Malaysia is gifted with conventional energy resources such as oil and gas as well as renewables like hydro, biomass and solar energy. As far as biomass resources in Malaysia are concerned, Malaysia has tremendous agricultural biomass and wood waste resources available for immediate exploitation. This energy potential of biomass resource is yet to be exploited properly in the country.
Taking into account the growing energy consumption and domestic energy supply constraints, Malaysia has set sustainable development and diversification of energy sources, as the economy’s main energy policy goals. The Five-Fuel Strategy recognises renewable energy resources as the economy’s fifth fuel after oil, coal, natural gas and hydro. Being a major agricultural commodity producer in the region Malaysia is well positioned amongst the ASEAN countries to promote the use of biomass as a source of renewable energy.
Major Biomass Resources in Malaysia
Agricultural crops e.g. sugarcane, cassava, corn
Agricultural residues e.g. rice straw, cassava rhizome, corncobs
Woody biomass e.g. fast-growing trees, wood waste from wood mill, sawdust
Malaysia is the world’s leading exporter of palm oil, exporting more than 19.9 million tonnes of palm oil in 2017. The extraction of palm oil from palm fruits results in a large quantity of waste in the form of palm kernel shells, empty fruit bunches and mesocarp fibres. In 2011, more than 80 million tons of oil palm biomass was generated across the country.
13MW biomass power plant at a palm oil mill in Sandakan, Sabah (Malaysia)
Processing crude palm oil generates a foul-smelling effluent, called Palm Oil Mill Effluent or POME, which when treated using anaerobic processes, releases biogas. Around 58 million tons of POME is produced in Malaysia annually, which has the potential to produce an estimated 15 billion m3 of biogas.
Rice Husk
Rice husk is another important agricultural biomass resource in Malaysia with very good energy potential for biomass cogeneration. An example of its attractive energy potential is biomass power plant in the state of Perlis which uses rice husk as the main source of fuel and generates 10 MW power to meet the requirements of 30,000 households.
Municipal Solid Wastes
The per capita generation of solid waste in Malaysia varies from 0.45 to 1.44kg/day depending on the economic status of an area. Malaysian solid wastes contain very high organic waste and consequently high moisture content and bulk density of above 200kg/m3. The high rate of population growth is the country has resulted in rapid increase in solid waste generation which is usually dumped in landfills.
Conclusion
Biomass resources have long been identified as sustainable source of renewable energy particularly in countries where there is abundant agricultural activities. Intensive use of biomass as renewable energy source in Malaysia could reduce dependency on fossil fuels and significant advantage lies in reduction of net carbon dioxide emissions to atmosphere leading to less greenhouse effect. However, increased competitiveness will require large-scale investment and advances in technologies for converting this biomass to energy efficiently and economically.
Wood processing industries primarily include sawmilling, plywood, wood panel, furniture, building component, flooring, particle board, moulding, jointing and craft industries. Biomass from wood processing industries is generally concentrated at the processing factories, e.g. plywood mills and sawmills. The amount of waste generated from wood processing industries varies from one type industry to another depending on the form of raw material and finished product.
Biomass from Wood Processing
The waste resulted from a wood processing is influenced by the diameter of logs being processed, type of saw, specification of product required and skill of workers. Generally, the waste from wood industries such as saw millings and plywood, veneer and others are sawdust, off-cuts, trims and shavings. Sometimes, it becomes a complex task to select the best scroll saws for wood cutting.
Sawdust arise from cutting, sizing, re-sawing, edging, while trims and shaving are the consequence of trimming and smoothing of wood. In general, processing of 1,000 kilos of wood in the furniture industries will lead to wood waste generation of almost half (45 %), i.e. 450 kilos of wood. Similarly, when processing 1,000 kilos of wood in sawmill, the waste will amount to more than half (52 %), i.e. 520 kilo of wood.
The biomass wastes generated from wood processing industries include sawdust, off-cuts and bark. Recycling of wood wastes is not done by all wood industries, particularly small to medium scale wood industries. The off-cuts and cutting are sold or being used as fuel for wood drying process. Bark and sawdust are usually burned.
Recycling of Wood Wastes
The use of wood wastes is usually practised in large and modern establishment; however, it is commonly only used to generate steam for process drying. The mechanical energy demand such as for cutting, sawing, shaving and pressing is mostly provided by diesel generating set and/or electricity grid. The electricity demand for such an industry is substantially high.
