Biofuels and Biomass Systems PDF

Faculty of Engineering and Applied Science MECE3260U-Introduction to Energy Systems Biofuels and Biomass Systems Dr. Ibrahim Dincer Professor of Mechanical Engineering OUTLINE  Introduction  CO2 Balance  Biomass  Com...

Faculty of Engineering and Applied Science MECE3260U-Introduction to Energy Systems Biofuels and Biomass Systems Dr. Ibrahim Dincer Professor of Mechanical Engineering OUTLINE  Introduction  CO2 Balance  Biomass  Combustion-Gasification-Pyrolysis  Biofuels  Biogas  Biodigestion and Biodigesters  Micro gas turbines  Case Study  Closing Remarks 2  Introduction It is one of the oldest energy sources on the earth. Biomass originates from the photosynthesis portion of the solar energy distribution and includes all plant life (terrestrial and marine), all subsequent species in the food chain, and eventually all organic wastes. Biomass resources come in a large variety of wood forms, crop forms, and waste forms. The basic characteristic of biomass is its chemical composition in such forms as sugar, starch, cellulose, hemicellulose, lignin, resins, and tannins. Biomass energy (or bioenergy) can be used for commercial heat, electricity and transportation fuel applications. Energy crop fuel contains almost no sulfur and has significantly less nitrogen than fossil fuels [reductions in pollutants causing acid rain (SO2) and smog (NOx)]. http://www.ambbeijing.um.dk/NR/rdonlyres/04853A83-59E6- 40C7-8013 74E853784CC0/0/biomass_sources1.jpg Source: Google Images 3 CO2 Balance Biomass generates about the same amount of CO2 as do fossil fuels (when burned); but from a chemical balance point of view, every time a new plant grows, CO2 is actually removed from the atmosphere. The net emission of CO2 will be zero as long as plants continue to be replenished for biomass energy purposes. If the biomass is converted through gasification or pyrolysis, the net balance can even result in removal of CO2. Energy crops such as fast-growing trees and grasses are called biomass feedstocks. The use of biomass feedstocks can help increase profits for the agricultural industry. Source: AFS Biomass Ltd 4  http://www.sintef.no/upload/Energiforskning/Bilder/Energiprosesser/Energy_biomass_waste.gif Source: IMAM Ambiente Plant biomass energy is transformed by three major conversion processes 5  Combustion-Gasification-Pyrolysis  Combustion: A burning process, including the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species.  Gasification: A process that converts organic or fossil based carbonaceous materials into CO, H2, CO2 and CH4. It is achieved by reacting the material at high temperatures (>700°C), without combustion, with a controlled amount of oxygen and/or steam. The resulting gas mixture is called syngas (from synthesis gas or synthetic gas) or producer gas and is itself a fuel.  Pyrolysis: A thermochemical decomposition of organic material at elevated temperatures in the absence of oxygen, occurring typically at atmospheric pressure and operating temperatures between 400-800°C. 6 Biowaste to Energy (Kruger, 2006). A waste-to-energy plant Source: US-EIA 7 BIOFUEL: Gas or liquid fuel made from plant biomass, including wood, wood waste, wood liquors, peat, railroad ties, wood sludge, spent sulfite liquors, agricultural waste, straw, tires, fish oils, tall oil, sludge waste, waste alcohol, municipal solid waste, landfill gases, other waste, and ethanol blended into motor gasoline. (Kruger, 2006). www.natsource.com/markets/index.asp A fuel produced from dry organic matter or combustible oils produced by plants, including alcohols (from fermented sugar), bio diesel from vegetable oil and wood. www.esd.rgs.org/glossarypopup.html Fuels devised from biological materials including crops (especially trees) and animal wastes. www.ecifm.reading.ac.uk/glossary.htm 8  Biogas Termed as methane or gobar gas, it comprises a mixture of gases. Its composition varies with the type of (Kruger, 2006). organic material used. It is a fuel of high calorific value, resulting from anaerobic fermentation of biomass. The calorific power of biogas depends on the amount of methane in its composition, e.g., 5000 to 6000 kcal/m3. It can be used for stove heating, campaniles, water heaters, torches, motors, and other equipment. (Kruger, 2006). 9 Sunfad Electrical Group Co., Ltd. 10 Biodigestion and Biodigesters  Some key factors: material temperature (preferably: 30-35ºC), biodigestion acidity (i.e., pH: preferably: 6-8), nutrients (e.g., N2) and their concentration, concentration of solids (preferably: 7-9%). At these conditions, the biogas production per kilogram of raw material is higher and faster.  The biodigester is usually buried because underground temperatures are higher and more constant.  