GreenFlip

Guest Post by: Pankaj Lal, University of Florida

Bioenergy production has increased significantly in the last decade, and recent legislative efforts in U.S. such as the discussion draft for the American Clean Energy and Security Act of 2009 and the Energy Independence and Security Act of 2007 are expected to encourage even more growth. In the quest for energy sources to meet higher energy demand, the policy push for renewable energy, including woody biomass, is gaining momentum. Several other factors are also catapulting woody biomass use for energy. These include growing concerns about energy security and dependence on foreign oil, uncertainty associated with costs for fossil fuels such as petroleum, the possibility to improve forest health and reduce wildfire risk, and the potential to provide socio-economic benefits in the form of additional income from forestlands and new jobs.

Historically, woody biomass used for energy was comprised of waste from the production of lumber, pulp and paper, and other wood products. However, if bioenergy markets become competitive, use of woody biomass from logging residues, stands damaged by natural disturbances such as wildfire, pest outbreaks, storms, small diameter trees from thinning, plantations and other forests, and energy crops such as eucalyptus and poplar is quite possible. Biofuels from woody biomass, commonly called cellulosic or second generation fuels are shown to have advantages over starch-based fuels (corn ethanol for example) by avoiding the food versus fuel debate, reducing greenhouse gas (GHG) emissions, and yielding greater energy input-output ratio. However, several complex issues are influencing the development of these markets in economically efficient and environmentally benign ways. Some of the key issues that stand out are: biomass availability or supply; technology and market competitiveness; monetizing environmental benefits; soil, water and biodiversity impacts and  the uncertainty regarding interplay of carbon markets and  forest bioenergy.

Large variance in biomass supply estimates makes informed policy making difficult.  The available wood biomass supply information is, perhaps, essential to policymakers who establish renewable energy goals and formulate subsidies, credits, trade tariffs, and other interventions to realize those goals. On the bioenergy technology front, there is no emergent favorite technology.  Several technologies exist for converting wood biomass to liquid fuels, biopower, and bioproducts. While all technologies are proven to be possible, most of them are not yet economically competitive. Even for supposedly low hanging fruit in the country such as cofiring, there are significant challenges such as ash deposition, corrosion, and feedstock selection. Pubic research dollars are exploring all these technologies further in hopes of commercial success.

Another challenge seems to be the method of green accounting or integrated accounting, wherein social and environmental benefits accruing from woody bioenergy can be incorporated for unit cost analysis. This suggestion is consistent with findings that the public is willing to pay a premium for bioenergy to realize environmental benefits. This accounting approach can help in monetizing the benefits gained through GHG reduction. However, convincing general populace about non-market benefits and accounting still requires concerted efforts.

It is also imperative required that what woody biomass based energy should be sustainable. Bioenergy sustainability concerns regarding soil and water quality, biodiversity etc. range stand true for the whole supply chain — feedstock production, harvesting, transport, conversion, distribution, consumption, waste disposal– as well as those regarding job creation and societal benefit distribution. Several organizations at state (Forestry Departments for example), national (Environmental Protection Agency), and international (Global Bio-Energy Partnership and Roundtable on Sustainable Biofuels) are trying to develop guidelines and/or standards to ensure the environmental, economic, and social sustainability of bioenergy markets.

 Another factor that influences the bioenergy-GHG emission relationship is the impact of payment for carbon offsets as an incentive for GHG reduction. Carbon offsets are project-based initiatives involving specific activities to reduce, avoid or sequester GHG emissions and are tradable in carbon markets. With a carbon market proposed in future as per provisions of Waxman Markey Bill, it is hypothesized that forest owners can gain carbon credits through ‘additional’ carbon sequestered on their lands. However its viability as project offsets, whereby, needs to be assessed relative to other carbon offset options such as tillage change in agriculture, improving efficiency of power plants, clean coal technologies, timely and important.

It is fair to say that wood based energy markets, if steered appropriately, offer a promise to ensure energy security, promote environmental quality, and realize social benefits. However, several complex issues are influencing the development of these markets. Solutions to these issues would result in winners and losers. Therefore, not surprisingly, stakeholders are increasingly participating and debating these issues.  However, it is imperative that each side should respect the positions and arguments of the other and strive to move forward collectively.  A sustained dialogue through meaningful partnerships amongst biomass suppliers, biomass users, and representatives of civil society is critical to realize woody bioenergy market potentials. 

Bamboo charcoal and active carbon are new products developed in recent years. Bamboo being of special microstructure possesses extreme absorbing and other special capacities after carbonization. Their uses in the areas of new technology are of importance. 

 Variety of Bamboo Charcoal: There are many kinds of bamboo charcoal. In line with their origin, bamboo charcoal can be divided into two parts: raw bamboo charcoal and charcoal stick of chips. Raw bamboo charcoal is made of small sized bamboo, old bamboo, and bamboo tops, roots, which are not fit for making other bamboo products. Charcoal stick of chips is made of residue from bamboo processing industries. In the process of making different kinds of industrialized products, there will be residue, which should be broken in chips, dried, and pressed into sticks before carbonization.

