Full-Process Planning for Reclaimed Water Reuse Treatment Process Design in the Power Industry

I. General Planning Principles and Design Scope

1.1 Planning Background and Objectives

To implement national water conservation policies, reduce freshwater intake and wastewater discharge from power plants, and enhance water resource recycling efficiency, this plan aims to design a full-process reclaimed water reuse treatment system for various types of power plants (e.g., coal-fired, gas-fired, nuclear) that is technologically advanced, operationally reliable, and economically sound.

• Core Objective: To deeply purify non-conventional water sources, such as the power plant's own industrial wastewater, domestic sewage, or municipal wastewater treatment plant effluent (secondary treated), for reuse in the plant's most water-quality-critical processes, partially or fully replacing freshwater.

• Primary Reuse Directions:

  1. Circulating Cooling Water System Makeup: Largest water demand, with control requirements for hardness, salinity, organics, and microorganisms.

  2. Boiler Feedwater System Raw Water: Highest water quality requirements, requiring deep desalination, silica removal, and organics removal.

  3. Flue Gas Desulfurization (FGD) Process Water, Ash Sluice Water, Landscaping Water, etc.: Relatively lower water quality requirements, suitable as primary reuse targets.

1.2 Design Principles and Scope

• Design Principles:

  1. Quality-Based Recovery, Graded Utilization: Design differentiated treatment processes and reuse pathways based on wastewater quality and end-use point requirements, achieving "high-quality water for high-grade uses, lower-quality water for lower-grade uses."

  2. Source Optimization, Integrated Treatment: Survey water quality from all discharge points within the plant. Prioritize source segregation and resource-oriented pretreatment (e.g., neutralization of acid/alkali wastewater, oil removal from oily wastewater).

  3. Reliable Technology, Redundant Safeguards: Select mature, stable mainstream treatment technologies. Provide backup for key equipment (e.g., pumps, membrane systems). Implement online monitoring and automatic control of core water quality parameters.

  4. Economic Efficiency, Ease of O&M: Optimize process combinations to reduce capital and operating costs while meeting water quality requirements. The system design should facilitate operation, maintenance, and repair.

• Planning Scope: This plan covers the full process from source collection and pretreatment → core purification treatment → quality-based water distribution and conveyance → reuse system monitoring and chemical stabilization.

II. Full-Process Technical Planning Scheme

2.1 Process Selection and Route

Addressing the characteristics of high standards and large volumes for power plant reclaimed water reuse, the classic process route of "Enhanced Pretreatment + Dual-Membrane (UF+RO) Core Purification + Quality-Based Reuse + Intelligent Monitoring" is recommended. This route produces high-quality water, offers high system automation, and stable operation, making it the mainstream choice for large-scale power plant water reuse domestically and internationally.

2.2 Full-Process Flow Diagram and Explanation

Step-by-Step Process Explanation:

Step One: Equalization & Pretreatment Unit

1. Purpose: Homogenize water quality and quantity. Remove large particles, suspended solids, colloids, partial hardness, organics, and residual chlorine to provide stable, qualified feed water for subsequent membrane systems.

2. Key Units:

   • Equalization Tank: Buffers inflow fluctuations. Cooling equipment may be included to control temperature.

   • High-Rate Clarifier: Performs chemical softening, coagulation, and sedimentation by dosing lime, soda ash, coagulants, and flocculants. Efficiently removes hardness, turbidity, phosphorus, and some organics.

   • Dual Media Filtration: Multi-Media Filter (quartz sand, anthracite) further removes suspended solids. Activated Carbon Filter adsorbs residual organics, color, and oxidants (e.g., residual chlorine) to protect RO membranes.

Step Two: Core Advanced Treatment Unit (Dual Membrane)

1. Self-Cleaning Filter + Ultrafiltration (UF) System:

   • Function: Serves as precise pretreatment for RO. UF can remove nearly 100% of colloids, bacteria, viruses, and macromolecular organics, ensuring effluent SDI₁₅ < 3 and turbidity <0.2 NTU. It is the "guardian" for the long-term stable operation of the RO system.

2. Primary Reverse Osmosis (RO) System:

   • Function: Core desalination unit. Removes over 97% of dissolved salts, ions, small organic molecules, silica, etc. Permeate quality (conductivity typically <50 µS/cm) can meet requirements for cooling tower makeup and some industrial process water.

