Spiral nozzles occupy a unique position in the scrubber nozzle family: they are the only type that combines high flow capacity with excellent clogging resistance and the ability to produce both full cone and hollow cone spray patterns from a single one-piece body design. The spiral flow path — a continuous channel wrapped around the nozzle core — has no internal vanes, orifices, or moving parts that can clog, making spiral nozzles the default choice for FGD scrubbers handling limestone slurry, for any scrubber where the recirculated liquid contains suspended solids above 500 ppm, and for high-flow gas cooling and quenching duties where reliability under dirty conditions matters more than fine atomization. This guide covers spiral nozzle design and working principle, flow characteristics including the flow-pressure relationship Q = k√P and droplet size data across the full pressure range, the clogging resistance mechanism that sets spiral nozzles apart from all other types, material selection with quantified service life data for FGD slurry and chemical environments, application-specific guidance for FGD, chemical scrubbing, and gas cooling, and sizing and selection procedures for integrating spiral nozzles into scrubber systems. For a complete comparison of all scrubber nozzle types see the spray nozzle selection guide for wet scrubbers.
Key Takeaways
- Spiral nozzles are the only scrubber nozzle type that combines high flow capacity (up to 1,000 L/min) with excellent clogging resistance (5-15 mm free passage) — the one-piece spiral flow path eliminates the internal vanes and orifices that cause clogging in every other nozzle type.
- In FGD limestone slurry, an SS316L spiral nozzle erodes within 3-6 months while a silicon carbide ceramic spiral nozzle lasts 3-6 years. The 2-3x ceramic cost premium pays back in 6-12 months from avoided replacements and unplanned downtime.
- Spiral nozzles produce coarser droplets (300-1,500 microns SMD at 2 bar) than hollow cone nozzles — this is an advantage for packed bed irrigation and gas quenching where coarse droplets penetrate better, but a disadvantage for spray tower absorption where fine atomization maximizes mass transfer.
- A single 120-degree spiral nozzle at 1.5 m height covers a 5.2 m diameter circle — one nozzle per level theoretically covers a 5.0 m FGD tower, but 3-5 nozzles per level are standard practice for redundancy and distribution uniformity.
- Spiral nozzles cannot be disassembled for internal cleaning. The only cleaning method is chemical soaking followed by high-pressure flushing. If cleaning fails to restore flow within 10% of specification, the nozzle must be replaced — not repaired.
What Is a Spiral Nozzle?
A spiral nozzle is a single-fluid hydraulic nozzle that uses a spiral flow channel machined or cast into the nozzle body to impart a vortex motion to the liquid. Unlike full cone or hollow cone nozzles that rely on internal vanes, a spiral vane, or a orifice plate to create the spray pattern, the spiral nozzle has no internal components — the liquid follows a continuous spiral path from the inlet to the discharge orifice, emerging as a rotating cone that breaks into droplets at the nozzle exit. The one-piece construction eliminates all internal surfaces where solids can accumulate and clog, which is the fundamental advantage of spiral nozzles over every other scrubber nozzle type.
Design and Working Principle
The spiral channel inside the nozzle body is a constant-area or gradually tapering flow path that wraps around a central core. Liquid entering the nozzle at the base is directed into the spiral channel, where the tangential velocity component increases as the liquid approaches the discharge. At the nozzle exit, the rotating liquid sheet is ejected as a hollow cone that immediately breaks up into droplets. The spray angle — typically 60-170 degrees — is determined by the spiral channel geometry and the discharge diameter. Nozzles with wider spiral angles produce flatter spray patterns with larger coverage area and coarser droplets. Narrower angles produce more concentrated spray with finer droplets. The flow rate is governed by the cross-sectional area of the spiral channel and the discharge orifice diameter. Because there is no separate orifice to clog, spiral nozzles maintain their flow characteristics over the full service life until erosion gradually enlarges the flow path.
Full Cone vs Hollow Cone Spiral Nozzles
Spiral nozzles are available in both full cone and hollow cone variants, achieved by modifying the discharge geometry without changing the basic spiral flow path. Hollow cone spiral nozzles have a smooth discharge that allows the rotating liquid sheet to exit as a continuous annular sheet that breaks up into droplets downstream — producing the ring-shaped spray pattern characteristic of all hollow cone nozzles. Full cone spiral nozzles incorporate a small deflector or diffuser at the discharge that redirects a portion of the liquid from the outer annulus toward the center, filling the void and creating a solid cone pattern. The full cone variant has slightly smaller free passage than the hollow cone variant of the same size because the center deflector adds an obstruction, so for FGD slurry services where maximum clogging resistance is required, specify hollow cone spiral nozzles unless the application specifically requires a solid cone distribution for packed bed irrigation.
