Sugarcane is one of the most promising agricultural sources of biomass energy in the world. It is the most appropriate agricultural energy crop in most sugarcane producing countries due to its resistance to cyclonic winds, drought, pests and diseases, and its geographically widespread cultivation. Due to its high energy-to-volume ratio, it is considered one of nature’s most effective storage devices for solar energy and the most economically significant energy crop.
The climatic and physiological factors that limit its cultivation to tropical and sub-tropical regions have resulted in its concentration in developing countries, and this, in turn, gives these countries a particular role in the world’s transition to sustainable use of natural resources.
According to the International Sugar Organization (ISO), Sugarcane is a highly efficient converter of solar energy, and has the highest energy-to-volume ratio among energy crops. Indeed, it gives the highest annual yield of biomass of all species. Roughly, 1 ton of Sugarcane biomass-based on Bagasse, foliage and ethanol output – has an energy content equivalent to one barrel of crude oil.
Sugarcane produces mainly two types of biomass, Cane Trash and Bagasse. Cane Trash is the field residue remaining after harvesting the Cane stalk and Bagasse is the milling by-product which remains after extracting sugar from the stalk. The potential energy value of these residues has traditionally been ignored by policy-makers and masses in developing countries. However, with rising fossil fuel prices and dwindling firewood supplies, this material is increasingly viewed as a valuable renewable energy resource.
Sugar mills have been using Bagasse to generate steam and electricity for internal plant requirements while Cane Trash remains underutilized to a great extent. Cane Trash and Bagasse are produced during the harvesting and milling process of Sugarcane which normally lasts 6 to 7 months.
Around the world, a portion of the Cane Trash is collected for sale to feed mills, while freshly cut green tops are sometimes collected for farm animals. In most cases, however, the residues are burned or left in the fields to decompose. Cane Trash, consisting of Sugarcane tops and leaves can potentially be converted into around 1kWh/kg, but is mostly burned in the field due to its bulkiness and its related high cost for collection and transportation.
On the other hand, Bagasse has been traditionally used as a fuel in the Sugar mill itself, to produce steam for the process and electricity for its own use. In general, for every ton of Sugarcane processed in the mill, around 190 kg Bagasse is produced.
Low pressure boilers and low efficiency steam turbines are commonly used in developing countries. It would be a good business proposition to upgrade the present cogeneration systems to highly efficient, high pressure systems with higher capacities to ensure utilization of surplus Bagasse.
Being an agricultural economy, biomass energy potential in Pakistan is highly promising. Pakistan is experiencing a severe energy crisis these days which is resulting in adverse long term economic and social problems. The electricity and gas shortages have directly impacted the common man, industry and commercial activities.
The high cost of energy mix is the main underlying reason behind the power crisis. The main fuel for the local power industry is natural gas however due to the continued depletion of this source and demands elsewhere the power generation companies are now dependent on furnace oil which is relatively expensive.
The way out of this crisis is to look for fuel sources which are cheap and abundantly available within the country. This description and requirement is fulfilled by biomass resources which have been largely ignored in the past and are also available in sufficient quantities to tackle the energy crisis prevailing in the country.
Biomass Energy in Pakistan
The potential to produce power from biomass resources is very promising in Pakistan. Being an agrarian economy, more than 60% of the population is involved in agricultural activities in the country. As per World Bank statistics, around 26,280,000 hectares of land is under cultivation in Pakistan. The major sources of biomass energy are crop residues, animal manure and municipal solid wastes
Wheat straw, rice husk, rice straw, cane trash, bagasse, cotton sticks are some of the major crop residues in Pakistan. Sugar cane is a major crop in the country and grown on a wide scale throughout Pakistan. During 2010-2011, the area under sugarcane cultivation was 1,029,000 hectares which is 4% of the total cropped area.
Sugarcane trash which constitutes 10% of the sugar cane is currently burned in the fields. During the year 2010-11, around 63,920,000 metric tons of sugarcane was grown in Pakistan which resulted in trash generation of around 5,752,800 metric tons. As per conservation estimates, the bioenergy potential of cane trash is around 9,475 GWh per year.
