Energy from Biomass PDF

UNIVERSITẦ DEGLI STUDI DI PADOVA LM Energy engineering Renewable Energy Technologies Energy from biomass D. Del Col Sources: Jay J. Cheng, Biomass to R...

UNIVERSITẦ DEGLI STUDI DI PADOVA LM Energy engineering Renewable Energy Technologies Energy from biomass D. Del Col Sources: Jay J. Cheng, Biomass to Renewable Energy Processes, CRC Press, 2018 Converting Biomass to Energy - A Guide for Developers and Investors, International Finance Corporation, 2017  What is biomass ? Biomass is a broad spectrum of organic matter, both of vegetable and animal origin, which includes the biodegradable part of products and residues from agriculture, forestry and related industries, livestock waste as well as the biodegradable part of industrial and urban. Therefore biomasses are all the products of agricultural crops and forestry, residues from agricultural processing, waste from the food industry, algae, and, indirectly, all organic products deriving from the biological activity of animals and humans, such as those contained in municipal waste.  tree and herbaceous species deriving from agricultural and forest crops; agricultural and forest residues such as straw, pruning, twigs, bark, (paglie, potature, ramaglie, cortecce) etc.; agro-industrial residues such as pomace (vinacce), vegetable waste, etc.; zootechnical residues such as droppings, animal waste, etc.; the organic fraction of municipal solid waste (the so-called "wet" fraction). Residual biomass and biomass deriving from energy crops The biomasses deriving from energy crops can in turn be classified into - oleaginous crops (such as rapeseed, soy, sunflower, palm, etc.) colture oleaginose ( come colza, soia, girasole, palma, etc.) from which vegetable oils and biodiesel are produced, - alcohol-producing crops (such as sugar cane, sugary sorghum, sugar beet, corn, wheat, etc.) colture alcoligene (canna da zucchero, sorgo zuccherino, barbabietola da zucchero, mais, frumento, etc.) from which ethanol is produced, - and from ligno-cellulosic crops (which include perennial woody species such as poplar, black locust (robinia), eucalyptus, etc., and perennial herbaceous species such as common reed (canna) and miscanthus (miscanto), or annual herbaceous species such as fiber sorghum) used to produce combustible dry matter. Biomass data European Commission's Knowledge Centre for Bioeconomy https://ec.europa.eu/knowledge4policy/bioeconomy Bioenergy in EU 1. Biomass for energy (bioenergy) continues to be the main source of renewable energy in the EU, with a share of almost 60%. The heating and cooling sector is the largest end-user, using about 75% of all bioenergy. 2. Bioenergy contributes to the EU’s energy security, as most of the demand is met from domestically produced biomass (about 96% in 2016). 3. Forestry is the main source of biomass for energy (logging residues, wood-processing residues, fuelwood, etc.). Wood pellets, mainly for heating and electricity production, have become an important energy carrier. 4. Germany, France, Italy, Sweden and the UK are the largest bioenergy consumers in absolute terms, while the Scandinavian and Baltic countries, as well as Austria, consume the most bioenergy per capita. European Commission's Knowledge Centre for Bioeconomy https://ec.europa.eu/knowledge4policy/bioeconomy Photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in carbohydrate molecules, such as sugars and starches, which are synthesized from carbon dioxide and water. The photosynthetic efficiency is the fraction of light energy converted into chemical energy during photosynthesis in green plants and algae. Photosynthesis can be described by the simplified chemical reaction Schematic of photosynthesis in plants. The carbohydrates produced are stored 6 H2O + 6 CO2 + energy → C6H12O6 + 6 O2 in or used by the plant. where C6H12O6 is glucose (which is subsequently transformed into other sugars, cellulose, lignin, and so forth). ENERGY STORAGE IN PLANTS Rain COMBUSTION AND ENERGY CONVERSION Minerals PREPARATION Ash Biomass potential RESIDUAL BIOMASS (residues and waste of forestry, agricultural and agro-industrial origin; wet