LMS100 flexibility for modern power systems

Size: px

Start display at page:

Download "LMS100 flexibility for modern power systems"

Merryl Stewart
6 years ago
Views:

1 GE Power & Water Distributed Power LMS100 flexibility for modern power systems By Philip F. Tinne

2 2

3 Contents Abstract... 4 Introduction... 4 Satisfying the need for fast power... 5 The importance of moving output quickly Spinning Reserve Capability... 8 The ability to change fuel type... 8 Low emissions without using water Choice available on generators... 9 Conclusion... 9 About the author

4 Abstract Modern electrical power systems are facing unprecedented challenges from the introduction of increasing quantities of wind and solar energy. Not only can these renewable energy sources be dispersed and remote from where the power is needed, the renewable energy generation is typically highly variable with the time of day, month of the year, and overall weather patterns. In order to justify the high up-front cost of installing renewable generation, as well as to take advantage of the low operating costs, the balance of the power system must be designed to accommodate them in both normal operation, and when things start to go wrong. With the ability to start quickly, change output over a wide power range rapidly, burn fuel more efficiently than any machine in its class, and stay in emissions compliance to the most stringent levels, customers and system operators are finding the LMS100 the ideal solution to their power grid reliability needs. Nowhere is this better illustrated than California, a state with a renewable energy target of 33 percent by 2020, and 50 percent by In this state alone, 23 LMS100 gas turbine generators have been installed over a four year period, with an additional five units currently in construction and more sites in the planning phase. The LMS100 is truly seen as a facilitator to enable California to meet its ambitious renewable energy goals. Introduction The LMS100, now rated at up to 116 MW in power output, was introduced into commercial operation in It is the largest gas turbine in GE s aeroderivative product portfolio and is the most efficient open cycle gas turbine available to today s power generation industry. In addition to high efficiency especially important for continuous duty applications where fuel cost is a major factor the LMS100 is designed with features that make it suitable for cyclic operation. The LMS100 is able to start, stop, and move power output quickly and frequently with reduced impact upon maintenance cost, all while maintaining emissions to strict standards. The LMS100 achieves its excellent efficiency by operating at a high overall pressure ratio (up to 43:1) and a firing temperature in excess of 2,500 F. These operational characteristics are enabled by the use of an off-engine intercooler which cools the air between the low- and high-pressure compressors. The LMS100 utilizes advanced technologies from GE s heavy-duty frame gas turbines as well as GE s industry leading aircraft engines. By incorporating an aeroderivative core engine and a lightweight/high-strength power turbine, the engine is able to undergo large thermal and mechanical stress changes without a significant detrimental impact upon the hardware. Modern power grids incorporate a high proportion of intermittent renewable energy sources (wind and solar) that cause special problems in maintaining grid reliability. Power generators have always been required to adjust output quickly in order to match the demand upon the system, but with the introduction of a high proportion of wind and solar energy the net load that the other energy sources are required to respond to can change much more rapidly and over much wider ranges than previously. This has been well documented by California ISO with publication of their duck curve. Ideally, the steep load ramps that the non-wind and solar sources are required to respond to would be fully satisfied by (1) demand management; (2) energy storage; and (3) the most efficient fossil fuel sources, which are combined cycle natural gas power plants. Unfortunately, to fully equip a system in this way to achieve the required level of reliability would be cost prohibitive, and likely result in a poor overall environmental impact. Thus the problem of satisfying the most severe and prolonged ramps in the system net load can be solved by having simple-cycle gas turbines available with the ability to start and stop quickly, and move output at a very fast rate. With high-efficiency, excellent hot-day power output, fast starts and the ability to provide very fast load ramps, the LMS100 is the ideal solution to many of the power grid reliability issues. 4

Satisfying the need for fast power The North American Electric Reliability Corporation (NERC) is responsible for the reliability of the bulk power grid and ensuring compliance with the mandatory

