Key Takeaways & Executive Findings
- •• • Bypass valve opening must be >50% and at least 2 bypass pipes are required to maintain uniform flow field in the reactor under varying flue gas loads. • • At 100% flue gas load, the empty reactor pressure loss is 911 Pa; at lower loads, it reduces to approximately 500 Pa, indicating improved energy efficiency. • • For flue gas loads below 70.59% of design capacity, optimal flow field is achieved by closing 2 bypass valves and adjusting the remaining 2 valves within 50%–100% opening. • • The bypass design enhances particle collision and reduces dead zones, thereby increasing desulfurization efficiency and operational stability across a wide load range.
Abstract
The semi-dry desulfurization process in circulating fluidized beds (CFB) is sensitive to reactor flow field, which directly impacts desulfurization efficiency. To accommodate variable flue gas loads while maintaining constant Venturi tube velocity, a bypass structure crossing the Venturi section was introduced between the reactor inlet and diffusion section. Numerical simulations using ANSYS Fluent were conducted to evaluate the effects of bypass valve opening and number of bypass pipes on flow field uniformity and pressure loss. Results indicate that for flue gas load variations, bypass valve openings must exceed 50% and at least two bypass pipes are required to ensure uniform flow distribution. At 100% flue gas load, the empty reactor pressure loss was 911 Pa, decreasing to approximately 500 Pa at lower loads. The optimized bypass configuration enables stable and uniform flow fields with reduced pressure loss across a wide load range of 50%–100%, offering an effective solution for enhancing desulfurization efficiency and operational adaptability in industrial applications.
1. Introduction
The steel industry faces stringent ultra-low emission regulations, particularly for sintering, pelletizing, and coking processes. Circulating fluidized bed (CFB) semi-dry desulfurization is favored for its low investment and high efficiency, but its performance degrades when SO2 concentrations exceed typical levels due to raw material variability. In a case study, SO2 inlet concentration rose to 3000 mg/m³, causing instability and elevated emissions. Existing CFB reactors struggle to maintain uniform flow and low pressure drop under fluctuating loads, limiting their adaptability.
This study introduces a novel bypass structure across the Venturi section to manage load variations without altering Venturi velocity. Numerical simulations systematically investigate the effects of bypass number and valve opening on flow field and pressure loss. The proposed design achieves uniform flow and reduced pressure drop across 50%–100% load, offering a practical upgrade for industrial desulfurization systems facing variable feed conditions.
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ZHU Shengjun, LIANG Baorui, SU Wei (2026). Numerical Simulation of a Circulating Fluidized Bed Desulfurization Reactor with Bypass. Journal of Environmental Engineering Technology. https://doi.org/10.13205/j.hjgc.202608019
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Frequently Asked Questions
What is the minimum bypass valve opening required to maintain uniform flow field under varying flue gas loads?
The numerical simulation indicates that bypass valve openings must be greater than 50% to ensure uniform flow distribution. Additionally, at least two bypass pipes are necessary. This threshold ensures that the flow field remains stable and avoids dead zones, which is critical for consistent desulfurization efficiency.
How does the bypass configuration affect pressure loss across the reactor at different loads?
At 100% flue gas load, the empty reactor pressure loss is 911 Pa. As the load decreases, the pressure loss reduces to approximately 500 Pa when bypass valves are optimally adjusted. This reduction in pressure drop lowers energy consumption and operational costs, making the system more efficient at partial loads.
What is the recommended bypass adjustment strategy for flue gas loads below 70.59% of design capacity?
For loads below 70.59%, it is recommended to close two bypass valves and adjust the remaining two valves within an opening range of 50% to 100%. This configuration yields the best internal flow field, ensuring uniform gas distribution and maximizing desulfurization efficiency.
How does the bypass design improve desulfurization efficiency compared to conventional reactors?
The bypass design introduces tangential airflow that enhances particle circulation and collision in the core region, reducing dead zones and increasing the residence time of desulfurizing agents. This leads to better gas-solid contact and higher desulfurization efficiency, even under variable load conditions.
What are the practical implications of this study for existing CFB desulfurization systems?
The findings provide a retrofit solution for existing systems facing high SO2 concentrations or load fluctuations. By incorporating a bypass structure and optimizing valve operations, plants can achieve stable performance across a wide load range (50%–100%) with lower pressure loss, thereby improving compliance with ultra-low emission standards while reducing operational costs.
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