Title of Invention | METHOD FOR REMOVING AMMONIA AND DUST FROM AN EXHAUST GAS EMITTED DURING THE MANUFACTURE OF FERTILISERS |
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Abstract | A method for removing ammonia and dust from an exhaust gas emitted during the manufacture of fertilisers, especially urea, in which the exhaust gas is introduced into a first washer and a cooling gas is introduced into a second washer and additional water is introduced into one washer and a watery solution is introduced into the other washer, whereby the exhaust gas as well as the cooling gas pass through at least one demister before coming out of the respective washer, is supposed to be further developed in such a way that the exhaust gas load can be significantly reduced. This is achieved, in that the additional water is initially introduced into a fine washing zone of the first washer bordered on the upper side by the demister and on the lower side by a fluid-impermeable separating floor, and sprayed on to the at least one demister and the resulting water solution in the fine water zone is subsequently guided into the second washer. |
Full Text | Method for Removing Ammonia and Dust from an Exhaust Gas Emitted During the Manufacture of Fertilisers The invention relates to a method for removing ammonia and dust from an exhaust gas emitted during the manufacture of fertilisers, mainly urea, in which the exhaust gas is introduced into a first washer and a cooling gas is introduced into a second washer, and additional water is introduced into one washer and a watery solution into the other washer, whereby the exhaust gas as well as the cooling gas passes through at least one demister before exiting out of the respective washer. During manufacture of ammonia-containing fertilisers or in fertilisers that can split ammonia, e.g. fertilisers containing urea, during the different process stages exhaust gas-flows containing ammonia and dust get emitted, which have to be purified before discharging into the atmosphere or recycling into the process. Such exhaust gases occur mainly during granulation and cooling. For removing dust from the exhaust gas exiting from the granulation and from the granulated cooling gas, we know of a generic method of the applicant. For conducting this method, two washers are foreseen, which are equipped respectively in the upper region with at least one demister. The exhaust gas stemming from the granulation is introduced into the first washer, while cooling gas is introduced into the second washer. For purification, additional water preferably purified or non-purified process water, is introduced into the washer below the demister in a counter-flow to the cooling gas. The watery solution coming out of the second washer is subsequently introduced into the first washer, similarly in a counter-flow to the purifying exhaust gas. It has been seen in practice that this known method still has scope for improvement. As the watery solution coming out of the first washer has to be further processed or further used, there is this endeavour to set the urea concentration in the watery solution as high as possible, in order to keep the energy consumption for evaporation the exiting watery solution as low as possible. In the hitherto process however, limits are set for this maximum concentration. The hitherto maximum value of urea concentration in the watery solution in the first washer is approximately 30% to 45%; higher concentrations are not possible, as in spite of the demister it cannot be completely avoided that urea-laden drops remain in the exiting exhaust gas and cause a corresponding high urea concentration in it. Therefore, it is the task of this invention to further develop a generic method in such a way that the exhaust gas load can be considerably reduced. This task is fulfilled with the help of the invention by a method of the kind mentioned above, in that the additional water is initially introduced into a fine washing zone of the first washer bordered on the upper side by the demister and on the lower side by a fluid-impermeable separating floor, and is sprayed on to the at least one demister, and the watery solution resulting in the fine washing zone is subsequently guided into the second washer. Thus, in deviation from the known method, the additional water is initially completely introduced into the additional fine washing zone provided in the first washer, into which the drops-laden exhaust gas enters before passing through the demister. On account of the additional water, a strong dilution takes place in the fine washing zone, so that the urea concentration of the drops gets significantly reduced. At the same time, there additionally follows the cleaning of the demister. On account of the strong dilution of the drops it is possible to significantly increase the urea concentration of the watery solution in the actual main washing zone of the washer, so that the energy consumption for the subsequent evaporation of the watery solution can be highly reduced. Besides, by means of conducting the method in this way it can be achieved that the dust load in the exhaust gas gets reduced from the hitherto attainable values of 50 mg/m3 to 20 mg/m3. The watery solution coming out the second washer is guided into the first washer in a known method, and obviously into the main washing