New batteries

The new batteries can withstand extremely high rates of charge and discharge which will cause electrodes used in conventional Li-ion batteries to rapidly deteriorate and fail. The greatest advantage of the new batteries is that charging laptop or cell phone in a few minutes, rather than an hour.
Construction
The new batteries are made from a carbon (C) nanorod base topped with a thin layer of nanoscale aluminum (Al) and a "scoop" of nanoscale silicon (Si), the structures are flexible and able to quickly accept and discharge Li ions at extremely fast rates without sustaining significant damage. The segmented structure of the nanoscoop allows the strain to be gradually transferred from the C base to the Al layer, and finally to the Si scoop. This natural strain gradation provides for a less abrupt transition in stress across the material interfaces, leading to improved structural integrity of the electrode.
Charging cycle
The anode structure of a Li-ion battery physically grows and shrinks as the battery charges or discharges. When charging, the addition of Li ions increases the volume of the anode, while discharging has the opposite effect. These volume changes result in a buildup of stress in the anode. Too great a stress that builds up too quickly, as in the case of a battery charging or discharging at high speeds, can cause the battery to fail prematurely. This is why most batteries in today's portable electronic devices like cell phones and laptops charge very slowly, the slow charge rate is intentional and designed to protect the battery from stress-induced damage. Due to their nanoscale size, nanoscoops can soak and release Li at high rates far more effectively than the macroscale anodes used in today's Li-ion batteries.
Limitation
A limitation of the nanoscoop architecture is the relatively low total mass of the electrode, according to the researchers and to solve this, the researchers are to trying to grow longer scoops with greater mass, or develop a method for stacking layers of nanoscoops on top of each other or to grow the nanoscoops on large flexible substrates that can be rolled or shaped to fit along the contours or chassis or chassis of the device.
The nanomaterial for a new breed of high-power rechargeable lithium (Li)-ion batteries has been  developed at Rensselaer Polytechnic Institute.

About biomass conversion technologies

Biomass composition
Biomass fuels consist of three main segments: wood, waste, and alcohol fuels. Wood energy is derived from the following sources: round wood, used primarily in the industrial and electric utility sectors; wood fuel, used predominantly in the residential and commercial sectors; and wood byproducts and wood waste, which are usually used in the industrial sector. The chemical composition of plant biomass varies among species and has approximately 25% lignin and 75% carbohydrates or sugars linked together in long chains or polymers as cellulose and hemi-cellulose. The lignin fraction consists of non-sugar type molecules that act as a glue holding together the cellulose fibers.
Biomass categories
• Solid Biomass, which includes tree, crop residues like rice husk, bagasse, coconut shells, jute waste, etc. and animal and human waste.
• Biogas which is obtained by anaerobically digesting organic material to produce combustible gas methane.
• Liquid biofuels which are obtained by subjecting organic materials to one of various chemical or physical processes to produce usable combustible liquid fuels.
Conversion methods
A number of technological options are available to make use of a wide variety of biomass types as a renewable energy source. Conversion may release energy directly in the form of heat/electricity or, may convert it into another form such as liquid biofuels or combustible biogas. There are basically three types of conversions:
• Thermal Conversion- A process in which heat is used to convert biomass into another chemical form.
• Chemical Conversion – A range of chemical processes may be used to convert biomass into other forms so that fuel may be used more conveniently, transported or stored.
• Biochemical Conversion- It involves anaerobic digestion fermentation and composting.
Gasification technology
Gasification is one of the most promising technologies in biomass applications particularly because of higher efficiency compared to boiler power systems, amenability to fuel synthesis and environmental friendly features. Biomass gasification has evolved over a long period, but it has not reached a solid commercial stage, except during periods of crises and only for some specific applications while, other gasification technologies, fed by fossil fuels, are currently widely used on industrial scales.
Historical evolution gas plants
The first producer gas plant was designed around 1850. After 1880 the technology found wider application. Producer gas plants used during the First World War were very well described in the literature. The application of small gasification systems for traction assumed enormous proportions by the end of Second World War. Approximately 1 million vehicles were powered by wood blocks, peat, charcoal or anthracite. When oil and gas took over the predominant part of coal and wood, the development of producer gas plants was limited to countries with exceptional local circumstances, such as South Africa where large pressurized Lurgi plants were in operation. It was only around 1970 that attention was paid again to small scale gasification of biomass especially in remote areas of developing countries. Some year’s later research and development programmes were initiated as a result of the energy crisis and concern for the environment. Many conference papers and workshop document these activities and present a good survey on recent research and development on biomass gasification.
Combustion in a controlled atmosphere is the conversion of solid or liquid to a gas. If the oxygen supply is restricted, incomplete combustion of fuel occurs releasing combustible gases such as CO,H2 and CH4. Investigations on Gas producer-Engine systems, a century old technology and forgotten art, have experienced renewed interest in recent years. More than 12000 gas producer plants were in operation in the United States and Canada during the 1920s and 1930's.
Austria, Finland, Germany and Sweden have increasing number of ongoing projects and initiatives since 1970. The development of this technology has been encouraged by the price of fossil fuels and an enhanced interest for biomass gasification as a future alternative. But this technology has not sufficiently achieved a sustainable commercial status. Experimentation activities, demonstration projects and pilot plants, have proved the future potential of the technology.
Small and large scale projects have followed different development routes. In the case of large scale, interest has shifted from electricity generation to biofuel production, primarily due to the failed demonstration projects of the technology coupled with combined cycle for electricity generation. On the other hand, in small scale projects, cogeneration applications have gained interest over heat production. Also in small scale experimentation the causes which have hindered the technology to reach the expected commercial stage has been the lack of resources to demonstrate its competitiveness. Objectives of achieving the success of gasification technology will depend on incentives created by all administrative levels.
Power generation modes
Biomass is a renewable source of energy that can be made use of effectively for thermal as well as electrical energy generation. The biomass based power plants are of smaller capacity, usually situated either at agro-based industries, where the biomass is generated or at a place where crop residue or other type of biomass is located. This decentralized power plant will help in supplying quality power and reduce the transmission and distribution losses. Biomass based power plants can either be as cogeneration or as independent power plant.
Cogeneration
Cogeneration is defined as generation of process heat and motive power by the sequential use of energy from a common fuel source. This is an energy efficient technology as it utilizes the low grade exhaust heat from the steam turbine for process heating. This enhances the efficiency of energy utilization from 35% in the conventional power generating system to 70-90% in the co generating system.
Combustion
Combustion route is an established and reliable system to generate power from biomass. This system consists of boiler, turbine, power evacuation scheme and interfacing with the grid. This system requires water treatment plant, deaerator, DM water plant and condensate polishing unit, condenser and cooling tower.