Recycling of wood wastes is not done by all wood industries, particularly by smallholders. These wastes are normally used as fuel for brick making and partly also for cooking. At medium or large establishments some of the wastes, like: dry sawdust and chips, are being used as fuel for wood drying process. Bark and waste sawdust are simply burned or dumped.
Importance of Heating Value
The heating or calorific value is a key factor when evaluating the applicability of a combustible material as a fuel. The heating value of wood and wood waste depends on the species, parts of the tree that are being used (core, bark, stem, wood, branch wood, etc.) and the moisture content of the wood. The upper limit of the heating or calorific value of 100% dry wood on a weight basis is relatively constant, around 20 MJ/kg.
In practice, the moisture content of wood during logging is about 50%. Depending on transportation and storing methods and conditions it may rise to 65% or fall to some 30% at the mill site. The moisture content of the wood waste in an industry depends on the stage where the waste is extracted and whether wood has been dried before this stage.
Biogas can be used in raw (without removal of CO2) or in upgraded form. The main function of upgrading biogas is the removal of CO2 (to increase the energy content) and H2S (to reduce risk of corrosion). After upgrading, biogas becomes biomethane and possesses identical gas quality properties as natural gas, and can thus be used as natural gas replacement. The main pathways for biomethane utilization are as follows:
Compressed natural gas (CNG) & diesel replacement – (bio-CNG for transport fuel usage)
Liquid natural gas (LNG) replacement – (bio-LNG for transport fuel usage)
Prior to practically all utilization options, the biogas has to be dried (usually through application of a cooling/condensation step). Furthermore, elements such as hydrogen sulphide and other harmful trace elements must be removed (usually trough application of an activated carbon filter) to prevent adverse effects on downstream processing equipment (such as compressors, piping, boilers and CHP systems).
Although biogas is perfectly suitable to be utilized in boilers (as an environmental friendlier source for heat and steam production), this option is rather obsolete due to the abundance of alternative sources from solid waste origin.
Most Palm Oil Mills are already self-reliant with respect to heat and steam production due to the combustion of their solid waste streams (such as EFB and PKS). Consequently, conversion to electricity (by means of a CHP unit) or utilization as natural gas, CNG or LNG replacement, would be a more sensible solution.
The biogas masterplan as drafted by the Asia Pacific Biogas Alliance foresees a distribution in which 30% of the biomethane is used for power generation, 40% for grid injection and 30% as compressed/liquefied fuel for transportation purpose (Asian Pacific Biogas Alliance, 2015).
For each project, the most optimal option has to be evaluated on a case to case basis. Main decision-making factors will be local energy prices and requirements, available infrastructure (for gas and electricity), incentives and funding.
For the locations where local demand is exceeded, and no electricity or gas infrastructure is available within a reasonable distance (<5-10 km, due to investment cost and power loss), production of CNG could offer a good solution.
Moreover, during the utilization of biogas within a CHP unit only 40-50% of the energetic content of the gas is converted into electricity. The rest of the energy is transformed into heat. For those locations where an abundance of heat is available, such as Palm Oil Mills, this effectively means that 50-60% of the energetic content of the biogas is not utilized. Converting the biogas into biomethane (of gas grid or CNG quality) through upgrading, would facilitate the transportation and commercialisation of over 95% of the energetic content of the biogas.
Within the CNG utilization route, the raw biogas will be upgraded to a methane content of >96%, compressed to 250 bar and stored in racks with gas bottles. The buffered gas (bottles) will be suitable for transportation by truck or ship. For transportation over large distances (>200km), it will be advised to further reduce the gas volume by converting the gas to LNG (trough liquefaction).
