In Detail

Twentyfour7.

WÄRTSILÄ TECHNICAL JOURNAL

01 2015 TORY COVER S

4–33 L I A T E D N I THEME pages ENERGY Es with GTs Comparin

g IC

INTERNAL COMBUSTION VS. GAS TURBINE ENGINE ENERGY

10 Defining true

flexibility

A comparison of gas-fired power generating technologies

28 Achieving energy

security

The role of fuel flexibility and low water use

MARINE

34 New LNG Tug

opens a market

First LNG Tug to operate in the Middle East

52 More power with

less money Fuel efficiency in key role

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Contents ENERGY Gas-fired power generation – a technology overview. . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Defining true flexibility – a comparison of gas-fired power generating technologies. . . . . . . . 10 Gas-fired efficiency in part-load and pulse operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Power plant performance under extreme ambient conditions . . . . . . . . . . . . . . . . . . . . . 22 Achieving energy security: the role of fuel flexibility and low water use . . . . . . . 28 MARINE

New LNG Tug opens a market . . . . . . . . . . . . . . . . . . . . 34 The new Wärtsilä Steerable Thruster family. . . . . . . 40 The new Wärtsilä LNGPac™ – a step towards greener shipping . . . . . . . . . . . . . . . 44 Increasing market share for Wärtsilä Controllable Pitch Propellers. . . . . . . . . . . . . 48 More power with less money. . . . . . . . . . . . . . . . . . . . . . 52 FUTURE

Smart monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

iPad Web

THIS ISSUE OF IN DETAIL is also available on iPad as a Wärtsilä iPublication app from Apple's Appstore, as well as in a browsable web version at http://indetailmagazine.com/.

Publisher: Wärtsilä Corporation, John Stenbergin ranta 2, P.O. Box 196, FIN-00531 Helsinki, Finland | Editor-in-Chief: Ilari Kallio | Managing editor and editorial office: Virva Äimälä | English editing: Tom Crockford, Crockford Communications | Editorial team: Tomas Aminoff, Marit Holmlund-Sund, Christian Hultholm, Dan Pettersson, Dinesh Subramaniam, Minna Timo, Susanne Ödahl | Layout and production: Spoon | Printed: April 2015 by PunaMusta, Joensuu, Finland ISSN 17970032 | Copyright © 2015 Wärtsilä Corporation | Paper: cover Lumiart Silk 250 g/m², inside pages UPM Fine 120 g/m² E-mail and feedback: [email protected]

issue no. 01.2015

Internal combustion engines (ICEs) have been around since the 19th century. These days, they are more relevant than ever when it comes to power generation and transportation. Today’s energy markets, characterized by an increasing amount of renewable power, call for fast start up and high ramp rate capabilities. Superior efficiency also in part load makes ICE the most suitable option for this kind of operation, far better than other technologies currently on the market like combined cycle gas turbines (CCGTs) and coal-fired plants. ICE also offers superior performance in extreme ambient conditions like high altitudes and high temperatures. According to the United Nations, by 2025 1.8 billion people will be living in countries or regions with absolute water scarcity, and two-thirds of the world population could live under water stress conditions. If you consider the map of where energy demand is expected to increase the most and compare it to a map of what parts of the world will suffer from the biggest water shortage, you’ll quickly come to the conclusion that these maps are identical in many places around the world. At Wärtsilä we have the ideal offering for covering the needs these maps present: our Dry Flexicycle power plants consume nearly 96% less water than a CCGT plant of similar size. Flexibility is not just about fast start up and other operational capabilities. The current oil price fluctuations are a reminder to us all that fuel flexibility is also very important. The capability to switch between various liquid and gaseous fuels is not only economical but comes with a lower risk too. Having said that, in the long run the world is increasingly turning towards gas: we see more gas solutions everywhere, on different kind of vessels. One of the latest is an LNG tug we will deliver to the Middle East. Our solutions go beyond engines – our broad offering covers all related gas equipment. Please acquaint yourselves with our latest LNGPac solution that not only has improved interfaces for installation and lower costs of operation, but also offers even more reliability, making it attractive to both shipyards and ship operators. All this neatly packed for better space utilisation. We are constantly scouting out new things to enhance our customers’ life. In this process, we trust open innovation and team up with startups for a very agile way of trying out new things. In this issue you can get a sneak preview on how one might monitor engines in the future. Enjoy your reading!

Ilari Kallio Vice President of R & D, Ship Power Engines Editor-in-Chief of In Detail

WÄRTSILÄ TECHNICAL JOURNAL | WWW.WARTSILA.COM

STATING THE CASE: ICE VERSUS GT The world’s power systems need flexibility – internal combustion engines can provide it

In this issue of In Detail, the Energy section features a theme topic: internal combustion engines (ICE) vs. gas turbines (GT). The differences between these two technologies, as well as their pros and cons, will be thoroughly reviewed from various angles. Dawn Santoianni, Managing Director of a technical communications firm and an accomplished writer on energy and environmental issues, will dive deeply into this topic. Ms. Santoianni is a combustion engineer by degree and has an impressive resumé. For instance, she was appointed by the U.S. Secretary of Energy to the National Coal Council, a federal advisory committee that provides guidance and recommendations on general policy matters related to coal. She is also a faculty member of The Oxford Princeton Programme, writing and teaching

courses on coal production, its utilization and regulations. In her position as a Topic Director and subject matter expert for the Our Energy Policy Foundation, Ms Santoianni helps facilitate substantive dialogue on energy policy issues for policymakers, the media and the public. With more than 20 years experience in the energy industry matters, she has worked collaboratively with utilities, municipalities, industry groups, research organizations, and engineering consultants. Her regulatory and policy experience includes testifying before a congressional subcommittee on the impacts of a proposed environmental regulation, producing an executive report for members of Congress, providing commentary on energy policy, regulatory impact analysis, and the editing of regulatory compliance documents.

