Wärtsilä 18V50SG the world s biggest four-stroke spark-ignited gas engine

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1 Marek SUTKOWSKI PTNSS 2011-SC-046 Wärtsilä 18V50SG the world s biggest four-stroke spark-ignited gas engine Abstract: In 2010 Wärtsilä introduced brand new four-stroke spark-ignited lean-burn gas engine to its portfolio. The new engine generates close to 19MW of power with efficiency about 46%. The product follows market needs and expectations for decentralised power generation combined with reliable and flexible operation. In this paper technical specification of the Wärtsilä 180V50SG will be presented. The description will include development background as well as the engine operation performance, emission levels and fuel requirements. The main components of the engine and applied technology will be also described. Finally, some typical applications of the Wärtsilä 18V50SG will be shown including the newest power plant concept for high-efficency decentralised power generation. The most significant operational features of the engine will be also covered in this paper. Key words: four-stroke spark-ignited lean-burn gas engine Wärtsilä 18V50SG największy na świecie czterosuwowy silnik gazowy o zapłonie iskrowym Streszczenie: W 2010 roku Wärtsilä wprowadziła do oferty nowy czterosuwowy silnik gazowy o zapłonie iskrowym spalający mieszanki ubogie. Nowy silnik ma moc nominalna prawie 19MW i charakteryzuje się sprawnością 46%. Ten nowy produkt jest odpowiedzią na zapotrzebowanie rynku silników gazowych oraz rosnących oczekiwań branży zdecentralizowanej energetyki charakteryzującej się wysoka pewnością działania oraz elastycznością pracy obiektów. Artykuł zaprezentuje dane techniczne silnika Wärtsilä 18V50SG. Opis będzie również zawierał tło całego procesu rozwoju nowego silnika oraz parametry operacyjne silnika takie jak osiągi, emisje oraz wymogi odnośnie paliwa gazowego, którym silnik może być zasilany. Dodatkowo najważniejsze komponenty silnika oraz zastosowana technologia zostaną uwzględnione w artykule. Ponadto artykuł przedstawi tez typowe zastosowania silnika Wärtsilä 18V50SG obejmując również najnowsza elektrownie koncepcyjna dla zdecentralizowanej wysokosprawnej energetyki. Ta część obejmuje również główne aspekty pracy tego silnika. Słowa kluczowe: czterosuwowy silnik gazowy o zapłonie iskrowym zasilany mieszanka uboga 1. Introduction The history of Wärtsilä gas engines starts in 1987 when the first gas-diesel engine was introduced. This technology was mainly dedicated to offshore applications, although it also could be used for power generation. In 1992 the development of the lean-burn sparkignited gas engine has started and the first sparkignited gas engine was released in [5, 6]. The engine offered very good performance and clean combustion (lean gas mixture) with self-learning and self-adjustable functions in control system. At the end of 20th century, the high-efficiency lean-burn Wärtsilä 34SG engine family based on the new Wärtsilä 32 diesel engine frame was introduced. This new engine family has replaced the old one and is dedicated to very efficient Wärtsilä gas power plants. New trends in power generation require combined high-efficiency, high-flexibility and highreliability technology. Decentralised power generation stations are getting bigger and they have to have several functions in energy system: grid stability, peak power generation, base-load operation etc. This creates many challenges and out-dated technology needs to be replaced. The Wärtsilä 18V50SG, the world s biggest four-stroke sparkignited gas engine is a response for these requirements. The engine introduced in 2010 provides power around 19 MW combined with highefficiency and flexibility. A huge experience gained by Wärtsilä over many years of gas engines devel- 1

2 opment results in high reliability and operation availability. 