Overall the effects and benefits from anaerobic digestion of POME and utilization of biomethane can be summarized as follows:
Enhanced self-sufficiency trough availability of on-site diesel replacement (CNG)
Expansion of economic activities/generation of additional revenues
Sales of surplus electricity (local or to the grid)
Sales of biomethane (injection into the natural gas grid)
Replacement of on-site diesel usage by CNG
Sales of bottled CNG
Reducing global and local environmental impact (through fuel replacement)
Reducing dependence on fossil fuel, and enhances fuel diversity and security of energy supply
Enhancement of local infrastructure and employment
Through electrical and gas supply
Through Fuel (CNG) supply
Co-Authors: H. Dekker and E.H.M. Dirkse (DMT Environmental Technology)
Note:This is the second article in the special series on ‘Sustainable Utilization of POME-based Biomethane’ by Langerak et al of DMT Environmental Technology (Holland). The first article can be viewed at this link
The concept of biomass energy is still in its infancy in most parts of the world, but nevertheless, it does have an important role to play in terms of sustainability in general and net-zero buildings in particular. Once processed, biomass is a renewable source of energy that has amazing potential. But there is a lot of work to be done to exploit even a fraction of the possibilities that would play a significant role in providing our homes and commercial buildings with renewable energy.
According to the U.S. Energy Information Administration (EIA), only about 5% of the total primary energy usage in the U.S. comes from biomass fuels. So there really is a way to go.
The Concept of Biomass Energy
Generally regarded as any carbon-based material including plants, food waste, industrial waste, reclaimed woody materials, algae, and even human and animal waste, biomass is processed to produce effective organic fuels.
The main sources of biomass include wood mills and furniture factories, landfill sites, horticultural centers, wastewater treatment plants, and areas where invasive and alien tree and grass species grow.
Whether converted into biogas or liquid biofuels, or burned as is, the biomass releases its chemical energy in the form of heat. Of course, it depends on what kind of material the biomass is. For instance, solid types including wood and suitable garbage can be burned without any need for processing. This makes up more than half the biomass fuels used in the U.S. Other types can be converted into biodiesel and ethanol.
Generally:
Biogas forms naturally in landfills when yard waste, food scraps, paper and so on decompose. It is composed mainly of carbon dioxide
Biogas can also be produced by processing animal manure and human sewage in digesters.
Biodiesel is produced from animal fats and vegetable oils including soybeans and palm oil.
Ethanol is made from various crops including sugar cane and corn that are fermented.
How Biomass Fuels Are Used
Ethanol has been used in vehicles for decades and ethanol-gasoline blends are now quite common. In fact, some racing drivers opt for high ethanol blends because they lower costs and improve quality. While the percentage of ethanol is substantially lower, it is now found in most gasoline sold in the U.S. Biodiesel can also be used in vehicles and it is also used as heating oil.
But in terms of their role in net-zero buildings:
Biomass waste is burned to heat buildings and to generate electricity.
In addition to being converted to liquid biofuels, various waste materials including some crops like sugar cane and corn can also be burned as fuel.
Garbage, in the form of yard, food, and wood waste, can be converted to biogas in landfills and anaerobic digesters. It can also be burned to generate electricity.
Human sewage and animal manure can be converted to biogas and burned as heating fuel.
Biomass as a Viable Clean Energy Source for Net-Zero Energy Buildings
Don’t rely on what I say, let’s look at some research, specifically, a study published just last year (2018) that deals with the development of net-zero energy buildings in Florida. It looked at the capacity of biomass, geothermal, hydrokinetic, hydropower, marine, solar, and wind power (in alphabetical order) to deliver renewable energy resources. More specifically, the study evaluated Florida’s potential to utilize various renewable energy resources.
Generating electricity from wind isn’t feasible in Florida because the average wind speeds are slow. The topography and hydrology requirements are inadequate and both hydrokinetic and marine energy resources are limited. But both solar and biomass offer “abundant resources” in Florida. Unlike most other renewable resources, the infrastructure and equipment required are minimal and suitable for use within building areas, and they are both compatible with the needs of net-zero energy.
The concept of net-zero buildings has, of course, been established by the World Green Building Council (GBC), which has set timelines of 2030 and 2050 respectively for new and all buildings to achieve net-zero carbon goals. Simplistically, what this means is that buildings, including our homes, will need to become carbon neutral, using only as much renewable energy as they can produce on site.
But nothing is simplistic when it comes to net-zero energy buildings (ZEB) ). Rather, different categories offer different boundaries in terms of how renewable energy strategies are utilized. These show that net-zero energy buildings are not all the same:
ZEB A buildings utilize strategies within the building footprint
ZEB B within the site of the property
ZEB C within the site but from off-site resources
ZEB D generate renewable energy off-site
While solar works for ZEB A and both solar and wind work for ZEB B buildings, biomass and biofuels are suitable for ZEB C and D buildings, particularly in Florida.
