To reveal the action mechanism of vibration frequency in alfalfa opening compression, a self-developed vibration compression test system was used to evaluate the variation of compression force during alfalfa open compression. A faster vibration frequency yielded a smaller compression force required for compressing alfalfa into blocks. Compared with free vibration compression, vibration compression was beneficial to release the internal stress of alfalfa block, reduce the forming pressure, and stabilize the high density. In the range of test vibration frequency, when the frequency was 15 Hz, the residual internal stress release ratio of alfalfa block was the highest, and the stable density of alfalfa block was the largest. Considering the pressure and alfalfa block density comprehensively, the optimized vibration frequency was approximately 15 Hz.

Compression alfalfa into briquettes is an effective way to solve the problem of storage and transportation. In the process of compression, heat is generated, which raises the temperature in the material. The appropriate temperature can improve the quality of alfalfa briquettes. In this paper, the effect of assisted vibration frequency, moisture content, and particle size on the compression temperature were tested. The results showed that when the vibration was applied, the material particle temperature in the mold rose significantly, and the core particle temperature rose faster than the edge temperature. The vibration frequency was the most significant factor affecting heat transfer in the three studied factors. When the moisture content and particle size were constant, the heat transfer effect increased first and then decreased with the vibration frequency, and it had an optimal value at 17 Hz. When the vibration frequency and particle size were constant, the heat transfer effect increased first and then decreased with the moisture content. It had an optimal value of 20%. The experimental results explained the effect of vibration frequency, moisture content, and particle size on temperature variation during alfalfa compression and provided a basis for reasonable process parameters.

In this study, iron concentrate and blast furnace dust were used as raw materials, and graphite was used as a reducing agent for mixing and briquetting. The briquettes were roasted in a high-temperature tube furnace at different temperatures and held for a certain time to simulate the pre-reduction sintering process. The effects of dust content, reduction time, and reduction temperature on the removal rate of zinc, potassium, and sodium and the metallization rate of the pre-reduction sintered products were investigated. The reduced briquettes were characterized by X-ray diffraction, scanning electron microscopy-energy dispersive spectroscopy, and flame atomic absorption spectroscopy to further explore the mechanisms of zinc, potassium, and sodium removal. The Zn removal rate and metallization rate increased gradually with the increase in dust content, reaching 97.57% and 87.14% at 30% dust content, respectively. Both K and Na removal rates reached a maximum of 83.57% and 94.78%, respectively, at 25% dust content. With the increase in reduction time and temperature, the removal rate of the three elements and the metallization rate gradually increased. When the briquettes with 20% blast furnace (BF) dust content were reduced at 1,200℃ for 20 min, the removal rates of zinc, potassium, and sodium reached 95.66%, 79.97%, and 91.49%, respectively, and the metallization rate reached 84.77%. It shows that the pre-reduction sintering process can effectively remove Zn, K, and Na from the BF dust and meet the requirements of subsequent BF production. The research results can provide some theoretical basis for industrial production.