biom2-x.txt
biom2-x.txt - - - - meth805\txt\pnt 3.7.5 ANAEROBIC DIGESTION
When a heap of vegetable or animal matter and weeds etc. die or decompose at the bottom of back water or shallow lagoons then the bubbles can be noticed rising to the surface of water. Some times these bubbles burn with flame at dusk. This phenomenon was noticed for ages, which puzzled man for a long time. It was only during the last 200 years or so when scientists unlocked this secret, as the decomposition process that takes place under the absence of air (oxygen). This gas, production of which was first noticed in marshy places, was and is still called as ?Marsh Gas?. It is now well known that this gas (Marsh Gas) is a mixture of Methane (CH4) and Carbon dioxide (CO2) and is commonly called as the ?Biogas?. harnessing this gas from any biodegradable material (organic matter) under artificially created conditions is known as biogas.
Anaerobic digestion, like pyrolysis, occurs in the absence of air; but in this case the decomposition is caused by bacterial action rather than high temperatures. It is a process which takes place in almost any biological material, but is favoured by warm, wet and of course airless conditions. It occurs naturally in decaying vegetation on the bottom of ponds,
Anaerobic digestion also occurs in situations created by human activities. and is generated in sewage or animal manure, landfill gas .a mixture mainly of methane and carbon dioxide; but major differences in the nature of the input, the scale of the plant and the time-scale for gas production lead to very different dealing with the two sources.
it appears that a mixed population of bacteria breaks down the organic material into sugars and then into various acids which are decomposed to produce the final gas, leaving an inert residue whose composition depends on the type of system and the original feedstock.
3.7.5.1 Biogas
is a valuable fuel which is in many countries produced in purpose built digesters filled with the feedstock like dung or sewage. Digesters range in size from one cubic metre for a small ?household? unit to more than thousand cubic meters used in large commercial installation or farm plants. The input may be continuous or in batches, and digestion is allowed to continue for a period of from ten days to a few weeks. The bacterial action itself generates heat, but in cold climates additional heat is normally required to maintain the ideal process temperature of at least 35 degrees Celsius, and this must be provided from the biogas. all the gas may be used for this purpose, the plant may still pay for itself through the saving in fuel needed to process the wastes. A well-run it will produce 200- 400 m3 of biogas with a methane content of 50% to 75% for each dry tonne of input.
LANDFILL GAS
the potential hazard led to the fitting of systems for burning it off; only in the 1970s that serious attention was paid to the idea of using this ?undesirable? product. In developing a site, each area is covered with a layer of impervious clay or?which encourages anaerobic digestion. The gas is collected by an array of interconnected perforated pipes buried at depths up to 20 metres in the refuse. In new sites this pipe system is constructed before the wastes start to arrive, and in a large well-established landfill miles of pipes, with as much as 1000 m3 an hour of gas being pumped out.
Increasingly, the gas from landfill sites is used for power generation. At
3.8 TECHNOLOGY EXAMPLES
3.8.1 Heat production with wood firing boilers (get for wood-heat study,
from editor: hello,this is the editor of meth805, this next part was cut out, but partly put back in, i felt it held a key for people with methane-digesters in colder climates.)3.8.1 Heat production with wood firing boilers
Most common process of biomass combustion is burning of wood. In developed countries replacing oil or coal-fired central heating boiler,can save between 20 and 60% on bills, because wood costs less than oil or coal. no global warming. and contains less sulphur than oil, less sulphate,less acid rain and in soil. Small wood burning storage tank so as to gather the heat energy from fuel. Automatic boilers are equipped with a silo containing wood pellets or wood chips. A screw feeder feeds the... manually fired boilers efecient from below 50% to 75-90%. automatically fired boilers reach 85-92% effeciency reached.
MANUALLY FIRED BOILERS :The principal rule is that manually fired boilers for fuelwood only have an acceptable combustion at the boiler rated output (at full load). At individual plants with oxygen control, the load can, however, be reduced to approx. 50% of the nominal output without thereby influencing neither the efficiency nor emissions. By oxygen control, a lambda probe measures the oxygen content in the flue gas, and the automatic boiler control varies the combustion air inlet.
