Peer-Reviewed Feature Article

By Tej Gidda, Tanya Bogoslowski, Duncan Millar, and Frederick A. Mosher

In the current global environment, a significant amount of attention is focused on the effect of man-made greenhouse gas (GHG) emissions on the phenomenon of climate change, as is evidenced by the burgeoning carbon market. The main regulating body that stipulates caps on emission levels from countries is the Kyoto Protocol, which the majority of participating countries have ratified (the United States being the key exception). Australia was the last major emitter to ratify the protocol, in December 2007. The implementation body for the Kyoto Protocol is the United Nations Framework Convention on Climate Change (UNFCCC; http://cdm.unfccc.int/index.html), which regulates the “trade” of emission reductions between countries. Other mechanisms exist at local levels throughout the world, with varying levels of compatibility with each other or the UNFCCC mechanisms. The proliferation of local, voluntary trading mechanisms, while providing a challenge from overall synchronization of carbon trade, further speaks to the arrival of the carbon market.

The Kyoto Protocol itself outlines emission reduction commitments. For example, Canada is required to reduce emissions to 6% below 1990 levels (http://unfccc.int/kyoto_protocol/background/items/3145.php). The United States also has a target (7% below 1990 levels) but has not ratified the protocol and thus is not obligated to meet this figure. It should be noted that even countries who have ratified the protocol are not necessarily in compliance or approaching compliance. Canada, for example, as of 2005, was approximately 25.3% above 1990 levels (http://www.ec.gc.ca/pdb/ghg/inventory_report/2005/2005summary_e.cfm), leaving a significant gap between actual emissions and Kyoto obligations.

The Clean Development Mechanism (CDM) is the UNFCCC instrument that establishes the rule base for transfer of emissions reductions achieved in developing countries to developed countries that have emission reduction targets. As of the end of January 2008, approximately 20% of all registered GHG projects at the CDM level involve the waste sector (http://cdm.unfccc.int/Statistics/index.html); more than a quarter of these projects are related to landfill gas (LFG) and account for the majority of the expected emissions reductions from the waste sector. The basic theory behind LFG systems for the reduction of GHG emissions is simple: The methane component of LFG is combusted in a flare or utilization technology, thereby preventing the emission of methane to the atmosphere (methane has approximately 21 times the global warming potential of carbon dioxide (http://cdm.unfccc.int/methodologies/PAmethodologies/approved.html). Quantifying the amount of methane combusted is relatively simple, requiring metering of landfill gas composition and flow rate, as well as some assumptions or measurements regarding the combustion efficiency of the flare or gas engine.

However, there are other considerations when dealing with the total life cycle analysis of an LFG system. For example, energy is required for the fabrication of the combustion technology, for the development of the LFG well field (including drilling activities), the supply of electricity to the blowers drawing the LFG from the waste, the production of piping and external equipment, and the transportation of all elements to the site. Energy consumption, manufacturing activities, and development of the site are all activities that have an associated GHG impact. The level of analysis of these steps required in a given reporting system varies according to the mechanism. For example, at the UNFCCC level, none of the greenhouse gas emissions associated with well field development are included in the assessment of total emissions reductions. When including an LFG utilization component, there is a further carbon footprint associated with the construction activities and materials, as well as a more complex dynamic from the standpoint of producing renewable electricity.

In this paper, the LFG emissions from a conceptual landfill in Ontario will be described and compared to the net emissions resulting from the construction of a LFG collection system and the emission reductions from the combustion of methane. This comparison provides information about the net effect of implementing LFG collection systems compared to allowing the LFG to vent to the atmosphere and provides a case study of an in-depth examination of net greenhouse gas emissions and reductions. The installation and operation of a LFG utilization project has also been considered in the analysis to demonstrate the relative benefits of producing renewable electricity. Finally, the implementation of the LFG utilization plant will be compared against wind power on an equal basis in order to compare the relative greenhouse gas benefits.

Methodology
This section outlines the basic assumptions behind the GHG assessment by describing the principles behind the analysis and identifying the key variables and input parameters utilized. There are many factors involved in the overall analysis of renewable energy generation, including the regulatory and economic environment and the other drivers involved; however, for purposes of this assessment, only the GHG benefits and costs associated with LFG flaring and utilization are considered.

