Xiaofeng Lu

Clamp-on ultrasonic flowmeters serve as an important tool for on-site testing of gas flow meters. However, its accuracy is significantly affected by the actual flow field, thus limiting its application scenarios. To address this issue, this study focuses on typical industrial disturbance structures and obtains the evolution and distribution of non-ideal flow fields downstream of disturbances through experiments and numerical simulations, as well as their effects on velocity and flow measurement errors. The results indicate that when traditional reflection or diagonal measurements were used in the downstream of disturbances, the flow deviation was largely dependent on the installation position and angle of the clamp-on ultrasonic flowmeter. This introduced significant uncertainty and bias, rendering it impossible to correct measurement results through quantitative coefficients. Utilizing a dual-channel measurement method can enhance measurement accuracy. When two sets of sensors perpendicular to each other were used to combine the reflection measurement path, the deviation fluctuation downstream of disturbances can be effectively controlled within the range of ±2%, irrespective of the installation angle. This measurement approach significantly reduced the distance limitations on the distance of the straight pipe section during the use of clamp-on ultrasonic flowmeters.

To meet the Chinese government’s energy-saving and emission-reduction policies, flexible peak regulation is necessary for traditional coal-fired boilers. Flexible peaking leads to large changes in boiler load, which affects the safety of the boiler water wall. In this paper, a 1000 MW ultra-supercritical unit was tracked for three years, and effective data were selected to study the temperature characteristics of the water wall under flexible peak regulation. The results show that the lower the load, the greater the temperature fluctuation of the water wall. The temperature distribution of the spiral water wall is more uniform. The position of the temperature valley value of the rear spiral water wall was found, and the load of more even temperature distribution was also found. The temperature change of the front vertical water wall was the most complex of all the water walls. The 643.9 MW load case showed different behavior to the temperature distribution of the water wall. The side water walls were heated evenly under the different loads. The characteristics of the temperature distribution of the side vertical water wall were found through statistical analysis. The fitting equation for the change rule of the temperature is presented. The higher the load, the better the equations. Finally, this paper gives some advice on how to avoid temperature deviation in the water wall, and the detailed research highlights the safe running of water walls.

Circulating fluidized bed (CFB) boilers offer a technically viable and environmentally friendly means for the clean and efficient utilization of solid fuels. However, the complex gas–solid two-phase flow processes within them have hindered a thorough resolution of prediction issues related to coupled combustion, heat transfer, and pollutant generation characteristics. To address the deficiencies in scientific research, meet the practical operational needs of CFB boilers, and comply with new carbon emission policies, conducting full-scale field tests on large-scale CFB boilers is needed, so that the complex gas–solid flow, combustion, and heat transfer mechanisms in the furnace can be comprehended. In this paper, issues related to large-scale CFB boilers, including the uniformity of air distribution, secondary air injection range, spatial distribution of oxygen consumption and combustion reactions, distribution of pollutant generation, hydrodynamic and heat transfer characteristics, coal feeding distribution characteristics, coal diffusion characteristics under thermal operating conditions, and engineering research on anti-wear technology, are reviewed. By integrating practical engineering applications, the basic methods and measurement techniques used in full-scale field tests for large-scale CFB boilers are summarized, providing a practical reference for conducting engineering tests with large-scale CFB boilers.

In this paper, the dynamic deposition behavior of Na-enriching Zhundong coal ash on tube bundles with varying longitudinal and transverse pitches was numerically studied. By using a modified critical viscosity model, an improved CFD deposition model has been established and key parameters, including deposit mass and morphology, particle trajectories and impaction and sticking probabilities, as well as the heat flux distribution, have been analyzed. The results show that the ash deposited on tubes in the first row is, respectively, 1.74 and 3.80 times higher than that on the second and third rows, proving that ash deposition in the downstream is lessened. As the longitudinal pitch increased from 1.50 D to 2.50 D, deposit mass in the downstream increased two times, suggesting that an increase in longitudinal pitch would aggravate ash deposition. The effect of transverse pitch, however, with the least deposit propensity at S_t/D = 1.75, is non-linear due to the joint effect of adjacent tubes and walls in affecting particle trajectory. In addition, due to the non-uniform distribution of the deposit, heat flux across the tube is the smallest at the stagnation point but becomes six times higher at two sides and the leeward, which makes the thermal damage of these sides to be warranted as a practical concern.

