How to make 'green' power with a simple-cycle gas turbine - PDF by ssi39810


									                       Northern Border Recovered Energy Project
                                         Basin Electric Power Cooperative

 How to make ‘green’ power
with a simple-cycle gas turbine

         decade or more ago the              organic Rankine cycle (ORC). The RB211 compressor drives—formerly
         technology leaders in               four compressor stations retrofit- vented to atmosphere—to Ormat,
         the electric power indus-           ted for energy recovery and elec- which converts the heat to electricity.
         try clearly were the inves-         tric generation to date supply a Basin buys all the electricity Ormat
tor-owned utilities. Today public            total of 22 baseload megawatts to generates under a 25-yr power pur-
power may be on equal footing, at            the Basin system (Figs 1-3). The chase agreement and delivers it to
least in the generation sector. Or it        opportunity nationwide, accord- the grid, over its local co-op mem-
might even be ahead of the IOUs.             ing to one source, may                          ber system. BEPC then inte-
   Basin Electric Power Cooperative          total 2000 MW, or more,                         grates this electricity with
(BEPC) offers several examples of            of emissions-free power                         other resources to provide
how public power is actively contrib-        (Sidebar 2).                                    firm power to its members.
uting to the advancement of electric         Basin’s alliance part-                             Basin’s Ron Rebenitsch,
generation technologies (Sidebar          ners in this landmark proj-                        PE, manager of member mar-
1). Reading through the Class of          ect are:                                           keting, says the utility invest-
2006 profiles of gas-turbine-based        n Ormat Technologies Inc,                          ed in more than 15 miles of
powerplant additions will uncover            Reno, Nev, the technol-                         69-kV line, plus substation
still more examples based on work            ogy and project devel-                          interconnections, to make
conducted by Austin Energy (Tex),            oper, and owner/opera-                          the project happen. The lines
Riverside Public Utilities (Calif),          tor of the proprietary          Rebenitsch      were constructed by Basin
Turlock Irrigation District (Calif),         energy recovery/power generation Electric members East River Electric
and others.                                  system at all four compressor sta- Power Co-op, Madison, SD, and Mor-
n	 “Green” power from GTs. Basin             tions.                                 Gran-Sou Electric Co-op, Flasher,
   is one of three major participants     n ONEOK Partners LP (which ND. The ability to interconnect with
   in the Northern Border Recov-             includes Northern Border Pipeline these members was an essential ele-
   ered Energy Project, which has            Co), Omaha, is the owner/operator ment of the project, he adds.
   confirmed the viability of recover-       of the 42-in.-diam pipeline and its        Locations of the ORC systems are
   ing heat from the exhaust of gas          compressor stations.                   at compressor stations 7, 9, 10, and
   turbines (GT) driving pipeline            Here’s how the business side of the 11 as shown on the map in Sidebar
   compressors and converting it          project works: ONOEK sells 825F- 3. The first system started in July,
   to “green” megawatts using an          950F+ exhaust from its Rolls Royce with the last one going into commer-

                                                                                       Existing compressor facilities
                                                Heat-recovery unit
                         Air-cooled condenser

1. Compressor Station 7 on the Northern Border pipeline, near St. Anthony, ND, is similar to the other stations retrofit-
ted 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                         Bypass stack
 midwestern states. Today the organization has 120 owner/                                                   Heat-recovery unit
 members that serve 2.5 million customers in nine states.          Gas turbine/
     Basin Electric’s primary mission is to provide reli-          compressor building
 able, 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.                                             product made from ammonium sulfate recovered in
     Basin Electric’s ongoing work to identify the technolo-         the gasification plant’s scrubber) and petrochemicals.
 gies that best serve the interests of its members has               Greenhouse gas CO2 is recovered and sent via dedi-
 given the co-op first-hand design, operating, and main-             cated pipeline to Saskatchewan for use in enhanced oil
 tenance experience in areas many others in the industry             recovery operations.
 know little about. For example:                                   n Developing distributed generation units that operate
 n Using an organic Rankine cycle (ORC) to produce pol-              on coal-bed methane. Basin’s three installations in the
    lution-free megawatts with exhaust heat recovered                coal fields, each consisting of three 5-MW Solar (San
    from gas turbines (GTs) driving pipeline compressors—            Diego) Taurus gas turbine/generators, are dispatched
    as described in the main text (photo).                           as needed for transmission support and peak power.
 n Developing the world’s first LMS100 project—the                   The GTs have a high simple-cycle heat rate and don’t
    industry’s latest and most efficient GT—to provide               operate often on this opportunity fuel, but they have
    95 MW of peak capacity 10 minutes after hitting the              a high availability and have run reliably when needed.
    “start” button. Initial operating experience at Groton is        O&M support is provided by one roving technician.
    profiled in a separate article within the Class of 2006        n Leveraging the value of wind-based generation to the
    portfolio.                                                       extent possible. Basin knows wind has a place in its
 n Pioneering the manufacture of pipeline-quality gas                portfolio but it is limited by resource availability. The
    from coal at subsidiary Dakota Gasification Co, Beulah,          co-op owns and operates 5.2 MW of wind-turbine
    ND. The facility produces daily about 150 million ft3 of         capacity and purchases 100% of the output from
    “natural” gas from 18,000 tons of lignite. It operates           approximately 130 MW owned and operated by FPL
    24/7 and has a lifetime availability of over 90%. In more        Energy LLC, Juno Beach, Fla. Additionally, Basin buys
    than 20 years of service, the facility has gone dark only        the output from several small projects, including a
    once. Process byproducts sold commercially include               unique 750-kW wind turbine owned by the Rosebud
    two fertilizers (anhydrous ammonia and a trademarked             Sioux Tribe in South Dakota.

