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PreheaterPrecalciner System Typical Length to Diameter ratio 11:1 There are still five jobs to be done Drying Preheating Calcining Sintering Cooling BURNER LOCATION FLAME OF BURNER Criteria for Modern Burner Design and Operation
Preheater/Precalciner System •Typical Length to Diameter ratio 11:1 •There are still five jobs to be done •Drying •Preheating •Calcining •Sintering •Cooling Preheater Precalciner Kiln 60% Fuel Split 40% BURNER LOCATION FLAME OF BURNER HMC / DP May 2000 Criteria for Modern Burner Design and Operation Key figures for burner design and operation: 1) Primary air rate: PA = 10 - 12%① ① based on stoichiometric combustion air; without transport air 2) Specific axial momentum: Gax = 7-10 N/MW② ② including fuel and transport air ➨ Minimum 200 mbar primary air fan, better 250 mbar Criteria for Modern Burner Design and Operation 3) Injection velocity coal: v = 25 - 30 m/s 4) Consider future use of AFR when purchasing a new burner: Foresee at least one additional channel in burner center Features of Actual Burners Pillard Rotaflam FLS Duoflex KHD Pyrojet Unitherm M.A.S Greco Pillard Burner Features: • Primary air fan with 250 mbar standard • Separate adjustment of burner tip cross section for axial and radial air FLS DuoFlex Features: • Primary air fan with 250 mbar standard • Adjustment of burner tip cross section (only the sum of axial and radial air) KHD Pyrojet Features: •Jet air with approx 1000 mbar axial air pressure (blower needed) • No adjustment possibility of tip cross sections Jet air Nozzles FLS Duoflex Burner with Gas Nozzle Fuel Oil Atomization Fixed orifice and variable pressure (e.g Pillard MYS) - Flow rate controlled by pressure (typically 40 bar) - Turn down ratio to Variable orifice and constant pressure (e.g FLS TFSM) - Flow rate controlled by needle valve (typically 25 bar) - Turn down ratio to Assisted atomisation with steam or compressed air - Turn down ratio 10 to (e.g LECHLER) - Approx 12% air or steam needed (5t/hOil 600kg/hAir) Mechanical Atomizers with Fixed Orifice and Variable Pressure Pillard MYS atomiser: Unitherm atomiser: Mechanical Atomizers with Fixed Orifice and Variable Pressure This type of atomiser is the most common for fuel oil The oil throughput is governed by the pressure of the fuel oil (within the range given by the selected discharge opening/orifice plate) With these atomisers the fuel oil flow in the atomiser head is usually subdivided into a tangential flow (also called primary circuit) and an axial flow (also called secondary circuit) By adjusting the pressure and thus the ratio of these components, it is possible to alter the spray angle of the fuel jet In general, an increase of the tangential oil pressure leads to intensified swirling of the oil which has the tendency to shorten the flame Typically the differential pressure between the two flows is in the range of 0,5 - bar (pressure of tangential is higher) The overall pressure is usually approx 40 bar However flame shape control is not only a result of atomiser adjustments, but also a function of primary air control Other Atomizer Types Mechanical atomiser with variable orifice and constant pressure: FLS type TFSM (needle valve principle) Assisted atomisation through steam or compressed air: Pillard FLS (TFSM) Type This type of atomiser employs the adjustable needle valve principle for throughput control By moving the needle back and forth, the open cross section of the orifice can be adjusted Needle valve atomisers are mainly used by FLS Atomising pressures is kept constant at 25 bar The turndown ratio is limited to 1:5 – 1:6 Compressed Air or Steam Atomizer Type This type of atomiser uses compressed air or steam instead of tangential oil to create an intense swirl in front of the orifice plate The advantage of these atomisers is the higher turndown ratio because even a small amount of oil can be atomised effectively with compressed air or steam Another advantage is that fuel oil with some solid impurities can also be atomised The disadvantage of these atomisers is the need for a significant amount of compressed air or steam (typical value: 0.1 – 0.12 kgAir/Steam/kgFuel) Waste oil/solvent in calciner Atomization air Oil Waste oil/solvent nozzle Atomization Air channels Oil channel Coal in a calciner Waste oil & coal in a calciner Waste oil Coal Kiln Burner Refractory - Damage • Water steam explosion • Reason: missing or inadequate evaporation holes or too fast heating up Quick Calculation of Burner Momentum Momentum = Velocity * Massflow Quick calculation of specific axial momentum Gax: Gax = %PA * vPA* 1/300 [N/MW] % PA = percentage of primary air [%] Primary air velocity (Bernoulli) : vPA = √ (2 * pTip / ρTip ) [m/s] pTip ≈ pressure at burner inlet - 5% [Pa] ρTip = air density at burner tip ≈ T = 50°C, p = ambient pressure Example: Amount of primary air: PA = 15%; pBurner Inlet = 200mbar → vPA = 158m/s → Gax = 7.9N/MW + 1N/MWfor Coal = 8.9 N/MW Consequences of Poor Burning Volatilisation of sulfur Build-ups Kiln unstable Ring formation Cyclone blockage Inlet temperature high Dust cycle higher Heat consumption high Incomplete combustion (CO) Production low Brick life reduced by unstable coating Availability low OEE and Quality low Free lime variation Early strength low