2017-052 Flaring ISRDate: August 4, 2017 Report No. 2017-052
INFORMAL STAFF REPORT
TO MAYOR AND CITY COUNCIL
SUBJECT:
Overview of landfill gas emissions and flaring
BACKGROUND:
During the Solid Waste departmental budget presentation on June 6th, the City Council requested
an update regarding landfill gas emissions and flaring. The below report provides information
regarding the landfill’s gas to energy generation plant, gas flaring, and the emissions associated
with each.
DISCUSSION:
Landfill gas is a natural byproduct of the decomposing organic material found in landfills and is
typically composed of approximately 50% methane, carbon dioxide, and various impurities. To
reduce emissions, the City of Denton and other landfills have implemented systems to capture
and convert landfill gas into electricity.
In 2004, the City of Denton contracted with DTE Biomass Energy (DTE) to build and operate a
landfill gas collection system and energy generation plant. By contract, DTE owns exclusive
rights to all of the City’s landfill generated gas, and in return, the City’s Solid Waste Fund
receives 12.5% of the plant’s gross revenue. The contract with DTE is a twenty year agreement
and will expire on March 31, 2024. At the end of the contract, the City has the option to purchase
DTE’s generating equipment.
Over the past several months, the volume of gas entering the collection system has exceeded the
capacity of DTE’s generation plant, and as a result, excess gas is being flared. Staff has met with
DTE to discuss the possibility of installing a second generator. However, the amount of excess
gas being flared is only approximately 200 standard cubic feet per minute (scfm). The current
engine being used to generate electricity at the landfill requires 550 scfm at 50% methane
content to operate, and the smallest engine category that DTE can install would require
approximately 350 scfm at 50% methane. Because of this situation, DTE has stated that
installing a second generator would not be feasible.
DTE has demonstrated a willingness to allow the City to capture and use excess landfill gas as
long as they have contractual assurances that they will have first rights to enough gas to continue
operation of the existing generator. However, the same market and technical conditions facing
DTE limit the feasibility for use of this gas for electricity generation by the City of Denton.
Staff also discussed the idea of capturing the excess gas and completing all necessary processing
and compression to produce “pipeline quality” natural gas. DTE has collection, processing, and
compression operations to produce pipeline quality natural gas at other landfill facilities,
although these facilities are larger and have more total gas yield than Denton. DTE analyzed this
option, and indicated that the cost to produce pipeline quality natural gas from the Denton
landfill would be in excess of 7 times the cost to buy natural gas from commercial sources.
Date: August 4, 2017 Report No. 2017-052
Staff requested information about emissions from the flaring operation and the latest emissions
testing from the electric generation engine. Total emissions in tons per year are summarized in
the table below. It is important to note that the amount of natural gas combusted by the engine
is about 2.75 times the amount that is combusted in the flare. Values in the table below are
therefore directly comparable in terms of total emissions from the engine and the flare, but are
not directly comparable in terms of emitted contaminants for a given amount of natural gas
combusted by each method. When normalizing by the same quantity of gas consumption by
each combustion method, the flare produces less nitrogen oxides (NOx) and volatile organic
compounds (VOCs), and a slight amount (about 7% more) carbon monoxide when compared to
the engine. In other words, the flare emissions create less ozone precursors when compared to
engine emissions
Table 1. Comparison of total emissions from the engine and flare, in tons per year
Engine Flare
Volatile Organic Compounds (VOC) 0.81 0.04
Nitrogen Oxides (NOx) 11.31 3.54
Carbon Monoxide (CO) 50.07 19.25
The emission summaries for both the engine and the flare do not include estimates of carbon
dioxide or carbon dioxide equivalents. However, carbon dioxide from landfill operations can be
considered to be mostly carbon neutral, since almost all of the products that are producing the
methane within the landfill are derived from fossil fuels.
Staff will continue monitoring the situation and market conditions for opportunities to reduce gas
flaring.
STAFF CONTACT:
Ethan Cox
Director of Solid Waste
Ethan.Cox@cityofdenton.com
(940) 349-7421