Urea Recovery Section Layout with Upstream Phase Separation
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Solution Overview
Problem
Existing urea production plants face capacity limitations in recovery sections during revamping operations, leading to high costs and inefficiencies due to increased water recycling and steam consumption, with existing solutions like pre-decomposers being costly and ineffective in reducing water content.
Innovation Solution
Incorporating a separator upstream of the pre-decomposer in the recovery section to create a two-phase flow, separating gaseous and liquid phases before decomposing ammonium carbamate, thereby reducing the load on pre-decomposers and condensers, and minimizing water recycling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the capacity of the synthesis section is increased during revamping operations, then the production capacity of urea is improved, but the recovery sections become a bottleneck and require significantly larger apparatuses which result in very high costs
Solution Approach 1:
The invention divides the single decomposer unit into two separate units: a pre-decomposer operating at high pressure and a decomposer operating at low pressure. This segmentation allows each unit to be optimized for its specific pressure condition, enabling the synthesis section capacity to be increased without proportionally increasing the size and cost of the recovery section apparatuses.
2Quantity of substance
If water is separated from urea in the carbamate decomposition sections, then water removal is achieved, but the converted ammonia is recycled back to the synthesis section resulting in decreased conversion to urea and greater steam consumption
Solution Approach 1:
The decomposition process is segmented into two stages: pre-decomposition at high pressure and final decomposition at low pressure. This segmentation allows water to be removed in the second stage from already decomposed carbamate, preventing the recycling of converted ammonia and reducing steam consumption while effectively removing water.
Solution Approach 2:
The pre-decomposer performs preliminary decomposition of carbamate before the solution enters the main decomposer. This preliminary action converts a portion of carbamate to ammonia and CO2 beforehand, so that when water removal occurs in the decomposer, the converted ammonia is not recycled back to the synthesis section, thereby reducing steam consumption.
3Productivity
If a pre-decomposer is installed upstream of the decomposer to increase recovery section capacity, then the capacity handling is improved, but the pre-decomposer becomes subject to high load and becomes a costly apparatus that does not substantially reduce water recycling
Solution Approach 1:
The decomposition function is segmented between a pre-decomposer operating at high pressure and a decomposer operating at low pressure. The pre-decomposer is designed to handle only the preliminary decomposition load, while the majority of the decomposition and water removal occurs in the decomposer at low pressure. This segmentation reduces the load and cost of the pre-decomposer while maintaining increased capacity.
Solution Approach 2:
The system changes the pressure parameter between the two decomposition stages: the pre-decomposer operates at high pressure (synthesis pressure) and the decomposer operates at low pressure. This parameter change allows the pre-decomposer to be smaller and less costly, as it only needs to handle preliminary decomposition, while the low-pressure decomposer handles the bulk of the process.
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
Reduces the size and thermal load of pre-decomposers and condensers, decreases water recycling, increases urea conversion, and lowers steam consumption, resulting in cost-effective capacity expansion.
Implementation Method 1
a line which supplies an aqueous solution containing urea to said at least one recovery section, said line comprising at least one intercepting member suitable for depressurizing the aqueous solution with formation of a two-phase flow
Implementation Method 2
a separator which receives said two-phase flow and separates the gaseous phase from the liquid phase
Implementation Method 3
a condenser, wherein said first gaseous stream and said second gaseous stream are at least partially condensed
Data Source
Figure 1
Figure 2~3
AI summary
Plant for the synthesis of urea comprising:a synthesis section (101), wherein ammonia (1) and carbon dioxide (2) react to give an aqueous solution (3) containing urea and ammonium carbamate; at least one recovery section fed with said depressurized aqueous solution and in a two-phase state, said recovery section comprising a separator (104,108) which processes said two-phase solution; a pre-decomposer (105, 109), a decomposer (106, 110) and a condenser (107, 111), wherein the gaseous streams obtained in the separator and in the decomposer are condensed in said condenser of the recovery section.