Spray Nozzles for
Slag Granulation & Lance Cooling
Liquid slag and oxygen lance operations represent two of the most thermally extreme spray environments in any industrial process. Slag granulation water must physically shatter a molten stream at over 1,400ยฐC using sheer hydraulic impact โ the nozzles carrying that water are exposed to direct radiant heat and intermittent steam blast with every pour. Oxygen lance and converter hood cooling circuits protect copper and steel hardware worth hundreds of thousands of dollars per campaign against radiant heat loads that exceed 500 kW/mยฒ during peak blowing. In both applications, nozzle performance is structural protection, not process optimization.
Slag granulation and oxygen lance cooling share a characteristic that distinguishes them from most industrial spray applications: the consequence of inadequate water delivery is not process inefficiency or product quality deviation โ it is direct destruction of expensive plant hardware. In slag granulation, a nozzle array that loses coverage allows molten slag to pool rather than granulate, eventually forming solid masses that block the granulation channel and require extended shutdown for removal. In lance and hood cooling, a nozzle that drops to partial flow allows the exposed metal to exceed its design temperature within a single blow cycle, causing permanent distortion or burn-through.
Both applications also share a demanding water service environment. Slag granulation water recirculates through systems that carry entrained slag fines and silica particles. Lance cooling circuits operate in environments where the nozzle body is exposed to the radiant heat field of the converter โ steam, CO fumes, and iron oxide fines are all present. The nozzle specification must address the mechanical environment (impact, thermal shock, abrasion) and the service water chemistry simultaneously.
Slag Granulation and Metallurgical Lance & Hood Cooling
Slag Granulation & Cooling
High-impact water curtains for granulated blast furnace slag (GBFS)Blast furnace slag โ the calcium-silicate byproduct of ironmaking โ exits the furnace at 1,350โ1,500ยฐC as a viscous molten stream flowing down the slag runner. To produce granulated blast furnace slag (GBFS), the material used as supplementary cementitious material in concrete, this molten stream must be quenched so rapidly that the slag is physically shattered into individual glassy particles before it can crystallize. The resulting granulated material has the amorphous glass microstructure that gives it pozzolanic activity โ if quenching is too slow, the slag partially crystallizes into a non-reactive merwinite and melilite phase that has no value as a cement replacement.
The granulation mechanism is primarily hydraulic impact, not evaporative cooling. High-velocity solid-stream and narrow flat-fan jets physically disrupt the cohesive molten slag stream, creating the rapid solidification condition required for glass phase formation. The water-to-slag ratio in granulation systems is typically 10:1 to 20:1 by weight โ far above what is needed for cooling alone โ because the primary requirement is the hydraulic energy to fragment the stream, not just the thermal capacity to absorb the heat.
Metallurgical Lance & Hood Spray Rings
External cooling rings protecting lance components during carbon blowBasic oxygen furnace (BOF) and electric arc furnace (EAF) oxygen lances inject high-purity oxygen into the liquid steel bath at supersonic velocities to burn out carbon and other impurities during the refining blow. The lance itself is water-cooled internally through a concentric tube design that circulates cooling water through the lance body during each blow. However, the external surface of the lance above the internal cooling zone, the lance support collar, and the converter mouth hood are all exposed to the intense radiant heat from the liquid steel bath and the combustion of the CO generated during decarburization.
External cooling rings โ circular spray headers mounted around the lance body at the converter mouth level โ provide supplemental surface wetting that protects these components from overheating during the blow cycle. The hood itself (the exhaust gas collection system above the converter mouth) faces similar radiant heat loads and is protected by water-cooled panels supplemented by spray cooling during periods of peak heat generation in the oxygen blow.
Slag Granulation: Why Hydraulic Impact Force Determines Product Quality
Granulated blast furnace slag commands a significant premium over air-cooled slag for its pozzolanic activity in cement production. That premium is entirely dependent on the amorphous glass content of the granulated product โ which is entirely dependent on the quench rate achieved during granulation โ which is entirely dependent on the hydraulic impact energy delivered by the granulation nozzles. The nozzle selection decision directly determines the market value of the slag byproduct.
The Physics of Granulation: Impact, Fragmentation, and Glass Formation
The glass transition temperature of blast furnace slag โ the temperature below which the slag solidifies in an amorphous rather than crystalline structure โ is approximately 700โ800ยฐC. For the slag to solidify in the glassy amorphous phase, it must pass through this temperature range faster than the nucleation rate of the crystalline phases. The critical cooling rate required to suppress crystallization is approximately 100โ1,000ยฐC/second, depending on the slag chemistry (basicity, AlโOโ content).