Even though this particular study is Florida-specific, it indicates the probability that the role of biomass energy will ultimately be limited, but that it can certainly help buildings reach a net-zero status.
There will be different requirements and benefits in different areas, but certainly professionals offering engineering solutions in Chicago, New York, London (Canada and the UK), and all the other large cities in the world will be in a position to advise whether it is feasible to use biomass rather than other forms of eco-friendly energy for specific buildings.
Biomass might offer a more powerful solution than many people imagine.
Waste-to-Energy is the use of modern combustion and biochemical technologies to recover energy, usually in the form of electricity and steam, from urban wastes. These new technologies can reduce the volume of the original waste by 90%, depending upon composition and use of outputs. The main categories of waste-to-energy technologies are physical technologies, which process waste to make it more useful as fuel; thermal technologies, which can yield heat, fuel oil, or syngas from both organic and inorganic wastes; and biological technologies, in which bacterial fermentation is used to digest organic wastes to yield fuel.
The global market for waste-to-energy technologies was valued at US$6.2bn in 2012 which is forecasted to increase to US$29.2bn by 2022. While the biological WTE segment is expected to grow more rapidly from US$1.4bn in 2008 to approximately US$2.5bn in 2014, the thermal WTE segment is estimated to constitute the vast bulk of the entire industry’s worth. This segment was valued at US$18.5bn in 2008 and is forecasted to expand to US$23.7bn in 2014.
The global market for waste to energy technologies has shown substantial growth over the last five years, increasing from $4.83 billion in 2006, to $7.08 billion in 2010 with continued market growth through the global economic downturn. Over the coming decade, growth trends are expected to continue, led by expansion in the US, European, Chinese, and Indian markets.
By 2021, based on continued growth in Asian markets combined with the maturation of European waste management regulations and European and US climate mitigation strategies, the annual global market for waste to energy technologies will exceed $27 billion, for all technologies combined.
Asia-Pacific’s waste-to-energy market will post substantial growth by 2015, as more countries view the technology as a sustainable alternative to landfills for disposing waste while generating clean energy. In its new report, Frost & Sullivan said the industry could grow at a compound annual rate of 6.7 percent for thermal waste-to-energy and 9.7 percent for biological waste-to-energy from 2008 to 2015.
The WTE market in Europe is forecasted to expand at an exponential rate and will continue to do so for at least the next 10 years. The continent’s WTE capacity is projected to increase by around 13 million tonnes, with almost 100 new WTE facilities to come online by 2012. In 2008, the WTE market in Europe consisted of approximately 250 players due in large to the use of bulky and expensive centralized WTE facilities, scattered throughout Western Europe.
Municipal waste management in Poland has changed dramatically since the early ’90s when, as part of Poland’s privatisation program, municipal authorities were freed of their waste management obligations. The combined Polish recycling rate for dry recyclables and organic waste has increased from 5% in 2004 to 21% in 2010, according to a Copenhagen Resource Institute (CRI) study Municipal Waste Management in Poland (2013). Another source provides similar, corroborating statistics, putting the dry recycling rate in Poland at 14% and the composting rate at 7%.
The latest Eurostat data (for 2011) shows that the upward trend continuing, with the total recycled and composted reaching 28%. That is rapid rate of improvement, but leaves Poland well below the latest EU-27 average of 40% (25% recycled and 15% composted) – so what prospect is there of Poland reaching the EU’s mandatory 50% target by 2020?
Responsibility for waste disposal shifted to householders, who were left to individually contract any waste collection company of their choice. In the hard economic climate a ‘cheaper-the-better’ mentality prevailed, which did little to encourage sustainable practices. There wasn’t even an obligation on householders even to sign up for waste collection.
Landfilling was – and remains – the most common way of handling waste, but accompanying reporting and tracking methods were inadequate. Statistically, quantities of waste produced were usually larger than those collected, with the missing tonnages usually being dumped in forests or burned in domestic boilers to avoid waste disposal costs. As a result, waste management became largely uncontrolled, with a 2011 report concluding that ‘’waste management is one of the most badly neglected and at the same time one of the most urgent environmental issues for Poland.’’
