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Secret Losses in Dedusting Systems Optimisation of Ducts & routing pays off! SEAISI Seminar Session KUALA LUMPUR NOVEMBER 21 – 22, 2011 Volker Knoth Carsten Pfundstein Agenda Introduction Pressure drop Dampers Mixing Benchmark figures Examples The following tasks are to be fulfilled by a duct system INTRODUCTION Transport Cooling Mixing Distribution Change of diameter Change of shape (e.g. oval ↔ rectangular ↔ round) Easy operation and maintenance Agenda Introduction Pressure drop Dampers Mixing Benchmark figures Examples Ducts and chambers are the main “consumer” of static pressure… PRESSURE DROP – CONSUMPTION DEC* Sum=65 % * Consumption of booster fan capacity Ducts and chambers are the main “consumer” of static pressure… PRESSURE DROP – FURNACE DIRECT EXHAUST Sum=77% A dedusting system consists of the combination of different geometries… DUCT GEOMETRIES – ELBOWS & BENDS For reference: Piece of straight duct with same gas speed Examples: j = 90° d = 1500 mm R = 1500 mm Dp = 110 Pa R = 1000 mm Dp = 230 Pa lequ. j h b R Dp = 90° = 1000 mm = 2000 mm = 1333 mm = 45 Pa h = 2000 mm b = 1000 mm Dp = 120 Pa Dp = 5 Pa/m Dp – Factor: lequ. = 22 – 9 m 2,1 – 2,7 lequ. = 46 – 24 m NOTE: Straight ducting with proper dimensions is usually not the major issue! Ratio of flow rates and angle between ducts are the keys to success… DUCT GEOMETRIES – MERGING & DIVIDING OFF GAS STREAMS Vd V Vd V b b Va Examples: b = 45° Va = Vd Dp = 25 Pa Va b b = 90° = 45° Va = Vd Va = Vd Dp = 65 Pa Dpa = 75 Pa Dp – Factor: 2,3 – 2,6 b = 90° Va = Vd Dpa = 170 Pa Even small deposits can have big impacts… DUCT GEOMETRIES – DUST DEPOSITS ACTING AS AN ORIFICE Calculation model D (based on orifice situation) d D Real situation h s Examples: D = 2.000 mm d = 1.900 mm T = 50 mm h = 135 mm s = 1.000 mm v = 22,1 m/s Dp = 12,5 Pa 0,5 · (D – d) = T = thickness of dust layer dust deposit layer D d T h s v Dp = 2.000 mm = 1.750 mm = 125 mm = 435 mm = 1.650 mm = 24,6 m/s = 65 Pa D d T h s v Dp = 2.000 mm = 1.600 mm = 200 mm = 705 mm = 1.910 mm = 31,1 m/s = 250 Pa (165 000 Nm³/h @ 100 °C = 225 400 Am³/h; initial gas speed for D = 2000 mm is 20 m/s) Dp – Factor: 5,2 – 20 In a dedusting system known or secret deficits exist in almost every case DEDUSTING SYSTEM KEY COMPONENTS Bag Fan House #1 Damper Mixing Canopy hood Distributing Stack Damper SWD Cooler DCD EAF DOB DOB = WCD Bag Drop-out box DCD = Down comer duct SWD = Single walled duct WCD = Water-cooled duct House #2 Fan What is your guess on the sum of the above examples? DUCT GEOMETRIES – QUICK & DIRTY ESTIMATION Assumptions Typical dedusting system with primary and secondary exhaust system Two bag houses installed after upgrade of overall capacity Typical static pressure supply of main fan Design of duct system not optimum, e.g. 5 000 Pa 90° elbows 4 pc unification of flows 1 pc dividing of flows 1 pc dust deposits (100 – 150 mm) 3 pc Additional pressure drop due to design (4x120+1x40+1x100+3x75) Pa = 845 Pa Percentage of available pressure level based on full fan capacity (5 000 Pa) 17 % based on net capacity* (~3 000 Pa) *net capacity = without bag house 28 % NOTE: even small items can sum up to remarkable levels of losses! What is your guess on the operational cost impact? DUCT GEOMETRIES – QUICK & DIRTY ESTIMATION Assumptions Typical dedusting system with primary and secondary exhaust system Two bag houses installed after upgrade of overall capacity Pressure losses due to design problems 845 Pa Total flow rate of the exemplary dedusting system at main fans 1 366 300 Am³/h 1 000 000 Nm³/h Temperature at bag main fans 100 °C Resulting power consumption wasted for the unnecessary pressure loss 315 kW Yearly operation time (320 d x 24 h) Annual energy consumption Cost impact NOTE: 7 680 h 2 430 000 kWh (0,05 €/kWh) the amount of wasted money on the operational cost side is more than you think! > 120 000 €/a Simple systems could help to save a lot of money COMPARISON BETWEEN BSE HIGH TEMPERATURE QUENCHING (HTQ) SYSTEM AND CONVENTIONAL COOLERS LIKE TUBULAR COOLER Pressure Drop Ratio HTQ : TC 1 : 5–6 2x 90° turn 2x diameter change 20 m „duct“ length with low speed No Booster Fan required for HTQ 2x 90° turn (minimum) 2 – 6x diameter