Spray tower

▍ Working principle

Its working principle is based on a mass transfer process involving full contact between the gas and liquid phases, with the core being the capture and absorption of pollutants by the scrubbing liquid.

1. Waste Gas Introduction: Acidic or dust-laden waste gas, powered by a fan, enters the tower tangentially or axially through the inlet at the bottom of the tower.

2. Flow Equalization and Preliminary Purification: The waste gas first passes through an airflow distribution plate, ensuring uniform distribution across the cross-section of the tower, preparing it for sufficient contact with the scrubbing liquid. Some larger particles are initially removed due to inertial collisions with the tower walls or liquid surface.

3. Reverse Spray Absorption (Core Component):

● A circulating water pump pumps the scrubbing liquid (water or specific chemical agents, such as NaOH solution for acid removal) from the storage tank at the bottom of the tower to the spray system at the top of the tower.

● The scrubbing liquid is efficiently atomized through several layers of spiral nozzles, forming a dense curtain of extremely fine droplets.

● As the exhaust gas flows counter-currently upwards through these droplet curtains within the tower, the gas and liquid phases come into intense contact:

● Inertial collision and interception: Particulate matter in the exhaust gas collides with the droplets due to inertia and is captured and intercepted.

● Absorption and neutralization: Acidic or alkaline gaseous pollutants (such as HCl, SO₂) are absorbed by the alkaline or acidic solution and undergo a neutralization reaction, producing harmless salts that dissolve in water.

● Reaction example: HCl + NaOH → NaCl + H₂O

4. Demisting and dehydration: The washed, humid gas rises to the demister at the top of the tower (usually a PP grid, swirl plate, or packed bed). The demister effectively separates the tiny liquid droplets entrained in the gas through changes in airflow direction, collisions, and centrifugal forces, preventing liquid from being carried out of the tower and protecting the downstream fans and pipelines. The dry, clean gas is finally discharged through the outlet.

5. Liquid Circulation and Discharge: After capturing pollutants, the washing liquid falls into the storage tank at the bottom of the tower due to its own weight. It is then pumped back by a circulating water pump for spraying, forming a cycle. When the concentration of pollutants in the washing liquid (such as salt content and pH value) reaches the set limit, the waste liquid is discharged to the sewage treatment system through automatic or manual control, and fresh washing liquid is added.

▍ Structural features

1. Vertical tower body made of PP material:

● Comprehensive corrosion resistance: PP material has excellent corrosion resistance to inorganic acids, alkalis and salt solutions, fundamentally solving the problem of easy corrosion and short lifespan of metal equipment.

● Lightweight and high-strength: The equipment is lightweight, making it easy to transport, install and hoist, and requiring minimal foundation support.

● Highly processable: It can be formed by welding PP sheets, has good sealing performance, and can be flexibly designed according to requirements.

2.High-efficiency sprinkler system:

● It uses a spiral nozzle, which has a large spray angle (usually 120°), provides comprehensive coverage, has good atomization effect, and is not easy to clog.

● The spray pipeline adopts a multi-layer design (usually 2-3 layers) to ensure that the washing liquid can completely cover the entire cross-section of the tower body, with no dead corners.

3. Packing layer (optional):

● Many traditional spray towers use PP material packing (such as multi-faceted hollow spheres or stepped rings) between the spray layers.

● Function: It greatly increases the gas-liquid contact area and contact time, improving mass transfer efficiency, especially significantly enhancing the absorption efficiency of gaseous pollutants.

4. Defogging device:

● Standard configuration includes a demister to ensure efficient gas-liquid separation and prevent mist entrainment.

5. Storage Tank and Circulation System:

● The bottom of the tower is an integrated storage tank, saving space.

● Equipped with a corrosion-resistant centrifugal pump, level gauge, valves, and an automatic pH monitoring and dosing system (optional) for automated operation.

6. Manholes and Viewing Windows:

● Multiple manholes are located on the side of the tower for easy access for maintenance and replacement of nozzles and packing.

● Equipped with a transparent PP viewing window for real-time observation of the spraying process and packing status.

▍ Core advantages

● High corrosion resistance: Constructed entirely of PP material, suitable for treating various corrosive waste gases, with a long service life (typically 8-15 years) and extremely low maintenance costs.

● High dust and gas removal efficiency: Highly efficient at removing particulate matter (especially micron-sized dust) and easily soluble gaseous pollutants.

● Mature technology and stable operation: As a classic technology, its design principles are mature, its operational reliability is high, and it is simple to operate and easy to manage.

● Low investment and operating costs: The equipment cost is relatively low, the washing liquid can be recycled, water consumption is low, and the main operating cost is the electricity consumption of the water pump and fan, making it economical.

● Flexible application: Different pollutants can be addressed by adjusting the composition of the washing liquid (e.g., adding NaOH, NaClO, H₂SO₄, etc.), making it widely adaptable.

▍ Scope of application

Traditional PP vertical spray towers are widely used in applications requiring the treatment of corrosive waste gases, particulate matter, and soluble gaseous pollutants:

● Chemical Industry: Acidic or alkaline waste gases such as hydrogen chloride, hydrogen fluoride, chlorine, nitrogen oxides, and ammonia generated during pesticide, dye, fertilizer, and pharmaceutical production.

● Electronics and Electroplating Industry: Sulfuric acid, hydrochloric acid, nitric acid, and chromic acid mist generated during semiconductor manufacturing, PCB etching, pickling, and electroplating processes.

● Metal Processing Industry: Acid mist and dust generated during aluminum profile oxidation, steel pickling, and stainless steel polishing.

● Laboratory Ventilation: Complex mixed waste gases emitted from fume hoods in university, research institution, and corporate laboratories.

● Waste Gas Pretreatment: As a pretreatment unit for incinerators (RTO/RCO), plasma, and photocatalytic oxidation equipment, used for cooling, dust removal, and removal of harmful components (such as sulfur and chlorine) that could poison the catalyst.

● Other applications: Garbage station deodorization (using alkaline spray to remove H₂S, and acid spray to remove NH₃), food processing, textile printing and dyeing, etc.

Limitations:

● Very low efficiency in treating VOCs (volatile organic compounds) that are insoluble in water or poorly soluble in detergents.

● Handling sticky dust (such as paint mist) can easily cause nozzle and packing blockage, requiring pretreatment measures such as pre-filtering.

● Anti-freezing measures for the equipment need to be considered in cold northern regions.