Achieving 100โ1,000ยฐC/second cooling rate in a molten slag stream is only possible through the combination of hydraulic fragmentation and water contact cooling. The solid-stream and narrow flat-fan jets first fragment the cohesive molten stream into individual droplets by impact โ the hydraulic energy of the jet disrupts the surface tension of the molten slag and shatters it into particles typically 1โ5 mm in diameter. These individual droplets then cool extremely rapidly because their large surface-area-to-volume ratio allows the water to extract heat from all sides simultaneously. A ribbon of uncollected molten slag cooling slowly on a surface reaches the glass transition range at a fraction of this rate, forming the crystalline phases that are non-pozzolanic.
Molten slag that escapes granulation as a coherent stream and solidifies in the granulation channel creates several serious plant hazards. First, the accumulated solid mass blocks the channel, preventing subsequent granulation runs and requiring manual entry for removal โ a confined-space hot work operation with significant safety risk. Second, if water contacts molten slag that has pooled in a depression rather than flowing freely, the explosive steam generation from water-slag contact (a "slag-water steam explosion") can project molten material and fragments with lethal force. Third, if the granulation pit floods with water before the slag flow has been properly granulated, the water-over-slag condition creates the same explosive risk. Correct nozzle selection and array geometry that prevents slag pooling is a process safety requirement, not merely a product quality preference.
Sizing the Granulation Header
Granulation header sizing must be calculated from the slag tap rate (tonnes per minute), the required water-to-slag ratio (typically 10:1 to 20:1 by weight), and the available water supply pressure. For a blast furnace producing 300 tonnes per hour of slag (5 tonnes per minute) at a water-to-slag ratio of 15:1, the granulation system requires 75 tonnes per minute of water โ 75,000 liters per minute โ delivered through the granulation header at the tap point. This flow rate is divided among the nozzle positions in the header, with each nozzle's individual flow rate determined by the orifice size and supply pressure.
The nozzle positions must be arranged to provide complete coverage of the slag runner cross-section at the granulation point. Standard granulation headers use two opposing rows of solid-stream or narrow flat-fan nozzles angled to intersect the slag stream from both sides simultaneously, with the jet intersection point located at the center of the slag stream. This bilateral impact geometry ensures maximum fragmentation energy per unit of slag mass passing through the impact zone.
- Verify nozzle free passage against the actual granulation sump water particle size distribution โ send a recirculated water sample for particle size analysis; the nozzle free passage must exceed the D99 particle size (the diameter below which 99% of particles fall) in the recirculated granulation water to provide adequate plug resistance over a full maintenance interval
- Size the granulation header for the peak tap rate, not the average โ blast furnace slag tap rates vary by up to 30โ50% between taps depending on furnace burden and operating rhythm; a header sized for average tap rate is undersized for peak flow events, and the resulting inadequate granulation during peak taps produces the highest proportion of partially crystallized material in the slag product
- Maintain the bilateral impact geometry โ both rows of the opposing granulation header must be active for effective granulation; a single-sided granulation impact deflects the slag stream rather than shattering it, producing larger particles with lower amorphous content; monitor individual nozzle flow rates in both header rows and replace any plugged or worn positions before the next tap
- Replace nozzles as complete header sets โ mixed new and worn nozzles in the granulation header produce non-uniform impact energy across the slag stream cross-section, creating bands of well-granulated material adjacent to partially granulated material in the same tap
Lance and Hood Cooling: Uniform Coverage as Structural Protection
An oxygen lance in a BOF vessel represents a significant capital investment โ lance body fabrication costs run to tens of thousands of dollars, and unplanned replacement due to heat damage requires a blow cycle interruption that disrupts the melt shop production schedule. The cooling ring is not supplemental equipment โ it is the primary means by which the lance body survives repeated campaigns at radiant heat loads that would destroy unprotected steel within minutes.
The Radiant Heat Environment Above the BOF Converter
During the oxygen blow, the BOF converter contains 200โ350 tonnes of liquid steel at approximately 1,600โ1,700ยฐC. The liquid bath surface radiates heat upward through the converter mouth in proportion to the fourth power of its absolute temperature โ the Stefan-Boltzmann radiation law means that a 1,700ยฐC bath radiates approximately 10ร more power per unit area than a surface at 1,000ยฐC. Peak radiant heat fluxes at the converter mouth can reach 300โ800 kW/mยฒ during the main decarburization period, when CO combustion above the bath further elevates the thermal load.
At 500 kW/mยฒ, an unprotected steel surface absorbs enough heat energy to raise its temperature at approximately 150โ200ยฐC per second, depending on the steel mass and thermal conductivity. Lance body sections above the internal cooling circuit water entry reach dangerous structural temperatures within 2โ3 minutes of unprotected exposure. The cooling ring must maintain a continuous water film on the lance body exterior at the converter mouth level throughout the blow โ not just during peak heat periods, because the transition from unprotected to steady-state water film coverage takes 30โ60 seconds for the water film to stabilize, which is too long relative to the heat-up rate of the exposed metal.
