There is growing interest in waste derived fuels in many developing countries as a means of utilizing waste and providing greater access to clean liquid fuels, while helping to address energy costs, energy security and global warming concerns associated with traditional petroleum fuels1. A look towards the municipal solid waste stream for an alternate source of energy may be considered to help alleviate some of these issues.

This report will discuss alternate methods and sources that could be considered in South Africa, that have been implemented in other countries with successful results. Although there are many different kinds of waste derived fuels, there will be a main focus on the following:

Second generation bio fuels

Anaerobic methane digester’s used in breweries

Tyre derived fuel, and

Plastic generated fuel

The before mentioned were chosen because of the viability of the implementation in South Africa. The sources of waste found in South Africa are in abundance, which can be used for various processes for the conversion of waste-to-fuel. The processes in which these wastes will be converted into a form of fuel will be discussed. The environmental impacts of using such fuels and the cost benefits associated with use in comparison to traditional fossil fuels, such as coal and oil derived fuels will also be discussed.

Second-generation bio fuels

A fairly recent classification has been made about certain bio fuels, which pertain towards plants that are grown and harvested for bio fuels. These classifications are namely "first generation" and "second generation" fuels2. Strictly speaking, there is no finite definition of each of these fuel types, but there is a main distinguishing factor that differentiates the two i.e. the feedstock used for the bio fuel. A first generation fuel uses only a specific portion of the above ground biomass produced by the plant (which is often edible). Second Generation bio fuels are fuels made from crop residue or woody crops that are inedible and essentially worthless for commercial use in terms of food production value. Crop residue is a by-product of many crops, which are harvested for commercial use. This section focuses on second-generation bio fuels that could be utilized in order to provide an alternative source of energy as opposed to being discarded into a landfill.

Second generation bio fuels may be classified in the terms of the process or processes that are used to covert this biomass into a form of fuel, namely biochemical and thermo chemical. The basic steps for biochemical processes include pre-treatment of biomass, saccharification, fermentation, distillation, the separation of solids, where these solids are converted into steam and power is generated through turbines3. Thermo chemical bio fuel conversions involve similar processes and at much higher temperatures and pressures which begin with pyrolosis or gasification. Gasification is more capital intensive, but the final product is a clean fuel that may be used directly in engines.

Figure 1. Process steps for thermo chemical production for gasification2C:UsersSmokeyDesktopasd.JPG

The use of thermo chemical processes would be more accepted in South Africa, as most of the needed equipment is commercially available. This negates the need to research and develop in order to begin using second-generation fuels. There are three forms of thermo chemically produced fuel that highly notable from gasification. They are Fishcher-Tropsch liquid (FTL), Dimethal ether (DME) and Alcohol fuel.

Fishcher-Tropsch liquid resembles a semi-refined crude oil, which can then be processed into diesel or jet fuel. There is no limitation of what type of biomass in particular, that cannot be converted into FTL. This process has already been operation in South Africa since the early 1950’s. PetroSA produces about 23000 barrels per day of processed fuel from FTL production.

Dimethyl ether is a colourless gas that can be a substitute for liquefied petroleum gas. DME is a good diesel engine fuel due to the absence of many impurities during combustion, but because it must be maintained under a certain mild pressure, it is not feasible to mix diesels. Thus, it is most suitable for a fleet of vehicles only using DME.

Alcohol fuel, such as ethanol or butanol can be produced by biomass through a process known as syngas processing. These alcohols have the potential to be used as a blending agent for alcohol2.

It is worthwhile to note the efficiency levels of fuel-to-petroleum, of Second generation bio fuels (e.g. cellulosic ethanol) as compared to traditional fossil fuel and first generation bio fuel (e.g. Corn ethanol) that is specifically grown to become a form of bio fuel. Although traditional fuel is just under twice as an efficient as second-generation bio fuels, production of second-generation bio fuel can be used to mitigate the amount of traditional fuel required in the day-to-day process. More research and development into the field of biomass conversion can significantly increase the efficiency levels.

Figure 2: Fuel to petroleum factors between first, second-generation fuels and fossil fuels2

C:UsersSmokeyDesktopenergy.JPG

The use of second-generation bio fuels in South Africa would have significant advantages. Biomass that would normally make its way to landfills could be used as a form of energy through different techniques or processes. This would help to reduce greenhouse emissions, as traditional fossil fuels would be used less. This form of energy can be considered as a sustainable source of energy, as long as crops are planted, furthermore since South Africa readily relies on its primary production for its economy, there will be ample biomass ready to be converted into a form of energy.

