RU2289471C1 - Method and the installation for preparation of the solution of carbamide - Google Patents

Abstract

FIELD: chemical industry; methods and devices for production of carbamide solution.

SUBSTANCE: the invention is pertaining to chemical industry, in particular, to the method and the installation for preparation of the carbamide solution applied as the agent for purification of nitrogen oxides from the exhaust gases of the combustion engines. The method of preparation of the carbamide solution provides for the dilution with the desalted water up to the necessary solution strength of the carbamide formed in its production process, desorption of the dissolved gases from the solution at its air blasting and the subsequent absorption of the impurities from the air by the solid adsorbent. If necessary the solution may be added with the agent to lower its freezing temperature. The installation for realization of the method consists of: the container of the source solution of the carbamide, the apparatus with the stirring device, the desorber, the adsorber, the means for feeding of the carbamide solution from the container of the source solution of carbamide into the apparatus with the stirring device, the means for feeding of the desalted water into the apparatus with the stirring device, the means for feeding of the carbamide solution from the apparatus with the stirring device into the desorber, the means for feeding of the air from the desorber into the adsorber, a means for feeding of the air into the desorber, the means for feeding of the air from the desorber into the adsorber. The technical result of the invention is development of the method and creation of the installation for preparation of the carbamide solution meeting the specification requirements for purification of nitrogen oxides from the exhaust gases of the combustion engines.

EFFECT: the invention ensures development of the method and creation of the installation for preparation of the carbamide solution meeting the specification requirements for purification of nitrogen oxides from the exhaust gases of the combustion engines.

4 cl, 1 dwg

Description

The invention relates to a method and apparatus for preparing a urea solution used as an agent for purification of nitrogen oxides from exhaust gases of internal combustion engines (primarily automobile ones).

The known technology of selective catalytic reduction of nitrogen oxides to elemental nitrogen in automobile exhaust gases (SCR - Selective Catalytic Reduction) when an aqueous urea solution containing an average of 32.5% urea is added to the exhaust gas stream (the composition complies with DIN V 70 070/2003) , from a special tank mounted on a car (International Road Transport, 2004, No. 4 (56)). The specified solution is produced by a number of European companies that are industrial producers of urea, for example under the names AdBlue (firm BASF), Air1 (firm Yara).

A known method for producing a urea solution for purifying engine exhaust gases by dissolving solid urea in demineralized water (DGMK-Research Report 616-1. AdBlue as a Reducing Agent for the Decrease of NO _x -Emissions from Diesel Engines of Commercial Vehicles, Hamburg : Deutsche Wissen-schaftliche Gesellschaft für Erdöl, Erdgas und Kohle-DGMK, 2003, p.10; www.dgmk.de/downstream/report_616-1_e.pdf). When using the most affordable prilled or granular urea with a particle size of 2-4 mm in this method, dissolution occurs rather slowly and is associated with significant energy costs, since the dissolution of urea in water is accompanied by heat absorption.

Closest to the proposed technical essence is a well-known method of preparing a urea solution intended for purification of engine exhaust gases, including diluting an aqueous urea solution formed during its production with demineralized water to the desired concentration (Yara-Brenntag Press Release, Hannover, 09/22/2004 ; www.airl.info/doc/PR_Yara_Brenntag_Air1_en_04.pdf) The initial urea solution, as a rule, has a concentration of 60-70%, although less concentrated solutions, for example, 40-50%, are formed at some stages of production. The resulting dilution of the solution of the required concentration is transported to gas stations, where it is used to refuel the appropriate devices installed on vehicles. During storage of urea solutions, hydrolysis processes take place in them, accompanied by a decrease in the urea content and the accumulation of dissolved ammonia, the excessive presence of which in the solution is undesirable from the point of view of the safety of car drivers and passengers. These processes can bring the quality of the solution beyond acceptable limits (at least 31.8% by weight of urea and not more than 0.2% by weight of ammonia according to DIN V 70 070/2003).

It follows from the essence of this known method that the installation necessary for its implementation for preparing a urea solution intended for cleaning exhaust gases of engines, including the capacity of the initial urea solution obtained during its production, an apparatus with a mixing device, means for feeding, is closest to the proposed one urea solution from the tank of the initial urea solution into the apparatus with a mixing device and means for supplying demineralized water to the apparatus with a mixing m device (Yara-Brenntag Press Release, Hannover, 22.09.2004). When storing a urea solution in a container, as described above, undesired urea hydrolysis processes occur in it.

The technical problem to which the invention is directed is to create a method and an installation that allows at any time to provide consumers with a urea solution, using it as an agent for cleaning nitrogen oxides from exhaust gases of internal combustion engines, a product that fully meets all technical requirements.

To solve this problem, a method is proposed for preparing a urea solution intended for purification of engine exhaust gases, which includes diluting with desalted water to the desired concentration of the solution formed in the process of urea production, characterized in that after dilution, dissolved gases are desorbed from the solution by blowing it with air and subsequent absorption impurities from the air with a solid adsorbent.

