Spray Nozzle Selection Guide for Wet Scrubbers: Types and Performance

The spray nozzle is the most critical component in a wet scrubber liquid distribution system — and the most commonly overlooked during design. Every scrubber’s performance depends on how effectively the liquid phase contacts the gas phase, and that contact happens at the nozzle. The wrong nozzle type reduces mass transfer efficiency by 20-50%, wastes recirculation pump energy through excessive pressure drop, and creates dry zones that allow untreated pollutant breakthrough. A properly selected nozzle delivers uniform liquid distribution, optimal droplet size for the mass transfer duty, reliable long-term operation without clogging, and minimum maintenance cost over the equipment life. This guide covers the complete spray nozzle selection methodology for wet scrubbers: the five main nozzle types — spiral, full cone, hollow cone, flat fan, and two-fluid — with quantified comparisons across flow range, spray angle, droplet size, free passage diameter, and clogging resistance; material selection across seven alloys and plastics with chemical compatibility data for common scrubber services; nozzle sizing using the flow rate-pressure relationship Q = k√P with a complete worked example for a 2.5 m diameter spray tower; multi-level spray system design for towers requiring staged gas-liquid contact; and practical guidance on connection types, header layout, installation quality verification, and maintenance scheduling. For an overview of scrubber types see the wet scrubber selection guide. For complete scrubber design with calculations see the scrubber design calculation guide.

Spray Nozzle Types for Wet Scrubbers

Five spray nozzle types serve the majority of wet scrubber liquid distribution duties. Each type produces a distinct spray pattern, droplet size range, and free passage diameter that determines its suitability for different scrubber configurations and liquid chemistries. The selection among them depends on the target mass transfer mechanism, the liquid properties, and the presence of suspended solids.

The free passage diameter — the largest solid particle that can pass through the nozzle without clogging — is the most important selection parameter for scrubbers handling slurry or dirty recirculated water. Spiral nozzles with 5-15 mm free passage handle limestone slurry containing particles up to 5 mm without blocking. Full cone nozzles at 3-8 mm free passage handle clean to moderately dirty water but clog rapidly when solids exceed 500 ppm. Hollow cone nozzles at 2-5 mm free passage require filtered liquid. Two-fluid nozzles at 1-3 mm free passage need the cleanest liquid of all types. The general rule: select a nozzle type whose free passage diameter is at least 3x the maximum particle size in the recirculated liquid. For FGD slurry with 2 mm maximum particle size, the nozzle must have at least 6 mm free passage — spiral nozzles are the only type that consistently meets this requirement.

Nozzle Spray Patterns and Coverage Arrangement

The spray pattern determines how the scrubbing liquid is distributed across the scrubber cross-section. Three factors govern the effectiveness of the distribution: the pattern type produced by each nozzle, the spacing between adjacent nozzles, and the arrangement pattern of the nozzle grid on the header.

Full Cone Pattern

Full cone nozzles produce a solid cone of liquid that fills the entire spray area with uniform distribution. The liquid flux — volume per unit area per unit time — is constant across the cone cross-section for a well-designed full cone nozzle. Typical spray angles range from 30 to 120 degrees. Full cone nozzles are the standard for packed bed scrubbers where the packing requires even liquid wetting across the entire bed surface without dry zones. The droplet size is relatively coarse at 500-2,000 microns SMD, which provides adequate irrigation without excessive mist generation that would overload the demister. Recommended operating pressure: 1-4 bar.

Hollow Cone Pattern

Hollow cone nozzles produce a ring-shaped spray with liquid concentrated at the outer annulus and minimal liquid in the center. Because all the liquid is accelerated to the same velocity and atomized into fine droplets (100-800 microns SMD at 2 bar), hollow cone nozzles provide more surface area per unit volume than full cone types — approximately 2-3x more at the same flow rate and pressure. The open center allows gas to pass through the spray without deflecting it, maintaining efficient countercurrent contact. Hollow cone nozzles are the default choice for spray tower scrubbers where gas absorption efficiency depends on fine droplet atomization. Recommended operating pressure: 2-5 bar.

Flat Fan Pattern

Flat fan nozzles produce a linear fan-shaped spray with a narrow included angle — typically 15-60 degrees — and uniform liquid distribution across the fan width. They are not used for primary gas-liquid contact in scrubbers. Their role is directional spray for mist eliminator washing, vessel wall cleaning, and duct flushing. In FGD scrubbers, flat fan nozzles are mounted above the chevron vane pack and angled to deliver the water wash spray across the full width of the vane bank. The narrow angle produces high-impact droplets that dislodge scale deposits from vane surfaces.

