Entrusting Party: Ningbo Dabo Semiconductor Co., Ltd.

1. Project Overview

2. Pollutant Analysis and Hazards

2.1 Main Pollutants

2.2 Formation and Hazards of Pollutants

2.2.1 Hazards to Human Health

2.2.2 Production Safety and Quality Risks

2.2.3 Ecological Environmental Impacts

3. Design Basis and Principles

3.1 Design Basis

• Environmental Protection Law of the People's Republic of China (Revised in 2015)

• Atmospheric Pollution Prevention and Control Law of the People's Republic of China (Revised in 2018)

• GB 16297-1996 Comprehensive Emission Standard of Air Pollutants

• GBZ 2.1-2019 Occupational Exposure Limits for Hazardous Factors in Workplace Part 1: Chemical Hazardous Factors

• GB 3095-2012 Ambient Air Quality Standards

• HJ/T 387-2007 Industrial Waste Gas Adsorption Purification Device

• HJ/T 477-2009 Flue Gas Wet Desulfurization Equipment

• GB 30799-2014 Emission Standard of Pollutants for Electronic Industry

• GB 50243-2016 Code for Acceptance of Construction Quality of Ventilation and Air Conditioning Engineering

• GB 50235-2010 Code for Construction and Acceptance of Industrial Pipeline Engineering

• Electrical industry national standards: GB 50054-2011 Code for Design of Low Voltage Power Distribution

• GB 50034-2013 Standard for Lighting Design of Buildings

• Special technical guidelines for waste gas treatment in semiconductor industry

• On-site survey data and production requirements of Ningbo Dabo Semiconductor

• Mature cases and technical data of acid mist treatment in domestic and foreign semiconductor enterprises

3.2 Design Principles

• Accurate Compliance Principle: The treated acid mist waste gas shall strictly comply with GB 30799-2014 Emission Standard of Pollutants for Electronic Industry, in which fluoride (calculated by F) ≤3mg/m³, hydrogen chloride ≤10mg/m³, sulfuric acid mist ≤4mg/m³, meeting the clean production requirements of the semiconductor industry.

• Classified Treatment Principle: According to the acid mist composition difference of different processes, the mode of "classified collection + graded treatment" is adopted. Hydrofluoric acid mist is collected and treated independently, and mixed acid mist is centrally purified to balance treatment efficiency and economy.

• Safety Adaptation Principle: Equipment and pipelines are made of acid corrosion-resistant materials, equipped with acid mist online concentration monitoring, emergency spray and automatic alarm systems to adapt to the clean and continuous production rhythm of semiconductor workshops without affecting production stability.

• Green and High-efficiency Principle: High-efficiency absorption technology is selected to improve acid liquid recycling rate; the water circulation system is optimized to reduce wastewater output; the equipment features low energy consumption and convenient operation and maintenance, conforming to the enterprise’s concept of energy saving and green production.

4. Design Objectives

1. The purification efficiency of acid mist waste gas is ≥99%. After treatment, fluoride (calculated by F) ≤3mg/m³, hydrogen chloride ≤10mg/m³, sulfuric acid mist ≤4mg/m³, nitric acid mist ≤5mg/m³, all complying with GB 30799-2014 and local environmental protection requirements.

2. A special exhaust funnel with a height of no less than 15 meters shall be built with standard sampling ports and online monitoring platforms to ensure sufficient high-altitude diffusion of purified waste gas and eliminate impacts on the surrounding environment.

3. The acid mist concentration at each operation point in the production workshop shall be controlled within the limit of GBZ 2.1-2019, including hydrofluoric acid ≤0.5mg/m³, hydrochloric acid ≤7.5mg/m³, sulfuric acid ≤1mg/m³, so as to completely eliminate pungent odor and improve the clean operating environment.

4. The system realizes automatic operation and intelligent monitoring with functions of over-standard alarm, equipment fault early warning and emergency disposal. The annual stable operation time is ≥8500 hours to adapt to the continuous production demand of semiconductor workshops.
   
   

   

5. Process Design and Description of Acid Mist Waste Gas Treatment

5.1 Process Selection Basis

• Targeted and thorough purification: Hydrofluoric acid mist adopts the dual mechanism of sodium hydroxide absorption and calcium chloride capture. Sodium fluoride is generated through acid-base neutralization, and insoluble calcium fluoride is formed via calcium salt reaction to avoid secondary pollution. Mixed acid mist is treated by multi-stage alkaline spraying and neutralization to ensure complete absorption of different acid components.

• Corrosion resistance adaptation: The main equipment is made of PVDF (Polyvinylidene Fluoride), and pipelines are made of FRPP (Fiber Reinforced Polypropylene), which can resist high-concentration acid mist corrosion and meet the strict environmental requirements of semiconductor workshops.

• Stable and reliable operation: The system is equipped with automatic liquid level control and pH adjustment devices. The dosage of chemicals can be automatically adjusted according to acid mist concentration to adapt to production load fluctuation and ensure stable treatment effect.

• Outstanding environmental performance: The absorption liquid is recycled. The regularly discharged wastewater has low fluoride ion concentration for convenient subsequent treatment. The collected calcium fluoride sediment is disposed of in compliance with regulations to realize pollutant reduction.

5.2 Process Flow Chart

5.2.1 Hydrofluoric Acid Mist Treatment Flow

5.2.2 Mixed Acid Mist Treatment Flow

5.2.3 Supporting System

5.3 Detailed Process Description

1. Accurate classified collection: Independent collection systems are set for acid mist from different processes. Closed hoods linked with epitaxial furnaces are adopted at etching stations to ensure no leakage of hydrofluoric acid mist. Side-absorption clean gas collecting hoods are installed at cleaning stations with wind speed controlled at 0.8-1.2m/s to avoid affecting workshop cleanliness. All gas collecting hoods are equipped with PP deflectors to reduce acid mist residue.

2. Pretreatment and impurity removal: Hydrofluoric acid mist firstly enters the pre-filter, where PVDF filter membrane removes entrained silicon powder particles to prevent pipeline blockage and tower packing scaling. Mixed acid mist is transported through anti-static pipelines to eliminate static risk caused by dust accumulation.

3. Core absorption and purification: ① For hydrofluoric acid mist: In the primary alkali absorption tower, 10% sodium hydroxide solution reacts with hydrofluoric acid to generate sodium fluoride with absorption efficiency up to 95%. Calcium chloride solution is added in the secondary fluoride capture tower to convert sodium fluoride into calcium fluoride sediment for further fluoride reduction. ② For mixed acid mist: Sodium carbonate solution is adopted in the primary alkaline spray tower to absorb hydrochloric acid mist and nitric acid mist to generate soluble salts. The secondary neutralization spray tower adjusts pH value to 6-7 for thorough neutralization of residual acid mist.

4. Defogging and discharge: The purified gas passes through a high-efficiency baffle demister to remove entrained liquid droplets (demisting efficiency ≥99%), then is lifted to a 15-meter-high exhaust funnel by anti-corrosion induced draft fan for discharge. Online monitoring equipment for fluoride and hydrogen chloride is installed on the exhaust funnel, with data uploaded to the enterprise central control room and environmental protection department platform in real time.

5. Wastewater and residue disposal: The circulating absorption liquid is tested regularly. When the fluoride ion concentration exceeds the standard, the wastewater is discharged into the collection tank and treated by chemical dosing and sedimentation before standard discharge. The calcium fluoride sediment generated by the hydrofluoric acid treatment system is dewatered and recycled by qualified institutions to realize standardized solid waste management.