Spiral Nozzle Flow Characteristics
Spiral nozzles follow the same fundamental flow-pressure relationship as all hydraulic nozzles — Q = k√P — but with higher flow coefficients per unit body size than any other type because the spiral flow path maximizes the flow area within a given nozzle diameter. A 1-inch spiral nozzle at 2 bar delivers 80-120 L/min, compared to 30-60 L/min for a full cone nozzle of the same connection size. This high flow density makes spiral nozzles the most compact solution for high-capacity scrubbers.
Flow Rate vs Pressure
For a typical 1-inch spiral nozzle with k = 55: at 1.5 bar, Q = 55 × √1.5 = 67 L/min; at 3 bar, Q = 55 × √3 = 95 L/min; at 5 bar, Q = 55 × √5 = 123 L/min. The flow range for standard spiral nozzles spans 10-1,000 L/min per nozzle, covering the full range of scrubber applications from small pharmaceutical scrubbers at 50 L/min total to large FGD towers requiring 15,000 L/min distributed across 40-60 nozzles. The recommended operating pressure for spiral nozzles in scrubber service is 1.5-4 bar. Below 1.5 bar, the spray pattern may not fully develop and the cone angle narrows. Above 4 bar, the energy cost per unit flow increases significantly and erosion accelerates, particularly in slurry service.
Spray Angle and Coverage
Spiral nozzles are available in spray angles from 60 to 170 degrees. For scrubber applications, 90-120 degree angles are standard for FGD spray towers, 120-170 degree angles for gas cooling and quenching where maximum coverage is needed, and 60-90 degree angles for packed bed scrubbers where a narrower spray provides better penetration through the packing. The coverage diameter follows the same relationship as other nozzles: D = 2 × H × tan(θ/2). For a 120-degree spiral nozzle at 1.5 m above the gas inlet: D = 2 × 1.5 × tan(60°) = 5.2 m coverage diameter — one nozzle covers a 5.2 m diameter circle. For a 5.0 m FGD tower, this means a single 120-degree spiral nozzle per level can theoretically cover the full cross-section, but engineering practice requires 3-5 nozzles per level arranged in a ring with a center nozzle for uniform distribution and backup in case one nozzle clogs.
Droplet Size and SMD
Spiral nozzles produce coarser droplets than hollow cone or vortex nozzles at the same pressure because the spiral flow path creates less shear than a conventional orifice design. At 2 bar, a spiral nozzle produces SMD of 500-1,500 microns depending on flow rate and spray angle, compared to 200-600 microns for a hollow cone nozzle. At 4 bar, spiral SMD drops to 300-1,000 microns. This coarser droplet size makes spiral nozzles better suited for applications where liquid distribution uniformity matters more than fine atomization — packed bed scrubbing, gas quenching, and FGD absorption where the mass transfer is limited by gas-phase resistance rather than liquid-phase resistance. For spray tower absorption where fine atomization is critical, use hollow cone or vortex nozzles instead.
Clogging Resistance
The clogging resistance of spiral nozzles is their defining advantage over every other scrubber nozzle type. The spiral flow path has no internal vanes, strainers, orifice plates, or any other obstruction that can trap solids. The free passage diameter — the largest spherical particle that can pass through the nozzle — is determined solely by the spiral channel width, which is typically 30-50% of the discharge diameter. A 1-inch spiral nozzle with a 10 mm discharge has a free passage of 5-8 mm. A comparable hollow cone nozzle with a 6 mm orifice has a free passage of only 2-3 mm because the internal vane that creates the hollow cone pattern occupies the center of the flow path.
For FGD scrubbers handling limestone slurry with typical particle sizes of 1-3 mm and occasional 5 mm agglomerates, a spiral nozzle with 8-12 mm free passage passes all particles without clogging. A full cone nozzle with 4-6 mm free passage clogs on the 5 mm agglomerates. A hollow cone nozzle with 2-4 mm free passage clogs on routine 2 mm particles. The field result: spiral nozzles in FGD service require cleaning or unclogging once every 3-6 months, compared to once every 1-4 weeks for full cone nozzles at the same conditions. In chemical scrubbers handling clean recirculated water (solids below 100 ppm), the clogging advantage is less significant, and the simpler design of a full cone or hollow cone nozzle may be more cost-effective. The general rule: if the recirculated liquid contains suspended solids above 500 ppm or has particles above 1 mm, specify spiral nozzles exclusively.
