Seawater Desalination Equipment

Seawater desalination equipment refers to specialized systems designed to convert high-salinity seawater (with a salt content typically ranging from 35,000 to 45,000 mg/L) into fresh water that meets standards for domestic drinking, industrial production (e.g., power plant make-up water, chemical process water), or agricultural irrigation. Its core objective is to remove dissolved salts, heavy metal ions, microorganisms, and suspended impurities from seawater through physical, chemical, or physicochemical means. This addresses the "freshwater shortage" in scenarios such as coastal areas, islands, and ocean-going vessels, making it a key technological equipment for alleviating the global water crisis.

Such equipment must cope with the "high salinity, high corrosiveness, and high biological activity" of seawater (e.g., seawater contains chloride ions that easily corrode metals, and algae/shellfish that can cause equipment blockages). Therefore, strict requirements are imposed on material selection (e.g., corrosion-resistant alloys, fiberglass-reinforced plastic), anti-pollution design (e.g., anti-biofouling), and energy consumption optimization. Additionally, technical solutions must be flexibly configured based on desalination scale (small islands process dozens of tons per day, while large-scale plants process hundreds of thousands of tons per day) and fresh water use (drinking/industrial purposes).

Mainstream Seawater Desalination Technologies and Core Equipment

In the global seawater desalination market, three mainstream technologies dominate: reverse osmosis (RO), distillation (including multi-effect distillation [MED] and multi-stage flash [MSF] distillation), and electrodialysis (ED/EDR). The principles, structures, and characteristics of the equipment corresponding to each technology differ significantly:

1. Reverse Osmosis (RO) Seawater Desalination Equipment – Most Widely Used (Accounting for Over 60% of Applications)

Core Principle

It leverages the "sieving effect" of semipermeable reverse osmosis membranes: under high pressure (typically 5.5–8.0 MPa, required to overcome seawater osmotic pressure), water molecules in seawater can pass through the membrane pores, while dissolved salts (e.g., Na⁺, Cl⁻), colloids, microorganisms, and organic matter are retained by the membrane. Ultimately, fresh water is produced with a desalination rate of over 99.5%.

Core Equipment Composition

• Pretreatment System: Addresses seawater-induced pollution of RO membranes and is critical for stable equipment operation

  • Mechanical filtration (quartz sand filters, precision filters): Removes sediment and suspended particles (particle size > 5 μm) from seawater to prevent membrane surface scratches;
  • Ultrafiltration (UF) equipment: Traps colloids, algae, and microorganisms (e.g., seaweed, bacteria) to avoid membrane pore blockages;
  • Scale prevention/inhibition treatment: Adds scale inhibitors (e.g., organophosphonates) or uses electromagnetic scale inhibitors to prevent calcium and magnesium ions in seawater from forming calcium carbonate and calcium sulfate scales on the membrane surface;
  • Disinfection equipment (sodium hypochlorite generators, UV sterilizers): Kills microorganisms in seawater to prevent biofilm adhesion on the membrane surface (biofouling is one of the main causes of RO membrane failure).

• Core Desalination Unit:

  • High-pressure pump: Provides sufficient pressure for seawater (adjusted based on seawater salinity; higher pressure is required for high-salinity seawater). It is the core of system energy consumption, accounting for 60%–70% of the total energy consumption of the RO system;
  • Reverse osmosis membrane modules: Mostly adopt "spiral-wound membranes" (large surface area, high desalination rate) made of aromatic polyamide (resistant to seawater corrosion and stable in desalination rate). Multiple membrane modules are usually connected in series/parallel to increase water production;
  • Energy recovery device (ERD): Recovers residual pressure from concentrated brine (high-salinity seawater that does not pass through the membrane) to reduce the energy consumption of the high-pressure pump (saving 30%–50% of energy, and is a standard component of modern RO equipment).

• Post-treatment System:

  • Degassing device: Removes residual carbon dioxide (CO₂) from desalinated water to prevent acidic water quality;
  • Mineral adjustment: Adds an appropriate amount of calcium and magnesium ions to fresh water (e.g., via limestone filter tanks) to improve taste (for drinking scenarios) or prevent pipeline corrosion (for industrial scenarios);
  • Disinfection equipment (UV or ozone): Kills residual microorganisms in desalinated water to ensure compliance with the National Standard for Drinking Water Quality (GB 5749-2022).

