Note: Descriptions are shown in the official language in which they were submitted.
METHOD FOR QUANTIFYING FUGITIVE METHANE EMISSIONS RATE USING
SURFACE METHANE CONCENTRATION
RELATED APPLICATIONS: NONE
BACKGROUND OF INVENTION
1. Field of Invention
This invention relates generally to methods for measurement and estimation of
fugitive methane
emission rates from the surface of a landfill or any other source of fugitive
methane emission
specifically using concentration of fugitive methane near the surface of the
emitting source.
2. Description of the Related Art
Landfill gas (LFG) is a by-product of natural decomposition of organic
materials in landfills that
can create unsafe air quality, health issues, unpleasant odours, and
contribute to global climate
change. LFG predominantly consists of methane (CH4) and carbon dioxide (CO2);
both being
potent greenhouse gases (GHG). While CO2 produced in the waste sector (e.g.
municipal landfills,
wastewater treatment plants, and burning of non-fossil fuel waste) is not
accounted for as a GHG
due to its biogenic origin, the fugitive emission of CH4 from landfills is of
significant concern
(IPCC, 2006) in terms of global warming potential (GWP). Methane is a
naturally occurring GHG
with a GWP 28 to 34 times greater than carbon dioxide over a 100-year
timeframe (IPCC, 2013).
In Canada, about 3% of the 2010 national GHG emissions were reported to be
from the waste
sector, of which about 91% was attributed to fugitive methane emissions from
landfills
(Environment Canada. 2012).
Methane is an important GHG with a much shorter atmospheric lifetime,
approximately 10 years,
in comparison with other greenhouse gases (Bogner and Matthews, 2003).
Accordingly, changes
made to CH4 emission sources can affect the atmospheric concentrations on
relatively shorter
timescales.
Attention to methane emissions from landfills has grown significantly due to
the fact that emission
reduction from landfills is amongst the most feasible and cost-effective
measures to reduce
greenhouse gas emissions (Kormi et al, 2018). However, quantifying landfill
fugitive methane
emissions is challenging due to the high temporal variability and spatial
heterogeneity. Thus,
development of reliable and cost-effective methods for measurements of
landfill methane
emissions is critically important.
Various methods have been attempted by scientists and practitioners over the
past few decades.
The most widely method seemingly more favorable for the purpose of regulatory
compliance
assessment is the use of flux chamber which directly measures methane emission
flux from the
surface of landfills. In addition to chamber methods, other methods including
but not limited to
eddy covariance and co-advected proxy tracer plume measurements and methods
relying on
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remote sensing and plume mapping have been used (Gardiner et al., 2017; Detre
etal., 2018; Kormi
et al., 2017; Goldsmith et al., 2012; Gollapalli et al., 2018; Monster et al.,
2014; Innocenti et al.,
2017; Delkash et al., 2016; Allen et al., 2018). Chamber-based measurements
are relatively easy
to conduct as emissions can be estimated from the rate of change of CH4
concentration in a
chamber, the footprint area of the chamber and volume of the chamber. However,
the chamber
method suffers practical drawback due to the typically heterogeneous nature of
the landfill
resulting in high spatial variability of emissions (Riddick etal., 2018).
Eddy covariance (EC) methods have also been studied for methane emission
estimation from
landfills over longer periods of time, Xu etal. (2014). Eddy covariance which
calculates a gas flux
from the covariance between vertical wind speed and gas concentration at a
high sampling rate has
the main advantages of providing mean flux estimates over a larger area and
being automated. The
drawbacks however are that the emission in the fetch needs to be homogeneous
and that the
measurement needs to be carried out on a topographically flat surface to
obtain meaningful results
(Riddick et al., 2018).
Using acetylene as the tracer gas is the current state of the art tracer gas
dispersion measurements
for determining methane emissions from landfills. Measurements of the tracer
gas and methane
concentrations are made downwind of the source (Monster etal. 2015). The
tracer gas dispersion
technique relies on the assumption that full mixing between the tracer and
landfill plume has
occurred at the point of monitoring (Rees-White et al., 2018). A key
logistical limitation of the
tracer release method is that it requires a mobile measurement team to
coordinate with the person
releasing the gas and then traverse an accessible road perpendicular to the
landfill plume in the
time it takes for the plume to travel from the release site. Furthermore, it
should be ensured that
the tracer gas is well mixed with the landfill methane as insufficiently mixed
plumes can invalidate
the co-advection assumption, result in large uncertainties in the emission
estimate (Riddick et al.,
2018).
