Vent Line for Ammonia Plant Shift Converter Reheat
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Solution Overview
Problem
Ammonia and hydrogen plants face challenges in quickly restarting production after temporary shut-downs due to the sensitivity of low and medium temperature shift catalysts to condensing steam, which can damage them if not properly reheated above the dew point.
Innovation Solution
A vent line is arranged downstream from the low or medium temperature shift converters, allowing for reheating with synthesis gas at reduced pressure (3-7 bar) using an inlet pressure reducing valve and a vent valve to control dew point, thereby avoiding nitrogen circulation and potential water condensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the plant is shut down and then restarted using conventional methods, then the catalyst can be heated, but water condensation occurs on the catalyst which damages it and requires lengthy nitrogen circulation heating procedures
Solution Approach 1:
The patent changes the pressure parameter of the synthesis gas from normal operating pressure (20-50 bar) to reduced pressure (3-7 bar) during the reheating phase. This pressure reduction lowers the dew point temperature of the gas, allowing the catalyst to be heated without water condensation. The vent line connected to the LTS converter enables this pressure control, and after heating, the system returns to normal pressure for operation.
2Temperature
If nitrogen circulation is used to heat the catalyst after shut-down, then the catalyst temperature increases, but the process is time-consuming and requires 8-24 hours
Solution Approach 1:
The patent introduces synthesis gas at reduced pressure as an intermediary medium to transfer heat to the catalyst. Instead of using nitrogen circulation, the synthesis gas serves as the heating medium that can be controlled to prevent condensation. This intermediary approach allows direct heating of the catalyst without the time-consuming nitrogen circulation process.
Solution Approach 2:
The patent performs preliminary pressure reduction before introducing the synthesis gas for heating. By预先 reducing the pressure to 3-7 bar through the vent line, the system prepares the gas conditions to prevent condensation before the heating process begins, enabling direct and rapid catalyst reheating without subsequent condensation damage.
3Temperature
If synthesis gas is introduced at normal operating pressure to reheat the catalyst, then heating is effective, but water condensation occurs on the catalyst surface
Solution Approach 1:
The patent changes the pressure parameter from normal operating pressure (20-50 bar) to reduced pressure (3-7 bar) during catalyst reheating. This pressure reduction directly lowers the dew point of the synthesis gas, preventing water condensation on the catalyst surface while still allowing effective heat transfer. The vent line enables this pressure control mechanism.
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 significantly reduces the time required for plant re-startup by avoiding catalyst damage and eliminating the need for nitrogen heating, saving 8-24 hours of re-starting time.
Implementation Method 1
said vent line allowing the shift converter(s) to be re-heated with process gas at a low pressure (typically 3-7 bar), and by an inlet pressure reducing valve and a vent valve, said valves facilitating the pressure control, thereby controlling the dew point in the MTS and/or the LTS catalyst
Implementation Method 2
an inlet pressure reducing valve and a vent valve, said valves facilitating the pressure control, thereby controlling the dew point in the MTS and/or the LTS catalyst
Data Source
AI summary
In an ammonia or hydrogen plant comprising a desulfurisation section, a reforming section and a shift section, where the shift section comprises a low temperature shift converter and a medium temperature shift converter, a vent line is arranged downstream from the low temperature shift converter and the medium temperature shift converter in order to allow the shift converters to be re-heated with process gas at a low pressure (typically 3-7 bar). This way condensation of water vapour in the process gas is avoided. By applying this vent line it becomes possible to save significant time, more specifically 8-24 hours, for restarting the production after temporary shut-down thereof, because a heat-up of the LTS/MTS converter in circulating nitrogen is avoided.