zone of the first washer foreseen below the separating floor, into which also the exhaust gas enters. For separating the fine washing zone and the main washing zone of the first washer a bubble tray is used. Basically, also other separating floors can be used that are fluid-impermeable but gas-permeable. In order to reduce the ammonia concentration in the exhaust gas, in another advantageous extension it is foreseen that an acid is introduced into the fine washing zone of the first washer. For example, sulphuric acid or nitric acid can be used. Such an acid treatment is basically known, e.g. from EP 0 440 932 Bl. In order to energy-wise optimise further processing of the watery solution coming out of the first washer, it is foreseen that in the main washing zone of the first washer a urea concentration of 40 - 60 %, preferably 55%, is set. In this way, the energy consumption for the evaporation can be clearly reduced without this very high urea concentration in the watery solution leading to problems during purification of the exhaust gas, because, as already mentioned earlier, in the fine washing zone a strong dilution of the drops entering into this zone takes place. The invention is described in details below on the basis of the drawing. The following are shown: Fig. 1 A principle scheme for conducting the method; and Fig.2 A detail of fig. 1 in a special extension. A plant for conducting the method first has a first washer 1 and a second washer 2. A preliminary purifying stage 3 is connected before the first washer 1. In the upper region of the first washer 1 a demister 4 is arranged, just like the demister 5 in the second washer 2. The first washer 1 is divided into two washing zones, whereby below the demister 4 a fluid- impermeable but gas-permeable separating floor 12 (e.g. bubble tray) forming a fine washing zone 14, as well as an outlet 11 are arranged. Below the separating floor 12 the main washing zone 21 of the first washer 1 is situated. The above-mentioned plant parts are components of a plant for manufacturing fertilizers, especially urea, and are connected to a granulator and a cooler that are not shown. Exhaust gas laden with ammonia and dust is guided out of the not shown granulator, first into the preliminary purifying stage 3, as indicated by an arrow 6. The exhaust gas passes through the preliminary purifying stage 3 and is introduced into the main washing zone 21 of the first washer 1. Similarly, laden cooling gas is directly fed into the second washer, as indicated by an arrow 7. Additional water, preferably purified or non-purified process water, is fed directly to the fine washing zone of the first washer 1, where the water feed line is indicated by arrows 8, 9. The water feed line enters within the washer 1 below the demister 4 into spraying heads 10 directed upwards in such a way that the additional water gets sprayed against the demister and thus cleans it. The additional water gets mixed with the drops passing through the separating floor 12 and leads to a strong dilution in urea concentration of the drops, so that the drops reveal a urea concentration of only 1 to 4 %, even when the urea concentration in the main washing zone 21 lies between 55 to 60 %. In this way, the additional water gets enriched and comes out as watery solution through the outlet 11, to which a pipe 13 is connected that enters into the second washer 2, whereby the watery solution is guided into the second washer 2. After passing through the preliminary purifying stage 3, the exhaust gas to be purified thus first enters into the main washing zone 21 of the first washer 1, in which perforated bases 22 or something similar are arranged, and then passes through the separating floor 12 into the fine washing zone 14, in which on account of mixing with the additional water a strong dilution and reduction of drops adhering to the exhaust gas takes place. The exhaust gas subsequently passes through the demister 4 and then comes out purified at the head of the first washer 1 (arrow 15). The cooling gas to be purified enters in the lower region (arrow 7) into the second washer 2, in which similarly perforated bases 23 are arranged, in order to pass in counter-flow through the introduced watery solution and subsequently through the demister and come out purified at the head of the second washer (arrow 16). The respective sump/bottom product in both washers 1 and 2 is circulated in the usual way as indicated by the corresponding cycles 17 or 18. From the cycle 18 the watery solution is branched off and fed to the preliminary purifying stage 3 through a pipe 19. From the preliminary purifying stage 3 watery solution and exhaust gas thus enter into the main washing zone 21 of the first washer 1. Due to the significant dilution and purification effect in the fine washing zone 14 it is possible to set a urea concentration in the watery solution of approximately 60% in the main washing zone 21 of the first washer 1, i.e. the watery solution coming out of the washer 1 (pipe 24) then has a urea concentration of 60%, so that when compared to the state-of-the-art technology this watery solution can be evaporated with much lesser energy consumption for the purpose of further utilisation. In spite of this high urea concentration in the main washing zone 21, on account of conducting the method with