 2. ORC and how it converts waste heat into ‘green’ electricity
     Most powerplant engineers are familiar with the Rankine       health considerations probably would eliminate the first
     cycle. Simply put, steam produced in a fossil-fired or        two from consideration.
     nuclear steam generator is expanded in a turbine which           Cycle efficiency typically ranges from 10% to 20%
     drives a generator to convert the work into electricity. A    depending on the temperature of the heat source. An
     disadvantage of using water as the working fluid is the       economically viable, megawatt-size ORC system prob-
     high temperature and pressure required to make the cycle      ably would require a heat source with a minimum temper-
     run efficiently.                                              ature in the 280F-290F range. Also, the ORC would have
         By contrast, organic compounds can perform the            to be located near the heat source and a cooling medium
     same function as water/steam but at much lower pres-          available to condense the vapor.
     sures and temperatures. Thus an organic Rankine cycle            Ormat Technologies Inc, Reno, Nev, is a leader in ORC
     (ORC) is better suited for recovering low-grade heat and      technology and one of relatively few firms to achieve
     converting it into electricity. This should not come as       commercial success. Its packaged system is called
     news: Several ORC plants ranging in capability from a         Recovered Energy Generation (REG). The company has
     few hundred kilowatts to a few megawatts have been            installed several megawatt-size REG facilities worldwide
     installed over the last two decades and are generating        and these are said to demonstrate long-term sustainable
     electricity using heat rejected from industrial processes     results. The standalone, pre-engineered generating units
     as well as that available in diesel-engine jacket water and   come in sizes from 200 kW to 22 MW.
     geothermal resources.                                            Here’s how the system works: Gas-turbine exhaust
         Several organic compounds—including CFCs, ammo-           heat is transferred to a thermal fluid circulating through
     nia, and pentane—have been used to match the cycle            the recovery unit shown at the left in the diagram. The hot
     to the level of heat available. Today, environmental and      thermal oil boils organic fluid (pentane) in the vaporizer

60                                                                               COMBINED CYCLE JOURNAL, Fourth Quarter 2006
                                                                                        this endeavor, the Northern Border
                                                                                        Recovered Energy Project earns the
           Preheaters    Vaporizer      Generator     Recuperator                       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 proj-
                                                                                        ects totaling more than 800 MW—
                                                                                        including 350 MW in the US. A posi-
                                                                                        tive 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 for-
                                                                                        ward. This translates to a GT-pow-
                                                                                        ered 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
                                                                          Turbine       congestion.
                                                                                            Projects in North America that
                                                                                        helped to support the Basin decision
                                                                                        are a similar installation in Canada,
2, 3. Equipment required for an organic Rankine cycle is relatively large               which was installed in 1999, and one
compared to a conventional generating unit rated at 5.5 MW                              at a Louisiana natural-gas process-
                                                                                        ing plant, which has three years of
cial operation in October. Names of         few months of operation provide the         operating experience.
the towns closest to the distributed        stimulus for others in the industry             The Gold Creek Generation
energy centers are St. Anthony, ND,         to take similar steps, thereby cre-         Facility,	located in the Grande Prai-
and Wetonka, Clark, and Estelline in        ating the opportunity for conserv-          rie area of Alberta, obtains its heat
South Dakota.                               ing energy and reducing pollutant           from a TransCanada Pipelines main-
   The impressive results recorded          emissions nationwide (on a mega-            line compressor and produces 6.5
by these four facilities in their first     watt basis). For its leadership in          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 condi-
    Vaporized 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
                                                                            Exhaust              Turbine/generator  Condenser
losses and maintains a constant head on the sys-               stack
    Advantages of the ORC over a conventional
Rankine cycle for the Northern Border project
include the following:                                                                                                 Fan
                                                           Gas-                          Vaporizer
n Pentane freezes at -200F, thereby eliminating the        turbine
   potential for damage associated with the use exhaust                             Heat-
   of water in a winter environment typical of the                               transfer     Preheater             Recuperator
   Dakotas.                                                                         fluid
n The expense of installing, operating, and main-
   taining a water treatment system is eliminated.
n Pentane’s thermodynamic properties allow much                  Heat-recovery unit              Pentane
   higher condensing pressures than are possible for
   steam. This permits use of shorter turbine blades                                         Storage/expansion tank
   and minimizes ingress of air into the system. Lat-
   ter mitigates the need for vacuum maintenance.

