Hot rolling dust removal typically employs two methods: ventilation dust removal and spray dust removal. Ventilation dust removal uses a hood to collect fumes, conveying the dust through flues to subsequent dust collectors for purification. Spray dust removal involves spraying water mist to reduce the temperature of the fumes, increase particle size and density for effective dust collection.
The advantage of ventilation dust removal is its high efficiency, but it requires large equipment due to the significant volume of air processed, necessitating powerful fans and dust removal devices. This method incurs high capital and operational costs. In recent years, spray dust removal has been widely adopted because it only requires water sources and less equipment, which are activated only when dust is present. This approach significantly reduces the operating expenses and simplifies maintenance.
Given the instantaneous and concentrated nature of hot rolling dust, spray dust removal proves more economical.
Spray dust removal works by non-elastic collisions between spray droplets and dust particles, causing the latter to coalesce, grow in size, separate, and settle. Key factors for improving the efficiency of spray dust removal in hot rolling include:
1) Selecting appropriate nozzles based on flow rate, coverage area, and particle size. Nozzle arrangements generally require multi-layer setups; each layer’s spray coverage should exceed the dust area; there must be reasonable overlap between spray patterns without gaps.
2) For single-fluid nozzles, sufficient inlet water pressure is necessary to ensure proper spray particle size and coverage. For dual-fluid nozzles, water and air pressures need to be properly matched according to nozzle characteristic curves to avoid insufficient water volume and excessively large spray particle sizes.
In hot-rolled strip production, the primary concern is suppressing and eliminating iron oxide scale generated during high-speed rolling. To inhibit dust generation, a row of fan-shaped nozzles should be arranged above and below the strip at the mill exit, with their spray directed toward the gap between the strip and rolls. Additionally, conical nozzles should capture dust along its upward diffusion path, causing it to settle near the mill.
Besides nozzles, stable water supply is ensured by pumps, steady pressure is maintained by pressure regulators, and electromagnetic valves control nozzle operation in sync with strip production.
During scale removal from slab surfaces, the produced dust features large particles moving at high speeds. Typically, splash guards and reverse spray water are added before and after scale removal points to prevent splashing. Reverse spray nozzles should provide substantial impact force and moderate flow rates, selecting fan-shaped water nozzles.
