Energy from the Wind - Wind Turbines

Renewable Energy: Wind Power

GAS CONDITIONING FOR POWER GENERATION USING GASIFIER

Need for gas cleaning
Biomass gasification is a process of converting biomass to a combustible gas in a reactor, known as gasifier, under controlled conditions. During gasification, biomass is subjected to partial pyrolysis under sub-stoichiometric conditions. A typical gasifier plant consists of a reactor, which receives air and solid fuel and converts them into gas, followed by a cooling and washing train where the impurities are removed. The clean combustible gas at a nearly ambient temperature is a must for running diesel-generator sets in dual fuel mode or gas engine generator sets suitable for running on producer gas alone. In thermal applications, the cooling and cleaning of the raw gas is limited to the requirements of the thermal process.
The gasification system development has also included extensive research and development on product gas cleanup. Raw gases contain particulates, tars, ammonia, and other impurities that interfere with equipments and downstream processes and components or create emission problems. For low-technology thermal applications where the product gas is simply burned to provide heat, such as a cement kiln, the gas clean-up requirements may be minimal. However, high technology systems such as fuel cells and gas turbines or systems using synthesis gases require clean fuel gases. Extensive clean up may also be required to meet the environmental regulations even in relatively undemanding applications. There are examples of failure due to non-adherence of critical fuel quality requirements with end-use.
In 1993, the International Energy Agency (IEA), Bioenergy Gasification Activity repared a document summarizing the status of gas clean-up systems. This document identified primary gas contaminants, discussed unit operations that could potentially remove such contaminants, and discussed gas-cleaning strategies in relation to the end-use of the product gas. Since then, progress has been made in developing a better understanding of the chemistry and mechanisms of hot gas cleanup and conditioning as evinced by recent gasification systems which have incorporated technologies to improve gas cleanup.
Gas ontaminants
Gasification processes, particularly updraft gasification produces a dirty gas that has a relatively low level of purity and includes toxic chemicals and other contaminants besides carbon monoxide, hydrogen, methane, carbon dioxide, nitrogen and water vapor. Pollutants such as tars, dust, and ash are also present, in relatively high concentrations, in these crude gases. Following a gasification process the crude gas must normally be cleaned of tar, filtered, purified and cooled before it is used in many energy-producing applications.
Cleanup systems
Gas cleanup systems may contain several components individually or in combination viz., cyclones, scrubbers, or filters; each of which removes one or more contaminants. Systems producing gas must deal with the cleanup of five primary contaminants including:
· Particulates
· Alkali compounds
· tars
· nitrogen-containing components
· Sulphur
Various gas-conditioning systems employed are:
Barrier Filters – Rigid, packed bed filters, bag filters, sieve-plate scrubbers, wet scrubbers, cyclone filters, electrostatic precipitators, sand bed filters, water wash towers and catalytic thermal tar destruction beds.
The application of particulate removal technologies to biomass gasification systems in general has matured over the past decade. Cyclones are routinely being used for bulk particulate removal, and technologies including bag filters and wet scrubbers are being used in large-scale systems. While this progress is incremental in nature, it is required for wide- spread deployment of gasification technologies. Based on the available data except for the catalytic tar crackers, none of the gas cleaning systems can meet a targeted cleaning objective exceeding 90 %.

Biomass gasifier

Biomass gasification is a process of converting biomass to a combustible gas in a reactor vessel, known as gasifier under controlled conditions. The combustible gas, known as producer gas has a composition of approx. 19 % CO, 10 % CO2, 50% N2, 18% H2 and 3 % CH4. This gas has a calorific value of 4.5 - 5.0 MJ/cubic metre. It has to be cooled and cleaned before using in internal combustion engines for power generation purposes.
Biomass fuel
A wide range of woody biomass in the form of wood or agro residue can be used in the gasifier. In general any biomass that has a density of more than 250 kgs per cubic meter can be used for gasification. Biomass from trees of Eucalyptus, Casuarina, Acacia, Albizzias, Cassia siamea and many other species and agricultural residues such as coconut shell, husk, fronds, corn cobs, corn stalks, mulberry stalks, briquettes of biomass or saw dust, coffee husk, groundnut husk, rice husk etc. can be used as fuel in fuel specific gasifiers.
Conversion efficiency
High Conversion efficiency from solid Biomass to gaseous fuel of upto 85% in hot gas mode, 75% in cold gas mode and 65% with rice husk is possible. Each Kg of biomass can producer 2.5 to 3.0 cubic meters of gas having a average calorific value of 4.5 - 5.0 MJ/cubic metre. During power generation through gen set upto 85% diesel saving is possible in duel fuel mode.

