Energy Conservation Work Shop on Knowledge exchange Platform on Best practices in Iron & Steel Industry By MCJ Energy Engineers Pvt Ltd
Who We are? MCJ Energy Engineers Pvt Ltd serving in energy conservation field for past 23 years and also an Accredited Energy Auditor & Empaneled Energy Consultant with BEE and EESL (MOP). Involved in Conducting 20+Baseline audit associate with EESL. 13 Monitoring and verification audit under 1 st PAT cycle. 20 Mandatory energy audit under EC ACT 2001 for Diverse Industries Thermal Power Plant, Cement, Iron and Steel and Paper and Pulp Industries. A total of 120+ energy audit have been done.
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Schematic Diagram of Steel Plant
Case Study on DRI Plant (350 TPD) Actual Mass Balance of Kiln (Basis 1 Kg Sponge Iron): Input T/Hr Kg Output T/Hr Kg Pellet Ore 20 1.538 Sponge Iron 13 1 Coal 22.6 1.738 Char 3.3 0.25 Air 60.69 4.669 Flue Gas 6.74 Dolomite 0.582 0.045 7.99 7.99 Comparison of Theoretical Mass Balance vs. Actual Mass Balance & Its Result: Instead of 1.43, consumption of ore is 1.53 i.e. 6.9% higher than the stoichiometric ratio. This implies that the ore contains 6.4% impurity which finally comes out with char.
Similarly coal consumption is 1.73 instead of 0.64 i.e. 107.3% higher than the theoretical requirement. The extra amount 1.73 0.64 = 1.09 Kg is used as fuel to supply the heat required to make up additional losses. The reductant part of coal is 0.64 Kg and the fuel part 1.09 Kg. Therefore total heat supplied to the kiln in the process of making 1 Kg sponge iron is 3889.84 Kcal. We have already seen that theoretical heat supplied to the kiln to produce 1 Kg of sponge iron is 2058.12 Kcal and actual is 3365.41 Kcal. Therefore, Thermal efficiency of the Kiln is 2058.12/3365.41 = 61.15%.
Comments: 1.To produce 13 ton of sponge iron, 8.32 tons of coal are used as reducing agent which contributes to 20.30 MKcal of heat. 14.28 tons of coal used as fuel which releases 34.85 MKcal of heat. Total heat input to the kiln per hour is 55.17 MKcal. 2) Heat loss thru flue gas is much less (44%) compared to theoretical one and value wise it is 24.53 MKcal/hr. Its Used through WHRB to generate 7 MW. 3) In this manufacturing process the products (sponge iron + char) are generated at high temp (around 1000 C) and they need to be cooled below 100 C before they are sent to subsequent handling processes. 4) Cooling is done in rotary cooler 7.7 Mkcal is been energy wasted and 13% of the input.
5) On contrary, two major heat loss areas are most often overlooked by the plant people-loss of fixed carbon thru char and skin loss due to high surface temp of the kiln. 6) High percentage of fixed carbon is found in char. Fixed carbon is the major contributor of heat in coal. Loss of fixed carbon leads higher demand of coal in the process. This loss is 7.13% or 3.96 MKcal/hr. 7) Similarly skin loss (which is the combination of radiation & convection loss) is 8.13MKcal/hr or 14.16%. 8) These two losses put together is around 27% of the total heat input.
Heat Balance
Temperature C Temperature at different stage of Kiln 1400 Temperature in different zone 1200 1000 800 600 400 200 0 1 2 3 4 5 6 7 8 9 10 11 12 Series2 1 2 3 4 5 6 7 8 9 10 11 12 Series1 858 905 1029 1052 1060 1082 1110 1144 1113 1043 1028 1032
Energy Saving opportunity : 1. Flue gas Temperature at WHRB ESP outlet - 145 C. 2. Scope of Heat Recovery in cooler which is used to cool down the hot sponge iron from 1000 1050 C to 60 100 C. Waste Heat Recovery APH for PA fan for sponge Iron Kiln: To Kiln Air ESP Outlet / ID Fan Inlet Duct APH PAB Fan
The Hot gases from WHRB of the Kiln at 140 160 Deg C would be taken into APH after ESP. After the exchange of the heat with the incoming primary air blower( PAB) air the hot flue gas will be sent back to stack through ID fan. Air from atmosphere is taken as suction by PAB fan and then forced through APH and then transmitted through suitable ducting to the kiln primary air inlet. Saving: The Air pre Heater system reduces heat requirement = 571320 Kcal/Hr Coal Saving = 103.88 kgs/hr = 2.494 tons/day Reduction in CO2 Emission = 5.935 tons/ day
Waste Heat Recovery ORC Power Project based on Kiln shell heat recovery Waste heat recovery is one of the most important development fields for the organic Rankine cycle (ORC). It can be applied to heat and power plants for example a small scale cogeneration plant on a domestic water heater. The working principle of the organic Rankine cycle is the same as that of the Rankine cycle. Purpose of the ORC focuses on the recovery of low grade heat power, so a superheated approach like the traditional Rankine cycle is not required. A fluid with a high latent heat and density will absorb more energy from source in the evaporator and thus reduce the required flow rate, size of the facility and pump consumption.
