Introduction
What is Waste-to-Energy (WTE)
Energy recovery from waste that cannot be recycled into usable heat, fuel or electricity using a variety of processes such as combustion, gasification, anaerobic digestion, landfill gas recovery and pyrolization is called waste-to energy (WTE).
Current Issues
Municipal solid waste consists of kitchen waste, electronics, light bulbs, used tires, plastics, yard waste and old paint among many other things. In recent years, the recycling of waste products has gone up, but still the amount of MSW generated per year is on the rise. Currently, only 33% of the total MSW can be recovered through recycling, but 67% of the waste ends up in landfill or is incinerated (WEO, 2011). Traditional methods like landfill require an empty land of enormous size, which is an issue for many countries. Besides, the wastes dumped on landfill can contaminate the groundwater and surface water. Decomposition of the municipal waste generates methane gas that can pose a threat to the environment. Incineration is another method through which the waste is combusted to reduce the volume, but that also generates a large quantity of green gases. This essay will discuss the importance of municipal solid waste management through MSW combustion technique and its financial and commercial viability.
Awareness
Figure 1: Handling of MSW in EU countries (Funk, Milford and Simpkins, 2013)
Awareness about the waste to energy techniques is not widespread. For example, countries like Sweden, Netherlands and Denmark recycle 40% of their energy and use waste to energy techniques to process the MSW for more than 50% of the waste and send only about 5% of the waste to landfill (Funk, Milford and Simpkins, 2013). On the other hand, a developed neighboring country of Denmark, the UK recycles only 35% of its MSW, and uses waste to energy (WTE) techniques to process MSW for only 5-7% of the waste and sends a large percentage of waste to landfill (Funk, Milford and Simpkins, 2013). Even in the USA, the penetration of WTE techniques to process MSW is significantly low and landfill is the most used technique.
Why This Technology?
Apart from recycling, which is the cleanest, environment friendly and most energy efficient way to process MSW, modern WTE combustion techniques are a better option than traditional combustion or landfill methods. In the modern incineration WTE technique, the volume of the waste is reduced to as low as 4% of the initial volume. Also, this process generates electricity.
Technical Process of Converting Waste to Energy
Most of the municipal solid waste are organic and are generally processed through open combustion following the traditional method, which produces greenhouse gases such as carbon-di-oxide, Sulphur and nitrogen oxides. Almost no energy is recovered in the traditional open combustion process. Mass Incineration is a combustion process in which wastes are first lifted into a chamber where the burning takes place. This burning process releases lot of energy, which is then used to boil water and generate steam. This superheated steam is then used to rotate a turbine generator (EPA, 2015). The rotation of turbine generator produces electricity. The byproduct of this thermal process is ash. Much of the ash is collected and sent to landfill. In the baghouse through a filtering system particulates are captured. This baghouse filtering system can remove up to 99% of the particulates. These captured fly ash particles are then collected onto funnel shaped receptacles. These particulates are then transported using an enclosed conveyer to the ash discharger. Before mixing the particulates with the bottom ash, particulates are wetted to prevent dust (EPA, 2015). Ash residue is then transported to the dispatched area via an enclosed conveyer and then further transported in leak proof trucks to the landfill area. In some of the mass incineration plants bottom ash is further processed to separate out recyclable scrap metals. The diagram below shows the energy recovery process in a mass incineration plant (EPA, 2015).
Figure 2: MSW Combustion Process (WEO, 2011)
Statistics of Present Studies and Efficiency
Figure 3: Spittelau incineration plant in Vienna (WEO, 2011)
Waste to energy techniques are largely used in Scandinavian countries and some countries in Europe. However, in the greater part of the world, WTE it is not widely used. However, as time is nearing when landfill can no longer remain as a viable option for waste management and traditional combustion will be harmful for the environment; an increasing number of government bodies will begin to use WTE techniques. One of the largest WTE plants located in Netherland processes close to 100 million tons of MSW and runs an electricity plant with a capacity of 110MW (REA, 2011). Apart from that, Austria also operates one of the most successful gasification plants. Both of these plants are able to achieve an energy efficiency of 30% and the amount of ashes generated is only between 4% -7%, depending on the composition of the MSW (WEO, 2011).
Estimated Cost and Budget Analysis
There are several researches conducted on WTE and its economic viability. Below is made a comparative study between the cost and benefit of a WTE plant with the help of a few examples.
Cost and Budget Analysis
A typical city with a population of at least 1 million people and with medium density of industries produces close to 600,000 tons of waste per year (Rodriguez, 2011). Cities like New York produce waste, which is almost 10 times that value. On the other hand, small cities like Columbus may produce MSW close to the average figure of 600,000. If it is assumed that a city has budget to install one WTE combustion plant, then the installation of one WTE combustion plant of capacity of 600,000 tons will require an investment of about $400 million and a yearly operating cost of $20 million (Rodriguez, 2011).