Implementation in South Africa for the use of second-generation bio fuel would demand the support of the local government in order to be a success. Such support would include:

Considering direct grants for development of second-generation bio fuels.

Financial incentives for companies to take this venture.

Create policies to support the creation and use of second generation fuel and

Create regulatory mandates for bio fuels to help the start the bio fuel industry.

Should South Africa not be able to fully utilize the capacity of second generation bio fuels, it is always possible that biomass may be exported to other countries in order to used elsewhere in the world where processing is possible.

Beer waste products used as fuel.

One should not underestimate the power of beer. According to the South African Breweries (SAB) who supplies beer to 75 different countries, the annual amount of beer made is 3.1 billion litres4. It can be seen that the brewing process produces a large amount of waste. If the waste could be utilised in the form of energy it would benefit the brewery as well as the environment.

"Saving the earth, one beer at a time" is the slogan of Eric Fitch’s company, Purpose Energy Inc5.

American Eric Fitch has come up with an invention that solves the problem of waste produced through the brewing process. By the use of an anaerobic methane digester, he has found a way to convert the breweries waste into natural gas. Fitch said, "They have a really high by-product production rate"6 it is becoming increasingly challenging for the breweries to get rid of these by-products.

The barley, yeast and spent hops left over from the brewing process are moved to the digester where energy is extracted and then it is reused in the brewery. The digester that has been installed at Magic Hat Brewery in South Burlington. The digester is about 15m in diameter and can hold 1.8 million litres of slurry. The digester can produce 200 cubic feet of the biogas per minute5. This is very innovative as the brewery effectively has its own power supply in the back of the factory. This digester will save the amount of waste that needs to be disposed of. Although the digester costs four million dollars to construct, its implementation will save on costs in the long term.

Other processes include bio-energy recovery systems, which convert the breweries wastewater into natural gas, which is used as fuel in the brewing process. This is used in 83% of Anheuser- Busch’s Breweries, the makers of Budweiser. Whereas some European Breweries dry the spent grain and it is then burnt. The heat and energy generated is used in the manufacturing process5.

We as South Africans drink 2.530 mega litres of beer a year according to a survey done in 20047. Although most of the spent hops are sold off as animal feed, it would be more beneficial to have a digester of our own, to supply the breweries of South Africa with a new source of energy. South African Breweries Limited have seven breweries in South Africa, if they could adopt the conversion of waste from the brewing process into energy it would not only save them money but reduce the carbon footprint of South Africa.

Alrode Brewery, a part of the SAB has actually developed a biogas recovery plant of their own. Using an anaerobic digester, the waste material such as spent grain and wastewater is generated into methane gas. This system is very efficient as 90% of the 5 million litres of waste generated in a day is converted into biogas, which is 85% methane. The biogas generated is then burnt in a boiler to boil water and produce steam, which is used in the brewing process again. The incorporation of the biogas as a source of energy prevented around 10 tons of coal being burnt in a day, which in turn saves around R7000 a day in costs4.

Alrode is just the first to incorporate this new source of energy, two of SAB’s other breweries, Rosslyn Brewery north of Pretoria and Newlands Brewery in Cape Town are going to incorporate anaerobic digesters as well in the near future4.

Using the anaerobic digester will cut down the breweries dependency on coal and reduce its carbon footprint, but it also reduces the amount of waste going to landfill sites. Instead, the waste is being utilised in the generation of energy. The potential for this type of energy recovery is tremendous as SAB produces beer for over 75 countries. If SAB could implement an anaerobic digester in every one of their breweries, the amount of waste that could be reduced would be astronomical, not to mention the environmental benefits. A much more fulfilling way of dealing with waste than simply wasting it. Saving the world a beer at a time seems to be quite feasible for a country that loves the product.

Figure 3: The anaerobic digester at Alrode brewery in Gauteng

Scrap tyres used as fuels

Old used transport tyres (scrap tyres) are a growing concern for the entire planet. Worldwide, about a billion tyres are sold annually8. The scrap tyres eventually end up in landfills around the world as piles of scrap tyres. These scrap tyres where designed in such a way that they will not biodegrade anytime soon. These stockpiles of scrap tyres lead to problems such as breeding grounds for rodents and mosquitoes, wasted space in landfills and health hazards, such as fires: "In August 1998, a grass fire ignited 7 million tyres near a town of Tracey in California’s San Joaquin Valley, sending a plume of soot and noxious gas thousands of feet into the air. State authorities originally expected the fire to burn for about two weeks, but it endured for two and a half years"8. Tyre fire outbreaks are a big concern for South Africa as a lot of scrap tyres are illegally being dumped in open veldts or behind informal settlements.