Tape Calandering of Solid oxide fuel cell

Solid oxide fuel cell
A solid oxide fuel cell (SOFC) produces electricity directly from oxidizing a fuel and has a solid oxide or ceramic, electrolyte. Advantages of solid oxide fuel cells include high efficiency, long-term stability, fuel flexibility, low emissions, and relatively low cost. The largest disadvantage is the high operating temperature which results in longer start-up times and mechanical and chemical compatibility issues.
Methods of fabrication
Currently, all R&D efforts are focused on fabrication methods of ceramic SOFC components.
SOFC components manufacturing processes.
Stiff structural ceramic parts can be manufactured by:
Extrusion
Dry pressing
Tape casting and
Calandering
Functional ceramic parts can be manufactured by:
Screen printing
Slurry coating
EVD, PVD and
Plasma and flame spraying
Tape Calandering
In Tape Calandering , a continuous thin sheet or tape of controlled thickness is produced. A high intensity mixer is used to mix the ceramic powder, binder and plasticiser. The mixing results in heating-up the batch and softening the binder to form a plastic mass. Then, the mass is rolled to form a thin, flat tape using a two-roll mill, and adjusting the spacing between the two mills controls the tape thickness.
This technique is used to fabricate monolithic FCs via a co-sintering process, where the individual tapes are laminated in a second rolling operation, and FCs with very thin electrolyte layer, which enables to operate at low temperatures (600 ºC) is produced.
The fabrication details of typical 2 cm2 area fuel cell components which includes preparation of anode, electrolyte, cathode cermet pastes, nickel net (60 mesh and grip on anode side) are given below.
• Anode: NiO,
• Cathode: perovskite Ca0,9La0,1MnO3 (CLM),
• Electrolyte (SDCm-1)
Cermet proportions
• Anode: Electrolyte cermet, at: 1:1, % by volume
• Cathode/electrolyte cermet, at 1:1 % by volume
• Binder : 3% Teflon by mass to every component
• Nickel net dimensions: Anode: 22x22 mm,
• Anode/Cathode thickness: 0.5 mm each, including nickel net
• Electrolyte thickness: 0.5 mm
• Sintering of samples: 600 °C, 2 h under nitrogen atmosphere

