Design for the Environment/Garbage to Energy

This page is part of the Design for the Environment course

Energy from waste is a category of electrical generation facilities that extracts the chemical energy present inside municipal waste and converts it into electricity. Energy from waste facilities reduce human-induced strain on the environment by reducing demand for other dirtier electricity sources, such as coal. Some types of these facilities have the added benefit of reducing the amount of garbage that goes into a landfill.

There are several types of energy from waste facilities, but three common ones are landfill gas, incineration, and gasification. There are examples of all three of these facilities in Canada, and they are generally owned by private industrial companies wishing to profit by selling electricity to the grid. For this comparison, the landfill gas option was represented by EPCOR’s Clover Bar Landfill in Edmonton, Alberta; Algonquin Power’s Energy from Waste incineration facility in Brampton, Ontario; and PLASCO’s gasification facility in Ottawa, Ontario.

Project Information
       Section 1 Group A18 Aziza, Arial Brooks, Jonathan Hoffer, Ronald (Hoffer.ronnie) Lundy, Steven (Steven.lundy)

Highlights and Recommendations:
Landfill gas, incineration, and gasification all generate electrical energy from municipal waste. The landfill gas facility requires a pre-existing landfill, whereas the gasification and incineration facilities can be built anywhere, so long as garbage trucks have access to them.

A comparison of landfill gas, incineration, and gasification on the basis of environmental friendliness showed that gasification is the best option. A streamlined life-cycle analysis (SLCA) implies that landfill gas is the most environmentally friendly option. However, as the scores are similar for all three alternatives, a conclusion as to the best alternative cannot be drawn based on this rough comparison.

A cost analysis shows gasification to be the most economical in terms of capital costs. At $1217.6 per kilowatt of power, the cost of construction per unit power capacity of the plant is lowest for gasification. As all three facilities in this comparison are privately owned and operated, accurate operating cost data is scarce. The available data shows that landfill gas has the lowest operating cost of the three facilities, at $18 per megawatt-hour of energy.

The economic input/output life-cycle analysis (EIOLCA) shows gasification to be the most environmentally friendly energy from waste option. In the categories of toxic releases, greenhouse gas emissions, and air pollutant emissions, gasification creates fewer emissions than the other two options, especially in the implementation phase.

These three alternatives are associated with various societal issues that affect their suitability for installation in different situations. The offensive smell and tremendous land consumption of landfills are negative influences on the overall public opinion of landfill gas, but the actual burning of the gas in a turbine is a well-proven process trusted by the public. Incineration is associated with severe toxic emissions, which would be justified in the event of a failure of the plant’s exhaust scrubbers. Gasification is a less proven technology than landfill gas or incineration, and thus receives increased skepticism from investors and community members alike.

Functional Analysis
Following is a basic description of how each of the three alternatives accomplishes the task of converting garbage into electricity.

Landfill Gas
As trash in a landfill decomposes, it releases a mixture of gases composed 40-60% of methane. The remainder is mostly CO2 with and trace amounts of other non-methane organic compounds (NMOCs). Many areas require by law that these gases be collected and flared to reduce their impact on the environment. Instead of flaring it, the landfill gas (LFG) can be collected, cleaned and used to supplement natural gas in the production of electricity.

To extract the LFG there are vertical perforated pipes throughout the landfill which are attached to a pump or compressor. The gas is pumped to a treatment plant where it is upgraded to a higher quality through a number of processes. It is then transferred to a chamber that extracts malodorus chemicals and then funneled through chambers with chemicals which bind to the CO2.

After it has been treated, the LFG is up to a level where it can be used to supplement a primary supply of natural gas. The gas is burned to fire boilers create steam which is used to drive steam turbines and generate electricity.

Incineration
Incineration is an effective chemical process by which everyday waste is converted into usable energy, supplying electricity to the very municipality that created the waste in the first place. Garbage trucks dump their waste in a storage area known as the tipping floor, from which it can be transported to a large hopper as required. The hopper feeds the waste into the primary combustion chamber with the aid of a transfer ram where it is burned for 6 hours. Throughout the burning process the transfer ram is continuously moving the trash around to ensure that no areas are left unburned. The remaining ash is removed and used for landfill cover, while the combustible gas material is sent to a secondary chamber where it is further combusted. The heat generated by this secondary combustion process is utilized in a boiler to generate the steam used to drive a power-turbine, which in turn generates electricity which can then be both sold/distributed and used internally. The toxic flue gases generated by the process are treated with hydrated lime, powdered activated carbon, and catalytic reactors, before being released into the environment in a much safer form. Obvious advantages to the process are that it essentially takes what is otherwise landfill trash and reduces it to ashes while capturing the energy stored within. Not only does this drastically reduce the waste being dumped in landfills – an issue that is very prominent today because of the required space and environmental concerns due to released toxins – but it also makes use of the otherwise wasted energy inherent to the waste. Disadvantages are that many toxic gases are still being released into the atmosphere as a result of the combustion process, and an incineration facility is extremely expensive to build and maintain.