Cotton is another major cash crop in Pakistan and is the main source of raw material to the local textile industry. Cotton is grown on around 11% of the total cropped area in the country. The major residue from cotton crop is cotton sticks which is he material left after cotton picking and constitute as much as 3 times of the cotton produced.
Majority of the cotton sticks are used as domestic fuel in rural areas so only one-fourth of the total may be considered as biomass energy resource. The production of cotton sticks during 2010-2011 was approximately 1,474,693 metric tons which is equivalent to power generation potential of around 3,071 GWh.
Cotton sticks constitute as much as 3 times of the cotton produced.
Pakistan is the world’s fourth largest producer of milk. The cattle and dairy population is around 67,294,000 while the animal manure generation is estimated at 368,434,650 metric tons. Biogas generation from animal manure is a very good proposition for Pakistan as the country has the potential to produce electrical energy equivalent to 23,654 GWh
Municipal Solid Waste
The generation or solid wastes in 9 major urban centers is around 7.12 million tons per annum which is increasing by 2.5% per year due to rapid increase in population and high rate of industrialization. The average calorific value of MSW in Pakistan is 6.89 MJ/kg which implies power generation potential of around 13,900 GWh per annum.
Sugarcane trash (or cane trash) is an excellent biomass resource in sugar-producing countries worldwide. The amount of cane trash produced depends on the plant variety, age of the crop at harvest and soil and weather conditions. Typically it represents about 15% of the total above ground biomass at harvest which is equivalent to about 10-15 tons per hectare of dry matter. During the harvesting operation around 70-80% of the cane trash is left in the field with 20-30% taken to the mill together with the sugarcane stalks as extraneous matter.
Cane trash’s calorific value is similar to that of bagasse but has an advantage of having lower moisture content, and hence dries more quickly. Nowadays only a small quantity of this biomass is used as fuel, mixed with bagasse or by itself, at the sugar mill. The rest is burned in the vicinity of the dry cleaning installation, creating a pollution problem in sugar-producing nations.
Cane trash and bagasse are produced during the harvesting and milling process of sugarcane which normally lasts between 6 to 7 months. Cane trash can potentially be converted into heat and electrical energy. However, most of the trash is burned in the field due to its bulky nature and high cost incurred in collection and transportation.
Cane trash could be used as an off-season fuel for year-round power generation at sugar mills. There is also a high demand for biomass as a boiler fuel during the sugar-milling season. Sugarcane trash can also converted in biomass pellets and used in dedicated biomass power stations or co-fired with coal in power plants and cement kilns.
Burning of cane trash creates pollution in sugar-producing countries
Currently, a significant percentage of energy used for boilers in sugarcane processing is provided by imported bunker oil. Overall, the economic, environmental, and social implications of utilizing cane trash in the final crop year as a substitute for bunker oil appears promising. It represents an opportunity for developing biomass energy use in the Sugarcane industry as well as for industries / communities in the vicinity.
Positive socio-economic impacts include the provision of large-scale rural employment and the minimization of oil imports. It can also develop the expertise necessary to create a reliable biomass supply for year-round power generation.
Recovery of Cane Trash
Recovery of cane trash implies a change from traditional harvesting methods; which normally consists of destroying the trash by setting huge areas of sugarcane fields ablaze prior to the harvest. There are a number of major technical and economic issues that need to be overcome to utilize cane trash as a renewable energy resource. For example, its recovery from the field and transportation to the mill, are major issues.
Alternatives include the current situation where the cane is separated from the trash by the harvester and the two are transported to the mill separately, to the harvesting of the whole crop with separation of the cane and the trash carried out at the mill. Where the trash is collected from the field it maybe baled incurring a range of costs associated with bale handling, transportation and storage. Baling also leaves about 10-20% (1-2 tons per hectare) of the recoverable trash in the field.
