The structure of the dissolved air flotation (DAF) tank in a high-efficiency dissolved air flotation (DAF) machine is a core module affecting solid-liquid separation efficiency. Its design directly determines the contact efficiency between microbubbles and suspended solids, the stability of floc flotation, and the quality of the effluent. A DAF tank typically consists of a flow stabilization chamber, a dissolved air release chamber, a separation chamber, a water collection system, and a sludge scraping device. The structural parameters of each area need to be optimized collaboratively to achieve efficient separation.
The flow stabilization chamber is the pretreatment unit of the DAF tank. Its function is to eliminate the damage to microbubbles caused by raw water turbulence. If high-speed flowing raw water directly contacts dissolved air water, shear forces will cause microbubbles to break or merge, reducing the probability of bubble adhesion to suspended solids. The flow stabilization chamber, by enlarging the water flow cross-section or installing baffles, uniformly slows down the water flow, creating a stable environment for subsequent bubble-floc bonding. For example, some designs employ a folded plate reaction structure, using multi-stage baffles to extend the water flow path, enhancing the flocculation effect while reducing kinetic energy impact, ensuring that microbubbles maintain their intact shape before entering the release chamber.
The dissolved air release chamber is a crucial area for bubble generation, and its structure directly affects bubble size and distribution uniformity. The release chamber is typically separated from the separation chamber by a partition. Dissolved water is released under reduced pressure through the release device, forming microbubbles with a diameter of 20-100 micrometers. The orifice diameter, number, and arrangement of the release devices must match the dissolved air efficiency of the dissolved air tank: if the release device orifice diameter is too large, the bubble diameter will be too large, and the flocs will easily break due to excessive buoyancy after adhering to them; if the orifice diameter is too small, the number of bubbles will be too large, which may cause bubble coalescence and reduce the proportion of effective bubbles. Some high-efficiency dissolved air flotation machines use multi-stage release devices to achieve a gradient distribution of bubble size through layered release, adapting to the separation needs of suspended solids of different densities.
The separation chamber is the core area of the air flotation process, and its structural parameters play a decisive role in the separation efficiency. The depth of the separation chamber must balance the floc floating time and the equipment footprint: if the depth is too shallow, the flocs will be carried away by the water flow before they float sufficiently; if the depth is too deep, it will increase equipment costs and may affect the separation effect due to water flow disturbance. The width-to-length ratio of the separation chamber also needs optimization, typically adopting a length-to-width ratio of 3:1 to 5:1 to extend the water flow path and reduce short-circuiting. Furthermore, vertical plates or perforated plates can be installed within the separation chamber to guide the flow, enhancing the contact between flocs and air bubbles by altering the water flow direction, while simultaneously suppressing the formation of three-dimensional vortices and improving separation stability.
The water collection system has a significant impact on the effluent quality. Traditional dissolved air flotation (DAF) tanks often use peripheral water collection, which can easily lead to some flocs being drawn into the effluent due to uneven water flow. High-efficiency dissolved air flotation machines optimize the water collection process through a perforated plate water collection system or an air bubble filter chamber: perforated plates are evenly arranged at the bottom of the separation chamber, achieving uniform water collection through small-diameter openings, reducing interference with the floc layer; the air bubble filter chamber utilizes multiple partitions and water collection plates to form a gradient filtration zone, allowing clear water to pass through multiple filter screens during its ascent, further trapping residual flocs and improving effluent transparency.
The structural design of the scum scraper affects the efficiency of scum removal. Traditional scum scrapers often use chain or reciprocating scrapers, which are prone to scum breakage or secondary settling due to excessive scraper speed or improper angle. High-efficiency dissolved air flotation (DAF) machines employ a variable frequency speed control (VFD) scraper system, automatically adjusting the scraper speed based on scum thickness while optimizing scraper angle and material to minimize disturbance to the scum layer. Some machines are also equipped with a scum thickening device, further reducing the scum's moisture content through gravity settling for easier subsequent processing.
The flow field characteristics of the flotation tank are crucial for structural optimization. Computational fluid dynamics (CFD) simulations can analyze water velocity distribution, bubble rise trajectories, and floc movement patterns, providing theoretical support for structural parameter adjustments. For example, simulation results show that installing a small-pitch vertical plate device at the bottom of the separation chamber enhances vertical water stratification, reduces horizontal short-circuiting, and makes the floc's upward path more vertical, significantly improving separation efficiency. The structure of the dissolved air flotation tank in a high-efficiency dissolved air flotation machine needs to be optimized in a coordinated manner across aspects such as flow stabilization, release, separation, water collection, and sludge scraping. Through flow field regulation, structural innovation, and intelligent control, efficient adhesion and stable separation of microbubbles and suspended solids can be achieved, ultimately achieving the dual goals of improving effluent quality and reducing operating costs.