Nozzle Grid Arrangement: Triangular vs Square

When multiple nozzles are installed on a header, the spacing and arrangement of the nozzles determine whether the liquid coverage is uniform or contains dry gaps. Two standard arrangement patterns are used: square pitch and triangular pitch. In a square arrangement, nozzles are spaced at equal distances along two perpendicular axes. Square pitch is simpler to design and install but leaves larger unsprayed diamond-shaped gaps between four adjacent nozzles. In a triangular (staggered) arrangement, each row is offset by half the spacing distance, placing each nozzle equidistant from its six neighbors. Triangular pitch provides 15-30% more uniform coverage than square pitch at the same nozzle density because it eliminates the diamond gaps. The standard design practice for spray tower scrubbers is triangular pitch with nozzle spacing equal to 1.2-1.5x the individual nozzle coverage diameter, providing 30-50% overlap between adjacent spray cones. For a 2.5 m diameter tower with hollow cone nozzles covering 1.0 m diameter each, triangular spacing at 0.7 m centers requires approximately 12-16 nozzles per level arranged in 3-4 concentric rings with a center nozzle.

Multi-Level Spray Design

Spray towers requiring high removal efficiency — 99% or above for acid gases — use multiple spray levels stacked vertically in the tower shell. Each level consists of a dedicated header ring with its own nozzle array and is fed by a separate pump or a common pump with individual flow control. The number of levels is determined by the gas residence time requirement and the mass transfer coefficient of the pollutant-scrubbing liquid system.

Single-Level Spray Systems

Single-level systems are adequate for scrubbers with removal efficiency targets below 90%, for highly soluble pollutants such as HCl or NH₃ where mass transfer is rapid, or for gas cooling and quench duties where the primary objective is temperature reduction rather than mass transfer. A single level with 8-12 hollow cone nozzles at 2-4 bar provides sufficient liquid-gas contact for these duties at liquid-to-gas ratios of 2-4 L/m³. The advantage of single-level design is simplicity — one pump, one header, minimum vessel height requirement of 3-4 m above the gas inlet.

Two-Level Spray Systems

Two-level systems are the standard configuration for chemical scrubbers targeting 95-99% removal efficiency. The lower level operates at higher flow rate (60-70% of total) to provide bulk absorption and quench the incoming gas. The upper level operates at finer atomization pressure (3-5 bar versus 2-3 bar for the lower level) to polish residual pollutant concentrations. The two levels are typically spaced 1.5-2.0 m apart vertically, with the upper level nozzles staggered relative to the lower level to ensure complete gas contact. Total liquid-to-gas ratio for two-level systems: 4-7 L/m³. This configuration handles most acid gas scrubbing duties including SO₂ absorption with caustic or lime slurry.

Three-Level Spray Systems

Three-level systems are specified for FGD scrubbers in power plants burning high-sulfur coal (above 2% sulfur) where removal efficiency must exceed 99.5% to meet EPA emission limits. The lower level handles bulk SO₂ absorption, the middle level provides polishing, and the top level functions as a polishing stage that also pre-saturates the gas before the mist eliminator to prevent scaling on demister surfaces. Each level in an FGD three-level system has its own dedicated recirculation pump — typically 8,000-15,000 L/min per pump for a 5.0 m diameter tower — with the upper level pump operating at higher head to overcome the increased static height. The spacing between levels in FGD towers is 1.8-2.5 m, providing total gas contact height of 4-6 m. Total L/G ratio for three-level FGD systems: 8-15 L/m³. The nozzle count for a 5.0 m FGD tower ranges from 40-60 spiral nozzles total across three levels, with each level using a different spray angle to optimize coverage — wider angles (120-150 degrees) on lower levels, narrower angles (90-120 degrees) on upper levels where the gas has lower pollutant concentration.

Nozzle Materials for Scrubber Service

Nozzle material selection directly determines service life and maintenance cost. The wrong material causes nozzle failure from corrosion (enlarged orifice, degraded spray pattern, increased flow rate) or erosion (loss of internal geometry, reduced flow resistance, uneven spray distribution). Both failure modes reduce scrubber efficiency gradually — often undetected until a stack test failure reveals the problem.