Making Economic and Financial Case for WTE Combustion Process
If it is assumed that WTE combustion plant will utilize 90% of the time for processing the WTE to produce energy, then it is estimated to produce about 350 GWh of energy, which is equivalent to $35 million as revenue for the plant every year. This means that the WTE plant will be able to generate an operational profit of $15 million every year only from the generation of electricity (Rodriguez, 2011). The plant can sell the ash produced through incineration and make an additional $1-2 million every year. Also, WTE plant can apply for carbon credit and get another $3-4 million worth of carbon credit points (Rodriguez, 2011). The government should keep a gate fee for people who will be using it. If a gate fee of $25/ton is levied, then the payback period for the investment will take 17 years (Rodriguez, 2011). If the cost of capital is more than 4.5%, then the project will not be profitable, and in order to make it profitable, the gate fee needs to be increased.
Potential Energy Saving
Processing of waste through combustion produces energy. The energy efficiency of the plants are 30% for large plants and between 15-20% for small plants (Rodriguez, 2011). For small plants, it is difficult to justify energy saving or investment if they are not running at full potential. However, larger size plants can give substantial energy benefits. For example, a plant with a capacity of handling 500,000 tons of waste can produce a net electric energy (subtracting the energy the plant uses for its operation) is close to 300GWh annually. One large plant has the potential to save energy equivalent to 300GWh (Rodriguez, 2011).
Practicalities and Challenges
One of the major challenges of running combustion units are the greenhouse gases and fly ashes, which cause environmental damage if not managed and processed properly. In most of the modern plants, fly ashes and flue gases are treated and converted into sludge so that they cannot contaminate air.
One of the major problems with WTE combustion units is that the smaller combustion units are not financially viable. Only very large combustion units are financially profitable to operate. However, larger units require a huge initial investment. Initial investment can range from $100 million to $500 million. That is a barrier to implementation of WTE combustion units in many countries.
Advantages and Disadvantages
Advantages and Benefits
Incineration is the most practical method of waste management. It saves a lot of money in landfills, transport and also reduces carbon footprint. The sheer reduction in space required to landfill relieves huge pressure on land. This will give a huge advantage and benefit to urban areas. Landfills also create a lot of pest and insects. A 250 ton per day combustion unit can also produce close to 6.5 MWs of electricity, which can save about $3-4 million per year. Some cold countries also use the heat for heating commercial buildings.
Disadvantages
As discussed above, combustion plant has been a turnoff for municipalities because of its high investment cost. Small towns or even small cities cannot afford to build a WTE combustion plant as it requires huge waste to remain profitable and energy efficient. Dioxins produced as a by-product in those plants are cancerous and should be treated carefully.
Conclusion
As not all MSW can be recycled, landfills and combustion traditionally dominated the way MSW is handled. However, both of these techniques have adverse environmental impact and give economic value by processing the MSW. However, WTE combustion can be used to produce energy from the MSW and can also reduce the greenhouses gases generated by the traditional waste management techniques. This process can generate electricity and ashes all of which are useful for further use. Socially, economically and environmentally, the WTE process is beneficial, but financially, it is challenging to establish and operate WTE combustion plants. However, with lower cost of capital investment, social taxation and gate fees, WTE combustion projects can be made profitable.
References
Rodriguez, M. (2011). Cost-Benefit Analysis of a Waste to Energy Plant for Montevideo and Waste to energy in Small islands. Columbia University. Retrieved on 21st April, 2015 from <http://www.seas.columbia.edu/earth/wtert/sofos/Rodriguez_thesis.pdf>
World Energy Organization (WEO). (2013). Waste to Energy. Retrieved on 21st April, 2015 from < http://www.worldenergy.org/wp-content/uploads/2013/10/WER_2013_7b_Waste_to_Energy.pdf>
Funk, K., Milford, J and Simpkins, T. (2013). Waste Not, Want Not: Analyzing the Economic and Environmental Viability of Waste-to-Energy (WTE) Technology for Site-Specific Optimization of Renewable Energy Options. National Renewable Energy Laboratory (NREL). Retrieved on 21st April, 2015 from < http://www.nrel.gov/docs/fy13osti/52829.pdf>
Renewable Energy Association (REA). (2011). Energy from Waste: A Guide for Decision- Retrieved on 21st April, 2015 from <http://www.r-e-a.net/pdf/energy-from-waste-guide-for-decision-makers.pdf>
Environmental Protection Agency (EPA). 2015. Wastes-Non Hazardous Waste. Municipal Solid Waste. Retrieved on 21st April, 2015 from <http://www.epa.gov/waste/nonhaz/municipal/wte/basic.htm>
