The biomass gasification process; It is the process of converting to a combustible gas heat conversion technology with solid fuel. Delimited oxygen, air, steam or combinations thereof initiate the reaction.The gas produced carbon monoxide, carbon dioxide, hydrogen, methane, water and coal particles, along with nitrogen, it includes residues such as ash and tar. After the produced gas cleaning boilers, engines, turbines are used to produce heat and power. Biomass gasification technique, oil-fired power and therefore a high output can be obtained a gas turbine fuel to be used in providing heat.
Renewable biomass and fuels derived from biomass will be able to easily replace the use of fossil fuels in power today that provides environmental benefits.
Biomass ensuring the provision of resources is more expensive fossil fuels. But sustainable biomass alongside fossil fuels endangered by being a renewable resource is an important element of global energy. In addition to reducing greenhouse gas emissions and the carbon cycle, support the green industry with the development of the rural economy. Biyokült the gas obtained by gasification of fuels with minor modifications was used in place of natural gas can be expanded in the future easily and a large part of the energy used in areas where natural gas is supplied from this fuel.
Obtained by gasification of biomass fuel gas heat cleaned and burned directly in boilers that produce steam for electricity generation or in the Stirling engine can be used in 20-30% efficiency. In turbine pressure gasification power generation efficiency of 40% or more it can be made.
Gasification is a technology known since the late 18th century. especially for developing countries where biomass is available now playing an important role in the future than it has been proven since years. A known issue is that of the biomass used as an energy source several disadvantages. with a low energy density (about 16-20 MJ / kg) of raw biomass resources if burned directly provides very low efficiency and cause indoor and outdoor air pollution to occur at higher levels thereunder.
Gasification is a thermochemical gas fuels derived from biomass conversion process. I.e. with biomass gas thermochemical conversion is converted into a fuel. The purpose of modernized biomass energy production technology and reducing emissions during use to increase the density of the fuel.
Gasification Chemistry
On the basis of solid carbon fuel, it is located oxygen and hydrogen compositions. The biomass gasifiers are oil under high heat.
Gasification Process Phase Four is split up:
a) Oxidation
C + O2 = CO2 + Heat
H + O2 = H2O + Heat
Biomass, organic molecule, carbon (C) and hydrogen (H), in accordance with the above reaction, oxidation heat energy as they are released. These reactions are exothermic reactions where the temperature vented. These are respectively transformed into carbon dioxide and water vapor. ash as a result of combustion of the combustible inorganic minerals found are also becoming clear.
b) Pyrolysis (distillation)
Organic materials pyrolysis name given to the thermal fragmentation process occurs when heated in oxygen. 500-600 ° C in an oxygen atmosphere up to do the heating; gas components can condense volatile substances, charcoal and ash released. When out high-temperature gas generating components and wood gas are released.
The pyrolysis process takes place as follows: oxygen-free environment can break down complex organic molecules in the region of 400-600 ° C as well, since it does not gas, tar and bitumen released.
c) reaction (carbonization)
Umeda carbonization; wood, peat, organic materials such as coal and undergo chemical degradation under vacuum. This also takes place in the region at different temperatures (150-500 ° C). As a result of the carbonization process the resulting gas components: 50% CO2, 35% CO, 10% CH4, other hydrocarbons and approximately 5% of the calorific value of the mixture h2’dir.gaz 8.9 MJ / m3. The carbonized wood and tar mAsIndAki liquid products are aqueous parts.
d) Gasification (Reduction)
the gasification of organic substances is up to about 500 ° C temperature pyrolysis stage process wherein carbon gases (calorific value of 20 MJ / m3, and may be) and tar is obtained. Heating the water vapor reacts with the carbon to 1000 ° C when exiting CO and H2 are produced. variable oxygen content depending on the feedstock for the gasification process input additional oxygen may be required.
In gasification, does not exceed 30% of the biomass moisture is important. Humidity increases the calorific value of the gas is reduced. In addition, as the volume of combustible gas, CO emissions decreased CO2 emissions are increasing. If the partial burning of calories burned waste vegetable 4.5-6 MJ / m3 gas are produced.
Naturally occurring carbon dioxide and a second process in accordance with the reaction hydrogen reduction reaction are converted into carbon monoxide and hydrogen. As well as coal tar and coal becomes gasified tar will be formed in accordance with the art. Gases generated combustible gas is decreased and the particulate matter concentration in the product.