Bio-oil from mico algae

Micro algae
Microphytes or micro algae are microscopic algae, typically found in freshwater and marine systems. They are unicellular species which exist individually, or in chains or groups. Depending on the species, their sizes can range from a few micrometers (µm) to a few hundreds of micrometers. Unlike higher plants, micro algae do not have roots, stems and leaves. Micro algae, capable of performing photosynthesis, are important for life on earth; they produce approximately half of the atmospheric oxygen and use simultaneously the greenhouse gas carbon dioxide to grow photoautotrophically. Micro algae have higher photosynthetic efficiency, larger biomass, faster growth and higher content of components preferable for pyrolysis compared to those lignocellulosic materials and been suggested as very good candidates for fuel production.
Pyrolysis
Pyrolysis is a most efficient process for biomass conversion and it can compete and replace nonrenewable fossil fuels. Pyrolysis process can be tuned to yield char, liquid or gas as products. Liquid bio-oil obtained from pyrolysis can be readily stored or transported and has lower nitrogen and sulfur contents which favor its use as transportation fuel. In recent years fast pyrolysis process for biomass has attracted a great attention for maximizing liquid yields compared to slow pyrolysis as almost no flowing bio-oil products were directly produced from slow pyrolytic process.
Fast pyrolysis
Fast pyrolysis is a high temperature process in which biomass is rapidly heated in the absence of oxygen. The essential features of a fast pyrolysis process are very high heating and heat transfer rates, carefully controlled pyrolysis reaction temperature of around 500◦C, short vapor residence times of less than 2 s and rapid cooling of the pyrolysis vapor. Further a greater amount of high quality bio-oil can be continuously produced.
Mico algae bio-oil
Bio oil can be produced using fast pyrolysis from mico algae at temperature of 500◦C with a heating rate of 600◦Cs−1 and the sweep gas (N2) flow rate of 0.4m3/h and a vapor residence time of 2–3 s. The bio-oil yields vary from 17.5 to 23.7%. By continuously processing micro algae by the fast pyrolytic process high-quality bio oil can be obtained. The process is time saving and requires a lower energy input compared to the slow pyrolytic process. The contents of carbon and hydrogen of bio-oils from micro algae are higher than those of oil from wood. The bio-oils of micro algae are characterized by low oxygen contents with higher H/C ratios than the bio-oil from wood, sunflower bagasse and cotton straw and stalk. The decrease in the oxygen contents of bio-oils from micro algae compared to the bio-oil from higher plants such as wood is important because the high oxygen content is not attractive for the production of transport fuels Low oxygen content of mico algae bio-oils makes it more stable than the bio-oil from wood. Compared with the bio-oil from wood, the bio-oil from micro algae has higher heating value (about 1.4 times of that of wood), lower viscosity and lower density. These physical properties of bio-oil of micro algae make it more suitable for fuel oil use than pyrolysis oils from lignocellulosic materials.