AUTOMATICALLY FIRED BOILERS
Despite simple construction, most of the automatically fired boilers can achieve an efficiency of 80-90% and a CO emission of approx. 100 ppm (100 ppm = 0.01 volume %). For some boilers, the figures are 92% and 20 ppm, respectively. An important condition for achieving these good results is that the boiler efficiency during day-to-day operation is close to full load. For automatic boilers, it is of great importance that the boiler nominal output (at full load) does not exceed the max. output demand in winter periods. In the transition periods (3-5 months) spring and autumn, the output demand of the dwelling will typically be approx. 20-40% of the boiler nominal output, which means a deteriorated operating result. During the summer period, the output demand of the dwelling will often be in the range of 1-3 kW, since only the hot water supply will be maintained. This equals 5 -10% of the boiler nominal output. This operating method reduces the efficiency - typically 20- 30% To stop deteriorated summer operating add with it a storage tank and solar collectors.
3.8.2 MANUALLY-FIRED BOILERS , BURN-THROUGH
Nearly all old-fashioned cast iron stoves act on the burn-through principle: air comes in from below and passes upwards through the fuel. the wood burns very quickly. The gases do not burn very well, since the boiler temperature is low. Most of the gas goes up the chimney, and the energy with it. flu-gases have a very short space in which to give off their heat to the boiler in the convection section. effeciency = below 50%.
Underburn boiler: is very different from a burn-through one. The air is not drawn through all the fuel at once, but only through part of it. Only the bottom layer of wood burns; the rest dries out and gives off its gases very slowly. Adding extra air (so-called ?secondary air?) direct to the flames burns the gases more effectively. In modern underburning boilers the combustion chamber is ceramic lined, which insulates well and keeps the heat in. This gives a high temperature of combustion, burning the gases most effectively. An underburning boiler typically has a useful effect of 65-75%.
In reverse combustion boilers: too, air is only added to part of the fuel. As in underburning, the gases leave the fuel slowly and are burnt efficiently. Secondary air is also led into an earthenware-lined chamber, giving a high temperature of combustion. The flue gas has to pass through the entire boiler, giving it plenty of time to give up its heat. The useful effect is typically of the order of 75-85%. Some reverse combustion boilers have a blower instead of natural draught. effecient boiler:How good a boiler is partially depends on the energy in the fuel that it transfers. efficiency of a boiler means between the energy in the hot water and that in the wood: of the order of 80-90%. boilers can burn wood logs up to 80 cm long.
Power output(kW) Wood consumption(kg/hr) Wood-consumptionin heating-season(m3)
18 4 10
25 6 15
32 7 20
50 13 30
80 18 50
Wood heating value 15-18 MJ/kg.
STORAGE TANK :It almost always pays to buy a storage tank when installing a wood burning boiler. A storage tank holds water that has been heated up by the boiler. The extra cost repays itself very quickly, and it is easier to fire properly. Shortly after lighting up, combustion is clean and the boiler starts producing masses of heat. Without a storage tank to take up the heat, the water will rapidly get too hot and the damper will have to be shut to stop it boiling. reduced amount of air leads to smoky,incomplete combustion.
But with a hot water tank you can fire away and store the heat. The water in the boiler cannot overheat because it goes into the tank. The damper remains open and combustion continues at high efficiency. When you need heat in the radiators, it comes from the storage tank. The size of the storage tank depends on the amount of heat the house needs and the efficiency of boiler.
BURNING WOOD COMBINED WITH SOLAR HEATING -pause-
If you do decide to install a wood burning unit, it is recommended also to consider putting in solar heating. The wood burning boiler and the solar panels can frequently use the same storage tank, reducing the cost of the system as a whole. Make sure first that the storage tank is suitable for the purpose. it makes it unnecessary to have a fire going in summer just to get hot water. And it is cheaper to ?burn? solar energy than wood! fuel choice:
Whatever fuel you decide to use, it must be dry. (editor:heh heh, thats what
you think, read about jean-pain, or explain the heat coming from your own body). Newly felled timber has 50% water and so is useless for...
