to be added. This not only costs for natural gypsum, but also the costs for the preparation of the same can be saved. Compared to the teaching of DE 41 231 55, burnt lime, which is obtained during the cement production process, can thus be used for SO ₂ incorporation.

The NH ₃ not yet reacted in the high-temperature zone can, according to one embodiment of the process according to the invention, be used in a subsequent catalytic system for further denitrification. The catalyst may be a high-bed fixed-bed catalyst or a fine-grained catalyst added to the exhaust gas. As a result, unreacted ammonia from the non-catalytic stage (SNCR) can still be used for denitrification.

In further processes according to the invention, the residue used according to the invention is introduced into the catalytic zone of the denitrification process (ie at 300-400.degree. C.). Embodiment:

The raw materials are ground in a raw meal mill. The raw meal is then preheated over several cyclone stages in countercurrent to the exhaust gas flow. It is also possible to use grate or shaft preheaters. The use according to the invention of the desulfurization residue is possible in all types of plant.

In the exemplary embodiment according to FIG. 3, the raw meal R passes through a cyclone preheating 1, 2, 3, 4 to a rotary tube 6 and passes through a calcining zone in which the deacidification of the calcium carbonate contained in the raw meal R takes place.

For this purpose - not shown in the figure - a bunker for the storage of desulfurization residue, a stirred tank for preparing the solution and a nozzle for introducing the solution into the riser shaft 5 required. In the prevailing in the gas riser shaft 5 temperatures of 800-HOO ⁰ C immediately after the evaporation of the water, the ammonia component of the desulfurization residue R is released and mixed with the coming of a main burner 7 exhaust gas. The addition of a 40 percent solution, prepared from 40 wt .-% desulfurization residue with the composition given in Table 1 and 60 wt .-% of water has proven to be advantageous in experiments. When using 513 kg / h solution amount and a NH ₃ / NO molar ratio of 0.57, an emission reduction in the purified exhaust gas A to 380 mg NO ₂ / Nm ^{3 could be} achieved. The legal limit of approval of 800 mg / Nm ³ could be safely adhered to during the experiment. It can be assumed that even greater nitrogen oxide reductions can be achieved by optimizing the introduction of the solution and thus better mixing of the solution with the exhaust gas.

The injection took place in the above example in the riser shaft. In principle, the injection is possible wherever a temperature of 750 to 1100 ° C prevails.

Claims

Claims:

1. Use of originating from a desulfurization, ammonia-releasing residue for denitrification of combustion exhaust gases.

2. Use according to claim 1, characterized in that the ammonia releasing residue comprises ammonium sulphate.

3. Use according to claim 1 or 2, characterized in that the ammonia-releasing residue has an ammonia content of 2 to 26 wt .-%, preferably from 12 to 24 wt .-%.

4. Use according to one of claims 1 to 3, characterized in that the ammonia-releasing residue originates from a desulfurization in the context of mineral oil processing.

5. Use according to one of claims 1 to 4, characterized in that the ammonia-releasing residue has a vanadium content of 0.1 to 9 wt .-%, preferably from 1 to 5% by weight.

6. Use according to one of the preceding claims, characterized in that the ammonia-releasing residue is used in the form of an aqueous solution, as a suspension or in the form of pellets.

7. Use according to claim 6, characterized in that the ammonia-releasing residue in a 40% solution, preferably prepared from made of 40 wt .-% desulfurization residue and 60 wt .-% water, is present.

8. Use according to one of the preceding claims, characterized in that the ammonia releasing residue is used in mixture with another ammonia-donating substance.

9. Use according to one of the preceding claims, characterized in that the ammonia-releasing residue is the combustion exhaust gases in the temperature zone of 750-HOO ⁰ C, preferably from 800-HOO ⁰ C is supplied.

10. Use according to one of the preceding claims, characterized in that the ammonia-releasing residue is the combustion exhaust gases in the temperature zone of 300-400 ⁰ C is supplied.

11. Use according to one of the preceding claims for denitrification of combustion exhaust gases from caloric combustion plants or firing systems of the building materials industry, in particular a plant for the production of cement.

12. A process for the production of cement, wherein raw meal and aggregates in countercurrent to a combustion exhaust gas stream in an incinerator from a first temperature zone having a temperature between 300 and 400 ⁰ C in a second temperature zone with a temperature between 750 to 1100 ⁰ C is promoted characterized in that at least in the first or the second temperature zone, at least one ammonia-emitting residue is added to the denitrification of the combustion gases.

13. The method according to claim 12, characterized in that a vanadium-containing residue for denitrification of the combustion gases before or in the first temperature zone at a temperature between 300 and 400 ⁰ C is added.

14. The method according to claim 12 or 13, characterized in that one of the residue for denitrification of the combustion gases in the second temperature zone at a temperature between 750 to 1100 ⁰ C, preferably between 800 and 1100 ⁰ C is added.