Installation of ORC have no direct effect on fuel saving, but as it generates electricity and will partially avoid electricity being consumed from the power generated from the power plant, using coal as a fuel. So there will be a fuel saving in terms of saving in coal consumption of the total unit. Saving : Mass flow rate Sponge iron inlet temperature Sponge Iron Outlet Temp Thermal Energy ORC Recovery Net Power Power Plant Capacity Water Inlet Temperature Water outlet Temperature Total energy Saving = 16300 kg/hr = 1000 Deg C = 120 Deg C = 1260.5 KwTh = 138.5 Kwe = 125 Kwe = 130 Kw = 90 deg C = 145 Deg C = 2550 units per day Energy Saving from ORC considering 330 Days of operation Coal Saving from APH, 330 days of operation Total Investment Payback Annual Saving = 18.81 Lakh unit Amount= Rs 75.24 Lakh/year @ Rs 4 per unit Saving : 823.02 Mt of coal : Rs 20.6 Lakh/year @ Rs 2500/Mt Rs 95.84 Lakh Rs 608.9 Lakh 6.3 Years
Case Study on Coke Oven Plant The productivity and coke quality are affected by several factors such as Initial charging temperature, rate of heating, moisture content, bulk density, cooking time and temperature of carbonization uncontrollable: Controllable: Oven Operation Moisture Content In coke Uncontrollable: Quantity of coal blend Coal Cake Breakage and Bulging
Temperature in C Pressure in mmwc Temperature in C 1350 1300 1250 1200 1150 1100 1050 Temperature Temperature 1339 1282 1263 1262 1219 1232 1212 1187 1165 1136 1059 1 2 3 4 5 6 7 8 9 10 11 Oven No -0.5-1 -1.5-2 -2.5-3 -3.5-4 Comparision of Temperature and Pressure Oven No Temperature C 1 2 3 4 5 6 7 8 9 10 11 1350 1300 1250 1200 1150 1100 1050 High negative pressure and temperature will be on higher side. With By-pass temp: 203 C, Chimney: 204 C is found to be satisfactory but still temperature in chimney can be reduced. Flue gas temp: 956 C, Boiler I/L: 906 C a drop in 50 C in flue gas between Outlet of gas oven and Boiler Inlet due to cleaning process. ID fan in Waste heat recovery Boiler is operating at -27 mmwc Pressure Oven No Pressure mmwc Linear (Pressure mmwc) 11 10 9 8 7 6 5 4 3 2 1-0.7-2.5-2.1-1.5-1.5-3.9-3.3-2.6-1.9-1.2 1 2 3 4 5 6 7 8 9 10 11-2.6
Heat Input Heat Output Calorific value of coal 7441.25 X 10³ Kcal Calorific value of coke 5583.803 X 10³ Kcal Calorific value of coke 711.54X 10³ Kcal Calorific value of 1067.31 X 10³ Kcal oven gas coke oven gas Sensible heat in coke 323.707 X 10³ Kcal Sensible heat in 11.094 X 10³ Kcal coke oven gas Heat Consumed* 1166.86 X 10³ Kcal 8152.79 X 10³ Kcal 8152.79 X 10³ Kcal Coke: it carries both sensible heat and potential energy. Potential energy can be obtained by combustions. Sensible heat cannot be used because coke cannot be used directly in blast furnace. It is to quenched and then stored for future use. Coke oven gas: it also contains potential energy and sensible heat. One should consider usage of sensible heat and potential energy of coke oven gas. Gas existing from coke oven contains, among gaseous constituents, dust. Hence, cleaning is required which may lead to loss of sensible heat. 14MW of Waste heat recovery boiler is used recover heat in coke oven gas.