2. Engine technology & design The Wärtsilä 18V50SG engine benefits from well-proven Wärtsilä lean-burn spark-ignited gas engine concept as well as from the Wärtsilä 18V50DF dual-fuel engine technology. The Wärtsilä 18V50SG engine is built on the same frame like the Wärtsilä 50DF and the Wärtsilä 18V46 diesel engine. The Wärtsilä 18V50SG is turbo-charged fourstroke medium-speed engine with ported gas injection and a spark ignition system with a prechamber. The engine stroke is 580 mm (the same like in the Wärtsilä 18V46) and bore is 500 mm (increased from 460 mm like in Wärtsilä 18V50DF). The main engine data are presented in the Table 1. Table 1. The Wärtsilä 18V50SG engine data [9] Cylinder configuration 18V Cylinder bore / stroke 500 / 580 mm Speed 500 or 514 rpm Mean piston speed 9.7 or 9.9 m/s Compression ratio 11:1 V-angle 45 Engine length mm Engine width mm Engine height mm Engine weight kg A nodular cast has been chosen for the engine block due to its strength and stiffness. Advanced foundry technology results in a pipe-free engine block with integrated oil and water channels. The engine block has large crankcase covers for easy maintenance access. The crankshaft design provides very good bearing conditions and very high stiffness, since the cylinder spacing is only 1100 mm. Each cylinder liner is equipped with two sensors for continuous temperature monitoring. Typically for Wärtsilä engines, pistons are made of the lowfriction composite type with aluminium skirt and forged steel top. The Wärtsilä 18V50SG engine has been designed for optimal cooling and heat recovery. The open-interface cooling system has four circuits: cylinder cooling (jacket), charge-air hightemperature cooling, charge-air low-temperature cooling and lube-oil cooling. The lubricating oil system includes a wet oil sump, an engine-driven main pump as well as an electrically driven prelubricating pump, cooler and filters. The prelubricating system is used before engine starting; it helps to reduce wear of engine components. A specially designed pre-chamber combines low NO x emission, extended spark plug life, rapid ignition and stable combustion with high combustion efficiency. Its shape was developed from smaller spark-ignited gas engine i.e. Wärtsilä 20V34SG, optimized with 3-dimentional CFD simulations and then verified during many hours of engine test runs. The ignition module is integrated into the Wärtsilä Engine Control System (WECS), which sets the global ignition timing. The module itself sets individual ignition timing for each cylinder to provide the most efficient combustion and to avoid knock. The spark plug was developed together with spark plug suppliers to withstand high cylinder pressures and temperatures which negatively affect typical spark plug lifetime. In the Wärtsilä 18V50SG, engine ported-gasadmission technology is used which is identical to the one from Wärtsilä 18V50DF and eliminates the risk of backfire in the air intake manifold, gives a good load response and enables a different delivery of gas fuel to each cylinder. The main gas admission valves are located right upstream of the inlet valves. Each cylinder is controlled separately by WECS, which is continuously monitoring parameters like engine load and speed, exhaust temperatures and pressure inside each cylinder. The prechamber receives gas via mechanically-driven hydraulically- controlled valve. This solution has proven to be very reliable and provides excellent ignition properties of pre-chamber mixture. All Wärtsilä 18V34SG engines are equipped with two turbo-chargers, which were chosen for their minimum flow losses and very good efficiency. A charge air pressure reaches 450 kpa at full load operation. The engine has a pneumatic starting system with starting valves in the cylinder heads on one bank only. Valves are operated by an air distributor while starting limiter valves switch off the starting system as soon as the engine runs. The Table 2 presents typical life time for main the Wärtsilä 18V50SG engine components. The components life time is based only on total operating hours and the engine starts, stops or loading history have no influence on maintenance schedule. Table 2. The Wärtsilä 18V50SG main components life time [9] Engine component Typical life time (operating hours) Piston Piston rings Cylinder liner Cylinder head Inlet valve and valve seat Exhaust valve and valve seat Crankshaft bearings Camshaft bearing Main gas admission valve Pre-chamber valve Pre-chamber

3 Ignition coil on plug Engine operation & performance In lean-burn engines, the peak temperature is kept low which results in a low NO x emission, reduces the knock tendency and enables a high thermal efficiency. Unfortunately, too lean mixture can lead to misfiring and high emission of unburned hydrocarbons. The WECS is designed to control every cylinder separately and to keep each cylinder in its optimal operating window (Fig.1). Fig.1. The Wärtsilä 18V50SG cylinder optimal operating window [8] The system is based on cylinder pressure measurements supported by exhaust gas temperature measurements, engine speed measurements and turbocharger speed measurements. The engine can operate at 500 rpm or 514 rpm and the brake mean effective