SS316L covers approximately 65% of scrubber nozzle applications at moderate cost. Upgrade to ceramic for FGD scrubbers handling limestone slurry at 5-20% solids — an SS316L spiral nozzle in FGD service erodes and loses its spray pattern within 3-6 months, while an aluminum oxide or silicon carbide ceramic nozzle operates 3-5 years at the same conditions. The cost premium for ceramic over SS316L (2-3x) pays back within 6-12 months from avoided replacement labor and downtime. Use silicon carbide (SiC) over aluminum oxide (Al₂O₃) when the liquid contains hydrofluoric acid — Al₂O₃ reacts with HF and dissolves, while SiC is inert. Use PP or PVDF for low-temperature acid scrubbers below 80°C where the cost of metal alloys is not justified. Use Hastelloy C276 for wet chlorine gas scrubbers, concentrated HCl above 5%, or any service where pH drops below 2.0 and chlorides exceed 5,000 ppm. Use titanium for marine scrubbers handling seawater or sodium hypochlorite bleach solutions.

Nozzle Sizing and Selection

Sizing scrubber nozzles requires calculating the total recirculation flow rate from the scrubber design L/G ratio, dividing it by the number of nozzles determined by the coverage arrangement, and selecting a specific nozzle size that delivers the required flow at the available pump pressure with the target spray pattern and droplet size.

Flow Rate vs Pressure: Q = k√P

Every spray nozzle follows the same fundamental relationship between flow rate and inlet pressure: Q = k × √P, where Q is the flow rate (L/min), k is the nozzle flow coefficient specific to each nozzle design and orifice size, and P is the pressure at the nozzle inlet (bar). The exponent of 0.5 means that doubling pressure increases flow by only 41%. To achieve twice the flow, either increase pressure by 4x — which quadruples pump power consumption — or select a nozzle with a larger k-factor. The practical implication for scrubber design: the operating pressure should be selected first based on the droplet size requirement (2-4 bar for most scrubbers), and the nozzle size should then be selected to deliver the required flow at that pressure. Never design the pump around the nozzle — design the nozzle train around the pump pressure.

Droplet Size and Sauter Mean Diameter

The Sauter mean diameter (SMD or d₃₂) is the droplet size parameter used for mass transfer calculations because it preserves the volume-to-surface-area ratio of the entire spray. Smaller SMD means more interfacial area per unit volume of liquid and therefore higher mass transfer rates. The SMD decreases with increasing pressure following the relationship SMD ∝ P⁻⁰·³⁰ to P⁻⁰·⁴⁰ depending on nozzle type. For a hollow cone nozzle at 2 bar, SMD is approximately 400-600 microns. Increasing to 4 bar reduces SMD to 300-450 microns — a 25-30% reduction that increases surface area by 40-50%. The trade-off: finer droplets are more easily entrained in the gas stream, increasing mist eliminator loading. For spray tower absorption, target SMD of 200-500 microns balances mass transfer efficiency against demister carryover. For packed bed scrubbers, coarser droplets of 500-2,000 microns are adequate and preferable to minimize mist generation.

Coverage and Overlap Calculation

The coverage diameter of a single nozzle at a given height above the target zone is calculated from the spray angle: D = 2 × H × tan(θ/2), where D is the coverage diameter (m), H is the vertical distance from nozzle to target (m), and θ is the full spray angle (degrees). For a hollow cone nozzle with 90-degree spray angle mounted 1.0 m above the gas inlet zone: D = 2 × 1.0 × tan(45°) = 2.0 m coverage diameter. Standard practice requires 30-50% overlap between adjacent nozzles, meaning the effective coverage per nozzle is reduced to 50-70% of the calculated diameter. For triangular pitch arrangement, the effective spacing S = D × 0.6 to 0.7. For the 2.0 m coverage nozzle above, spacing at 0.65 × 2.0 = 1.3 m. The number of nozzles per level is approximately the tower cross-sectional area divided by the effective coverage area per nozzle, rounded up to the nearest integer that fits the triangular pattern.

Worked Example: Sizing a Spray Tower Nozzle System

Given: A spray tower scrubber handling 30,000 m³/hr of flue gas containing 800 ppm SO₂. Tower internal diameter: 2.5 m. Target removal: 98%. Scrubbing liquid: 5% caustic solution (NaOH). Design L/G ratio: 5 L/m³. Target SMD: 300-400 microns for adequate mass transfer.