Power plant performance under extreme ambient conditions.

The new Wärtsilä Steerable Thruster family.

With a glance. A new take on engine monitoring.

Wärtsilä has power plants operating in the harshest climates around the world.

First field applications include the propulsion units for an offshore vessel and a harbour tug.

Together with Korulab, Wärtsilä built a prototype for monitoring engines from your wrist.

MORE ON PAGE 22

MORE ON PAGE 40

MORE ON PAGE 56

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[ ENERGY / IN DETAIL ]


Gas-fired power generation – a technology overview AUTHOR: Dawn Santoianni

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WÄRTSILÄ TECHNICAL JOURNAL 01.2015

International policies to reduce carbon emissions and increase the deployment of renewable energy have posed challenges for maintaining a reliable, efficient electric supply. As a result, flexible gas-fired generation has taken a central role in power systems around the world.

With natural gas producing only half the carbon emissions as coal per kilowatt-hour, displacing coal-fired power with natural gas-based power can help achieve emissions reductions goals. But perhaps more important, as variable renewable energy production from wind and solar are added to electric grids, the need for responsive, dispatchable power is increasing. Gas turbines and internal combustion engines (ICEs) are flexible generating assets that are filling this crucial role. The use of gas turbines for generating electricity dates back to 1939 [1]. Today, gas turbines are one of the most widelyused power generating technologies in part because of their load-following capabilities. ICE power plants are based on the wellknown reciprocating engine technology

used in automobiles, trucks, construction equipment, marine propulsion, and backup power applications. ICE technology is being deployed for a wide range of service, from baseload operation to distributed energy installations where reliable, fast-ramping power is needed. Combustion occurs continuously in gas turbines, as opposed to ICEs in which combustion occurs intermittently. The differences in how the technologies produce electricity from fuel affect key performance characteristics. This article presents an overview of gas turbines, ICEs and combined cycles, highlighting the fundamental differences between the technologies. Subsequent articles in this issue explore the performance of gas turbine and ICE technologies from

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Fig. 1 – Three primary sections of gas turbines are the compressor, the combustion chamber and the turbine.

flexibility, efficiency and derating perspectives.

How do gas turbines work? In gas turbines, an air-fuel mixture is burned, creating hot gases that spin a turbine to produce power. It is the production of hot gas during fuel combustion, not the fuel itself that gives gas turbines their name. Although gas turbines can be designed to burn alternative fuels, the vast majority gas turbines worldwide operate on natural gas. The thermodynamic process used in gas turbines is the Brayton cycle. Gas turbines are comprised of three primary sections: the compressor, the combustion chamber (or combustor) and the turbine. The compressor can be either axial flow or centrifugal flow. Axial flow compressors are more common in power generation because they have higher flow rates and efficiencies. These types of compressors are comprised of multiple stages of rotating and stationary blades (or stators) through which air is drawn in parallel to the axis of rotation and incrementally compressed as it passes through each stage. The acceleration of the air through the rotating blades and diffusion by the stators increases the pressure and reduces the volume of the air. Although no heat is added, the compression of the air also causes the temperature to increase. (Figure 1)

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Fig. 2 – Spark-ignited ICE during compression stroke.

The compressed air is mixed with fuel injected through nozzles. The fuel and compressed air can be pre-mixed or the compressed air can be introduced directly into the combustor. The fuel-air mixture ignites under constant pressure conditions and the hot combustion products (gases) are directed through the turbine where it expands rapidly and imparts rotation to the shaft. The turbine is also comprised of stages, each with a row of stationary blades (or nozzles) to direct the expanding gases followed by a row of moving blades. The rotation of the shaft drives the compressor to draw in and compress more air to sustain continuous combustion. The remaining shaft power is used to drive a generator which produces electricity. Approximately 55 to 65 percent of the power produced by the turbine is used to drive the compressor. To optimize the transfer of kinetic energy from the combustion gases to shaft rotation, gas turbines can have multiple compressor and turbine stages. Because the compressor must reach a certain speed before the combustion process is continuous – or self-sustaining – initial momentum is imparted to the turbine rotor from an external motor, static frequency converter, or the generator itself. The compressor must be smoothly accelerated and reach firing speed before fuel can be introduced and ignition can occur. Turbine speeds vary widely by manufacturer and design, ranging from 2000 revolutions

per minute (rpm) to 10,000 rpm. Initial ignition occurs from one or more spark plugs (depending on combustor design). Once the turbine reaches self-sustaining speed – above 50% of full speed – the power output is enough to drive the compressor, combustion is continuous, and the starter system can be disengaged.

Enhancing gas turbine performance The fuel-to-power efficiency of a gas turbine is optimized by increasing the difference (or ratio) between the compressor discharge pressure and inlet air pressure. This compression ratio is dependent on the design. Gas turbines for power generation can be either industrial (heavy frame) or aeroderivative designs. Industrial gas turbines are designed for stationary applications and have lower pressure ratios – typically up to 18:1. Aeroderivative gas turbines are lighter weight compact engines adapted from aircraft jet engine design which operate at higher compression ratios – up to 30:1 [2]. They offer higher fuel efficiency and lower emissions, but are smaller and have higher initial (capital) costs. Aeroderivative gas turbines are also more sensitive to the compressor inlet temperature. The temperature at which the turbine operates (firing temperature) also impacts efficiency, with higher temperatures leading to higher efficiency. However, turbine inlet temperature is limited by the thermal


Fig. 3 – Engine hall at Goodman Energy Center in Kansas, USA showing Wärtsilä ICEs.

conditions that can be tolerated by the turbine blade metal alloys. Gas temperatures at the turbine inlet can be 1200ºC to 1400ºC, but some manufacturers have boosted inlet temperatures as high as 1600ºC by engineering blade coatings and cooling systems to protect metallurgical components from thermal damage. Because of the power required to drive a gas turbine compressor, energy conversion efficiency for a simple cycle gas turbine power plant is typically about 30 percent, with even the most efficient designs limited to 40 percent. A large amount of heat remains in the exhaust gas, which is around 600ºC as it leaves the turbine.

