- direct combustion,
- gasification,
- combined heat and power (CHP),
- anaerobic digestion,
- aerobic digestion.
Benefits of biomass heating
The use of biomass in heating
systems is beneficial because it uses agricultural, forest, urban and
industrial residues and waste to produce heat and electricity with less effect
on the environment than fossil fuels.
This type of energy production has a limited long term effect on the
environment because the carbon in biomass is part of the natural carbon cycle;
while the carbon in fossil fuels is not, and permanently adds carbon to the
environment when burned for fuel (carbon footprint).
Historically, before the use of fossil fuels
in significant quantities, biomass in the form of wood fuel
provided most of humanity's heating.
Drawbacks of biomass heating
On a large scale, the use of biomass
takes agricultural land out of food production, reduces the carbon
sequestration capacity of forests, and extracts nutrients from the soil.
Combustion of biomass creates air pollutants and adds significant quantities of
carbon to the atmosphere that may not be returned to the soil for many decades.
Using biomass as a fuel produces air
pollution in the form of carbon monoxide,
NOx
(nitrogen oxides), VOCs (volatile
organic compounds), particulates and other pollutants,
in some cases at levels above those from traditional fuel sources such as coal
or natural gas.
Black carbon
– a pollutant created by incomplete combustion of fossil fuels, biofuels, and
biomass – is possibly the second largest contributor to global warming.
In 2009 a Swedish study of the giant brown haze that periodically covers large
areas in South Asia determined that it had been principally produced by biomass
burning, and to a lesser extent by fossil-fuel burning.
Researchers measured a significant concentration of 14C, which is associated with recent
plant life rather than with fossil fuels.On combustion, the carbon from
biomass is released into the atmosphere as carbon dioxide (CO2). The amount of carbon stored in dry wood is approximately
50% by weight.When from agricultural sources, plant matter used as a fuel can be replaced by
planting for new growth. When the biomass is from forests, the time to
recapture the carbon stored is generally longer, and the carbon storage
capacity of the forest may be reduced overall if destructive forestry
techniques are employed.
The biomass-is-carbon-neutral proposal put forward in the early 1990s has been superseded by more recent science that recognizes that mature, intact forests sequester carbon more effectively than cut-over areas. When a tree’s carbon is released into the atmosphere in a single pulse, it contributes to climate change much more than woodland timber rotting slowly over decades. Current studies indicate that "even after 50 years the forest has not recovered to its initial carbon storage" and "the optimal strategy is likely to be protection of the standing forest".
The biomass-is-carbon-neutral proposal put forward in the early 1990s has been superseded by more recent science that recognizes that mature, intact forests sequester carbon more effectively than cut-over areas. When a tree’s carbon is released into the atmosphere in a single pulse, it contributes to climate change much more than woodland timber rotting slowly over decades. Current studies indicate that "even after 50 years the forest has not recovered to its initial carbon storage" and "the optimal strategy is likely to be protection of the standing forest".
Biomass heating in our world
The oil price increases since 2003
and consequent price increases for natural gas and coal have increased the
value of biomass for heat generation. Forest renderings, agricultural waste,
and crops grown specifically
for energy production become competitive as
the prices of energy dense fossil fuels rise. Efforts to develop this potential may
have the effect of regenerating mismanaged
croplands and be a cog in the wheel of a
decentralized, multi-dimensional renewable energy industry. Efforts to promote
and advance these methods became common throughout the European Union
through the 2000s. In other areas of the world, inefficient and polluting means
to generate heat from biomass coupled with poor forest practices have
significantly added to environmental
degradation.
Buffer tanks
Buffer tanks, sometimes referred to
as 'thermal stores' are crucial for the efficient operation of all biomass
boilers where the system loading fluctuates rapidly, or the volume of water in
the complete hydraulic system is relatively small. Using a suitably sized
buffer vessel prevents rapid cycling of the boiler when the loading is below
the minimum boiler output. Rapid cycling of the boiler causes a large increase
in harmful emissions such as Carbon monoxide,
dust, and NOx,
greatly reduces boiler efficiency and increases electrical consumption of the
unit. In addition, service and maintenance requirements will be increased as
parts are stressed by rapid heating and cooling cycles. Although most boilers
claim to be able to turn down to 30% of nominal output, in the real world this
is often not achievable due to differences in the fuel from the 'ideal' or test
fuel. A suitably sized buffer tank should therefore be considered where the
loading of the boiler drops below 50% of the nominal output – in other words
unless the biomass component is purely base load, the system should include a
buffer tank. In any case where the secondary system does not contain sufficient
water for safe removal of residual heat from the biomass boiler irrespective of
the loading conditions, the system must include a suitably sized buffer tank.