Step 1: Calculate total recirculation flow rate.
Q_liquid = 30,000 m³/hr × 5 L/m³ = 150,000 L/hr = 2,500 L/min

Step 2: Select nozzle type and pressure.
Hollow cone nozzles at 3 bar provide SMD of approximately 350 microns — within the target range. K-factor for a typical 90-degree hollow cone nozzle at this condition: k = 18 L/min/√bar.

Step 3: Calculate single nozzle flow rate.
Q_nozzle = 18 × √3 = 18 × 1.73 = 31.1 L/min per nozzle

Step 4: Determine number of nozzles required.
N = 2,500 / 31.1 = 80 nozzles total

Step 5: Determine number of levels.
For 98% SO₂ removal at 5 L/m³, a two-level system is appropriate. Distribute 60% of nozzles on the lower level (48 nozzles) and 40% on the upper level (32 nozzles).

Step 6: Verify coverage for each level.
Tower area: A = π × 1.25² = 4.91 m². For 48 nozzles on the lower level in triangular pitch with 1.3 m spacing: coverage radius per nozzle = 1.0 m at 1.0 m height (90-degree angle), effective coverage per nozzle after 50% overlap = 0.5 × π × 1.0² = 1.57 m². Total coverage: 48 × 1.57 = 75.4 m² — providing 15x coverage overlap, which is excessive. Reduce to 24 nozzles on the lower level (spacing 1.3 m, 4 rings + center) and 16 on the upper level (spacing 1.6 m, 3 rings + center). Total: 40 nozzles. Recalculate Q_nozzle = 2,500 / 40 = 62.5 L/min. Required k = 62.5 / √3 = 36.1 L/min/√bar. Select a larger nozzle with k = 36.

Step 7: Verify pump pressure.
Header friction loss at 2,500 L/min in a 6-inch header: approximately 0.4 bar. Static head from pump centerline to upper level nozzles at 6 m: 0.6 bar. Strainer loss (clean): 0.2 bar. Nozzle pressure required: 3.0 bar. Total pump discharge pressure: 3.0 + 0.4 + 0.2 + 0.6 = 4.2 bar. Add 15% margin: 4.8 bar. Select pump for 2,500 L/min at 4.8 bar.

Result: Two-level spray system with 24 hollow cone nozzles (90°, k=36) on the lower level and 16 on the upper level, fed by a pump rated for 2,500 L/min at 4.8 bar. Total tower height including levels and disengagement: approximately 7-8 m. Expected SO₂ removal: 98% at design conditions.

High Pressure vs Low Pressure Nozzle Systems

The operating pressure of a scrubber nozzle system is determined by the droplet size requirement and the available pump head. Two distinct pressure ranges are used in scrubber applications, each with different equipment requirements and operating costs.

Low-pressure systems (1-4 bar) are the standard for the majority of scrubbers. At 2-4 bar, hollow cone nozzles produce SMD of 300-600 microns — adequate for most gas absorption duties. The pump power requirement is modest: for a 2,500 L/min system at 3 bar, pump power is approximately 2,500 × 3 / (600 × 0.75) ≈ 17 kW assuming 75% pump efficiency. Low-pressure nozzles are less expensive and have larger free passage diameters (3-8 mm for full cone, 5-15 mm for spiral) that resist clogging. Operating costs at 3 bar: approximately $8,000-12,000 per year per 1,000 L/min at $0.10/kWh for 8,000 hr/year operation.

High-pressure systems (6-10 bar) are used when fine atomization below 200 microns SMD is required, typically for NOx absorption, fume control, or applications where the pollutant has low solubility in the scrubbing liquid and requires maximum gas-liquid interfacial area. High-pressure nozzles produce SMD as low as 100-200 microns at 7-10 bar but have smaller free passage diameters (1-3 mm) that require liquid filtration to 200 microns or better. The pump power at 8 bar for the same 2,500 L/min flow: 2,500 × 8 / (600 × 0.75) ≈ 44 kW — 2.6x the low-pressure system. Annual energy cost: $21,000-31,000 per 1,000 L/min. Specify high-pressure systems only when the process requirement cannot be met at 4 bar. Consider a two-fluid atomizing nozzle (which uses compressed air to achieve fine atomization at lower liquid pressure) as an alternative to high-pressure liquid systems.

