Still in Finland, the development of gasification system of CFB (circulating fluidized bed) was also developed since 1983. Gasification operates at temperatures of 800 - 1000oC and there depending on fuel and its use. Fuel is introduced into the bottom of the gasifier (over a certain distance from the distributor). On entering the reactor fuel will experience fast drying and pyrolysis also occurs. Results of pyrolysis gas will move upward. Some sections of the charcoal will move downward while the other carried by the flow and into the cyclone. In the cyclone, charcoal will be separated and put back into the bottom of the reactor where the coal will be burned with air from the distributor.
Fig. CFB gasification concept in Finland [1].
Facts on the ground shows that the use of biomass fuel manifold-jeramian straw and MSW (municipal solid waste) often contain chlorine, alkali metals, and aluminum in large quantities. The high levels of that material cause corrosion and fouling problems in boilers. For that washing gas (gas cleaning) needs to be done before the gases from the gasification put into the boiler.
In Finland, the hot gas cleaning methods developed since 1997 in particular by VTT. Gas from the gasifier at a temperature of 400oC is filtered using a chlorine sorbent too late binding. The decline can be done to 400oC temperature preheated gasification air and feed water to the boiler. The gas is cooled and then cleaned in bag filters. Calcium hydroxide is injected into the gas before entering the bag filter to bind HCl. The gas is clean and then inserted into the burner.
In contrast to the CFB is more economical for large size (40-100 MW), for medium size (15-40 MW) gasification system can be used BFB (bubbling fluidized bed). In Finland, BFB gasification system capacity of 40 MW have been operated in 2001.The figure below shows the concept of BFB in Finland. Gas cleaning system in the CFB can be used also in the BFB.
Fig. BFB gasification system in Finland [1].
Wood chips updraft gasification system developed in Denmark in 1996. Gasification is then combined with the gas engine capacity of 650 kW and has been in operation for 16,000 hours [2].
In a larger capacity of 42,000 MWe / year and 70,000 MWth / year began operating in 2006 with a construction budget of 20 jt €. Operation of the gasification temperature is 850oC FB. Gas from the gasifier is cooled and cleaned in the filter and scrubber. Tar processed in catalytic tar reformer before the gas is inserted in 3 gas engine capacity 2MWe respectively.
In other countries, the development of gasifier can be seen in several tables below.
Table. Some countries are developing gasification cofiring [3].
Table. IGCC plants in several countries [3].
Table. CFB gasification with gas engine in some countries [3].
From the above explanation can be taken several important conclusions:
Downdraft gasification system has the characteristics: suitable for capacities up to 15 MWth.
Updraft gasification system has the characteristics: suitable for capacities up to 25 MWth. The fluidized bed gasification systems: CFB suitable for medium capacity (15-40 MWth) and BFB suitable for large capacity (40-100 MWth). Updraft gasification system is more flexible to the quality of biomass fuels that are used but achieve high tar levels.
Downdraft gasification system is generally specific to a particular biomass fuel quality, requires low water content, and low ash content as well. Gas generated more heat than the updraft system and only requires a gas cleaning technique is simpler.
Until now many research and development activities focused on the purification of gases from the gasification system. Nevertheless, some institutions have claimed to successfully perform gas purification according to standardized.
Gasification systems with fuel together (cofiring) have the advantage because the flexibility of fuel and emissions can be regulated in accordance with the composition.
On a small scale, fixed bed gasification system is better especially at high electrical efficiency to 36%.
Commercialization of the system is still constrained on economic aspects. From the technical aspect of the main obstacle lies in the handling of ash and water exhaust.
Ref:
[1] ____, 2002, Review of Finnish biomass gasification Technologies, technical report, VTT, Finland. Available in: http://www.gastechnology.org/webroot/downloads/en/IEA/OPETReport4gasification.pdf.Accessed: 05/07/2007 16:45.
[2] Jakobsen, H.J. and Helge, T., 2005, the breakthrough in biomass gasification, Denmark. Available at: http://www.dbdh.dk/pdf/ren-energy-pdf/side14-17.pdf accessed: 05.07.2007 17:06.
[3] Kwant, KW, 2004, Status of gasification in Countries Participating in the IEA and GasNet Activity August 2004, the IEA Bioenergy gasification and gasification EU Network. Available at: http://energytech.at/pdf/status_of_gasification_08_2004.pdf.Accessed: 05/07/2007 17:49.
(sumber: Sumber:kajian-energi.blogspot..com)
Still in Finland, the development of gasification system of CFB (circulating fluidized bed) was also developed since 1983. Gasification operates at temperatures of 800 - 1000oC and there depending on fuel and its use. power flushing Birmingham
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