Spiral Nozzle Materials
The material selection for spiral nozzles follows the same chemical compatibility logic as all scrubber nozzles, but with one additional constraint: the spiral flow channel geometry is more susceptible to erosion than a simple orifice because the liquid follows a long, curved path. Abrasion-resistant materials are therefore more important for spiral nozzles than for other types when handling slurry.
| Material | Max Temp (°C) | Relative Cost | Erosion Resistance (Slurry) | Corrosion Resistance | FGD Service Life |
|---|---|---|---|---|---|
| SS316L | 400 | 1.0x | Poor | Good — chlorides < 2,000 ppm | 3-6 months |
| Al₂O₃ Ceramic | 800 | 2.5x | Excellent | All except HF | 2-4 years |
| SiC Ceramic | 800 | 3.5x | Superior | All including HF | 3-6 years |
| Hastelloy C276 | 650 | 3.5x | Good | Superior — wet Cl₂, HCl | 5-8 years |
| PP (Polypropylene) | 80 | 0.3x | Poor | Good — acids, bases | 2-4 years (clean) |
For FGD scrubbers, ceramic spiral nozzles are the standard. SS316L erodes rapidly in limestone slurry — the spiral channel widens and the spray pattern degrades within 3-6 months. Ceramic (aluminum oxide or silicon carbide) resists erosion and maintains the spray pattern for 2-6 years. The cost premium of ceramic over SS316L pays back within 6-12 months from avoided replacement labor. For chemical scrubbers with clean recirculated water at temperatures below 80°C, PP spiral nozzles at 0.3x the cost of SS316L provide adequate service life. For scrubbers handling wet chlorine, hydrochloric acid above 5%, or extreme pH conditions, Hastelloy C276 spiral nozzles are the only reliable option.
Spiral Nozzle Applications
Spiral nozzles are specified in three primary scrubber applications where their unique combination of high flow capacity, clogging resistance, and coarse droplet size provides clear advantages over other nozzle types.
FGD Scrubbers
Flue gas desulfurization scrubbers are the largest single market for spiral nozzles. An FGD spray tower handling flue gas from a 500 MW coal-fired power plant recirculates 30,000-60,000 L/min of limestone slurry at 5-20% solids, as covered in the EPA wet scrubber design manual. The slurry contains particles of calcium carbonate, calcium sulfate, and calcium sulfite ranging from 1 to 5 mm. Spiral nozzles with 8-15 mm free passage and silicon carbide construction are the only nozzle type that operates reliably at these conditions — hollow cone nozzles would clog within hours. A typical 5.0 m diameter FGD tower uses 40-60 spiral nozzles across three spray levels, each nozzle delivering 300-800 L/min at 1.5-3 bar. The nozzle arrangement uses 120-150 degree spray angles on the lower level for maximum coverage and 90-120 degree angles on the upper levels for more concentrated spray. For FGD nozzles, specify hollow cone spiral pattern (larger free passage) in silicon carbide ceramic. Replace ceramic nozzle inserts only when chipped or cracked — typically every 3-6 years depending on slurry abrasiveness.
Chemical Scrubbers with Dirty Water
Chemical scrubbers that recirculate liquid from a sump containing reaction byproducts, precipitated solids, or entrained particulate benefit from spiral nozzles even when the particle concentration is below 500 ppm. The safety margin against clogging eliminates the need for the operator to monitor nozzle performance daily. In HCl scrubbers where the recirculated water absorbs acid gas and the pH is controlled by caustic addition, sodium chloride and sodium sulfate can precipitate as fine solids that accumulate in low-velocity zones and periodically dislodge as particle slugs. A spiral nozzle passes these slugs without interruption; a full cone nozzle at the same conditions may clog 2-4 times per year, each requiring a maintenance intervention. For chemical scrubbers, PP spiral nozzles at 80°C or below provide the most cost-effective solution. For higher temperatures, specify SS316L or Hastelloy depending on chloride concentration.
Gas Cooling and Quenching
Spiral nozzles are widely used for direct-contact gas cooling and quenching in incinerator off-gas systems, steel mill BOF gas cooling, and cement kiln exhaust handling. These applications require high flow rates (200-1,000 L/min per nozzle), coarse droplets that evaporate completely without wetting the duct walls, and absolute reliability — a clogged quench nozzle in an incinerator can allow hot gas above 800°C to reach downstream equipment. The coarse droplet size of spiral nozzles (500-1,500 microns SMD at 2 bar) is an advantage in quenching because large droplets penetrate the hot gas stream better than fine mist and evaporate more slowly, reaching further into the duct before complete vaporization. For gas cooling, specify wide-angle spiral nozzles (120-170 degrees) at 2-4 bar with SS316L or Hastelloy construction depending on gas composition. Install 2-4 nozzles in a ring around the duct, angled to create a full-coverage curtain.