 Charcoals are of different shapes: cylinders, pieces, chips and powder. In line with the temperature of carbonization charcoals can be divided into three groups: charcoal of low, medium and high temperature. Physical and mechanical properties of charcoal differ due to different temperature of carbonization. Charcoal for regulating humidity is made at temperature of 600 degrees Celsius, that for absorbing is at 700 – 800 degrees Celsius, and for higher electric conductivity is higher than 1000 degrees Celsius. According to their uses charcoal is defined as fuel, water purifier, for cooking, for improving soil, for regulating room humidity, for preservation of vegetables, fruits and flowers, for deodorizing, for conducting electricity etc.

Process of making bamboo charcoal

Bamboo is an organic matter with high polymer content, composed of cells of different shapes and properties. The process of making bamboo charcoal is the process of heating and resolution, which can be divided into four stages according to the change in temperature, show in the adjoining table.

Methods of Charcoal making: There are two different methods of charcoal making: dry distillation (pyrogenic decomposition), and direct kiln burning.

 The main equipment for pyrogenic decomposition is a cauldron for distillation. Bamboo material should be pre-dried to decrease the water content to +/- 20% before loading into the cauldron for pyrogenic decomposition. The mixed steam gas is to be processed in jar-separator and in condenser for retrieving bamboo vinegar liquid and bamboo tar. In this process, the oxidation of bamboo material is lower, and the rate of production is higher.

In the process of direct kiln burning, the heat resulting from fuel burning curls up to the top of the kiln and spreads in the kiln. Most of the heat moves about in the upper part of the kiln, the rest of it radiates on all sides, step by step goes down to dry and pre-carbonize the bamboo material. In the process of carbonization, a small part of bamboo material is being oxidized and burnt, raising the temperature in the kiln and removing volatile matter. The smoke and steam moves in circles, and regulating the temperature in the kiln. Thus the canonization and refining process is complete producing bamboo charcoal fine and close in texture. In this process the bamboo material undergoes stages of pre-drying, drying, pre-carbonizing, carbonizing, refining and natural cooling. The temperature differs in different stages. The temperature of refining stage influences the density and electric conductivity of charcoal greatly. The rate of production through this method is low and the quality of charcoal is not stable.

Utility

1. Bamboo Charcoal: Bamboo charcoal is used as water purifier (drinking water, sewage and industrial water treatment), air purifier, medical applications, deodorizing agent, soil improvement, etc

Bamboo Active Carbon: Bamboo active carbon can be used for water and gas treatment, refining coarse sugar, refining wines and edible oils, pharmaceuticals and cosmetic applications, filters in atomic reactors, improving soil through nitrogen fixation, as electrodes in microelectronic technology, etc.

Charcoal is next only to firewood in terms of meeting the energy needs of rural communities. The decreasing availability of wood and the greater need for its sustainable use necessitate the use of alternative sources of energy. Bamboo charcoal is one such source. It has a high calorific value and can be produced using simple equipment that can be made locally. Honeycomb briquettes extruded using powdered bamboo charcoal (calorific value of 26-29 MJ/kg) and the producer gas generated during char production (average calorific value 4,520 kJ/nm3) is both good sources of energy. In one hour, a thermal gassifier can produce 100 kg of charcoal from 400 kg or bamboo. Therefore, in 24 hours, 2.5 tons of charcoal can be produced from about 10 tons of bamboo. This translates into an annual production of 625 tons of charcoal using 2,500 tons of bamboo, assuming 250 days of operation. A supply chain set up to service this scale of production would financially benefit a large number of producers, while reducing deforestation and increasing energy security.

The Biomass Feedstock Development Program at Oak Ridge National Laboratory (ORNL) recently released a publication entitled Bamboo: An Overlooked Biomass Resource? Bamboo is the common term for a group of woody grasses comprised of 1250 species. It is relatively fast growing and attains maturity within five years. The shortest species stands only four inches (10 cm) at maturity while the tallest reach 130 feet (40 m) with stem (culm) diameters of 12 inches (30 cm).

Most bamboo species grow in the tropics; however, some varieties occur naturally in subtropical and temperate zones of all continents except Europe. The growing zone ranges from latitudes 46 °N to 47 °S and from sea level to over 13,000 feet (4,000 m) in elevation. Asia alone has over 1000 species, most of it in natural stands. Current major bamboo-producing-and-using countries include China, India, Bangladesh, Indonesia, and Thailand.

Approximately 1,500 commercial applications of bamboo have been identified. These applications may be divided into the following broad categories:

• Construction and reinforcing fibers—agricultural and fishing tools, handicrafts, musical instruments, furniture, civil engineering (bridges, scaffolding), and buildings (house frames, walls, window frames, roofs, interior dividers).

• Paper, textiles, and boards—this also includes rayon, plywood, oriented strand board, and laminated flooring.

• Food—bamboo shoots are widely used in Chinese and other Asian cuisine.