How do internal combustion engines work? In ICEs, the expansion of hot gases pushes a piston within a cylinder, converting the linear movement of the piston into the rotating movement of a crankshaft to generate power. ICEs are characterized

by the type of combustion: spark-ignited (SG) or compression-ignited, also known as diesel. The SG engine is based on the Otto cycle, and uses a spark plug to ignite an air-fuel mixture injected at the top of a cylinder. In the Otto cycle, the fuel mixture does not get hot enough to burn without a spark, which differentiates it from the Diesel cycle. In diesel engines, air is compressed until the temperature rises to the autoignition temperature of the fuel. As the fuel is injected into the cylinder, it immediately combusts with the hot compressed air and expanding combustion gases push the piston to the bottom of the cylinder. Each movement of the piston within a cylinder is called a stroke. ICEs are described by the number of strokes to complete one power cycle and the speed of crankshaft (expressed in revolutions per minute, rpm). For electric power generation, four-stroke engines are predominately used. During the intake stroke, the premixed

air and fuel (SG engines) or air (diesel engines) is drawn into the cylinder as the piston moves down to “bottom dead center” position. During the compression stroke in SG engines, the air-fuel mixture is compressed by the piston and ignited by a spark from a plug. Auto-ignition in SG engines is prevented with proper limits on the compression ratio. (Figure 2) In diesel engines, the fuel is injected into the cylinder near the end of the compression stroke when the air has been compressed enough to reach the autoignition temperature. Combustion of the air-fuel mixture causes an accelerated expansion of high pressure gases, which push the piston to the bottom of the cylinder during the power stroke, imparting rotation to the crankshaft. Combustion occurs intermittently – only during the power stroke – whereas in gas turbines combustion occurs continuously. As the piston is returned to the top of the cylinder

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during the exhaust stroke, the products of combustion (exhaust gases) are pushed out an exhaust valve. Multiple cylinders are connected to the crankshaft, oriented so that while some pistons are imparting rotation to the crankshaft during their power strokes, other pistons are being pushed back to the top of the cylinders during their exhaust strokes.

Optimizing ICE performance The size and power of an ICE is a function of the volume of fuel and air combusted. Thus, the size of the cylinder, the number of cylinders and the engine speed determine the amount of power the engine generates. By boosting the engine’s intake of air using a blower or compressor – called supercharging – the power output of the ICE can be increased. A commonly used supercharger is a turbocharger, which uses a small turbine in the exhaust gas path to extract energy for driving a centrifugal compressor. Diesel engines are generally more efficient than SG engines, but also produce more nitrogen oxides (NOx), sulfur dioxide (SO2), and particulate matter (PM). SO2 and PM formation is a function of the fuel, with natural gas producing low emissions. The formation of NOx is coupled with combustion temperature. In SG engines, premixing of air with the fuel to produce “lean” conditions (more air than is needed for combustion) has the effect of lowering the combustion temperature and impeding NOx formation. In a power plant, many SG or diesel ICEs are grouped into blocks called generating sets: every engine is connected to a shaft which is connected to its electric generator. These generating sets provide modular electric generating capacity and come in standardized sizes, ranging from four (4) to 20 MW. Wärtsilä ICE power plants are highly efficient with simple cycle efficiencies of 46 to 49 percent, surpassing the performance of steam electric or simple cycle gas turbine power plants. (Figure 3)

Increasing efficiency with combined cycle To increase the overall efficiency of electric power plants, multiple processes can be combined to recover and utilize the residual heat energy in hot exhaust gases. The term “combined cycle” refers to the combining of multiple thermodynamic cycles to generate

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power. Combined cycle operation employs a heat recovery steam generator (HRSG) that captures heat from high temperature exhaust gases to produce steam, which is then supplied to a steam turbine to generate additional electric power. The process for creating steam to produce work using a steam turbine is based on the Rankine cycle. After exiting the steam turbine, the steam is sent to a condenser which routes the condensed water back to the HRSG. The HRSG is basically a heat exchanger, or rather a series of heat exchangers. It is also called a boiler, as it creates steam for the steam turbine by passing the hot exhaust gas flow from a gas turbine or ICE through banks of heat exchanger tubes. The HRSG can rely on natural circulation or utilize forced circulation using pumps. As the hot exhaust gases flow past the heat exchanger tubes in which hot water circulates, heat is absorbed causing the creation of steam in the tubes. The tubes are arranged in sections, or modules, each serving a different function in the production of dry superheated steam. These modules are referred to as economizers, evaporators, superheaters/reheaters and preheaters. The economizer is a heat exchanger that preheats the water to approach the saturation temperature (boiling point), which is typically supplied to a thick-walled steam drum. The drum is located adjacent to finned evaporator tubes that circulate heated water. As the hot exhaust gases flow past the evaporator tubes, heat is absorbed causing the creation of steam in the tubes. The steam-water mixture in the tubes enters the steam drum where steam is separated from the hot water using moisture separators and cyclones. The separated water is recirculated to the evaporator tubes. Steam drums also serve storage and water treatment functions. An alternative design to steam drums is a once-through HRSG, which replaces the steam drum with thin-walled components that are better suited to handle changes in exhaust gas temperatures and steam pressures during frequent starts and stops. In some designs, duct burners are used to add heat to the exhaust gas stream and boost steam production; they can be used to produce steam even if there is insufficient exhaust gas flow. Saturated steam from the steam drums or once-through system is sent to the superheater to produce dry steam which

is required for the steam turbine. Steam conditions acceptable for the steam turbine are dictated by thermal limits of the rotor, blade, and casing design. Preheaters are located at the coolest end of the HRSG gas path and absorb energy to preheat heat exchanger liquids, such as water/ glycol mixtures, thus extracting the most economically viable amount of heat from exhaust gases.

