Design for the Environment/Converting Garbage to Energy

This page is part of the Design for the Environment course



The accumulation of solid waste is a serious issue as cities continue to grow. Toronto is one such city that has been challenged by this issue. When Toronto closed the Keele Valley Landfill, waste was diverted to a dump in Michigan. Between January and August 2007, approximately 441,363 tonnes of solid waste (which could fill 74 trucks) was sent to the Michigan landfill daily. However, the Michigan dump has given the Toronto Solid Waste Management until 2010 to reroute their garbage to another location. As a result, several options of how to deal with Toronto's trash must be assessed for the client, the Toronto Solid Waste Management. This article focuses on the broad option of converting the garbage into energy as it deals with the issue of solid waste accumulation and provides an additional energy source. The option is divided into three alternatives, a baseline alternative which is using gas generated from landfills and two newer alternatives which are incineration and gasification. Two of these alternatives are currently in place in Toronto. The city recently opened the Green Lane Landfill which could be an adequate source of landfill gas. In addition, the City of Brampton, situated near Toronto, has an incineration facility. There is no gasification facility in Toronto; the nearest facility is an experimental facility located in Ottawa. Each alternative will be compared based on their functional, environmental, cost and social impacts.

Project Information
MIE315, Section 2, Group B15

Khalil Heileman [Heileman]

Micael Tecle   [teclemic]

Animesh Roy [Royanimesh]

Sara Makaremi [Makaremi]

Highlights and Recommendations
In terms of environmental impacts, gasification is the best alternative for dealing with Toronto's solid waste. As indicated by the chart below, the gasification alternative has the strongest results in the EIOLCA and the highest score in the SLCA. However, it should be noted that the SLCA is a subjective analysis and the EIOLCA is based on many assumptions. Gasification is also supported by the fact that it does not have a lot of social controversies surrounding it, unlike incineration. Because of the social controversies, incineration, a more established alternative, meets heavy public resistance. The main issue with gasification is that the technology is relatively new. As a result, there is not a lot of available experience in handling gasification facilities. In addition, gasification is an expensive process and this cost will be carried on to taxpayers. Using landfill gas is another common alternative, however this alternative does little to reduce the large volumes of garbage generated by Toronto. The Toronto Solid Waste Management should continue developing landfill gas technologies at the Green Lane Landfill; however, gasification technology should be researched to make it cheaper.

Functional Analysis
The main function of each alternative is to convert garbage into energy. The energy conversion should be accompanied by a reduction in garbage volume. As each alternative uses different kinds of garbage, for the sake of a simple comparison, only plastics and organics as input garbage will be considered. Organic garbage releases energy in all of the alternatives. Although plastics yield little energy in landfill gas, they are critical for energy yield in incineration and gasification. As a result, the impact of plastics cannot be overlooked. Other garbage streams like metals have no energy yield in all processes, so their effects can be disregarded. Since all of the alternatives are supposed to receive their garbage stream from the city of Toronto, the impacts of collecting garbage will be ignored. Each of the processes are broken down into five life stages: resource provisioning, process implementation, primary process operation, secondary process operation and end of life.

Baseline Alternative: Landfill Gas to Energy

Landfill gas (LFG) is produced upon the anaerobic decomposition of waste buried in the landfill. This process is carried out by anaerobic microorganisms. This gas is primarily composed of methane (CH4) and carbon dioxide (CO2), with trace amounts of other components such as oxygen compounds, sulphur compounds and hydrocarbons. The produced LFG is collected and extracted from vertical gas wells located in the landfill, treated, and subsequently used to generate electricity. The utilization of LFG to generate electricity usually involves the use of either internal combustion engines or steam turbines. The primary advantage of using LFG to generate power lies in the fact that the process makes optimal use of the inevitable presence of landfills. Furthermore, the presence a gas collection system reduces the amount of gas seeping through the landfill and escaping into the atmosphere.

