Sulfuric Acid Absorption Heat Recovery via High-Temperature Flash Steam
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Solution Overview
Problem
In the sulfuric acid contact process, a significant fraction of the heat generated by the absorption of sulfur trioxide into sulfuric acid is wasted or used inefficiently, as existing methods are limited in recovering this heat as high-pressure steam, which is valuable for power generation and process operations.
Innovation Solution
A process where sulfur trioxide is contacted with a sulfuric acid stream in a primary heat recovery absorption zone, and the heat is transferred to a boiler feed water stream through an array of countercurrently flowing heat exchangers, allowing the boiler feed water to flash and generate steam at high pressure, thereby recovering a high fraction of the absorption heat as high-pressure steam.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If conventional absorption acid coolers are operated at maximum inlet temperature of about 110°C, then the heat of absorption can be recovered, but the steam generation capability is limited and energy utilization is inefficient
Solution Approach 1:
The patent raises the inlet temperature of the absorption acid cooler from the conventional 110°C to 200°C or higher, fundamentally changing the operating parameters to enable more effective heat recovery and high-pressure steam generation
Solution Approach 2:
The absorption acid cooler is designed to serve multiple functions: it cools the absorption acid, generates high-pressure steam for power generation, and preheats boiler feed water, thereby maximizing energy utilization
2Productivity
If heat exchangers are used to transfer heat from absorption acid to boiler feed water, then steam generation increases, but the device complexity increases
Solution Approach 1:
The heat recovery system is divided into multiple heat exchangers arranged in series, with each unit handling a specific portion of the heat transfer task, allowing for modular design and operation
Solution Approach 2:
The heat exchangers are arranged in a nested configuration where boiler feed water flows through tubes while absorption acid flows in the shell, with flash steam generation occurring in reduced pressure zones between heat exchanger stages
3Loss of energy
If absorption acid cooler temperature is increased above 110°C, then more heat can be recovered, but material corrosion resistance becomes a limiting factor
Solution Approach 1:
The patent specifies using Fe/Cr alloys with particular chromium content to construct heat exchanger components exposed to hot concentrated sulfuric acid, providing both high-temperature heat recovery capability and corrosion resistance
Solution Approach 2:
The patent introduces a specially selected Fe/Cr alloy as an intermediary material between the aggressive hot sulfuric acid and the heat transfer function, allowing high-temperature operation while protecting against corrosion
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 process effectively recovers at least 60% to 97% of the heat of absorption as high-pressure steam, enhancing energy recovery and reducing the sensible heat load on waste heat boilers, allowing for increased steam generation and improved energy utilization.
Implementation Method 1
a source gas comprising sulfur trioxide is contacted in a primary heat recovery absorption zone with a sulfur trioxide absorption acid stream comprising liquid sulfuric acid, thereby transferring sulfur trioxide from the source gas to the absorption acid stream and heating the absorption acid stream by heat of absorption
Implementation Method 2
Heat is transferred from the absorption acid stream to a boiler feed water stream in an array of heat exchangers
Implementation Method 3
The boiler feed water stream is allowed to flash in a reduced pressure zone in the boiler feed water flow path between two successive heat exchangers in the series, thereby generating steam and cooling the boiler feed water stream in the reduced pressure zone
Implementation Method 4
Steam generated in the reduced pressure zone is separated from the cooled boiler feed water stream
Data Source
AI summary
A contact process for manufacture of sulfuric acid in which the vapor phase heat of formation of sulfuric acid in the sulfur trioxide conversion gas and the heat of absorption of SO3 in sulfuric acid is recovered by transfer of heat from the absorption acid to high pressure boiler feed water that is fed to a waste heat boiler where steam is generated at a pressure of at least 40 bar by transfer of heat from sulfur dioxide combustion gas.