These stockpiles of scrap tyres keep growing at an alarming rate as every vehicle adds to this waste stream. Landfills in South Africa have now implemented laws about the discarding of tyres to reduce them being dumped into landfills, but this has lead to illegal dumping of tyres. The laws and legislations that have been brought in, in many countries have lead to the development of alternative uses for scrap tyres.

Many of the alternatives uses for scrap tyres have been developed to reduce the amount of scrap tyres in landfills. These uses include using whole scrap tyres to make highway crash barriers, boat bumpers in harbours, barriers on racetracks, a variety of agricultural purposes, and many more small-scale applications. The whole tyre can also be retreaded. The scrap tyres can also be cut, punched or stamped to produces products such as tyre swings, soles of shoes, floor mats, belts, gaskets, seals, muffler hangers, shims, washers, road backfill, insulation, horse arenas and many more applications9. Scrap tyres can also be crumbed and mixed with a urethane binder to make sidewalks, playground surfaces and basketball courts9. These small applications solve only a small amount of the waste problem.

There are some big scale operations that solve more of the waste problem, these include the tyre derived fuel industry, civil engineering applications and ground (shredded) rubber applications and rubberized asphalt concrete.

The focus of this section will be on the tyre derived fuel industry. This will cover a few details about shredded tyres but will focus more on the incineration and chemical processes that break tyres down into oil and other valuable fuels.

Most tyres are shredded for tyre-derived fuels but this is dependent on the machinery used. This is the process of putting the whole tyre into a shredding machine where it is shredded into small pieces and the steel and carbon black is removed for further recycling before the shredded rubber is sent to an incinerator or another facility.

Scrap tyres whole and shredded are being used in incinerators to help with the generation of heat. This heat can be used to fire kilns in concrete manufacturing or used to heat water to produce steam for turbines that produce electricity. Burning of tyres produce the same amount of energy as oil and 25% more energy than conventional coal. The ash residue of tyre-derived fuel may contain a lower heavy metal content than some coals9. Most tyres-to-energy facilities will mix shredded tyres with coal, oil, wood or other fuels before burning them10. Although some facilities do burn tyres by themselves.

The process involves adding the tyres to the incinerator in different percentages of the overall mixture, from a 100% in some plants to only 10% in other plants. The burning of the mixture creates heat and this will heat up a number of boilers (depending on plant) which creates steam. The steam will power turbines creating electricity. This is a very widely used method of getting rid of scrap tyres all over the world because most countries are depended on coal-powered electricity. The tyres can be easily implemented into this process without spending capital to build a new plant. There are out lays in buying a shredding machine (if needed) and getting the scrap tyres. There is also an outlay of money to improve the filter system of the power plants to handle the new ash that is released by the burning of tyres. The by-products of burning tyres can also be used by other industries. The non-hazardous by-products include steel, zinc oxide and gypsum.

This is a viable option for scrap tyres in South Africa. South Africa has a large stockpile of scrap tyres that grows daily. There is already a company in Cape Town that collects and shreds tyres. South Africa is reliant on coal-operated power stations. Using tyres that are 25% more energy efficient then coal can improve the output of the coal-operated power stations; this can reduce the shortage of supply of electricity and cut back on coal usage. The use of scrap tyres as part of the burning mixture will reduce the coal usage and cost, this will allow the country to build up a coal supply or increase exports while removing the growing threat of scrap tyres. The money saved on coal can be spent on buying more scrap tyres or improving the power stations. It can also lead to cleaner, greener electricity that can be cheaper in price. The tyre burning process produces by-products that can be sold to increase income; this also saves resources and provides a cheaper alternative to manufactures. If this option is selected it could lead to more jobs in the tyre collection and disposal industry, coal industry, power stations and the selling and using of by-products. This is a great option for South Africa, and something that the government and Eskom must investigate to improve the electricity generated and to reduce landfills.

The other option is to break the tyre down into its basic components or raw materials. Below are a couple of examples of different types of machines that are in the final stages of production around the world that if accepted will change the way people look at tyre waste. These systems break down the tyres in to basic components that are sold off, but the machines are mostly run by the gases that are produced from the process, so they are using tyres-to-energy concepts and not tyres being recycled, though it could be seen as a combination of both.

