Urea Plant Flow Reversal Prevention via Reactor Effluent Monitoring
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Solution Overview
Problem
Natural-circulation CO2-stripping urea synthesis loops are prone to unexpected changes in liquid/gas ratio or density, which can lead to flow reversal, causing sudden pressure increases and potential ammonia release, especially during startup phases.
Innovation Solution
Incorporating means to detect flow rate and direction in the reactor effluent flow line, such as differential pressure sensors or ultrasonic flow meters, to monitor and control the flow, preventing reverse flow and ensuring stable operation by generating alarms or automated interventions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If natural-circulation loop is used to reduce complexity and energy consumption, then device complexity and energy use are reduced, but flow reversal risk increases due to unexpected changes in liquid/gas ratio or density
Solution Approach 1:
The patent implements a feedback control system using a flow meter to continuously monitor the flow rate in the reactor effluent line. The measured flow rate is fed back to a controller that adjusts the reactor level valve position to maintain stable forward flow and prevent reverse flow conditions, thus resolving the reliability issue while keeping the natural circulation architecture
Solution Approach 2:
The patent replaces purely mechanical gravity-based natural circulation with a hybrid system that uses electronic sensors (flow meter) and control mechanisms (reactor level valve adjustment) to detect and prevent flow reversal, substituting mechanical instability with sensor-based monitoring and active control
2Ease of operation
If reactor level valve is used to control liquid level and circulation, then flow control is simplified, but accurate flow rate monitoring becomes difficult especially during startup when valve is closed
Solution Approach 1:
The patent places the flow meter upstream of the reactor level valve to measure flow rate before the valve closes during startup. This preliminary measurement allows the control system to detect approaching reverse flow conditions and take preventive action by adjusting the valve position before flow reversal occurs, enabling accurate monitoring even when the valve will soon close
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
Prevents flow reversal and ensures accurate flow control, maintaining stable operation and safety during startup phases without modifying main pressure vessels, offering a cost-effective and easy implementation for existing plants.
Implementation Method 1
differential pressure sensor between at least two selected points of said reactor effluent flow line
Implementation Method 2
circulation of the process streams is governed by gravity and/or difference of density
Implementation Method 3
a different density between one vessel and another is determined mainly by a different composition or gas/liquid ratio
Data Source
AI summary
A plant for synthesis of urea with a CO2-stripping process, comprising a natural-circulation synthesis loop, said loop including at least a urea reactor (1), a carbon dioxide stripper (2) and a condenser (3), said reactor, stripper and condenser operating substantially at the same elevated pressure, said loop comprising also a reactor effluent flow line (5), connecting said urea reactor to said stripper, which comprises means (15) for directly or indirectly detecting the flow rate and/or the direction of the flow through said reactor effluent flow line (5).