Global biomass gasification research activities

Gasification
Gasification has been receiving attention throughout the world. Based on the current stage of development of thermochemical conversion technologies, gasification provides potential for near-term deployment, while pyrolysis will help to meet longer-term biofuels goals and in providing a route to renewable gasoline, diesel and jet fuel. Biomass gasification is a complex thermochemical process that begins with the thermal decomposition of a lignocellulosic feedstock. This is followed by partial oxidation or reforming of the fuel with a gasifying agent—usually air, oxygen, or steam—to yield raw syngas. The raw gas composition and quality are dependent on a range of factors, including feedstock composition, type of gasification reactor, gasification agents, stoichiometry, temperature, pressure, and the presence or lack of catalysts.
Work is being carried out on the gasification of variety of biomass such as municipal solid wastes, agricultural wastes and forest residues for different applications such as heat/power generation, production of syn-gas, methane, and hydrogen etc.It is reported that in the near future, the use of gasification to convert solid wastes into ready-to use fuel could literally solve several environmental problems at the same time.
A great number of small-scale fixed bed gasifiers are available around the world. So far successful applications have been seen in Finland, and Denmark where the gas is used for combustion in a boiler. Also other countries have demonstrated small fixed bed gasifiers with success for 1000 hours of operation in a year for power production. Biomass gasification devices aboard generally are large-scale, of high automation degree with complex techniques, and concentrated on power generation and thermal application. Their gasification efficiencies can reach 60-90%, and combustible gas has a caloric value of 17-25MJ/m3.
In the early 1980’s, rice husk-based gasification device was developed in China, using a down-draft fixed-bed gasifier of volume varying from 60 kW to 160 kW, which were applied in the local food industry and were also exported. The biomass power plant developed in China produces a valuable gas named producer gas - Syngas (Synthetic gas). The biomass (agricultural), used for this purpose is straw like materials such as: Rice stems, rice husks, cotton stalks, corn stalks, millet stalks, wood dust, cane trash, wheat straws, hemp palm husks and other forms of biomass. This system can produce electric power in the range of 200kW 6.0MW by using a few parallel modular units.
Since Biomass itself is almost sulfur free, the gasification process will not produce any sulfur oxide emissions (SOx). However, fuels such as diesel and HFO contain a considerable amount of sulfur. HFO could have as much as 4% sulfur and therefore requires special additional treatment to neutralize these emissions.
Similarly the gasification of biomass produces very low concentrations of nitrous oxide emissions (NOx) when manufacturing the Syngas and thereafter leads also to low emissions in the combustion engines.

In other EU countries, electricity from biomass is an option only lately starting to be considered by Greek companies. However, the currently used gasification technologies are still far from satisfactory. The main challenges faced is non-stable gas production process caused by local hot spots existing in the gasifier, non-flexibility to diverse biomass types, difficulty of scale-up, and low quality of product gas. Despite the great number of developments at different industries and the pilot plants available around the world, there are only a few that achieve a commercial operation.

Advanced technical level on the field of producer gas has been mastered by many countries such as Sweden, the United States, Italy, and Germany. In recent years, the United States had a breakthrough in biomass pyrolysis gasification, and researched and manufactured a set of biomass comprehensive biomass gasification set with gas turbine generation system for large-scale generation.

Country wise activities in brief
Australia
The Commonwealth Scientific and Industrial Research Organization (CSIRO), Australia's primary publicly funded research organization, is collaborating with the Cooperative Research Centre (CRC) for Coal in Sustainable Development, to operate an advanced coal gasification research facility. CSIRO has also established partnerships with other public entities and industry participants to tackle several gasification issues including researching technologies to measure coal conversion reaction processes, advancing coal and char reactivity knowledge, examining coal slag flow in gasifiers, and studying the water-gas-shift reaction in syngas processing.
Canada
The CANMET Energy Technology Centre-Ottawa (CETC-O) a R&D arm of Natural Resources Canada represents Canada's primary gasification R&D facility. CETC-O's research involves developing gasification, syngas treating, and H2 production technologies.
China
The Thermal Power Research Institute (TPRI) is a Chinese research organization devoted mainly to researching technologies and equipment of fossil-fired power plants, including gasification development.
Germany
The Federal Ministry of Economics and Labor (BMWi) in Germany initiated a R&D program called COORETEC (CO2 reduction technologies) leading to a wide variety of research projects in gasification with the goal of realizing zero-emission power plants.
India
The Indian Ministry of Power operates the Central Power Research Institute (CPRI) which engages in fossil fuel gasification research. The Ministry of New and Renewable Energy performs biomass gasification research for developing rural power generation.
Japan
In Japan, the New Energy and Industrial Technology Development Organization (NEDO) is coordinating the Multi-purpose Coal Gasification Technology Development (EAGLE). This program is aimed at developing the most advanced oxygen-blown, single-chamber, dual stage, spiral-flow gasifier that can efficiently produce syngas.
South Africa
Development of fluidized-bed gasification technology at the Council for Scientific and Industrial Research (CSIR) in South Africa has been supported by the recently-formed South African National Energy Research Institute (SANERI).
United Kingdom
The Department for Business Innovation & Skills (BIS), in the U.K. is working with the Engineering and Physical Sciences Research Council (EPSRC), the British Coal Utilization Research Association (BCURA), industry, and international partnerships to advance gasification technology.
Other Countries
Other countries are also involved in gasification R&D to varying degrees. The links subsection offers other resources on the world of gasification research.