Alkaline fuel cell stack design

Alkaline fuel cell stack design involves working out the details of optimum configuration of the individual module, array or pack to develop the required output. The basic concept in the design being the assembly of pair of electrodes, provision of hydrogen and oxygen gases to the appropriate electrodes and supply of electrolyte into the individual cell assemblies. Cascading the electrode pairs is possible in many different ways. The basic configuration can be either mono or bipolar with either internal or external manifolding. Also electrolyle supply by matrixing or stagnant boundary or by circulation are the various possibilities. The technique to be adopted in the stack boundary or by circulation are the various possibilities. The technique to be adopted in the stack fabrication mainly depends on the limitation in materials to be used.
Stack design concepts
Various possibilities of stack disign are possible, The options for air electrode of hydrophilic and hydrophobic nature with electrolyte circulation by pump / fan or by natural respiration are possible.
Internal manifolding where electrolyte and gas manifolds arranged internally or external manifolding is possible..
The choice of internal or external manifolding have their inherent problems. The external type has all plumbing works done externally which are amenable for easy maintenance, while the choice of polarity and coupling depends on the capacity. In the internal type cell reliability of fluid transfer depends on seals and O rings and the maintenance requires dismantling of cell assembly.
Stack designs
The stack design adopted by various investigators are described below:
Filter press type: Hydrogen - oxygen fuel cell have circular frame and electrodes. The frame consists of rooms for KOH, H2 and O2. There are six passages two each for entry and exit of electrolyte, hydrogen and oxygen and the frame was clamped by six bolt holes. The electrolyte and gas diffuse radially inwards and leave radially out. This design akins to Grove's design concept.
Monocell construction: The monocell of the actual design contains seven structural components. The central matrix of 20.4 x 20.4 x 0.025cm is connected by means of film gluing with an epoxy frame layer, with the later supported with Teflon mesh screen. Adjacent nickel collectors of the electrodes consist of galvanised screens which are soldered and filled with tin at two opposite edges and sealed in the frame zone after having been charged with catalyst.
Bipolar alkaline fuel cell battery: This consists of bipolar cells, separator packages, electrolyte frame and end plate assembly. The electrodes are rectangular size and framed with suitable slots for gas and electrolyte entry.