Combined cycle gas turbines – operational limitations The overall efficiency of fuel-to-electric power conversion for gas turbines can be as low as 30 percent. This means that twothirds of the latent energy of the fuel ends up wasted, much of it as thermal energy in the hot exhaust gases from the combustion process. By recovering that waste heat to produce more useful work in a combined cycle configuration, gas turbine power plant efficiency can reach 55 to 60 percent. In combined cycle gas turbine (CCGT) plants, the output produced by the steam turbine accounts for about half of the CCGT plant output. There are many different configurations for CCGT power plants, but typically each GT has its own associated HRSG, and multiple HRSGs supply steam to one or more steam turbines. For example, at a plant in a 2x1 configuration, two GT/HRSG trains supply to one steam turbine; likewise there can be 1x1, 3x1 or 4x1 arrangements. The steam turbine is sized to the number and capacity of supplying GTs/HRSGs. Designs and configurations for HRSGs and steam turbines depend on the exhaust gas characteristics, steam requirements, and expected power plant operations. Because the exhaust gases from a gas turbine can reach 600ºC, HRSGs for GTs may produce steam at multiple pressure levels to optimize energy recovery; thus they often have three sets of heat exchanger modules – one for high pressure (HP) steam, one for intermediate pressure (IP) steam, and one for low pressure (LP) steam. The high pressure steam in a large CCGT plant can reach 40 – 110 bar. With a multiplepressure HRSG, the steam turbine will have multiple steam admission points. In a three-stage steam turbine, HP, IP and LP steam produced by the HRSG is fed into the turbine at different points. There are operational limitations


Fig. 4 – Wärtsilä Flexicycle power plant based on ICEs.

associated with operating gas turbines in combined cycle mode, including longer startup time, purge requirements to prevent fires or explosions, and ramp rate to full load. As the HRSGs are located directly downstream of the gas turbines, changes in temperature and pressure of the exhaust gases cause thermal and mechanical stress. When CCGT power plants are used for load-following operation, characterized by frequent starts and stops or operating at part-load to meet fluctuating electric demand, this cycling can cause thermal stress and eventual damage in some components of the HRSG [3]. The HP steam drum and superheater headers are more prone to reduced mechanical life because they are subjected to the highest exhaust gas temperatures. Important design and operating considerations are the gas and steam temperatures that the module materials can withstand; mechanical stability for turbulent exhaust flow; corrosion of HRSG tubes; and steam pressures that may necessitate thicker-walled drums. To control the rate of pressure and temperature increase in HRSG components, bypass systems can be used to divert some of the GT exhaust gases from entering the HRSG during startup. The HRSG takes longer to warm up from cold conditions than from hot conditions. As a result, the amount of time elapsed since last shutdown influences startup time. When

gas turbines are ramped to load quickly, the temperature and flow in the HRSG may not yet have achieved conditions to produce steam, which causes metal overheating since there is no cooling steam flow. In 1x1 configurations, the operation of the steam turbine is directly coupled to the GT/HRSG operation, limiting the rate at which the power plant can be ramped to load.

Flexicycle: combined cycle efficiency with responsiveness The FlexicycleTM power plant is a combined cycle power plant with unique characteristics based on Wärtsilä gas or dual-fuel ICEs. Because ICEs convert more of the fuel energy into mechanical work, they have higher simple cycle efficiencies, averaging near 50 percent. The exhaust gases from ICEs are around 360ºC, much lower temperature than GT exhaust. Due to the lower exhaust gas temperatures, HRSGs designed for ICE power plants are much simpler in design, creating steam at one pressure level – approximately 15 bar. The steam turbine process adds approximately 20% to the efficiency of the Flexicycle power plant. (Figure 4) In a Flexicycle power plant, each ICE generator set has an associated HRSG. Bypass valves are used to control the admission of steam to the steam turbine when an engine set is not operating. One engine can be used to preheat all the HRSG

exhaust gas boilers with steam to keep the HRSGs hot and enable fast starting. Flexicycle power plants combine the advantages of high efficiency in simple cycle and the modularity of multiple engines supplying the steam turbine. The steam turbine can be run with only 25 percent of the engines at full load, or 50 percent of the engines at half load. For a 12-engine power plant of around 200 megawatts (MW), this means only three of the engines need to be operating to produce enough steam to run the steam turbine. The result is a very efficient power plant that retains the operational agility of a power plant based on simple-cycle engines.

References [1] “Neuchâtel Gas Turbine.” ASME. The American Society of Mechanical Engineers, n.d. Web. 27 Jan. 2015. . [2] Almasi, Amin. “Large Aero-Derivative Gas Turbines for Power Generation.” Power Engineering. PennWell Corporation, 01 Jan. 2012. Web. 27 Jan. 2015. . [3] Aurand, Jonathan D. “HRSG Cycling Assessment.” CCJ Online Combined Cycle Journal. CCJ Online Inc., n.d. Web. 27 Jan. 2015. 100%/min • Frequency balancing

50 40

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Wärtsilä 34 gas power plant

(*) A power plant with e.g. 10 gensets can correspondlingly operate at 3% of its total nominal output.

Fig. 1 – Loading and unloading of a Wärtsilä 34 gas power plant.

minutes. Startup time is a significant metric for flexibility, but comparison of different technologies and designs is complicated by the way startup time is measured by different manufacturers. The startup time quoted can be from push of the start command or from ignition. In the case of gas turbines, this difference in “start” definition can be as much as 20 minutes. Further, it is important to differentiate between the ramp time to full load versus partial load.