change 1x distribution of flow 80 m duct with medium speed 3x 180° turn 1x unification of flow Booster Fan S = required for TC Agenda Introduction Pressure drop Dampers Mixing Benchmark figures Examples Dampers are the regulating installation and need attention… DAMPERS – TYPES Multi-blade Type (twin rotation) Butterfly Type Multi-blade Type (counter rotation) Rotation direction for closing damper Dampers behave differently according to their design… DAMPERS – FLOW PATTERN & TURBULENCE Dampers are the regulating installation and need attention… DAMPERS – INFLUENCE ON FLOW RATE Damper curve for 4 – blade single blade design No precise control at low flow rates possible with butterfly damper Multi-blade damper characteristic more linear than butterfly damper Dampers are the regulating installation and need attention… BENEFITS OF A SMART DAMPER CONTROL SYSTEM Improved dedusting efficiency in Am³/kWh Reduction of specific dedusting cost in cost/t Control and visualisation of the entire dedusting system Protection of valuable equipment Simplification of emission control Optimised maintenance work Data trending for better process understanding and delay tracking Attractive cost/performance ratio for a quick return on investment Agenda Introduction Pressure drop Dampers Mixing Benchmark figures Examples Some problems derive from hidden processes… MIXING – A KEY ELEMENT FOR LIFE TIME AND PERFORMANCE Example: Optimisation of mixing Canopy Duct Canopy Duct DEC Duct Duct to Bag House DEC Duct Duct to Bag House NOTE: The duct to bag house is split vertically into two ducts feeding two lines. Left design: left duct = left bag house side encounters much more heat and dust load. Optimised right design distributes heat and dust well balanced to both sides. Some problems derive from hidden processes… MIXING – A KEY ELEMENT FOR LIFE TIME AND PERFORMANCE Example: Unbalanced load to bag filter lines after mixing chamber Canopy Duct Canopy duct Right bag house inlet Taverage = 84,5 °C DEC duct DEC Duct Left bag house inlet Taverage = 157,0 °C Green & red stream lines show bad mixing and unbalanced distribution. Improper mixing and unbalanced distribution leads to strong differences in bag house line inlet temperature. NOTE: Theoretical computer simulation results have been proven by real measurements. Symmetrical design is a good choice in many cases… MIXING – A KEY ELEMENT FOR LIFE TIME AND PERFORMANCE Mixing of DEC and SEC is done quick and uniformly before arriving at first split. Agenda - 23 - Introduction Pressure drop Dampers Mixing Benchmark figures Examples Some easy to calculate figures show you the potential… BENCHMARK FIGURES – WHERE IS YOUR SYSTEM? kW = specific energy consumption of dedusting system = sum of all energy consumers of system (fans, water pumps, compressors, etc.) t/h = productivity of steel production related to the investigated system Am³/h = total flow rate of system after main fans Specific energy consumption [kWh/t] = Dedusting system efficiency [Am³/kWh] = energy consumption [kW] productivity [t/h] total flow rate [Am³/h] energy consumption [kW] Some easy to calculate figures show you the potential… BENCHMARK FIGURES – WHERE IS YOUR SYSTEM? ACTION DEMAND DIAGRAM kWh/t 60 ! ? ? ? ? ? ? ? ? ? ? ? 20 Am³/kWh 200 650 Depending on the system and level of revamping the sky is the limit… BENCHMARK FIGURES – WHAT IS POSSIBLE? CUSTOMER EXAMPLES Change of specific cost (Cost/Am³) (Operational cost) Plant A -13 % Upgrade 15 % Plant B -20 % Upgrade new total 25 % -52 % 109 % -49 % 100 % Plant C -33 % Upgrade Plant D new Plant E Upgrade Change of specific flow rate (Am³/kWh*) (Dedusting system efficiency) 44 % -45 % 75 % -20 % 25 % -33 % * kWh = electrical power consumption at main fans Average 56 % Agenda Introduction Pressure drop Dampers Mixing Benchmark figures Examples High pressure losses due to convoluted duct routing EXAMPLE OF HIGH PRESSURE LOSSES High pressure losses due to sharp edges and elbows EXAMPLE OF HIGH PRESSURE LOSSES Not only reduction of operational costs … CUSTOMER EXAMPLE – ASIA before after Simplifying of arrangement by applying the KISS (Keep It Simple and Stupid) principle Thank you for your attention Questions? Please ask? Volker Knoth Carsten Pfundstein