BIOMASS : THERMOCHEMICAL CONVERSION & BIOCHEMICAL CONVERSION

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1 BIOMASS : THERMOCHEMICAL CONVERSION & BIOCHEMICAL CONVERSION Dott. Ing. Paolo Castaldo

2 KYOTO PROTOCOL The objective of Kyoto Protocol is to reduce Greenhouse Gas Emissions : In Europe by 2012 : - 8% (compared to 1990 baseline year ) In the World by 2012: - 5.2% (compared to 1990). To achieve these levels is necessary use Renewable Resources, as Biomass.

3 DEFINITION OF BIOMASS : - Biomass is any organic material of vegetable and animal - According to EU Directive 2001/77/CE : This directive aims at promoting electricity obtained from Renewable Energy Sources (RES): Biomass : The biodegradable fraction of products, waste and residues from agriculture (including vegetal and animal substances), forestry and related industries; Also the biodegradable fraction (organic fraction) of industrial and municipal waste.

4 BIOMASS 14th EUROPEAN CONFERENCE LATEST TECHNOLOGIES IN RENEWABLE ENERGY Biomass contains different types of products: agricultural waste (pruning trees, urban green, cereals, wheat, barley), forest industry waste(woodchips, sawdust, branches, leaves, bark), residues from cattle farms, energy crops (sunflower, beet, soybean, potatoes, corn, etc.), perennial crops (sugar cane, kenaf), arborre crops (poplar, willow, etc.), organic fraction of industrial and municipal waste.

5 The process of converting biomass into energy are basically based on thermochemical processing. Energy neither created nor destroyed, but is transformed (Lavoisier). It occurs in various forms : Mechanical Energy Thermal Energy Chemical Energy

6 Mechanical Energy : In mechanical, energy (E) is the ability to produce work (L) : E = t W dt [J] (S.I. ) Other units are : [kwh] 1kWh = 3.6 MJ ton of oil equivalent [Tep] 1Tep = 41.86GJ While is possible to convert all the mechanical energy into heat, not worth the back. Infact according to the second principle of thermodynamics (Kelvin Planck), inlet heat Q h is converted partially into work L, the remainder is transformed into outlet heat Q c Q h Closed System Q c L

7 Thermal Energy : Energy in heat form moves by : - Conduction - Convection - Radiation Quantity of heat that passes through the surface da in direction n in infinitesimal time of observation dt Fourier Postulate : dq n = -λda dt( T/ n) λ: conductivity T : temperature T(x,y,z,t) In stationary regime monodimensional : T(x)

8 Chemical Energy Biomass is a natural converter capable of converting solar energy into chemical energy. Biomass is the oldest form of exploitation of solar energy directly or indirectly resulting from the photosynthesis process. Plants by means of the chloroplasts, which contain chlorophyll, capture solar energy converting carbon dioxide (CO 2 ) of the atmosphere into organic matter (glucose C 6 H 12 O 6 ).

9 Chemical reaction of photosynthesis process : n CO 2 + n H 2 O + E (CH 2 O) n + n O 2 Considering the stoichiometric coefficients : 6 CO H 2 O + E C 6 H 12 O O 2 1 mole of glucose has energy content equal to 2872 kj This process let to convert the carbon dioxide of atmosphere,combined with water from the soil, in organic matter. E = h ν photons (light quantum) (ν( : frequency; h = Planck constant, where h = * [J s] )

10 The primary aim is to transform Biomass in a managing form to use it. The Biomass is energy converter, producing: heat, gas fuel, liquid fuel, electric energy. The conversion processes of biomass in energy can be divided into two major categories : Biochemical Conversion Thermochemical Conversion

11 Biochemical Conversion : Materials with ratio (carbon/nitrogen) C/N < 30 and moisture > 30% (Products( suitable for the biochemical conversion: industrial wastewater, wastewater civil (urban waste water), organic fraction of municipal solid waste, animal wastes, aquatic crops, crop by-products (leaves and stems of beets, potatoes, etc) ). Anaerobic Digestion : (The anaerobic digestion plants can be fueled by residual with high moisture content) Is a biological process in an oxygen-free environment by the action of bacteria (as Escherichia Coli, Salmonella Tiphimurium, etc) which transform organic waste in Biogas (composed of more than 70 % methane CH 4 with the remaining 30% carbon dioxide CO 2 ).

12 Anaerobic Digestion in wastewater treatment plants : Solid waste from sewer wastewater depurated to the receiving water : Mechanical treatment 6-7 : Biological treatment Sludge Classic block diagram Depuration plant 8 : Chemical treatment 9 : Anaerobic Digestion 10 :Dehydration & sludge disposal Are used Digesters (being closed vessels), so that almost all gas is collected and used as fuel; this because the Biogas is composed primarily of methane which is a greenhouse gas that has an effect twenty times higher than the carbon dioxide.