introduction of additional water into the fine washing zone 14 it is possible to even achieve urea concentrations to the tune of 1 to 4% in the fine washing zone 14. The urea concentration in the second washer 2 is approximately 10%. As shown in fig.2, it is additionally foreseen that an acid is introduced into the fine washing zone 14 for reducing the ammonia load in the exhaust gas, as indicated by an arrow 20. For this, a portion of the watery solution coming out of the outlet 11 of the first washer 1 is recycled out of the pipe 13 in the cycle through a pump 25 for introducing the acid into the fine washing zone 14. As acid, sulphuric acid or nitric acid can be used. Such an acid treatment is basically known, e.g. from EP 0 440 932 Bl. Addition of acid (flow 20) takes place in a corrosion-resistant, self-suctioning nozzle after the pump (e.g. blast nozzle) whose influx is regulated. The pressure line of the pump can be wholly or partly used as drive jet flow. This method is basically suitable also alternatively for a washer in which several demisters are vertically arranged. The additional water is then guided in a suitable manner first into a fine washing zone of the washer for the exhaust gas coming out of the granulation. WE CLAIM: 1. Method for removing ammonia and dust from an exhaust gas emitted during manufacture of fertilizers, especially urea, in which the exhaust gas is introduced into a first washer (1) and a cooling gas is introduced into a second washer ((2), and additional water (8,9) is introduced into one washer and watery solution is introduced into the other washer, whereby the exhaust gas as well as the cooling gas pass through at least one demister (4,5) before coming out of the respective washer, characterized in that the additional water is initially introduced into a fine washing zone (14) of the first washer bordered on the upper side by the demister and the lower side a fluid- impermeable separating floor (12) and is sprayed on to the at least one demister (4,5) and the resulting watery solution in the fine washing zone is subsequently guided into the second washer. 2. Method as claimed in claim 1, wherein the watery solution coming out of the second washer is introduced into the main washing zone of the first washer provided below the separating floor, into which the exhaust gas also enters. 3. Method as claimed in claim 1 or 2, wherein a bubble tray is used as separating floor. 4. Method as claimed in claim 1 or one of the following claims wherein an acid is introduced into the fine washing zone of the first washer. 5. Method as claimed in claim 1 or one of the following claims wherein in the main washing zone of the first washer an urea concentration of 40-60%, preferably 55%, is set. A method for removing ammonia and dust from an exhaust gas emitted during the manufacture of fertilisers, especially urea, in which the exhaust gas is introduced into a first washer and a cooling gas is introduced into a second washer and additional water is introduced into one washer and a watery solution is introduced into the other washer, whereby the exhaust gas as well as the cooling gas pass through at least one demister before coming out of the respective washer, is supposed to be further developed in such a way that the exhaust gas load can be significantly reduced. This is achieved, in that the additional water is initially introduced into a fine washing zone of the first washer bordered on the upper side by the demister and on the lower side by a fluid-impermeable separating floor, and sprayed on to the at least one demister and the resulting water solution in the fine water zone is subsequently guided into the second washer. |
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01025-kolnp-2006 assignment.pdf
01025-kolnp-2006 correspondence others.pdf
01025-kolnp-2006 description(complete).pdf
01025-kolnp-2006 international publication.pdf
01025-kolnp-2006 international search authority.pdf
01025-kolnp-2006-abstract-1.1.pdf
01025-kolnp-2006-claims-1.1.pdf
01025-kolnp-2006-correspondence others-1.1.pdf
01025-kolnp-2006-description(complete)-1.1.pdf
01025-kolnp-2006-priority document.pdf
1025-KOLNP-2006-CORRESPONDENCE.pdf
1025-KOLNP-2006-EXAMINATION REPORT.pdf
1025-KOLNP-2006-GRANTED-ABSTRACT.pdf
1025-KOLNP-2006-GRANTED-CLAIMS.pdf
1025-KOLNP-2006-GRANTED-DESCRIPTION (COMPLETE).pdf
1025-KOLNP-2006-GRANTED-DRAWINGS.pdf
1025-KOLNP-2006-GRANTED-FORM 1.pdf
1025-KOLNP-2006-GRANTED-FORM 2.pdf
1025-KOLNP-2006-GRANTED-SPECIFICATION.pdf
1025-KOLNP-2006-REPLY TO EXAMINATION REPORT.pdf
1025-KOLNP-2006-TRANSLATED COPY OF PRIORITY DOCUMENT.pdf
Patent Number | 249748 | |||||||||
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Indian Patent Application Number | 1025/KOLNP/2006 | |||||||||
PG Journal Number | 45/2011 | |||||||||
Publication Date | 11-Nov-2011 | |||||||||
Grant Date | 08-Nov-2011 | |||||||||
Date of Filing | 21-Apr-2006 | |||||||||
Name of Patentee | UHDE GMBH | |||||||||
Applicant Address | FRIEDRICH-UHDE-STRASSE 15, 44141 DORTMUND | |||||||||
Inventors:
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PCT International Classification Number | B01D 53/58 | |||||||||
PCT International Application Number | PCT/EP2004/009886 | |||||||||
PCT International Filing date | 2004-09-04 | |||||||||
PCT Conventions:
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