Gasification
Before processing, the incoming garbage has all bulk metals removed. The remaining garbage is shredded and sent to the refining chamber, where the gasification process takes place. In this chamber, the shredded garbage is subjected to a high heat of 700 degrees Celsius. At this temperature, the garbage volatizes and is changed to a blend of gases. This gas rises to the refining chamber, where it hits a plasma torch, operating at 1200 degrees Celsius. This torch further reduces this gas to a combination of steam, carbon monoxide, and hydrogen, as well as other contaminants. The hydrogen and carbon monoxide, also know as Syngas, is burned in an internal combustion engine generator, which converts the chemical energy of the Syngas to electrical energy. A steam turbine generator uses the heat from combustion to produce more electricity. The remaining solids enter the carbon recovery vessel. In this chamber they are subjected to another plasma torch to drive off the remaining carbon. The result is a solid glass slag. Potable water is another by-product of the reaction. Advantages include diversion of garbage from landfills and the relatively low toxic emissions of the clean-burning Syngas engines. Disadvantages include reliability issues, as this is the newest technology of the three alternatives.

Streamlined Life-cycle Analysis (SLCA)
The Streamlined Life-Cycle Assessment (SLCA) method of evaluating alternatives is designed to give a quick comparative analysis of the environmental impacts of each alternative at each stage in its life. It is a 5*5 matrix in which each cell contains the score for an environmental aspect of one of the five life stages. A score of 0 denotes poor environmental performance, a score of 4 denotes excellent environmental performance, and 1, 2, and 3 are in between. All 25 cells for each alternative are summed, and the higher the total score, the better the environmental performance in relation to the other alternatives.

The biggest advantages of SLCA are its simplicity and the speed with which the analysis can be performed. The simplicity, however, is also a drawback, as is the lack of detail accounted for and the lack of precision afforded by having a scoring scale of only 0-4. Furthermore, placing equal emphasis on each cell in the matrix is rarely realistic. For example, gaseous residues from the Primary Process Operation are orders of magnitude larger than those from Implementation, yet they are both given equal weight in this matrix.

By the SLCA, landfill gas is the environmental leader. However, the SLCA gives only a rough comparison of alternatives, and so if all three alternatives score similarly, as in this case, no conclusion can be drawn as to which alternative is best.

It is worth noting that the Primary Process Operation, Solid Residue cell was somewhat challenging to fill in, particularly for the landfill gas option. Landfill gas does not produce any solid residues intrinsically, because it simply uses what is already in a landfill. Gasification and incineration do have solid by-products, but it is important to consider that these by-products weigh less than the amount of garbage they diverted from the landfill. For this comparison, the garbage in the landfill itself is considered as a solid residue in the complementary process operation, not the primary. This is because most landfill gas plants are built on existing landfills; landfills are usually not built with electricity generation in mind.

Cost Analysis
Cost analysis examines possible options based on the financial impact they generate over the lifespan of each individual life span. For the three garbage to energy options, the direct costs are comprised of the capital costs involved in building the facility, the operating costs required to keep the facility running, and the final disposal cost of the facility.

Capital Costs
The garbage to energy industry is highly privatized. It is therefore very difficult to get accurate or detailed information regarding the financial requirements of a plant. Using estimations of these costs based on available information, an approximate value of the capital costs of each plant was generated, as shown below.

Variable Costs
The variable costs of running one of the described power plants may come from a number of sources. Most notable would be the power required to run the plant itself, the wages of the employees, and transportation of the fuels. For the most part, transportation costs may vary considerably, as the plants may have any location, close to the supply of garbage, or quite far. In the case of the three representative power plants mentioned above, the power plants were close to the city, and the transportation costs were represented in large by the tipping fees required to send the trash there and the amount of trash processed per day. The estimates of the operating costs of the plant are show here.

The financial information available shows that gasification and landfill gas present much cheaper options than incineration

Economic Input / Output Life-cycle Analysis (EIOLCA)
EIOLCA is a quantitative analysis used to estimate the total environmental impact of an option by detailing how much money is spent on the various associated sectors. The EIOLCA tool uses the amount entered and the known output of those sectors to generate a quantitative summary of the total environmental impact of that option. The impact may be in terms of greenhouse gases (metric tons CO2 equivalence MTCO2E), conventional air pollutant emissions (metric tons MT), toxic releases (kilograms kg), or several others.

Implementation
The following information details the environmental impact of the implementation phase of the three garbage to energy options.

As can be seen in the above information, the gasification option generates the  least harmful environmental impact during the implementation phase

Operation
In the case of power plants in general, the major environmental impact is in fact generated in the operations. In this phase the plant burns its fuel to generate the power. The fumes from this burning contain various pollutants. The following information details the stack emissions generated during the operations of the power plants.

Societal Analysis
The environmental impact of an option is not limited to the toxins and greenhouse gases produced during the life span of the plane. The impacts can include noise, odours, land use and safety related issues. These issues may or may not be considered when choosing one of the possible options.

Landfill Gas
The use of landfill gas to produce energy represents the utilization of an utterly detrimental sector to reduce the environmental footprint made by the energy sector and the waste sector. However the use of the gas requires a landfill, which takes up significant amounts of land. The landfill leaches toxins into the soil and emits offensive odours which decrease the desirability of the area as a living area.

Incineration
Incineration addresses the growing concern that municipal waste accumulates and occupies large tracts of land for many years. There is a general concern, however, that the burning of garbage will decrease the air quality in the surrounding community and may pose health issues to people in the immediate area.

Gasification
Gasification is a clean burning process, reducing the amounts of greenhouse gases emitted, and reduces the dependency on dirty fuels such as coal and oil. Furthermore, there are fewer odours emitted by the plant, and the process results in a better air quality than if a dirty fuel had been burned.