Downloaded 30 times
Uploaded byTesfaldet Gebregerges
Biomass drying for combustion
This document summarizes a seminar on optimizing biomass drying for combustion. [1] Biomass comes from various sources like wood, waste, and algae and is dried to increase its heating value before combustion. [2] A model was developed to analyze drying kinetics and optimize drying time, rate, energy needs. [3] Experiments using thermogravimetric analysis characterized wood drying and the model was used to evaluate design parameters and maximize annual profit from a drying process.
Biomass drying for combustion
- 1. HKUST EVNG Seminarseries
- 2. o ptimum Biomass Drying for Combustion – A Modeling Approach Tesfaldet G tgaa@ust.hk March-11-2013
- 4. Contents • Biomass Types •Biomass to Energy Routes • Biomass drying for heating value Enhancement-Modeling and optimization • Results • Discussions • Future work
- 5. Biomass Types • Notlimited to woody biomass and crops . • Includes some organic wastes with high moisture contents like sludge ,microalgae and etc .
- 6. Biomass to EnergyRoutes •While biomass with moisture levels of 55 - 65wt% can sustain combustion, the optimum moisture content is 10wt% - 15wt%. http://www.toyo-eng.co.jp/en/product_line/environment/baiomass/index.html
- 7. Why Drying? • Burningbiomass with high moisture content : • reduces the combustion temperature • incomplete combustion • undesirable reaction products • requires a large amount of auxiliary fuel to make it combustible • Drying of biomass: – Can increase the combustion efficiency, reduce pollution and improve operation. • BUT – Drying of biomass is an expensive process that requires huge capital investment and energy input. • Therefore ,the level of drying should be optimized.
- 8. Biomass Drying forcombustion-Modeling GOAL • To develop a validated model of the drying kinetics of solids like wood, solid wastes and sludge for heating value enhancement before combustion process. • To use the model to analyze the drying time , moisture removal rate ,Energy requirement and design parameters for practical drying of solids. How? • Material and energy balances, heat transfer and drying kinetics.
- 9. Drying process • Regardlessof drying particle shape, there exists simultaneous heat and mass transport.
- 10. Drying….. Solid in Heat source? Air in Heater Hot air Exit air Solid out Air •TGA………………..…☑ •Temperature ……☑ •TG-DSC……………. ☒ •Humidity ………….☑ •Dryer Type …....…☒ •Velocity ……………☒ •Drying models……☒
- 11. Things to do AirHeater • Mathematical model- Psychometric analysis Dryer • Drying kinetics models- • Experiment-Thermogravimetric analysis (TGA) • Sample (Type, shape, moisture content) Product value • Heating value enhancement.
- 12. Air heater • Thecorresponding property change of air for moisture removal from the solid is calculated by making use of psychometric relations (equations). • The air heater cost was determined for the required air property change.
- 13. Dryer • For sizingthe dryer as well as determining the level of the drying, it is important to obtain the drying kinetics of which the drying rate inside the dryer is calculated.
- 14. Drying Kinetics models •General forms: 1. Diffusion based model….Fick’s Diffusion Equation 2. Thin layer drying curve based models (log, modified log)
- 15.
- 16. Experimental Drying kineticsdetermination • The moisture ratio is determined using TGA. 1 0.9 0.8 0.7 Moisture Ratio 0.6 60°C 0.5 70°C 0.4 80°C 0.3 90°C 0.2 0.1 0 0 100 200 300 400 500 600 Drying Time (sec) -20.2 -20.3 lnDeff -20.4 -20.5 ln(Deff) -20.6 -20.7 -20.8 y = -2045.x - 14.71 R² = 0.936 -20.9 0.0027 0.0028 0.0029 0.003 0.0031 1/T
- 17. The product value •Monetary value gained upon drying.
- 18.
- 19. Objective Function • Maximizingthe net annual profit (AP) of the process represented by : AP= Product value- (Heater cost +Dryer cost+ Operating Cost) • Operating cost=Steam cost Constraints 1. Air preheated temperature, 60oC Ta,2 110oC 2. Relative Humidity of the exhaust air, RH3 60% 3. The LHV of the final product, LHV 15MJ/Kg 4. Residence time > 100sec • Solver • Standard GRG Non-linear Solver-Excel.
- 20. Design parameters Parameters Value Feed rate of wood chips, Ws,1 (Kg/hr) 5000 Moisture ratio of the wood feed, X1 1 Temperature of the wood feed, Ts,2 ( C) 25 Pressure of the air feed, Pa,1 1atm or 101325Pa Temperature of the air feed, Ta,1 ( C) 25 Relative Humidity of the air feed, RH1 (%) 50 Temperature difference of air and solid at the dryer outlet, DT ( C) 5 Air heater Cost, Chtr ($/yr) 500 + 100 A 0.8 Dryer Cost , Cdyr ($/yr) 5000 + 5000 V 0.6 Steam Cost, CLP ($/kW) 0.1 Heat value of wood ($/kW) 0.05 Specific Heat of Air, Cpda( kJ/kg-C) 1.006 Specific Heat of Wood, Cpds, (kJ/kg) 1.2566 Specific Heat of Water Vapor, Cpv , (kJ/kg-C 1.89 Specific Heat of Water, Cpw, (kJ/kg-C) 4.186 Latent Heat of Water, LHw, (kJ/kg-C) 2270 Latent heat of LP steam, LHLP (KJ/Kg) 1999 Size of the wood , L, (m) 0.0005 Annual operation time, top (hrs) 2000
- 21. Results Base Case/1 Case 2 Case 3 Case 4 (L=0.05m) (L=0.0005m) (L=0.005m ) (L=0.05m) Moisture content of the dried wood, X3 (wt %) 17 17 17 43 LHV of the dried wood, LHVs (KJ/kg) 15000 15000 15000 9698 Solid residence time, t (hr) 0.11 8 247 0.03 Air feed rate, Wa,1 (kg/hr) 179,496 83,358 158,187 59,842 Air preheated temperature, Ta,2 (°C) 62 97 107 60 Air Exhausted Temperature Ta,3 (°C) 35 43 78 35 Heater Cost ($/yr) 50,250 71,138 160,818 21,161 Dryer Cost ($/yr) 21,495 219,008 1,700,822 12,237 Energy Cost ($/yr) 357,913 353,818 766,027 119,324 Product Value ($/yr) 1,260,453 1,260,453 1,260,453 1,172,979 Annual Profit ($/Yr) 830,795 616,489 -1,367,214 1,020,258
- 22. Discussion • The optimumsolutions indicated that the size of the wood chips strongly affects the economy. • When the size of the wood chips become too large, the drying time becomes too long thus significantly increases the dryer size and energy cost. • Another observation is that if a lower heating value of the dried wood chips is acceptable, the profitability is resumed. • in order to satisfy the constraint of minimum heating value without upsetting the environment and/or operation of the combustion process when drying too large or too wet biomass, auxiliary fuel is one of the options to be considered.
- 24. Research on pipeline,,,,,, Differential Scanning Calorimetry (DSC) -Exactly we can predict heat flow!
- 25. Thank you Go green!