SU767091A1 - Method of control of ammonium carbamate recuperation process - Google Patents

Description

This invention relates to the automation of technological processes and can be used in the production of urea. The closest to the present invention is a method for controlling the ammonium carbamate recovery process by controlling the feedstock consumption — to the synthesis column, controlling the temperature, pressure, and the level of separation of liquids in the apparatus for separation of the urea synthesis water. The known method has organic possibilities in terms of reducing the energy costs of the process due to the lack of techniques that provide the optimal degree of separation of the urea synthesis water. The purpose of the invention is to reduce energy costs for the process. This goal is achieved in that according to the method of managing the ammonium carbamate recovery, obtained by the interaction of carbon dioxide and ammonia with its subsequent stepwise distillation by controlling the flow rate of the raw material in the synthesis column, adjusting the temperature, pressure and level of the liquid section in the apparatus for separation of the urea synthesis, the consumption of carbon dioxide gas to the synthesis column is extremely controlled depending on the density of the liquid in the urea-rich layer in the apparatus for separation of the water with intestine urea, and the flow rate of ammonia in the synthesis column is adjusted for the steam flow rate to the heat exchanger of the first distillation stage. The drawing shows a block diagram of a control system that implements the proposed method. The method of controlling the carbamate recovery process is carried out as follows. Ammonia, carbon dioxide and recycle to the synthesis of ammonium carbamate stream, which also contains ammonia, water and urea, respectively, enter the synthesis column 1 through pipelines 2, 3 and 4. The reaction mixture from the synthesis column 1 passes the heat exchanger - heat utilizer 5, where it gives off part of the heat, for example, to the urea solution going to the residue through the pipeline 6, and in the form of a uniform cooled

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liquids through conduit 7 are sent to apparatus 8, for the HHHH nJiajBa synthesis of urea, in which it is stratified into two liquids. The urea-enriched stream through conduit 9 enters the first stage distillation column 10 and further to the subsequent processing and release of the process, and the enriched carbamate is transferred from the apparatus 8 to the synthesis column with a pump.

 The chilled tempered temperature of the reaction mixture is stabilized with regulator 12 complete with sensor 13 and control valve 14, temperature in column 10 of the first distillation step is stabilized with sensor 15 / regulator 16, valve 17 for feeding steam into a heat sherbmennik 18

first distillation step. In order to ensure stable operation of the apparatus 8 for separating the urea synthesis float, a regulator 19 is used with a sensor 20 level of phase separation, acting by means of valve 21 on the bypass stream recirculated on the synthesis of substances.

The consumption of fresh carbon dioxide in the synthesis column 1 is controlled by a valve 22 operating from an extreme regulator 23, which continuously searches for the minimum density value of the urea-rich liquid layer measured by the densitometer sensor 24. The signals from flow sensors 25 and 26 of fresh carbon dioxide and ammonia, respectively, are fed to the input of a ratio controller 27 supporting

6, using valve 28 on the ammonia pipe 2 into the synthesis column 1, a predetermined ratio of initial reagents, for example, a 100% excess of ammonia. The value of the task is determined by the signal from the sensor 29 of the steam flow meter to the heat exchanger 18 of the first distillation stage.

The pressure in synthesis column 1 and apparatus 8 for meltTyOEsGmIchevina splitting is measured by pressure sensor 30 and maintained by regulator 31 acting on throttling valve 32. Work stabilizing regulators 12, 16, 19 and 31 are based on automatic CMB continuous comparison of set values of stabilized parameters (temperature of llav, urea, temperature of the liquid phase in column 10, even of the section of liquids in the apparatus 8 and pressure in pipeline 7, respectively) with the current values of these parameters. In case of deviation of the measured values of the parameters of the RT parameters, the corresponding controller generates the error signal and then the control signal in accordance with

767091

with the law implemented by each regulator and aimed at re-establishing a given value of its setpoint.

The regulator 27 for the ratio of the consumption of fresh reagents to the synthesis column 1 maintains the flow rate of ammonia depending on the time-varying consumption of carbon dioxide with a change in the amount of excess ammonia over the stoichiometrically necessary amount of it depending on the flow rate of steam in the heat exchanger 18 of the first distillation stage. For example, according to the synthesis conditions, a 100% excess of ammonia is provided. However, due to the presence of recycling, the composition and amount of which can vary depending on the operating mode of the column 1, the apparatus 8 for separation of the urea synthesis water and the column 10 of the first stage distillation, the exhaust gases from which also usually return to the synthesis The overall value of the excess ammonia, as well as the residence time of the reactants in the system, can vary significantly. Any deviation from the conditions of synthesis and separation from optimal conditions leads to an increase in the ammonium carbamate content in the urea-enriched layer, and consequently, an increase in steam consumption for its decomposition and gas distillation during the distillation of the melt, as well as an increase in the density of the urea-enriched layer Extreme regulator 23, operation in a step-by-step reverse mode, based on the principle of remembering the extremum of a controlled parameter (minimum density of a liquid layer enriched in urea), looks for the right direction to decrease Whether the increase in the regulatory effect of the load-modify the carbon dioxide, and the ratio controller 27, stabilizing the predetermined value changes the surplus of ammonia, followed by changing the flow rate of carbon .gaza ammonia in kolrnnu 1 synthesis. At the same time, the correction signal from the sensor 29 of the flow meter uv increases. The signal for setting the value of the excess ammonia is shortened, which makes it possible to shorten the transient process and more quickly restore the optimal mode of separation of the urea synthesis stream.

Claims (1)

1. Japanese patent 16964/71, cl. 16 A 811 (prototype).