Synthesis Gas Stream Splitting for Metal Dusting Mitigation
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Solution Overview
Problem
Current processes for treating synthesis gas streams in ammonia and hydrogen plants are limited by the destructive mechanism of metal dusting, which restricts the efficient utilization of waste heat due to high carbon monoxide partial pressures, leading to reduced steam superheating and increased steam generation, thus affecting the specific energy consumption and competitiveness of these plants.
Innovation Solution
The process involves splitting the synthesis gas stream into two substreams, where one substream undergoes partial CO conversion before entering the steam superheater, reducing the carbon monoxide content and activity, while the other substream bypasses the steam generator to achieve higher steam superheating temperatures, thereby reducing metal dusting potential and optimizing heat utilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the synthesis gas is cooled in a steam generator to utilize waste heat, then steam is generated, but the high carbon monoxide partial pressure causes metal dusting attack on metal surfaces
Solution Approach 1:
The process stream is divided into two separate streams: one stream is cooled in the steam generator to generate steam, while the other stream bypasses the steam generator and is used for CO conversion. This segmentation allows the system to utilize waste heat for steam generation without exposing the CO conversion equipment to metal dusting conditions, as the bypass stream maintains higher temperature and lower carbon activity.
Solution Approach 2:
The bypass stream acts as an intermediary that provides hot process gas for CO conversion without directly cooling in the steam generator. This intermediary stream transfers thermal energy to the first stream in a heat exchanger, enabling waste heat utilization while protecting the CO conversion reactor from metal dusting attack by maintaining it in the high-temperature bypass stream.
2Productivity
If the steam superheating temperature is increased to reduce steam generation, then energy efficiency improves, but metal dusting attack increases due to higher temperatures
Solution Approach 1:
The process gas stream is segmented into two paths: the bypass stream provides high-temperature gas for CO conversion without cooling, maintaining conditions unsuitable for metal dusting, while the first stream is cooled for steam generation. The segmented approach allows high-temperature operation for productivity without exposing equipment to metal dusting conditions.
Solution Approach 2:
The invention changes the parameters of the process gas by splitting it into two streams with different temperatures and compositions. The bypass stream maintains high temperature and low carbon activity suitable for CO conversion, while the first stream is cooled to generate steam. This parameter change allows the system to operate at high temperatures for efficiency without creating conditions for metal dusting in the steam generation equipment.
3Productivity
If CO conversion is performed at high temperatures to maintain equilibrium, then conversion efficiency is limited, but metal dusting resistance improves
Solution Approach 1:
The process gas is segmented into a bypass stream for CO conversion and a first stream for steam generation. The bypass stream maintains high temperature conditions that favor metal dusting resistance while the first stream is cooled for efficient steam generation. This segmentation allows the system to operate the CO conversion at temperatures that balance conversion efficiency with metal dusting resistance.
Solution Approach 2:
The invention changes the temperature parameter of the process gas by creating two separate streams. The bypass stream maintains higher temperature (above 450°C) which improves metal dusting resistance while still allowing CO conversion to proceed. The first stream is cooled to lower temperatures for efficient steam generation. This parameter change resolves the contradiction by allowing different temperature conditions in different parts of the system.
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 results in a significantly lower carbon activity and increased steam superheating temperatures, reducing steam generation and furnace requirements, allowing for more efficient heat utilization and lower steam export, thus enhancing the energy efficiency and competitiveness of ammonia and hydrogen plants.
Implementation Method 1
CO+H2OCO2+H2 (3) It is an equilibrium reaction which is exothermic
Implementation Method 2
the process gas after reforming is typically present at very high temperatures. Optimal utilization of the very high-value waste heat
Implementation Method 3
further cooled in a steam superheater
Implementation Method 4
The carbon diffuses into the surfaces and forms carbides here with the base material
Implementation Method 5
It is an equilibrium reaction which is exothermic
Data Source
AI summary
A process can be used to treat a synthesis gas stream comprising steam reforming firstly in a primary reformer and subsequently in a secondary reformer. Crude synthesis gas exiting the secondary reformer may be cooled in a steam generator and then further cooled in a steam superheater. The crude synthesis gas stream after exiting the secondary reformer may be split into at least two gas substreams, of which only a first gas substream is fed to the steam generator. A second gas substream may be supplied to the steam superheater, bypassing the steam generator. Only the first gas substream, after flowing through the steam generator, may be subjected to a CO conversion reaction in a first CO conversion reactor before the first gas substream is supplied to the steam superheater.