I. Process Background
Flue-gas desulfurization wastewater originates from the slurry discharge of the absorption tower (including bypass streams enriched in Cl⁻), and is typically characterized as a highly saline, high‑suspended‑solids, strongly corrosive effluent. The treatment process generally follows the conventional “three‑tank system (neutralization + precipitation + flocculation) + thickening tank + plate‑and‑frame filter press” sequence: first, Ca(OH)2 is added in the neutralization tank to adjust the pH to around 9, precipitating heavy metal hydroxides; next, a chelating agent (such as TMT‑15) is dosed in the precipitation tank to capture heavy metals like mercury and cadmium; then, PAM is introduced in the flocculation tank to form large floc particles; finally, the sludge settles out at the bottom of the thickening tank, with the supernatant recycled and the underflow sent to the filter press for dewatering into a cake prior to off‑site disposal.
The sludge concentration at the thickening tank’s underflow directly determines whether chemical dosing in the three‑tank system is optimized and whether the filter press feed is operating at its best—too low a concentration indicates insufficient chemical addition or inadequate thickening time, leading to higher operating costs and reduced filtration efficiency; too high a concentration can clog pumps and pipelines. Therefore, online density monitoring of the thickening tank underflow (or the filter press feed line) is critical for the stable operation of a zero‑discharge flue‑gas desulfurization wastewater treatment system.
II. Pain Points of Traditional Density Measurement Solutions
• Flue‑gas desulfurization wastewater contains Cl⁻ levels exceeding 20,000 mg/L and extremely high sulfate concentrations; its strong corrosivity can corrode ordinary stainless steel instruments through within a few months;
• The wastewater is laden with heavy metal precipitates, fine CaSO4 crystals, flocs, and other impurities, making contact‑type instruments (mass flowmeters, differential pressure, tuning fork, and ultrasonic reflection types) highly prone to fouling—especially at the thickening tank underflow, where scaling occurs rapidly and accuracy degrades noticeably within a week of operation;
• The wastewater treatment process involves chemical dosing, resulting in a complex and variable slurry composition that places extremely high demands on the density meter’s anti‑interference capability;
• While gamma‑ray density meters are resistant to fouling, they constitute a radiation source; power plant wastewater treatment rooms are often cramped with frequent personnel patrols, posing challenges to safety management.
III. PS7000 Solution
Addressing the severe corrosion, intense fouling, and complex media characteristics of flue‑gas desulfurization wastewater, the PS7000 offers a tailored solution: the pipe section lining can be selected from corrosion‑resistant materials such as PTFE or rubber, and the probe along with the flow path is fully equipped to withstand Cl⁻, SO4²⁻, heavy metal ions, and the highly oxidizing environment found in flue‑gas desulfurization wastewater. Installation locations can be chosen either at the thickening tank underflow pump outlet or on the plate‑and‑frame filter press feed line, with flexible configuration based on the customer’s process priorities.
Figure 3 Schematic Layout of Online Density Measurement in the Flue‑Gas Desulfurization Wastewater Treatment System
Key Technical Advantages of the PS7000 in This Operating Condition ▸ PTFE/rubber/ceramic lining options: confidently handles complex media such as Cl⁻, SO4²⁻, heavy metals, and flocculants; ▸ Non-contact ceramic probe: completely eliminates fouling and wear, eliminating the need for shutdowns for cleaning; ▸ Acoustic impedance method is insensitive to changes in the chemical composition of the medium; pH swings and fluctuations in chemical dosing do not affect measurement stability; ▸ 0–80% full-scale coverage: a single instrument can handle everything from the thickener underflow (8%–15%) to the feed-concentration stage of the filter press; ▸ ExdⅡCT6Gb explosion-proof version available, meeting the explosion-proof requirements of hazardous areas in some power plants; ▸ Supports a 4G module, enabling remote transmission of wastewater treatment plant data to the central control room or the environmental protection department’s monitoring platform. |
IV. Customer Value
Comparison Dimension | Conventional Contact-Based Solutions | PS7000 Solution |
Material Corrosion Resistance | Corrosion and perforation within a few months | PTFE/rubber lining · Long-term stability |
Anti-scaling capability | Scale-induced inaccuracy within 1 week | Non-contact · Never fouls |
Reagent Dosage Optimization | Blind addition · High cost | Precise dosing based on density data |
Filter press efficiency | The feed concentration fluctuates significantly | Feed stability · Reduced filter cake moisture |
Shutdown Maintenance | ≥ 2 times per month | Year-round maintenance-free operation |
In a zero‑discharge project for flue‑gas desulfurization wastewater at a certain 1,000 MW ultra‑supercritical unit, the PS7000 replaced the previously used nuclear‑source density meter and was installed on the thickening tank underflow pump outlet line. Over the past year of operation, the instrument has required no disassembly or maintenance, and its measurement data has consistently remained within 0.5% deviation of manual sampling and laboratory analysis results, providing a reliable basis for automated chemical dosing and the efficient operation of the plate‑and‑frame filter press, thereby significantly enhancing the stability and operational efficiency of the wastewater treatment system.