COMBINED CYCLE JOURNAL, Fourth Quarter 2006                                                                                       61
         The Route to
                                                                          3. Who is Northern Border?
        Effective                                                                     Port of Morgan

 Generator Rotor                                                                       Central
                                                                                                       1 2
                                                                                                           3              Central
 Maintenance                                                                                                   4          Power
 Leads in One         Experts in                                                                               District
                 winding design,                                                                                                            11
 Direction...       manufacture                                                                                 Rushmore
                                                                                                                                               12    South
                                                                                                                                        East L&O 13 Central
                                                     & installation.                                                                    River
                                                                                           Tri-State                                                    Ventura

                                                                          Northern Bor-
                                                                          der Pipeline                                    ft3/day) and interconnects with
                                                                          Co was formed                                   many other pipelines serving
                                                                          in 1978 as a                                    midwestern markets.
                                                                          Texas general                                       Thirteen simple-cycle gas-tur-
                                                                          partnership and now is owned by              bine-powered compression stations
                                                                          ONEOK Partners LP and TC Pipe-               serve what is still known as the
tooth-                                                                    Lines LP. Northern Border con-               Northern Border Pipeline despite
top cracking,                                                             structed a natural-gas pipeline              the company name change (map).
turn insulation                                                           that today extends from the Mon-             Stations 7, 9, 10, and 11 have been
migration, other issues?                                                  tana/Saskatchewan border near                retrofitted with heat-recovery sys-
                                                    Any ventilation
                                                                          the Port of Morgan, Mont, more               tems that enable the production of
                                                                          than 1200 miles to North Hayden,             5.5 MW at each site. Station 7, near
                                                        or winding        Ind. It carries about one-fifth of           St. Anthony, ND, is the site profiled
                                                             style.       the gas imported from Canada                 in the text. The other three stations
                                                                          to the US (more than 2.5-billion             are in South Dakota.

              Example of unit with rotor turn                            Maxim Power Corp, Calgary, in 2001.           areas. The pipeline company has no
              insulation migration problems.
                                                                         The company is a global developer/            operating responsibility for the heat-
                                                                High-    operator of independent power-gen-            recovery/power-generation systems,
                                                               speed     eration facilities.                           which typically are operated remote-
                                                           balancing        Electricity produced by the Gold           ly. They are tended to by a pair of
                                                        and running      Creek baseload Ormat ORC—air-                 roving O&M technicians who serve
                                                     electrical tests.   cooled option—is sold through the             all four facilities.
NEC has Specialized
Engineering Solutions™                                                   Alberta Power Pool which recently                 Most of the pipeline compressors,
                                                                         was merged into the Alberta Electric          including the four equipped by ORCs,
developed to
                                                                         System Operator. Power hits the grid          are driven by Rolls Royce RB211
address known                                                            through the 25-kV distribution sys-           engines with nominal ratings of near-
OEM                                                                      tem operated by ATCO Electric Ltd,            ly 40,000 hp. The ORCs have had
problems.                                                                Edmonton, on behalf of rural electri-         minimal impact on pipeline opera-
                                                                         fication associations.                        tions. Connection of the GT exhaust
                                                                            Enterprise Products Operat-                duct to the ORC required only a
                                                                         ing LP’s	 Neptune Gas Plant in                short outage period. Additional ORC
                                                                         Centerville, La, produces 100% of             installations on the Northern Border
                                                                         the facility’s power needs, plus some         pipeline are under consideration by
                                                                         for sale, with a 4.5-MW ORC serv-             ONEOK.
                                                                         ing two GT-driven compressors.                    Ormat’s Schochet says all North-
                                                                         The saving associated with self gen-          ern Border projects have met expecta-
                                                                         eration, combined with income from            tions; any operational concerns were
Call Us Today!                                                           power sales, reportedly will pay back         addressed before the end of 2006. Nor-
National Electric                                                        the initial investment in less than           mal monitoring and operation of the
                                                                         five years.                                   facilities are done remotely; two rov-
Coil, your best
                                                                            The Northern Border installa-              ing O&M technicians maintain a peri-
destination                                                              tion.	Al Behrens, director of analysis        odic onsite presence. System avail-
for generator rotor                                                      and asset optimization for ONEOK,             ability is 98% and expected to remain
rewind and repair                                                        says the recovery of energy from              that way for the life of the facility, he
services.                                                                pipeline compressor operations was            continues. Reasons for the positive
(614) 488-1151                                                           considered for several years before           outlook: Working fluid is at relatively
                                                                         approaching Ormat.                            low temperature and pressure (less
NEC utilizes ISO 9001:2000 certified quality management systems.
                                                                            The ORCs are located within the            than 200 psig) for a power-generation
For more details, visit our website at   confines of the ONEOK compressor              system, and the turbine/generator
                                                                         stations, but in separate fenced-in           operates at 1800 rpm. ccj
62                                                                                                         COMBINED CYCLE JOURNAL, Fourth Quarter 2006

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