Part of the reliability obligation of a BA is to maintain sufficient reserves to handle normal, yet unpredictable variations in load, as well as contingency events, such as the loss of the largest

5 Satisfying the need for fast power The North American Electric Reliability Corporation (NERC) is responsible for the reliability of the bulk power grid and ensuring compliance with the mandatory reliability standards. NERC publishes guidelines to assist the responsible entities, typically Balancing Authorities (BA s), in planning for and satisfying their reliability obligations. Part of the reliability obligation of a BA is to maintain sufficient reserves to handle normal, yet unpredictable variations in load, as well as contingency events, such as the loss of the largest generating unit in their area of responsibility. Thus the Operating Reserves are split between Regulating Reserves and Contingency Reserves. Regulating Reserves are generally spinning (meaning a generator is already synchronized to the grid), and Contingency Reserves may be spinning or non-spinning. In nearly all cases, whether spinning or non-spinning, Contingency Reserves are currently defined as the power available within 10 minutes of being requested. Being obligated to the 10-minute start time requirement to qualify as a Non-Spinning Contingency Reserve, GE s gas turbine products are designed to start and go to full output within a 10-minute window whenever possible without detrimental impact to the life of the equipment. All of GE s aeroderivative products, including the LMS100, offer a start to full output inside 10 minutes, sometimes significantly less. In order to satisfy fire protection safety codes all gas turbines must, prior to light-off, satisfy certain requirements so that no combustible gases are trapped in the exhaust system. There are several ways to accomplish this, and typically the most efficient way to do this for GE's aeroderivative products is to conduct a duct purge and shutdown bottle test that provide purge credit for an 8-day window, a credit that can be continuously renewed by a simple unfired motoring of the core engine with its starter motor each 8-days. With purge credit (or alternative methods to meet the fire protection codes) the LMS100 can be reliably started, synchronized and loaded to full output within the 10-minute contingency reserve time period. It should also be noted that GE is now offering an 8-minute start to full load without parts life impact, and less than this is possible with some impact. Figure 1. LMS100 Five-Unit Start Demonstration. Figure 1 shows the actual performance of a five-unit LMS100 site where the plant control system was configured to start all units at the same time. As shown by this data, the output actually selected that day was available in 9 minutes, with full output being available inside 10 minutes. GE's LMS100, first introduced in

The importance of moving output quickly Balancing Authorities are required to contribute, in proportion to their size, to the maintenance of frequency on the power grid.

6 The importance of moving output quickly Balancing Authorities are required to contribute, in proportion to their size, to the maintenance of frequency on the power grid. This is done by changing the output of generating units in the upward and downward direction; upward if system load is increasing, downward if system load is decreasing. If the power generating unit is not on a large power grid, but on an isolated system operating in island mode (such as a mining operation or data center) then the ability of the generator to move output quickly and precisely is of even greater importance. To have upward regulation ability the generator must be initially set at a level below full output such that there is headroom for upward regulation. All gas turbines lose efficiency as output is reduced but all gas turbines are not equal in this regard. By virtue of being a very highly efficient, high pressure ratio, three-shaft machine, with seven variable geometry compressor airfoil stages, the LMS100 operates with superior part-load efficiency. P min is the term used to define the minimum steady-state power that a generator can be parked at. This is typically set by the lowest power at which the machine will satisfy the EPA s requirements for criteria pollutant emissions, and at P min the pollutant that is most challenging to meet is carbon monoxide (CO), this being inversely proportional to the power setting. The LMS100 can typically operate at a P min of about 25 MW (~75% below full output) while satisfying stringent CO emissions requirements without installation of excessive amounts of exhaust system oxidation catalyst. Two customers use the LMS100 with a P min set as low as 17 MW. While the machine is regulating power (upwards and downwards) the exhaust emissions need to stay in compliance with the EPA s requirements, as specified in the site s air permit. In the case of GE s SAC (Single Angular Combustor) aeroderivative machines, depending upon the site location, exhaust NO x control is achieved by controlling combustor flame temperatures with water injection, and where regulations require it, further reducing NO x with an exhaust Selective Catalytic Reduction (SCR) unit. The SCR utilizes a diluted ammonia solution to react the NO x into nitrogen and water vapor, both being normal constituents of air. The amount of ammonia vapor fed to the unit needs to be appropriate to the power setting and fuel flow rate, so maintaining compliance with the NO x requirements requires changing power on the unit at a rate that the SCR ammonia injection control can match. The LMS100 can continuously maintain the most stringent standards of exhaust NO x compliance while changing loads at a rate in excess of 50 MW/min. As will be discussed, the LMS100 has the capability to move much faster than 50 MW/min, but this might result in exhaust NO x being briefly outside the required standards. Since NO x and CO compliance are generally monitored on a one-hour rolling average basis this is not likely to be a problem unless the unit is being subjected to continuous and severe load changes over this one-hour average emissions reporting period. 6

