CFBC Ash Hydration and Recycling for Low-Acid Gypsum Production
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Solution Overview
Problem
Existing methods for desulfurization in circulating fluidized bed combustors require a large amount of sulfuric acid when converting fly and bottom ashes to gypsum, as the sulfurization efficiency is low, typically less than 50%, leading to excessive acid usage.
Innovation Solution
A method involving the combustion of sulfur-containing carbonaceous materials with limestone, followed by hydration and recycling of ashes to enhance desulfurization, and subsequent reaction with a sulfuric acid solution under controlled temperatures to produce gypsum with reduced acid consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If limestone is used for in-situ desulfurization in CFBC, then sulfur removal is achieved, but the sulfurization efficiency is low (less than 50%) and a large amount of sulfuric acid is required for ash conversion
Solution Approach 1:
The patent applies preliminary action by conducting a first desulfurization process in the CFBC furnace using limestone to convert sulfur-containing materials before the ash conversion process. This preliminary desulfurization removes a portion of sulfur from the exhaust gas, reducing the sulfur content in the generated ashes and consequently reducing the amount of sulfuric acid needed in the subsequent conversion process to gypsum.
Solution Approach 2:
The patent changes the chemical composition parameters of the desulfurization agent by using limestone (CaCO3) that decomposes to form calcium oxide (CaO), which then reacts with sulfur dioxide. The process optimizes the calcium-to-sulfur ratio and controls reaction conditions to achieve better sulfurization efficiency, thereby reducing the acid consumption in later stages.
2Object-affected harmful factors
If limestone is directly injected into the furnace for desulfurization, then sulfur dioxide removal is achieved, but calcium sulfate formation on ash particle surfaces suppresses further desulfurization reactions
Solution Approach 1:
The patent segments the desulfurization process into two distinct stages: first, in-situ desulfurization in the CFBC furnace where limestone is injected to remove sulfur dioxide from exhaust gas; second, a separate ash conversion process where the generated ashes are reacted with sulfuric acid solution. This segmentation prevents the suppression effect from completely halting the desulfurization process and allows for optimized conditions in each stage.
Solution Approach 2:
The patent uses the fly ash and bottom ash particles as intermediaries that carry calcium compounds from the first desulfurization stage into the second conversion stage. These ash particles serve as a medium that transports the calcium species, which then react with sulfuric acid solution to form gypsum, thereby continuing the sulfur removal process in a controlled manner.
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 method significantly decreases the amount of sulfuric acid required for converting ashes to gypsum, achieving a 21% increase in calcium sulfate mass fraction and minimizing wastewater production.
Implementation Method 1
Limestone can be thermally decomposed into quicklime (CaO) and carbon dioxide at around 600° C.
Implementation Method 2
Calcium oxide (CaO) reacts with sulfur dioxide and oxygen to produce calcium sulfate
Implementation Method 3
hydrating at least a portion of the preliminary fly and bottom ashes to form a hydrated material
Implementation Method 4
reacting the secondary fly and bottom ashes with a sulfuric acid solution
Data Source
AI summary
A method of combusting a sulfur-containing carbonaceous material with ash treatment includes: feeding a feed containing the sulfur-containing carbonaceous material and limestone into a furnace; combusting the feed in the furnace so as to generate preliminary fly and bottom ashes; hydrating the preliminary fly and bottom ashes to form a hydrated material; recycling the hydrated materials into the furnace so as to generate secondary fly and bottom ashes; and reacting the secondary fly and bottom ashes with a sulfuric acid solution.