fraction of Municipal Solid Waste) BIOMASS FROM ENERGY CROPS (oleaginous crops; alcohol-producing crops; ligno-cellulosic crops)  ENERGY EFFICIENCY OF THE PHOTOSYNTHESIS 50% of the energy of the solar spectrum can be effective (0,4-0,7 μm) _________________ 40% remains after reflection (about 20% is in fact reflected) 30% of this is exploitable (70% losses of the photochemical conversion process) 60% of this can be accumulated (40% is used by the plant for its own metabolism) REMAINS IN THEORY 7% if the climatic and nutritional conditions were ideal everywhere ACTUALLY 0.15-0.30% on average, with peaks 1%  ESTIMATE OF THE POSSIBLE MAXIMUM CONTRIBUTION OF BIOMASS TO ENERGY NEEDS Average solar irradiation 1400-1750 kWh/(m2 year), which correspondes to 1250-1500→ toe/(ha year) 7% →90-110 toe/(ha year), which corresponds to about 210-250 t/(ha year) of dry matter growth (LHV = 18 MJ/kg = PCI) ACTUALLY: max 30-60 t/(ha year) → η = 1 - 2 % on average 5-15 t/(ha year) → η = 0,15 – 0,5 %  ESTIMATE OF THE POSSIBLE MAXIMUM CONTRIBUTION OF BIOMASS TO ENERGY NEEDS Every year on Earth a total equivalent of 200 billion tons of carbon equivalent are fixed through photosynthesis, corresponding in energy to 72 Gtoe / year (6 times the current global annual energy requirement). Of course, only a small fraction of this is practically exploitable for the needs of society. The European estimate of the technically usable potential is 400 Mtoe / year, corresponding to 20-25% of current energy consumption. In Italy the estimate of the technically exploitable RESIDUAL biomass is 31 Mt / year of dry matter (25 Mt from the agro-forestry sector and 6 Mt from the industrial sector), corresponding to 7% of current energy needs. However, this is difficult to exploit for the high degree of territorial dispersion.  Biomass characterization The properties that are of the greatest importance include the following: 1. Moisture content 2. Proximate analysis a. Ash content b. Volatile matter content c. Fixed carbon 3. Ultimate analysis (elemental composition) 4. Heating value 5. Bulk density 6. Alkali metal content Jay J. Cheng, Biomass to Renewable Energy Processes, CRC Press, 2018 Moisture content is the amount of water in the biomass expressed as a percentage of the material’s weight. The complication in the use of moisture is that it can be expressed on a wet basis (MCw), dry basis (MCd), and on a dry ash-free basis (MCd-af ). Since moisture has a very significant effect on the overall conversion process, the basis on which the moisture has been reported should always be properly mentioned, and moisture content on a wet basis is the most commonly used basis. Increasing the moisture content of biomass from 0% to 40%, can decrease the heating value in MJ/kg by about 66%. A proximate analysis is the evaluation of the yield of various products obtained upon heating under controlled conditions. The proximate analysis is used to determine the volatile matter, the fixed carbon content, and the amount of ash. The biomass is heated to 400°C–500°C in an inert atmosphere, and under these conditions, it decomposes into volatile matter and solid char. The amount of volatile matter determines how easily the biomass can be gasified, which will affect the design of both boilers and gasifiers. The portion that remains after the determination of the volatile matter consists of fixed carbon and ash. This residue is usually combusted in the presence of oxygen to determine the fixed carbon and ash content. The volatile matter in biomass varies between 70% and 80% as compared to coal, which has volatile matter content of 20%–35%. As a result, the behavior of biomass in a gasifier is significantly different from that of coal. Biomass is easier to gasify and results in a higher amount of volatile gases that are formed upon heating. The ash content of biomass is also important because it results in the production of a waste stream that will need to be disposed. The chemical composition of the ash will especially affect its behavior at high temperatures, and this will impact the removal method and the disposal cost. The ash content in wood is usually