Partial oxidation of biogas to hydrogen

The conversion of gaseous hydrocarbons to hydrogen can be achieved in many ways. Partial oxidation with air is one of the options. In this process methane in the biogas with oxygen in air to form hydrogen in a bed of catalyst.
Principle
This commercial process route is basically the result of sequential combustion reactions in which the gas is burnt with deficit oxygen (nearly 30 % of stoichiometric requirement). Depending on the feed -stock the product gas may require purification of sulphur compounds and CO2 - removal. The advantage of dispensing with an external heat source favours the partial oxidation step, since the oxidation of CO supplies the necessary heat.
Process flow
The biogas containing 55-60 % methane , 40 % CO2 and traces of H2 S is first dehydrated and then purified from H2 S. The gas is then sent to the partial oxidizers to form hydrogen. Depending on the composition of the outlet gas from the oxidizer methanation of residual carbon oxides can be incorporated. Finally a Co2 scrubber may be added depending on the type of fuel cell to be used in the power plant.
Process
The process occuring in the partial oxidizer is
CH4 + 0.5 O2 = Co + 2H2
The process requires oxygen, which may be separated and supplied from air and is favoured by moderately high pressure. It is understood that due to residence time limitations, the process approaches equilibrium leaving some residual methane and carbon in the product gas. Hence CO2 needs to be scrubbed and recycled in the plant (Balthasar).
Need for pure oxygen
If air is used instead of oxygen the separation of hydrogen from nitrogen is difficult. Hence oxygen at a purity of at lease 95 % and has to be used in large scale systems. Pressure of notrogen could be accepted in small scale fuel cell applications. After all the cathode gas (air) contains 80% nitrogen. The process has thus to be modified for operation on air in this particuler study.
Factors controlling the process
As the partial oxidation proceeds through a flame reaction, it is necessary to moderate the flame temperature, preferably by means of steam. The raw gas composition is controlled by the oxygen to methane ratio and by the steam addition. In order to reduce the oxygen consumption for the oxidation step the biogas and steam has to be preheated and have to be metered precisely to the reactor.
The operating conditions vary with the non-catalytic reactors.
Pressure: 60 to 90 bar. Reaction temperature: 1200 to 1370 C.
Under catalytic partial oxidation a commercial process, topsoe SBA has specified the following conditions.
Pressure: up to 30 bar or more. Temperature: 90c.
Catalyst: Ni
Feed-stock gas and super heated steam are mixed and preheated to 60c and mixed with oxygen
Reactor
The reactor may be a refractory lined stainless steel vessel with one or more burners. In order to initiate the reaction part of the gas has to be burnt inside the reactor. Johnson Matthey Ltd. report in their patent a reactor made of SS tube with entry for gas at the middle of the reactor and exit for product gas from the end. As gas entry is made near the middle of catalyst bed, they have observed a higher temperature of 450 c at the tip and a uniform temperature of 280 c surrounding the hot zone. This is claimed to be superior to at once through reactor. The reactor may then have multiple (4 or 5 entries from the sides).
A theoretical model developed by Opris et. al describes the temperature and product distribution profiles along the length of the reactor. This fits well with the commercial data. The reactor requires a minimum length for complete partial oxiation of methane leading to a continuous supply of hydrogen at a fixed concentration.
Catalysts
The catalyst used by Johnson Matthey let. in their Hot Spot TM reactor contained 0.01 to 5 wt % platinum and from 1 to 15 wt % chromium oxide supported on a refractory solid such as silica. The support may be monolith honeycomb or particles with a maximum size of 1.5 mm.
Catalyst deactivation
The successful economic and technical utilization of the process depends on the avoidance of free carbon deposition which decreases the catalyst surface area resulting in lower reaction rates. It is suggested that carbon deposition shall be avoided by operational techniques rather than by inhibition.
Product gas
The hot product gas is expected to have the following composition on a dry basis.
Hydrogen and CO, 93 % by volume
Carbon dioxide, 5 % by volume
Nitrogen and argon, 1.5 % by volume
Methane, 0.6 % by Volume
The reactor effluent needs rapid cooling to freeze the gaseous equilibria established at the high temperature reactor by a direct water quench or by heat exchange. The product gas then has to be washed free of carbon-sulphur compounds, carbon dioxide and inert gases.

Natural gas as a source of hydrogen

A common misconception about natural gas is that it is running out quickly. In fact, there is a vast amount of natural gas estimated to still be in the ground. According to latest estimate of Energy Information Administration (EIA) of proved natural gas reserves, the total available future supply can be available for more than about 100 years of supply at current rates of consumption in the case of US alone. Natural Gas is one of the principle sources of energy for many of our day-to-day needs and activities.
Chemical composition of natural Gas
Component Range (mole %)
Methane 87 - 96
Ethane 1.5 - 5.1
Propane 0.1 - 1.5
iso – Butane 0.01 - 0.3
normal – Butane 0.01 - 0.3
iso – Pentane trace - 0.14
normal – Pentane trace - 0.04
Hexanes plus trace - 0.06
Nitrogen 0.7 - 5.6
Carbon Dioxide 0.1 - 1
Oxygen 0.01 - 0.1
Hydrogen trace - 0.02
Specific Gravity 0.57 - 0.62
Gross Heating Value (MJ/m3), dry basis: 36.0 - 40.2
Hydrogen can be generated from natural gas with approximately 80% efficiency and the steam reforming of methane or natural gas usually produces bulk hydrogen. The primary methods in which natural gas is converted to hydrogen are:
(1) reaction with either steam (steam reforming),
(2) oxygen (partial oxidation), or
(3) both in sequence (auto thermal reforming).
Steam-Methane Reforming
Steam reforming is a process in which high-temperature steam (700°C–1000°C) is used to produce hydrogen from natural gas. In steam reforming, methane reacts with steam under high pressure in the presence of a catalyst to produce hydrogen, carbon monoxide, and a relatively small amount of carbon dioxide. Heat is supplied for the reaction to proceed. In the second stage carbon monoxide and steam are reacted using a catalyst to produce carbon dioxide and more hydrogen. Carbon dioxide and other impurities are removed from the gas stream, leaving essentially pure hydrogen using pressure-swing adsorption.
Partial Oxidation
In Partial oxidation process methane in natural gas reacts with oxygen in air to form hydrogen in a bed of catalyst. This commercial process route is basically the result of sequential combustion reactions in which the gas is burnt with deficit oxygen (nearly 30 % of stoichiometric requirement). Depending on the feed -stock the product gas may require purification of sulphur compounds and CO2 - removal. The advantage of dispensing with an external heat source favours the partial oxidation step, since the oxidation of CO supplies the necessary heat. Partial oxidation is an exothermic process—it gives off heat. The process is, typically, much faster than steam reforming and requires a smaller reactor vessel. As can be seen from the chemical reactions of partial oxidation (below), this process initially produces less hydrogen per unit of the input fuel than is obtained by steam reforming of the same fuel.
Auto thermal reforming (ATR)
Auto thermal reforming (ATR) uses oxygen and carbon dioxide or steam in a reaction with methane. Auto thermal reactor concepts for the heat integrated coupling of endothermic and exothermic reactions are required for an efficient on-site production of hydrogen from natural gas for use in fuel cells. The reaction takes place in a single chamber where the methane is partially oxidized. The reaction is exothermic due to the oxidation. When the ATR uses carbon dioxide the H2: CO ratio produced is 1:1; when the ATR uses steam the H2: CO ratio produced is 2.5:1 The advantage of ATR is that the H2: CO can be varied, this is particularly useful for producing certain second-generation biofuels.

