I. Process Background
The AFT tower is a key piece of equipment in power plant flue-gas desulfurization and deep treatment systems for desulfurization wastewater, commonly used for the circulation, absorption, and concentration of high-concentration desulfurization slurry, as well as for pretreating by-product salt crystallization. In a typical process, high‑temperature flue gas (or process gas) enters from the bottom of the tower and comes into countercurrent contact with the slurry sprayed down through multiple stages inside the tower. The slurry at the tower bottom is repeatedly pumped back to the spray layer by a circulation pump, creating intense gas–liquid mass transfer that gradually concentrates the slurry to a high‑density range of 30% to 60%. When the slurry density at the tower bottom reaches a set value, it must be promptly discharged to downstream crystallizers and centrifuges to precipitate and remove the by‑product salt crystals.
The slurry in this section exhibits extreme characteristics—high concentration, high viscosity, high abrasiveness, and a strong tendency to crystallize at the measurement interface. Real‑time, continuous, and reliable monitoring of the slurry density in the tower bottom circulation loop is the core basis for the safe operation of the AFT tower and the automation of the discharge process.
II. Pain Points of Traditional Density Measurement Solutions
• High‑viscosity slurry: Differential pressure instruments’ impulse lines are highly prone to blockage, making stable operation nearly impossible.
• Crystallizing media: The slurry rapidly forms crystals at the measurement interface when the temperature changes, coating the sensor surface and causing “false high” readings or even complete failure.
• Highly abrasive conditions: Hard, suspended particles in the slurry quickly wear down contact probes, resulting in extremely short service lives.
• Wide measurement range: From about 20% at the start of circulation to around 60% during discharge, a single instrument must cover this broad span, a challenge traditional meters struggle to meet while balancing accuracy and range.
• Gamma‑ray concentration meters face mounting safety, compliance, and maintenance‑cost pressures; power plants generally prefer non‑nuclear solutions for new projects.
III. PS7000 Solution
The PS7000 is installed on the discharge line of the AFT tower’s bottom slurry circulation pump, using a non‑contact acoustic impedance method to measure slurry density. When the PS7000 detects that the tower bottom density has reached the process setpoint (e.g., 50%), it sends a discharge‑trigger signal to the DCS, automatically opening the discharge valve to send the high‑density slurry to downstream crystallizers. Once the density drops back to the process lower limit, discharging ceases, achieving fully automated closed‑loop control of slurry circulation and discharge.
Figure 4: Schematic diagram of online density measurement and discharge control in an AFT tower (high‑concentration desulfurization slurry treatment tower)
Key Technical Advantages of the PS7000 in This Process Condition ▸ The linear frequency-modulated Chirp algorithm maintains stable echo‑analysis performance even for highly viscous, high‑concentration slurries; ▸ A single unit covers the entire range from 0 to 3,000 kg/m³ (approximately 0 to 80% concentration), eliminating the need for multiple instruments operating in tandem; ▸ The non‑contact ceramic probe fundamentally addresses the three major challenges of crystallization encrustation, wear, and clogging; ▸ The high‑temperature model can accommodate medium temperatures up to 120°C, making it suitable for applications in the AFT tower sump where medium temperatures are relatively high; ▸ An explosion‑proof ExdⅡCT6Gb option is available, meeting the explosion‑proof requirements for flue‑gas desulfurization wastewater treatment and areas containing SO2, NH3, and other hazardous substances; ▸ Slurry density data drives the discharge valve interlock logic, ensuring stable feed density into the crystallizer and significantly improving the separation efficiency of downstream centrifuges. |
IV. Customer Value
Comparison Dimensions | Conventional/Nuclear Source Solutions | PS7000 Solution |
Measurement Range Coverage | Multiple instruments are required for segmented measurement | 0–80% single-unit coverage |
Crystallization/Blockage Mitigation | Frequent crystallization failures | Non-contact · Unaffected |
Automated Discharge | Reliance on human experience-based judgment | Density interlock automatic discharge |
Operational Safety | Radiation safety management and control | Intrinsically safe with no radiation |
Mold Feed Stability | Large fluctuations · Affect crystal particle size | Stability · Improved by-product salt quality |
In a certain salt chemical–power plant cogeneration project in Qinghai, the potassium chloride slurry in the AFT tower bottom was near saturation, with a crystal content of 30% to 40% and a temperature fluctuating between 5°C and 20°C. After the PS7000 was put into operation, two weeks of continuous comparative testing showed that its readings consistently agreed with laboratory measurements within a deviation of 0.5% to 0.8%, with no anomalies even during peak concentration periods, fully validating its high accuracy and reliability under extreme conditions such as those in the AFT tower. This solution has now been adopted by several power plants in similar projects as a standardized approach for density measurement in high‑concentration desulfurization slurry treatment towers.