Sizing and Selection
Selecting spiral nozzles for a scrubber application follows the same general nozzle sizing procedure with one modification: the free passage requirement takes priority over flow rate and pressure. Determine the maximum particle size in the recirculated liquid, multiply by 3 to set the minimum free passage, select a spiral nozzle size that provides that free passage, and then verify that the selected nozzle delivers the required flow rate at the available pressure.
Step 1: Measure or estimate the maximum particle size in the recirculated liquid. For FGD slurry with a Hydrocyclone that removes particles above 2 mm, the maximum particle size entering the nozzles is approximately 2 mm. Minimum free passage: 3 × 2 = 6 mm.
Step 2: From the spiral nozzle manufacturer’s catalog, select a nozzle size with free passage at least 6 mm. A 1.5-inch spiral nozzle typically has 8-12 mm free passage. The corresponding flow range at 2 bar is 150-300 L/min depending on spray angle.
Step 3: Calculate the total recirculation flow rate from the scrubber L/G ratio. For an FGD tower treating 100,000 m³/hr of flue gas at L/G = 10 L/m³: Q_total = 100,000 × 10 / 60 = 16,667 L/min.
Step 4: Determine the number of nozzles. For a 5.0 m diameter tower, a single-level spray system requires 10-15 nozzles in a ring-plus-center arrangement. For three levels, 30-45 nozzles total. With 45 nozzles, each nozzle delivers 16,667 / 45 = 370 L/min. At 2 bar, a 1.5-inch 120-degree spiral nozzle with k = 260 delivers Q = 260 × √2 = 368 L/min — close to the target. Adjust the nozzle size or operating pressure to fine-tune. At 2.2 bar: Q = 260 × √2.2 = 386 L/min, which is within the acceptable ±5% tolerance for system design.
Step 5: Verify coverage. For a 1.5-inch 120-degree spiral nozzle at 1.8 m mounting height above the gas inlet: D = 2 × 1.8 × tan(60°) = 6.2 m. A single nozzle covers the 5.0 m tower diameter, but the arrangement of 15 nozzles per level in a ring pattern with 30-50% overlap ensures uniform distribution and provides redundancy if individual nozzles clog.
Maintenance
Spiral nozzles require less maintenance than any other scrubber nozzle type because of their clogging resistance, but they are not maintenance-free. The most common failure mode is erosion of the spiral channel from abrasive particles in the liquid, which gradually increases the flow rate at the same pressure and degrades the spray pattern.
Inspection: Inspect spiral nozzles every 6 months in slurry service, every 12 months in clean service. Measure the flow rate at a reference pressure and compare to the baseline recorded at installation. An increase of more than 15% indicates erosion — the spiral channel has widened and the nozzle should be replaced before the spray pattern degrades to the point of uneven coverage. A decrease of more than 15% indicates partial blockage from a particle too large to pass (rare in spiral nozzles) or scale buildup on the discharge surfaces from crystallization.
Cleaning: Unlike other nozzle types, spiral nozzles cannot be disassembled for internal cleaning because the spiral channel is an integral part of the one-piece body. Clean by soaking the entire nozzle in dilute acid (2-5% HCl for mineral scale) or solvent (for organic deposits), followed by high-pressure water jetting through the inlet and outlet. Never use wire brushes or metal tools inside the spiral channel — any surface damage to the spiral flow path changes the spray pattern permanently. If soaking and jetting do not restore the flow rate to within 10% of specification, replace the nozzle.
Replacement: Replace ceramic spiral nozzle inserts only when chipped, cracked, or when flow rate has increased by more than 20% due to erosion. Replace SS316L spiral nozzles every 12-18 months in slurry service or when erosion is visible. Replace PP spiral nozzles every 3-5 years or when embrittlement is visible. For nozzles in high-temperature gas cooling service above 400°C, inspect after each thermal cycle — thermal shock can crack ceramic inserts, particularly when the quench water is cold.