A second alternative is for the cane trash to be shredded and collected separately from the cane during the harvesting process. The development of such a harvester-mounted cane trash shredder and collection system has been achieved but the economics of this approach require evaluation. A third alternative is to harvest the sugarcane crop completely which would require an adequate collection, transport and storage system in addition to a mill based cleaning plant to separate the cane from the trash .
A widespread method for cane trash recovery is to cut the cane, chop into pieces and then it is blown in two stages in the harvester to remove the trash. The amount of trash that goes along with the cane is a function of the cleaning efficiency of the harvester. The blowers are adjusted to get adequate cleaning with a bearable cane loss.
On the average 68 % of the trash is blown out of the harvester, and stays on the ground, and 32 % is taken to the mill together with the cane as extraneous matter. The technique used to recover the trash staying on the ground is baling. Several baling machines have been tested with small, large, round and square bales. Cane trash can be considered as a viable fuel supplementary to bagasse to permit year-round power generation in sugar mills.
Thus, recovery of cane trash in developing nations of Asia, Africa and Latin America implies a change from traditional harvesting methods, which normally consists of destroying the trash by setting huge areas of cane fields ablaze prior to the harvest. To recover the trash, a new so-called “green mechanical harvesting” scheme will have to be introduced. By recovering the trash in this manner, the production of local air pollutants, as well as greenhouse gases contributing to adverse climatic change, from the fires are avoided and cane trash could be used as a means of regional sustainable development.
Cane Trash Recovery in Cuba
The sugarcane harvesting system in Cuba is unique among cane-producing countries in two important respects. First, an estimated 70 % of the sugarcane crop is harvested by machine without prior burning, which is far higher than for any other country. The second unique feature of Cuban harvesting practice is the long-standing commercial use of “dry cleaning stations” to remove trash from the cane stalks before the stalks are transported to the crushing mills.
Cuba has over 900 cleaning stations to serve its 156 sugar mills. The cleaning stations are generally not adjacent to the mills, but are connected to mills by a low-cost cane delivery system – a dedicated rail network with more than 7000 km of track. The cleaning stations take in green machine-cut or manually cut cane. Trash is removed from the stalk and blown out into a storage area. The stalks travel along a conveyor to waiting rail cars. The predominant practice today is to incinerate the trash at the cleaning station to reduce the “waste” volume.
Sugarcane is one of the most promising agricultural sources of biomass energy in the world. Sugarcane produces mainly two types of biomass – sugarcane trash and bagasse. Sugarcane trash is the field residue remaining after harvesting the sugarcane stalk while bagasse is the fibrous residue left over after milling of the sugarcane, with 45-50% moisture content and consisting of a mixture of hard fibre, with soft and smooth parenchymatous (pith) tissue with high hygroscopic property.
Bagasse contains mainly cellulose, hemicellulose, pentosans, lignin, sugars, wax, and minerals. The quantity obtained varies from 22 to 36% on sugarcane and is mainly due to the fibre portion in the sugarcane and the cleanliness of sugarcane supplied, which, in turn, depends on harvesting practices.
The composition of bagasse depends on the variety and maturity of sugarcane as well as harvesting methods applied and efficiency of the sugar processing. Bagasse is usually combusted in furnaces to produce steam for power generation. Bagasse is also emerging as an attractive feedstock for bioethanol production.
It is also utilized as the raw material for production of paper and as feedstock for cattle. The value of Bagasse as a fuel depends largely on its calorific value, which in turn is affected by its composition, especially with respect to its water content and to the calorific value of the sugarcane crop, which depends mainly on its sucrose content.
Moisture contents is the main determinant of calorific value i.e. the lower the moisture content, the higher the calorific value. A good milling process will result in low moisture of 45% whereas 52% moisture would indicate poor milling efficiency. Most mills produce Bagasse of 48% moisture content, and most boilers are designed to burn Bagasse at around 50% moisture.
Bagasse also contains approximately equal proportion of fibre (cellulose), the components of which are carbon, hydrogen and oxygen, some sucrose (1-2 %), and ash originating from extraneous matter. Extraneous matter content is higher with mechanical harvesting and subsequently results in lower calorific value.