The basic conceptual design of the flare and utilization facility was based on a conceptual system at a mid-sized landfill in Ontario, Canada. There are a number of such facilities in Ontario and the basic parameters and sizing have been derived from in-house data regarding construction and operation of numerous installations. For simplification of calculations, it has been assumed that a utilization facility and flare having precisely the same landfill gas consumption will be installed at the site. While this is not likely to reflect reality, the GHG costs and benefits realized from flaring and utilization systems conceptualized in this manner can be compared without normalizing for system capacities. Additionally, no changing capacities have been applied to the total landfill gas available for recovery and flaring or utilization: This creates a situation that could be best represented by a site that generates far in excess of the amount of LFG required for combustion and that maintains high levels of generation for a long period of time. The relative effect of changes in gas availability will not substantially alter the numerical analysis, as each scenario is treated in the same way.

GHG Quantification Approach
The overall assumption and conceptual design basis for the system assumes that 1,200 cubic feet per minute of LFG is received by the flare and utilization facility. It has been assumed that 1,200 cubic feet per minute is available at the site for 20 years total. This timeline has been assumed because of the availability of Ontario government-issued renewable energy electricity purchase contracts that are valid over a 20-year time frame (of note, the price for this electricity purchase is 11 cents per kilowatt-hour, with an escalator clause for inflation). The availability of such contracts has greatly increased the feasibility of and interest in LFG utilization in Ontario. The basic size of the LFG flare/utilization facility has been set at 1,200 cubic feet per minute to represent the approximate amount of LFG (at 50% methane) that would be required to run three Caterpillar G3516 LFG engines, each outputting 925 kW gross.

For comparison purposes, it has been assumed that the flare and utilization facility run over the same basic period. A flaring-only simulation has been created. The utilization simulation uses the basic carbon footprint of the flaring and well field development for the flaring-only simulation. Conceptually, this assumes that a LFG collection well field and backup flare would have to be available for the utilization facility, and adds the utilization facility and electricity generation components to the analysis.

LFG Combustion
Estimation of GHG emission reductions from the combustion of LFG (in either a flare or LFG engine) is relatively straightforward. The total amount of LFG is metered, the methane composition, typically obtained through a gas analyzer, is assessed, and the total volumetric flow of methane to the combustion device is assessed. The volumetric flow is then converted to a mass flow through definition of a methane density, typically set at a standard temperature and pressure through use of a mass compensated flow meter. The total mass of methane is then corrected for the combustion efficiency of the flare or engine, and the resulting mass is multiplied by a global warming potential (GWP) for methane of 21. There is some variance in this latter number, but this is the accepted parameter at the UNFCCC stage, and represents the greater ability of methane to contribute to global warming as compared to carbon dioxide. The conversion is necessary because the standard unit of greenhouse gas emission measurement globally is on the basis of tonnes of carbon dioxide. Where a gas such as methane is corrected to carbon dioxide equivalents, the denotation utilized is generally eCO₂ (equivalent metric tonnes of carbon dioxide), and this is the basic unit traded as a greenhouse gas credit.

While the emission reductions from combusting LFG are relatively simple to calculate, the corresponding emissions created by implementing the LFG collection well field, flare, and utilization facility require a more complex overall analysis and a number of different emission factors. It is important to note that not every conceivable GHG factor has been quantified in this approach, but the majority of the key variables have been assessed and it is expected that the overall conclusions provide a realistic description of the overall carbon footprint. Further refinement of the factors and amounts, or inclusion of additional factors, is not expected to significantly alter the conclusions. However, in order to account for other potential greenhouse gas effects, a factor increase has been applied to the construction materials and activity basis for the development of the flaring and utilization facility. In the former case, an additional 10% load has been added to account for additional factors; in the latter case, an additional 25% load has been added. These factors ensure that the overall greenhouse gas consequences of constructing the facilities are assessed on a conservative basis. The basic approach is herein outlined.

	Table 1

Construction Materials
The overall construction of an LFG well field has a number of materials involved, such as HDPE piping and well chambers, concrete for condensate chambers, use of sand and granular for bedding, manufacturing of key equipment such as blowers, flares, and LFG engines, and ancillary construction materials for the flaring pad and utilization facility. The manufacturing of these components each has an individual carbon footprint due to the extraction of the basic materials and the energy required during the manufacturing process. Where possible, the amount of specific material used in construction (steel, concrete, wood, granular, sand, etc.) has been calculated or estimated and a specific carbon emission factor has been applied. Table 1 provides a list of emission factors carried for the manufacturing of the construction materials. Carbon emission factors are generally presented in tonnes of eCO₂ per tonne of material used. There are a number of sources of carbon emission factors, including the Intergovernmental Panel on Climate Change, the UNFCCC, and Natural Resources Canada (http://www.nrcan.gc.ca/com/index-eng.php); a combination of emission factors have been utilized in this study to represent the carbon footprint of the different materials used.

