Suxia Ma

Single-screw expanders can recover pressure energy from compressed gas, but measured shaft output depends on both operating conditions and prototype geometry. This study compares two compressed-air prototypes with built-in volume ratios of 2.04 and 3.13 and documents heated-supply transients for the 2.04 prototype. Cold-state tests covered 1400–3000 r/min and nominal regulated pressures of 1.0–1.8 MPa, with direct prototype comparisons at 1.4–1.8 MPa. At 1.8 MPa, the 3.13 prototype produced 102.8–126.7 W at 1400 r/min and 170.1–202.7 W at 3000 r/min. Its recorded output exceeded that of the 2.04 prototype by 10.8–24.4% and 1.0–10.6%, respectively, across the reported source-pressure intervals. These differences concern complete configurations because casing thickness and exhaust-port dimensions also differed. Power increased less than proportionally to speed between the endpoints; normalized linear fits describe the 1.8 MPa data within the tested range. Instrument-only expanded power uncertainty was 0.21–1.00% across the cold-state matrix under the stated specification assumptions. Several 1.0 MPa records were non-monotonic, but their physical origin remains unresolved without repeatability statistics. Five heated-supply runs at nominal settings of 435–500 K showed delayed temperature rises and intermittent pressure fluctuations. Missing mass flow, synchronized hot-state shaft power, and complete uncertainty information preclude efficiency comparisons and quantification of the net benefit of heating.

Axial solids concentration profile in circulating fluidized bed (CFB) risers is a key parameter governing heat transfer, gas–solid contact, and heating surface erosion in CFB boilers. Prediction of this profile is essential for furnace design and operational optimization. In this study, a comprehensive axial solids concentration profile correlation was developed for CFB risers handling Geldart-A and B particles. Extensive experimental data were collected from the literature and supplemented by our own measurements in a 20 m high CFB test rig under a wide range of operating conditions, covering superficial gas velocities of 3–6 m·s-1, particle sizes of 75–280 μm, and both dilute-phase transport and fast fluidization regimes. The correlation consists of three components: a dense-phase region correlation, a dilute-phase region correlation, and a comprehensive axial profile correlation based on the exponential decay law, with explicit distinction between the two flow regimes. Validation against experimental data demonstrates that the comprehensive correlation performs well under various superficial gas velocities, riser pressure drops, and particle sizes. The proposed correlation has few input parameters and high computational efficiency, making it a practical tool for the design of heating surface arrangement, as well as for the prediction and control of axial solids concentration profiles during CFB boiler design.

The gas-solid flow regime in a CFB boiler furnace exhibits multi-state superposition along the furnace height. Under fast fluidization conditions, the specific flow regime in the dense phase region remains controversial, and accurate identification of this regime is of great significance for optimizing wide-load boiler operation. In this study, an improved Hilbert-Huang Transform (HHT) method was applied to analyze the pressure fluctuation signals in the dense phase of four quartz sand fractions with different particle size ranges (50–100 μm, 100–150 μm, 150–250 μm, and 250–300 μm) under superficial gas velocities of 3–6 m·s-1. The results show that the dense-phase flow regime is governed by both particle size and gas velocity. For the 50–100 μm fine particles (mostly Geldart-A), the medium-frequency energy proportion is 62.69% at 3 m·s-1, indicating a turbulent fluidization state. As gas velocity increases above 4 m·s-1, the medium-frequency energy proportion drops below 10%, bubble activity disappears, and the flow tends to become homogeneous. For coarse particles larger than 100 μm (Geldart-B), the medium-frequency energy proportion remains between 60% and 78% throughout the gas velocity range of 3–6 m·s-1, indicating that the dense phase remains in bubbling or turbulent fluidization. As gas velocity increases or particle size decreases, the medium-frequency energy proportion gradually declines, reflecting a transition from bubbling to turbulent fluidization. Based on these experimental findings, it can be inferred that in industrial CFB boilers, where the bed material in the dense phase has a much wider particle size distribution including a substantial fraction of Geldart-D particles, the dense phase is expected to be in bubbling or turbulent fluidization depending on the gas velocity, with bubbling fluidization prevailing under low-load conditions. This study confirms the applicability of the improved HHT method for regime identification in the dense phase under wide particle size distribution conditions and provides a theoretical basis and diagnostic tool for flow regime regulation in industrial CFB boilers under wide-load operation.