For every 100 tons of Sugarcane crushed, a Sugar factory produces nearly 30 tons of wet Bagasse. Bagasse is often used as a primary fuel source for Sugar mills; when burned in quantity, it produces sufficient heat and electrical energy to supply all the needs of a typical Sugar mill, with energy to spare. The resulting CO2 emissions are equal to the amount of CO2 that the Sugarcane plant absorbed from the atmosphere during its growing phase, which makes the process of cogeneration greenhouse gas-neutral.
35MW Bagasse and Coal CHP Plant in Mauritius
Cogeneration of bagasse is one of the most attractive and successful biomass energy projects that have already been demonstrated in many sugarcane producing countries such as Mauritius, Reunion Island, India and Brazil. Combined heat and power from sugarcane in the form of power generation offers renewable energy options that promote sustainable development, take advantage of domestic resources, increase profitability and competitiveness in the industry, and cost-effectively address climate mitigation and other environmental goals.
The Philippines is mainly an agricultural country with a land area of 30 million hectares, 47 percent of which is agricultural. The total area devoted to agricultural crops is 13 million hectares distributed among food grains, food crops and non-food crops. Among the crops grown, rice, coconut and sugarcane are major contributors to biomass energy resources.
The most common agricultural wastes in the Philippines are rice husk, rice straw, coconut husk, coconut shell and bagasse. The country has good potential for biomass power plants as one-third of the country’s agricultural land produces rice, and consequently large volumes of rice straw and hulls are generated.
Rice is the staple food in the Philippines. The Filipinos are among the world’s biggest rice consumers. The average Filipino consumes about 100 kilograms per year of rice. Though rice is produced throughout the country, the Central Luzon and Cagayan Valley are the major rice growing regions. With more than 1.2 million hectares of rain-fed rice-producing areas, the country produced around 19 million tons of rice in 2019.
The estimated production of rice hull in the Philippines is more than 2 million tons per annum which is equivalent to approximately 5 million BOE (barrels of oil equivalent) in terms of energy. Rice straw is another important biomass resource with potential availability exceeding 5 million tons per year across the country.
With the passing of Biofuels Act of 2006, the sugar industry in the Philippines which is the major source of ethanol and domestic sugar will become a major thriving industry. Around 380,000 hectares of land is devoted to sugarcane cultivation. It is estimated that 1.17 million tonnes of sugarcane trash is recoverable as a biomass resource in the Philippines.
In addition, 6.4 million tonnes of surplus bagasse is available from sugar mills. There are 29 operating sugar mills in the country with an average capacity of 6,900 tonnes of cane per day. Majority is located in Negros Island which provides about 46% of the country’s annual sugar production.
The Philippines has the largest number of coconut trees in the world as it produces most of the world market for coconut oil and copra meal. The major coconut wastes include coconut shell, coconut husks and coconut coir dust. Coconut shell is the most widely utilized but the reported utilization rate is very low. Approximately 500 million coconut trees in the Philippines produce tremendous amounts of biomass as husk (4.1 million tonnes), shell (1.8 million tonnes), and frond (4.5 million tonnes annually).
Maize is a major crop in the Philippines that generates large amounts of agricultural residues. It is estimated that 4 million tonnes of grain maize and 0.96 million tonnes of maize cobs produced yearly in the Philippines. Maize cob burning is the main energy application of the crop, and is widely practiced by small farmers to supplement fuelwood for cooking.
Sugar industry has always occupied a prominent position in the Mauritian economy since the introduction of sugarcane around three centuries ago. Mauritius has been a world pioneer in establishing sales of bagasse-based energy to the public grid, and is currently viewed as a model for other sugarcane producing countries, especially the developing ones.
Sugar factories in Mauritius produce about 600,000 tons of sugar from around 5.8 million tons of sugarcane which is cultivated on an agricultural area of about 72,000 hectares. Of the total sugarcane production, around 35 percent is contributed by nearly 30,000 small growers. There are more than 11 sugar factories presently operating in Mauritius having crushing capacities ranging from 75 to 310 tons cane per hour.