The first tyre-to-energy machine discussed is built by Changing World Technologies in Philadelphia that can change almost anything into oil. They have developed what they call the thermal depolymerisation process, or TDP. Thermal depolymerisation is the process of taking materials apart at the molecular level. The machine and process is designed to handle almost all types of waste (carbon-based) including tyres. The scrap tyres go in one side and come out on the other side as three products, all valuable and environmentally benign. The three products are high-quality oil, clean-burning gas, and purified minerals that can be used as fuels, fertilizers, or speciality chemicals for manufacturing11.

The process is to first grind the waste and add water to make it into a slurry, next it goes through a series of tanks and pipes, that heat, pressurise, digest and break down the mixture. The first phase is adding water, heat and pressure to the system; this allows partial depolymerisation to take place. The thermal depolymerisation machine can raise the heat and pressure levels to the precise level that breaks down the long molecular bonds. Phase two is a quick drop in pressure, which releases about 90 percent of the slurry’s free water. The remaining mixture goes into a second-stage reactor similar to the coke ovens used to refine oil into gasoline11.

The mixture is reheated and then passed through vertical distillation columns; hot vapour flows up, condenses, and flows out from different levels. Gases from the top of the column, light oils from the upper middle, heavier oils from the middle, water from the lower middle, and powdered carbon from the bottom. The gas recovered in the process is used on-site in the plant to heat the process. The process cooking and cooking times varied depending on the mixture going in or the chemicals that are wanted out in the end. Once the process is complete, the end products are collected. The process is very energy efficient, above 85%. Tyres yield some oils, but more minerals and other solids. As can be seen from the diagram. 100 pounds (45.4 Kg) of tyres produce 44 pounds (20 Kg) of oil, 10 pounds (4.5 Kg) of gas, 42 pounds (19 Kg) of carbon and metal solids and 4 pounds (1.8 Kg) of water11.

Figure 4: The thermal depolymerisation process11

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The next process is turning tyres into oil. This can be done by liquefaction or by pyrolysis. The liquefaction process involves shredding the tyre then feeding it into a liquefaction reactor containing hot oil at 371 deg Celsius (700F) 12. The rubber is melted into the oil, usually old engine oil and liquefied into two types of oil, a light condensate oil and a heavier more viscous tar-like oil. The light oil is extracted from the top of the reactor and the heavy tyre oil from the bottom. The lighter oil is further processed into diesel or heating oil, while the heavier oil being further processed into marine, heating or lube-oil. Both oils need to be further processed to remove other components such as nylon tuff and reinforcing wire, which can be recycled12.

The pyrolysis process involves shredding the tyre and it is conveyed to a reactor where hot hydrocarbon vapours containing combustible gas and vaporized oil are produced12. This leaves solids of carbon black and steel, which are removed, for further processing and recycling. The solids are removed by water-washing or spraying techniques. The gases are fed into a condenser where most of the oil vapours are condensed and the resulting liquid oil drawn off from the bottom of the condenser and sorted. The remaining gases are pressurized and used as fuel in the pyrolysis process making the system self-sufficient in energy12.

The next option comes from Delta Energy in Berthold. This facility feeds scrap tyres into one end and gets energy out the other end. The process recovers every bit of energy that was expended to produce the tyres. They use a reactor with a special chemical compound that breaks apart the tyre. The reactor breaks 99 percent of the tyre down onto something useful, from natural gas to diesel fuel to carbon. Each tyre produces the equivalent of 10.6 litres (2.8 gallons) of oil13.

All these alternative options can be implemented in South Africa if the process are passed as acceptable methods of getting rid of scrap tyres. Due to the process being so new a large capital will be needed to get the machinery in to South Africa and operational. These process can be legislised by the government to allow Sasol to get the machinery and scrap tyres at a reasonable price. Sasol can then produce a cheaper oil and bring down its petrol prices. This can boost the entire economy as petrol prices won’t have to be controlled by foreign markets. It can also lead to more job creation in the petrol sector.

Plastic waste recovery as fuel source

Typical plastic waste from a household can lead into harmful effects. Most harmful effects associated with plastic waste, come from chemicals that leach from the plastic to the environment once it has been dumped14. According to the International Plastic Task Force, plastic waste can break down and release toxins that harm the environment, animals and the general public.