Additionally, the relationship between the emission rate and the gas
concentration at a given
location is dependent on the meteorological conditions and local topography,
preventing accurate
quantification of the emission rate.
Remote sensing techniques represent a more integrated approach for
quantification of methane
flux. These techniques have gained popularity in recent years. One of these
techniques is the Radial
Plume Mapping (RPM) methodology recognized by the US-EPA as "other test method
10 (OTM-
10)" since July 2006 (USEPA, 2006). This technique uses optical remote sensing
(ORS)
instrumentation to characterize gas emissions from non-point sources. Some of
these ORS
instruments include; (i) Open-Path Fourier Transform Infrared (OP-FTIR)
spectroscopy, (ii)
Ultraviolet Differential Absorption Spectroscopy (UV-DOAS), and (iii) Open-
Path Tunable Diode
Laser Absorption Spectroscopy (OP-TDLAS) (USEPA, 2007).
The RPM techniques carry many advantages over the "close range measurement"
methodologies,
such as the flux chamber technique. However, the relatively high cost of the
RPM method, as well
as the uncertainties associated with the possible effect of the methane plume
buoyancy on the
results, made the flux chamber methodology a more suitable option for the
present invention.
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Prior to the applicant's invention, no methods were known to utilize a
relationship between surface
concentration of fugitive methane from a landfill surface and the emission
rate of methane typically
or as an accepted standard method measured using flux chamber. More
specifically, prior to this
invention, a correlation between the concentration of fugitive surface
concentration of methane
and methane flux or emission rate that can be generalized to other typically
similar landfills, only
through adjustment of barometric pressure has not been developed.
Several embodiments of the present invention relate to a methodology using
which fugitive
methane emission can be characterized and quantified for further applications
such as reporting
methane emissions for regulatory purposes, evaluating performance of landfill
bio-covers and
identifying hotspots in terms of methane emission.
SUMMARY
In accordance with several embodiments of the invention, a method wherein the
fugitive methane
emission rate is calculated based on surface concentration of fugitive methane
measured using
surface scanning.
In one embodiment of the method in accordance with this invention, this method
is based upon a
strong correlation developed between landfill surface methane concentration
(SMC, part per
million volume (ppmv) CHO and methane emission rate (MER, g CH4/m2/d).
In one embodiment, landfill is a confined or semi-confined space wherein
different types of waste
materials are disposed of following a standard procedure prescribed by local,
regional, national or
international authorities and regulatory bodies.
In a preferred embodiment, landfill as defined above, receives municipal solid
waste that includes
organic materials which can decompose and generate methane.
In one embodiment, the landfill is equipped with a cover or a cap through
which fugitive methane
generated as a result of anaerobic decomposition of organic material inside
the landfill is emitted
to the atmosphere.
In one embodiment, the landfill is equipped with landfill gas collection
system through which all
gases including methane generated within the body of landfill excluding the
portion emitted
fugitively into the atmosphere are collected for further processing.
In one embodiment, the cap over the landfill will be made of layers of
different earthen or synthetic
materials aimed at reducing fugitive methane emission.
In preferred embodiment, quantification of fugitive emission is critically
important to quantify the
landfill contribution to overall greenhouse gas emission and climate change.
In one embodiment, the landfill is divided into several zones. In preferred
embodiment, the zones
are selected based on geometry, type of cover, type or status of vegetation
including but not limited
to healthy and stressed, other visual observation, expected emission levels
and pre-sampling results
if such results are available.
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In preferred embodiment, measurement of surface methane concentration (SMC) is
completed
through a modified version of an existing protocol for qualitative assessment
of emissions from
municipal landfills established by the United States Environmental Protection
Agency (US EPA)
(Title 40 CFR Pat 60, Standards of Performance for Municipal Solid Waste
Landfills).
In preferred embodiment, SMC values are adjusted accounting for effects of
barometric pressure
rate of change during sampling campaign.
In one embodiment, adjusted SMC data are integrated for each measurement zone
to calculate an
average adjusted SMC for each zone.
In preferred embodiment, the adjusted average SMC in each zone is correlated
with the average
methane flux measured within each zone based on standard protocols available
including but not
limited to the Flux Chamber method.
In preferred embodiment, the resulting correlation in form of an equation can
be used under a
variety of methane emitting surfaces such as landfills, to calculate methane
emission rate solely
based on surface methane concentration requiring none, minimum or limited
number of emission
rate measurements through methods such as flux chamber.
In preferred embodiment, the method presented in this invention can be used in
a variety of
landfills where methane emission rate is to be reported.