Case Study On Blast Furnace
Performance of the blast furnace is depending upon: productivity Quality of Raw material Operation of blast furnance Ratio of feeding Raw material Quality of Raw material: Ash content Sulphur CSR (coke strength after reaction) CRI (coke reactivity index) micum indexes (M40 or I 40 and M10 or I 10) Sinter Parameters Desired value Actual Value CaO/SiO2 2.10 ± 0.07 2.11 MgO (%) 1.80 ± 0.20 2.28 SiO2 (%) 5.75 ± 0.30 5.87 FeO (%) < 8.00 8.56 P (%) < 0.050 0.05 Na2O+K2O (%) < 0.090 0.2 ZnO (%) < 0.015 - RDI (%) < 20.0 NA
Flux Iron Content Burden HOT Blast temperature Pulverized coal and Oxygen enrichment Ratio of Raw Materials: Raw Mix: Iron ore + Sinter + Flux Fuel Mix: Coal + PCI Coke Consumption: 0.515 T/THM PCI Consumption : 0.127 T/THM Operating Parameters: Top Pressure Silicon Content Iron Ore 33% Sinter Iron Ore Sinter 67%
Energy Saving Measures Increase in 10% of burden mix use results decrease in coke consumption by 2%. So increasing 5% burden mix will reduce 1% of coke consumption. Specific Energy consumption: 5284.19 Kcal/THM Average monthly use of Coke= 24350.767 MT Saving =243.50 MT New Specific energy consumption = 5244.4 Kcal/THM Reduction In CO₂ Emission= 19318.2 Tons per day
Sinter Plant Measures These parameters are affectively analyzed by drawing relationship between the below given following. AL2O3 SCC 1.Al2O3 Vs Carbon Input 2.FeO Vs Tumbler index 3.Bed Permeability Vs Burn Through Point 4.Burn Through Point Vs FeO Fixed C Feo Bed Permeability Feo SCC Tumbler Index BTP BTP The parameter which determine permeability of sinter bed. 1. Pressure drop across bed 2. Air Flow Rate
Pressure Profile of Sinter Plant -878-887 -884 Pressure (mmwc) Bellow 1 Bellow 2 Bellow 3 Bellow 4 Bellow 5 Bellow 6 Bellow 7 Bellow 8 ESP I/L ESP O/L -839-841 -882-882 How pressure drop across wind box will affect permeability and what purpose of permeability? Maximum air inflation through air bed it gives complete consumption of fuel so specific fuel consumption will be reduced. -854-904 -946 Δp can be increased by increasing the driving force across the bed i.e. under grate suction for sinter machine. But for a particular sinter machine, under grate suction depends on exhauster capacity & suction track dimensions. As per design pressure drop at ESP O/L should be -1100mmWC but they are achieving around -950 to -850 mmwc. If suction pressure is high then recirculating lines will be high that means pressure drop should be maintained as per requirement.
Case Study on Captive Power plants The efficiency is the different between losses and energy input. Parameters which influence Boiler efficiency Uncontrollable: GCV value of coal. Properties of coal. (%Carbon, %ash, %Hydrogen, %Nitrogen,%oxygen, %Moisture) Ambient Temperature. Controllable: Flue gas Outlet temperature at APH outlet. %O₂, % CO₂ and %CO in flue gas. Loss of Ignition
> Three 30TPH AFBC are consider for this case. > The graph which compares design and Actual efficiency. > Deficit in efficiency of boiler will be discussed further. 90 80 70 60 50 40 30 20 10 0 Design Vs Actual Efficiency AFBC -1 AFBC -2 AFBC-3 Design 84 84 84 Actual 75.43 78.51 76.53 79 78.5 78 77.5 77 76.5 76 75.5 75 74.5 74 73.5
Heat Balance of Boiler
Flue gas temperature Vital Parameters %O₂ in Boiler Loss if ignition %O2 LOI Flue gas temperature AFBC-1 11 7 146 AFBC-2 4.9 7 134.03 AFBC-3 9.6 7 142
Reason for High LOI possible: LOI of 7% 1. There is severe Fluctuation in operating Load, FD air is Decreased or increased as per Load fluctuation. 2. PA was lesser than necessary. 3. FD was lesser than necessary. 4. The Furnace draft was maintained at Low instead of design draft. The operation indicates Air velocity already in decreased condition irrespective of load. The main reason was identified that the air settings indicated insufficient air in the system, causing LOI as unburn carbon.