Hydrogen Production Technologies

Various technologies that can be used to produce hydrogen, they are:
(1) reforming of natural gas to hydrogen,
(2) conversion of coal to hydrogen,
(3) use of nuclear energy to produce hydrogen,
(4) electrolysis,
(5) use of wind energy to produce hydrogen,
(6) production of hydrogen from biomass, and
(7) production of hydrogen from solar energy.
Methods of hydrogen generation
Compared with other fossil fuels, natural gas is a cost-effective feed for making hydrogen, in part because it is widely available, is easy to handle, and has a high hydrogen-to-carbon ratio, which minimizes the formation of by-product carbon dioxide (CO2). The primary methods in which natural gas is converted to hydrogen are:
(1) reaction with either steam (steam reforming),
(2) oxygen (partial oxidation), or
(3) both in sequence (autothermal reforming).
Reaction of carbon monoxide with steam (water-gas shift) over a catalyst produces additional hydrogen and carbon dioxide, and after purification, high-purity hydrogen is recovered.
Since natural gas is a mixture containing carbon monoxide, carbon dioxide and unconverted methane bulk hydrogen is usually produced by the steam reforming of methane or natural gas. At high temperatures (700–1100 °C), steam (H2O) reacts with methane (CH4) to yield syngas.
CH4 + H2O → CO + 3 H2 + 191.7 kJ/mol
In a second stage, further hydrogen is generated through the lower-temperature water gas shift reaction, performed at about 130 °C:
CO + H2O → CO2 + H2 - 40.4 kJ/mol
Essentially, the oxygen (O) atom is stripped from the additional water (steam) to oxidize CO to CO2. This oxidation also provides energy to maintain the reaction. Additional heat required to drive the process is generally supplied by burning some portion of the methane.
In most cases, carbon dioxide is vented to the atmosphere today, but there are options for capturing it in centralized plants for subsequent sequestration. For distributed generation, the cost of sequestration appears prohibitive.
Integrated steam reforming / co-generation- It is possible to combine steam reforming and co-generation of steam and power into a single plant. This can deliver benefits for an oil refinery because it is more efficient than separate hydrogen, steam and power plants.
In spite of the above facts, natural gas can not be considered as a long-range fuel for centralized plants for the hydrogen economy. Whether it will be possible to utilize partial oxidation or autothermal reforming for the distributed generation of hydrogen appears to depend on developing new ways of recovering oxygen from air or separating product hydrogen from nitrogen. This is needed because conventional, cryogenic separation of air becomes increasingly expensive as unit size is scaled down. Membrane separations, in contrast, appear amenable to this application and may provide the means for producing small, efficient hydrogen units. A mass-produced hydrogen appliance suitable for distributed generation in fueling stations is to be developed.

