Solution

Exhaust Gas Treatment Solutions by Industry

Industrial exhaust gas composition varies dramatically by process, chemical input, and operating temperature. A generic “scrubber” approach rarely delivers optimal results. XICHENG engineers each system based on a detailed gas-phase analysis — pollutant identification, inlet concentration (mg/Nm³), gas temperature, humidity, particulate loading, and emission limits per your local regulations.

Below we detail the most common industrial scenarios we solve, the underlying treatment chemistry, and our recommended system configurations.

1. Chemical & Petrochemical

Typical Pollutants

HCl (hydrogen chloride), SO2 (sulfur dioxide), H2S (hydrogen sulfide), Cl2 (chlorine), NH3 (ammonia), HF (hydrogen fluoride), and mixed VOCs from reactor vents, distillation columns, storage tank breathing losses, and flaring operations.

Treatment Approach

Chemical absorption is the primary mechanism. Acid gases (HCl, SO2, HF) are absorbed by alkaline scrubbing solutions (NaOH, Ca(OH)2, or Na2CO3) in a counter-current packed bed. H2S removal often uses oxidative scrubbing with NaOCl or chelated iron catalysts. For mixed acid-alkali streams, we design multi-stage towers — Stage 1 targets acid gases with alkaline media, Stage 2 targets NH3 with acidic media (H2SO4), and Stage 3 provides activated carbon polishing for residual VOCs.

XICHENG Configuration

• Tower type: Vertical counter-current packed bed, PP or FRP body, 2-3 stages
• Packing: High-surface-area PP pall rings or structured packing, 1.5-3.0 m bed depth per stage
• Liquid distribution: Full-cone PP spray nozzles, L/G ratio 2-5 L/m³
• Mist elimination: Chevron-type PP demister with 99% removal of droplets >10 μm
• Instrumentation: pH-controlled chemical dosing with automatic makeup, differential pressure monitoring
• Capacity: 50-215,000 m³/h, removal efficiency >95% for acid gases

2. Electronics & Semiconductor

Typical Pollutants

HF from wafer etching and quartz cleaning, HCl from CVD chamber cleaning, SiH4 (silane) and TEOS from PECVD processes, NH3 from nitridation, and organic solvent vapors (PGMEA, acetone, IPA) from photolithography.

Treatment Approach

Semiconductor exhaust demands ultra-high removal efficiency and particulate-free output. HF is highly corrosive and requires PP or PPS construction — standard FRP resins degrade in concentrated HF environments. The scrubber must handle variable flows as process tools cycle on/off, so we incorporate VFD-driven fans and variable-speed recirculation pumps. For pyrophoric gases (silane), a dedicated burn/wet scrubber with thermal decomposition followed by packed bed absorption is used.

XICHENG Configuration

• Material: PP or PPS (polyphenylene sulfide) — HF-resistant, low-leach, flame-retardant UL 94 V-0
• Multi-point extraction: Individual tool connections with isolation dampers
• Water quality: UPW (ultra-pure water) compatible recirculation system to prevent ionic contamination
• Post-treatment: HEPA H14 filter housing after scrubber for cleanroom return air compliance
• Monitoring: Continuous HF and HCl sensors with auto-shutdown interlock

3. Pharmaceutical & Laboratory

Typical Pollutants

Formaldehyde, dichloromethane, chloroform, methanol, acetonitrile, and trace API (active pharmaceutical ingredient) dust from R&D labs, pilot plants, and full-scale synthesis suites. Biological safety level (BSL) labs add bioaerosol concerns.

Treatment Approach

Pharmaceutical exhaust requires VOC capture efficiency above 95% with regulatory documentation. For solvent-laden streams, we combine condensation recovery (shell-and-tube condenser, chilled water or glycol) with activated carbon adsorption for the non-condensable fraction. For formaldehyde specifically, a water scrubber with sodium bisulfite (NaHSO3) addition achieves >98% removal by forming water-soluble hydroxymethanesulfonate.

XICHENG Configuration

• Fume hood integration: VAV (variable air volume) control, ASHRAE 110 / EN 14175 compliant face velocity
• Ductwork: PP or stainless steel, welded joints, negative pressure throughout
• Treatment train: Acid scrubber → water scrubber with NaHSO3 → activated carbon bed (2 vessels, lead-lag configuration)
• Carbon monitoring: Breakthrough detection via PID sensor, automatic switchover
• Documentation: IQ/OQ/PQ validation packages available

4. Electroplating & Surface Treatment

Typical Pollutants

Chromic acid (CrO3) mist from hard chrome plating, sulfuric acid mist from anodizing and pickling, HCl fumes from acid dipping, HNO3 fumes from bright dipping and passivation, and cyanide-containing mists from cyanide-based plating baths (zinc, copper, cadmium).