Gas turbine startup During startup, a gas turbine undergoes a sequence of increasing compressor spin to reach firing speed, ignition, turbine acceleration to self-sustaining speed, synchronization, and loading. There are numerous thermo-mechanical constraints during startup of the gas turbine, including limits on airflow velocity through the compressor blades to prevent stall, vibrational limits, and combustion temperature limits to prevent turbine blade

fatigue, with the significant parameter being the turbine inlet temperature. In combined cycle operation, the heat recovery steam generator (HRSG) imposes additional thermal limitations, as the high temperature environment subjects HRSG components to thermal stress [2]. The HRSG is directly coupled to the gas turbine, so changes in turbine exhaust gases induce flow, temperature, and pressure gradients within the HRSG. These gradients must be carefully controlled to prevent adverse impacts such as material fatigue, creep (damage caused by high temperatures) and corrosion [3]. In addition, the steam turbine can restrict the gas turbine loading rate if the steam temperature leaving the HRSG exceeds steam turbine limits. To avoid this, the gas turbine is ramped to hold points (held at steady load) to allow steam temperatures and pressures to rise slowly within allowable material limits. It takes longer to start the HRSG and steam turbine from cold conditions than from hot conditions. The definition of

“hot” conditions varies by manufacturer, but is generally defined as within eight (8) to 16 hours of HRSG shutdown. As a result, the amount of time elapsed since last shutdown greatly influences startup time. Once-through HRSGs are used by some manufacturers to overcome the startup thermal and pressure limitations that exist with steam drums. Combined cycle gas turbines (CCGTs) are also subject to purge requirements to prevent auto-ignition from possible accumulation of combustible gases in the gas turbine, HRSG and exhaust systems. The purge is required before the unit is restarted. Purge times depend on the boiler volume and air flow through the HRSG, and are typically set to about 15 minutes. This purge time adds to the overall start time. In order to enable faster startup and ramping, CCGT manufacturers have attempted to decouple the gas turbine startup from the HRSG and steam turbine warm-up. Bypass systems are used to isolate the steam turbine, ultra-low nitrogen

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oxides (NOx) combustion systems are used to reduce emissions while ramping, and attemperators maintain steam temperatures within appropriate limits [4]. A “purge credit” allows the system purge to be completed at shutdown, eliminating the requirement for a redundant purge at next startup [5]. The purge credit can only be used in some HRSGs that have no duct burners and where the gas turbine is fired on natural gas only. These improvements have resulted in higher CCGT ramp rates and startup times of about 30-35 minutes, about half the time for conventional hot start that would require purge and gas turbine holds. However, rapid cycling imposes increased CCGT maintenance costs [6]. In simple cycle, published start times for gas turbines are about 10 to 15 minutes.

ICE startup An ICE power plant can start and ramp to full load very quickly due to rapid ignition of fuel within the cylinders and the coordinated starting of multiple generating sets. Wärtsilä ICE power plants employ high efficiency lean-burn technology that can reach full load in as little as two (2) minutes under “hot start” conditions. To meet “hot start” conditions, cooling water is preheated and maintained above 70°C, engine bearings are continuously prelubricated, a jack up pump supplies prelubrication to the generator bearings, and the engine is slow turning (cycling). The Wärtsilä 34SG power plant requires only 30 seconds to complete startup preparations, speed acceleration, and synchronization to the grid. Loading to full power occurs rapidly in just 90 seconds. Startup time is not affected by the amount of time the unit had been previously shut down. The Wärtsilä 50SG power plant takes seven (7) minutes to reach full load. Under cold startup conditions, the Wärtsilä 34SG power plant can reach full load in 10 minutes and the Wärtsilä 50SG in 12

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minutes. FlexicycleTM power plants offer advantages over CCGTs as sufficient steam pressure can be generated with only a subset of the engines operating.

Rapid startup for flexible power generation Figure 2 shows a startup time comparison of the Wärtsilä 34SG and Wärtsilä 50SG power plants with simple cycle and combined cycle gas turbine plants from manufacturers GE, Alstom, and Siemens. All startup times are measured from operator initiation of the start sequence. As can be seen from the graph, Wärtsilä power plants provide quick start ability under 10 minutes, which meets system operator requirements. Unlike CCGTs, hot start conditions in a Wärtsilä power plant can be maintained regardless of how long the engines had previously been inactive.

Ramp rate: how fast is fast? Because solar and wind generation can change within minutes, electric grid operators rely on dispatchable units that can provide additional load (or curtail load) on the same timescale as variations in renewable output. The increase or reduction in output per minute is called the ramp rate and is usually expressed as megawatts per minute (MW/min). Ramp rates of most industrial frame gas turbine models are advertised as 10 MW/min up to 100 MW/ min, with an average of about 25 MW/ min. Ramp rate depends on generating unit capacity, operating conditions (whether unit is just starting up or operating at a minimum load hold point) and optional technologies for reducing startup time and increasing ramp rate. The ramp rate of a gas-fired power plant also depends on the number of units and configuration. For example, a ramp rate of 100 MW/min is based on multi-turbine plant designs, such as a 2x1 CCGT (net power output of 750 MW) where each gas turbine is rated to ramp

at 50 MW/min. While ramp rate in MW/ minute is a valuable metric, it is important to understand the operating conditions under which advertised ramp rates can be achieved.