Briquetting of powdery biomass

The process of briquetting consists of applying pressure to a mass of particles, with or without a binder and converting it into a compact mass. The end product may be in a solid geometrical form or in the form of hollow cylinders which may be a solution to the large volume, low-density products having high transportation/handling cost problems associated with biomass. Cow dung cakes, fuel balls made with coal dust, half burnt cinder as well as hand compressed special fuel lumps are some of the prime examples. High-density briquettes are also made by power driven machines to make wood like solid briquettes from powders/dust of various materials.The vital requirement of briquette formation form wood biomass is the destruction of the elasticity of the wood, which could be done either by high pressure or by previous heat treatment or by a combination of both. There are two processes of briquetting, namely, direct compaction and indirect compaction after pyrolysing or carbonization of the residue.

Direct compaction

In this ease, the briquettes may be prepared with or without binding agents.

a) Without binding agents: This process involves two steps: Pretreatment of biomass through application of high pressure in the range of 120 - 200 MPa at which condition the biomass gets heated to a temperature of about 182°C and the lignin begins to flow and acts as binder. Compaction or densification of material: The powdered biomass is densified through briquetting machines available in the capacity range of 100 - 300 kg/h or more operating by electric power. The cost of such briquetting units depends upon the capacity.

b) With binding agents: In this process, the briquetting machines operate at lower pressure range of 50 - 100 MPa and are powered by electricity. This process requires additional binders like molasses, lingo-sulphonate, sodium silicate, dung slurry etc. Such machines are available in the capacity range of 100 to 400 t / h.

Indirect compaction

Pyrolysis is the process or destructive distillation of organic materials heated at slow rate to about 270°C in the absence of oxygen. During process of pyrolysis, solid char, liquid tar and combustible gases are produced besides organic liquids. The nature and quantum of these products depend on various factors such as composition of biomass, and residence time in kiln and temperature. During the pyrolysis, the fibre content of the biomass is broken which latter facilitates in briquetting of charcoal. The obtained charcoal is briquetted through extrusion process.

Arecanut husk - biomass

To the Indians, Malayans, or the Indonesians, betel-nut chewing is as familiar as chewing gum to the Americans. In India the use of arecanut and its cultivation constitute a distinct agricultural practice scarcely less important than that of other economic crops. Arecanut husk is mainly used for manufacturing of thick boards, fluffy cushions, non-woven fabrics, thermal insulation and wrapping paper. Areca husk is used as a substrate for mushroom cultivation. Arecanut husk fibre is generally longer than woolenised jute,. Although value added products can be created with the areca husk, these practices do not seem to be really popular, because still piles of areca husk remains after processing in the developing countries. On a weight basis, the husk is 60 to 80% of the whole fruit. The husk fiber itself is mainly constituted of cellulose. A sun-dried areca husk has a mass loss of 28-33% when compared to a green husk. The major constituents of arecanut are pectin at 1.5-3.6%, protopectine at 1.5-2.1%, hemi cellulose at 35-65.8%, lignin at 13-26%, furfuraldehyde at 18.8% and ash at 4.4% and moisture content varying from 91% when very tender to 74 % when ripe.

Internal versus external reforming of natural gas for fuel cell

Natural gas contain hydrocarbons molecules consisting of hydrogen and carbon. Using a device called a fuel processor or a reformer, hydrogen can be split off the carbon in a hydrocarbon relatively easily and then use hydrogen to drive fuel cell.The reforming may be done internally or externally.Internal reforming increases stack cost by about 33%, but in small units this increase is more than offset by the cost of the reformer and its heat and steam supply. In large systems, a single central reformer may be cost effective, since the rate of internal reforming decreases with pressure. The process may therefore not to be too effective in pressurized stacks that may be cost effective in the multi megawatt size range. The four percentage points will then be more than made up for by the use of a steam bottoming cycle. To a first approximation, it is reasonable to assume that the internal and external reforming systems may result in about the same costs. External reforming will also certainly allow multi fuel capability, since internal reforming has so far only been shown suitable for natural gas and methanol. Heavy fuels, such as fuel oils, will require higher steam carbon ratios and specialized reforming systems, which will lower system efficiency by about 3% points compared with the value for external reforming natural gas units.

