Natural grass as bioenergy

we can get a significant amount of energy from land which is currently not being used, for minimal input and without disrupting the local wildlife too much or diverting land currently used for food.

Science Deobfuscator

Bioenergy receives a lot of attention as a fossil-fuel alternative.  In principle, it’s a renewable resource, as well as being approximately carbon neutral (it neither adds nor removes carbon dioxide from the atmosphere, though this depends on the crop).  Some popular types of bioenergy are ethanol derived from corn, sugar cane, switch grass, palm oil, as well as fast-growing trees like poplar and willow.  These latter two are generally not made into liquid energy (i.e. they cannot be used to power automobiles), but in Europe they are gaining popularity in homes and industry when the wood is chipped and pressed into energy-dense pellets.

    Bioenergy is not without its problems, however.  Ethanol derived from corn diverts a food product into the energy sector, raising food prices.  In the tropics, conversion of native forests to bioenergy plantations for palm oil is a significant driver for deforestation as well as indirect carbon…

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FROM WASTE TO ENERGY

Sweden sends just 1% of its residential solid waste to the landfill, recycling 50% and thermally processing 49% for heat and power generation in their WTE plants (waste to energy).

Planet Earth Weekly

wast managemet sweeden

By Lin Smith

August 11, 2013–Sweden, a country of 9 million people, is one of our planet’s leaders in creating a plan to reduce greenhouse gas emissions. Their goal is to achieve a completely oil free economy by 2020, replacing fossil fuels with renewable alternatives before “climate change undermines national economies worldwide and diminishing oil supplies force astronomical price increases.” Their renewable alternative–turning trash into power! Although at the present time Sweden relies on other forms of energy, burning of garbage accounts for an equivalent of 810,000 homes being heated and the electrical equivalent of 250,000 homes being powered. The waste to energy plants are burning garbage faster than Swedes can produce it, so their solution? Import garbage from Norway!

Sweden sends just 1% of its residential solid waste to the landfill, recycling 50% and thermally processing 49% for heat and power generation in their WTE plants…

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Thermal Conversion of Wastes

Thermal (or thermochemical) conversion systems consist of primary conversion technologies which convert the waste into heat or gaseous and liquid products. These technologies can be classified according to the principal energy carrier produced in the conversion process. Carriers are in the form of heat, gas, liquid and/or solid products, depending on the extent to which oxygen is admitted to the conversion process (usually as air).

Combustion

Direct combustion is the best established and most commonly used technology for converting wastes to heat. During combustion, waste is burnt in excess air to produce heat. The first stage of combustion involves the evolution of combustible vapours from wastes, which burn as flames. Steam is expanded through a conventional turbo-alternator to produce electricity. The residual material, in the form of charcoal, is burnt in a forced air supply to give more heat. The main products of efficient combustion are carbon dioxide and water vapor, however tars, smoke and alkaline ash particles are also emitted. Minimization of these emissions and accommodation of their possible effects are important concerns in the design of environmentally acceptable waste combustion systems.

Co-Firing

Co-firing or co-combustion of biomass wastes with coal and other fossil fuels can provide a short-term, low-risk, low-cost option for producing renewable energy while simultaneously reducing the use of fossil fuels. Co-firing involves utilizing existing power generating plants that are fired with fossil fuel (generally coal), and displacing a small proportion of the fossil fuel with renewable biomass fuels. Co-firing has the major advantage of avoiding the construction of new, dedicated, waste-to-energy power plant. An existing power station is modified to accept the waste resource and utilize it to produce a minor proportion of its electricity. Co-firing may be implemented using different types and percentages of wastes in a range of combustion and gasification technologies. Most forms of biomass wastes are suitable for co-firing. These include dedicated municipal solid wastes, wood waste and agricultural residues such as straw and husk.

Gasification

Gasification systems operate by heating wastes in an environment where the solid waste breaks down to form a flammable gas. The gasification of biomass takes place in a restricted supply of air or oxygen at temperatures up to 1200–1300°C. The gas produced—synthesis gas, or syngas—consists of carbon monoxide, hydrogen and methane with small amounts of higher hydrocarbons.  Syngas may be burnt to generate heat; alternatively it may be processed and then used as fuel for gas-fired engines or gas turbines to drive generators. In smaller systems, the syngas can be fired in reciprocating engines, micro-turbines, Stirling engines, or fuel cells. There are also small amounts of unwanted by-products such as char particles, tars, oils and ash, which tend to be damaging to engines, turbines or fuel cells and which must therefore first be removed or processed into additional fuel gas. This implies that gasifier operation is significantly more demanding than the operation of combustion systems.

