Coal-Washing Wastewater in Power Plants: What a Two-Stage CDFU Dissolved-Air Flotation Train Delivers
In the continuous production process of coal-fired power plants, the purification of coal-washing wastewater is a key environmental protection task. When a plant pre-treats, processes and burns coal, operations such as washing, screening and dewatering generate large amounts of coal-washing wastewater. The water carries suspended particles such as coal dust and silt, dissolved organic components including phenols and aromatic hydrocarbons, oil and grease, heavy metal ions such as lead, cadmium and mercury, and other inorganic salts. Its character is set by four traits: a large discharge volume, complex composition, high suspended solids concentration and high oil content - which together make purification genuinely difficult.
Why the Pollutants Matter Beyond the Pipe
The pollutants do more than degrade water quality; each one threatens the surrounding environment in its own way. High concentrations of suspended solids easily cause pipeline blockage and equipment wear. Oil and grease are difficult to remove completely and may cause secondary pollution if handled improperly. Heavy metal ions are significantly toxic and endanger the health of living organisms. And sharp fluctuations in water quality place stringent demands on whatever technology is expected to cope with them.
Where the Conventional Methods Run Out
The technologies previously used by coal-fired power plants mostly relied on conventional methods - sedimentation, filtration, coagulation and air flotation. These can partially remove suspended solids and oil, but the shortcomings are obvious. Treatment efficiency is limited and effluent quality fluctuates greatly, making it difficult to continuously meet discharge requirements. The process produces large amounts of oily sludge, which is expensive to dispose of, occupies a large area and requires considerable manpower for operation and maintenance. And in the face of frequent water quality changes, conventional processes have weak resistance to load fluctuations, with no effective countermeasures.
The Two-Stage CDFU Route
To overcome the limitations of existing technologies, SINOKLE has introduced an innovative coal-washing wastewater treatment process for coal-fired power plants, whose key equipment is a two-stage CDFU cyclonic dissolved-air flotation system. Based on purely physical methods and combined with a number of advanced patented technologies, it achieves efficient, stable and eco-friendly wastewater purification.
The steps are deliberately simple. The wastewater first enters a collection tank for preliminary filtration to separate larger debris, and then enters the two-stage CDFU cyclonic dissolved-air flotation unit for deep treatment. Inside the CDFU system, high-pressure dissolved-air water is injected into the wastewater to form a large number of micro-bubbles. By virtue of the unit's special cyclonic structure, these bubbles fully contact and adhere to suspended particles, oil and other pollutants in the wastewater, lifting them to the liquid surface and thereby separating the pollutants. The treated wastewater then enters the downstream purification unit, further ensuring that water quality meets discharge or reuse standards.
What the Numbers Say
The performance figure that decides the comparison is this: with influent oil and suspended solids both ≤1000 mg/L, the effluent oil and suspended solids after treatment are both ≤20 mg/L. Crossing from a thousand down to twenty, in two flotation stages and without chemistry, is what the two-stage arrangement buys.
The Advantages That Follow
Compared with the previous technology, the new process offers outstanding advantages in several respects. Resistance to load fluctuations is strong, so variable water quality still produces stable effluent. Treatment efficiency is high, with the two-stage CDFU cyclonic dissolved-air flotation system efficiently separating pollutants. The flow is simple and physics-dominated, which simplifies the stages and lowers operating costs. Less oily sludge is generated, reducing the burden of downstream disposal. No chemical dosing is needed throughout the process, making it a green process. And the system runs fully automatically in a closed mode with a small footprint, low manual operation and maintenance requirements, and simple management - improving overall treatment efficiency and operational control.
Taken together, those properties give the process broad application potential: solid technical support for the environmental protection practice of coal-fired power plants, and a practical step toward sustainable operation across the industry.
Inside the Two-Stage Arrangement
The reason for running two CDFU stages rather than one lies in the nature of the load. Coal-washing water arrives with both coarse, fast-settling solids and fine, slowly floating material, and a single stage has to choose which fraction it treats well. The first stage takes the brunt - stripping the bulk of the suspended particles and free oil so the second stage sees a steadier, lighter load - while the second stage polishes the fine droplets and residual solids that survived the first pass. Because each stage regenerates its own micro-bubble field from high-pressure dissolved-air water, the flotation intensity never depends on how dirty the previous stage was.
The cyclonic structure earns its place in the same economy. Swirling flow extends the contact path between bubbles and particles, so a bubble that would otherwise rise straight up sweeps through more of the water column and collides with more pollutant particles on the way. More collisions per bubble means less dissolved-air water per tonne treated - and that is where the low operating cost ultimately comes from.