Waste Management Legislation
Even after joining the EU in 2005, Poland didn’t rush to introduce reforms to improve practices and help to meet recycling targets. Only recently has Poland introduced several pieces of new waste related legislation, including:
Act on maintaining cleanliness and order in municipalities (2012);
Act on Waste (2012); and
Act on management of packaging and packaging waste (2013).
The first of these was revolutionary in that it gave responsibility for municipal waste collection and disposal back to municipalities. Now they are required to organise garbage collection and the separate collection of biodegradable waste and recyclable materials such as paper, metal, glass and plastic. It is expected that the new law will improve waste management control measures on a local level and greatly reduce the illegal dumping and trash burning.
The Act on Waste helps tackle the previous ‘free for all’ amongst collectors – it obliges waste handlers to act in a manner consistent with waste management principles and plans adopted at national level (by the Council of Ministers), regional level (Voivodeship) and local level (Municipality).
Poland has also this year adopted a new National Waste Management Plan, which states that an essential step towards improving the recycling rate in Poland is to increase landfill fees for recyclable, compostable or recoverable material. If acted upon, this could greatly increase the incentive to divert important municipal waste streams from landfill. The Polish market is clearly responsive to cost: in 2008 after landfill tax was significantly raised, there was a substantial reduction in waste being landfilled.
Declaration of bin-dependence
Although Polish citizens have always had to pay directly for waste collection, the new legislation has made some substantial changes to the payment system. There are now three different calculation methods. Each household is subject to a standard fee, which is then adjusted to reflect either:
The number of people living in a household;
The number of square metres covered by the property; or
The number of cubic metres of water used by the household per month.
The first of these options seems to be the most reasonable and has proven the most popular.
Municipalities are left to determine the standard collection fee, which as a result varies from region to region. Some municipalities charge at little as 3 Polish Zloty (around £0.56) per household, per person, per month, while some charge 20 Zloty (around £3.75).
The standard charge is also affected by a declaration made by the householder regarding waste segregation. If a property owner declares that they have separated out recyclable materials then they pay considerably lower fees. In some municipalities, this could be as low as 50% of the usual charge. Only those who declare that they don’t want to recycle pay full price. It’s rare that people do so: who would pick the most expensive option?
The problem is that some householders declare that they recycle their waste while in reality they don’t. Unfortunately, abusing the system is easy to get away with, especially since the new scheme is still in its early stages and is not yet stable. Monitoring recycling participation in order to crack down on such abuses of the system represents quite a challenging task.
Future Perspectives
Transformation periods are always hard and it is common that they bring misunderstanding and chaos. It isn’t surprising that there are problems with the new system which require ironing out, and the new legislation is nevertheless welcome. However, there is still much work to be done to provide sufficient and sustainable waste management in Poland. This will include such measures as educating the population, improving waste separation at source and securing waste treatment capacity.
Perhaps most importantly, Poland needs to take immediate action to develop its municipal waste treatment capacity across the board. If the 2020 recycling target is to be met, the country will require material recovery facilities, anaerobic digestion and in vessel composting sites, and household waste and recycling centres; and if more waste is to be diverted from landfill it will also need energy from waste (EfW) incinerators and mechanical biological treatment facilities.
According to Eurostat, only 1% of waste in Poland was incinerated in 2011. It has been confirmed so far that an EfW plant will be developed in each of Poland’s 11 biggest cities. Fortunately for Poland, the development of waste treatment installations is quite generously funded by the EU, which covers up to 80% of the total cost: EU subsidy agreements have already been signed for three of the planned EfW plants. The remaining cost will be covered by central, regional and local government.
The CRI paper presents three different scenarios for the future recycling rate in Poland. One of them is very optimistic and predicts that Poland has a chance to meet the 2020 recycling requirements, but each is based simply on a regression analysis of recent trends, rather than an analysis of the likely impact of recent and planned policy measures. What it does make clear, though, is that if Poland continues to progress as it has since 2006, it will reach the 2020 target. How many EU countries can claim that?
Note: The article is being republished with the kind permission of our collaborative partner Isonomia. The original version of the article can be found at this link.
