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.

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.

Gas flowmeters are a key reference for natural gas trade settlement. To advance on-site verification technology, this paper presents air and natural gas flow test systems employing a clamp-on gas ultrasonic flowmeter, and systematically investigates the effects of pipeline parameters, pressure conditions, transducer usage, and noise reflection on measurement accuracy. Quantitative results show that measurement errors can be controlled within ±2% by selecting appropriate transducer types and installing them beyond 20D downstream of disturbances. Moreover, the proposed dual-transducer synchronous measurement—using two sets of transducers at the same location in different acoustic directions and averaging the results—effectively suppresses radial velocity effects, reducing installation and flow-related errors to within ±1.5%. Installing a single layer of acoustic damping material (≥30 mm beyond the transducer) further improves the coherent signal-to-noise ratio above 30 dB, ensuring reliable performance under noisy conditions. These quantitative findings offer practical guidelines for on-site calibration of natural gas flowmeters, contributing to improved fairness in gas trade measurement.