2. Distillation Seawater Desalination Equipment – Suitable for Large-Scale Industrial/Energy Linkage Scenarios

Distillation is based on the physical process of "seawater heating and vaporization → steam condensation → fresh water". It has strong anti-pollution capabilities (not affected by seawater turbidity or microorganisms) but high energy consumption. It is mostly used in scenarios with "waste heat available" such as power plants and chemical plants.

(1) Multi-Effect Distillation (MED) Equipment

• Principle: Seawater is sequentially fed into multiple series-connected "evaporation chambers". The steam generated by evaporation in the previous effect (low temperature and low pressure) serves as the heat source for the next effect, enabling seawater in the next effect to evaporate at a lower temperature. This achieves "cascaded heat utilization" and reduces energy consumption (saving over 60% of energy compared to single-effect distillation).

• Core Equipment:

  • Evaporation tube bundles/plate evaporators: Seawater flows inside tubes or between plates, and is heated to evaporate and generate steam;
  • Condensers: Condense the steam from the last effect into fresh water;
  • Brine circulation pumps: Drive concentrated brine to circulate between effects and control seawater concentration (to avoid salt crystallization and blockages).

• Applicable Scenarios: Large coastal power plants (utilizing power generation waste heat) and industrial parks (with a daily processing capacity of over 10,000 tons). The fresh water can be directly used as boiler make-up water or industrial water.

(2) Multi-Stage Flash (MSF) Distillation Equipment

• Principle: Seawater heated to a certain temperature (90–120℃) is sequentially introduced into "flash chambers" with decreasing pressure levels. Under low pressure, seawater undergoes rapid "flash evaporation" (instant vaporization), and the generated steam is condensed into fresh water, while concentrated brine is discharged from the system.

• Core Equipment:

  • Heating furnace: Preheats seawater to the required temperature (accounts for high energy consumption, approximately 70% of the total system energy consumption);
  • Flash chambers (multiple series-connected): Control the pressure gradient in each chamber to achieve continuous flash evaporation;
  • Heat recovery units: Utilize steam generated by flash evaporation to preheat raw seawater and recover heat.

• Characteristics: Mature technology and extremely strong anti-pollution capabilities (can treat high-turbidity or oil-contaminated seawater), but its energy consumption is higher than that of MED and RO. Currently, it is mainly used in large-scale desalination plants in regions with high energy costs such as the Middle East.

3. Electrodialysis (ED/EDR) Seawater Desalination Equipment – Suitable for Small-Scale/Brackish Water Scenarios

Core Principle

It utilizes the "selective permeability" of ion exchange membranes: under the action of an electric field, cations (e.g., Na⁺, Ca²⁺) in seawater move toward the cathode and pass through cation exchange membranes, while anions (e.g., Cl⁻, SO₄²⁻) move toward the anode and pass through anion exchange membranes. Eventually, low-salinity fresh water is formed in the "freshwater compartments", and high-salinity concentrated brine is collected in the "brine compartments". EDR (electrodialysis reversal) is an improved version that can automatically clean fouling on the membrane surface by periodically reversing the electric field, enhancing anti-pollution capabilities.

Core Equipment

• Ion exchange membranes (cation exchange membranes/anion exchange membranes): Key consumables that must be resistant to seawater corrosion and have high ion selectivity;
• Electrodes and electrode compartments: Provide an electric field, usually using ruthenium-coated titanium electrodes (resistant to chlorine corrosion);
• Membrane stack: Composed of multiple alternating "freshwater compartment – brine compartment – ion exchange membrane" units, and is the core unit for desalination.

Applicable Scenarios

• Small-scale fresh water demand (e.g., island residents' water use, ocean-going vessels) with a daily processing capacity of 10–500 tons;
• Brackish water desalination (salt content: 5,000–20,000 mg/L, lower than that of seawater) with energy consumption lower than that of RO (only 0.5–2.0 kWh per cubic meter of fresh water).