Coal Gasification as Energy Future

 

Coal gasification technology developed by the Center for Mineral and Coal Technology (tekMIRA) on Coal Utilization Technology Center, Palimanan West Java, applied to dual-fuel diesel power generation.

Coal gasification is the process of converting coal into gas products that can be used for fuel, as well as industrial raw materials chemistry. Gasification unit consists of the reactor, the cooling gas (scrubber), catcher tar (tar electrostatic precipitator) gas cleaning (washing tower), the separator vapor (fog drop), blowers and pool shelters tar (tar pond).

With the application of this technology, besides the dependence on fuel could be reduced, and will indirectly reduce the burden of subsidies, due to high world oil prices, also will increase the added value of coal, increase foreign exchange earnings and employment opportunities.
I

ndonesia's coal reserves estimated at 91 billion tones, with production levels ranging from 200-300 million tones per year, then the life of the mine will be able to reach 100 years, it is quite safe for the sustainability of industrial coal users, while also more economical.
One success story of making fuel from coal gasification process is the South African Coal Oil and Gas Corporation, known as South Africa's Sasol, which is currently producing synthetic gas by 55 million Nm3/hari using penggas Lurgi, and produce synthetic oil as much as 150 thousand barrels per day through the Fischer-Tropsch synthesis.

Currently, Sasol employs 170 thousand employees, either directly or indirectly, which represents 2% of formal sector employment in South Africa. In addition, Sasol also contributed 4% of GDP or about U.S. $ 7 billion, as well as supplying 40% of domestic fuel needs of South Africa (28% of coal)

Coal Gasification Process

 

The process of coal gasification is a process that converts coal from a solid fuel into gaseous fuel. The unwanted material such as sulfur compounds and ash is removed from the gas by using a specific method that can produce clean gas and can be streamed as an energy source.

As known, when the fuel burned, chemical energy is released in the form of heat. Combustion occurs when the oxygen contained in air reacts with the carbon and hydrogen contained in coal and produces CO2 and water and heat energy. Under normal conditions, with proper air supply will convert all the chemical energy into heat energy.

If the air supply is reduced, the chemical energy released from coal will be reduced, and the compound of new gas will be formed from the half -combustion process. Compounds formed gas comprises H2, CO, and CH4 (methane), which still has the potential chemical energy that has not been released. In the form of gas, the potential energy will be more easily transferred and used for energy source in other processes, such as burning in boilers, diesel engines, gas turbine, or processed to become other synthetic materials (raw material to replace natural gas). The gas from coal gasification is also called syngas (synthetic gas). With advanced process, syngas can be processed into a liquid. This process is called coal liquefaction (coal liquefaction). His method is diverse, including Fischer-Tropch, Bergius, and Scroeder.

To be able to produce gas from coal with a maximum, the supply of oxygen must be controlled. Below are some schemes gasifiers, for simple types. Details of the workings, advantages and disadvantages of each type will be further discussed later. (sumber : beritaenergy.wordpress)

Drying Coffee With Coffee Husk Gasification

 

Coffe tree

As grain converts into rice that produced 20 to 24% rice husks, the coffee is also produced 78 to 80% coffee husk instead produce base coffee for drinks. The coffee husk is dry and contains 20 to 22 % coffee husk waste. The calorific value of the coffee husk waste is range 3800 to 4000 kcal per kg means that 2 to 3 kg of coffee husks contain energy equivalent to a liter of kerosene. While to dry or produce 1 ton of coffee market required an average 250 liters of kerosene for the drying process.

Kerosene burner with consumes 20 to 25 liters of kerosene per hour to 3.5 tons of coffee drying dry hs must be on 18 to 20 hours.

Test gasifier with coffee husks as the efficiency and impact on the improvement of environmental quality, CO2 emissions of CO2 neutral.

Gasifier model 70 x 70 cm square in size with a height of 2 meters installed as a test in the coffee plantation unit Malang Sari Banyuwangi, Indonesia.

It is still produced charcoal byproducts for bio-fertilizer with organic C and nutrients over 20% as well as other nutrients.

Gasification in Finland

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].

Table. Fixed bed gasification systems for power production in several 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)

Success histories of gasification development

 

In Finland, research and development activities gasification began in the 1970s. In the 1980s, the application of simple gasification air system first performed and main combined heat and power plant burning lime (lime kilns). Furthermore, in 1986 successfully built updraft gasification systems that produce heat 5 MWth. In almost the same time, gasification systems CFB (circulating fluidized bed) was also built with a power output of 15-35 MWth for the needs of pulp-paper industry (pulp). In the 1990s, IGCC (integrated gasification combined cycle) is also introduced, but because it needs huge resources into further development constraints [1]. Biomass gasification systems are generally only suitable for small and medium scale up to 10 MWe power.