During the sugar extraction process, about 1.8 million tons of Bagasse is produced as a by-product, or about one third of the sugarcane weight. Traditionally, 50 percent of the dry matter is harvested as cane stalk to recover the sugar with the fibrous fraction, i.e. Bagasse being burned to power the process in cogeneration plant. Most factories in Mauritius have been upgraded and now export electricity to the grid during crop season, with some using coal to extend production during the intercrop season.
Surplus electricity is generated in almost all the sugar mills. The total installed capacity within the sugar industry is 243 MW out of which 140 MW is from firm power producers. Around 1.6 – 1.8 million tons of bagasse (wet basis) is generated on an annually renewable basis and an average of around 60 kWh per ton sugarcane is generated for the grid throughout the island.
The surplus exportable electricity in Mauritian power plants has been based on a fibre content ranging from 13- 16% of sugarcane, 48% moisture content in Bagasse, process steam consumption of 350–450 kg steam per ton sugarcane and a power consumption of 27-32 kWh per ton sugarcane.
In Mauritius, the sugarcane industry is gradually increasing its competitiveness in electricity generation. It has revamped its boiler houses by installing high pressure boilers and condensing extraction steam turbine. All the power plants are privately owned, and the programme has been a landmark to show how all the stakeholders (government, corporate and small planters) can co-operate. The approach is being recommended to other sugarcane producing countries worldwide to harness the untapped renewable energy potential of biomass wastes from the sugar industry.
Global demand for fuel efficiency, environmental quality and energy security have elicited global attention towards liquid biofuels, such as bioethanol and biodiesel. Around the world, governments have introduced various policy measurements, mandatory fuel blending programmes, incentives for flex-fuel vehicles and agricultural subsidies for the farmers. In India, the government launched Ethanol Blended Petrol (EBP) programme in January 2013 for 5% ethanol blended petrol. The policy had significant focus on India’s opportunity to agricultural and industrial sectors with motive of boosting biofuel (bioethanol and biodiesel) usage and reducing the existing dependency on fossil fuel.
The Government of India initiated significant investments in improving storage and blending infrastructure. The National Policy on Biofuels has set a target of 20% blending of biofuel by 2017. However, India has managed to achieve only 5% by September 2016 due to certain technical, market and regulatory hurdles.
In India, sugarcane molasses is the major resource for bioethanol production and inconsistency of raw material supply holds the major liability for sluggish response to blending targets. Technically speaking, blend wall and transportation-storage are the major challenges towards the biofuel targets. Blending wall is the maximum percent of ethanol that can be blended to fuel without decreasing the fuel efficiency.
Various vehicles are adaptable to various blending ratio based on the flexibility of engines. The technology for the engine modification for flex fuel is not new but making the engines available in India along with the supply chain and calibrating the engine for Indian conditions is the halting phase. The commonly used motor vehicles in the country are not effectual with flex fuel.
Sugarcane molasses is the most common feedstock for bioethanol production in India
Ethanol being a highly flammable liquid marks obligatory safety and risk assessment measures during all phases of production, storage and transportation. The non-uniform distribution of raw material throughout the country, demands a compulsory transportation and storage, especially inter-state movement, encountering diverse climatic and topographic conditions.
Major ethanol consumers in India are potable liquor sector (45%), alcohol based chemical industry (40%), the rest for blending and other purposes. The yearly profit elevation in major sectors is a dare to an economical ethanol supply for Ethanol Blending Programme. Drastic fluctuation in pricing of sugar cane farming and sugar milling resulted to huge debt to farmers by mill owners. Gradually the farmers shifted from sugarcane cultivation other crops.
Regulatory and policy approaches on excise duty on storage and transportation of ethanol and pricing strategy of ethanol compared to crude oil are to be revised and implemented effectively. Diversifying the feedstocks (especially use of lignocellulosic biomass) and advanced technology for domestic ethanol production in blending sectors are to be fetched out from research laboratories to commercial scale. Above all the knowledge of economic and environmental benefits of biofuel like reduction in pollutants and import bills and more R&D into drop-in biofuels, need to be amplified for the common man.
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