Depreciation methods

Depreciation is a fixed cost and represents the loss of value of an asset which may be the result of physical wear and tear, chemical degradation or economic or technological obsolescence. Since depreciation is time dependent, it is normally expressed as a rate. The energy equipment will normally depreciate even if the plant is shut down. Main methods used to calculate the depreciation are:
The straight line
The declining balance
The sum-of-the-years-digits
The sinking fund
These methods assume that an asset has a certain predetermined service life at the end of which its value will have decreased to zero, or a residual junk or salvage value. The rate of ‘write-off’ affects the calculation of savings.

Economic assessment of energy projects

The purpose of any energy conservation project is to save money by using less energy or using energy more efficiently. The economic assessment of energy projects can often be complex as it encompasses the engineering techniques required to evaluate the magnitude of energy savings, as well as the economic principles involved in assessing if capital investment in the project is justified. Operating costs can be divided into two categories as Fixed costs (f.c) and Variable costs (v.c) and the total cost (t.c) is the sum of fixed and variable costs.
Fixed costs are those, which do not vary with output even if the output is zero and include interest, depreciation of plant for example, boilers, electrical equipment, recuperators, rates/rent on housing of energy equipment, insurance on plant, wages and certain maintenance costs.
Variable costs are those which do very with output and include fuel, water, certain maintenance and wages.
The break-even point is a good indication of how vulnerable the energy conservation project is to changes in market conditions and have a low break-even point.
In practice the relationships are not strictly linear when the project is analyzed as a maximum-minimum problem. Such an analysis generally involves differential calculus and is called an optimization study.

Top wind turbine manufacturers

* Acciona Energy (Spain)
* Aeronautica Windpower (USA)
* Alstom Ecotècnia (Spain)
* A Power Energy Systems ltd. (China)
* Boeing (USA) only experimental. Dismantled.
* Bornay (Spain) [12]
* Cascade Wind Corp. (USA)
* Clipper Windpower (USA)
* Daewoo Shipbuilding & Marine Engineering (Korea)
* DeWind (Germany/USA) - bought by Daewoo Shipbuilding & Marine Engineering in 2009
* Doosan (Korea)
* Emergya Wind Technologies (Netherlands)
* Endurance Wind Power (Canada)
* Enercon (Germany)
* Gamesa Eólica (Spain)
* General Electric (USA)
* Goldwind (China)
* Hanjin (Korea)
* Home Energy International - Producer of the Energy Ball (The Netherlands)
* Hyosung (Korea)
* Hyundai Heavy Industries (Korea)
* IMPSA (Argentina)
* INVAP (Argentina)
* Lagerwey - gone bankrupt in 2003 succeeded by Wind Energy Solutions, Emergya Wind Technologies, Harakosan and DarwinD (Netherlands)
* Lagerwey Wind (The Netherlands)
* Mitsubishi Heavy Industries (Japan)
* NEG Micon, now part of Vestas
* Nordex (Germany)
* Northern Power Systems (USA)
* Norwin A/S (Denmark)
* PacWind (USA)
* Raum Energy Inc. (Canada - Global supplier of 1.3kW and 3.5kW systems)
* REpower (Germany) - bought by Suzlon in 2007
* Samsung Heavy Industries (Korea)
* Scanwind (Norway) - bought by General Electric in 2009
* Siemens (Denmark / Germany)
* Sinovel (China)
* Southwest Windpower (USA)
* SoyutWind (Turkey)
* STX Corporation (Korea)
* Suzlon (India)
* Vestas (Denmark), the world's largest manufacturer of wind turbines
* Vensys (Denmark / Germany)
* Windiva Energy (India)
* Windflow (New Zealand)

Source:Wikipedia

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Biomass composting

Biomass is the organic matter derived from plants as a result of the photosynthetic conversion process. Biomass energy is derived from plant and animal material, such as wood from forests, residues from agricultural and forestry processes, and industrial, human or animal wastes. Biomass resources include forest litter, agricultural residues; urban wastes, energy crops, industrial bio-waste etc., where as biomass fuels include fuel wood, charcoal, rice husk, plant residues and animal dung.It is possible to extract energy from these wastes besides converting them into fertiliser. The most popular conventional method of disposal of bio-waste is composting. Composting is the bio degradation of the constituents in the wastes over a period of several days by the microbial activity where pathogens are destroyed, organic matter is decomposed into a stable, humus like substance along with heat (60 deg or more) production. The major by-products are carbon dioxide, water and heat while the main product is compost which is a good soil builder or conditioner containing small amount of the major plant nutrients.