In most developed countries, legislation that banned shopkeepers from providing plastic bags to customers had been implemented in order to reduce plastic waste disposal. However, the significance of this had a small impact as compared to the amount of plastic waste that is disposed, globally. Europe on its own produces about 60 million tons of plastic waste and has remained a major region contributing about 25% of the global total waste15. There are two main problems associated with plastic waste, (i) Raw material for plastic production (crude oil) is non renewable (ii) Most plastic wastes are not bio-degradable, land fill plastic waste will not degrade for hundreds of years15.

The issue of plastic waste remains a huge crisis around the globe, as plastic is the most disposed waste into the environment. This called for emergency innovations as to how best to re-use or recycle plastic waste as source of energy. Plastic can store energy, which may be recovered by various ways namely: (i) Municipal incineration in energy-from-waste incinerators, the heat of plastic waste burnt at high temperature, which is used for production of electricity or steam, (ii) Production of alternative fuels from plastic waste, the fuels are used in various manufacturing processes and in power stations.16

Most developed countries have adopted the technology of re-using or recycling plastic waste as source of energy, countries like Austria, Belgium, Denmark, Germany, Netherlands and Switzerland. The benefit of this is that these countries produce electricity for approximately 7 million households and heat for 13.4 million households through energy from plastic waste. This also reduces CO2 emissions as less coal is burnt per year, approximately reduced by 23 million tones which is equivalent to taking 11 million cars off the road.19 The energy from this waste route indicates to be a viable option to best deal with plastic and tyre waste as it is economically and environmentally beneficial.

Arentsen H et al17 has provided a flow diagram following the life cycle stages for different plastic recycling options, and the end source of energy that is produced from each process.

Figure 5: Life cycle for different plastic recycling options

Re-useMechanical recyclingChemical recycling feedstockChemical recycling fuel recovery recoveryIncineration energy recovery

Collection and transport

Collection and transport

Collection and transport

Collection and transport

Collection and transport

Dismantling

Washing and sorting

Sorting

Pyrolysis/ gasification

Combustion

EnergyRefurbishingGrinding and meltingHydrogenation/ crackingFuelsRemanufactured productPolymer pelletsMonomers

The recycling a is

The recycling and re-use process is recommended as the cheapest and easiest options of recovering plastic waste (International Plastic Task Force). This is because community and individual members of households can participate in this process by dumping plastic waste at dedicated bins, recycling the used plastic products to be remanufactured. The chemical recycling process is considered as the most expensive process as it requires expensive machinery and trained personnel to operate, its end products are mostly utilized in developed countries as replacement for coal to generate electricity and heat. Alternatively, monomers are used as raw materials for manufacturing new polymers.

Implementing Energy from waste technology within South Africa can help the country to overcome it terrible problems of diminishing landfills, shortage of energy and insufficient supply of electricity from Eskom due to the poor quality of coal they use to generate electricity. About 70% of South Africa’s energy needs are met from coal (including over 92% of electricity generation and 30% transport fuels)18. Although cheap by international standards, buying coal involves significant costs for energy-intensive processes. Coal becomes more expensive the further you are from the coalmine.

If the government can provide necessary infrastructure or plants to perform Energy from waste technology, the country will benefit economically and environmentally. More jobs will be created. Direct jobs during construction of infrastructure, and indirect jobs during the operational and maintenance of the infrastructure. Less CO2 gases will be discharged into the environment, as less coal will be burnt as a source of energy. Funding should be allocated to research groups within South Africa to carry out a feasibility study abroad to find out if the country is capable to implement such technology.

Conclusion

This report has reviewed a variety of alternate fuels and alternate fuel production processes and the environmental impacts that occur. Each of the 4 main points have been discussed for the implementation of South Africa, where each of the discussed municipal solid waste has been shown that it may be used as an alternative source of fuel through the necessary process. Although it can be seen that these processes have many environmental benefits such as reducing the amount of waste that is disposed of, longer life span of landfills and the reduction of our carbon footprint, the technologies described in this report often show cost implications that hinder the progress of waste-derived-fuel. Costs would be saved in the long term but in a country such as South Africa, the capital costs to get the necessary processes up and running are too great.

Companies or facilities are usually viewed as taking the initiative in coming up with new and innovative ways of dealing with our country’s waste products. There are important roles for Government to help support the development and execution of fuel-from-waste initiatives through financial incentives or legislation. Even with supportive policies and infrastructure available, time will be needed before fuel derived waste will be able to make an impact in South Africa. This due to the development, research and demonstration requirements needed to reach any form of commercial stage.

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