Gasifier Types
a) fixed-bed gasifier in
Fixed bed gasifiers are designed and operated quite easily. They are therefore suitable for small and medium power and thermal energy use. But keep the same operating temperatures in each region and in the gas phase reaction is difficult to mix a sufficient rate zone. As a result, the quantity of gas products generated unpredictable and therefore not purposeful use of large-scale power preferences.
I. The upward flow gasifiers
The upward flow of fuel in the gasifier, the air flow given up the hill given below. Fuel is dry as they extend downwards; Undergoes pyrolysis; gasification, and since this type of gasifier main advantages of simplicity, low internal heat exchange, depending on whether the gas exit temperature and a high gasification efficiency. internal heat exchange through the fuel is dry and can be used on top of the gasifier fuel with a high moisture content accordingly. That should be done without any pre-drying the gasification process. Moreover, this type of gasifier can work with fuel particles of small size. This biomass having a broad size range, it is eligible to be gasified with different particle sizes and moisture. Disadvantages of the upflow fixed bed gasifier amount of tar and pyrolysis gas of the pyrolysis products in large quantities not been burned. However, high amount of tar is an undesirable situation in terms of energy applications since it requires substantially tar cleanup.
II. Downflow gasifier
Downstream of the gasifier air / oxygen and biomass is fed from the top. Fuel and gas motions will be the same way and the gas leaves the reactor from the bottom. Remove the produced gas from the bottom of the reactor. In contrast to the up-flow gasifier, downstream in the gasifier, the heat transfer between the biomass and the gas is very low. Thus the output gas temperature is relatively high, downstream most important advantage of the gasifier, the gas produced comprises very low amounts of tar.
The downstream disadvantages of the gasifier;
• The gas contains high levels of dust and ash, and therefore had to make the oxidation of the ash components.
• There are relatively strict rules on fuel. Regular flow to ensure is that they obstruct each other in the narrow part, pyrolysis is sufficient space for the down flow of gas and furnace size of the materials to be used to make up the heat transfer area should be identical between about 4-10 cm. It is therefore necessary to adjust the biomass size.
• The moisture content of the biomass must be below 25%.
• The high temperature of the flue gas leads to lower gasification efficiency
III. Counter-flow gasifier
Counter-flow gasifier are designed for the use of charcoal. gasification of charcoal yielded results at very high temperatures in the furnace area. Opponents flowing out from the air descends down the side of the gasifier feed. The resulting gases are drawn from points on the same level on the opposite side and the outlet temperature is between 800-900 ° C. The air inlet of the January gas outlet is located in the middle of the area took place. It is taken from the bottom of the gasifier. These types of gasifiers are suitable for low tar content of fuels. Because the tar yield is high. The advantage of the system it can be produced at low dimensions. The disadvantage response to the need for high quality charcoal is low tar conversion.
IV. Open-flow gasifier
Open-flow gasifier, in particular pure substances with low concentrations (eg. Rice hulls) was designed for. Because of low density, blocking the passage of fuel or will be made to eliminate the bottlenecks blocking the flow state. Rotary grill like special machines may be added to the system to be adjusted the mixing of the ash and fuel. Particularly rice hulls, require continuous ash evacuation system because of the high ash content. It is open at the top of the gasifier and a pool of water that the air here in the lower part of the ashes given to the existing system is fixed.
b) the fluid bed gasifier for
• The inner surface of the bed is still covered with granulated particles (silica or ceramic)
• Reduced biomass gasification bed parts of the inlet is at the bottom.
• bed biomass is heated at a certain temperature is sufficient for partial combustion and gasification.
• pyrolysis and burning all over the bed conversion process takes place.
• Biomass parts of biomass particle size of less than 10 cm, although fluid, moisture content should not be more than 65%.
• While not contain tar in the gas produced in the lower fluidized bed, the particle content is greater than fixed beds.
• If the pressure is produced in the gasifier pressure gas is more suitable for use in electrical and power generation in gas turbines.
Bubbling Fluidized Bed Gasifier
In this type of gasifier, the gas velocity for the rising of the solid particles forming the bed must be sufficiently high. Thus, the bed expands and as a bubbling liquid. sand with a relatively large mass of gas, bed temperature keeps in balance. bubbling fluidized bed gasifier which is designed to move all of the ash and in this case, requires the use of cyclones or electrostatic precipitators for particulate control.