Pyrolysis

Pyrolysis is thermal decomposition occurring in the absence of oxygen. During pyrolysis process, waste is heated either in the absence of air (i.e. indirectly), or by the partial combustion of some of the waste in a restricted air or oxygen supply. This results in the thermal decomposition of the waste to form a combination of a solid char, gas, and liquid bio-oil, which can be used as a liquid fuel or upgraded and further processed to value-added products. High temperature and longer residence time increase the waste conversion to gas and moderate temperature and short vapour residence time are optimum for producing liquids. Pyrolysis technologies are generally categorized as “fast” or “slow” according to the time taken for processing the feed into pyrolysis products. Using fast pyrolysis, bio-oil yield can be as high as 80 percent of the product on a dry fuel basis. Bio-oil can act as a liquid fuel or as a feedstock for chemical production.

Biomass Cogeneration

GE H series power generation gas turbine. This...

Biomass conversion technologies transform a variety of wastes into heat, electricity and biofuels by employing a host of strategies. Conversion routes are generally thermochemical or biochemical, but may also include chemical and physical. Physical methods are frequently employed for size reduction of biomass wastes but may also be used to aggregate and densify small particles into pellets or briquettes.

A wide range of conversion technologies are under continuous development to produce biomass energy carriers for both small and large scale energy applications. Combustion is the most widely used technology that releases heat and can also generate power by using boilers and steam turbines. The simplest way is to burn the biomass in a furnace, exploiting the heat generated to produce steam in a boiler, which is then used to drive a steam turbine. At the smaller scale, biomass pellet and briquette combustion systems mainly used for domestic and industrial heat supply are experiencing growing demand in some countries due to their convenience.

Advanced technologies include biomass integrated gasification combined cycle (BIGCC) systems, co- firing (with coal or gas), pyrolysis and second generation Biofuels. Second generation Biofuels can make use of biochemical technologies to convert the cellulose to sugars which can be converted to bioethanol, biodiesel, dimethyl ester, hydrogen and chemical intermediates in large scale bio-refineries.

Biomass fuels are typically used most efficiently and beneficially when generating both power and heat through a Combined Heat and Power (or Cogeneration) system. A typical CHP system provides:

  • Distributed generation of electrical and/or mechanical power.
  • Waste-heat recovery for heating, cooling, or process applications.
  • Seamless system integration for a variety of technologies, thermal applications, and fuel types into existing building infrastructure.

CHP systems consist of a number of individual components—prime mover (heat engine), generator, heat recovery, and electrical interconnection—configured into an integrated whole. The type of equipment that drives the overall system (i.e., the prime mover) typically identifies the CHP unit.

Prime movers for CHP units include reciprocating engines, combustion or gas turbines, steam turbines, microturbines, and fuel cells. These prime movers are capable of burning a variety of fuels, including natural gas, coal, oil, and alternative fuels to produce shaft power or mechanical energy.

A biomass-fueled Combined Heat and Power installation is an integrated power system comprised of three major components:

  1. Biomass receiving and feedstock preparation.
  2. Energy conversion – Conversion of the biomass into steam for direct combustion systems or into biogas for the gasification systems.
  3. Power and heat production – Conversion of the steam or syngas or biogas into electric power and process steam or hot water

The lowest cost forms of biomass for generating electricity are residues. Residues are the organic byproducts of food, fiber, and forest production, such as sawdust, rice husks, wheat straw, corn stalks, and sugarcane bagasse. Forest residues and wood wastes represent a large potential resource for energy production and include forest residues, forest thinnings, and primary mill residues.  Energy crops are perennial grasses and trees grown through traditional agricultural practices that are produced primarily to be used as feedstocks for energy generation, e.g. hybrid poplars, hybrid willows, and switchgrass. Animal manure can be digested anaerobically to produce biogas in large agricultural farms and dairies.

To turn a biomass resource into productive heat and/or electricity requires a number of steps and considerations, most notably evaluating the availability of suitable biomass resources; determining the economics of collection, storage, and transportation; and evaluating available technology options for converting biomass into useful heat or electricity.

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