Fig. Bioner Gasification in Finland [1].

With updraft system, biomass is inserted from the top of reactor. The presence of air and steam from below the reactor that moves up causing the biomass will have a series of processes. During the trip biomass from top to bottom reactor, biomass will experience drying, pyrolysis, gasification and combustion. Ash removed from the bottom of the reactors. Gas results updraft gasification process systems containing oil and tar in large numbers. The resulting gas temperature is low (80-300oC for biomass or 300-600oC for coal). Bottom ash (bottom ash) generally burn completely and leaves no burning charcoal in the amount that can be ignored. Dust generated is also relatively low because the gas velocity used was also low and is caused also by the "filtering effect" on the drying and pyrolysis [1].

Because the amount of tar produced quite a lot, then the gases from the gasification can not be directly inserted into the internal combustion engine (IC, internal combustion). Because the tar too, so that piping system needs to be cleaned once per 2-6 weeks depending on the type of fuel used.

In 1980, thermal power from the gasification Bionerr Finland is 1.5 MWth. The fuel used is wood chips, forest waste, peat, straw, pellets, coal and mix. With a moisture content of wood used by 41%, the gases released from the gasification process is 30% CO, 11% H2, 3% CH4, 7% CO2, and 49% N2 with 6.2 equivalents HHV MJ/m3n. Tar produced between 50-100 g/m3n. In 1986, the capacity of 8 units Bioneer Finland is 4-5 MWth.

Year 1999-2001 was developed type of updraft gasification combined with downdraft with a capacity of 500 kWth. As is known, type of downdraft gasification tar yield is lower than other types of updraft. This is because tar brought together the results of pyrolysis gas and then goes into the gasification and high temperature combustion. In the area of gasification and combustion of this, then tar will unravel. The result of the gases from this downdraft gasification system after filtered and cooled can be directly inserted into the internal combustion engine. However, on the commercialization tahun2 not yet done, because to ensure that low-tar required type of biomass with high quality.

The next development occurred in 1997's with still using the system downdraft and updraft gasification system. Two types of gas are separated and clean gases can be directly inserted into the internal combustion engine, while the gases are dirtier (with more tar) is used for the boiler. Planned capacity in 2001 is 2 MW (1.1 MWth and 450 Kwe). Gasification was built in Tervola, Finland.

Fig. Gasification Entimos Oy, in Tervola, Finland [1].

 

Fig. Sampe of gasification wood boilers

 

[1] ____, 2002, Review of Finnish Biomass Gasification Technologies, technical report, VTT, Finland.

Gasification theory

 

Gasification is a process technology that converts solid material into gas. This process can be performed on fuels such as biomass, coal, and charcoal from the oil refinery process. Gasification wood and boilers also important think in gasificaion area. The gases coming out of the gasification process are mostly carbon dioxide (CO2), carbon monoxide (CO), hydrogen (H2) and methane (CH4).

Gasification is different with pyrolysis and combustion. The three distinguished based on the needs of air needed during the process. If the amount of air / fuel (AFR, air fuel ratio) equals 0, then the process is called pyrolysis. If the AFR is required during the process of less than 1.5, then the process is called gasification. If the AFR is needed during the more than 1.5, then the process is called combustion (see picture below).

Fig. Differences pyrolysis, gasification and combustion.

Gasification material including gasification wood reactor can be divided by:
1. based on fluidization mode.
2. Based on the direction of flow.
3. Based on the gasification agent during the process.

Based on fluidization mode, gasification reactor can be divided into fixed bed gasification, moving bed, fluidized bed, and entrained bed. Type of gasification can be described as follows.

Fig. Differences moving bed, fluid bed, and entrained bed gasifier.

Based on the direction of flow, gasification reactor can be divided into unidirectional flow gasifier (downdraft gasification) and counterclockwise flow gasifier (updraft gasification). In downdraft gasification, gas flow direction and the direction of solids flow is equally down. In updraft gasification, solids flow downward direction while the direction of gas flow upward.

Based on the need for gas gasification process, there are air gasification and steam gasification. Air gasification where gas is used for the gasification process is the air while the steam gasification uses steam during the process. ((Sumber:kajian-energi.blogspot..com)

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