II. Circulating Fluidized Bed Gasifier
The most important advantage of the circulating fluidized bed gasifier is its ability to process different composition and moisture content of raw materials. However, as in the clumping said bubbling bed.High alkali-containing fuels leads to aggregation of the particles in the bed and consequently lose its system fluid property. There is no upper limit of capacity in these systems. Capacity can be determined completely by the use of biomass or domestic energy needs.
• Gasification agent is generally air of atmospheric pressure, but greater than 100mW gas in the turbine gasification pressure on it may be advantageous.
• Due to the low temperature (around 850 ° C) is not complete combustion and ash content in small quantities is dangerous.
Biomass gasification Procedure
Fossil fuels, traditional energy sources such as nuclear energy and large-scale hydraulic projects are they dominate the world energy market. Other energy sources are not sufficient to compete with the traditional sources. The use of biomass energy are of great interest in recent years by research and development units and governments. In order to provide many forms of biomass energy is generated in different ways.
ensure reliability and process for the gasification of biomass fuel efficiency of process details need to be finalized. All biomass gasifier types in size, the determination of moisture and ash content is very important. often it leads to the formation of technical problems in the preparation of the missing fuel gasification process. So good organization and control method of fuel preparation is very important.
Areas of use of the gasification gas
Tar, coal ash and other waste products as are known to increase the generated gas. The gas produced in the internal combustion engine needs to be cleaned of tar and particulates to burn.Content of the combustible gas produced mainly carbon monoxide, hydrogen and hydrocarbon gases (depending on the raw material) and mixed in different ratios of nitrogen. Gasification reaction with the nitrogen containing gas heating value compared to other gas in the produced gas composition is relatively low (4 to 6 MJ / m3).
The energy content of the produced gas, in internal combustion engines, boilers, and is suitable for use in the oven, but the nitrogen-containing gas is not recommended for medium and long transport.When gas is obtained with a high energy density of biomass gasification as the oxidant instead of air to ensure complete combustion of pure oxygen or steam used capacity.
Although it has low thermal value of gas turbine engines and in the production of electricity or the internal combustion engine has been used gasified solid biomass as an energy source. This method can be used to modernize and be used as fuel gas release less harmful emissions of traditional fuels. Gasification is known as a way to assess the solid biomass.
Gasification and Sustainable Future
There is no doubt that natural energy sources as biomass itself is a source of energy that can be renewed indefinitely.
• Gasification is a power generation technology that can produce more clean energy.
• Among renewable energy technologies is a technology that raw materials be used in different combinations.
• Fossil fuels are sulfur dioxide, nitrogen oxides and radioactive fields (nuclear) kirletilirk the atmosphere, rather than direct combustion emissions in the use of gasification technology can be reset in a big way.
• The gasification method with eld e The gas quality improvement can be achieved in more efficient heat and power in use in the machine.
• Fossil fuel and radioactive power is a technology that enables rather than put biomass.
• Gasification of waste conversion technology (up to urban waste from agricultural residues) is one of a kind in terms of providing a convenient and high-quality energy.
Gasification Disadvantages
the disadvantage is the need to look at biomass gasification Consequently. If it takes confidence in how the environment has disadvantages that are described in terms of damage to health. These disadvantages;
• Smell
• Noise
• Combustion / explosion hazard
• CO poisoning
• Contracting gas
• Drain outlet (gas originating from the cleaning process)
Biomass gasification in the hydrogen sulfide odor similar to ammonia and carbon oxy-sulphide odor.Tar also has a sharp odor. smell coming from the sewage gas may also be caused by tar and fly ash. The noise caused by the operation of the machine during operation. If gas leaking fuel or fumes into the atmosphere from the system if the environment can be done in the ignition explosion.
solid fuel tank in the biomass gasification process, combustible dusts, fuel drying and constitute the main risk factor produced gas. When inhaled, carbon monoxide is colorless and odorless, which creates a dangerous toxic effects.
• The most important factor in the less used; According to the production and storage of petroleum products to be more laborious and requires different units for operating the gas production system.
• The gasifier system mainly; a gasifier unit, cleaning unit and the energy conversion (combustion or combustion engine) occurs.
• gasification is not the most important problem to produce gas. The gas produced internal combustion engines to be usable to provide the physical and chemical properties.
• There is a homogeneous mixture of combustible gas produced in the gasifier, and physical and chemical properties of the gas as a function of time (composition, energy content, pollution) vary.
• There is no storage tank from internal combustion engines with the gasifier. Therefore it creates storage problems. The produced gas engine is very well cleaned before being burned.
Source: Directorate General of Renewable Energy