The preferred embodiment relies solely on significantly cost effective and
less time-consuming
measurement of surface methane concentration as an advantage to the existing
methods such as
using flux chambers for methane emission rate measurement.
The one embodiment, the equation can be recalibrated and/or validated for a
new methane emitting
site or a methane emitting site with significantly different surficial
features through additional yet
limited number of flux chamber measurement data points.
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DETAILED DESCRIPTION OF THE INVENTION
A unique approach was developed under this research allowing for
quantification of the fugitive
methane emissions rate (MER) from the entirety of a given landfill surface
area at a considerably
lower cost in comparison with the conventional methods. The core of the
proposed method is to
use measured surface methane concentration (SMC) data obtained through surface
scan by
handheld devices such as a portable flame ionization detector (FID). The
correlation between SMC
data and MER values was developed based on representative emission rate values
measured using
flux chamber technique and adjustments made in terms of barometric pressure
fluctuations during
the fieldwork. The resulting equation can be used to simply predict the
methane flux through the
surface of any given landfill (active, cover soil, or biocover), using SMC
data which are obtained
through a less costly method.
In this invention, this method may be accomplished through the following
steps:
(i) Area of interest or the project boundary such as landfill footprint is
divided into several
zones denoted as Z,, based on one or more of the following attributes of a
given site;
landfill or otherwise:
a. The geometry of the site,
b. Type of cover including but not limited to earthen covers, geosynthetics,
biocover
and a combination of different types of covers
c. Type of vegetation,
d. Status of vegetation in terms of density, health and level of stress
e. Other visual observations,
f. Expected emission levels in terms of concentration or rate based on any
previous
field measurement records
g. Expected or anticipated emission levels in terms of concentration or rate
based on
the results of previous emission rate or concentration modeling
(ii) Measurement of SMC is completed through any of existing or future
protocols and
standards for qualitative assessment of emissions from municipal landfills
established
by regulatory or otherwise organizations such as the US EPA, Title 40 CFR Pat
60,
Standards of Performance for Municipal Solid Waste Landfills,
(iii) SMC values are adjusted to SMCa accounting for effects of barometric
pressure rate of
change during sampling campaign,
(iv) SMCa data are integrated for each measurement zone to calculate an
average SMCa for
each zone denoted as SMCa.,, and
(v) SMCa_, values in form of data points or measurements for each zone is
correlated
linearly to quantitative measurement data points of MER, which is the Average
Methane Emission Rate for Zone Z,
(vi) The correlation as shown in Equation 1, and in Figure 4, results in a
Correlation Factor
Cf.
MERa_i = SMC, X Cf A SMC, Equation 1
CA 2955844 2019-05-21
Where:
MER = average methane emission rate for zone Z, in g CH4/m2/d
SMCa_, = average surface methane concentration for zone Z, in ppmv CH4
Cf = Correlation factor
For every calculated numeric value of the SMC,, for each zone, a corresponding
MERa can be
calculated using Equation 1 and the line shown in Figure 4 denoted as
Correlation.
Values for the correlation factor and variation are developed under this work
and provided through
the correlation and the total methane emission from the project boundary
abbreviated as ET can be
then calculated as:
ET = xMERa_, x3.65 x 104) Equation 2
Where:
ET = total annual methane emission from the project boundary in tonnes/year
A, = Footprint Area of zone Z, in m2
MERa_, = average methane emission rate for zone Z, calculated from Equation 1
in g CH4/m2/d
3.65 x 10-4 = unit conversion multiplier
Note: The default correlation factor Cf is developed by completing a
quantitative field
measurement of MER using the US EPA flux chamber methodology for various zones
with
different emission levels, qualitative assessment of SMC for the same areas,
and plotting the SMC
data against the MER values. Similar exercise can be repeated, when possible
and desired, to
calculate a site-specific value for Cf.
A) Zoning: Zoning of a site is necessary only if different areas of the site
are expected to have
significantly different methane emission rates. This is done prior to
completing the field
measurements. The area of interest is divided into different zones based on
expected levels of
methane emission rates such as landfill crest, side slopes, type of cover,
type of vegetation, etc..
While the end results in form of the estimated total methane emission from the
site will remain the
same, zoning of the site will help identifying the areas with higher emission
rates.
B) Field measurement abbreviated as SMC: Surface methane concentration of each
zone is
measured by continuous and instantaneous sampling of air using a portable
device with minimum
detection limit of 0.0001% methane or 1 part per million or ppm. One of the
devices that can be
used to measure SMC with this accuracy is portable Flame Ionization Detector
denoted as FID to
measure the concentration of total organic compounds measured as methane at
the landfill surface.