Where more complex equipment is employed (LFG engines, blowers, electrical components), a simplifying assumption has been made. The weight of equipment has been used in conjunction with the primary construction material (such as steel or aluminum) and a total quantity of material has been subjected to the appropriate material emission factor.

A further important factor is the transportation of all materials to the site. As most of the materials are available locally, the transportation distances have been assumed to be low. The net calculations involve assessment of the type of vehicle that will be involved in transporting materials, and the type and estimated amount of fuel utilized (generally diesel). The use of diesel fuel in transportation vehicles has a corresponding GHG emission calculated through assessing a diesel-fuel intensity figure. This calculation essentially estimates the amount of carbon dioxide produced and emitted by combusting diesel. A further factor is added to this value to account for the upstream carbon dioxide intensity of manufacturing diesel fuel.

For purposes of these calculations, it has been assumed that all system components are available within a 200-kilometer radius (200 kilometers has been applied for all applicable distances). The only exception is the main equipment in the utilization facility such as the LFG engines, which have been assumed to travel 1,000 kilometers to reach the site. The emission factor assumed for the diesel fuel production and consumption involved in the transportation of construction materials is provided in Table 2.

	Table 2

Construction Activities
During the actual construction of the well field and flaring/utilization facilities, a number of pieces of heavy equipment will be employed at the site. These include cranes, drill rigs, backhoes, bobcats, etc. Generally, each of these pieces of equipment utilizes diesel fuel for operation and thus the same basic calculations as employed in estimating transportation costs of materials are applied. In this case, the total estimated use of individual pieces of equipment is balanced against typical fuel consumption, and the diesel fuel combustion and upstream manufacturing factors are applied. Emission factors for the production and combustion of diesel are provided in Table 2.

	Table3

Electricity Consumption and Generation
The flaring-only facility includes electricity consumption for the LFG blower and ancillary equipment. The utilization facility has similar consumption of electricity for operation of the mechanical and electrical systems but also has a net production of electricity. The use of electricity to power systems has a corresponding greenhouse gas emission because the production of electricity has a carbon footprint. For example, consumption of electricity in a region highly dependent on coal for generation has a high carbon footprint (generally expressed as tonnes of eCO₂ per megawatt-hour). Where a large portion of the electricity generation grid is supplied by hydroelectric or nuclear power, the carbon footprint is low because these generation sources do not produce mass emission of carbon dioxide. In either case, there is an upstream effect of transporting fuel to these generation facilities and constructing the physical works. Both direct emission from the plants and the upstream effects have been added to assess a total electrical generation carbon footprint in tonnes of eCO₂ per megawatt-hour. Table 3 provides a percentage breakdown of the fuel production sources in Ontario, as well as the emission factor for the fuel production and transportation for electricity generation and the emission factor for electricity consumption in Ontario.

In Ontario, the primary forms of electricity are nuclear and hydroelectric, with some coal and renewable generation. As a result, the resulting electricity-based emission factor is relatively low. This has a twofold effect. First, the cost of using electricity to power systems at the conceptual LFG flaring/utilization facility is relatively low from a GHG standpoint. However, the value of electricity produced by the utilization facility is also low, under assumption that the renewable electricity generated by LFG utilization will offset the “dirtier” electricity associated with the local grid. The relative effects of electricity vary from region to region according to the local grid parameters.

For the purposes of this analysis, it has been assumed that the flaring-only simulation derives electricity from the grid. In the case of the utilization facility, the facility draws electricity from the grid to satisfy its internal demands (parasitics) and then exports its net electricity to the grid to offset the general grid-distributed supply.

Maintenance and Decommissioning
As noted above, the total time frame under consideration is 20 years. As a result, the basic analysis is concerned with more than simply the construction and implementation activities associated with the plants. The electrical consumption for operation of the systems is discussed above. In addition to this, assumptions have been made relative to maintenance of the flaring and utilization systems. In the former case, an assumption has been made primarily related to the LFG-collection well field. Specifically, on a yearly basis, two wells are replaced, requiring additional materials and drilling activities that produce a specific carbon consequence. In the case of the utilization facility, oil changes for the LFG engines have been estimated and balanced against oil production emission factors. Additionally, the mass loss of oil in the combustion engines has been calculated based on real data and the combustion intensity for oil has been assessed accordingly.

Additional factors relating to decommissioning of the systems after the 20-year project cycle have also been assumed. In reality, it is not likely that an LFG collection field would be decommissioned after 20 years, but to provide an equitable basis for comparison, this has been assumed. The assumption may be more valid for the utilization facility following the termination of the power sales agreement, although it is expected that the facility would have a longer usable lifespan than 20 years. For purposes of this assessment, it has been assumed that the total diesel fuel required for decommissioning is 10% of that used during construction activities for the flaring system and 25% of that used during construction of the utilization facility. Additionally, assumptions have been made regarding transportation of the system components to a recycling or disposal center. For purposes of this discussion, it has been assumed that components are not transported more than 200 kilometers.

