1. business and industrial
2. energy
3. electricity

Northern Border Recovered Energy Project
Basin Electric Power Cooperative
How to make ‘green’ power
with a simple-cycle gas turbine
A
decade or more ago the
technology leaders in
the electric power industry clearly were the investor-owned utilities. Today public
power may be on equal footing, at
least in the generation sector. Or it
might even be ahead of the IOUs.
Basin Electric Power Cooperative
(BEPC) offers several examples of
how public power is actively contributing to the advancement of electric
generation technologies (Sidebar
1). Reading through the Class of
2006 profiles of gas-turbine-based
powerplant additions will uncover
still more examples based on work
conducted by Austin Energy (Tex),
Riverside Public Utilities (Calif),
Turlock Irrigation District (Calif),
and others.
n “Green” power from GTs. Basin
is one of three major participants
in the Northern Border Recovered Energy Project, which has
confirmed the viability of recovering heat from the exhaust of gas
turbines (GT) driving pipeline
compressors and converting it
to “green” megawatts using an
organic Rankine cycle (ORC). The RB211 compressor drives—formerly
four compressor stations retrofit- vented to atmosphere—to Ormat,
ted for energy recovery and elec- which converts the heat to electricity.
tric generation to date supply a Basin buys all the electricity Ormat
total of 22 baseload megawatts to generates under a 25-yr power purthe Basin system (Figs 1-3). The chase agreement and delivers it to
opportunity nationwide, accord- the grid, over its local co-op meming to one source, may
ber system. BEPC then intetotal 2000 MW, or more,
grates this electricity with
of emissions-free power
other resources to provide
(Sidebar 2).
firm power to its members.
Basin’s alliance partBasin’s Ron Rebenitsch,
ners in this landmark projPE, manager of member marect are:
keting, says the utility investn Ormat Technologies Inc,
ed in more than 15 miles of
Reno, Nev, the technol69-kV line, plus substation
ogy and project develinterconnections, to make
oper, and owner/operathe project happen. The lines
Rebenitsch
tor of the proprietary
were constructed by Basin
energy recovery/power generation Electric members East River Electric
system at all four compressor sta- Power Co-op, Madison, SD, and Mortions.
Gran-Sou Electric Co-op, Flasher,
n ONEOK Partners LP (which ND. The ability to interconnect with
includes Northern Border Pipeline these members was an essential eleCo), Omaha, is the owner/operator ment of the project, he adds.
of the 42-in.-diam pipeline and its
Locations of the ORC systems are
compressor stations.
at compressor stations 7, 9, 10, and
Here’s how the business side of the 11 as shown on the map in Sidebar
project works: ONOEK sells 825F- 3. The first system started in July,
950F+ exhaust from its Rolls Royce with the last one going into commer-
Heat-recovery unit
Air-cooled condenser
Existing compressor facilities
Bypass
stack
1. Compressor Station 7 on the Northern Border pipeline, near St. Anthony, ND, is similar to the other stations retrofitted for heat recovery and ‘green’ power generation
COMBINED CYCLE JOURNAL, Fourth Quarter 2006
59
1. Basin Electric serves 120 members with a mixture of traditional,
state-of-the-art generation
Basin Electric Power Cooperative, Bismarck, ND, a “super”
generation and transmission (G&T) co-op, was formed
in 1961 by 67 distribution cooperatives located in eight
midwestern states. Today the organization has 120 owner/
members that serve 2.5 million customers in nine states.
Basin Electric’s primary mission is to provide reliable, low-cost power to member companies. It produces
electricity from a variety of generation resources and
buys some from others; most of the power it generates
comes from coal. The utility, which ranks among the top
10 co-ops nationwide in terms of generating capability,
has a pooling agreement with the Western Area Power
Administration to deliver its power to member companies
across the federal transmission system. The co-op also is
a member of the Mid-Continent Area Power Pool, which
provides backup generation in the event Basin cannot
meet demand on its own.
Basin Electric’s ongoing work to identify the technologies that best serve the interests of its members has
given the co-op first-hand design, operating, and maintenance experience in areas many others in the industry
know little about. For example:
n Using an organic Rankine cycle (ORC) to produce pollution-free megawatts with exhaust heat recovered
from gas turbines (GTs) driving pipeline compressors—
as described in the main text (photo).
n Developing the world’s first LMS100 project—the
industry’s latest and most efficient GT—to provide
95 MW of peak capacity 10 minutes after hitting the
“start” button. Initial operating experience at Groton is
profiled in a separate article within the Class of 2006
portfolio.
n Pioneering the manufacture of pipeline-quality gas
from coal at subsidiary Dakota Gasification Co, Beulah,
ND. The facility produces daily about 150 million ft3 of
“natural” gas from 18,000 tons of lignite. It operates
24/7 and has a lifetime availability of over 90%. In more
than 20 years of service, the facility has gone dark only
once. Process byproducts sold commercially include
two fertilizers (anhydrous ammonia and a trademarked
Bypass stack
Heat-recovery unit
Gas turbine/
compressor building
product made from ammonium sulfate recovered in
the gasification plant’s scrubber) and petrochemicals.