3. Secondary Reverse Osmosis (RO) System (Optional):

   • Function: Provides polishing desalination of primary RO permeate. Permeate conductivity can be reduced to <5 µS/cm, meeting raw water requirements for high-pressure boiler feedwater or higher-standard process water.

Step Three: Quality-Based Distribution and Concentrate Treatment Unit

1. Quality-Based Distribution:

   • High-Standard Line: Secondary RO permeate (or primary RO permeate) undergoes further purification via Electrodeionization (EDI) or a Mixed Bed, producing water with resistivity up to 5-18 MΩ·cm, suitable directly as boiler feedwater.

   • Standard Line: Primary RO permeate enters the reuse water tank. After stabilization treatment with scale/corrosion inhibitors and biocides, it is pumped to the circulating cooling water system.

   • Lower-Standard Line: Pretreated effluent or a portion of primary RO permeate, after simple disinfection, is used for applications with lower water quality requirements.

2. Concentrate Treatment: Concentrate from the RO system (approx. 25-40% of feed) is high in salinity and requires specialized treatment. A process like "Advanced Oxidation Pretreatment + Evaporation/Crystallization" can be used to achieve Zero Liquid Discharge (ZLD), with crystalline salts disposed of off-site.

Step Four: Intelligent Monitoring & Chemical Dosing Unit

• Plant-Wide DCS/PLC Control: Enables fully automated monitoring and interlocking control from water intake to reuse.

• Online Instruments: Online analyzers (pH, conductivity, turbidity, hardness, ORP, residual chlorine, TOC, etc.) are installed at key points for real-time water quality feedback.

• Fully Automatic Chemical Dosing: Automatically and precisely doses coagulants, antiscalants, reducing agents, biocides, etc., based on online instrument signals and flow rates, ensuring stable system operation.

III. Key Design Parameters and Economic Analysis

3.1 Main Unit Design Parameters (Example: 1000 m³/h Reuse Capacity)

3.2 Economic Analysis

• Capital Cost Estimate: Capital cost per unit flow is approximately 8,000 - 15,000 RMB/(m³/h). Total investment for a 1000 m³/h system is about 80-150 million RMB. Membrane systems, evaporation/crystallization systems, and automation control systems account for a significant portion.

• Operating Cost: 2.5 - 4.5 RMB per cubic meter of product water.

  • Power Consumption: 1.0-1.8 RMB/m³ (high-pressure pumps, blowers, etc.)

  • Chemicals: 0.5-1.0 RMB/m³

  • Membrane Replacement: 0.5-1.0 RMB/m³

  • Evaporation/Crystallization Energy: 0.5-1.0 RMB/m³ (allocated to concentrate treatment)

  • Labor & Maintenance: 0.3-0.7 RMB/m³

• Benefit Analysis:

  • Water Savings: Based on 1000 m³/h, annual freshwater savings are approximately 8 million tons, leading to significant water cost savings.

  • Environmental & Social Benefits: Drastically reduces wastewater discharge, enhances corporate social image, and aligns with policy direction.

  • Investment Payback Period: Typically 3-8 years, depending on local water/electricity prices and reuse rate.

IV. Implementation Recommendations and Conclusion

1. Source Water Quality is Fundamental: Conduct at least one full year of water quality monitoring on the intended reuse source to obtain comprehensive, accurate design data.

2. Robust Pretreatment is Key: The success of pretreatment directly determines the lifespan and operating costs of the UF and RO systems and must be prioritized.

3. Modularity and Phased Construction: Adopt modular design for membrane systems, reuse water tanks, etc., allowing for phased construction and commissioning aligned with plant water demand growth.

4. Professional Operation & Maintenance: Recommend entrusting operation to an experienced third party or establishing an in-house professional team. Develop comprehensive preventive maintenance, chemical cleaning, and membrane replacement protocols.

Conclusion: This full-process planning scheme provides a technically reliable and economically viable path for reclaimed water reuse in the power industry. Through the system integration of "Enhanced Pretreatment + Dual Membrane + Quality-Based Reuse + Intelligent Monitoring," it not only enables highly efficient water resource recycling, effectively reducing plant water consumption and discharge, but also enhances the plant's operational economics and environmental performance. It is a vital component in building "Green Power Plants" and "Smart Power Plants."