GAS CLEANING IN GASIFIERS

Need for gas cleaning

If the gas is to be feed to the engine, it must be cleaned and conditioned. In case of down draft gasifier the gas which is usually hot and dusty may have up to 1% tar particulates. Proper clean up system increases reliability and avoids failure of gasifier system. The total combined tar and particulates allowable for engine is less than 5 mg/Nm3 which amounts 99% removal of dust particles .For effective removal a gas cleanup system must be designed based on magnitude, size and nature of containments.

Gas cleanup goals

To meet the required cleaning goals the first step is to select a gasifier design that minimize production tar and particulates and next step is to have clean up systems that removes articulates, tar and containments effectively. The gas cleanup goals are to remove solids which are abrasive, tar mist which can cause inlet valves, rings and other moving parts to stick and hence need thorough removal for reliable engine operation. Another drawback with the tar is that it usually contains the impurities nitrogen and sulphur in the structure, which during combustion of the fuel gas produce their corresponding oxides. Successful gasifier engine system requires gas cleanliness standards from 10 to even less than 1 mg/Nm3. Tar levels of different gasifier indicate that updraft gasifers generate 5- 20% tar and downdraft gasifers upto 1%.

Tar formation

Thermal decomposition of wood does not progress at even pace but results in the production of gas, char ( the main slow proylisis product) and tar by transferring heat to surface of the particle and subsequent heat penetration by conduction. Temperature development inside the particle, and corresponding intrinsic reaction kinetics dominate the decomposition rate and product distribution. The vapours formed inside the pores are subjected to further cracking leading to formation of addition gas and/or stabilized tars. The longer residence of vapour molecules inside larger particles (at lower temperature) can explain the increased formation of tar incase of slow pyrolysis. When the vapour products enter the surrounding gas phase, they can still decompose further if they are not condensed. The degradation products from the biomass constituents include organic acids like formic and acetic acid giving oil at low pH of about 2 to 4 which can attack mild steal. With high temperatures the tar components become heavier due to the greater extent of gas phase reactions, which convert the primary formed tar components to more stable and heavier non-substituted aromatic compounds.

Composition

The composition of wood tar is an awesome mixture of phenolic and non phenolic compounds that has taxed the capabilities of several analytical laboratories for over a century. Characterization continues even today. The major molecular species identified in hard wood and soft wood tars and pyrolignous acids are reported to be Pyridine (C5H5N) and Lutidine (C7H9N).The tar which may be mixture of higher hydrocarbon and water in mist form have wide range of boiling points ranging from 100-400 C. They contain fine char particles in the exit stream from 700-6000 mg/Nm3 acting as nucleation sites for tarry vapours. Tar is usually defined as the condensable organic compounds in the fuel gas, those compounds, which at ambient temperatures have a sufficiently low vapour pressure. By this definition tar contents may vary with the sampling and analytical method. Tar is a group of organic compounds including phenol, naphthalene and PAH (poly aromatic hydrocarbons) and their substituted derivatives.

Gas purification

For operating engine, pure gas is needed. The composition and quantity of dust drawn from a producer depends on the type of producer employed and the fuel used. The first step in processing the raw gas is to cool it at the gas producer exist so that tarry liquid may condense. A gas producer, which gives tar free gas, is supposed to contain less than 10 mg of total contaminants per Nm3 of producer gas. For normal type Imbert type downdraft gasifier dust loads are reported vary from 0.5 to 5 g/m3 gas when using wood blocks of 4XX4cm. Modern gas cleaning and purifying plants are varied in type but comprise of the following units:

• One or more cyclones or centrifugal separators
• Expansion box or dust separator
• Cooling tubes or boxes
• Baffle separators
• Filtering and purifying devices

cyclones or centrifugal separators may consist of single or multiples and built over dust collecting chamber. In cooling tubes gas is led through a set of tubes with header and collecting chambers having gills for air surfaces. Baffles separators are largely employed. In cylindrical or oblong containers plates are arranged within causing a change of flow path which results in deposition of large solid particles. Filtering and purifying devices may be of different types. (i) dry filtering in scrubbers packed with coke wood wool, wire wool at the bottom and fitted with cloth bags or trays at the top, (ii) washing by light petroleum by bubbling through oil or water or light petroleum, (iii) filtration in a scrubber moistened with water or oil filled with gravel, coke, wood wool, metal turnings or cork

Producer can employ can employ a variety of combinations mentioned above. Cloth filters are rarely used where water or steam is used in gasification as these filters get quickly clogged with a type of paste formed during operation. The practical option is the need for reduced time for cleaning the purification chains. In olden day gasifiers used for mobile uses built in cleaning devices such as brushes or scrappers were provided to reduce the time required for cleaning out these filters.