Alternative 1: Incineration

The more recent alternative is using an incinerator where garbage is burned directly to extract energy. The advantage of incineration is that energy can be yielded at the same time as large reductions in garbage volumes are taking place. However, the disadvantages of this process include its output of ashes and toxic chemicals. Bottom and fly ashes, toxic metals such as mercury, acid gases and dioxins are some of the by products of incineration that have high negative impact on the environment as well the public health. . Some of these are highly toxic pollutants, especially dioxin which could cause serious health problems such as cancer, neurological damage, thyroid damage, respiratory issues. It is clear that extreme caution is required to minimize the amount of toxic products from being released in to the atmosphere when using the incineration method. Consequently, the control system for the reduction of toxic products could be undesirably expensive. See chart below for cost analysis of the overall system.

Alternative 2: Gasification

In the final alternative which is the gasification process where carbon-based waste are heated at high temperature (700ºC) and pressure. CO and H2 are removed from the complex blend of gas resulting from the process to produce a fuel gas, called Syngas. To avoid oxidation, this endothermic process is implemented in an oxygen-limited chamber .The process yields three by-products:

1-accumulation of inert solid slag from non-volatile waste which is vitrified to be used in road pavements and asphalt

2-sulphur that can be added to soil

3- heavy metals such as mercury that should be disposed safely in landfill

According to PlascoEnergy of Ottawa, One tonne of garbage results in 150 kg of slag, 5 kg of sulphur and 1.3 kg of heavy metals. It should be noted that chlorine-rich plastics such as PVC cannot be gasified due to their sever emissions. They can be gasified only if the chlorine content is removed. The contaminants emerging from gasification depend on the quality of the equipment and the processing temperature. Oil refining industry uses the hydrogen from Syngas to purify fuels and to enhance heavy crude oil. Conventionally, natural gas was used to provide the required hydrogen. However, the cost of natural gas has been increasing. Therefore, the new technology helps refiners to convert low-value feedstock to valuable hydrogen and to generate power needed for refining infrastructure at the same time.

Streamlined Life Cycle Assessment (SLCA)
The SLCA is a semi-quantitative approach for life cycle assessment of alternatives. It comprises a matrix of 5×5 where each alternative is given a score between 0 (most adverse environmental impact) to 4 (least environmental impact). The total score for each life stage and environmental impact is obtained by adding the corresponding scores in each row and column. The columns are divided into five life stages, that is process implementation, resource provisioning, primary process operation, secondary process operation and end of life. The rows are divided into process inputs (material and energy) and process outputs (gaseous, liquid, solid). The following matrices are created for the SLCA comparison:

 Landfill Gas SLCA Chart

The above table shows that the process implementation stage, which involves the construction of the landfill and power-generating facility, has the most adverse effect on the environment. The primary materials used in the construction of these facilities are concrete, steel, clay, geosynthetics and sand. While none of these materials are toxic, steel production makes use of virgin iron ore as well as energy-intensive furnaces in many of stages. While the process implementation phase of using LFG to generate power can be seen to be energy-intensive, no other feasible alternatives are present.

The overall process of using LFG to generate power received low score in the "Gaseous Residues" sector. This is primarily due to the emissions of sulphur dioxide (SO2), nitrous oxides and volatile organic compounds (VOCs) that can take place during the combustion of LFG.

Incineration SLCA Chart

Gasification SLCA Chart

From the above table it can be predicted that resource provisioning and secondary process (cleaning and filtering) are the life stages with the least environmental impact. This results from the fact that the material input to the process is invaluable waste and the environmental impacts mainly result from collection and haulage activities. In contrast, building the infrastructure for the facility requires construction materials such as steel and cement. Steel production from virgin ore uses energy intensive-furnaces, while production of one tonne of cement releases one tonne of CO2. Also, the mechanical devices such as turbines and torches in the facility are manufactured from metal alloys. Therefore, the process implementation requires a higher material and energy input compared to the other life stages.

Cost Analysis
The cost analysis presents a method to compare the costs of each alternative at different life stages. The analysis also provides economic information that can be input into the EIOLCA model software available at http://www.eiolca.net/. The EIOLCA will be discussed in the following section. Some of the dollar values in the cost analysis are converted to their $1997 equivalent using the inflation calculator.