The residual heat from a
biomass unit varies greatly depending on the boiler design and the thermal mass
of the combustion chamber. light weight, fast response boilers require only
10ltr/kW, while industrial wet wood units with very high thermal mass require
40ltr/kW
Types of biomass
heating systems
The use of Biomass in heating
systems has a use in many different types of buildings, and all have different
uses. There are four main types of heating systems that use biomass to heat a
boiler. The types are Fully Automated, Semi-Automated, Pellet-Fired, and
Combined Heat and Power.
Fully
automated
Fully automated systems operate
exactly how they sound. Chipped or ground up waste wood is brought to the site
by delivery trucks and dropped into a holding tank. A system of conveyors then
transports the wood from the holding tank to the boiler at a certain managed
rate. This rate is managed by computer controls and a laser that measures the
load of fuel the conveyor is bringing in. The system automatically goes on and
off to maintain the pressure and temperature within the boiler. Fully automated
systems offer a great deal of ease in their operation because they only require
the operator of the system to control the computer, and not the transport of
wood.
Semi-automated
or "surge bin"
Semi-Automated or "Surge
Bin" systems are very similar to fully automated systems except they
require more manpower to keep operational. They have smaller holding tanks, and
a much simpler conveyor systems which will require personnel to maintain the
systems operation. The reasoning for the changes from the fully automated
system is the efficiency of the system. Wood fire fueled boilers are most
efficient when they are running at their highest capacity, and the heat
required most days of the year will not be the peak heat requirement for the
year. Considering that the system will only need to run at a high capacity a
few days of the year, it is made to meet the requirements for the majority of
the year to maintain its high efficiency.
Pellet-fired
The third main type of biomass
heating systems are pellet-fired systems. Pellets are a processed form of wood,
which make them more expensive. Although they are more expensive, they are much
more condensed and uniform, and therefore are more efficient. In these systems,
the pellets are stored in a grain-type storage silo, and gravity is used to
move them to the boiler. The storage requirements are much smaller for
pellet-fired systems because of their condensed nature, which also helps cut
down costs. these systems are used for a wide variety of facilities, but they
are most efficient and cost effective for places where space for storage and
conveyor systems is limited, and where the pellets are made fairly close to the
facility
Agricultural
pellet systems
Sub category of pellet systems are
boilers or burners capable of burning pellet with higher ash rate (paper
pellets, hay pellets, straw pellets). One of this kind is PETROJET pellet
burner with rotating cylindrical burning chamber.
In terms of efficiencies advanced pellet boilers can exceed other forms of
biomass because of the more stable fuel charataristics. Advanced pellet boilers
can even work in condensing mode and cool down combustion gases to 30-40°C,
instead of 120°C before sent into the flue.
Combined
heat and power
Combined heat and power systems are
very useful systems in which wood waste, such as wood chips,
is used to generate power, and heat is created as a byproduct of the power
generation system. They have a very high cost because of the high pressure
operation. Because of this high pressure operation, the need for a highly
trained operator is mandatory, and will raise the cost of operation. Another
drawback is that while they produce electricity they will produce heat, and if
producing heat is not desirable for certain parts of the year, the addition of
a cooling tower is necessary, and will also raise the cost.
There are certain situations where
CHP is a good option. Wood product manufacturers would use a combined heat and
power system because they have a large supply of waste wood, and a need for
both heat and power. Other places where these systems would be optimal are
hospitals and prisons, which need energy, and heat for hot water. These systems
are sized so that they will produce enough heat to match the average heat load
so that no additional heat is needed, and a cooling tower is not needed.
SUBSCRIBERS - ( LINKS) :FOLLOW / REF
/ 2 /
Findleverage.blogspot.com
Krkz77@yahoo.com
+234-81-83195664
No comments:
Post a Comment