Critical Input Variables
All input parameters to the overall GHG assessment have been based on actual materials utilized during the construction of an actual landfill gas flaring and utilization facility in Ontario. The emission factors balanced against the material usage have been taken from a Natural Resources Canada database of compiled factors. The attached tables portray the relevant input parameters.

The following sections will present the results of the above analysis as well as comparison between the different scenarios and some indication of the breakdown according to the overall carbon footprint. Refer to Table 4 for a summary table of the results.

LFG Collection and Flaring
The total greenhouse gas footprint for the LFG collection and flaring construction and operation are as follows. The total construction activities for the well field and flaring compound result in emissions of 544 tonnes of eCO₂. Approximately 65% of this total relates to material manufacturing and transportation (transportation accounts for approximately 7% of this subtotal). The remaining 35% corresponds to the installation activities related to development of the field and the flaring pad (including such activities as grading and site preparation).

Ongoing operation costs for the flaring facility produce 50 tonnes of eCO₂ per year (approximately 9% of the total emission created during construction). This is composed of electricity usage for the blower and equipment (94% of total), with the balance generated by replacement of two wells on a yearly basis.

In comparison, the total emission reductions achieved by the 1,200-cubic-feet-per-minute flare are quite large. The year-to-year emission reduction is 108,069 tonnes of eCO₂ for a net yearly benefit of 107,503 tonnes of eCO₂ in year 1 (lower because of construction activities), and 108,019 tonnes of eCO₂ for all other years with the exception of year 20, when decommissioning activities reduce the emission reduction to 107,995 tonnes of eCO₂.

Compared to the total amount of emission reductions achieved, the GHG consequences of constructing and operating the flaring facility are very small. On a 20-year basis, the total emissions from the project are 1,541 tonnes of eCO₂, or less than 0.1% of the emission reductions achieved. The overall payback (balancing construction costs versus emissions reduced) in terms of GHG accounting is less than one week. Clearly, the relative value of implementing LFG-flaring systems from a greenhouse gas perspective is extremely high.

The above results suggest that the relative value of LFG collection and flaring systems will be similarly positive despite the size of the landfill. Based on the results, a LFG system at even small landfills will generate a net positive benefit in terms of emission reductions.

Landfill Gas Collection and Utilization
As indicated above, the basic calculations for the LFG utilization system take into account the construction of the well field (to supply the utilization facility) and the flare (as backup to the facility).

The total utilization facility-only costs of construction equal 2,396 tonnes of eCO₂; these include the contribution of the well field and flare, which are specified above. Of the utilization-only contributions, approximately 5% of the total GHG cost relates to installation of the works, with the balance attributed to materials manufacturing and transportation to the site.

The ongoing operating costs of the utilization facility produce 465 tonnes of eCO₂; this value includes the maintenance related to the well field and the utilization facility and additionally includes the electricity consumption required for operation of the plant. It has been assumed that the utilization facility operates at 95% uptime and that the parasitic consumption of electricity is approximately 5% of the gross output; the net output of the plant is 2,636 kW from the three LFG engines.

The GHG benefit of producing this electricity in Ontario (i.e., displacing the grid electricity supply) is 6,711 tonnes of eCO₂ on an annual basis for a total of 134,238 tonnes of eCO₂ over the 20-year duration of the contract. Note that the combustion-related emissions reductions are unchanged from the flaring-only scenario, under assumption that 1,200 cubic feet per minute of LFG is being combusted in the plant. Total year-to-year emission reductions from the utilization facility are 114,781 tonnes of eCO₂ with the exception of year 1 (construction activities) and year 20 (decommissioning).

Of note, the GHG benefits provided by electricity generation are just under 6% of the total emission reductions. This essentially identifies that the direct combustion of methane is the primary benefit from implementing this system. In part, this is due to the high global warming potential of methane and, in this case, the relatively low grid-emission factor in Ontario. The split between direct emission and electrical offset GHG benefits will, of course, change according to the jurisdiction. Where the primary mechanism of electrical generation is coal, a grid emission intensity of approximately 1,000 kilograms of carbon dioxide per megawatt-hour produced is reasonable. At this level, the total electrical offset emission reductions on a year-to-year basis are closer to 130,000 tonnes of eCO₂; electrical offset benefits increase to 23,000 tonnes of eCO₂ per year, or approximately 18% of the total. It is expected that the total electrical offsets available from LFG utilization will under no circumstances be higher than 20% of the total (direct emission plus offsets) but could potentially be lower than the 6% calculated in this study for jurisdictions with smaller contributions from coal-fired electrical generation.