pressure is equal to 2.2 MPa, which provides 1045 kw (at 500 rpm) or 1070 kw (at 514 rpm) of power per cylinder with a maximum firing pressure of 17.8 MPa. The engine has 90% mechanical efficiency and over 47% overall efficiency. The engine is usually integrated with an electrical generator on a common frame base with electricity generating efficiency of the set 46%, which results in kw of electrical power at 500 rpm [8, 9]. The gas fuel requirements for continuous engine operation at full load are presented in the Table 3 and the engine performance data are presented in the Table 4. The Wärtsilä 18V50SG engine is design according to the newest requirements regarding flexible power generation. The engine is able to reach full load within 10 minutes from start signal. The engine efficiency doesn t change much over very wide load range (from 50% to 100% load), which is very beneficial when part load operation is required for a longer time. In emergency situation the engine can start-up and load-up even quicker. The start-up and loading procedures are shown in the Figures 2 and 3. Table 3. The Wärtsilä 18V50SG gas fuel requirements for continuous full load operation [9] Lower heating value Min. 28 MJ/m³ Methane number Min. 70 Methane contents, CH 4 Min. 70% Hydrogen sulphide, H 2 S Max. 0.05% Hydrogen, H 2 Max. 3% Condensates Not Allowed Ammonia Max. 25 mg/m³ Chlorine + Fluorine Max. 50 mg/m³ Particles or solids 50 mg/m³ Max. (content and size) 5 m Gas inlet temperature Range 0 60 C Table 4. The Wärtsilä 18V50SG performance data at full load [9] Mean effective pressure 2.20 MPa Maximum firing pressure 17.8 MPa Power per cylinder 1045 kw (500 rpm) 1070 kw (514 rpm) Engine mechanical efficiency 90% Engine overall efficiency 47.4% Electricity generating set efficiency 46.2% NO x emission 1.2 g/kwh CO emission 1.06 g/kwh HC emission 3.2 g/kwh Typical CO2 414 g/kwh Particulates emission 0,064 g/kwh Formaldehyde 0,27 g/kwh Total sound power level 129 dba Fig. 2. The Wärtsilä 18V50SG start-up procedure (514 rpm nominal speed) [9] The successive loading can be combined with load steps, if the engine is operating in island mode (speed control). The minimum continuous load is 30%. The maximum permissible load step which may be applied at any given load is presented in the Figure 4. Furthermore the stated values are limited to a running engine that has reached nominal oper- 3

4 ating temperatures, or for an engine which has been operated at above 30% load within the last 30 minutes. Fig. 3. The Wärtsilä 18V50SG loading and unloading curves [9] Fig. 4. The Wärtsilä 18V50SG instant loading steps [9] 4. Typical applications All Wärtsilä gas engines can be used as a power source in pumping stations for pipelines and the dual-fuel engines can be also used for marine purposes. The Wärtsilä spark-ignited gas engines and dual-fuel ones are mainly dedicated for power generation applications. Wärtsilä gas power plants can operate in parallel to the grid or in island mode. They can be controlled at site or remotely and can be connected to condition based maintenance centre where Wärtsilä service personnel has access to plant operation system, as well as engine operation system and they even check signals from particular sensors mounted on the engine. The Wärtsilä has delivered already more than 700 spark-ignited engines to more than 200 gas power plants and their total power is more than 5000 MW. Also the Wärtsilä 46 and the Wärtsilä 50DF that share frame and components design with Wärtsilä 50SG have impressive reference record: more than 700 engines and more than 10 GW of their total power. The Wärtsilä 18V50SG engine is meant to replace the Wärtsilä 20V34SG in new gas power plants projects with plant output over 150 MW. The engine can operate on pipeline quality natural gas as well as on liquefied natural gas (LNG). Typical Wärtsilä gas power plants are used as power source for industry (mining, cement, petroleum etc.), for local utilities (airports, hotels etc.) or as part of an electrical grid system. The engine can be core part of combined cycle gas power plant. This solution requires exhaust gas steam boilers and a steam turbine. By implementing this power generation capacity of plant can be increased by 8% to 10% and electricity generation efficiency can reach totally over 50%. The Plains End power plant is excellent example of the Wärtsilä spark-ignited engine application as important part of an electricity generation system (Fig. 5). The plant is located in Denver in USA. The first phase (Plains End I) was delivered in 