Two-Fluid Atomizing Nozzles

Two-fluid nozzles (also called pneumatic atomizing nozzles) use compressed air or steam to atomize the scrubbing liquid into droplets of 10-100 microns SMD — 5-10x finer than hydraulic nozzles at the same liquid pressure. The liquid is supplied at 1-4 bar while the atomizing gas is supplied at 2-6 bar. The internal mixing chamber combines the liquid and gas streams, and the gas expansion at the nozzle orifice breaks the liquid into a fine mist. Two-fluid nozzles are specified for scrubbers treating low-solubility pollutants (NOx, CO, trace organics) where maximum gas-liquid interfacial area is required, for fume control applications where the visible plume must be eliminated, and for scrubbers where the liquid flow rate is too low for effective hydraulic atomization. The trade-offs: compressed air consumption of 0.5-2.0 Nm³ per liter of liquid atomized, requiring an air compressor sized 2-3x the equivalent high-pressure pump power; smaller free passage (1-3 mm) requiring filtration to 200 microns; and higher maintenance from the additional compressed air system components. Typical application: pharmaceutical scrubber treating trace solvent vapors at 500 m³/hr gas flow with 5 L/min caustic recirculation — a two-fluid nozzle at 3 bar liquid / 4 bar air produces 40-micron droplets that achieve 99.5% removal of acetone, compared to 85% with a hydraulic hollow cone nozzle at 4 bar.

Connection Types and Header Design

The nozzle connection to the liquid distribution header must be selected for the operating pressure, chemical environment, and frequency of nozzle removal for inspection and cleaning. Three connection types dominate scrubber nozzle installations.

Threaded connections (1/4″ to 2″ NPT or BSP) are the most common for scrubber nozzles up to 100 L/min per nozzle at pressures below 6 bar. Threaded connections are economical and reliable but require thread sealant (PTFE tape or paste) compatible with the chemical environment. For PP or PVDF nozzles, use male threads with a PTFE seal washer — plastic threads can gall and seize if overtightened. The removal time for a threaded nozzle during maintenance: approximately 10-20 minutes if accessible, longer if corrosion has seized the threads.

Flanged connections (ANSI 150# or 300#, or DIN/PN equivalents) are used for large nozzles above 100 L/min, high-pressure systems above 6 bar, and any installation where the nozzle weight exceeds 5 kg. Flanged connections provide a positive seal with a gasket that is easily replaced during maintenance. The flange size for a 500 L/min spiral nozzle is typically 2-3 inches. Removal time: 5-10 minutes per nozzle.

Quick-connect couplings with Viton or PTFE seals are specified for FGD scrubber nozzles that require frequent removal for inspection — typically 12-20 nozzles inspected per month on a rotating basis. A quick-connect coupling reduces nozzle removal time from 20 minutes (threaded) to 2-3 minutes per nozzle, saving 3-5 hours per inspection round for a 20-nozzle sample. The coupling consists of a body welded to the header branch and a mating adapter on the nozzle, secured with a locking sleeve or latch. Quick-connect couplings cost 2-3x the equivalent threaded connection but pay back within 12-18 months in reduced maintenance labor for large FGD systems with 40-60 nozzles.

Header design guidelines: The liquid header should be sized for a minimum flow velocity of 1.5 m/s to prevent solids settling and a maximum of 4 m/s to limit erosion at branch connections. Use a ring-header design for towers above 1.5 m diameter — a circular pipe around the tower circumference with nozzle branches on the underside. Provide a drain valve at the header low point and individual isolation valves for each nozzle branch in services where nozzles may need replacement while the scrubber is operating. Design the header supports for the full weight of the pipe, liquid, and nozzles plus a 50% safety factor for the dynamic load during operation.

Nozzle Testing and Quality Verification

Every scrubber nozzle should be tested before installation to verify that it delivers the specified flow rate at the design pressure and produces the correct spray pattern. Nozzles from major manufacturers — Spraying Systems Co., BETE, LORRIC, CYCO — are flow-tested at the factory and marked with the measured k-factor, but field verification is recommended for critical scrubbers where a single undersized or oversized nozzle degrades overall performance.

Flow rate testing: Measure the flow rate at the design pressure using a calibrated flow meter or a bucket-and-stopwatch method for small nozzles. The measured flow rate should be within ±5% of the manufacturer’s catalog value at the same pressure. Nozzles outside this tolerance should be rejected or replaced. For a 40-nozzle system, test at least 10 nozzles (25% sample) and accept the batch if all tested nozzles fall within ±5% and the average is within ±2% of the target.