As further perspective on the overall results, the relative cost of constructing and operating the utilization facility is less than 9% of the total electrical offsets produced over 20 years; as a function of the total emission reductions, the cost of the utilization facility is about 0.5%. In comparison to the flaring-only scenario, the total cost-benefit analysis for the individual systems results in approximately the same net benefit. Over 20 years, the flaring only scenario equates to net 2.16 million tonnes of eCO₂ in emission reductions, while the utilization facility equates to 2.28 million tonnes of eCO₂.

To put the above numbers into a different perspective, the average emission of GHG from cars, on average, is 5 tonnes of eCO₂ per car per year. The conceptual utilization facility indicated above therefore reduces the equivalent of approximately 23,000 cars worth of carbon-dioxide emission every year.

In either the flaring or the utilization case, the paybacks and overall benefits from a GHG standpoint are extremely high. For the GHG investment, the emission reductions achieved are significant. Again, the primary benefit is from direct combustion of the methane component of LFG, but the electrical production benefit begins to increase as the emission factor of the electrical grid increases.

Comparisons to Wind Power
Of particular interest is the comparison of an LFG-utilization facility to another renewable energy, wind power. Each energy source has its corresponding GHG benefits and costs. It should be apparent based on the above analysis that a wind farm providing the same quantity of electricity to the grid as a utilization facility will show a strong bias in favor of the utilization facility given the added and significant contributions of methane destruction. This comparison will be reinforced in this section.

First, a utilization facility and wind farm producing 2,363 kW of net electricity over a 20-year time frame will each produce a net emission reduction of 134,238 tonnes of eCO₂ in Ontario, as both technologies provide the same basic benefit from an emissions avoidance standpoint. Of note, to provide this quantity of electricity, a wind farm would need to be developed that included 26 windmills, each of 0.5 MW in gross production and with an average uptime of 20%. Of immediate benefit, the utilization facility will have a greater steady state delivery of electricity to the local grid, with uptimes of 95% and above.

The GHG costs of producing this electricity at the LFG utilization facility have been discussed in the above sections. The relative cost of producing wind power over a 20-year time frame is anywhere from 7 to 20 kilograms of carbon dioxide per megawatt-hour (http://www.woodlawnwind.com.au/_PDF/_Sections/19.pdf), or between 2.5% and 6.8% of the total emission reductions produced by the electricity generated. Strictly considering electricity generation greenhouse gas benefits from the utilization facility, the equivalent number is about 9%; however, this does not take into account the total emission reductions achieved by combusting substantial quantities of methane.

The total emission reductions from the utilization facility are 2.28 million eCO₂ over 20 years. The conceptual wind farm would total 134,238 tonnes of eCO₂ over 20 years. In other words, it would require a wind farm comprising 480 windmills (0.5 MW each; 20% uptime), generating 48 MW of net electricity to equal the GHG reductions achieved by the LFG utilization facility over a 20-year period. At best (under assumption of a grid-intensity factor of 1,000 kilograms of eCO₂ per megawatt-hour), it would require a wind farm of approximately 150 windmills generating 15 MW of net electricity to equate the greenhouse gas value of the LFG utilization facility.

Conclusions
Generally, the value of LFG combustion at a landfill is high from a GHG standpoint. In the current environment of emissions trading and carbon exchange, the immediate financial advantage of such systems is clear. A life cycle analysis of GHG emissions and emission reductions, taking into account the carbon footprint of constructing and operating LFG flaring and utilization systems serves to further reinforce the overall value. The approximate greenhouse gas costs relative to the emissions reductions over a 20-year period for the conceptual LFG utilization system are less than 1%. The majority of the greenhouse gas benefit (greater than 90%) is derived from the combustion of the methane component of LFG, but the relative percentage can be expected to change according to the location of the facility and the dominant electrical generation in the local grid. A comparison against wind power highlights a fairly intuitive assertion, namely that on a net electrical output basis, an LFG-utilization facility provides far greater GHG reductions because of the methane destruction component.

References
The emission factors utilized in this study have been taken from a Natural Resources Canada database. The material amounts have been calculated from construction drawings and specifications related to in-house databases of projects that have been constructed and scaled as necessary to fit the conceptual project.

Tej Gidda, PhD, P.Eng; Tanya Bogoslowski; Duncan Millar, P.Eng; and Frederick A. Mosher, P. Eng. are employed by Conestoga-Rovers and Associates in Waterloo, ON.

MSW - May/June 2008

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