Full-Cone Nozzle Geometry for Cooling Ring Design
The geometry of a full-cone nozzle is particularly suited to cooling ring applications because the circular spray pattern from each nozzle position in the ring fills a circular zone on the lance body surface โ when multiple full-cone nozzles are equally spaced around the ring circumference, the resulting coverage is inherently uniform in the circumferential direction with minimal overlap engineering. A flat-fan nozzle ring requires careful angular alignment to ensure that adjacent fan patterns overlap at the lance surface without leaving unwetted gaps between them, which depends critically on the standoff distance between the ring and the lance body. Full-cone rings are more tolerant of installation variation in standoff distance and nozzle angular alignment. Contact NozzlePro with your lance body outer diameter and ring mounting distance for a nozzle spacing and spray angle recommendation for your specific geometry.
- Design the cooling ring for coverage at minimum nozzle count minus one โ a ring designed for exact coverage with all nozzles operational provides zero redundancy; if any nozzle plugs or loses flow, the sector it was covering immediately becomes a potential hot spot; design the ring so that single-nozzle loss still provides at least 70% coverage of the previously covered sector
- Use 316L SS manifold pipe and fittings throughout the cooling ring supply circuit โ the environment above the BOF converter contains SOโ, CO, iron oxide fume, and condensed steam that aggressively corrode carbon steel pipe fittings within weeks; 316L SS provides adequate service life between planned outages; avoid galvanized fittings that lose their zinc coating rapidly in the corrosive converter atmosphere
- Verify cooling ring nozzle condition visually before each blow โ a plugged nozzle that missed the pre-shift inspection causes a partial dry sector during the blow; a 30-second visual check of all nozzle positions during the ring commissioning water test before lance insertion prevents the structural damage from an uncorrected plugged position
- Match nozzle orifice size to the cooling water supply system pressure and required flow rate per nozzle position โ cooling ring nozzles that are undersized for the supply pressure produce high-velocity jets that provide good local impact but limited coverage area; nozzles that are oversized produce low-velocity spray that provides poor coverage uniformity at large standoff distances
Nozzle Selection by Steelmaking Application
Contact NozzlePro with your slag tap rate, runner geometry, lance body diameter, ring mounting distance, and service water particle loading. Both applications require site-specific geometry calculations before nozzle selection.
| Application | Nozzle Type | Impact / Pressure | Critical Requirement | Material |
|---|---|---|---|---|
| BF slag granulation โ primary impact header | Solid-stream, high-capacity | Maximum impact / 4โ8 bar | Bilateral opposing jets at slag stream; min. 20โ30 mm free passage; 10:1โ20:1 water-to-slag ratio; replace as complete header sets | 316L SS or SiC |
| BF slag granulation โ curtain coverage nozzles | Narrow flat-fan, 15ยฐโ30ยฐ | High impact curtain / 3โ6 bar | Dense overlapping curtain at slag runner width; large free passage for recirculated granulation water with slag fines | 316L SS or SiC |
| Granulation pit cooling spray โ secondary zone | Full-cone, high-flow | Coarse coverage / 2โ4 bar | Cooling and dust knockdown in granulation pit; large free passage for sump water recirculation; 316L SS body | 316L SS |
| BOF oxygen lance external cooling ring | Full-cone, uniform ring distribution | Uniform film / 0.5โ3 bar | 100% circumferential coverage; design for n-1 nozzle redundancy; continuous operation during blow; 316L SS body and manifold | 316L SS |
| BOF converter hood spray cooling | Full-cone, panel coverage | Panel wetting / 0.5โ2 bar | Uniform coverage of hood panel exterior surfaces; evaporative supplemental cooling; 316L SS in CO/steam/fume environment | 316L SS |
| EAF electrode and roof cooling rings | Full-cone, small-diameter ring | Uniform film / 0.5โ2 bar | EAF roof and electrode collar operate at higher radiant heat load than BOF lance; Hastelloy C-276 for aggressive EAF fume environment | Hastelloy C-276 for EAF service |
| Ladle and tundish cooling sprays | Full-cone or flat-fan, external | Surface wetting / 2โ5 bar | External cooling of ladle shells and tundish covers between heats; 316L SS; large free passage for recycled cooling water | 316L SS |
Materials for Steelmaking Spray Service
316L SS throughout for lance, hood, and granulation service in CO/steam/fume environments. SiC for granulation nozzle bodies where combined thermal shock, abrasion from slag fines, and acidic condensate attack exceed 316L SS service life. Hastelloy C-276 for EAF electrode cooling in aggressive fume environments.
Slag Value and Lance Life Both Depend on the Same Nozzle Decision.
Granulation nozzle selection determines GBFS glass content and cement value. Lance cooling ring geometry determines blow cycle reliability and hardware life. Contact NozzlePro with your runner geometry, tap rate, lance diameter, and service water conditions.