Ultra-fine CaCO3 Absorbent for CFB Boiler Sulfur Reduction
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Solution Overview
Problem
Conventional methods for reducing sulfur dioxide emissions in circulating fluidized bed boiler plants require high Ca/S ratios, leading to excessive calcium oxide in ash, decreased thermal efficiency, and additional equipment for treating fly ash, which complicates sulfur reduction and ash disposal.
Innovation Solution
Feeding ultra-fine calcium carbonate particles with a median particle size of 10 to 20 µm into the furnace, allowing for efficient calcination and rapid reaction with sulfur dioxide, reducing the amount of calcium oxide in ash and enabling its direct use in a semi-dry sulfur-reduction stage downstream, thereby minimizing the need for additional sorbent and equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high Ca/S ratios (3-4) are used to achieve desired sulfur reduction efficiency in the furnace, then sulfur reduction efficiency is improved, but the amount of calcium oxide in ash increases making ash disposal difficult and thermal efficiency decreases
Solution Approach 1:
The sulfur reduction process is divided into two segments: (1) furnace-based reduction using calcium carbonate particles to achieve partial sulfur reduction, and (2) semi-dry scrubber-based reduction downstream to achieve final sulfur reduction. This segmentation allows each stage to operate at optimal conditions without requiring excessive calcium carbonate feeding, thus maintaining thermal efficiency while achieving high overall sulfur reduction efficiency.
Solution Approach 2:
Instead of attempting complete sulfur reduction in the furnace (which would require excessive calcium carbonate and reduce thermal efficiency), the invention applies partial action by achieving only a portion of the required sulfur reduction in the furnace (Ca/S ratio of 1.5-3.0), and completing the reduction in the semi-dry scrubber downstream.
2Reliability
If high Ca/S ratios (3-4) are used to achieve desired sulfur reduction efficiency in the furnace, then sulfur reduction efficiency is improved, but the amount of calcium oxide in ash increases making ash disposal difficult
Solution Approach 1:
The sulfur reduction process is divided into two segments: (1) furnace-based reduction using calcium carbonate particles to achieve partial sulfur reduction, and (2) semi-dry scrubber-based reduction downstream to achieve final sulfur reduction. This segmentation allows each stage to operate at optimal conditions without requiring excessive calcium carbonate feeding, thus maintaining thermal efficiency while achieving high overall sulfur reduction efficiency.
Solution Approach 2:
Instead of attempting complete sulfur reduction in the furnace (which would require excessive calcium carbonate and reduce thermal efficiency), the invention applies partial action by achieving only a portion of the required sulfur reduction in the furnace (Ca/S ratio of 1.5-3.0), and completing the reduction in the semi-dry scrubber downstream.
3Duration of action of moving object
If conventional particle sizes (100-300 µm) are used for calcium carbonate, then particle residence time in the furnace is sufficient, but a dense CaSO4 layer forms on the particle surface preventing core reaction and requiring excess limestone
Solution Approach 1:
The invention changes the critical parameter of particle size from conventional 100-300 µm to ultra-fine 10-30 µm. This parameter change fundamentally alters the reaction mechanism: ultra-fine particles react completely before being entrained by flue gas, eliminating the dense layer formation problem and achieving high sulfur reduction efficiency without requiring particle circulation or excess limestone.
Solution Approach 2:
The ultra-fine calcium carbonate particles undergo preliminary calcination to calcium oxide and then rapidly react with sulfur dioxide during their brief residence time in the furnace. This preliminary action ensures complete reaction before particles are entrained and transported to the semi-dry scrubber, eliminating the need for subsequent particle circulation.
4Reliability
If calcium carbonate is fed at high rates to achieve complete sulfur reduction in the furnace, then sulfur reduction efficiency is improved, but the endothermic calcination reaction decreases thermal efficiency
Solution Approach 1:
The sulfur reduction process is divided into two segments: (1) furnace-based reduction using calcium carbonate particles to achieve partial sulfur reduction, and (2) semi-dry scrubber-based reduction downstream to achieve final sulfur reduction. This segmentation allows each stage to operate at optimal conditions without requiring excessive calcium carbonate feeding, thus maintaining thermal efficiency while achieving high overall sulfur reduction efficiency.
Solution Approach 2:
Instead of attempting complete sulfur reduction in the furnace (which would require excessive calcium carbonate and reduce thermal efficiency), the invention applies partial action by achieving only a portion of the required sulfur reduction in the furnace (Ca/S ratio of 1.5-3.0), and completing the reduction in the semi-dry scrubber downstream.
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 achieves higher than 80% sulfur reduction in the furnace and overall sulfur reduction of more than 98%, with improved calcium utilization and reduced limestone consumption, while simplifying ash handling and thermal efficiency.
Implementation Method 1
the CaCO3 calcines to calcium oxide (CaO)
Implementation Method 2
Because calcination of CaCO3 to CaO is an endothermic reaction
Implementation Method 3
the CaO reacts with the sulfur oxides to produce calcium sulfate (CaSO4)
Implementation Method 4
a CFB boiler comprises a particle separator which separates a portion of the entrained particles
Implementation Method 5
the bed is fluidized by introducing fluidizing gas through the bottom of the furnace by a relatively high nominal velocity
Implementation Method 6
complementing SO2 reduction in a semi-dry sulfur dioxide reduction device, such as a dry CFB scrubber or a spray dryer
Data Source
Figure 1
Figure 2
AI summary
A method of reducing sulfur dioxide emissions of a circulating fluidized bed boiler plant (10), comprising the steps of: feeding sulfur containing carbonaceous fuel to a furnace (12) of the boiler; feeding calcium carbonate containing absorbent having a predetermined d50 particle size to the furnace; feeding oxygen containing gas to the furnace and combusting the fuel with the oxygen, whereby the sulfur is oxidized to sulfur dioxide; calcining the calcium carbonate to calcium oxide in the furnace and utilizing a portion of the calcium oxide to sulfate a first portion of the sulfur dioxide to calcium sulfate in the furnace; discharging flue gases, containing a second portion of the sulfur dioxide, and particles, including calcium oxide particles, entrained with the flue gases from the furnace; separating a first portion of the entrained particles from the flue gases in a particle separator (14) having a cut-off size, and returning the separated particles to the furnace (12); conveying a second portion of the entrained particles with the flue gases from the furnace (12) to a semi-dry sulfur-reduction stage (38) arranged downstream of the furnace, and reducing the sulfur dioxide content of the flue gases in the semi-dry sulfur-reduction stage (38), wherein the predetermined d50 particle size of the calcium carbonate containing absorbent is smaller than 50 % of the cut-off size of the particle separator.