A palm oil plantation yields huge amount of biomass wastes in the form of empty fruit bunches (EFB), palm oil mill effluent (POME) and palm kernel shell (PKS). In a typical palm oil mill, empty fruit bunches are available in abundance as fibrous material of purely biological origin. Energy potential of empty fruit bunches is attractive as it contains neither chemical nor mineral additives, and depending on proper handling operations at the mill, it is free from foreign elements such as gravel, nails, wood residues, waste etc.
However, EFB is saturated with water due to the biological growth combined with the steam sterilization at the mill. Since the moisture content in EFB is around 67%, pre-processing is necessary before EFB can be considered as a good fuel.
Unprocessed EFB is available as very wet whole empty fruit bunches each weighing several kilograms while processed EFB is a fibrous material with fiber length of 10-20 cm and reduced moisture content of 30-50%. Additional processing steps can reduce fiber length to around 5 cm and the material can also be processed into bales, pellets or pulverized form after drying.
There is a large potential of transforming EFB into renewable energy resource that could meet the existing energy demand of palm oil mills or other industries as well as to promote sustainability in the palm oil industry. Pre-treatment steps such as shredding/chipping and dewatering (screw pressing or drying) are necessary in order to improve the fuel property of EFB.
Pre-processing of EFB will greatly improve its handling properties and reduce the transportation cost to the end user i.e. power plant. Under such scenario, kernel shells and mesocarp fibres which are currently utilized for providing heat for mills can be relieved for other uses off-site with higher economic returns for palm oil millers.
The fuel could either be prepared by the mills before sell to the power plants, or handled by the end users based on their own requirements. Besides, centralized EFB collection and pre-processing system could be considered as a component in EFB supply chain. It is evident that the mapping of available EFB resources would be useful for EFB resource supply chain improvement. This is particular important as there are many different competitive usages. With proper mapping, assessment of better logistics and EFB resource planning can lead to better cost effectiveness for both supplier and user of the EFB.
A covered yard is necessary to store and supply a constant amount of this biomass resource to the energy sector. Storage time should however be short, e.g. 5 days, as the product; even with 45% moisture is vulnerable to natural decay through fungi or bacterial processes. This gives handling and health problems due to fungi spores, but it also contributes through a loss of dry matter trough biological degradation. Transportation of EFB is recommended in open trucks with high sides which can be capable of carrying an acceptable tonnage of this low-density biomass waste.
For EFB utilization in power stations, the supply chain is characterized by size reduction, drying and pressing into bales. This may result in significantly higher processing costs but transport costs are reduced. For use in co-firing in power plants this would be the best solution, as equipment for fuel handling in the power plant could operate with very high reliability having eliminated all problems associated with the handling of a moist, fibrous fuel in bulk.
Pyrolysis of scrap tires offers an environmentally and economically attractive method for transforming waste tires into useful products, heat and electrical energy. Pyrolysis refers to the thermal decomposition of scrap tires either in the absence or lack of oxygen. The principal feedstocks for pyrolysis are pre-treated car, bus or truck tire chips. Scrap tires are an excellent fuel because of their high calorific value which is comparable to that of coal and crude oil. The heating value of an average size passenger tire is between 30 – 34MJ/kg.
Pyrolysis is the most recommended alternative for the thermochemical treatment of waste tires and extensively used for conversion of carbonaceous materials in Europe and the Asia-Pacific. Pyrolysis is a two-phase treatment which uses thermal decomposition to heat the rubber in the absence of oxygen to break it into its constituent parts, e.g., pyrolysis oil (or bio oil), synthetic gas and char. Cracking and post-cracking take place progressively as the material is heated to 450-500°C and above.
Process Description
The pyrolysis method for scrap tires recycling involves heating whole or halved or shredded tires in a reactor containing an oxygen free atmosphere and a heat source. In the reactor, the rubber is softened after which the rubber polymers disintegrate into smaller molecules which eventually vaporize and exit from the reactor. These vapors can be burned directly to produce power or condensed into an oily type liquid, called pyrolysis oil or bio oil.
Some molecules are too small to condense and remain as a gas which can be burned as fuel. The minerals that were part of the tire, about 40% by weight, are removed as a solid. When performed well a tire pyrolysis process is a very clean operation and has nearly no emissions or waste.