Landfill Gas Cost Analysis

The above table lists the capital and annual costs associated with constructing and subsequently operating and maintaing a landfill with a power generation facility. It should be noted that the entire project spans 40 years. The initial 20 years involves filling up the landfill to its capacity and subsequently closing it. The next 20 years involves generating power from the closed landfill using the LFG generated from it. Although the entire project spans 40 years, the annual costs for “Process Implementation” and “Primary and Secondary Processes” can be compounded into a single 20-year period while constructing the EIOLCA model. This is because they are each applied over a period of 20 years, and their periods of implementation do not overlap.

Incineration Cost Analysis

The above financial analysis was directly obtained from a report performed for the new incineration site that is being considered to be constructed in the Durham/York region, Ontario. Assumptions made by the report on cost analysis include:
 * The facility would operate at a capacity level of 140,000 tonnes per year
 * EU stands for European Union standard. The EU standard table including the
 * Since this is just a proposal report, the analysis done by the experts was for worst case scenarios.
 * The life span is assumed to be 20 years.
 * The energy output is assumed at 14MW capacity

Gasification Cost Analysis

The following table summarizes the cost analysis of a 56 MW integrated biomass gasification combined cycle power plant.

The above values are obtained by assuming that 140,000 tonnes of garbage is processed by gasification annually. For the resource provisioning stage, it should be noted that waste transportation cost strongly depends on the location of the plant. If the plant is far from the municipality, where the garbage is collected, more energy will be required to transport the garbage. From above values it can be concluded that the primary process has the highest cost among the life stages. The complexity of gasification process that requires the integrity of several operating processes and the cost of electricity to run electric heaters, turbines, steam cycles, etc result in its high operating cost. Moreover, depending on the input waste to the system, some mechanical pre-processing of the feedstock is required after the recyclable materials and metals and inerts are removed. Coarse shredding, fine shredding, sorting and elaborate front-end processing are a few examples .This complexity requires high capital investment. As a consequence, its application was previously focused only on destroying hazardous waste.

Economic Input Output Life Cylce Assessment (EIOLCA)
The EIOLCA is used to obtain quantitative information about environmental impacts of the process life stages. The United States Department of Commerce has divided the American economy into hundreds of economic sectors. Of these sectors, the ones that are inputs in the different life stages of each alternative process are analyzed. These inputs are measured in dollars and the dollar values are input into a software available at http://www.eiolca.net/. Since the software is based on information available in 1997, all dollar values must be converted to 1997 dollars. The software then outputs values of the input sector contribution to the environmental impacts. The impacts highlighted in this EIOLCA are global warming potential (GWP) measured in metric tons of CO2 equivalents, conventional pollutants (CO, NOx, SO2, VOC and PM10) in metric tons, energy use in terajoules and toxic releases in kgs. The inputs made for the EIOLCA model are all annual expenditures. Capital costs are taken into account by being equally distributed over the predicted lifespan of the process.

Landfill Gas



For the gasification process, the GWP chart obtained from EIO-LCA reveals that the contribution of resource provisioning to the global warming is 50%. This could be predicted from the fact that waste haulage is the main activity in resource provisioning stage. At this stage truck transportation contributes to high CO emissions; as it is depicted in the conventional pollutants graph. The truck usage also explains why the resource provisioning stage of gasification has the highest energy use. High emissions of CO can lead to global warming. In contrast to resource provisioning, process implementation and primary process have negligible conventional pollutant emissions. The primary process has the highest toxic air releases from the conversion of garbage into syngas.

Societal Analysis
Baseline: Landfill Gas

A portion of society has concerns about noise, odours and low aesthetic appeal of landfills. Because of the effects of landfills, few people want to live near one. As a result, issues between the landfill and neighboring communities arise often.

Alternative 1: Incineration

There has been strong public opposition for the incineration facility proposed for Durnham region near Toronto due to its highly contaminating process. In fact, about 43 doctors and many citizens have signed a petition to express their opposition on the proposed construction of the facility. They are skeptical about the proposed control system of the facility that would supposedly minimize toxic releases. . The resistance to the proposed Durnham incinerator demonstrates that many inhabitants of Toronto are not willing to accept incineration as a solution to Toronto's garbage problem.

Alternative 2: Gasification

Gasification may lead to societal concerns due to litter, dust and noise that mostly result from the haulage activities.