Starting loading capability versus ramp rate The starting loading capability is often quite different than the advertised ramp rate for gas turbines. Gas turbine ramp rates of 35–50 MW/min are achievable only after the unit has reached self-sustaining speed. The fastest loading gas turbine models produce 30 percent load delivery after 7 minutes and take nearly 30 minutes to reach full output under hot start conditions [7]. Wärtsilä 34SG engines have true quick start capability – an effective ramp rate of 50 percent per minute, reaching full load within 2 minutes. For a 200 MW plant, this equates to 100 MW/min. The starting load delivery of Wärtsilä power plants and gas turbines is compared in Figure 3, showing the percentage of load delivered 7 minutes after startup. This assumes optional gas turbine technology for enabling fast loading and is based on manufacturer-published ramp rates. The fast startup time of Wärtsilä ICE provides a significant operational advantage over gas turbines. As gas turbines are just producing output, both the Wärtsilä 34SG and Wärtsilä 50SG engines have already reached full load. Operational ramp rates of Wärtsilä engines and the most popular industrial frame gas turbine models of similar size (200 MW) are compared in Figure 4, with ramp rate expressed in two metrics – MW/ minute and percent of full load per minute. Once running and at nominal operating temperatures, Wärtsilä power plants can adjust output up or down rapidly. Wärtsilä power plants can ramp from 10 percent to 100 percent load (or down) in just 42 seconds. This means that a power plant comprised of 12 Wärtsilä 50SG engines has an effective operational ramp rate of 288


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Wärtsilä 34SG power plant under hot start conditions: 70°C cooling water temp, prelubrication of the engine and gen bearings Wärtsilä 50SG power plant under hot start conditions: 70°C cooling water temp, prelubrication of the engine and gen bearings Simple cycle industrial (heavy duty) gas turbine under hot start conditions: GE, Alstom GE FlexEffiency CCGT under hot start conditions: purge credit, Rapid Reaponse, startup within 8 hours of shutdown Siemens F-class CCGT under hot start conditions: auxiliary steam, stack dampers maintain HRSG temperature and pressure

Fig. 2 - While combined cycle gas turbines can take over 30 minutes to start, Wärtsilä ICE power plants can start and reach full load in less than 10 minutes.

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Ramp rate Nominal 200 MW power plant

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Loading rate (MW/minute)

Fig. 4- Wärtsilä engines have a significantly higher operational ramp rate than gas turbines of similar size.

MW/minute – significantly faster than a comparably sized gas turbine.

Economies of numbers provides greater flexibility Over the course of a century, the trend in the electric power industry had been toward ever increasing generating unit sizes and plant capacities. Centralized power plants were built using custom-engineered technology of massive size. Conventional wisdom was that “bigger is better” as the capital costs per unit of capacity and production costs declined with increasing unit size, delivering economies of scale driven in part by improved steam turbine efficiencies. The push for higher outputs and efficiencies directly led to the development of combined cycle, necessitating larger gas turbines with higher firing temperatures that enabled exhaust gas heat recovery to drive a steam turbine. While in the 1950s the firing temperature of gas turbines was about 800°C and average turbine size was around 10 MW, by the 1990s advanced gas turbines averaged over 100 MW and had firing temperatures exceeding 1300°C. However, large gas turbines required considerable on-site construction and assembly, and could not easily adjust load to meet fluctuating demand. Modularized smaller-scale generating units operated in parallel and deployed as needed to match the

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changing power requirements began to serve an important function for the stability of electric transmission grids. This shift toward “economies of numbers” provides reliability, construction, and efficiency benefits. ICEs are ideally suited to modular use, as sets of 4 – 30 MW engine units can provide a range of incremental part load power without sacrificing efficiency. For example, a Wärtsilä power plant that has 28 modular Wärtsilä 34SG engine units, each sized at approximately 10 MW, can deliver a range of output from just a few MW to over 270 MW. Due to the modular design of Wärtsilä power plants and rapid startup, the engines can be loaded and unloaded individually. By operating only a subset of the engines at full load to produce the desired output, high efficiency is maintained. Modularity offers simplified maintenance features and quality benefits, as components are prefabricated in a factory-controlled environment and tested. Prefabricated power generation modules are selfcontained components of the system that are designed to interface with auxiliary power plant systems. As a result, the timeframe to plan, engineer and construct a power plant is shortened. Because generating units are incrementally sized, a wide range of plant capacities and fuel options – including multi-fuel use – can be designed.

Expanding power needs in the future can be met with the addition of more engine units and ancillary modules, rather than the construction of a new power plant. Wärtsilä ICE modularity provides built-in redundancy in case of unit outages or maintenance without significantly affecting overall full plant output.

Limitations to gas turbine flexibility Gas turbine power plants, which have traditionally required significant on-site assembly, have begun to be designed in a modular fashion to shorten construction time. Modularity in architecture provides limited operational flexibility for gas turbines, however. This is due to the size of units, small number of units, and efficiency tradeoffs for simple cycle versus combined cycle. Industrial gas turbines for power generation may be 100 – 350 MW apiece and have limits on the lower range of output at which they can operate. This minimal load, or “turndown” percentage, is bounded by emissions limits. When the gas turbine operates at low load, the compressor airflow may not be enough to support conversion of carbon monoxide (CO) into carbon dioxide (CO2) in the combustion chamber. Gas turbines are generally constrained to a turndown of 30 to 40 percent of full load to meet emissions regulations [8]. A simple cycle power plant with two gas turbines can


Load Coal power plants Gas generation

Wind generation

Plains End 1 & 2 power plants Flexible generation

Fig. 5 - Screen shot from a dispatch center shows the drop off in wind generation (green line) and rapid ramp up of Plains End power plant to compensate. Compared to the fast ramping of the Wärtsilä plant, gas turbine output (purple line) increases more slowly (Source: Colorado Dispatch Center, Xcel Energy, USA).

adjust plant output down to about 15 to 20 percent of full load by operating only one turbine, but efficiency is limited to about 30 percent. Combined cycle operation introduces more complexity into the operating parameters of the gas turbine plant. Modular architecture for CCGT power plants consists of one to four gas turbines, HRSGs for each gas turbine, and a common proportionally-sized steam turbine. The lower load limit is affected by the turbine exhaust temperature, which must be high enough to generate sufficient steam pressure in the HRSG to power the steam turbine. Emissions-compliant turndown for CCGT plants is usually 40 to 50 percent of full load. For example, a combined cycle power plant design based on 200 MW gas turbines (in a 2x1 configuration) has a rated output of over 600 MW, limiting turndown ability to about 300 MW. In comparison, a Flexicycle power plant based on Wärtsilä ICEs does not have similar restrictions on load turndown because sufficient steam pressure can be developed by operating only 25 percent of the engines.

