Regenerative SO2 Recovery from Effluent Gases
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Solution Overview
Problem
Conventional methods for removing sulfur dioxide from effluent gases face challenges such as low energy efficiency, high capital and operating costs, and equipment corrosion due to water vapor absorption, especially in gases with low sulfur dioxide concentrations, which also affect the material and energy balance in sulfuric acid plants.
Innovation Solution
A regenerative absorption/desorption process that enhances energy efficiency by cooling the absorption zone to increase the sulfur dioxide absorption capacity, recovering energy from the wet contaminant gas stream, and using a buffered aqueous solution with a polyprotic carboxylic acid salt as the sorbent to selectively absorb and recover sulfur dioxide, while also recycling steam generated from condensed water vapor for stripping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional absorption methods using aqueous base streams are used to remove sulfur dioxide, then sulfur dioxide removal efficiency is improved (over 95% removal), but energy consumption and operating costs increase due to lime consumption and solids disposal
Solution Approach 1:
The patent recovers sulfur dioxide from the absorption process by heating the saturated absorbent solution to drive off SO2, which is then condensed and reused. This eliminates the need for continuous lime consumption and solids disposal, converting a linear consumable process into a closed-loop regenerative system that recovers both the contaminant and the absorbent.
Solution Approach 2:
The patent changes the temperature parameter to regenerate the absorbent. By heating the saturated absorbent solution to elevated temperatures, the solubility equilibrium shifts, driving off absorbed SO2 and regenerating the absorbent for reuse, thereby reducing ongoing material consumption and waste disposal needs.
2Reliability
If sulfur dioxide concentration in effluent gas is low (below 4-5% by volume), then environmental compliance is improved, but water balance and energy balance problems arise in sulfuric acid plants
Solution Approach 1:
The patent extracts water vapor from the low-concentration effluent gas stream by condensing it in a condenser. This separates the water component from the sulfur dioxide, allowing the SO2 to be recovered in a concentrated form suitable for sulfuric acid plant feed requirements, while the condensed water can be disposed of or reused separately.
Solution Approach 2:
The patent performs preliminary concentration of sulfur dioxide by condensing water vapor before the gas enters the sulfuric acid plant. This pre-treatment step ensures that the gas stream meets the minimum concentration requirements for autothermal operation of the catalytic converter, preventing energy balance problems downstream.
3Quantity of substance
If effluent gas is cooled to reduce water vapor content, then sulfuric acid plant material balance is improved, but capital and energy expenditures increase
Solution Approach 1:
The patent merges the water vapor condensation function with the existing sulfur dioxide absorption and recovery process. The condenser is integrated into the recovery system, and the condensed water is utilized in the absorption liquid preparation, eliminating the need for separate water removal equipment and reducing overall capital requirements.
Solution Approach 2:
The patent makes the effluent gas stream serve its own water removal needs through self-condensation. The gas is cooled to a temperature where water vapor condenses naturally, providing the cooling water needed for the absorption process without requiring external cooling systems or additional energy input.
4Reliability
If sulfur dioxide concentration is below 4-5% by volume, then emission control is improved, but autothermal operation of catalytic converter becomes insufficient
Solution Approach 1:
The patent performs preliminary concentration of sulfur dioxide by removing water vapor through condensation before the gas enters the catalytic converter. This ensures the gas stream achieves the minimum concentration threshold needed for autothermal operation, where the heat of conversion is sufficient to maintain catalyst temperature without external heating.
Solution Approach 2:
The patent changes the concentration parameter of the sulfur dioxide stream by removing water vapor. This increases the partial pressure and concentration of SO2 to levels that enable exothermic conversion to generate adequate heat for autothermal catalyst operation, transforming a sub-threshold stream into a self-sustaining process.
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 achieves high energy efficiency in sulfur dioxide recovery, reduces capital and operating costs, and minimizes equipment corrosion, effectively addressing the challenges of low sulfur dioxide concentrations and water vapor absorption, while maintaining a stable material and energy balance.
Implementation Method 1
contacting the feed gas stream with the buffered aqueous solution in the absorption zone, thereby absorbing sulfur dioxide from the feed gas stream into the buffered aqueous solution
Implementation Method 2
The sulfur dioxide dissolves in water forming sulfurous acid (H2SO3) that in turn reacts with the base to form a salt
Implementation Method 3
cooling the absorption zone to enhance the sulfur dioxide absorption capacity of the buffered aqueous solution
Implementation Method 4
heating the sulfur dioxide-containing absorption liquor in the desorption zone to a temperature and/or pressure at which the sulfur dioxide is released from the absorption liquor
Implementation Method 5
The water vapor contained in the effluent gas is condensed, and the condensed water vapor is used to strip the sulfur dioxide from the absorption liquor
Data Source
AI summary
A contaminant gas is removed from a feed gas in two absorption and stripping circuits operated in tandem. The gas is first passed through a rich gas absorber producing a rich absorption liquor from which contaminant gas is stripped in a rich liquor stripper. A lean gas exiting the rich gas absorber is passed through a lean gas absorber, producing a lean absorption liquor from which contaminant gas is stripper in a lean liquor stripper. Regenerated absorption media exiting the respective strippers are recirculated to the respective absorbers.