-no end-
When a heap of vegetable or animal matter and weeds etc. die or decompose at the bottom of back water or shallow lagoons then the bubbles can be noticed rising to the surface of water. Some times these bubbles burn with flame at dusk. This phenomenon was noticed for ages, which puzzled man for a long time. It was only during the last 200 years or so when scientists unlocked this secret, as the decomposition process that takes place under the absence of air (oxygen). This gas, production of which was first noticed in marshy places, was and is still called as ?Marsh Gas?. It is now well known that this gas (Marsh Gas) is a mixture of Methane (CH4) and Carbon dioxide (CO2) and is commonly called as the ?Biogas?. harnessing this gas from any biodegradable material (organic matter) under artificially created conditions is known as biogas.
Anaerobic digestion, like pyrolysis, occurs in the absence of air; but in this case the decomposition is caused by bacterial action rather than high temperatures. It is a process which takes place in almost any biological material, but is favoured by warm, wet and of course airless conditions. It occurs naturally in decaying vegetation on the bottom of ponds,
Anaerobic digestion also occurs in situations created by human activities. and is generated in sewage or animal manure, landfill gas .a mixture mainly of methane and carbon dioxide; but major differences in the nature of the input, the scale of the plant and the time-scale for gas production lead to very different dealing with the two sources.
it appears that a mixed population of bacteria breaks down the organic material into sugars and then into various acids which are decomposed to produce the final gas, leaving an inert residue whose composition depends on the type of system and the original feedstock.
3.7.5.1 Biogas
is a valuable fuel which is in many countries produced in purpose built digesters filled with the feedstock like dung or sewage. Digesters range in size from one cubic metre for a small ?household? unit to more than thousand cubic meters used in large commercial installation or farm plants. The input may be continuous or in batches, and digestion is allowed to continue for a period of from ten days to a few weeks. The bacterial action itself generates heat, but in cold climates additional heat is normally required to maintain the ideal process temperature of at least 35 degrees Celsius, and this must be provided from the biogas. all the gas may be used for this purpose, the plant may still pay for itself through the saving in fuel needed to process the wastes. A well-run it will produce 200- 400 m3 of biogas with a methane content of 50% to 75% for each dry tonne of input.
LANDFILL GAS
the potential hazard led to the fitting of systems for burning it off; only in the 1970s that serious attention was paid to the idea of using this ?undesirable? product. In developing a site, each area is covered with a layer of impervious clay or?which encourages anaerobic digestion. The gas is collected by an array of interconnected perforated pipes buried at depths up to 20 metres in the refuse. In new sites this pipe system is constructed before the wastes start to arrive, and in a large well-established landfill miles of pipes, with as much as 1000 m3 an hour of gas being pumped out.
Increasingly, the gas from landfill sites is used for power generation. At
3.8 TECHNOLOGY EXAMPLES
3.8.1 Heat production with wood firing boilers (get for wood-heat study,
from editor: hello,this is the editor of meth805, this next part was cut out, but partly put back in, i felt it held a key for people with methane-digesters in colder climates.)3.8.1 Heat production with wood firing boilers
Most common process of biomass combustion is burning of wood. In developed countries replacing oil or coal-fired central heating boiler,can save between 20 and 60% on bills, because wood costs less than oil or coal. no global warming. and contains less sulphur than oil, less sulphate,less acid rain and in soil. Small wood burning storage tank so as to gather the heat energy from fuel. Automatic boilers are equipped with a silo containing wood pellets or wood chips. A screw feeder feeds the... manually fired boilers efecient from below 50% to 75-90%. automatically fired boilers reach 85-92% effeciency reached.
MANUALLY FIRED BOILERS :The principal rule is that manually fired boilers for fuelwood only have an acceptable combustion at the boiler rated output (at full load). At individual plants with oxygen control, the load can, however, be reduced to approx. 50% of the nominal output without thereby influencing neither the efficiency nor emissions. By oxygen control, a lambda probe measures the oxygen content in the flue gas, and the automatic boiler control varies the combustion air inlet.
