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Abstract: The high-efficiency fiber filter, a novel type of filter, has achieved excellent results in the pretreatment of low-temperature, low-turbidity, and low-silica source water in our plant: effluent turbidity decreased from 3–5 mg/L to below 1 mg/L; silica content decreased from 0.5–3 mg/L to below 0.5 mg/L; and the silica content in feedwater, boiler water, and steam was significantly reduced, with the boiler system achieving a 100% silica compliance rate.
Keywords: High-efficiency fiber filter; Low-temperature turbidity removal; Silicon removal
Since its commissioning, the demineralized water quality at the power workshop demineralized water station of Qianguo Refinery has deteriorated
severely. The silica content in the industrial water ranges from 0.80 to 3.50 mg/L, and the turbidity ranges from 5 to 10 mg/L. This has resulted in the
silica content in boiler feedwater reaching 80 to 100 μg/L (the standard is ≤30 μg/L), with a maximum of 150 μg/L. The silica content in steam has also reached 80 to 100 μg/L (the standard is ≤20 μg/L). In particular, the silica content reaches as high as 90 μg/L when steam desuperheated from the
feedwater is sent to the primary and secondary catalytic converters. This directly threatens the safe operation of the thermal system, the safe
production of users of the primary and secondary catalytic converters, the compliance of the turbine units, and the biennial overhaul of key
equipment. The excessive turbidity caused the desalination equipment to be overburdened, especially the contamination of ferrous, silica, and organic
matter caused the conductivity of the desalinated water to be substandard, shortening the service life of the resin [1]. The original pretreatment
system of our plant was raw water → cation exchange bed → anion exchange bed, which could no longer meet the requirements for treating this low-
temperature, low-turbidity, low-silica water. It is necessary to strengthen the removal of silica and turbidity in the pretreatment system. In order to
achieve the purpose of removing silica and reducing turbidity, our plant selected a high-efficiency fiber filter for pretreatment. Since its
commissioning, the system has been effective and can fully meet the production requirements. The system is as follows: low-turbidity, low-silica water → high-efficiency filter → cation exchange bed → decarbonator → intermediate water tank → anion exchange bed → desalinated water tank → boiler
feedwater.
Structural Characteristics of High-Efficiency Fiber Filters
High-efficiency fiber filters are a type of filter with a novel structure. Fiber bundles are vertically suspended on a porous plate to form a filter media layer. A pressurization chamber is installed within the fiber filter media. The fiber density of the filter layer is adjusted by filling and draining the pressurization chamber. After the pressurization chamber is filled with water, the filter operates. Pre-filtered water enters from the bottom of the equipment, and clean water is drawn out from the top. After the pressurization chamber is drained, the filter is cleaned. By controlling the water volume in the pressurization chamber, the bulk density of the filter media can be adjusted, and the operation and cleaning of the filter can be easily achieved according to the effluent water quality requirements. An air distribution system and upper and lower water distribution baffles are installed at the bottom. The water filling of the pressurization chamber is automatically controlled, and the entire equipment can be automatically controlled.
Characteristics of Filter Media and Filter Layer
High-efficiency fiber filters use fiber bundles as filter media. Several fiber bundles are arranged at a certain density in the filter to form a loose and easy-to-clean filter layer. When a certain volume of water is filled into the pressurization chamber, the fibers are under a certain compaction state. The water to be filtered flows through the fiber bundles under pressure, thus achieving filtration. During cleaning, the water in the pressurization chamber is discharged, the fiber bundles are loosened, and water is used to flush out the trapped material along the fiber bundle extension direction, thus achieving cleaning and regeneration.
Influence of Filter Layer State on Filtration Performance
Pollution Capacity: During operation, water flows in from the side of the filter layer with larger pores and flows out from the side with smaller pores. Sludge can penetrate deep into the filter layer and be adsorbed and trapped, effectively utilizing the entire filter layer's pollution trapping function and increasing the pollution trapping capacity. Tests show that the pollution trapping capacity of high-efficiency fiber filters can reach 8–10 kg/m². Filtration Accuracy: High-efficiency fiber filters feature a large specific surface area and strong adsorption capacity in their filter media. The presence of a compacted zone on the effluent side ensures sufficient media density, effectively protecting water quality. During cleaning, the fibers remain loose, allowing for thorough cleaning. These factors contribute to the high filtration accuracy of the high-efficiency fiber filter, resulting in excellent water transparency and near-zero turbidity after filtration.
Due to the use of soft packing material, the filter bed density can be adjusted in real-time via a pressure chamber, allowing for timely adjustment of filtration accuracy.
Filtration Resistance: While the compacted zone increases filtration resistance, its thickness constitutes only a small portion of the total filter bed thickness (experiments show it typically accounts for around 20%), resulting in a relatively high overall porosity and minimal total head loss. The head loss of a clean filter bed is generally 0.02–0.03 MPa, and this parameter can also be adjusted via the pressure chamber.
Filtration Flow Rate: The low filtration resistance and high filtration accuracy allow the high-efficiency fiber filter to operate at flow rates exceeding 30 m/h.
High-efficiency fiber filters are highly effective in pretreatment of low-temperature, low-turbidity, and low-silica water, achieving an average turbidity removal rate of over 90% and a silica removal rate of over 80%.
High-efficiency fiber filters provide excellent protection for anion and cation exchange beds. Compared with quartz sand filters, they have lower self-consumption of water, larger interception capacity, better effluent quality, significantly reduced acid and alkali consumption in anion and cation exchange beds, and a larger cycle water production capacity.
