Adiabatic Stripping Section for Urea Synthesis Loop
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Solution Overview
Problem
Conventional urea synthesis processes, such as self-stripping and CO2-stripping, face challenges in achieving high conversion yields without increasing the duty of downstream equipment, and are limited by equipment size in large plants.
Innovation Solution
The process involves an adiabatic stripping section using carbon dioxide as a stripping medium, allowing for a higher N/C ratio in the reactor and independent control of N/C ratios in different sections, with carbon dioxide split between reactor, adiabatic, and thermal stripping sections to enhance conversion yield and reduce steam consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the reactor is operated with higher ammonia excess to increase conversion yield, then the conversion yield improves, but the duty of downstream equipment increases due to surplus ammonia that must be separated and condensed
Solution Approach 1:
The stripping process is divided into two independent sections: adiabatic stripping and thermal stripping. The adiabatic stripping section removes surplus ammonia without requiring steam heating, while the thermal stripping section handles the remaining decomposition. This segmentation allows the reactor to operate with higher ammonia excess for improved conversion yield, while the adiabatic section prevents excessive ammonia from overwhelming the downstream equipment.
Solution Approach 2:
The adiabatic stripping section acts as an intermediary between the reactor and the thermal stripping section. It pre-treats the urea solution by removing a portion of the ammonia and carbamate through adiabatic decomposition, thereby reducing the load on the downstream thermal stripping section and condenser system.
2Ease of operation
If conventional self-stripping or CO2-stripping processes are used, then the process is simple to operate, but equipment size becomes excessively large in large plants
Solution Approach 1:
The stripping function is segmented into adiabatic and thermal sections, each with specific roles. The adiabatic section handles the bulk of ammonia and carbamate removal through decomposition without external heating, significantly reducing the size requirements of downstream equipment compared to conventional single-stage thermal stripping or CO2-stripping processes.
Solution Approach 2:
The process changes the operating parameters of the stripping section by introducing adiabatic conditions (without external heating) for part of the stripping process. This parameter change allows for more compact equipment design while maintaining effective ammonia and carbamate removal, addressing the equipment size issue in large plants.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach increases conversion yield to 68-75%, reduces steam consumption by 15-30%, and allows for simpler and less expensive medium-pressure section design, enabling higher production capacity and reduced ammonia recovery, while also reducing equipment size and energy consumption.
Implementation Method 1
a urea solution produced in said reactor is subjected to an adiabatic stripping process in an adiabatic stripping section, with carbon dioxide as a stripping medium
Implementation Method 2
obtaining a liquid urea solution and a vapour phase containing ammonia and carbon dioxide
Implementation Method 3
said urea solution obtained in said adiabatic stripping process is further subject to thermal stripping in said thermal stripping section
Implementation Method 4
Heat supplied by the steam results in the partial decomposition of the carbamate into carbon dioxide and ammonia
Implementation Method 5
A vapour phase containing ammonia and CO2 produced in the stripper is condensed in a high-pressure condenser
Data Source
AI summary
A process and a related plant layout for producing urea are disclosed, wherein the high-pressure loop (1) comprises a synthesis reactor (2), a thermal stripper (3), a condenser (4), and an adiabatic CO2 stripper (10) disposed upstream said thermal stripper, separating a vapour phase (13) containing ammonia from the urea solution (9) discharged from the reactor, and recycling said vapour phase to the reactor. The adiabatic stripper (10) can be incorporated in a reactor (200) having a top reaction zone and a bottom adiabatic stripping zone. A revamping method for a conventional urea plant in accordance with the inventive process is also disclosed.