AUTOMATICALLY FIRED BOILERS
Despite simple construction, most of the automatically fired boilers can achieve an efficiency of 80-90% and a CO emission of approx. 100 ppm (100 ppm = 0.01 volume %). For some boilers, the figures are 92% and 20 ppm, respectively. An important condition for achieving these good results is that the boiler efficiency during day-to-day operation is close to full load. For automatic boilers, it is of great importance that the boiler nominal output (at full load) does not exceed the max. output demand in winter periods. In the transition periods (3-5 months) spring and autumn, the output demand of the dwelling will typically be approx. 20-40% of the boiler nominal output, which means a deteriorated operating result. During the summer period, the output demand of the dwelling will often be in the range of 1-3 kW, since only the hot water supply will be maintained. This equals 5 -10% of the boiler nominal output. This operating method reduces the efficiency - typically 20- 30% To stop deteriorated summer operating add with it a storage tank and solar collectors.
3.8.2 MANUALLY-FIRED BOILERS , BURN-THROUGH
Nearly all old-fashioned cast iron stoves act on the burn-through principle: air comes in from below and passes upwards through the fuel. the wood burns very quickly. The gases do not burn very well, since the boiler temperature is low. Most of the gas goes up the chimney, and the energy with it. flu-gases have a very short space in which to give off their heat to the boiler in the convection section. effeciency = below 50%.
Underburn boiler: is very different from a burn-through one. The air is not drawn through all the fuel at once, but only through part of it. Only the bottom layer of wood burns; the rest dries out and gives off its gases very slowly. Adding extra air (so-called ?secondary air?) direct to the flames burns the gases more effectively. In modern underburning boilers the combustion chamber is ceramic lined, which insulates well and keeps the heat in. This gives a high temperature of combustion, burning the gases most effectively. An underburning boiler typically has a useful effect of 65-75%.
In reverse combustion boilers: too, air is only added to part of the fuel. As in underburning, the gases leave the fuel slowly and are burnt efficiently. Secondary air is also led into an earthenware-lined chamber, giving a high temperature of combustion. The flue gas has to pass through the entire boiler, giving it plenty of time to give up its heat. The useful effect is typically of the order of 75-85%. Some reverse combustion boilers have a blower instead of natural draught. effecient boiler:How good a boiler is partially depends on the energy in the fuel that it transfers. efficiency of a boiler means between the energy in the hot water and that in the wood: of the order of 80-90%. boilers can burn wood logs up to 80 cm long.
Power output(kW) Wood consumption(kg/hr) Wood-consumptionin heating-season(m3)
18 4 10
25 6 15
32 7 20
50 13 30
80 18 50
Wood heating value 15-18 MJ/kg.
STORAGE TANK :It almost always pays to buy a storage tank when installing a wood burning boiler. A storage tank holds water that has been heated up by the boiler. The extra cost repays itself very quickly, and it is easier to fire properly. Shortly after lighting up, combustion is clean and the boiler starts producing masses of heat. Without a storage tank to take up the heat, the water will rapidly get too hot and the damper will have to be shut to stop it boiling. reduced amount of air leads to smoky,incomplete combustion.
But with a hot water tank you can fire away and store the heat. The water in the boiler cannot overheat because it goes into the tank. The damper remains open and combustion continues at high efficiency. When you need heat in the radiators, it comes from the storage tank. The size of the storage tank depends on the amount of heat the house needs and the efficiency of boiler.
BURNING WOOD COMBINED WITH SOLAR HEATING -pause-
If you do decide to install a wood burning unit, it is recommended also to consider putting in solar heating. The wood burning boiler and the solar panels can frequently use the same storage tank, reducing the cost of the system as a whole. Make sure first that the storage tank is suitable for the purpose. it makes it unnecessary to have a fire going in summer just to get hot water. And it is cheaper to ?burn? solar energy than wood! fuel choice:
Whatever fuel you decide to use, it must be dry. (editor:heh heh, thats what
you think, read about jean-pain, or explain the heat coming from your own body). Newly felled timber has 50% water and so is useless for...
-no end-
posted by Arise! at 5:03 PM
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