Treatment Approach

Chromic acid mist requires high-efficiency mesh pad mist eliminators in addition to packed bed scrubbing — hexavalent chromium (Cr6+) is both highly toxic and subject to strict emission limits (typically <0.05 mg/m³). The scrubber uses a reducing agent (sodium metabisulfite or ferrous sulfate) to convert Cr6+ to Cr3+, which precipitates as hydroxide. Cyanide mists require hypochlorite oxidation at pH >10.5 to convert CN- to cyanate (CNO-) and then to CO2 + N2.

XICHENG Configuration

• Tank covers: Custom PP lip exhaust hoods for each plating tank, with manual or pneumatic lids
• Ductwork: PP round duct, sized for 0.3-0.5 m/s capture velocity at tank surface
• Scrubber: Single or dual-stage PP packed bed with chemical injection skid (reducing + oxidizing agents)
• Mist elimination: Two-stage — mesh pad + chevron demister, total droplet removal >99.5%
• Wastewater: Integrated neutralization tank with pH control before discharge

5. Steel & Metallurgy

Typical Pollutants

SO2 from sintering and blast furnace operations, NOx from combustion and reheating furnaces, heavy metal fumes (Zn, Pb, Cd) from galvanizing and smelting, HCl and iron oxide particulates from pickling lines, and CO from incomplete combustion.

Treatment Approach

Steel mill exhaust is characterized by high temperature (150-400°C), high particulate loading, and large gas volumes. We typically deploy a Venturi pre-scrubber for simultaneous particulate removal (>10 μm) and gas quenching, followed by a counter-current packed bed absorber for SO2 and HCl removal. For NOx control, selective non-catalytic reduction (SNCR) with urea or ammonia injection or wet scrubbing with H2O2 or NaOCl + NaOH is applied depending on inlet NOx concentration and required removal rate.

XICHENG Configuration

• Pre-treatment: Venturi scrubber with adjustable throat, ΔP 50-150 mm H2O, quench + dust removal
• Main scrubber: FRP construction, high-temperature vinyl ester resin, 2-3 packing stages
• Chemical system: Lime slurry or NaOH, automated pH control, solids settling tank with sludge removal
• Stack: FRP self-supporting stack with sampling ports at regulatory heights (15-60 m typical)
• CEM: Continuous emission monitoring for SO2, NOx, O2, and particulates per local permit requirements

6. Battery & Energy

Typical Pollutants

NMP (N-methyl-2-pyrrolidone) vapor from cathode coating lines, HF from electrolyte (LiPF6) decomposition, organic carbonates (DMC, EMC, EC) from electrolyte filling, and cobalt/nickel/manganese dust from electrode material handling.

Treatment Approach

Lithium battery manufacturing has two distinct exhaust streams. The coating line exhaust contains high-concentration NMP (500-5,000 ppm) which is both expensive and a VOC — we deploy condensation recovery (water-cooled + chilled water, ~85-90% recovery) followed by activated carbon adsorption for the remainder. The formation/aging exhaust contains electrolyte vapors — a water scrubber hydrolyzes LiPF6 into HF and H3PO4, which are then neutralized by alkaline scrubbing. Electromagnetic interference (EMI) from formation equipment requires careful sensor shielding.

XICHENG Configuration

• Coating line: Condenser (shell-and-tube, 7°C chilled water) → carbon adsorber (honeycomb type, 2 vessels) → NMP recovery tank
• Formation: PP water scrubber → NaOH packed bed scrubber → demister → stack
• Material note: PP and PPS only — FRP may degrade with some electrolyte decomposition products
• Explosion protection: ATEX-rated fans and ductwork for organic carbonate vapor streams (LEL monitoring)
• Capacity: Designed per production line throughput (MWh/year basis)

7. Painting & Coating

Typical Pollutants

VOCs (toluene, xylene, ethylbenzene, MEK, MIBK, butyl acetate) from spray booth exhaust, paint overspray particulates (wet and dry), isocyanates from polyurethane curing, and styrene from gel coat application in composites manufacturing.

Treatment Approach

Paint booth exhaust combines both particulates and VOCs. The first stage is always particulate removal — either a dry filter bank (for low-volume operations) or a water wash / Venturi booth (for high-volume lines) that captures 90-99% of overspray. For VOCs, the choice depends on concentration and flow: activated carbon for low-to-medium concentrations (<1,000 mg/Nm³), RTO (regenerative thermal oxidizer) for high concentrations (>2,000 mg/Nm³) with heat recovery, or zeolite rotor concentrator + RTO for large air volumes with low VOC concentrations (<500 mg/Nm³). Isocyanates require special attention — they react with water to form inert polyurea and are best handled by high-efficiency dry filtration followed by carbon adsorption.