Efficiency With 11 & 9.6 % O2 it will be either leakage from air pre heater tube or air ingress. Flue gas temperature is 10 C higher than design but it can be bring back to normal once O2% is under desired level. Desired Values: % O2 LOI Flue gas temperature AFBC-1 4.5 4 134 85 AFBC-1 Actual Vs Design 80 75 70 Desired Actual AFBC-1 83.78 75.43
Efficiency Efficiency %O2 LOI Flue gas temperatur e AFBC-2 4.9 4 134.5 85 84 83 82 81 80 79 78 77 76 75 AFBC-2 Actual Vs Design Desired Actual AFBC -2 83.79 78.51 %O2 LOI Flue gas temperatur e AFBC-3 4.5 4 134 86 84 82 80 78 76 74 72 AFBC-3 Actual Vs Design Desired Actual AFBC-3 83.84 76.53
27.4 28.3 66.4 61.77 78.9 96 Performance on Economizer AFBC -1 AFBC- 3 ECO-1 ECO-3 Gas temperature at Economizer IN C 350 461 Gas temperature at Economizer OUT C 225 264 FW temperature at economizer IN C 107.5 122 FW temperature at economizer OUT C 173.9 218 HEAT GAINED BY FEED WATER EFFECTIVENESS % HEAT TRANSFER
Performance on Air-Preheater Calculation: Actual Air temperature at APHout : 117 C Design Air temperature at APHout : 137 C Desired Air Temperature at APHout : 127 C Heat pick up @ 117 C Kcal/hr : 832158 Kcal/hr Heat Pick up @ 127 C Kcal/hr: 932418 Kcal/hr GCV of Coal Kcal/Kg : 3100 Saving in Kcal/hr = 100260 Kcal/hr = 100260/3100 = 32.34 kg/hr Reduction in CO₂ = 76.96 kg/hr Total saving = Rs 6.50 Lakh /annum Investment = Rs 6 lakh Payback = 11 Month Calculation: Actual Air temperature at APHout : 122 C Desired Air Temperature at APHout : 133 C Heat pick up @ 122 C Kcal/hr : 2022872.6 Kcal/hr Heat Pick up @ 133 C Kcal/hr: 2275732.86 Kcal/hr GCV of Coal Kcal/Kg : 3100 Saving in Kcal/hr Reduction in CO₂ Investment Payback = 252859.26 Kcal/hr = 252859.26/3100 = 81.56 kg/hr = 194.11 kg/hr = Rs 8 Lakh = 6 Month
Case study on Boiler Feed Pump Parameter Units Design s value Flow m³/hr NA Pressure Kg/cm2 110 Power Kw 250 No of stages 11
Each feed control valve controls the quantity of the flow w.r.t the boiler drum level. Pressure drop across each equipment in the feed water circuit is estimated and as shown in the below table Parameters Pressure drop Approximately, 13 kg/cm2 is the pressure drop is taking place across the control valve. FRS (Flow 2 regulation station) ECO 3 Static head 3 Pipe losses 1 Total 9 kg/cm2 Boiler drum level is being controlled by three element control valve. This automatic flow based control valve operates based on the level of the boiler drum. As per the drum level the open % of the control valve varies. Flow controlling with the control valve is not an energy efficient mechanism. The loss happening across the control valve can be minimized / reduced by reducing the speed of the pump. With 11 stages of Boiler FEED PUMP each stage produces 10 kg/cm2. At present discharge pressure is 94.5 Kg/cm2. so only 9.5 stages are in operation doing useful work.
Recommendation: Blinding of one stage in BFP doesn t make any difference but it will make difference power consumption by motor as each stage consume 25 KW. Saving calculation: Present power consumption = 250 kw Savings at 8% = 20 kw Yearly savings (kwh) = 20 kw *8000 hours = 176000 kwh Yearly savings in Rs. = 176000 kwh x Rs. 4/kWh= Rs. 704000 Investment = Rs 1Lakh Payback = 2 month
Temp In C Case Study on LP heater Performance assessment 100 90 80 70 60 50 40 30 20 10 0 C C C C Temperature FW Heaters out Design vs measured Temperature FW Heaters In Temperature Extr Steam to Heaters Terminal Temperature Difference (TTD) measured 83.59 50.28 88.72 8.31 Design 91.08 49.08 94.08 2.871 100 90 80 70 60 50 40 30 20 10 0 1. Extraction Steam temperature is Low due to low pressure compared to design which is 5.6% 2. With Inlet Feed water temperature is 2.4% more than design. 3. Outlet feed water temperature is 8.2% less than Design. 4. TTD is more than design. 5. By considering Low Input and Same low output with TTD as supportive parameter also less than Design. 6. We can conclude that LP heater working satisfactory.