Spray pattern verification: Visually inspect the spray pattern at the design pressure using a test stand with a backlit target. The spray should be continuous and uniform — no streaks, gaps, or distortion. Full cone nozzles should fill the entire cone cross-section; hollow cone nozzles should show a clear center void with uniform liquid distribution around the annulus. Flat fan nozzles should produce a straight fan with even distribution. The spray angle should be within ±5 degrees of the manufacturer’s specification.

Documentation: Record the measured k-factor, spray angle, and visual pattern assessment for each tested nozzle. Tag each nozzle with its measured k-factor and install nozzles on the header in groups of matching k-factors (±2%) to ensure uniform flow distribution across the tower cross-section. Nozzles with higher-than-average k-factors should be installed on the upper level where higher flow is beneficial; lower k-factor nozzles on the lower level.

Nozzle Maintenance and Clogging Prevention

A partially clogged nozzle does not show up on the pump pressure gauge. The pump maintains the same discharge pressure while the clogged nozzle delivers less flow, and the remaining unclogged nozzles slightly increase their individual flow to compensate. The first sign of nozzle problems is often a failed stack emission test. The EPA wet scrubber for particulate matter manual provides additional guidance on nozzle system design and maintenance for emission compliance. A systematic maintenance program prevents this.

Upstream filtration is the most effective clogging prevention measure. Install a Y-strainer or basket strainer with 500-800 micron mesh on the recirculation pump discharge line before the nozzle header. For FGD scrubbers handling slurry, install a hydrocyclone to remove particles above 200 microns from the recirculation stream, or use a settling tank with 2-3 minutes retention time. For two-fluid nozzles with 1-3 mm free passage, install a 200-micron cartridge filter on the liquid line and a 5-micron coalescing filter on the compressed air line to remove oil and water aerosols.

Inspection frequency: Inspect nozzles every 3 months in clean service (clear water, no solids), monthly in fouling service (slurry, scaling tendency). Remove and disassemble a representative sample — 10-20% of the total nozzle count per inspection cycle — focusing on nozzles at the outer edge of the spray pattern where scaling is most severe. Nozzles in the center of the tower typically foul less because the higher local liquid velocity keeps deposits suspended.

Cleaning methods: Clean clogged nozzles by soaking in dilute acid (2-5% HCl for mineral scale / calcium carbonate / gypsum), solvent soak (for organic deposits / tars / polymers), or high-pressure water jetting (max 5,000 psi for metal nozzles, 2,500 psi for plastic). Never use wire brushes, drill bits, or metal picks to clean nozzle orifices — these damage the precision internal geometry and permanently change the spray pattern and flow rate. After cleaning, verify the flow rate is within ±5% of the original specification. If the flow rate has increased by more than 15% at the same pressure, the orifice has eroded and the nozzle needs replacement. If the flow rate is still more than 15% below specification after cleaning, the nozzle has permanent internal blockage and needs replacement.

Replacement schedule: Replace SS316L nozzles every 5-8 years in clean service or when the orifice diameter has increased by 15% from erosion. Replace ceramic nozzle inserts only when chipped or cracked — ceramic does not erode but can fracture from thermal shock or mechanical impact. Replace PP/PVDF nozzles every 3-5 years or when embrittlement from UV exposure or chemical attack is visible. Replace Hastelloy and titanium nozzles only when corrosion damage is visible — typically 10-15+ year intervals.

Nozzle Selection by Scrubber Type

The table below maps the six main scrubber configurations to the recommended nozzle type, spray pattern, pressure range, and material. Use this as a first-pass selection guide and verify with the nozzle manufacturer before finalizing.

For packed bed scrubbers, the priority is distribution uniformity — use full cone nozzles with 30-50% overlap on a ring header, 6-12 nozzles for a 2.0 m diameter column. For spray towers, the priority is droplet size — use hollow cone nozzles at 3-5 bar to produce 300-500 micron droplets. For FGD scrubbers, the priority is clogging resistance — use spiral nozzles in ceramic with a minimum 8 mm free passage. For low-solubility gas absorption, use two-fluid nozzles that produce sub-100 micron droplets for maximum mass transfer area, or high-pressure hydraulic vortex nozzles if compressed air is not available on site.