• Bioenergy feedstocks—no references were found in the literature concerning the use of bamboo as an energy feedstock.

A mature planting of bamboo forms a dense stand with little light penetration. Bamboo is semi-deciduous, with leaves shed at the end of the growing season or for species on a two-year cycle, during the following growing season. Plants that have a biennial pattern of leaf emergence typically also exhibit strong shoot production in the year when leaves are not shed.

One of the more interesting aspects about bamboo is its rapid growth. The plant will send out rhizomes (underground horizontal plant stems) tens of meters in all directions that are 12 to 20 inches (30 to 50 cm) beneath the surface. Shoot buds appear on the sides of these rhizomes, and with the onset of warm spring weather, the buds lengthen and form a compact upright shoot that penetrates the ground’s surface. The plant now concentrates on growing the culm, without branches, as fast as possible. Tall species of bamboo have been observed to grow as much as 20 inches (0.5 m) per week. After the shoot reaches the same height as other culms, leafy branches appear near the top of the culm. Growth over the following years consists of thickening the walls of the culm and increasing the wood density.

Another interesting phenomenon about bamboo is its flowering patterns. A few species are known to flower frequently, even annually, and a few species flower a few culms at a time.

However, for the majority of bamboo species, the entire clump at a location will produce flowers and then die back over the next two to three years. For most of the latter species, flowering happens every 30 to 40 years although for some species the period is over 60 years. This infrequency of flowering makes bamboo hard to study and partially accounts for the lack of knowledge about bamboo.

Since bamboo is propagated vegetatively by planting rhizomes, it may not be known where the plant is in its flowering cycle. This uncertainty of when flowering and die-back may occur has long been a concern with bamboo growers. However, the ORNL report states that “…the threat of catastrophic flowering need not pose an economic problem for bamboo growers, as long as uneven-aged propagation material is maintained, and entire stands are replaced before they approach flowering age.”

For fuel analysis, nine bamboo samples representing three different species at three different ages were collected. The publication lists the proximate, ultimate, and elemental analyses for these nine samples. The typical moisture content for freshly field-harvested bamboo is approximately 15 percent. The ash content of all samples was one percent or less, with no correlation between ash content and bamboo sample or age of sample apparent. This ash content is similar to other woody biomass materials.

Volatiles in the samples ranged from 63 to 75 percent with the balance fixed carbon and, again, no correlation between volatiles and bamboo sample or sample age was determined. Heating values were comparable to wood at 16 million to 16.5 million Btu/ton (19.09 to 19.57 GJ/t) on a dry basis.

Three bamboo characteristics—low nitrogen content, low chlorine content, and low alkali indices—are particularly significant for combustion of bamboo. Alkali indices (defined as pounds of alkali oxide per million Btu of energy content) range from 0.23 to 0.7 (0.1 to 0.3 kg/GJ), generally below the limit of 0.4 to 0.8 lb/MMBtu (0.17 to 0.34 kg/GJ) known to cause adverse fouling and slagging in combustion systems. The presence of chlorine has been shown to increase the volatility of alkali metals during combustion. However, the low chlorine values present in bamboo samples suggest that the potassium that is present is unlikely to be volatile and therefore not a problem.

Bamboo must be grown vegetatively and 1-2 year old rhizome cuttings of 12 to 20 inches (30 to 50 cm) in length with nodes and buds present are sometimes used. Younger rhizomes provide the best results. Propagation with rhizome cuttings with at least a foot of culm attached also gave better results. Typically up to eight years are required to achieve a good stand and the final stand height may not be reached until 15-20 years have elapsed.

Harvesting of traditionally grown bamboo is un-mechanized and labor intensive, especially if only selected culms are to be harvested. Research in India suggests that clear-cutting does not significantly damage bamboo stands, so it may be possible to use machinery such as modified sugar-cane harvesters. The Western and Southeastern Regional Biomass Energy Programs sponsored bamboo harvesting tests in Alabama in the late 1990’s using a flail-cutter-head harvester developed at Texas A&M Kingsville and obtained acceptable harvesting results for bamboo approximately 30 feet tall.

Bamboo has frequently been characterized as having a high productivity; however, the ORNL study did not substantiate this characterization. Values for productivity in the literature range from 1 ton/acre/year (2.2 t/ha/year) in Northern India to 7 tons/acre/year (15.5 t/ha/year) in Central Japan. Data from the United States is very limited. Data from stands in South Alabama that were aged 14 to 20 years averaged 2.7 to 3.9 tons/acre/year (6.1 to 8.6 t/ha/year). These figures exclude branches and leaves, which accounted for 14 percent of the above-ground biomass. The ORNL report speculates that based on figures available from overseas, as well as the limited trials conducted in the US, intensively managed bamboo stands with fertilization may be capable of producing over 4.5 tons/acre/year (10 t/ha/year) under Southeast US conditions.

For additional information, contact the American Bamboo Society, c/o Michael Bartholomew, 750 Krumkill Road, Albany, NY 12203-5976, http://www.bamboo.org/abs/index.shtml.