2002 and has twenty Wärtsilä 18V34SG engines generating together 111 MW with 41% of electricity generation efficiency. Originally plant was meant to be peaking power plant started once per day only for covering peak power demand. Soon after plant operation started client (PG&E National Energy Group) discovered great potential for flexible gas fired power plants and has changed operation profile by providing grid stability service as support for growing wind power plants capacity in that region. The client also ordered the extension of existing power plant (Plains End II) with fourteen Wärtsilä 20V34SG engines providing additional 118 MW with 44% of electricity generating efficiency. The Plains End gas power plant can generate up to 230 MW and full power of the plant can be reached in less than 5min. The plant is started and ramped-up when wind generated electricity decreases as a result of wind behaviour. This kind of operation requires over 1000 starts and stops per year on average. The short start-up time or frequent starts has no influence on the maintenance schedule. Fig. 5. Examples of Wärtsilä power plants as typical applications of the Wärtsilä 18V50SG. Top: 230 MW flexible grid stability gas power plant Plains End I & II (Denver, USA); bottom: 308 MW base load gas power plant Sangachal (Azerbaijan) [1] 4

5 Another potential application example for the Wärtsilä 18V50SG comes from the Caspian Sea area. The largest so far Wärtsilä gas power plant is located in Azerbaijan. The plant is based on eighteen Wärtsilä 18V50DF gas engines and is located near the biggest oil terminal in that region. This 308 MW gas power plant started operation at the end of 2008 and is a very important component of the country power generation system. 5. Summary The Wärtsilä 18V50SG gas engine is the newest Wärtsilä lean-burn gas engine dedicated to the most efficient large Wärtsilä gas power plants. The engine is the world s biggest 4-stroke spark-ignited gas engine and its design is based on advanced technology and sophisticated solutions providing excellent performance, reliable operation, easy maintenance and long life of engine components. The Wärtsilä 18V50SG is a very efficient (47.4% overall efficiency) and powerful (over 19 Nomenclature / Skróty i oznaczenia WECS Wärtsilä Engine Control System / silnikowy system automatyki i sterowania wärtsilä Bibliography / Literatura [1] Gas power plants, Wärtsilä Corporation brochure [2] Klimstra J.: The road to obtaining the ultimate performance of gas engines opportunities and challenges, 5 th Dessau Gas Engine Conference proceedings, 2007 [3] Kuurio H.: Wärtsilä large gas power plants a modular approach offering a wide range of capabilities, Twentyfour7 Wärtsilä Quarterly Magazine , pp , 2006 [4] Sutkowski M.: The combustion systems in the high-power stationary internal combustion engines, XX International Symposium on Combustion Process proceedings, 2007 MW) engine suitable for flexible power generation. The engine can operate on pipeline quality natural gas or on liquefied natural gas (LNG). The engine maintenance schedule is based on operating hours and is independent from the number of start and stops. The multi-unit design enables high part-load plant efficiency, excellent plant availability and reduced need for back-up capacity. A start-up procedure and engine loading-up to full load takes all together only 10 minutes. Wärtsilä gas power plants with Wärtsilä 18V50SG engines offer also combined cycle solution which increases plant efficiency to the level of 50%. It provides also stepwise investment with smaller risk and optimized profit generation. Wärtsilä gas power plants provide full integration and excellent flexibility and high performance in all ambient conditions, which is a valuable characteristic for modern decentralized power generation. WOIS Wärtsilä Operators Interface System / interfejs systemu operacyjnego Wärtsilä [5] Sutkowski M., Latvasalo T.: The 20V34SG a high-efficiency lean-burn gas engine for highly efficient Wärtsilä gas power plants combustion systems in the high-power stationary internal combustion engines, Combustion Engines PTNSS-2007-SC1, pp , 2007, PL ISSN [6] Wärtsilä 34SG engine technology, Wärtsilä [7] Wärtsilä 50DF engine technology, Wärtsilä [8] Wärtsilä 50SG engine technology, Wärtsilä [9] Wärtsilä 50SG performance manual, Wärtsilä report Mr Marek Sutkowski, PhD, MSc, Eng. Senior Development Manager in Gas Plants at Wärtsilä Finland. Dr inż. Marek Sutkowski starszy kierownik ds. rozwoju w dziale elektrowni gazowych, Wärtsilä Finland. 5