Si₃N₄ ceramics with a microscale rice leaf structure (MRLS) and titanium alloy were connected via brazing, and the influence of the surface microstructure on the ceramic connection was analyzed. MRLS fabrication is an efficient and high-degree-of-freedom method that can be used to change a material’s surface morphology and wettability. The MRLS was obtained at a laser power of 110 W, with line spacings of 100 and 50 μm. The laser-treated surface included nanoparticles and micro particles, exhibiting a coral-like structure after agglomeration. When the MRLS was used to braze the titanium alloy, no defects were observed at the brazing interface, and the formation was excellent. Throughout the brazed joint, the MRLS remained intact and formed a strong metallurgical bond with the brazing filler metal. A finite element analysis was performed to study the cross-sectional morphology after joint fracture; from the load-time curve, it was found that the MRLS on the surface not only helped improve the mechanical occlusion and brazing area at the interface, but also helped generate compressive stress on the Si₃N₄ side. Crack propagation was hindered, thereby increasing the joint strength.

A four-stage condensers in series system was adopted to solve the problems of insufficient condensation of high-temperature pyrolysis steam and difficulty in the classification and recovery of pyrolysis oil, where the internal fluids conducted countercurrent convection heat exchange. A steady-state physical and mathematical model of a single condenser was established to clarify the discipline of heat transfer between the internal fluids. Meanwhile, the model of pyrolysis steam coupled multi-stage condensers was proposed with the help of the model compound firstly. A numerical simulation was carried out and the results showed that when the number of condensers in series was four, the heat transfer process of the system reached saturation, and the heat exchange of the cold and hot fluids was completely realized, and it was of little significance to continue to connect more condensers in series for the condensation of pyrolysis steam. To quickly condense the hot fluid, the key was to increase the mass flow rate of the cold fluid in the first-stage condenser. Compared with the experimental values, the calculated values of hot fluid outlet temperature were not higher than 10%, indicating that the model was highly reliable.

A special dual-tube reactor-dual fluidized bed reactor (DFBR), including an external heat exchanger (EHE) and a bypass, was designed to solve the problems that the waste heat of the hot fluid cannot be fully utilized and the reaction temperature cannot be accurately adjusted. Two connection schemes of DFBR and EHE with their thermodynamic equilibrium models and algorithms were proposed, and the optimal scheme was obtained by comparing the outlet temperature and thermal load. The results of the thermodynamic and operating characteristics of the optimal scheme showed that the hot fluid and the cold fluid had positive and negative effects on the heat transfer process, respectively. Increasing the cold fluid mass flow rate in the main stream can enhance the thermal load of the system and increasing the cold fluid mass flow rate in the bypass helped to increase the thermal load of DFBR, even exceeding that of EHE. Adding a bypass can adjust temperature precisely and increasing the inlet temperature can more effectively increase the adjustment range of the reaction zone temperature. The experimental results showed that introducing a bypass can significantly reduce the calculation deviation (12.8%), which decreased with the increasing temperature.