Spiral Nozzle vs Other Types
The table below compares spiral nozzles against the other main scrubber nozzle types across the decision-critical parameters for scrubber service. The comparison assumes similar connection sizes and operating at 2 bar unless otherwise noted.
| Parameter | Spiral | Full Cone | Hollow Cone | Two-Fluid |
|---|---|---|---|---|
| Free passage (mm) | 5-15 | 3-8 | 2-5 | 1-3 |
| Max flow at 2 bar (L/min) | 1,000 | 500 | 400 | 50 |
| Droplet size SMD (μm at 2 bar) | 300-1,500 | 500-2,000 | 100-800 | 10-100 |
| Clogging resistance | Excellent | Moderate | Good | Low |
| Spray pattern options | Full or hollow cone | Full cone only | Hollow cone only | Full or hollow |
| Erosion resistance | Good (ceramic: excellent) | Moderate | Moderate | Fair |
| Relative cost per nozzle | 1.0x (baseline) | 0.7-0.9x | 0.7-0.9x | 2-4x |
| Suitable for slurry | ✅ Yes | ⚠️ Marginal | ❌ No | ❌ No |
| Suitable for clean liquid | ✅ Yes | ✅ Yes | ✅ Yes | ✅ Yes |
Choose spiral nozzles when the liquid contains solids above 500 ppm, when maximum reliability with minimum maintenance is required, or when high flow rates per nozzle are needed to minimize the number of nozzles in the header. Choose full cone nozzles for clean service packed bed scrubbers where the lowest cost per nozzle is the priority. Choose hollow cone nozzles for spray tower absorption where fine atomization is critical and the liquid is clean. Choose two-fluid nozzles only when sub-100 micron droplets are required and compressed air is available. For the complete nozzle selection methodology see the spray nozzle selection guide for wet scrubbers.
FAQ
What makes spiral nozzles clog-resistant?
The spiral flow path has no internal vanes, orifices, or obstructions. Liquid follows a continuous spiral channel through the nozzle body, and any solid particles that enter the nozzle pass through the channel and exit without accumulating. The free passage diameter — 5-15 mm depending on nozzle size — is 2-4x larger than a comparable full cone or hollow cone nozzle.
Are spiral nozzles suitable for all scrubber types?
Spiral nozzles are most advantageous in FGD scrubbers, chemical scrubbers with dirty recirculated water, and gas cooling/quenching applications. For clean-service spray towers where fine atomization is needed for gas absorption, hollow cone nozzles produce finer droplets and may achieve higher mass transfer efficiency. For packed bed scrubbers with clean liquid, full cone nozzles provide equal performance at lower cost.
What is the typical lifespan of a spiral nozzle in FGD service?
A silicon carbide ceramic spiral nozzle in FGD limestone slurry lasts 3-6 years. An SS316L spiral nozzle at the same conditions erodes within 3-6 months. The ceramic nozzle’s 2-3x cost premium pays back within 6-12 months from avoided replacement labor and unplanned downtime.
How do I clean a spiral nozzle that has clogged?
Soak the nozzle in dilute acid (2-5% HCl for mineral scale) or solvent (for organic deposits), then flush with water at high pressure through both the inlet and outlet. Never insert wire brushes or metal tools into the spiral channel — any surface damage permanently degrades the spray pattern.
Can a spiral nozzle produce both full cone and hollow cone patterns?
Yes, spiral nozzles are available in both variants. Hollow cone spiral nozzles have a smooth discharge for maximum free passage. Full cone spiral nozzles use a small center deflector that fills the spray void. Specify hollow cone for FGD slurry (larger free passage), full cone for packed bed irrigation (more uniform distribution).
What spray angle should I use for FGD scrubber spiral nozzles?
120-150 degrees for the lower spray level (maximum coverage, coarser droplets) and 90-120 degrees for upper levels (narrower coverage for residual SO₂ polishing). For gas cooling and quenching where the nozzle is mounted in a duct, use 120-170 degree angles to create a full-coverage curtain.
Conclusion
Spiral nozzles are the most reliable scrubber nozzle type for demanding services involving suspended solids, slurry, or high flow rates. Their one-piece spiral flow path eliminates the internal obstructions that cause clogging in other nozzle types, and their high flow capacity per unit body size reduces the number of nozzles required for a given duty. The selection of ceramic construction for abrasive FGD slurry extends service life from months to years compared to metal nozzles. For clean-liquid services where fine atomization or lowest first cost is the priority, other nozzle types may be more appropriate — but for any scrubber where clogging is a risk, spiral nozzles are the default choice.
XICHENG EP LTD supplies spiral nozzles in full cone and hollow cone patterns, with spray angles from 60 to 170 degrees, in materials from PP and SS316L through aluminum oxide and silicon carbide ceramic, Hastelloy C276, and titanium, in flow rates from 10 to 1,000 L/min per nozzle. Contact our applications engineering team with your scrubber type, liquid chemistry, and flow requirements for a spiral nozzle selection recommendation and quote.