Urea Demonstration Project

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Urea Project

Project Location

This is a Steady State project and is stored at:

..\SysCADXXX\Examples\81 Urea\Demo Urea Project.spf

Features Demonstrated

1. Various processes including synthesis, decomposition, hydrolysis, granulation, separation, evaporation, condensation and off gas scrubbing.
2. Reactions including Reaction Heat Exchange.
3. Heat Exchanger model (Build 138) or Shell and Tube Heat Exchanger 2 (Build 139 or later).
4. Gas Pump model.
5. User Property Calculations
6. Use of General and PID controllers.
7. Use of sample Excel report.

Brief Description

• This project simulates a Urea plant. Ammonia (NH3) and carbon dioxide are reacted together to form a urea solution. The urea solution undergoes decomposition and a two-stage evaporation process to produce urea melt. The urea melt is granulated to produce solids urea granulated product. This model is provided as a template, starting data is an estimate only.

Project Configuration

Synthesis Circuit

• Liquid carbon dioxide is reacted with liquid ammonia in a Reactor to produce liquid Urea and other by-products. The reactions occur at 180 °C and 140 barg pressure.
• A PID controller is used to control the Nitrogen to Carbon ratio in the Reactor outlet by varying the feed rate of the carbon dioxide gas.
• The offgas from the reactor is scrubbed with carbamate recycle solution.

Recirculation Circuit

• Urea solution from the Synthesis circuit is undergoes decomposition reactions in the Low Pressure (LP) Decomposer. The reactions occur at 180 °C and 4.5 barg pressure.
• Over half of the urea is converted to ammonium carbamate.
• The offgas from the decomposer mixes with the waste water off gas stream and a series of condensation and separation processes produce an offgas stream and a carbamate recycle stream which is returned to the Synthesis circuit.

Evaporation Circuit

• Concentrated urea solution from the Recirculation circuit is passed through a two-stage evaproation process at 135 °C and 0.3 bar pressure (second stage).
• A small fraction of the water evaporates while a small fraction of the urea decomposes to carbon dioxide and ammonia.
• The product from the evaporation process is a urea melt stream.
• The offgas from the evaporators is condensed and after separation of the non-condensables, a condensate stream is produced. The feed to the condensation is under vacuum but the final product is at atmospheric pressure.

Water Treatment Circuit

• Condensate from the Evaporation circuit is passed through a series of heat exchangers, scrubbers and a hydrolyser to produce an effluent water stream and an offgas stream.
• Steam is fed to bottom scrubber and hydrolyser.
• Within the hydrolyser, any remaining urea and biuret are decomposed to carbon dioxide and ammonia.

Granulation Circuit

• Urea melt from the Evaporation circuit is sent to a granulator which produces a granulated solid urea product and an offgas stream.
• Ambient air is fed to the granulator after a pressure boost in the Air Fan.
• A PID controller is used to control the final moisture content of the urea product by varying the evaporation of water in the granulator.
• A PID controller is used to control the temperature of the urea product by varying the amount of ambient air fed to the granulator.

Setting up and Viewing User Property Calculation

• One focus of this example is to show the user how to add in a user property calculation for their project. Once defined, the user property calculation will be available for all the unit operations in the project.
  1. In Step 2 of Edit Configuration file, add the user property calculation on the Calculations tab.
  2. One User Property Calculation has been added for NtoC, the elemental ratio of nitrogen to carbon. This will be visible on the Qo/QFeed/QProd tabs on the access window.

Notes:

1. Indirect heating and cooling flows are not shown. Instead Reaction Heat Exchange (RHX) functionality is employed.
2. Pumps and compressors are not included, pressures are set in vessels.
3. Reaction extents are set in Reaction Blocks directly.
4. Generally, all reactions occur in the liquid phase. Product gases are evolved afterwards.

Excel Report

• Urea Demo Report shows an example of a report that can be easily setup using the provided default 04DetailedReport.xlsx file.