Hydrogen Plant Shutdown Sequencing for Reforming Catalyst Protection
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Solution Overview
Problem
Existing methods for shutting down ammonia production plants result in significant emissions and cost due to venting of process gas, and can cause temperature shocks that damage catalysts and increase downtime.
Innovation Solution
A method involving gradual reduction of fuel gas supply to the reforming unit without proportionate reduction in process gas, followed by stopping the process gas supply, to maintain temperature and prevent catalyst damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the process gas supply is stopped immediately during shutdown, then the shutdown time is reduced, but temperature shock occurs that damages catalysts and increases downtime
Solution Approach 1:
The method applies preliminary action by reducing the fuel gas supply before stopping the process gas supply. This preparatory step lowers the reactor temperature in advance, preventing temperature shock when the process gas is subsequently stopped, thereby protecting the catalysts while maintaining shutdown efficiency
Solution Approach 2:
The invention changes the temperature parameter gradually by controlling the fuel gas reduction rate. By adjusting the fuel gas supply at a controlled rate before process gas shutdown, the reactor temperature decreases progressively, avoiding sudden temperature changes that would damage catalysts
2Ease of operation
If the fuel gas supply is reduced proportionately with process gas during shutdown, then the temperature control is simplified, but temperature shock occurs that damages catalysts
Solution Approach 1:
The method applies dynamics by making the fuel gas reduction non-proportionate and time-dependent. Instead of reducing fuel gas in direct proportion to process gas reduction, the fuel gas supply is reduced at a controlled rate that is independent of the process gas shutdown rate, allowing dynamic temperature management that protects catalysts
3Ease of operation
If the methanization unit is stopped first during shutdown, then the shutdown sequence is simplified, but significant emissions and natural gas venting occur
Solution Approach 1:
The invention applies inversion by reversing the conventional shutdown sequence. Instead of stopping the methanization unit first and then dealing with process gas venting, the method stops the process gas supply first (after fuel gas reduction) and maintains methanization operation, thereby eliminating the need to vent natural gas and significantly reducing emissions
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
Significantly reduces emissions, eliminates venting of natural gas, and shortens shutdown time while preserving catalysts and reducing operational costs.
Implementation Method 1
The sulfur-free natural gas feedstock is then subjected to a catalytic steam reforming step, in a reforming section comprising of one or more reforming units, such as a pre-reformer, and/or a primary and secondary reformer, to form hydrogen and carbon monoxide.
Implementation Method 2
In the catalytic shift conversion, carried out in one or more shift reactors, usually first in a high-temperature shift reactor operating at a temperature between 340 °C and 420 °C, the carbon monoxide is converted into carbon dioxide and more hydrogen.
Implementation Method 3
subsequently in a low-temperature shift reactor operating at a temperature between 190 °C and 220 °C, the carbon monoxide is converted into carbon dioxide and more hydrogen.
Implementation Method 4
the hydrogen-rich stream leaving the CO2 removal unit is catalytically methanized in a methanation unit (hereinafter also referred to as a methanator) to remove any small residual amounts of carbon monoxide or carbon dioxide from the hydrogen.
Implementation Method 5
To produce the desired final product ammonia, the purified hydrogen is then catalytically reacted with nitrogen (derived from process air) to form anhydrous liquid ammonia. This step is known as the ammonia synthesis loop - also known as the Haber-Bosch process.
Data Source
Figure 1~2
AI summary
The present application provides for a method for the shutdown of a chemical plant comprising a hydrogen production system, in particular an ammonia production plant, where the hydrogen production system comprises a reforming unit, in particular a primary reformer with a furnace and a reactor, one or more shift reactors, a CO2 removal unit and a methanation unit; wherein a reforming unit, in particular the primary reformer reactor, is supplied with a feed of a gaseous hydrocarbon, and wherein the reforming unit, in particular the furnace of the primary reformer reactor, is supplied with a fuel gas; wherein the method comprises the steps of (i) reducing the fuel gas supply to the reforming unit, in particular to the furnace of the primary reformer, thereby reducing the temperature in the reforming unit; and then (ii) stopping the supply of the gaseous hydrocarbon process gas to the reforming unit, in particular to the reactor of the primary reformer.