Actual performance demonstrates true flexibility Wärtsilä ICEs are perfectly suited to cycling, as the ability to quickly startup and ramp up or down in load does not affect the

maintenance schedule. In addition to a fast startup time, Wärtsilä engines can stop within one minute and have lower emissions due to lean-burn technology. The difference in performance between gas turbines and Wärtsilä power plants is evident in Figure 5, which presents a screen shot from an actual dispatch center in Colorado, U.S. The Plains End power plant units (red and white load curves) were used to compensate for a sudden drop off in wind output, rapidly starting and ramping to full load within minutes. By contrast, gas turbines (purple load curve) ramped up at a much slower rate from a low load. This underscores that advertised ramp rates and startup times do not always reflect operational capability, and illustrates the true flexibility provided by Wärtsilä power plants.

References [1] Ellison, James F., Leigh S. Tesfatsion, Verne W. Loose, and Raymond H. Byrne. Project Report: A Survey of Operating Reserve Markets in U.S. ISO/ RTO-managed Electric Energy Regions. Rep. no. SAND2012-1000. Sandia National Laboratories, Albuquerque NM. [2] Pasha, Akber, and Darryl Taylor. “HRSGs for Next Generation Combined Cycle Plants.” Power Engineering. PennWell Corporation, 01 July 2010. Web. 27 Jan. 2015. .

[3] Taylor, Darryl, and Akber Pasha. “Economic Operation of Fast-Starting HRSGs.” POWER Magazine. Access Intelligence, 01 June 2010. Web. 27 Jan. 2015. . [4] Strebe, Martin-Jan, and Arvo Eilau. “The Evolution of Steam Attemperation.” POWER Magazine. Access Intelligence, 01 Nov. 2012. Web. 27 Jan. 2015. . [5] Moelling, David S., and Peter S. Jackson. “Startup Puge Credit Benefits Combined Cycle Operations.” POWER Magazine. Access Intelligence, 01 June 2012. Web. 27 Jan. 2015. . [6] Lefton, Steven, Nikhil Kumar, Doug Hilleman, and Dwight Agan. The Increased Cost of Cycling Operations at Combined Cycle Power Plants. Tech. no. TP203. Sunnyvale, CA: Intertek, 2012. [7] “7HA Gas Turbine (60 Hz).” GE Power Generation. General Electric, n.d. Web. 27 Jan. 2015. . [8] Probert, Tim. “Fast Starts and Flexibility: Let the Gas Turbine Battle Commence.” Power Engineering International. PennWell Corporation, 06 Jan. 2011. Web. 27 Jan. 2015. W32GD, W34DF and W34SG Wärtsilä 46 > W46GD, W50DF and W50SG Wärtsilä 34DF > Wärtsilä 34SG Wärtsilä 50DF > Wärtsilä 50SG A reset maintenance schedule is granted for the DF and SG conversions.

Three gas conversion technologies Wärtsilä offers three gas conversion technologies: SG (spark-ignited) gas-only engines DF (dual-fuel) engines, an engine optimized for running on gas with the possibility of running on HFO (heavy fuel oil) or LFO (light fuel oil) in back-up mode GD (gas-diesel) engines that run on HFO, LFO, crude, natural gas and associated gas The SG engines are lean-burn Otto cycle gas engines. In the process, gas is mixed with air before the inlet valves. During the intake period, gas is also fed into a prechamber, where the gas mixture is rich compared to the gas mixture in the cylinder. At the end of the compression phase the mixture of air and gas in the prechamber is ignited by a

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spark plug. The flames from the nozzle of the prechamber ignite the gas/air mixture in the main combustion chamber. After the working phase, the cylinder is emptied of exhaust gas and the process is repeated. In the gas mode the dual-fuel engine utilizes the lean-burn Otto combustion process. The gas is mixed with air before the intake valves during the air intake period. After the compression phase, the gas/air mixture is ignited by a small amount of liquid pilot fuel (LFO). After the working phase, the exhaust gas valves open and the cylinder is emptied of exhaust gases. The inlet air valves open when the exhaust gas valves close. In the event of gas flow interruption, the engine switches automatically to the backup fuel system (LFO, HFO) without load reduction, utilising the conventional diesel process. The gas-diesel engine utilises the diesel combustion process in all operational modes. In gas mode the gas is injected at high pressure after the pilot fuel and ignited by flame from the pilot fuel injection. The GD engine can instantly be switched to liquid fuel mode during operation. The liquid fuel can be LFO, HFO or crude oil. In this case, the process is the same as the conventional diesel process. The GD process tolerates variations in the gas quality allowing the utilization

of associated gases that have earlier been simply flared at oil fields. The GD concept requires very few engine modifications and allows true fuel flexibility.

Environmental drivers urge marine conversions Environmental demands force ship operators to make fast decisions concerning the emission levels of their fleet. The most pressing regulations are for those operating within Emission Control Areas (ECA). The regulation concerning the ECAs came into force in the beginning of 2015. For operating in the ECAs, LNG is the most viable solution for its low emissions and attractive price. Other solutions for low emissions include methanol, low sulphur fuel (MDF) and SOx scrubbers. Whichever route the customer chooses to reduce emissions, Wärtsilä aims to provide the optimal solution. The rising interest in LNG has encouraged the construction of LNG infrastructure and the building of bunkering facilities in major ports. Wärtsilä is playing an instrumental role in this development. Fuel conversion of a vessel must always be based on a comprehensive feasibility study providing information on the scope of the required changes, risk analysis, costs, payback time and the time required for the


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Percent of Full Output

conversion. Each case is unique. Of vessel types, good candidates for gas conversions include tankers, RoRo vessels, RoPax vessels and smaller ferries. One of the biggest challenges with gas conversions is finding space for the LNG storage and processing equipment. A lot is involved with converting a vessel to operate on LNG. The question is not only of getting the engine to run on gas. The best option may be to look at it as a process, as illustrated below.

