A water treatment project for a thermal power plant in the East China
A water treatment project for a thermal power plant in the East China
A water treatment project for a thermal power plant in the East China region was commissioned in July 2021. The system produced qualified water by December 2021, and as of April 2024, the desalination rate of the entire system remains above 98%, with no significant difference compared to the initial operation. Below are the optimization examples of the reverse osmosis (RO) system and some related data.
Operating Parameters of the Primary RO System
|
Recent Operating Parameters of the Primary RO System |
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|
RO Membrane Model |
Water Temperature (°C) |
Feed Water Conductivity (µS/cm) |
Feed Water (pH) |
Product Water Flow (t/h) |
Concentrate Flow (t/h) |
Product Water Conductivity (µS/cm)
|
Inlet Pressure (Bar) |
Interstage Pressure (Bar) |
Concentrate Pressure (Bar) |
Membrane Desalination Rate (%) |
|
DA-HSRO-4040 |
25.5 |
952.3 |
7.3 |
106.4 |
37.2 |
17.2 |
10.8 |
10.3 |
9.7 |
98.2 |
|
DA-HSRO-4040 |
25.5 |
952.3 |
7.3 |
112.5 |
37.4 |
17.1 |
10.6 |
9.5 |
8.5 |
98.2 |
|
DA-HSRO-4040 |
25.5 |
952.3 |
7.3 |
110.2 |
37.5 |
18.6 |
11.2 |
10.7 |
9.9 |
98.1 |
For detailed performance parameters of the DA-HSRO-4040 membrane, please refer to:
https://www.amembrane.com/Products2/46.html
Project Overview
The water source is surface water, which is treated by coagulation and then stored in a reservoir. Initially, the system did not include online chlorine monitors for the ultrafiltration (UF) product water and RO feedwater. To prevent chlorine leakage, a small amount of sodium hypochlorite (NaClO) was added before the PCF filter, and the dosage of reducing agents was increased to maintain a very low ORP to remove residual chlorine. Although this method effectively controlled the leakage of residual chlorine, it also led to insufficient chlorine pre-treatment, resulting in severe microbial contamination.
Optimization Plan
After on-site investigation and analysis, it was decided to install an online chlorine monitor in the UF product water main and the RO feedwater main to accurately control the chlorine levels required for each process stage. The optimized process flow is as follows:
Reservoir → Chemical Feed Pump → (Sodium Hypochlorite) PCF Filter → Raw Water Heater → Raw Water Tank → UF Feed Pump → Self-Cleaning Filter → Ultrafiltration Unit → (Online Chlorine Monitor 1) UF Water Tank → Primary Feed Pump → (Antiscalant, Reducing Agent, Non-Oxidizing Biocide) → (Online Chlorine Monitor 2) Security Filter → Primary High-Pressure Pump → Primary RO Unit → Primary Product Water Tank → Brine Pump → Secondary RO Unit → Secondary Product Water Tank → EDI Feed Pump → EDI Unit → Deionized Water Tank.
Process Description
1.Reservoir: Surface river water is stored in the reservoir for use.
2.Chemical Feed Pump: Water from the reservoir is pumped to the PCF filter.
3.PCF Filter: Sodium hypochlorite is added at the inlet of the PCF filter to remove suspended solids, particulate matter, and disinfect the water.
4.Raw Water Heater: This equipment is used to heat the incoming water, possibly to improve the efficiency of subsequent treatment steps or to meet specific process requirements.
5.Raw Water Tank: Water after preliminary treatment is stored as raw water.
6.UF Feed Pump: Water from the raw water tank is pumped to the ultrafiltration unit.
7.Self-Cleaning Filter: Further removal of impurities in the water to protect the subsequent ultrafiltration unit.
8.Ultrafiltration Unit: Removal of small particles, colloids, bacteria, etc., from the water.
9.Online Chlorine Monitor 1: Initial detection of chlorine content in the water to improve the efficiency of subsequent water treatment.
10.UF Water Tank: Storage of water after ultrafiltration.
11.Primary Feed Pump: Water from the UF water tank is pumped to the primary RO unit.
12.Chemical Addition: Antiscalants, reducing agents, and non-oxidizing biocides are added before the water enters the primary RO unit.
13.Online Chlorine Monitor 2: Re-detection of chlorine content in the water to ensure it meets the requirements for subsequent treatment.
14.Security Filter: Removal of small impurities in the water to protect the high-pressure pump and RO unit.
15.Primary High-Pressure Pump: Provides sufficient pressure for the primary RO unit to operate normally.
16.Primary RO Unit: Further removal of dissolved solids, organic matter, bacteria, etc., from the water.
17.Primary Product Water Tank: Storage of water produced by the primary RO unit.
18.Brine Pump: Water from the primary product water tank is pumped to the secondary RO unit.
19.Secondary RO Unit: Enhanced removal of dissolved solids, organic matter, bacteria, etc., from the water.
20.Secondary Product Water Tank: Storage of water produced by the secondary RO unit.
21.EDI Feed Pump: Water from the secondary product water tank is pumped to the EDI unit.
22.EDI Unit (Electrodeionization): Further removal of ions from the water using an electric field and ion exchange membranes.
23.Deionized Water Tank: Final storage of deionized water after treatment by the EDI unit.
Design of the Primary RO System
1.RO Membrane Model: DA-HSRO-4040
2.High Treatment Capacity: The system is designed to achieve a capacity of 3×110 t/h.
3.Optimized Membrane Configuration: A 18:9 membrane ratio with a 6-core design.
4.High Recovery Rate: The recovery rate reaches up to 75%.
Chlorine Control Management
1.The residual chlorine in the UF product water is relatively stable. The raw water is surface water with mild pollution, and the residual chlorine is almost zero when it enters the reservoir. To prevent microbial growth in the fiber bundle (PCF) filter inlet, sodium hypochlorite (NaClO) is continuously added to increase the residual chlorine in the raw water. An online chlorine monitor is installed in the UF product water main, and the residual chlorine is controlled between 0.5 and 0.8 mg/L.
2.After the addition of reducing agents at the RO feedwater point, the online chlorine monitor continuously monitors the residual chlorine, ensuring that the chlorine index is 0 mg/L.
3.Manual re-measurement checks are performed at the timed sampling points of the online chlorine monitors to ensure the accuracy of chlorine monitoring.
4.The UF and RO systems share the same cleaning tank, cleaning pump, and some cleaning pipelines. To avoid residual chlorine in the cleaning pipelines (vertical pipes) from oxidizing the RO membrane elements, non-oxidizing biocides have been used for chemical cleaning of the UF system since the system was commissioned. Sodium hypochlorite (NaClO) has never been used for UF cleaning, effectively preventing potential damage to the RO membranes from residual chlorine in the shared cleaning pipelines.