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SMC measurement is completed following the protocols similar to US EPA
protocol for qualitative
surface methane emission monitoring under Title 40 CFR Part 60, Subpart WWW.
Method
includes instantaneous sampling of air at 2.5 to 10 cm above landfill surface
and on paths of
approximately 30 m. Reducing the distance between the measurement paths which
is
recommended to be 10 m or less, will increase number of samples and accuracy
of the results. The
SMC measurement field work can be completed only when the landfill cover soil,
bio-cover, or
other form of covers is not saturated, and wind speed is less than 16 km/hr
equal to about 4.5
m/sec. The SMC readings are recorded at minimum every 5 to10 seconds at
sampling points
approximately every 1 to 2 m along the sampling route or path. These readings
are separately
collected for each zone along with GPS records, time of sampling, climate
conditions, ambient
temperature and barometric pressure. Figure 1 shows an example of how a site
boundary is divided
into different zones and how sampling path should be in an example zone.
C) Other field readings and field data adjustments:
Variations in the weather conditions, and in particular the barometric
pressure abbreviated as BP,
have an impact on rate of methane fugitive emissions from landfill's surface.
Higher emission rates
at landfills are reported to occur at lower ambient pressures. In general,
variations in atmospheric
pressure happen due to several factors including;
- Auto oscillation of air which is reported to have an insignificant
effect,
- Daily warming and cooling of air caused by solarization causing diurnal
variations, and
- Passage of atmospheric pressure lows and highs leading to long term
variations.
Therefore, short term daily and long term seasonal variations in atmospheric
pressure should be
considered when conducting methane fugitive emission measurements at a
landfill site. The
present methodology includes development of an equation for adjusting the
calculated MER values
for effect of barometric pressure fluctuations at time of sampling. The true
value of MER at the
landfill could be measured when the atmospheric pressure remained constant,
causing an
equilibrium condition between landfill and the surrounding environment. The
following equation
was developed through finding a good correlation between change in MER values
and rate of
change in barometric pressure.
Therefore, the MER values should be adjusted to the true values presented as
MERa, based on the
recorded AP/t at the time of sampling relative to the equalized condition
meaning that AP/t equals
zero.
MERa = MER x (1 + 1.9731 x 1AP/t) ^ (AP/t / AP/0 Equation 3
Where:
AP/t = change in barometric pressure over time during sampling
AP/t /1AP/tIwould be equal to -1 or +1, represent the sign of the AP/t. This
adjustment for effect of
BP shall be made once on either measured SMC data or calculated MER at the end
as suggest in
Equation3. If field data is intended to be adjusted before calculation of MER,
Equation 4 below
can be used to find adjusted SMC, based on which true value of MER can be
calculated.
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SMCa = SMC x (1 + 1.9731 x IAP/t1) A (AP/t /IAP/t ) Equation 4
D) Data compilation and analyses:
This invention is based on the correlation that was found between SMC and MER.
This correlation,
illustrated in Figures 3 and 4 below, was developed through extensive field
measurement on 12-
hectare area consisting of 12 different measurement zones.
As shown in Figure 3, plotting the SMCa data against the MERa values showed a
reasonable
correlation between these two values.
Based on this correlation;
MER = SMC x (0.32 0.034) + (1.39 0.755) Equation 5
Where:
MER = methane emission rate in g CH4 m-2 d-1
SMC = surface methane concentration in ppmv CH4
The development of this invention can be practically very important in the LFG
management
industry, saving time and money when full scale fugitive methane emission
measurements are
required. Another very important application of this methodology is
performance review and/or
quantification of methane emission from surfaces with very low methane
emissions such as bio-
cover systems, bio-filters, and bio-window systems.
Main objective of these systems is to minimize methane emission to the
atmosphere, making it
almost impossible to use conventional methods, such as flux chamber technique,
for quantification
of the remaining methane emission through these systems.
BRIEF DESCRIPTION OF THE FIGURES
Figure 1. One zone (e.g. Zone A) with 1 ha footprint requiring 1 km of
sampling path (with 10
m spacing) and 500¨ 1000 SMC readings
Figure 2. Correlation between rate of change in BP and adjusting multiplier
for MER
Figure 3. Averaged surface methane concentration (SMCa) and methane emission
rate (MERa)
for 12 measurement zones
Figure 4. Correlation between SMC and MER values
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