BIOMASS TECHNOLOGY Presented by Kiran Koshy Instructor : Dr.Ward Jewell
Overview What is Biomass? What are the different types? What are the pros & cons of Biomass Energy? What are the driving forces in the construction of Biomass Plants in US? What are the different Conversion Technologies?
Introduction Biomass , defined as all organic matters. one of the most wide-spread energy resources world wide. Its high availability and dispersed location enable it to be used for decentralized power generation. Biomass Power called “Carbon Neutral Electricity” now provides enough electricity to light about 8.5 million American Homes.
Biomass It’s a renewable energy source used to generated electricity (Biopower), fuels(Biofuels) and even to produce heat. Biomass Includes wood, Agricultural wastes, Municipal solid waste, Forest residues, construction debris, paper mill Scrap etc. It may also include plant or animal matter used for production of fibers or chemicals.
Watch this video to understand how biomass power is meeting America’s energy needsFrom Biomass Power Association(BPA) www.usabiomass.org
Biomass Pros & Cons.. Pros.. Improves the health of our forests. Provides waste disposal alternatives. Reduce GHG emissions. Reduce Criteria pollutants. The biomass energy is cost effective.
Cons.. The cost of installing and maintaining the infrastructure for processing the biomass is very expensive.. The food Vs. fuel debate. It is just not economical to produce, grow and transport biomass. It sometimes depend on seasonal crops like corn for ethanol production.
Forces driving US in the construction of Bio Power Plant Reduces our dependence on expensive foreign oil. Greatly reduce the Green house emissions. Provides a way to dispose the waster materials. Implementation of carbon credit. The need of additional generation capacity in US. “Biomass power provides ‘green’ electricity about 8500MW a year providing enough electricity to light about 8.5million American homes”.
Fundamental Forms of Energy use “Traditional Domestic” use in developing countries (fuel wood, charcoal & agricultural residues ) for household cooking, has conversion efficiency between 5% & 15% “Modern Industrial” experimenting with technologically advanced thermal conversion technologies having expected conversion efficiency between 30% &55%. Newer “Chemical Conversion Technologies”(fuel cell) has the maximum theoretical conversion efficiencies of thermal units. “Biological Conversion techniques” – Anaerobic digestion for biogas production and fermentation for alcohol.
Biomass to energy conversion technologies has to deal with feedstock-which can be highly variable in mass,density,size,moisturecontent and Intermittent supply. Modern technologies use fossil for drying, preheating
1.Direct Combustion Most of todays biomass plants are Direct fired system. Uses mostly solid Fuel biomass. The biomass fuel is burned in a boiler to produce high pressure steam that is used to power a steam turbine driven power generation. Boilers are differentiated by their configuration, size & quality of steam or hot water produced. Boiler size is measured in fuel input in MMbtu/hr & also by output in pounds of steam/hr. Typical boiler and steam turbine produce about 10MW electric output from 100 Mmbtu/hr heat input.
The average energy conversion efficiency is approximately 20% for the industry and the average plant size is 20 MW, with the largest approaching 75 MW. The small average plant size and low efficiency level has led to electricity costs in the 8-12 cent/kWh range.
a.Cofiring Biomass Cofiring in coal power plant
Cofiring One of the most cost effective conversion technologywhere biomass fuels sources like wood waste, waste paper, wood residues and Sawdust is cofired with coal. (The amount of biomass ranging from 5 to 15 % of the total heat input to the boiler.) It is the practice of mixing biomass with fossil fuels. Cofiring is typically used when either the supply of biomass is intermittent or the moisture content of the biomass is high. Cofiring of biomass with coal is principally viewed as a fuel cost reduction strategy. Co-firing biomass with coal has the potential to produce about 26 GW by 2020.
Worldwide about 40% of electricity is produced using coal. If only 5% of coal energy is replaced by biomass in all coal – fired power plants, this would result in CO2 emission reduction of around 300Mton CO2/Year Usually the cost of biomass fuels must be equal to or less than the cost of coal per unit of heat for Cofiring to be economically successful. Some utilities reduce fuel costs by Cofiring with biomass (The Tennessee Valley Authority, for example, estimates that it will save $1.5 million per year in fuel costs Cofiring with biomass at its Colbert plant.). The Cofiring efficiency is 35-45%. 182 Cofiring operations in united states (of which 114 or 63% have been at industrial facilities,32 at utility owned power plants,18 at municipal boilers,10 at educational institutions and 8 at federal facilities.) - According to Federal energy management program
Thermochemical Process Gasification Pyrolysis Under controlled temperature and oxygen condition these process convert biomass feedstock into energy carriers such as producer gas, oils or methanol through internal combustion engines and gas turbines.