In order to meet the flexibility operation needs of coal-fired units under the goal of carbon peak and carbon neutralization, it is imperative for circulating fluidized bed (CFB) units to participate in deep peak regulation. By systematically summarizing deep peak regulation operation practice of existing SC and subcritical-parameter-levels CFB units, the feasibility of deep peak regulation technology of an ultra-supercritical (USC) CFB unit under development and being built is analyzed and demonstrated; meanwhile, the deep peak regulation capacity of the boiler is also predicted. The results show that by analyzing the structural characteristics and design performance of the USC-CFB boiler, for technical problems such as stable combustion under low load, hydrodynamic safety, denitration performance under wide load, and rapid boiler load change rate existing in deep peak regulation, technical measures were implemented by selecting advanced boiler furnace type, adopting good design technology of the secondary rising water wall and uniformity design of bed temperature and bed pressure, strengthening the reducing atmosphere inside the furnace, improving the performance of wear-resistant refractory materials, quickly controlling the furnace bed material stock under variable load, optimizing the control strategy of CFB unit, and so on. The boiler achieved good operation characteristics and good deep peak regulation performance, and the pollutant emissions can steadily achieve ultra-low emission standards. When the USC-CFB unit participates in deep peak regulation, the minimum stable combustion load of the boiler can reach 20~30% BMCR, and a boiler load change rate under 30% BMCR or above could reach 1.5~2% BMCR/min, while that below 30% BMCR could reach 1% BMCR/min. The research results can provide references for the deep peak regulation of in-service supercritical (SC) CFB units and design optimization of similar USC-CFB units.

Based on the field test of a 600 MW supercritical circulating-fluidized bed boiler, this paper optimizes the secondary air pipe layout scheme of a 660 MW ultra-supercritical circulating fluidized bed boiler with a similar furnace structure and carried out a numerical simulation on its air distribution uniformity. The secondary air box of the 660 MW ultra-supercritical circulating-fluidized bed boiler adopts a variable section design, and the secondary air branch pipe adopts a separate air inlet mode. The experimental results showed that the oxygen concentration was uniform near the rear wall, but all exhibited a “decrease–increase–decrease” profile along the horizontal line, which indicated that the trajectory of the secondary air jet was first in the shape of bending downward and then upward. To achieve a more uniform secondary air distribution for supercritical CFB boilers, further optimization of the layout of the bellows and branch pipes should be considered. Numerical results showed that the deviation rate of the internal and lower secondary air reached 17%, and there was optimization space for the secondary air branch pipe layout of the boiler. Its uniformity can be increased by adding valves and other measures. The velocity deviation of the secondary air of the 660 MW ultra-supercritical circulating-fluidized bed boiler can be within 3% by means of separate air supply and pipe diameter change, and better uniform air supply can be achieved to reduce the speed deviation by adding valves and adjusting the combustion.

This study verified the effect of steel slag as alternative bed material on ash deposition in circulating fluidised bed (CFB) burning high‐sodium Zhundong lignite (ZD). Sample of ZD was burned in a lab‐scale CFB at 950°C, and the obtained fly ash and ash deposits were characterised. Results showed that the presence of steel slag bed material leads to the abundance of Na (2.39 wt%) in fly ash. Na‐bearing minerals such as Na₂SO₄, Na₂Si₂O₅ and NaCl of low melting points had been identified, resulting in severe ash deposition on heat transfer surfaces than that with quartz as bed material. This could be mitigated by incorporating 10 wt% oil shale semi‐coke (SC) into ZD, among which Na was captured by aluminosilicate and retained in the interior of SC as (Na, Ca)Al(Si, Al)₃O₈ of high melting point. Na in the fly ash thus decreased to 1.05 wt% and in the form of high melting‐point Na(AlSi₃O₈). In addition, ESEM confirms that the SC particles after capturing Na still had an ash fusion temperature of 1280°C, which were insufficient to induce bed particle agglomeration.

The use of the Maisotsenko cycle (M-Cycle) in traditional wet cooling towers (TWCTs) has the potential to reduce the costs of electricity generation by cooling water below the inlet air’s wet-bulb temperature. TWCTs cannot provide sufficient cooling capacity for the increasing demand for cooling energy in the power and industrial sectors—especially in hot and wet climates. Due to this fact, an experimental system of an M-Cycle cooling tower (MCT) with parallel counter-flow arrangement fills was constructed in order to provide perspective on the optimal length of dry channels (l_dry), thermal performance under different conditions, and pressure drops of the MCT. Results showed that the optimal value of l_dry was 2.4 m, and the maximum wet-bulb effectiveness was up to 180%. In addition, the impact of air velocity in wet channels on the pressure drops of the novel fills was also summarized. This study confirms the great potential of using the M-Cycle in TWCTs, and provides a guideline for the industrial application and performance improvement of MCTs.