Case Study on HP heater Performance assessment 1. Extraction Steam temperature is Low due to low pressure compared to design which is 4.9% 2. With Inlet Feed water temperature is 4.2% less than design. 3. Outlet feed water temperature is 6.4% less than Design. 4. TTD is greater than design. 5. By considering Low Input and Same low output with TTD as supportive parameter also greater than Design. 6. So it can be concluded that HP heaters need to be checked.
HP HEATER MEASURED DESIRED FW temp outlet (ºC) 190.13 193.86 FW temp inlet (ºC) 139.06 139.06 FW flow (TPH) 47 47 SATURATION Temp. (ºC) 194.8 194.8 Sp. Heat of water(cp) 4.19 4.19 HEAT (KJ/kg) 37442300.9 38176849.8 HEAT (Kcal/hr) 8948934.57 9124496.163 HEAT LOSS (Kcal/hr) 175561.6 GCV OF COAL(Kcal/kg) 4015 FUEL LOSS (TPA) 365.47 Considering 50% achievable 183 FUEL COST (Rs./Ton) 4500 SAVINGS (LPA) 8 Investment 5 Payback 8 Months Saving Calculation
Case Study on cooling Tower Parameter Unit CW-1 CW-2 CT outlet temp To C 28.2 32 CT Inlet temp Ti C 36.9 38 Wet Bulb Temperature of air Tw C 25.5 26.5 Flow m3/hr 2130 2992 Efficiency of cooling Tower 75.44 52.17 Range C 8.6 6 Approach C 2.8 5.5 COMPARISION CHART CW-1 CW-2 75.44 52.17 8.6 5.5 2.8 2.8 Efficiency Range C Approach C
Condenser Performance associate with cooling Towers Parameter Unit Conden ser-1 Condenser -2 Unit Load MW 5.5 5.5 vacuum Kg/cm² -0.91-0.87 Condenser CW inlet temp C 28.3 32 Condenser CW outlet temp C 36.9 38 Condenser CW flow m³/hr 1950 2992 1. Vacuum in Condenser is getting deteriorated due to Outlet cooling water from cooling tower. 2. Approach to maintain between 3-4 C. 3. Where flow of Cooling tower is 2992 m3/hr but capacity of cooling tower is around 2160 m3/hr and required is 2980m3/hr. so the cooling tower need to be upgraded to required capacity or to be replace cooling tower. Rise in cooling water temperature C 8.6 6
Recommendation and Saving Calculation Recommendation: CW-2 cooling tower need to be upgraded or to be replaced. Saving Calculation: 1. Condenser Vacuum can be maintained and to improve the desired vacuum of -0.91 Kg/cm2 Comparision of Heat Rate The estimated steam savings/mw = 0.27 Ton/MW Turbine heat Rate Kacl/hr The steam savings/hr = 0.27 x 5.5 Linear (Turbine heat Rate Kacl/hr) = 1.49 tons 3982.11 The equivalent generation per hr = 0.24 MWh Taking 60% achievement = 0.144 MW 3838.83 The Annual generation @ 0.85% = 881.28 MWh The estimated savings in cost @ Rs 5 = Rs.44 Lakh Vaccum -0.87 Vaccum -0.91
2. The ΔT of the cooling water across cooling tower will be improved and flow of the cooling water can be further be reduced. By mass balance between present and improved operating conditions M1 X cp X Δt1 = M2 X cp X Δt2 M1 X Cp X (38-32) = M2 X cp X (38-28) M2 = 0.4 M1 Hence 15 % reduction in flow is possible on conservative side. 15% power reduction in Cooling Water Flow. 3. Present Power consumption of pump (Cw-1 and Cw-2) = 251 Kw Power saving Saving @ Rs 5 = 251*0.15*330*24 = 271080 kwh = Rs. 14 Lakh Total saving In Kw = 881280 + 271080 = 1152360 kwh Total Saving in Rs. Total Investment for new cooling tower = 58 Lakh = Rs 120 Lakh Pay back = 25 month or 2 years
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