The heating rate of tire is an important parameter affecting the reaction time, product yield, product quality and energy requirement of the waste tire pyrolysis process. If the temperature is maintained at around 450oC the main product is liquid which could be a mixture of hydrocarbon depending on the initial composition of waste material. At temperature above 700oC, synthetic gas (also known as syngas), a mixture of hydrogen and carbon monoxide, becomes the primary product due to further cracking of the liquids.
Schematic for Pyrolysis of Scrap Tires
The nature of the feedstock and process conditions defines the properties of the gas, liquid and solid products. For example, whole tires contain fibers and steel while shredded tires have most of the steel and sometimes most of the fiber removed.
Processes can be either batch or continuous. The energy required for thermal decomposition of the scrap tires can be in the form of directly-fired fuel, electrical induction and or by microwaves (like a microwave oven). A catalyst may also be required to accelerate the pyrolysis process.
Useful Products
The high acceptance of pyrolysis for the treatment of scrap tires is due to the fact that the derived oils and syngas can be used as biofuels or as feedstock for refining crude oil or chemical products. The pyrolysis oil (or bio oil) has higher calorific value, low ash, low residual carbon and low sulphur content.
The use of pyrolysis oil in cement kilns, paper mills, power plants, industrial furnaces, foundries and other industries is one of the best uses of scrap tires. Pyrolysis of scrap tyres produces oil that can be used as liquid fuels for industrial furnaces, foundries and boilers in power plants due to their higher calorific value, low ash, residual carbon and sulphur content.
The solid residue, called char, contains carbon black, and inorganic matter. It contains carbon black and the mineral matter initially present in the tire. This solid char may be used as reinforcement in the rubber industry, as activated carbon or as smokeless fuel.
Even though palm kernel shell has many similarities with wood pellets, it is not easy to reduce its size which makes it difficult for its optimum cofiring with coal in power plants and industries. Few years ago, Indonesia had exported PKS to Poland for cofiring purposes but because PKS was difficult to make powder (low grindability) it made cofiring performance poor, so the use of PKS for cofiring is currently discontinued.
To improve the quality of PKS, especially for the use of cofiring, PKS must be processed with torrefaction (mild pyrolysis). With the torrefaction process, it becomes easier to make powder from PKS, so that the desired particle size for cofiring is easier to obtain. Another advantage of the torrefaction process is that the caloric value of PKS will also increase by about 20%, Torrified biomass is hygroscopic which means ease in indoor as well as outdoor storage.
During the torrefaction process, PKS is heated at a temperature of around 230 to 300 °C in the absence of oxygen. With continuous pyrolysis technology, torrified PKS production can be carried out at large capacities. The need for biomass fuel for electricity generation is also large, usually requiring 10 thousand tons for each shipment. PKS torrified producers must be able to reach this capacity. The production of 10 thousand tons of PKS that are burned can be done per month or several months, for example, to reach 10 thousand tons it takes 2 months because the factory capacity is 5000 tons per month.
In general, the advantages of the PKS torrefaction process are as follows:
It increases the O/C ratio of the biomass, which improves its thermal process
It reduces power requirements for size reduction, and improves handling.
It offers cleaner-burning fuel with little acid in the smoke.
Torrefied PKS absorbs less moisture when stored.
One can produce superior-quality PKS pellets with higher volumetric energy density.
Pelletizing of torrefied PKS can be an option to increase the energy density in volume basis. The pelletizing process resolves some typical problems of biomass fuels: transport and storing costs are minimized, handling is improved, and the volumetric calorific value is increased. Pelletization may not increase the energy density on a mass basis, but it can increase the energy content of the fuel on a volume basis.
Africa, especially West Africa, which has many palm oil plantations and also the location where the palm oil trees originate, can supply torrified PKS to Europe to meet its rapidly-increasing biomass fuel demand.
In Africa, palm kernel shell is generally produced from PKO mills. CPO production is generally carried out on a small scale and only processes the fiber portion of the palm oil fruit. This palm oil mesocarp fibre is processed to produce CPO, while the nut that consist kernels and shells are processed elsewhere to produce the main product of PKO (palm kernel oil). PKO mills are usually quite large by collecting nuts from these small scale CPO producers. PKS is produced from this PKO mills.
