SU118094A1 - The method of regeneration of ammonia and carbon dioxide in the production of urea - Google Patents

Description

The present invention relates to the field of gas distillation recovery after the synthesis of urea-ammonia and carbon dioxide.

There is a known method for the regeneration of these gases by separating ammonia and carbon dioxide by selective absorption of carbonic acid with monoethanolamine with an aqueous solution, followed by a two-stage solution regeneration after absorption.

According to the proposed method, the separation of these gases is carried out in three stages using two absorbers: an aqueous solution of monoethanolamine for carbon dioxide and an aqueous solution of monoammonium phosphate for ammonia.

In the first stage, the monoethanolamine absorbs all carbon dioxide and / 4 parts of ammonia (from the initial amount) with an aqueous solution, most of which remains in the gas phase and returns to the production cycle of the synthesis.

In the second stage, the resulting solution of monoethanolamine containing carbon dioxide and ammonia is subjected to one-step regeneration at a temperature of 140 ° and elevated pressure.

The regeneration waste gases containing carbon dioxide and ammonia in a 1: 1 ratio are sent for absorption by the monoammonium phosphate solution. In this case, ammonia is completely absorbed, and the carbon dioxide remaining in the gas phase is directed to the synthesis cycle.

The third stage is that, after absorption of ammonia, the resulting solution undergoes regeneration at atmospheric pressure and a temperature of 100-105 °. Released ammonia is also sent to the urea synthesis cycle.

 118094-2 -

An example of the method.

In the attached figure, the scheme of gas distillation recovery after urea synthesis is presented.

Distillation gases after the synthesis of urea, containing about 52Vo of ammonia, 33% carbon dioxide and 15% water vapor (by weight) are fed to the absorption column 1, irrigated with a regenerated 30% aqueous solution of monoethanolamine. In this process, the formation of carbonates and bicarbonates of monoethanolamine proceed.

2RNH2-g-N.O + CO (RHNH,) - COg (RHNH,), СО3 + H, O + CO2. ± 2ННЛтННСОз, where R denotes the group - СН2-СН - OH.

The process is carried out at atmospheric pressure and a temperature of 70 °.

The absorption coefficient for carbon dioxide absorption by a 30% aqueous solution of monoethanolamine in a packed column is about 9 / ca/.w ,, Q atm.

Simultaneously with the absorption of carbon dioxide, about a quarter of the ammonia supplied from the gas also absorbs.

The remaining MaiCca ammonia (% of the initial amount) upon leaving the absorption tower is cooled in the tubular condenser 2 and returned to the synthesis cycle in an amount of approximately 50% of the distillation with the gases.

The ammonia water formed in the condenser 2 is sent to the desorption of ammonia into the distillation column, from which the released ammonia returns 1c also to the synthesis cycle.

The outgoing aqueous solution of monoethanolamine from the absorption column enters collector 5, whereupon pump 4 is fed to regeneration column 5.

The solution is preheated by the tenla of the regenerated solution, the passage through the heat exchanger 6.

The monoethanolamine solution regeneration column is a tower with | Sadok, having tubular heating in the lower part and cooling elements in the upper part 7. The regeneration is carried out under normal conditions adopted in factory practice, i.e. pressure and temperature of 140 °.

As a result of the regeneration of the solution and the partial separation of water vapor in the condenser 7, a gas of approximately the following composition is obtained: 45i / o 002; 45% NHs and 10% water vapor by volume. The reflux from the condenser is returned to the reflux of the upper packed portion of the regeneration column.

The regenerated solution, having passed the heat exchanger 6, is cooled additionally with water in the refrigerator 8 and is fed into the absorption column /.

The gas leaving the regenerator 5 is fed to the absorption in the absorption column 9, irrigated with an aqueous solution of monoammonium phosphate with a content of 25% or more NH4H2PO4.

Absorption is carried out at 50 ° and atmospheric pressure.

When this occurs, ammonia is chemisorbed by the reaction: NH4H2P04 + NHs (NH4) 2HPO4.

The carbon dioxide 9 not absorbed in the absorber is released from the basis mass of water vapor in the condenser condenser 10 and returns to the synthesis cycle.

The reflux formed in the condenser 10 is directed to the irrigation of the top of the absorption column 9. The solution flowing out of the column enters collection 11, from where pump 12 is fed for regeneration into

column / 5. The pre-solution is preheated by the heat of the regenerated solution in the heat exchanger 14.

Regeneration is carried out at atmospheric pressure and a temperature of 100-105 °.

Column 13 is similar in its design to column 5. Ammonia released as a result of the regeneration of the mono-ammonium phosphate solution is freed from water vapor in the condenser condenser 15 and is sent to the synthesis cycle. Reflux from the condenser cooler partially returns to irrigation of the top of the nozzle of the regeneration column 13, and partially enters collection 16, where condensate from condenser 2 also flows. From the collection ammonia water is directed to the desorption of ammonia by pump 17 to the distillation column.

Desorbed ammonia there also enters the synthesis cycle.

The consumption of materials per 1 ton of urea is 4-5 m of a 30% aqueous solution of monoethanolamine, 10 m of a 20-25Vo-Horo solution or a 5. / Vt of a 45% aqueous solution of monoammonium phosphate.

The ammonia and carbon dioxide emitted are sufficiently pure to meet the requirements of the urea production gases.

Subject invention

The method of ammonia and carbon dioxide regeneration in the production of urea by selective absorption of myoethanolamine and monoammonium phosphate with aqueous solutions followed by separation of these gases from solutions, characterized in that, in order to more completely separate ammonia and carbon dioxide, the process is carried out in three stages, namely: in the 1st stage, it absorbs all carbon dioxide and / 4 part of ammonia with an aqueous solution of monoethanolamine, returning the remaining amount of it to the synthesis cycle; in the 2nd stage, all carbon dioxide obtained as a result of the absorption of ammonia from the gases of regeneration of the spent solution of monoethanolamine is recycled into the synthesis cycle; in the 3rd stage, as a result of the regeneration of the monoammonium phosphate solution, ammonia absorbed in the 1st stage by the monoethanolamine solution is returned to the synthesis cycle.

No. 118094