There are many types of fans used in the metallurgical industry, but relatively speaking, there are certain difficulties. The three types that can represent the design and manufacturing level of fans are axial flow compressors, sintering induced draft fans, and blast furnace gas pressure recovery turbine power generation devices. The following takes these three types of fans as examples to discuss their future development trends. In general, the technical level abroad is higher than that in China. The advanced technical level abroad is the future development trend that China should actively strive for.

Axial flow compressors have the characteristics of high efficiency, large capacity, and wide range of performance adjustment. At present, all blast furnaces with a volume of more than 1000 cubic meters abroad use axial flow compressors. As an axial flow compressor for blast furnace blast, its flow rate has reached 10000 cubic meters per minute, the pressure has reached 0.69 MPa, and the power has reached 70000 kW.

Axial flow compressors have unique design structures and good aerodynamic performance (the overall polytropic efficiency is 87% – 91%, and the adjustable range of maximum flow and minimum flow is more than doubled), as well as advanced high-level three-levelization and electronic control systems. Its structural characteristics are: the casing is of horizontal split type, made of gray cast iron (or cast steel), and the designed pressure-bearing value on the exhaust side can reach 0.7 – 1.2 MPa. The rotor is of equal inner diameter type, multi-stage segmented disk structure, and the moving and stationary blades all adopt the modified original NACA blade profile of the United States. Adopting a fully adjustable stationary blade structure can double the flow range compared to a compressor with fixed stationary blades. The flow range of the ARI series axial-centrifugal composite isothermal compressor produced by the company is 1400 – 7500 cubic meters per minute, and the pressure ratio is 7 – 11. This product has a relatively high technical level.

In recent years, in order to improve the efficiency of axial flow compressors, Sulzer has adopted a mixed reaction degree design method to improve the inter-stage matching. Reducing the gap between the top of the moving blade and the casing can also improve the performance and efficiency of the compressor. In terms of reducing the noise of axial flow compressors, foreign countries mostly focus on sound insulation and noise reduction. The measures are:
(1) Adopting a thickened cast casing to weaken noise scattering;
(2) Adopting sound insulation enclosures and mufflers to reduce noise diffusion.

Using a computer as the central command system for adjustment to realize the automatic adjustment and optimal operation of axial flow compressors.

As the main flue gas exhauster matched with the sintering machine, the power consumption of the sintering induced draft fan accounts for more than 50% of the total power consumption of the sintering plant. Moreover, since the medium it transports is sintering flue gas with a large amount of dust, therefore, improving efficiency, reducing energy consumption, strengthening wear-resistant measures, and increasing service life are still the main technical issues of sintering induced draft fans.

The air volume of the sintering induced draft fan depends on the sintering area of the sintering machine; the pressure depends on the thickness of the sintering material layer.

The large-scale development of sintering machines (sintering machines with an area of 1000 square meters can be produced) and thick material layers (reaching 700 mm) have promoted the development of sintering induced draft fans in the direction of large air volume and high negative pressure. The maximum flow rate of sintering induced draft fans is 40000 cubic meters per minute, the maximum pressure is 19620 Pa, and the maximum power is 14500 kW.

Due to the limitations of manufacturing process conditions and transportation conditions, the sintering induced draft fans matched with extra-large sintering machines often adopt a parallel connection of two machines.

Wear-resistant measures for sintering induced draft fans:
(1) The serrated middle disk can not only improve the airflow distribution at the impeller outlet and reduce GD2, but also avoid the erosion of the middle disk by flue gas;
(2) The blades are equipped with replaceable wear-resistant liners (the surface of the liners is surfacing with tungsten carbide);
(3) The replaceable conical disk protects the middle disk from wear;
(4) The casing is equipped with vortex liners and side liners;
(5) Surface coating Applying ceramic anti-wear coatings, resin coatings, quartz powder and water glass coatings, etc.;
(6) Surface strengthening treatment Surfacing, thermal spraying, boronizing, laser surface hardening, high-frequency quenching, etc.

At present, foreign countries are conducting research on the two-phase flow (solid particles and sintering flue gas) in the aerodynamic design calculation of sintering induced draft fans, trying to further solve the wear problem of sintering induced draft fans from the aspect of aerodynamics.

Japan has the fastest development and highest level of this device. According to statistics from 1987, there are 47 blast furnaces with a volume of more than 1500 cubic meters, and 38 sets of TRT devices are installed; there are 38 blast furnaces with a volume of more than 2000 cubic meters, and 35 sets of TRT devices are installed. At present, whether in terms of the quality, quantity, or efficiency of TRT devices, Japan is in a leading position.

With the development of blast furnaces towards large-scale and high-pressure furnace tops, foreign TRT devices are developing towards dry type, axial flow type, and adjustable stationary blades.

The axial flow turbine rotor is generally 2 or 3 stages, mostly using a blade profile with a reaction degree of 50%. The moving blades are made of SUS630 stainless steel with corrosion fatigue resistance. The casing is welded with steel plates or can also be made of high-strength cast iron. Generally, it is radial inlet and axial exhaust (or radial exhaust at the lower part). The shaft seal is generally nitrogen-sealed, and recently non-contact mechanical seals are also used.

Most foreign axial flow TRT devices adopt the stationary blade angle adjustment method to expand the operating range, which is beneficial to reducing noise, improving the reliability of the expansion turbine, and will not affect the fluctuation of blast furnace pressure.