The nut cracker machine separates kernel and shell
The distance between Africa and Europe is also closer than Europe to Malaysia and Indonesia. Currently, even though Europe has produced wood pellets for their renewable energy program to mitigate climate change and the environment, the numbers are still insufficient and they are importing wood pellets from the United States and Canada in large quantities. European wood pellet imports are estimated to reach more than 1.5 million tons per year. Torrified PKS from West Africa can help in meeting the biomass fuel demands for power plants across Europe.
To improve the quality of biomass, especially for cofiring purposes, biomass waste can be processed with torrefaction (also known as mild pyrolysis). With the torrefaction process, it becomes easier to make powder (high grindability) so that the desired particle size for cofiring of biomass is easier to obtain. Another advantage of the torrefaction process is that the caloric value of biomass increases by about 20%. Torrified biomass is essentially hydropobic which means ease in storage including outdoor storage. This condition also makes it easier to handle and use, in addition to reduction in transportation costs.
What is Torrefaction?
Torrefaction, which is currently being considered for effective biomass utilization, is also a form of pyrolysis. In this process (named for the French word for roasting), the biomass is heated to 230 to 300 °C without contact with oxygen. For comparison, pyrolysis of biomass is typically carried out in a relatively low temperature range of 300 to 650 °C compared to 800 to 1000 °C for gasification. Torrefaction is a relatively new process that heats the biomass in the absence of air to improve its usefulness as a fuel.
Torrefaction, a process different from carbonization, is a mild pyrolysis process carried out in a temperature range of 230 to 300 °C in the absence of oxygen. During this process the biomass dries and partially devolatilizes, decreasing its mass while largely preserving its energy content. The torrefaction process removes H2O and CO2 from the biomass. As a result, both the O/C and the H/C ratios of the biomass decrease.
Benefits of Biomass Torrefaction
Torrefaction of biomass improves its energy density, reduces its oxygen-to-carbon (O/C) ratio, and reduces its hygroscopic nature. Torrefaction also increases the relative carbon content of the biomass. The properties of a torrefied biomass depends on torrefaction temperature, time, and on the type of biomass feed.
Torrefaction also modifies the structure of the biomass, making it more friable or brittle. This is caused by the depolymerization of hemicellulose. As a result, the process of size reduction becomes easier, lowering its energy consumption and the cost of handling. This makes it easier to cofire biomass in a pulverized coal-fired boiler or gasify it in an entrained-flow reactor.
Another special feature of torrefaction is that it reduces the hygroscopic property of biomass; therefore, when torrefied biomass is stored, it absorbs less moisture than that absorbed by fresh biomass. For example, while raw bagasse absorbed 186% moisture when immersed in water for two hours, it absorbed only 7.6% moisture under this condition after torrefying the bagasse for 60 minutes at 250 °C (Pimchua et al., 2009). The reduced hygroscopic (or enhanced hydrophobic) nature of torrefied biomass mitigates one of the major shortcomings for energy use of biomass.
In biomass, hemicellulose is like the cement in reinforced concrete, and cellulose is like the steel rods. The strands of microfibrils (cellulose) are supported by the hemicellulose. Decomposition of hemicellulose during torrefaction is like the melting away of the cement from the reinforced concrete. Thus, the size reduction of biomass consumes less energy after torrefaction. During torrefaction the weight loss of biomass comes primarily from the decomposition of its hemicellulose constituents. Hemicellulose decomposes mostly within the temperature range 150 to 280 °C, which is the temperature window of torrefaction.
As we can see from figure above, the hemicellulose component undergoes the greatest amount of degradation within the 200 to 300 °C temperature window. Thus, hemicellulose decomposition is the primary mechanism of torrefaction. At lower temperatures (< 160 °C), as biomass dries it releases H2O and CO2. Water and carbon dioxide, which make no contribution to the energy in the product gas, constitute a dominant portion of the weight loss during torrefaction.
Above 180 °C, the reaction becomes exothermic, releasing gas with small heating values. The initial stage (< 250 °C) involves hemicellulose depolymerization, leading to an altered and rearranged polysugar structures. At higher temperatures (250–300 °C) these form chars, CO, CO2, and H2O. The hygroscopic property of biomass is partly lost in torrefaction because of the destruction of OH groups through dehydration, which prevents the formation of hydrogen bonds.
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