Stamdard semi-spade rudder

15 10 5 0 –100

Power plant operators look for greater efficiency and lower emissions

–80

–60

–40

–20

0

20

40

60

80

100

Rudder steering force (% of prop. thrust)

Energopac reduces flow separation behind the propeller hub and creates less drag than conventional rudder systems.

6 Full scale Energopac

5 Design configuration

The trend towards gas conversions of power plants derives mainly from the demand for greater fuel efficiency and lower emissions, as well as the growing availability of gas and its low price compared to HFO. Power companies are either replacing HFO engines with gas or DF engines or converting their HFO engines to gas or DF mode. The site-specific objectives may, however, vary. For example, power plants located in the vicinity of oil and gas fields are increasingly converted to utilise associated gas, which would otherwise be flared. Energy companies in need of peaking power look for gas power plants with fast starting and stopping capabilities that require a minimum amount of fuel for stand-by energy. For these cases Wärtsilä has developed its Smart Power concept. Since 2000 Wärtsilä has carried out conversions on more than 20 power plants, totalling 914 MW. In addition to engine conversion, Wärtsilä’s power plant conversion concept may include all the aspects from safety to reliability of operation. After the conversion, the power plant is upgraded according to the latest Wärtsilä design. The evaluation of a new case typically starts with a desktop study which reveals the technical history of the power plant, the best solution for the customer’s needs, the scope of the conversion, risks, the time span required for the conversion, costs and the expected payback time. In addition to the installation of the gas delivery and pressure control system and changes to the engine, a conversion may also include modifying or upgrading such critical components and systems as the engine cooling system, fuel system, automation and exhaust gas system.

Wärtsilä Energopac

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Model scale Energopac Improved propeller design

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Reference design

3 2 1 0 1st

2nd

3rd

Vibration frequency (nth harmonic of blade passage)

A standars propeller-rudder design compared with th improved design using Energopac. The reduction in pressure pulses, due to a more homogenous water inflow into the propeller, results in lower vibration and increased comfort onboard the vessel.

Process of converting a vessel to operate on LNG.

Budgeting

Preliminary feasibility study

Feasibility study Basic design

Request for proposal Piping on deck Tank installation

Building specification Engine conversion

Sea trials and commissioning Hull modification

Start of conversion

Crewtraining Cleaning, painting, finishing

Equipment delivery

Conversion completed

Propulsion control upgrades

Piping and cabling Automation system upgrades

Class approval Risk analysis Conversion contract with shipyard Detailed design

Docking arrangements

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[ FUTURE / IN DETAIL ]

[ FUTURE / IN DETAIL ]

Terho Niemi and Christian Lindholm, co-founders at Korulab, worked with Wärtsilä’s Mikael Leppä (in the middle) on the wearable monitoring device.

Smart monitoring AUTHOR: Lena Barner-Rasmussen PHOTO: Karl Vilhjalmsson

Wärtsilä teamed up with software developer Korulab for making a prototype for a wearable monitoring device.

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As in most emergency cases, saving a few seconds can be the difference between catastrophe and just a scare. That certainly goes for engines, whether you are on a vessel or in a power plant. If essential parameters change for some reason, you want to know about it instantly. A vessel or a power plant is dotted with screens all over to make sure that the crew or operators are notified immediately if something is awry. But even though the captain is working around the clock, there are certain moments when the screens don’t reach him. That might change in the near future. Wärtsilä teamed up with Finnish software developer Korulab to make a proof of concept for a wearable device that the crew or operators can carry with them at all times, making sure that they are notified instantly if something isn’t right.

Prototype first The idea was born inside Mikael Leppä’s head as he visited the engine room of one of the vessels sailing out of Helsinki. Then he bumped in to Christian Lindholm, who for several years has been busy developing software for wearables, those tech gadgets that are projected to take over from the smartphone as the one thing we cannot live without. Part of Wärtsilä’s innovation team is situated in the Open Innovation House in Otaniemi, just outside Helsinki. The place is an innovation hub that has drawn researchers, startups like Korulab and even big corporations such as Wärtsilä to interact and come up with completely new concepts. Korulab has the best know-how when it comes to wearable software, so thoughts

quickly turned into actions as Leppä and Lindholm got started on a prototype. They received helping hands from Jonatan Rösgren and the whole Engine Automation team in Vaasa. “The cost for the actual hardware – the watch – is relatively low, making it possible to build a proof of concept and take it from there,” says Lindholm.

Vital info So the engines were given IP addresses making it possible to monitor the values on an individual cylinder level. Leppä chose what parameters to include and designed the user interface and Lindholm got busy with the software. All this in less than one month. While you can insert all sorts of features into a wearable, Leppä opted for just a few crucial parameters to make navigation simple. Lindholm adds that the info needs to be ‘glanceable’, in other words, easy to grasp with just a glance. “But still, all vital info like engine RPM, oil pressure, water temperature and exhaust gas temperatures can fit in,” says Leppä. These are all parameters that will behave unusually if something unexpected happens. Think of a vessel trying to dock at an oil platform in rough sea. If something is askew, every second counts. So far, the prototype has received lots of positive comments. “A wearable monitoring device can give the crew peace of mind,” says Leppä. So far, all there is to this project is this one prototype. But both Leppä and Lindholm are convinced that in the near future, all engines – both on vessels and in power plants – can be monitored from the wrist.

“Even though the captain is working around the clock, there are certain moments when the screens don’t reach him.” A wearable device makes it possible to monitor engine on the go.

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