13 Anaerobic Digestion in wastewater treatment plants : unheated digester inlet - sludge Outlet - Biogas Internal combustion alternative engines Biogas accumulation Electricity foam crust sludge in digestion Multiple layers digested and thickened sludge (reduction of volatile suspended solids by 50%)

14 Anaerobic Digestion in wastewater treatment plants : heated digester inlet - sludge Outlet - Biogas Electricity Internal combustion alternative engines Biogas accumulation Heat Cooler Pump

15 Anaerobic Digestion : A fresh sludge in condition of lack of oxygen could generate two types of fermentation : 1.Without input of fresh sludge - Putrefaction with decreasing ph (acid fermentation) and development of malodorous gases and corrosive at the same time (Hydrogen sulphide H 2 S) 2.Input of fresh sludge - basic fermentation (PH > 7) with development of odorless gas, as methane (CH 4 ) Anaerobic Digestion Digestion is the result of bacterial metabolism and is temperature sensitive. The natural process is about 2 months, but can be significantly reduced by increasing the temperature (through thermal power plant) with external heat release, promoting the kinetics of bacterial metabolism. The heating temperature of digester is C (m esophilic digestion). The gas produced can be used for the needs of the plant and for the production of electricity and heating.

16 Biogas from Landfill : Biogas extraction wells Pipeline alternator electricity generator Grid low tension - electricity transformer Landfill Filters Municipal solid waste (MSW) Internal combustion alternative engines The organic material is fermented by the action of anaerobic microorganisms producing biogas.

17 Thermochemical Conversion : Materials with ratio C/N > 30 and moisture < 30% (these types of material are suitable for combustion). The process is based on heating action, transforming the chemical energy of biomass in heat for the direct use of it and for production of electricity. The thermochemical conversion processes are based on the action of heat, which allows the chemical reactions necessary to turn matter into energy (most siutable products are: wood, cellulose and wood by-products (cereal straw, pruning residues, sawdust, wood chips), scraps of working (shells, hazel, rice husks, etc.).

18 Direct Combustion : The heat generated by combustion of biomass (generally in thermal power plant with good efficiency η = % ) is exploited in co-generation plants involving simultaneously thermal energy in conjunction with generation electricity. A benefit resulting from the Co - generation plants consists of a reduction of pollutant emissions into the atmosphere. The temperature of steam does not exceed 400 C, so it solved the problem of ashes that at such low temperatures remain solid.

19 In this discussion are considered n. 2 simplified schemes: a)co Co-generation plant with gas turbine b)co Co-generation plant with back pressure turbine (steam turbine) a - The compressor C sucks in air from outside, compresses adiabatically. The fluid compressed is sent in a combustion chamber where fuel combustion occurs. Combustible gases reach the turbine T making them expand adiabatically resulting in transfer of energy. b - Biomass is fed into the boiler by conveyor. The boiler provides heat Q 1 by generating steam; the turbine expand it, generating mechanical work. Heat is then transferred by condensing the steam through the cooling water circulating in the condenser and the pump returns the liquid to the required pressure from the boiler by closing the loop.

20 Scheme: a)co Co-generation plant with gas turbine Biomass Fuel CC The compressor C sucks in air from outside, compresses adiabatically. The fluid compressed is sent in a combustion chamber (CC) where fuel combustion occurs. Combustible gases reach the turbine (T) making them expand adiabatically resulting in transfer of energy (E).

21 Scheme: b) Co-generation plant with back pressure turbine (steam turbine) η = L/Q = η el. + η thermal = (L el. /Q 1 + ξ Q 2 / Q 1 ) η > 70% (electrical efficiency only 15%).

22 An application of Co-generation is District Heating,, which produces hot water at 120 C distributed in the urban area through a network of insulated pipes to buildings. Through a heat cooler, the hot water transfers heat to the condominium plant (domestic heating): -Heated environments, -Hot water for sanitary purposes -Avoid boilers, burners and chimneys Once given the heat, the water has dropped to 70 C, returns to Central to increase its temperature restarting the cycle.

23 District heating is composed of a transport network and a central production of heat. The optimal solution for domestic heating is through the use of pellet boilers for small plants (till 10 MW) and the system should be placed near the place of production of biomass (wood, crop land, sawmill, etc.). to avoid the incidence of transport that costs and contributes greatly to air pollution. In district heating systems, boilers with a grid, is possible to burn all the scraps of the wood (branches, bark, roots) also with high humidity. The most expensive part of a district heating is the distribution network, affecting the cost of investment between 50% and 80%.

