1. Overview
The traditional treatment method for slag removal systems in thermal power plants involves crushing the slag with a slag crusher, then pumping the slag water to a dewatering bin using a submersible pump at the furnace bottom. Most of the slag settles in the dewatering bin and is transported out from the bottom. A small portion of slag and water flows over the weir of the dewatering bin to a concentrator for sedimentation, and the clarified water is recycled.
Currently, domestic slag water treatment methods generally use sedimentation tanks, concentrators, ceramic filter brick pools, etc. A few manufacturers adopt the method of flocculation sedimentation + inclined tubes + sand filtration. The aforementioned treatment technologies all have various issues and are lacking in treatment capacity, operational stability, and reliability. For example, the sedimentation tank process has low suspended solids (SS) removal efficiency, poor effluent quality, large footprint, frequent tank cleaning with high workload; concentrators require low inlet SS content, have poor effluent quality, inclined tubes (plates) are prone to clogging and require manual cleaning, the slag discharge vertical pipe is easily blocked leading to poor sludge discharge, and rake collapse accidents often occur; ceramic filter brick pools have a large footprint, require manual cleaning and backwashing, frequent cleaning, and high labor intensity; the flocculation sedimentation + inclined tubes + sand filtration process requires low inlet SS content, needs a large pre-sedimentation tank, inclined tubes (plates) are prone to clogging, sand filters have high load and require frequent backwashing, and the filter layer is prone to hardening. The biggest issue with the above processes is their low resistance to shock loads; they cannot effectively treat slag water with SS > 3000 mg/L, especially when SS > 5000 mg/L.
In high-SS sewage treatment, the ZJ/DH-II High-Efficiency Sewage Purifier demonstrates significant technical advantages. It does not require a pre-sedimentation tank and can rapidly, continuously, and efficiently purify sewage with SS ≤ 30000 mg/L to 5–50 mg/L. This technology can treat sewage with SS up to ≤ 90000 mg/L, providing a new approach for high-concentration slag water treatment and solving the challenges in slag water reuse. 2. Scope of Application
Suitable for the treatment and reuse of concentrated slag water (including coal-containing wastewater) in thermal power plants;
Suitable for water plants in towns, industrial, and mining enterprises using various rivers, lakes, reservoirs, etc., with turbidity less than 3000 mg/L as water sources, serving as the main water purification device;
Has special adaptability to lake water sources with low temperature, low turbidity, and seasonal algae;
Used in metallurgical industry circulating water systems to effectively and significantly improve circulating water quality; 3. Main Features
Short process flow, low failure rate, stable and reliable operation;
Strong treatment capacity and high efficiency. The equipment can handle loads up to SS ≤ 3000 mg/L, with a maximum of SS ≤ 9000 mg/L;
High design load, wastewater retention time ≤ 30 min;
Small equipment footprint; the system does not require pre-sedimentation tanks, sewage regulation tanks, sludge tanks, or clear water tanks, and can be designed with ordinary transition pools to save space;
Good effluent quality after treatment, SS = 5–50 mg/L, preventing ash accumulation in cooling towers and water seal tanks, and allowing reuse for furnace sealing;
PLC control for high automation and low labor intensity;
Low sludge discharge volume, high sludge concentration, and low moisture content;
Easy operation, long filter media service life, backwashing cycle up to 0.5–1 month, with significant water and energy savings, and environmental, social, and economic benefits;
Equipment body maintenance-free, reducing maintenance workload;
Only one lift required for equipment operation, saving supporting electromechanical equipment investment and power consumption;
Factory production mode improves equipment precision, quality, aesthetics, and water production quality;
Factory production mode allows batch production, shortening construction periods. 4. Working Principle and Structure
The ZJ/DH-II High-Efficiency Sewage Purifier is an improved version of the original DH model, integrating physical and chemical reactions. It combines direct current coagulation, critical flocculation, centrifugal separation, shallow sedimentation, dynamic filtration, and sludge concentration sedimentation technologies, completing rapid multi-stage purification of wastewater in a single tank within a short time (25–30 min). The equipment achieves up to 99.9% SS removal and 40%–70% COD removal.
The purifier is a steel tank with a cylindrical upper-middle part and a conical lower part. From bottom to top, it consists of sludge concentration zone, coagulation zone, centrifugal separation zone, dynamic filtration zone, and clear water zone. Direct current coagulation and critical flocculation technologies replace the coagulation reaction tank. Flocculants and coagulants are added before and after the pump, using the pump, pipelines, and water flow to complete hydrolysis, mixing, double-layer compression, and adsorption neutralization. The water then enters the tank tangentially at high speed to quickly complete adsorption bridging and floc formation.
Centrifugal separation uses the high-speed swirl generated by tangential inlet to create centrifugal force, throwing suspended particles and flocs toward the tank wall. They slide down along the inner wall to the conical sludge concentration zone under the downward swirl and gravity. The wastewater spirals downward to a certain extent before converging toward the center, forming an upward swirl of clearer water that flows to the dynamic filtration zone above. In the centrifugal separation zone, suspended particles (flocs) larger than 20 μm are separated into the sludge concentration zone. The wastewater then enters the shallow sedimentation zone after centrifugal separation. The inclined tube sedimentation zone is designed based on shallow tank sedimentation theory. Dense inclined tubes are installed in the sedimentation area, allowing suspended impurities to settle in the inclined plates or tubes. Water flows upward along the inclined plates or tubes, and the separated sludge slides down to the bottom under gravity and is discharged collectively. This design improves sedimentation efficiency by 50%–60% and increases treatment capacity by 3–5 times in the same area. The effluent from the upper part of the shallow sedimentation zone enters the dynamic filtration zone for further adsorption filtration. The filtration zone uses suspended filter media with large surface area and strong adsorption capacity, capturing suspended solids larger than 5 μm. Filtration occurs in a dynamic state, so the filter media are not easily clogged, and adsorbed particles are easily dislodged and sink back to the separation zone, resulting in a long backwashing cycle (0.5–1 month). The wastewater is discharged after multi-stage solid-liquid separation and purification.
Suspended particles separated by centrifugal force, shallow sedimentation, and filtration enter the sludge concentration zone under centrifugal force and gravity. In the upper-middle part of the conical sludge hopper, particles aggregate into a whole under cohesive force, sinking together while maintaining relative positions. In the lower part of the sludge hopper, the SS is very high, squeezing liquid out from the gaps between particles. The solid particles are concentrated and compacted before being discharged from the conical bottom, with sludge moisture content generally ≤ 90% (sludge discharge volume is only 1/6 of traditional processes). 5. Typical Application Process
For power plant slag water renovation and new projects, the process varies slightly depending on the existing facilities and site conditions, but the basic system remains the same.
The overflow water from the slag extractor flows by gravity into the drainage tank, which serves as a regulation tank. The regulated sewage is lifted by a slurry pump, with flocculants and coagulants added before and after the pipeline mixer. Direct current coagulation reaction is completed in the mixer, and the water then enters the high-efficiency (swirl) sewage purifier. After centrifugal separation, gravity sedimentation, dynamic adsorption filtration, and sludge concentration, clear water is discharged from the top of the purifier and flows by gravity into the cooling tower. After cooling, the water temperature is 30–35°C, and it enters the clear water tank before being sent to reuse points via reuse pumps for furnace sealing and slag extractor chain cooling. The concentrated slag from the ash water treatment is discharged into the sludge tank and then sent to the slag extractor for cyclic treatment via sludge pumps.