Electrostatic precipitators

These have been in long use in industry to clean the gas very effectively. In principle, the dirty gas is passed through a chamber, containing high voltage negative electrode, which makes the all particles and droplets negatively charged. These are then migrating to positive electrode, which are then washed by water stream. 20 cm dia and 1 m long precipitator at 10-30kV was found to give excellent performance (99.85% collecting efficiency) in a 75 hp gas generator at SERI but suffered from short-circuiting by soot, tar and water, which was later solved. The power consumption was low, 1.5 W/hp with very low pressure drop.

Wet scrubbers:

Small difficult to capture droplets are made to grow in size with time until they are large enough to be capture by providing adequate residence time in the scrubber volume. Particles grow in size by agglomeration and condensation by particle collision . Wetted scrubbers have been used widely for cleaning and cooling the gas by creating maximum contact between gas and liquid media. There are several types such as impingement plate, packed bed, sieve plate, spray tower and venturi scrubbers.

Spray towers are simplest type having a cylinder fitted with spray nozzles. Particle collection is accomplished by counter current impact of gas with liquid droplets spray towers are well suited for dust loads over 50 g /Nm3.Cyclones spray scrubbers make use of the principle of spray towers and dry cyclone separator which improves particle capture efficiency. These are self cleaning and collect particles regardless of size with low pressure drop and efficiency more that 97%.

Sieve plate scrubbers have liquid flowing downwards over a serious of horizontal perforated sieve plates. The contact may be improved with bubble caps, impingement plates or sieve plates while the gas pass upwards. A typical scrubber has 90% efficiency.

Impingement plate scrubber is similar to sieve plate scrubber but arranged with impingement target. Gas passing through orifice produces spray droplets resulting in large between dust particles. Five to ten liters/minute of water flow is required per 1000 cfm of gas flow.

Venturi scrubbers capture large particles by impaction & impingement and rinse away the deposits. The atomized droplets present considerable surface area for fine particles to be captured by diffusion.

In ejector scrubbers, the velocity of contacting liquid scrubs the entrained gas in an ejector venture scrubber by imparting axial and tangential velocity to the liquid jet. They are well suited for very dirty corrosive or abrasive materials.

Packed bed scrubbers use saddle spheres, rings as packing to enhance gas liquid contact area. They are free draining and pressure drop is 20cm water gage for 15 cm deep bed with 12 mm spheres.

Tar cracking:

Tar can be reduced by properly cracking it either internally or externally to the gasifier. Temperature above 800 C rapidly destroys tar and promotes reaction with char. A tar cracking chamber may be added to gasifier in which small amount of oxgen or air can be added to crack the final trace quantities to as low as 50 to 500 ppm. Tarry gas can be passed over a bed of hydrocarbon cracking catalyst at temperature between 950 and 1040 C resulting in gas containing 10 to 100 ppm of tar. Using dolomite lime up to 900 C tar can be cracked as is used in Swedish gasifiers.