FAQ

What type of spray nozzle is best for a packed bed scrubber?

Full cone nozzles are the standard because they provide uniform liquid distribution across the packing surface. Use 6-12 full cone nozzles on a ring header at 1-3 bar with 30-50% overlap for a 2.0 m diameter packed bed scrubber. Spiral nozzles are an alternative when the recirculated liquid contains suspended solids above 500 ppm.

How do I calculate the number of nozzles needed for my scrubber?

Calculate the coverage diameter D = 2 × H × tan(θ/2), where H is nozzle height above the target and θ is the spray angle. Space nozzles so coverage circles overlap by 30-50%. Use triangular (staggered) pitch for 15-30% better coverage than square pitch. The number is the tower area divided by effective coverage per nozzle with the overlap factor applied.

Why do scrubber nozzles clog and how do I prevent it?

Clogging occurs from suspended solids, mineral scale (calcium carbonate, gypsum), biological growth, and corrosion products in the recirculated liquid. Install a Y-strainer with 500-800 micron mesh upstream of the nozzle header. For slurry services, add a hydrocyclone or settling tank. Select a nozzle with free passage diameter at least 3x the maximum particle size in the liquid.

What is the best material for FGD scrubber nozzles?

Silicon carbide (SiC) ceramic is the best material for FGD slurry nozzles. SS316L erodes within 3-6 months in limestone slurry at 5-20% solids. Ceramic nozzles last 3-5 years at the same conditions. Use SiC over Al₂O₃ if the slurry contains hydrofluoric acid — Al₂O₃ dissolves in HF while SiC is inert.

How does nozzle pressure affect scrubber efficiency?

Higher pressure produces smaller droplets, which increases gas-liquid interfacial area and improves absorption efficiency. Increasing pressure from 2 to 4 bar reduces SMD by 25-30% and increases surface area by 40-50%. However, pump energy doubles and nozzle erosion accelerates. The optimal balance for most scrubbers is 2-4 bar. For applications requiring droplet sizes below 200 microns, consider two-fluid nozzles instead of high-pressure hydraulic systems.

What is the difference between single-level and multi-level spray systems?

Single-level systems are adequate for removal below 90% or for highly soluble pollutants. Two-level systems are standard for 95-99% removal efficiency, with the lower level at higher flow for bulk absorption and the upper level at finer atomization for polishing. Three-level systems are used in FGD scrubbers requiring above 99.5% removal. Each additional level increases the L/G ratio by 2-4 L/m³ and adds 1.5-2.5 m of tower height.

How often should I inspect scrubber nozzles?

Every 3 months in clean service, every 1-2 months in fouling service. Inspect 10-20% of the total nozzle count per cycle on a rotating basis, focusing on outer ring nozzles where scaling is most severe. Immediately inspect all nozzles after any stack test failure or visible increase in liquid carryover.

Can I mix different nozzle types in the same scrubber?

Yes. Multi-level spray towers commonly use different nozzle types on different levels. The lower level may use full cone or spiral nozzles for bulk liquid coverage and gas quenching, while the upper levels use hollow cone or vortex nozzles for polishing absorption. Each level requires its own pump and header sized for the specific nozzle flow and pressure requirements.

Conclusion

The spray nozzle is a small component of a wet scrubber system — typically 1-3% of the total installed equipment cost — but its selection determines the effectiveness of the entire gas-liquid contact process. Choosing the correct nozzle type for the scrubber configuration, the right material for the chemical environment, the proper size and number for the required flow rate and coverage, and the appropriate pressure for the target droplet size ensures that the scrubber achieves its design removal efficiency with minimum energy consumption and maintenance cost. Nozzle selection should never be an afterthought in scrubber design — it is the single highest-leverage design decision for mass transfer performance. Systematic inspection and preventive maintenance prevents the gradual efficiency degradation that is the most common cause of scrubber emission compliance failures over time.

XICHENG EP LTD supplies spray nozzles for all scrubber types — full cone, hollow cone, spiral, flat fan, and two-fluid atomizing — in materials from PP and SS316L through ceramic, Hastelloy C276, silicon carbide, and titanium, in flow rates from 2 to 1,000 L/min per nozzle. Our applications engineering team provides complete nozzle system design services including nozzle selection, sizing calculations, header layout, and pump specification. Contact us with your scrubber configuration, operating conditions, and target removal efficiency for a nozzle system design recommendation and quote.