Greenhouse gas CO2 is recovered and sent via dedicated pipeline to Saskatchewan for use in enhanced oil
recovery operations.
n Developing distributed generation units that operate
on coal-bed methane. Basin’s three installations in the
coal fields, each consisting of three 5-MW Solar (San
Diego) Taurus gas turbine/generators, are dispatched
as needed for transmission support and peak power.
The GTs have a high simple-cycle heat rate and don’t
operate often on this opportunity fuel, but they have
a high availability and have run reliably when needed.
O&M support is provided by one roving technician.
n Leveraging the value of wind-based generation to the
extent possible. Basin knows wind has a place in its
portfolio but it is limited by resource availability. The
co-op owns and operates 5.2 MW of wind-turbine
capacity and purchases 100% of the output from
approximately 130 MW owned and operated by FPL
Energy LLC, Juno Beach, Fla. Additionally, Basin buys
the output from several small projects, including a
unique 750-kW wind turbine owned by the Rosebud
Sioux Tribe in South Dakota.
2. ORC and how it converts waste heat into ‘green’ electricity
Most powerplant engineers are familiar with the Rankine
cycle. Simply put, steam produced in a fossil-fired or
nuclear steam generator is expanded in a turbine which
drives a generator to convert the work into electricity. A
disadvantage of using water as the working fluid is the
high temperature and pressure required to make the cycle
run efficiently.
By contrast, organic compounds can perform the
same function as water/steam but at much lower pressures and temperatures. Thus an organic Rankine cycle
(ORC) is better suited for recovering low-grade heat and
converting it into electricity. This should not come as
news: Several ORC plants ranging in capability from a
few hundred kilowatts to a few megawatts have been
installed over the last two decades and are generating
electricity using heat rejected from industrial processes
as well as that available in diesel-engine jacket water and
geothermal resources.
Several organic compounds—including CFCs, ammonia, and pentane—have been used to match the cycle
to the level of heat available. Today, environmental and
60
health considerations probably would eliminate the first
two from consideration.
Cycle efficiency typically ranges from 10% to 20%
depending on the temperature of the heat source. An
economically viable, megawatt-size ORC system probably would require a heat source with a minimum temperature in the 280F-290F range. Also, the ORC would have
to be located near the heat source and a cooling medium
available to condense the vapor.
Ormat Technologies Inc, Reno, Nev, is a leader in ORC
technology and one of relatively few firms to achieve
commercial success. Its packaged system is called
Recovered Energy Generation (REG). The company has
installed several megawatt-size REG facilities worldwide
and these are said to demonstrate long-term sustainable
results. The standalone, pre-engineered generating units
come in sizes from 200 kW to 22 MW.
Here’s how the system works: Gas-turbine exhaust
heat is transferred to a thermal fluid circulating through
the recovery unit shown at the left in the diagram. The hot
thermal oil boils organic fluid (pentane) in the vaporizer
COMBINED CYCLE JOURNAL, Fourth Quarter 2006
Preheaters
Vaporizer
Generator
Recuperator
Generator
Turbine
2, 3. Equipment required for an organic Rankine cycle is relatively large
compared to a conventional generating unit rated at 5.5 MW
cial operation in October. Names of
the towns closest to the distributed
energy centers are St. Anthony, ND,
and Wetonka, Clark, and Estelline in
South Dakota.
The impressive results recorded
by these four facilities in their first
few months of operation provide the
stimulus for others in the industry
to take similar steps, thereby creating the opportunity for conserving energy and reducing pollutant
emissions nationwide (on a megawatt basis). For its leadership in
this endeavor, the Northern Border
Recovered Energy Project earns the
COMBINED CYCLE Journal’s 2007
Pacesetter Plant Award.
Experience. Ormat’s VP Dan
Schochet says the company’s ORC
project-development activities span
more than 20 years. Most experience
is in the geothermal area, with projects totaling more than 800 MW—
including 350 MW in the US. A positive return on investment has been
achieved from geothermal reservoirs
as low as 200F. But Schochet adds
that utility-scale applications require
heat source of about 300F or higher
to be economical.
“Realistically,” he continues, “you
need a 2- to 15-MW potential for
these types of projects to move forward. This translates to a GT-powered compressor station of at least
10,000 hp and assumes a top market
price of about 5 cents/kWh for the
electricity produced.” ‘Green’ power
still must compete with the generic
brand, Schochet advises. Basin’s
Rebenitsch adds that the cost of
interconnection can be significant
and/or challenging. Latter because of
congestion.
