Acetic Acid Buffering Additive for Flue Gas Desulfurization
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Solution Overview
Problem
The efficiency of coal-fired power plant flue gas desulfurization systems is limited due to rapid depletion of alkalinity, leading to pH drops and reduced sulfur dioxide capture, and current buffering techniques are cumbersome and inefficient.
Innovation Solution
A buffering additive containing acetic acid is introduced directly to the FGD system's sump or downstream, separate from the alkaline feed slurry, enhancing buffering capacity and inhibiting mercury re-emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If alkaline feed slurry is added to restore alkalinity, then sulfur dioxide capture efficiency is improved, but scale build-up increases
Solution Approach 1:
The system separates the buffering function from the alkaline feed slurry by introducing a buffering additive (ammonium carbonate or ammonium bisulfate) independently. This segmentation allows the buffering action to occur without the scale-building effects of concentrated alkaline slurry, resolving the contradiction between maintaining sulfur dioxide capture efficiency and preventing scale build-up.
Solution Approach 2:
The invention changes the chemical parameters of the buffering agent by using ammonium-based compounds instead of traditional hydroxide-based alkaline slurry. This parameter change enables buffering at lower pH levels (4.5-6.0) without the scale build-up associated with higher pH alkaline feeds, thus maintaining productivity while eliminating the harmful effect.
2Reliability
If buffering additive is added together with alkaline feed slurry, then buffering capacity is provided, but fine-tuning pH becomes more difficult
Solution Approach 1:
The system segments the addition of buffering additive from alkaline feed slurry, allowing independent control of each component. This separation enables operators to fine-tune pH by adjusting the buffering additive independently without the confounding effect of simultaneous alkaline slurry addition, thus maintaining both buffering capacity and operational ease.
Solution Approach 2:
The independent addition of buffering additive creates a feedback-controlled system where pH can be monitored and adjusted more precisely. The buffering additive can be added in controlled amounts to achieve the desired pH level, providing a feedback mechanism that simplifies pH fine-tuning while maintaining reliable buffering capacity.
3Productivity
If concentrated alkaline slurry is added to combat pH drop, then sulfur dioxide diffusion is maintained, but scale build-up increases
Solution Approach 1:
The invention changes the approach by using ammonium-based buffering additives that operate effectively at the target pH range (4.5-6.0) without requiring concentrated alkaline slurry. This parameter change maintains sulfur dioxide diffusion efficiency while avoiding the scale build-up caused by high-concentration alkaline feeds, as the buffering action occurs at lower, more manageable concentrations.
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 improves alkalinity control, reduces operating costs, and increases sulfur dioxide removal efficiency while minimizing scale build-up and mercury re-emission, allowing for more precise pH management and reduced water consumption.
Implementation Method 1
Weak acids can be useful for buffering. At the FGD system operating pH (4.5 to 6.0), weak acids will be neutralized. When sulfur dioxide diffuses into the water droplet, the neutralized acid gives up its associated alkali, providing an instant pH boost.
Implementation Method 2
The buffering additive, e.g. containing a weak acid, is typically introduced to the FGD system together with the alkaline feed slurry. The buffering additive will complex with the alkaline compound when added to the alkaline feed slurry, and this complexing will delay the additive's ability to react as a buffer.
Implementation Method 3
The acid is eventually neutralized by dissolution of solid alkali in the inner part of the water droplet and/or the bulk slurry solution within the alkaline reactant. However, the initial drop in pH at the surface of the water droplet decreases the efficiency of the FGD system by up to 15% because the lower pH causes sulfur dioxide diffusion to decrease.
Implementation Method 4
The alkaline reactant reacts with the sulfur dioxide to produce a slurry impregnated with sulfates. This slurry eventually falls to the FGD reaction tank and forms the sump.
Implementation Method 5
Sodium hydroxide, lime, limestone, barium hydroxide, potassium hydroxide, and potassium carbonate (e.g., in the form of potash) can be used to generate alkalinity in the alkaline reactant in order to convert sulfur dioxide to sulfurous and/or sulfuric acid and their neutralized species.
Data Source
AI summary
A flue gas desulfurization (FGD) system in which a buffering additive feed directly adds a buffering additive containing acetic acid to either the FGD sump or a stream of the system that is downstream of the sump. In a method for performing flue gas desulfurization, the buffering additive, containing acetic acid, is added to either the sump or the overflow. That is, the buffering additive is added to the FGD system separately from the alkaline feed slurry, which contains lime or limestone.