Operating steam turbines under low-flow conditions poses severe threats to structural safety due to flow-separation-induced aeroelastic instability. However, the exact sources of localized unsteady aerodynamic excitations in vortex-dominated regions and their explicit contribution to blade flutter under deep low-flow regimes remain unclear. To address this problem, this paper proposes a quantitative aeroelastic stability assessment method that combines unsteady pressure monitoring within key vortex zones with a one-way fluid–structure interaction (FSI) energy-based framework. Taking the 661 mm last-stage blade of a 350 MW LP steam turbine under 20% THA operating conditions as a representative study, numerical simulations were carried out to capture three-dimensional separated flow structures, isolate dominant unsteady excitation sources via fast Fourier transform (FFT) pressure spectrums, and evaluate traveling-wave flutter across various inter-blade phase angles (IBPAs) for the first three structural modes. The results indicate that flow separation initiates at the rotor root and forms a large-scale recirculation vortex blocking nearly 50% of the spanwise passage. Unsteady pressure monitoring demonstrates that this root recirculation vortex exhibits the maximum pulsation amplitude, serving as the primary source of unsteady aerodynamic excitation. Under fluid–structure coupling, the first three modes all reach their minimum aerodynamic damping coefficients at an IBPA of 45°. When accounting for mechanical damping, the total system damping for the first and second modes becomes negative at 45° IBPA, with the first mode dominating the flutter response. The main novelty of this work lies in revealing the spatial–temporal mechanism by which localized separation vortices govern blade flutter under deep low-flow conditions, providing a precise mapping between localized vortex dynamics and global aeroelastic stability to guide the safe operation of turbine blades.

Driven by the demand for energy conservation and high-efficiency utilization in combined heat and power (CHP) units, optimizing the primary heating network regulation of multi-source cascade heating systems—integrating high back-pressure exhaust steam, steam ejectors, and extraction steam—is essential for the minimum power generation energy consumption. This study examines a 2 × 660 MW direct air-cooling CHP system as a case, investigating the characteristics of three primary heating network regulation strategies—quality regulation, staged-flow quality regulation, and combined quality–quantity regulation—and evaluating the heating load distribution, energy consumption, and corresponding unit operating parameters required to meet the demand heating load in a multi-source cascade heating system. Additionally, parameter corrections are made for heating operations that do not meet the minimum anti-freezing flow constraint of the direct air-cooling island, taking into account the winter anti-freezing requirements. The optimization strategy aims to minimize power generation energy consumption in the multi-source cascade heating system. Results show that under the quality regulation method, the standard coal consumption rate for power generation is the lowest across all outdoor temperatures and load conditions, making it an effective energy-saving regulation strategy for the heating network.

This paper proposes two novel power-to-gas (P2G) coupled systems, namely a protonic ceramic electrolysis cell with a Sabatier reactor (PCEC-SR) and a solid oxide electrolysis cell with a methanation reactor (SOEC-MR). By constructing system-level process mechanisms and numerical models, a comprehensive thermoeconomic assessment and multi-objective optimization based on the NSGA-II algorithm were conducted. The results indicated that, by balancing energy conversion efficiency and system costs, the optimal operating ranges for both systems were clearly identified. Techno-economic analysis revealed that the SOEC-MR system currently exhibited stronger economic robustness; under current technological conditions, the total purchase equipment costs of the PCEC-SR system had to be reduced by at least 40.9% to achieve comparable commercial competitiveness. Furthermore, multi-objective optimization revealed the trade-off relationships between the two systems: the PCEC-SR exhibited superior thermodynamic performance, achieving a 1.4%-5.5% higher overall exergy efficiency at the optimal point, along with lower grid power consumption. In contrast, the SOEC-MR demonstrated advantages in economic performance, with a 14.9%-17.2% lower levelized cost of energy (LCOE). However, under scenarios targeting maximized production capacity, the PCEC-SR, owing to its unique pure hydrogen output mechanism, achieved an absolute methane production rate 33.7% higher than that of the SOEC-MR. This highlighted the significant engineering potential of PCEC-coupled systems for high-throughput, large-scale green fuel synthesis.

Coal pyrolysis is one of the key technologies for clean and efficient coal utilization in China, given its energy structure characterized by abundant coal but scarce oil and gas resources. However, conventional circulating fluidized bed (CFB) power plants are increasingly constrained by bottlenecks in energy efficiency, emissions, and economic performance, while existing coal pyrolysis technologies still face challenges in energy matching and insufficient synergetic optimization of low-carbon performance and value creation. To address these issues, this study proposes a coal-to-hydrogen, chemicals, and power (CtHCP) polygeneration system and compares it with a conventional CFB power generation system. First, system modeling and simulation were performed. Then, technical evaluation was carried out by establishing carbon and exergy balances to quantify carbon utilization and CO2 emission characteristics, enabling a comprehensive benchmarking analysis of energy efficiency, carbon utilization, and carbon emissions. Finally, the economic performance of the systems was evaluated based on product and feedstock market prices. The results show that the exergy efficiency of the CtHCP polygeneration system reaches 53.12%, which is significantly higher than that of the conventional CFB power generation system. The carbon utilization rate of the CtHCP system is 13.91%, and its CO2 emissions are reduced by 29.8%. Although the total investment cost of the CtHCP system is higher than that of the conventional CFB power generation system, its payback period is substantially shorter. Meanwhile, the CtHCP system demonstrates favorable economic feasibility and strong resilience to market fluctuations. This study provides a pathway for the synergistic optimization of energy efficiency, low-carbon performance, and economic benefits in conventional CFB power plants, and offers guidance for the development of coal-based polygeneration systems integrating chemicals, power, and hydrogen production.