To solve this problem, an installation for preparing a urea solution intended for cleaning exhaust gases of engines, including the capacity of the initial urea solution, an apparatus with a mixing device, a stripper, adsorber, means for supplying a urea solution from the capacity of the initial urea solution to an apparatus with a mixing device, is also proposed. means for supplying desalted water to the apparatus with a mixing device, means for supplying a solution of urea from the apparatus with a mixing device in desorb p, means for supplying air to the stripper, means for supplying air from the stripper to the adsorber.

The technical result that can be obtained by using the invention is to maintain the constancy of the quality indicators of a urea solution intended for purification of exhaust gases of engines.

If the climatic conditions in the area where the invention is carried out are such that the ambient temperature may be lower than -11 ° C (crystallization temperature of a urea solution with a concentration of 32.5% by weight), the proposed method can be supplemented by the step of adding an agent to lower the temperature freezing to a urea solution, and the proposed installation - means for supplying an agent to lower the freezing temperature in the capacity of the initial urea solution and / or apparatus with a mixing device.

The invention is illustrated by the attached drawing, which shows a diagram of a specific embodiment of the proposed installation that implements the proposed method.

In accordance with the drawing, the installation includes a receiving tank 1 for a urea solution, an apparatus 2 equipped with a mixing device, a stripper 3 equipped with devices for heating and mass transfer, an adsorber 4, a pump 5 for supplying a urea solution from a tank 1 to a device 2, a pump 6 for feeding urea solution from apparatus 2 to stripper 3, pump 7 for recirculation of urea solution from stripper 3 to apparatus 2, pipe 8 for supplying a urea solution to tank 1, pipe 9 for feeding to tank 1 and agent apparatus 2 to lower the temperature fidgeting, pipe 10 for supplying demineralized water from a reservoir (not shown) to apparatus 2, pipe 11 for supplying air to stripper 3, pipe 12 for supplying air from stripping 3 to adsorber 4, pipe 13 for transferring a urea solution to a device for refueling vehicles, a pipeline 14 for discharging air from the adsorber 4 into the atmosphere, means for supplying (if necessary) heat to the stripper 3 in the form of a pipeline 15 for supplying sharp steam.

The installation, the circuit of which is shown in the drawing, in continuous mode works as follows. A urea solution is introduced into the receiving tank 1 through a pipe 8, coming from urea producers, for example, in tankers. For this purpose, a solution with a concentration of 60-70%, formed in the main processing line for the production of urea, can be used. However, it is preferable to use a solution with a concentration of 40-50%, which is formed during the production of urea, for example, at the stage of purification of air leaving the apparatus for granulating and cooling the final product from urea dust. From the tank 1, the solution is pumped to the apparatus 2 as necessary by the pump 5, maintaining a constant solution level in it. Desalted water is supplied to the apparatus 2 through the pipeline 10 in the amount necessary to maintain the required concentration of urea in the solution (31.8 ÷ 33.3 wt%), and, if necessary, through the pipeline 9, an agent to lower the freezing temperature, which can also be served in a receiving tank 1. As desalted water can be used, for example, water purified using ion exchange resins, or steam condensate. Ethanol, monoethanolamine and other organic liquids can be used as an agent for lowering the freezing point. The solution in the apparatus 2 is constantly mixed and circulated with the help of pumps 6 and 7 through the apparatus 2 and the stripper 3. Air is supplied to the stripper 3 through the pipe 11 and, if necessary, is supported by the steam supplied through the pipe 15, depending on the specific conditions, temperature up to 100 ° С. In the process of purging a urea solution with air and steam on mass transfer devices (nozzle, plates), dissolved ammonia and carbon dioxide are removed from the solution in a stream of air, which is passed through a pipe 12 from desorber 3 to adsorber 4, where ammonia is absorbed by a layer of solid sorbent (for example, activated coal), and air with an admixture of carbon dioxide through the pipeline 14 is discharged into the atmosphere. The finished urea solution of the desired quality enters the device for refueling vehicles through pipeline 13.

The described installation can also operate in periodic mode. In this case, the finished urea solution of the required quality is sent to the vehicle refueling device (or to another consumer) directly from stripper 3.

Claims (4)

1. A method of preparing a urea solution intended for purification of engine exhaust gases, comprising diluting with desalted water to the desired concentration of the solution formed in the process of urea production, characterized in that after dilution, dissolved gases are desorbed from the solution when it is purged with air, followed by absorption of impurities from the air solid adsorbent. 2. The method according to claim 1, characterized in that an agent is added to the solution to lower the freezing temperature. 3. Installation for the preparation of a urea solution intended for purification of exhaust gases of engines, including the capacity of the initial urea solution, an apparatus with a mixing device, a stripper, an adsorber, means for supplying a urea solution from a container of an initial urea solution to a device with a mixing device, means for supplying desalted water into the apparatus with a mixing device, means for supplying a urea solution from the apparatus with a mixing device to the stripper, means for supplying air in the stripping p, means for supplying air from the stripper to the adsorber. 4. Installation according to claim 3, characterized in that it further comprises means for supplying an agent for lowering the freezing temperature into the capacity of the initial urea solution and / or apparatus with a mixing device.