XICHENG Configuration

• Capture: Downdraft or side-draft booth, 0.3-0.5 m/s face velocity, automated damper control
• Particulate stage: PP water wash with coagulant dosing (paint detackification) or multi-stage dry filter (G4+F7+F9)
• VOC stage: Activated carbon adsorber (4-6 cell, honeycomb type) with steam regeneration option
• Monitoring: Continuous VOC analyzer (FID), stack flow meter, temperature sensors

8. Waste Treatment & Odor Control

Typical Pollutants

H2S, NH3, mercaptans (methyl mercaptan CH3SH), organic sulfides (dimethyl sulfide, dimethyl disulfide), volatile fatty acids (VFA), trimethylamine, and bioaerosols from wastewater treatment plants, sludge handling, composting, and solid waste transfer stations.

Treatment Approach

Odor control systems typically treat very large air volumes at low pollutant concentrations — a typical municipal WWTP odor system might handle 50,000-200,000 m³/h. Treatment selection depends on H2S load: bio-trickling filters excel for low-to-moderate H2S loads (<50 ppm), converting H2S to H2SO4 via sulfur-oxidizing bacteria (Thiobacillus). Chemical scrubbers (NaOCl + NaOH, then H2SO4 for NH3) handle higher loads and peak events. Activated carbon (impregnated with NaOH or KI) provides final polishing and handles residual mercaptans that wet scrubbers miss. For enclosed facilities, dry media biofilters using wood chips/heather/compost offer a low-energy alternative.

XICHENG Configuration

• Collection: FRP or PP odour hoods/covers over channels, inlet works, sludge tanks, and screening areas
• Treatment train: Bio-trickling filter (structured plastic media, recirculating water) → chemical scrubber (NaOCl/NaOH stage + H2SO4 stage) → carbon polisher (KI-impregnated, 2 vessels lead-lag)
• Fan: FRP centrifugal, VFD control for diurnal flow variation
• Stack: FRP, dispersion modeled per AERMOD/ADMS for local odor standards
• Monitoring: H2S and NH3 sensors, online olfactometry for odor unit (OU/m³) trending

9. Textile & Printing

Typical Pollutants

VOCs (toluene, MEK, ethyl acetate, isopropyl alcohol) from printing inks and solvents, plasticizer fumes (DOP, DINP) from PVC-coated fabrics, formaldehyde from resin finishing, and fiber dust from cutting and sewing operations.

Treatment Approach

Textile finishing exhaust is typically low-to-moderate VOC concentration with intermittent peaks as production batches change. A two-stage system combining water scrub (for water-soluble solvents like alcohols and glycols) with activated carbon (for aromatic hydrocarbons and esters) provides flexible, cost-effective treatment. For high-temperature drying exhaust (120-180°C), a waste heat recovery coil pre-heats incoming fresh air and simultaneously cools the exhaust stream before it enters the scrubber, improving absorber efficiency and reducing energy cost. Plasticizer fumes (high boiling point, >300°C) tend to condense as sticky aerosols — a high-efficiency wire mesh demister or electrostatic precipitator upstream of the scrubber prevents fouling.

XICHENG Configuration

• Heat recovery: Run-around coil or plate heat exchanger, 50-70% heat recovery efficiency
• Pre-filter: G4 panel filter or electrostatic precipitator for fiber dust and condensed aerosols
• Scrubber: PP packed bed, water + surfactant for enhanced VOC absorption
• Polisher: Activated carbon (granular, 2 vessels), 800-1200 h carbon life at design concentration
• Exhaust fan: FRP centrifugal with spark-proof construction (ATEX Zone 2)

Material Selection Guide

Choosing the right material is critical for scrubber longevity and safe operation. The wrong material can fail catastrophically within weeks.