WOOD CHARCOAL

Wood charcoal which is called simply charcoal is made by carbonization (destructive distillation, i.e. heating in absence of air) of wood at 600C.
Physico-chemical changes during wood carbonization
Following four stages are involved in the carbonization of wood:
- When the temperature reaches 100-120C, initial decomposition of wood takes place resulting in the formation of little distillate gas containing acetic acid and water.
- Active distillation of wood takes place upto 350C till the process is exothermic producing liquid products (like acetic acid, methyl alcohol, pyroligneous acid, tar etc.) and gaseous products containing Carbon monoxide, carbon dioxide, nitrogen, hydrogen, hydrocarbons etc.
- From 350 to 600C, slow evolution of residual volatile matters (i.e. gases) from the wood/charcoal left in 3rd stage.
Products in wood carbonization
Charcoal is the solid product left after the carbonization of wood. Hot gases are cooled to separate wood gas and liquid into two layers. Upper layer of the liquid is prodigious acid and the lower level is wood tar. Pyroligneous acid is an aqueous solution of acetone, methyl alcohol, and acetone and wood spirit mainly. Wood tar can be fractionated to separate many chemicals. Besides it is used as a supplementary plant fuel. Normally matured dense wood gives dense charcoal on carbonization.
Typical product yields in wood carbonization
Product Yield % air dried
Charcoal 30
Pyrolignious acid 38
- Acetic acid 8
- Wood spirit 15
- Water 15
Wood tar 10
Wood gas 22
Scheme of wood carbonization
Carbonization of wood is done in open pit (primitive method, now obsolete), kilns or metal retorts. Pits and kiln are located in forests and retorts in factories.
In open pit carbonization wood is burned in large heaps with restricted air. Yield of charcoal is 20%, which is of inferior quality. Besides, gas and liquid by-products are lost to the atmosphere, as they cannot be recovered. Even the charcoal that we get from domestic wood burning ovens also comes in this category.
In charcoal kiln also, charcoal (of better yield and quality) is the only product as gases and liquid by-products are not recovered. Kiln is parabolic in shape having typical dimension, radius=3 meters, height=2.5 meters and capacity=30m3 of stocked wood.
Wood is stacked on the ground with one verticals central passage acting s the chimney and a horizontal passage at the bottom for introducing fire to the center. The kiln is covered with thick layers of grass, leaves etc. and then plastered with a mixture of earth soil and charcoal dust. Initial firing is done with grass and twigs and then the wood is partly burned to supply heat for the process. Carbonization time is 7-10 days. After that fire is extinguished with water and the kiln is allowed to cool for a week are least before the charcoal is taken out.
Carbonization in metal retorts is done at a low temperature of 350C. Retorts may be of four types namely:
-Externally fired (heated) batch retorts
-Externally fire continuous vertical retorts
-Internally heated batch vertical r retorts
-Internally heated continuous vertical retorts.
Most recent design is internally heated retorts which use-forced recalculation of heated inert gases evolved during carbonization. Besides, it employs efficient mechanical handling of wood and charcoal and has high thermal efficiency.
Characteristics of products of low temperature carbonization of wood are:
- Charcoal yield is high (35%)
- Ash content of charcoal is low (below 2.5%)
- Volatile matter in charcoal is high (up to 15%); hence it can be easily ignited and burns at low rates.
- Heating value of charcoal is high (7500Kcal/kg)
- Charcoals produced have high vapor adsorption capacity.
High temperature carbonization of wood.
It is mainly carried out for the production of town gas and chemicals besides for charcoal. Carbonization temperature is 1000-1200C. Besides, town gas (which can be used for heating of domestic ovens) the valuable liquid chemicals like creosote (used as a wood preservative), turpentine, light & heavy oils are produced. Product characteristics are:
- Charcoal yield= 25%
- Heating value of charcoal = 8000 kcal/kg
- Gas yield=850 Nm3 gas/ton dry wood
- Gross heating value of gas = 3000kcal/Nm3
- Composition of gas: CO2 =13% CmHn (unsaturated hydrocarbons) =2%
CO=24%, CH4=15%, N2 =1%, H2=45%.
Uses of charcoal
- Because of its large specific surface area (150-450 m2 /gm) and light and porous nature, it is used for removal of obnoxious and coloring materials from solutions, gases, vapors, petroleum products etc. By adsorption on its surface.
- It can be used as a feedstock for gasification to make producer gas, which is used for domestic and industrial heating. During Second World War, this producer gas was used as a fuel in road vehicles in many countries.
- It is used as a clean and smooth burning fuel in domestic heating ovens but it is a costly fuel.
- Previously it was being used for metallurgical furnaces but now it has been replaced by coke. In blast furnace using charcoal instead of coke, the charcoal consumption can be upto 1-ton charcoal/ton pig iron for capacity of the blast furnaces of,000 tons pig iron per year.
- It is used very widely as fuel for blacksmith’s and metalworker forge furnaces/ovens.
- It is raw material for the manufacture of carbon disulphide.
- It is mainly used as a domestic fuel in developing countries.
Composition of charcoal.
A typical composition of charcoal is given below:
C=80% O2&N2=15%,H2=2% and Ash =3%
Merits of charcoal as a fuel
- It has a very high specific surface area compared to coal (20-200m2/gm coal)
- Its ash content is very low (below 3%)
- Its calorific value is high (6500-8000 kcal/kg).
Demerits of charcoal as a fuel
Its mechanical strength is very poor, hence it gets crushed to powder in operation, which is easily swept away in a current of gases, and also it may prevent the proper flow of gases in the furnace.