Toyo Engineering Corporation

Mitsui Toatsu Chemicals, Incorporated

Haruyuki Morikawa

Hiroshi Ono

Hidetsugu Fujii

Akito Fukui

Shigeru Inoue

Genshi Nishikawa

Eiji Sakata

Keishi Sato

Yasuhiko Kojima

Kenji Yoshimoto

Shuhei Nakamura

Maghfuri Baharuddin

Yoshihiro Tajiri

Takuya Hayabuchi

Naohiro Teramoto

Suguru Watanabe

Provided are urea manufacturing method and apparatus, which can increase the conversion ratio into urea and to reduce the consumption of steam. The temperature of the reactor is increased by introducing the entire amount of raw material ammonia and introducing a portion of the decomposed gas from the stripper into the reactor. The raw material ammonia is preferably heated using the steam condensate generated in the purification step, and/or the steam generated by the heat of condensation of the decomposed gas and the unreacted substances in the condensation step. The heating temperature is preferably between 70 and 140&#xb0; C.

Urea manufacturing method and urea manufacturing apparatus

Method and apparatus that enable the more efficient manufacture of urea are provided. Before unreacted substances are removed from a urea synthesis solution obtained from a stripper, the urea synthesis solution is placed under pressure reduced from the synthesis pressure. Thus, a gas-liquid mixture is obtained. The gas-liquid mixture is heated with a decomposed gas from the stripper using a shell-and-tube heat exchanger, and then introduced into a purification system. In the heating, the gas-liquid mixture is introduced into the shell of the heat exchanger while the decomposed gas is introduced into the tube side of the heat exchanger.

The present invention relates to a method for producing a high-purity aqueous urea solution, utilizing a urea production process at least including a urea synthesis step of synthesizing urea from a raw material feed to produce a urea synthesis liquid, and a urea purification step of purifying the urea synthesis liquid to produce an aqueous urea solution with high urea concentration. The present invention includes a urea crystallization step of separating a part of the urea synthesis liquid and/or a part of the aqueous urea solution and crystallizing urea contained in the separated urea synthesis liquid and/or aqueous urea solution to produce solid crystal urea, and a mixing step of mixing the crystal urea with water to produce a high-purity aqueous urea solution. A high-purity aqueous urea solution to be produced is an aqueous urea solution with high purity suitable as a reducing agent for SCR.

Method for producing high-purity aqueous urea solution in urea production process

In a granulating process for preparing granular urea from an aqueous urea solution using a fluidized bed method or a fluidized, spouted bed method, an aqueous urea solution having a urea concentration of 94-98.5 wt % is used and the operational temperature of the fluidized bed is controlled in a range of 110-120&#xb0; C. to accelerate the drying of a granulated product to thereby give a granular urea product having a moisture content of 0.3 wt % or less.

Process for preparing granular urea product

A method for determining a urea concentration in an aqueous solution containing urea, includes: hydrolyzing the urea in the aqueous solution, measuring an electric conductivity &#x3c7; of the aqueous solution, and determining the urea concentration in the aqueous solution from the electric conductivity &#x3c7; using a correlation between the urea concentration and an electric conductivity.

Method and apparatus for determining urea concentration

Process for preparing granular urea

Disclosed herein is a process of synthesizing urea including reacting ammonia and carbon dioxide at a urea synthesis pressure and temperature in a urea synthesis zone, separating excess ammonia and unreacted ammonium carbamate from the thus-obtained urea synthesis melt as a gaseous mixture containing ammonia and carbon dioxide, recirculating the gaseous mixture to the urea synthesis zone, and, on the other hand, obtaining urea from an aqueous urea solution which has been obtained by separating the excess ammonia and unreacted ammonium carbamate. The above process features ingeniously combined conditions of various process steps. It produces urea using less high-pressure steam and recovers less low-pressure steam. A stripping operation making use of carbon dioxide can be effectively incorporated in the above process. The above process permits to cut the construction cost of a urea synthesis plant.

Process for synthesizing urea

In a process in which a urea synthesis effluent obtained by reacting ammonia with carbon dioxide is subjected to a stripping step of bringing the urea synthesis effluent into countercurrent contact with carbon dioxide under heating to obtain an aqueous urea solution containing a small amount of ammonia and ammonium carbamate, the improvement comprises first bringing the urea synthesis effluent is into contact with a separated gas evolved in the stripping step under adiabatic conditions or with a little cooling. The use of the above process enables a reduction in size of the stripper and a recovery of the high pressure steam without keeping the ammonia to carbon dioxide molar ratio lower than that of the conventional method.

Method of stripping unreacted materials in urea synthesis process

An inert gas containing carbon dioxide and ammonia and separated from a urea synthesis effluent under urea synthesis pressures is brought into contact with an absorbent along with unreacted carbon dioxide and ammonia separated in high pressure distillation at a pressure of from 10 to 25 kg/cm.sup.2 G to absorb substantially all of the carbon dioxide and the major portion of the ammonia, and is cooled to be separated from the resulting liquid ammonia and then is discharged. The inert gas can be treated with little or no danger of explosion by the above method.

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Chiba, Japan

Haruyuki Morikawa