24 District heating scheme : Cold water

25 Modern Plants use the Boiling Fluidised Bed (BFB). The steam temperature reaches 480 C and electrical efficiency of 25%, but with glassy ash deposits. Such combustion BFB is an alternative process to traditional methods of combustion in the boiler, especially when having solid fuels difficult to treat (irregular size, high levels water content, etc). Biomass is held in suspension through an appropriate air dose blown from below into the combustor. The fuel is distributed in a bed of inert (silica sand or alumina). - Efficiency > 90%

26 GASIFICATION Partial oxidation in lack of oxygen (using air-lower cost) at high temperature (1000 C), obtain synthetic fuel gas (S YNGAS) consisting of - CO (18 23%) - H 2 (18 23%) - CH 4 (6 9%) Fixed bed Gasifiers (the technology more used to obtain electricity is Downdraft Gasification ): consists of a cylindrical container and in the bottom there is a grid that supports the biomass and at the same time let the discharge of ash and the air passage. In Downdraft gasifiers the oxidant (air) flows in the same direction of fuel which is introduced from top of reactor and exits from the bottom passing for the grid. When the fuel meets the area of air inlet there is the reaction of gasification. The syngas produced by gasification with air has a low calorific power ( 4 6 MJ/Nm 3 ), since the air is composed primarily of nitrogen (N inert gas), that doesn t changes during the process and remains entirely in the final gas product.

27 % BIOMASS IN THE WORLD : BIOMASS % Mtep/year Milion terajoule/year Biomass in the World Developing Countries Industrialized Countries (USA : 3.2%) EUROPE Sweden, Finland, Austria from forest industry : % Italy : 2 3 % (according to the research report of Frost & Sullivan)

28 35% Other : 1%

29 The greatest contribution of renewable energies in terms of energy production in Europe is the Biomass: 64 %

30 Lower Heating Value H i of Biomass Biomass (dried matter) Hi [kcal/kg] Sugar cane bagasse 4500 Bark 4350 Sunflower stalks 4300 Poplar 4200 Willow 4200 Eucalyptus 4150 Sorghum 4200 Wood waste 4100 Straw 4100 Urban Solid Waste 2500

31 Lower Heating Value of Biomass The Biomass have a modest energy density compared to traditional fossil fuels, as crude oil, due to the moisture content of biomass (30% 50% by weight); so we have kcal/kg of Biomass compared to kcal/kg of crude oil. While we have 28 MJ/Nm 3 of Biogas (biomass) against 35,8 MJ/Nm 3 of Natural Gas (Methane) Very good heating value of Biomass. The main applications of biomass are energy production (bioenergy) and biofuels, for example to use for Local Public Transport in big cities as Rome, New York, Paris, London, Tokyo, etc.

32 Anaerobic Digestion in Europe and Cost Investment Anaerobic Digestion is considered one of the best technology for the production of energy. In Europe the Anaerobic Digestion is mainly related to depuration plants; there are approximately anaerobic digesters in U.E. Countries (Germany, Denmark, Austria, Switzerland, Italy, Sweden, etc.). The Cost of Investment of a Biogas Plant can be estimated approximately about : - Cost Investment : 2500 /kw installed (Investment of millions of euro Plants from 10 MW) - (So the Cost of Biomass Energy is the biggest obstacle); - Payback Time : Years. Net Present Value (NPV) = f (k : years; present costs; present revenues ). For NPV = 0 (PV = I ) we obtain 0 the PayBack Time (PBT), where I 0 Investment and PV is Present Value. is Initial So the Biggest obstacle still now is the economic investment; the main constraints are the cost of fulfillment plants, the cost of raw materials and the cost of transportation of biomass.

33 PayBack Time (PBT) : Present Value (PV) Initial Investment I 0 NPV = 0 (PV = I 0 => PBT = 18 Years)

34 Advantages and Disadvantages of Biomass -Disadvantages : The Cost of Energy from Biomass is still greater than the cost of Fossil Fuels. -Advantages : The economic gap is reduced if we consider the environmental aspects inside the cost benefit analysis. In fact Biomass is a clean and a Renewable Resource widely available locally everywhere in the World and helps to achieve the objectives of Kyoto Protocol. Biomass does not contribute to the greenhouse effect in atmosphere, unlike fossil fuels, because the CO 2 released into the combustion process is totally absorbed during the growth of Biomass (Photosynthesis Process) as Plants or Energy Crops ad hoc : Zero Emissions Impact.

35 CONCLUSION Biomass will play a strategic role (according to research report from Frost & Sullivan - Assessment for European Biomass of Energy Markets), since the growth of the price of crude oil (an exhaustible resource) and in terms of the attenuation of dependence on importation. The strategic objective set by European countries for 2020 is to produce 20% of energy from renewable sources ( ). The biggest obstacle still now is the economic investment; the main constraints are the cost of fulfillment plants, the cost of raw materials and the cost of transportation of biomass. Question slightly mitigated in some countries through government incentives. The point where should focus the current Governments Policy is the right balance between Economy and Environment, still tending much more towards the economy instead of environment. Respecting the Environment and Protect it for our generation and for generations to come, this is the main aim to be pursued.

36 THANKS FOR YOUR ATTENTION Dott. Ing. Paolo Castaldo