7 Figure 3. LMS100 Operation in Fast frequency Response. Figure 2. MW Output Vs Time in Automatic Generation Control. Figure 2 shows an example of an LMS100 operating in automatic generation control (AGC) with a P min set at 35 MW. This shows the amazing ramping capability of the LMS100. Ramping of an LMS100 in AGC is normally conducted at about 50 MW/min, although there is flexibility in this number to suit customer needs. As far as maximum ramp rates for contingency events are concerned meaning what the unit can really do if called upon by a severe system disturbance the LMS100 s heritage as an aircraft-engine derived gas turbine has clear advantages. Aircraft engines are required to be able to make rapid and large power changes. Large power output changes in both upward and downward directions can be made in seconds, and despite the increased inertia of an LMS100 power generation system compared to an aircraft engine, the LMS100 can also move extremely fast when necessary. Figure 3 shows an example of a very rapid movement in the output of an LMS100 unit when called upon to change power in response to an external signal (in this case a false frequency injection test). In this real-life example, at the time 17 seconds, the unit has been commanded to full output outside the normal MW ramp rate, and just 6 seconds later the output is 67 MW, for an average ramp rate over this period of 500 MW/min. Peak output in this case was 100 MW, occurring approximately 24 seconds after the initial signal was input to the control system. Similarly, very rapid ramp rates can be achieved in the downward direction, as would be required in response to a sudden loss of load on an isolated power system. Power output changes of the rate and magnitude shown in Figure 3 are very unusual for a power generation system, and if conducted on an occasional basis would not be expected to have any significant equipment life impact on an LMS100. If conducted on a daily basis some life impact could be expected, and GE would review this for the entire gas turbine and generator system. Thus GE would not expect these rapid power excursions to be recorded for parts life tracking unless they became a regular operating mode of the equipment. If they were to become a normal operating mode GE would request details of the expected operational profile and would conduct an engineering assessment. Normal parts life tracking for the LMS100 consists of recording start/stop cycles and large power output changes, and then factoring them against the nominal 10,000 cycle published life of the rotating structures of the engine. 7