Projects in North America that
helped to support the Basin decision
are a similar installation in Canada,
which was installed in 1999, and one
at a Louisiana natural-gas processing plant, which has three years of
operating experience.
The Gold Creek Generation
Facility, located in the Grande Prairie area of Alberta, obtains its heat
from a TransCanada Pipelines mainline compressor and produces 6.5
MW. The facility was purchased by
and then gives up some of its remaining heat to pentane
n The saturation curve for hydrocarbons is such that the
in the preheater before returning to the recovery unit.
working fluid remains dry under all operating condiVaporized pentane expands through the turbine and
tions—thereby eliminating the possibility of erosion
flows to the recuperator where it warms the ozone-benign,
damage to turbine buckets and nozzles often found in
organic working fluid returning from the air-cooled (as in the
steam systems.
Northern Border project) or water-cooled condenser.
A storage/expansion tank accommodates any
Bypass
Condenser
Exhaust
Turbine/generator
stack
losses and maintains a constant head on the sysstack
tem.
Advantages of the ORC over a conventional
Rankine cycle for the Northern Border project
Fan
include the following:
GasVaporizer
turbine
n Pentane freezes at -200F, thereby eliminating the
potential for damage associated with the use exhaust
HeatRecuperator
of water in a winter environment typical of the
transfer
Preheater
fluid
Dakotas.
n The expense of installing, operating, and maintaining a water treatment system is eliminated.
Pentane
Heat-recovery unit
n Pentane’s thermodynamic properties allow much
pump
higher condensing pressures than are possible for
Storage/expansion
tank
steam. This permits use of shorter turbine blades
and minimizes ingress of air into the system. Latter mitigates the need for vacuum maintenance.
COMBINED CYCLE JOURNAL, Fourth Quarter 2006
61
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62
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& installation.
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Central
Power
Northern Border Pipeline
Co was formed
in 1978 as a
Texas general
partnership and now is owned by
ONEOK Partners LP and TC PipeLines LP. Northern Border constructed a natural-gas pipeline
that today extends from the Montana/Saskatchewan border near
the Port of Morgan, Mont, more
than 1200 miles to North Hayden,
Ind. It carries about one-fifth of
the gas imported from Canada
to the US (more than 2.5-billion
Maxim Power Corp, Calgary, in 2001.
The company is a global developer/
operator of independent power-generation facilities.
Electricity produced by the Gold
Creek baseload Ormat ORC—aircooled option—is sold through the
Alberta Power Pool which recently
was merged into the Alberta Electric
System Operator. Power hits the grid
through the 25-kV distribution system operated by ATCO Electric Ltd,
Edmonton, on behalf of rural electrification associations.
Enterprise Products Operating LP’s Neptune Gas Plant in
Centerville, La, produces 100% of
the facility’s power needs, plus some
for sale, with a 4.5-MW ORC serving two GT-driven compressors.
The saving associated with self generation, combined with income from
power sales, reportedly will pay back
the initial investment in less than
five years.
The Northern Border installation. Al Behrens, director of analysis
and asset optimization for ONEOK,
says the recovery of energy from
pipeline compressor operations was
considered for several years before
approaching Ormat.
The ORCs are located within the
confines of the ONEOK compressor
stations, but in separate fenced-in
9
11
South
12
East L&O 13 Central
River
Ventura
NIPCO
ft3/day) and interconnects with
many other pipelines serving
midwestern markets.
Thirteen simple-cycle gas-turbine-powered compression stations
serve what is still known as the
Northern Border Pipeline despite
the company name change (map).
Stations 7, 9, 10, and 11 have been
retrofitted with heat-recovery systems that enable the production of
5.5 MW at each site. Station 7, near
St. Anthony, ND, is the site profiled
in the text. The other three stations
are in South Dakota.
areas. The pipeline company has no
operating responsibility for the heatrecovery/power-generation systems,
which typically are operated remotely. They are tended to by a pair of
roving O&M technicians who serve
all four facilities.
Most of the pipeline compressors,
including the four equipped by ORCs,
are driven by Rolls Royce RB211
engines with nominal ratings of nearly 40,000 hp. The ORCs have had
minimal impact on pipeline operations. Connection of the GT exhaust
duct to the ORC required only a
short outage period. Additional ORC
installations on the Northern Border
pipeline are under consideration by
ONEOK.
Ormat’s Schochet says all Northern Border projects have met expectations; any operational concerns were
addressed before the end of 2006. Normal monitoring and operation of the
facilities are done remotely; two roving O&M technicians maintain a periodic onsite presence. System availability is 98% and expected to remain
that way for the life of the facility, he
continues. Reasons for the positive
outlook: Working fluid is at relatively
low temperature and pressure (less
than 200 psig) for a power-generation
system, and the turbine/generator
operates at 1800 rpm. ccj
COMBINED CYCLE JOURNAL, Fourth Quarter 2006