Material	Chemical Resistance	Max Temp	Best For	Not Suitable For
PP (Polypropylene)	Excellent — HCl, H2SO4 (≤30%), HF, NaOH, most organics	100°C	General acid/alkali scrubbing, ductwork, tanks	Strong oxidizers (conc. HNO3, Cl2 gas hot), aromatics at elevated temp
PPS (Polyphenylene Sulfide)	Excellent — all PP-resistant chemicals, plus stronger oxidizers	200°C	Semiconductor HF scrubbers, high-temp acidic streams	Concentrated H2SO4 (>80%), chlorinated solvents hot
FRP (Fiberglass, Vinyl Ester)	Good — HCl, H2SO4, NaOH, Cl2 wet, most acids	120°C	Large towers, outdoor installations, high structural loads	HF (attacks glass fibers), strong alkalis hot, organic solvents
FRP (Fiberglass, Epoxy)	Good — alkalis, most salts, mild acids	100°C	Alkaline scrubbers, structural ductwork	Strong acids, oxidizing acids
SS 304	Fair — oxidizing acids (HNO3), atmospheric corrosion	400°C+	High-temperature dry exhaust, non-corrosive streams	HCl, H2SO4, Cl- (pitting corrosion), any wet acid
SS 316L	Fair — as 304 but better Cl- resistance (limited)	400°C+	Mildly corrosive, high-temp applications	HCl, HF, H2SO4 (will corrode), seawater (still vulnerable to crevice corrosion)
Halar (ECTFE) Coated SS	Outstanding — virtually all acids, alkalis, solvents	150°C	Ultra-aggressive chemical environments, boiling acids	High-velocity slurries (coating erosion), mechanical impact points

Common Gas Types & Removal Chemistry

Gas	Absorption / Removal Method	Typical Scrubbing Medium	Expected Efficiency
HCl (Hydrogen Chloride)	Chemical absorption — acid-base neutralization	NaOH 5-10% solution, or Ca(OH)2 slurry	95-99%
SO2 (Sulfur Dioxide)	Chemical absorption — forms sulfite/bisulfite	NaOH or Ca(OH)2 slurry; Na2CO3 for FGD	90-98%
HF (Hydrogen Fluoride)	Chemical absorption — forms fluoride salt	NaOH or KOH; Ca(OH)2 precipitates CaF2	95-99%
H2S (Hydrogen Sulfide)	Oxidative scrubbing or chemical absorption	NaOCl + NaOH (oxidative); chelated iron catalyst	95-99.5%
NH3 (Ammonia)	Chemical absorption — acid-base neutralization	H2SO4 5-10% solution forming (NH4)2SO4	95-99%
Cl2 (Chlorine)	Chemical absorption — reduction or alkaline scrubbing	NaOH (forms NaOCl + NaCl); or Na2S2O3	98-99.5%
NOx (Nitrogen Oxides)	Wet scrubbing — oxidation + absorption	H2O2 or NaOCl + NaOH; or urea SCR for high-temp	70-90% (wet); 85-95% (SCR)
CrO3 Mist (Chromic Acid)	Mesh pad + reducing scrubber	Na2S2O5 (sodium metabisulfite) reducing to Cr3+	99-99.9%
VOCs (General)	Adsorption — physical trapping in micropores	Activated carbon (granular or honeycomb); zeolite	90-99%
HCHO (Formaldehyde)	Chemical absorption with NaHSO3 addition	Water + NaHSO3 forming hydroxymethanesulfonate	95-98%

System Sizing Quick Reference

The scrubber diameter is primarily determined by the superficial gas velocity through the tower cross-section. For packed bed scrubbers, the design velocity is typically 1.0-2.0 m/s for random packing (PP pall rings, Raschig rings) and 1.5-3.0 m/s for structured packing.

Air Flow (m³/h)	Tower Diameter (m) — at 1.5 m/s	Typical Packing Height (m)	Recirculation Pump (m³/h)
1,000	0.5	1.5-2.0	3-5
5,000	1.1	2.0-2.5	15-25
10,000	1.5	2.0-3.0	30-50
20,000	2.2	2.5-3.0	60-100
50,000	3.4	3.0-3.5	150-250
100,000	4.9	3.0-4.0	300-500
150,000	6.0	3.5-4.5	450-750
200,000	6.9	4.0-5.0	600-1,000

This table provides preliminary sizing estimates. Final design dimensions depend on target removal efficiency, gas-liquid equilibrium data, temperature, and pressure drop constraints. Contact our engineering team for a detailed sizing calculation specific to your application.

Why Our Solutions Work

XICHENG delivers turnkey exhaust gas treatment solutions, not just equipment. What sets us apart:

• Chemistry-first design: We don’t guess at removal rates. Our engineers calculate absorption equilibria, mass transfer coefficients, and reaction kinetics for your specific gas mixture.
• Material expertise: 16 years of hands-on PP, FRP, and SS fabrication. We know what works — and what will fail — in real industrial conditions.
• Complete systems: Scrubber, pump, fan, ductwork, instrumentation, chemical dosing, and control panel — designed, fabricated, and tested as one integrated system.
• Documented performance: 2,600+ installations across 60 countries. CE × 3, ISO 9001, ISO 14001, SGS × 5 certified.
• Factory-direct value: No middleman, no reseller margin. You get the engineering quality of a premium supplier at factory pricing.

Contact our solutions team at xicheng023@outlook.com or WhatsApp for a free consultation and preliminary design.