8 Spinning Reserve Capability We have already discussed the ability of the LMS100 to operate at a low P min while maintaining emissions compliance with better-than-typical fuel efficiency. The headroom available to full output can be used to support the operator s Regulating Reserve requirement, or their Spinning Contingency Reserve requirement. The utilization of an LMS100 in this way will allow combined cycle power plants in the Balancing Authority (BA) to operate at full output and peak efficiency, thus enhancing overall system efficiency and reducing overall system emissions. If the LMS100 is to be utilized on any particular day to satisfy the spinning reserve requirement, there are additional options available to enhance its contribution. The installation of a synchronous condensing clutch will allow an LMS100 generator to remain synchronized to a grid and effectively operating as a synchronous motor with the gas turbine de-clutched and shut down. Thus the gas turbine is using zero fuel (hence zero emissions) and electrical power consumption from parasitic loads is low. Normally, synchronous condensers are operated in this manner to enable voltage support of a section of the power grid; the excitation of the motor field is adjusted to correct the grid power factor. Even if the gas turbine/ generator is in normal power generation mode it can be utilized for power factor correction, but in the synchronous condenser mode this capability is enhanced. A side-benefit to operating an LMS100 in synchronous condensing mode is that it can be used to satisfy the Spinning Reserve requirements of the BA. Per NERC (Glossary of Terms Used in NERC Reliability Standards, Updated September 24, 2014): Operating Reserve Spinning Generation synchronized to the system and fully available to serve load within the Disturbance Recovery Period following the contingency event. The LMS100 has demonstrated the ability to transition from the synchronous condensing mode to full power generation output within 10 minutes of being called to do so; thus the full output of the machine is able to qualify as spinning reserve while there is zero fuel consumption and reduced electrical load. This offers an excellent cost savings (in terms of fuel consumption, emissions production and wear and tear of equipment) over operating less capable generating units to meet spinning reserve requirements. If a synchronous condensing clutch is not installed almost the full output capability of the LMS100 can be made available by leaving the gas turbine operating at synchronous idle with the breaker closed and the power output set at minimum load, about 2 to 3 MW. In this condition, once the exhaust system oxidation and SCR catalysts have been allowed to reach operating temperature, the CO emissions will be at a level that meets the most stringent permit limits, and the unabated (i.e., without water injection) gas turbine NO x levels will be low enough to allow the SCR to bring the exhaust stack levels within permit limits. The fuel flow at this condition will be approximately 6,500 lb/hr of natural gas. As the P min is raised above 3 MW the efficiency of the unit will increase rapidly, meaning the fuel consumption will not increase in proportion to the power output. The ability to change fuel type The starting and normal load ramping capabilities of the LMS100 are very similar when operating on either natural gas or liquid fuel, the liquid fuel typically being diesel or kerosene. Normally liquid fuel is utilized as a back-up fuel to natural gas, but two LMS100 installations rely solely on diesel fuel, as do many of GE s LM2500 and LM6000 aeroderivative units. When the LMS100 is equipped with a dual fuel system, online transfers between fuel types can be made in either direction (gas to liquid, or liquid to gas), at any level of power output, up to full load. Some minor variation in output may be expected during the fuel transfer process. The ability to operate on liquid fuel is especially important in the NE USA where customers are subject to wintertime gas curtailments. 8

9 Low emissions without using water The LMS100 version discussed so far in this article utilizes water injection to the combustor to control flame temperature for NO x emissions control. This version of the gas turbine is the LMS100PA. An alternative approach to NO x control that does not require water injection is to use a staged burner system to control flame temperature within precise limits. This is the LMS100PB, of which two units are operating very successfully, and have been since the fall of At this time the LMS100PB model does not allow control of CO emissions to the more stringent regulatory standards below approximately 75 MW, which is generally considered too high in P min for a frequency regulation unit in the USA. However, recent combustor development rig testing has shown very favorable results, and GE is able to offer a 50 MW P min with stack CO emissions at 4 ppm for the LMS100PB model for delivery in At this time there are no plans to offer dual fuel capability for the LMS100PB model, but dual fuel capability will remain for the LMS100PA model, as well as the newly announced LMS100PA+, which offers a 10% power uprate over the LMS100PA. Conclusion The LMS100 has demonstrated outstanding flexibility characteristics to support modern power generation systems. As the most efficient open cycle gas turbine power generation system available, the LMS100 can consistently start rapidly, start and stop as frequently as required, and ramp the power output up and down very rapidly with reduced impact upon maintenance and emissions. As power grid codes are evolving in response to the impact of the growth in wind and solar energy the LMS100 is finding a unique position in its ability to support the reliability standards required by the evolving power generation system. Choice available on generators The LMS100 is available with a choice of generators. The two models currently offered have different inertia and capability curves, as well as options on cooling systems, to suit different customer requirements. Customers anticipating use in island mode should carefully review the different load accept capabilities of the two generators against their anticipated use. GE has material available to assist in this assessment. The generators also have different load rejection characteristics, and although this is generally not a concern item, this should still be discussed with GE, especially if the unit is to be used in island mode operation since it can influence the configuration of other plant systems. Inherent to the inertia difference between the generator models is the amount by which they support system inertia. Having a higher inertia may be of additional value when the LMS100 is employed on a small grid in which it is a significant proportion of the total generation available. 9