Gasification Is a high-temperature thermochemical conversion process, but the desired result in this case is the production of a combustible gas, Which is after appropriate treatment can be used for cooking, heat supply or by the secondary conversion method to produce electricity. This is achieved by the partial combustion of the biomass material in a restricted supply of air or oxygen, at high-temperature environment of around 1200- 1400 oC. can achieve considerably higher efficiencies of around 35%, with 45-50% as a near-term possibility.(An important thing to keep in mind is that higher efficiencies mean also lower emissions.) The main types of gasifier designs are - updraft (or counter current), downdraft (or co-current) and fluidised bed (bubbling, circulating or pressurized)
Operating principle of the updraft (counter-current) gasifier: In the updraft, or counter current, gasifier air is injected from the bottom and biomass enters at the top and moves down under the force of gravity, as it is gasified. The biomass material first goes through the drying phase, followed by the distillation (pyrolysis) and reduction phase and finally the combustion of the ungasified solid fraction. The relatively high energy efficiency of this type of gasifier is due to the efficient counter current heat exchange between the rising gases and descending biomass.
High concentration of tars and oils in the produced gas, which must go through intensive filtering and cleaning if it is to be utilised for generating electricity. The cleaning process reduces the overall efficiency and results in considerably higher investment costs.
Downdraft (co-current) gasifier The producer gas is drawn out from below, through the combustion zone. The biomass feedstock and air needed for gasification thus flow in the same direction. it produces a significantly cleaner gas with less tars. Have to keep the operating temperature , but difficult to achieve with the high moisture content of the biomass. Gas leaves the gasifier at a relatively high temperature, it needs to be cooled before usage in gas turbines or engines.
Fluidized Bed Gasifier Fluidized bed designs are most common in larger size plants, ranging from a few to several hundred MW. The biomass feedstock needs to be reduced to a small particle size, and is usually fed into the upper part of the gasifier. The produced gas often contains some quantities of tars and ash, hence gas clean-up must be a key part of the process, and is often the most challenging.
Gasification Initially BIG/STIG (Biomass Integrated Gasifier steam injected gas turbine) used. As technology matures BIG/GTCC (Biomass integrated Gasifier gas turbine combined cycle is used, Which has the energy conversion efficiency of 40% to 55% .comparable to the efficiency of modern coal electrical plant of 35% or less. Use of low grade feedstock with high efficiency makes this an economical method compared. The estimated cost to generate electricity from biomass ranges from 5.2 to 6.7 cents per kilowatt-hour.
Pyrolysis It’s a thermochemical Process. Pyrolysis—heating biomass in the absence of oxygen—produces a liquid bio-oil, which is used as a fuel for electricity generation.
Pyrolysis liquid fuel is easier to transport then either solid or gaseous fuels. pyrolysis plant doesn’t have to be located near the end-use point of the bio-oil, but can instead be located near the biomass resource supply. overall electrical efficiency in the range of 25 % to 50 %. Pyrolysis technology is in the early state of development and thus the development costs are still very high and not well established, but this also means that there is considerable scope for cost reduction
Anaerobic Digestion( Biochemical Process) It is a low temperature biochemical process. Produces a combustible gas – biogas from manure and crop residues Uses mixed bacterial cultures. Bacteria Converts 90 % feedstock into Biogas. Controlled anaerobic digestion requires an airtight chamber, called a digester. To promote bacterial activity, the digester must maintain a temperature of at least 68° F.
Anaerobic Digestion(Biochemical Process) The biogas produced in a digester (also known as "digester gas") is actually a mixture of gases, with methane and carbon dioxide making up more than 90 percent of the total. The energy content of digester gas depends on the amount of methane it contains. Methane content varies from about 55 percent to 80 percent. Typical digester gas, with a methane concentration of 65 percent, contains about 600 Btu of energy per cubic foot The advantages of anaerobic digestion when compared to thermochemical processes is that as a by-product it also produces a concentrated nitrogen fertilizer. The estimated cost of producing electric power from anaerobic digestion of animal manure is 3.7 to 5.4 cents per kilowatt-hour.
Conclusion Biomass energy generation can be called as the face of future energy generation technology. Biomass does not depend on climate changes like the solar and wind. Clean energy Readily available potential resource