By ADRIENNE BLUME
DALLAS -- At the Gas Processors Association's Tuesday
afternoon LNG forum, April Schroer from Noble Energy and
Timothy Miller from Audubon Engineering discussed the
conceptualization and design of Noble's Keota gas plant,
which will be Colorado's first liquefied natural gas (LNG)
The Keota facility, which was designed to process gas from
Noble's Denver-Julesburg (DJ) basin operations, was
originally conceived as a traditional gas processing plant.
However, Noble began examining other options for Keota as it
sought to bring in a clean energy alternative for fueling its
DJ rig engines.
Revamping the engineering plan.
At the FEED
stage, Noble studied the possible use of LNG as a means of
displacing diesel usage, reducing emissions
, assisting with
obtaining the company's operating license and saving fuel
costs. The abundant amount of shale gas available provided a
low-emissions, secure source of energy to fuel Noble's
Ms. Schroer recounted how Noble initially examined three
options for natural gas fuelfuel gas, compressed
natural gas (CNG) and LNG. Fuel gas was not determined to be
an optimal choice for the DJ basin operations due to its
inconsistent product quality. CNG was also rejected due to a
lack of CNG providers and because of the fuel's low energy
density relative to diesel. LNG, however, has a higher energy
density than diesel and consistent product quality, and a
number of turnkey options are available.
After choosing LNG as its main fuel source, Noble brought in
two dedicated rigs from another field for the LNG pilot test,
and it entered into a turnkey contract to provide a dedicated
LNG fuel supply. The demonstration was successful overall;
however, the company did experience a learning curve while
powering the rigs with 100% LNG.
Where Noble operates in the DJ basin, the nearest LNG source
is 400 miles away, which poses a problem if weather-related
LNG shipment delays cause rig downtime. Also, there is a
limited number of LNG providers in the area.
Noble picks dual-fuel power solution. Noble
then examined ways to continue using LNG while mitigating the
risk of downtime, Ms. Schroer explained. The company decided
to convert to a dual-fuel option, using both LNG and diesel
to mitigate the risk of a possible supply interruption. LNG
storage and vaporization units are used to transfer LNG to
the engines at Noble's drilling rigs.
The company purchased kits to run its generation sets on a
mix of fuels, providing flexibility to its drilling
operations. Now, instead of consuming 3,080 gallons per day
(gpd) of LNG, the rigs can run on half of that amount with
the dual-fuel generator sets, Ms. Schroer said. This required
significant monitoring and adjusting, as the compressors and
engines had to be loaded up and altered to accommodate both
LNG and diesel.
The introduction of LNG into the Keota plant, which took
place during the FEED stage, will secure a cost-effective
supply of LNG for Noble Energy and other operators in the DJ
basin. It will also enable greater natural gas use throughout
the supply chain. Chart Industries was selected to design and
manufacture the LNG facility. Design changes made to
integrate LNG include the addition of a gas pretreating
section and an adjustment to the original site plan.
The LNG facility will receive 8 million standard cubic feet
per day (MMscfd) of gas to make 100 thousand gpd (Mgpd) of
LNG, and the balance of the gas will be delivered to a gas
pipeline. Approximately 360 Mgal of LNG tank capacity is
required to support continued operations; six days of LNG
fuel are needed at present usage rates. The balance of the
LNG is available for bulk sales.
Mr. Miller explained how
Noble Energy chose a nitrogen refrigeration cycle for its LNG
process, which was determined to be less complex than the
more complex mixed refrigerant (MR) processalbeit less
efficient, requiring more horsepower. Mixed refrigerant was
also rejected based on the requirements of increased
monitoring, onsite storage of components, transport
difficulty, and the associated fugitive emissions
. After choosing the
nitrogen refrigeration technology
, Noble began working
with Chart to develop the process design.
Product specifications required CO2 to be less than 15 ppm in
the LNG sales gas, due to freezing concerns associated with
CO2 content above 50 ppm. The LNG also needed to contain 96%
methane, and the LNG process was required to have a provision
to remove ethane to meet LNG specifications. Depending on
market conditions, Noble may need to operate the Keota plant
in ethane-rejection mode.
Lessons learned and present progress.
Miller stressed that code determination must be started early
in the process for this type of project
. Also, project partners
must ensure that the air permit, the emissions
permit and the amine
handle a stricter CO2 specification. Also, as the increased
power requirements needed to power the LNG component came to
light, Noble decided to source grid power from the local
Finally, since the implementation of the dual-fuel LNG/diesel
concept at Keota was new for Noble, the company held many
face-to-face meetings with all parties involved in the project
, as a means of ensuring
transparency and eliminating risk for mistakes in project
design and execution. The
company also participated in facility tours of existing LNG
plants and gathered knowledge from other operators at trade
shows, like the GPA Annual Meeting.
In closing, Mr. Miller noted that Noble is presently wrapping
up the engineering phase of the Keota gas plant and is nearly
ready to move into the full construction