10 About the author Philip F. Tinne LMS100 Technical Sales Support Leader GE Power & Water s Distributed Power business A mechanical engineer by training, Phil has over 37 years of experience in the gas turbine and power generation industries. Starting his career with Rolls-Royce in England, Phil soon moved to the USA and has held a variety of positions in both the GE Aviation and GE Power & Water businesses. Roles have included performance engineering, flight test, systems engineering, sales and marketing and product management. After leading the LMS100 test program as Test Director, Phil then became responsible for developing improved installation and commissioning processes as well as assuring product reliability growth. After introduction of the first 26 LMS100 power plants to commercial operation, Phil assumed the role of the technical sales support leader for the product line, helping the sales expansion to continue. Phil s credentials include a B.Sc. in Mechanical Engineering from Liverpool Polytechnic and an MBA from Xavier University. 10

12 GE Power & Water s Distributed Power business is a leading provider of power equipment, engines and services, focused on power generation at or near the point of use. Distributed Power s product portfolio includes highly efficient industrial reciprocating engines and aeroderivative gas turbines that generate 100 kw to 116 MW of power for numerous industries globally. We provide lifecycle support for more than 39,000 aeroderivative gas turbines and reciprocating engines worldwide to help you meet your business challenges and success metrics anywhere and anytime. GE s global service network connects with you locally for rapid response to your service needs. Headquartered in Cincinnati, Ohio, Distributed Power employs about 5,000 people around the world. More information on GE Power & Water s Distributed Power: Solutions: Services: Cincinnati, Ohio, USA One Neumann Way, U120 Cincinnati, OH 45215, USA Houston, Texas, USA Clay Road Houston, TX 77041, USA Jenbach, Austria Achenseestraße Jenbach, Austria T Lima, Peru Av. Las Begonias 415 Piso 14 San Isidro Lima 27, Peru T Moscow, Russia Presnenskaya Naberezhnaya Moscow T Nairobi, Kenya The Courtyard General Mathenge Drive Westlands Nairobi, Kenya T Riyadh, Saudi Arabia 5th Floor Tatweer Towers Building No. 3&4 King Fahad Road Riyadh SA 11433, Saudi Arabia T Shanghai, China No.1 Hua Tuo Rd. Zhang Jiang Hi-Tech Park Shanghai , China T Waukesha, Wisconsin, USA 1101 West St. Paul Avenue Waukesha, WI , USA T Atlanta, Georgia, USA 2300 Windy Ridge Pkwy, 800N Atlanta, GA USA T Dubai, United Arab Emirates Dubai Internet City Building # 18, P.O. Box T Florence, Italy Via Pian dei Carpini, Florence, Italy T Houston, Texas, USA Clay Road Houston, TX 77041, USA Singapore Level 9, The Metropolis Tower 2 11 North Buona Vista Drive Singapore T Imagination at work GE Power & Water's Distributed Power business is a business unit of the General Electric Company. The GE brand and logo are trademarks of the General Electric Company General Electric Company. Information provided is subject to change without notice. All values are design or typical values when measured under laboratory conditions. GEA31906 (06/2015)

Introducing GE s Waukesha*

GE Power Raising the bar Introducing GE s Waukesha* 275GL*+ Breaking new ground in high-horsepower applications *Trademark of General Electric Company No matter how you assess performance, the 275GL+ challenges