The use of biomass and biodigesters introduces several advantages for rural applications, where leftover cultural and animal residues can be used to obtain biofertilizer (i.e., the organic material processed in biodigesters can be used as fertilizer).  Biomass and biodigesters can be used to provide necessary energy for illumination, heating, and to drive motors. (Kruger, 2006). 11 12 Micro Gas Turbines Thermal Systems - Wikidot They are originally designed for aircraft and helicopters and customized for customer- site electric user applications. Microturbines from 30 to 400 kW are available for small-scale distributed power either for electrical power generation alone, in distributed electrical power generation, or in combined cooling or heat and power systems. They can burn fuels, including natural gas, gasoline, diesel, kerosene, naphtha, alcohol, propane, methane, and digester gas. They operate on the nonideal Brayton open cycle with heat recovery. Thermoelectric power generators, and fuel cells may be integrated with a gas turbine generator. GreenPowerSystems.com 13 Most Typical Applications Peak shaving and base load power (grid parallel) Combined heat and power Stand-alone power Backup/standby power Ride-through connection Primary power with grid as backup Microgrid Energia Electrica 14  (Kruger, 2006). (Kruger, 2006). 15 BRAYTON CYCLE: Gas Turbine Cycles The Brayton cycle was first proposed by George Brayton for use in the reciprocating oil-burning engine that he developed around 1870. An open type Brayton cycle A closed-type air-standard Brayton cycle. 16 The mass, energy, entropy, and exergy balance equations for each component of the Brayton cycle. 17 Case Study: SOFC and Biomass Gasification Systems for Better Efficiency and Environmental Impact by Colpan et al. (2010) Objective: To compare, a conventional biomass fueled power production system (a steam turbine system using the heat recovered from the combustion of biomass) with an Integrated (advanced) biomass gasification and SOFC system in terms of efficiency and environmental impact as energy efficiency, exergy efficiency and specific greenhouse gas emission. Exhaust Biomass An Integrated biomass gasification and SOFC system Dryer Cyclone Filter SOFC Gasifier Heat recovery steam generator (HRSG) Steam to users DC power Inverter AC power Afterburner HRSG Pump Blower Air Water 18  Input Data Environmental temperature 25 °C System-II (continued) Type of biomass Wood Temperature of air entering the 850 °C Ultimate analysis of biomass [%wt 50% C, 6% SOFC dry basis] H, 44% O Pressure of the SOFC 1 atm Moisture content in biomass [%wt] 30% Cell voltage 0.7 V Exhaust gas temperature 127 °C Reynolds number at the fuel 1.2 System-I channel inlet Conditions of the steam entering 20 bar Excess air coefficient 7 the steam turbine (saturated) Active cell area 10x10 cm2 Pressure of the condenser 1 bar Number of repeat elements per 18 Isentropic efficiency of the steam 80% single cell turbine Flow configuration Co-flow Isentropic efficiency of the pump 80% Manufacturing type Electrolyte- Electricity generator efficiency 98% supported System-II Thickness of the air channel 0.1 cm Moisture content in biomass 20% Thickness of the fuel channel 0.1 cm entering the gasifier [%wt] Thickness of the interconnect 0.3 cm Temperature of syngas exiting the 900 °C Thickness of the anode 0.005 cm gasifier Thickness of the electrolyte 0.015 cm Temperature of steam entering the 300 °C Thickness of the cathode 0.005 cm gasifier Pressure ratio of the blowers 1.18 Molar ratio of steam to drybiomass 0.5 Isentropic efficiency of the blowers 0.53 Number of cells per SOFC stack 50 Pressure ratio of the pump 1.2 Temperature of syngas entering the 850 °C Isentropic efficiency of the pump 0.8 SOFC Inverter efficiency 0.95 19  (W net ) system 50 Results η el = n fuel ⋅ LHV 45 System-II System-II 40 35 ExP ExD + ExL Efficiency [%] ε= =1− 30 ExF ExF 25 20 15 System-I System-I 10 5 0 5 Electrical1 efficiency Exergetic2efficiency 4.5 Specific GHG emission [g-CO2.eq/Wh] m  Comparison of the electrical (energy) and exergetic 4 GHG efficiencies σ= (W net ) system 3.5 3 2.5 2 1.5 1 0.5 0 Comparison of the specific GHG emissions System-I System -II 20 Case Study 1: Case Study 2: Case Study 3: Case Study 4: Case Study 5: Biomass type: Corn straw, rice husk, bamboo wood Schematic diagram of the biomass gasifier and CASU 25 Case Study 6: An integrated waste-to-energy system design for the Durham Region in Ontario 26 Closing Remarks  Biofuels are important for sustainable development.  Biomass is a renewable and reliable source.  It is a key option for standby power, power quality and reliability, peak shaving, and cogeneration applications.  Low cost and environmental impact make them more attractive.  Integrated systems appear to be more efficient and more environmentally benign and hence more sustainable. 27