Greg Morales, Wärtsillä, Ecuador
Six Wärtsilä 18V32DF dual fuel engines will be installed at Spain’s biggest airport – Barajas in Madrid. The natural gas engines will provide electricity on a continuous basis for the busy air base.
Looking at Wärtsilä’s references worldwide, the engines usually generate power in the marine, industry and utility sectors. They are not often related to the aviation market. Yet, Wärtsilä is now diversifying as a supplier of power generation technology for airports, especially in the application of trigeneration – the continuous supply of electrical load, heating and cooling.
Early in 2003, AENA (Aeropuertos Españoles y Navegación Aérea), the Spanish Airport Authority, called for bids to supply thermal and electrical energy under a power purchase agreement (PPA) for a 20-year period. One of the bidders was Sampol (Sampol Ingeniería y Obras, S.A), a Palma de Mallorca-based engineering company, which teamed up with Wärtsilä. The overriding priority of the two partners was to develop a technically advanced, environmentally friendly and cost-efficient cogeneration plant that would guarantee the extremely high level of reliability necessary for this key facility in such an important location.
Sampol presented an offer in competition with bidders from Spain, Portugal and Germany. However, Wärtsilä was the only prime mover supplier able to present an offer based on an EPC (engineering, procurement and construction) approach. Wärtsilä’s strong technological support along with Sampol’s price competitiveness made Sampol the bid winner for the new combined heat and power (CHP) plant.
Two new terminals
The Madrid Barajas airport extension is one of the most important engineering and construction projects underway in Europe at the moment. It calls for the construction of two terminals: a main passenger terminal that includes ticketing, baggage handling and passenger embarkation; and a second satellite passenger terminal connected to the main terminal by underground train. The extension project also includes the addition of new runways, new freeways for access to the airport, and various airport related services.
The new trigeneration plant will be located in a newly commissioned building next to the newest and biggest runway (18R-36L) in operation at present. The engines and the heat production equipment each have their own clearly partitioned areas in the building. Wärtsilä is responsible for supplying the engineering, equipment, installation, commissioning and start-up of six dual fuel Wärtsilä 18V32DF dual fuel engines and their auxiliaries, the heat recovery boilers at the engine’s exhaust, the engine hall ventilation systems and the engine control system.
The 18V32DF will burn natural gas as the main fuel and light fuel oil (LFO) as the back-up fuel. However, the running hours in LFO are limited to a maximum of 200 h/year due to local environmental restrictions. Engine emissions comply with the local environmental laws. In addition to Spanish and European engineering and construction standards, the plant will also comply with the airport’s own regulations.
The CHP plant will generate a net output of 33 MW and will be connected to both the airport’s internal grid and the public grid. The plant will provide electricity on a continuous basis, as well as heating for the new terminals during the winter, and cooling during the summer.
Markings on the Bajaras airport overview indicate expansion plans for the site
Wärtsilä and Sampol entered into a preliminary agreement early in the summer 2003 and the EPC contract was signed in mid-September. Plant handover is expected to take place in July 2004. Wärtsilä’s engineers, managers and technicians from Finland, Chile, Ecuador and Spain form a strong team that will result in a high quality plant design, an economical and state-of-the-art installation, and a example of CHP technology for the airport market. Currently, Wärtsilä is negotiating an operation and maintenance contract with Sampol.
The Wärtsilä 18V32DF is a technically advanced engine for fuel economy and low emission rates. The 18V32DF running at 720 r/min with 60 Hz generators has an output of 5.8 MW and can reach 6 MW when switched to a speed range of 750 r/min and 50 Hz. Each cylinder produces 335-350 kW/cylinder. Efficiency for the gas genset and and back up fuel operation can be measured at 42.5 per cent and 41.9 per cent respectively.
If a gas shutdown occurs due to e.g. interruption of the gas supply, the engine is automatically and instantly switched over to fuel oil operation. When the situation has returned to normal the operator can transfer the engine back from back-up fuel to gas operation. This is possible at engine loads up to 80 per cent. This is a controlled transfer, decreasing fuel oil and increasing gas over a specified time of approximately one minute.
Gas admission and pilot fuel injection are both electronically controlled. This ensures that the correct air:fuel ratio can be set for each cylinder individually and that the minimum amount of pilot fuel can be injected while ensuring safe and stable combustion.
The 18V32DF has minimum of piping and external connections, ample safety margins and facilities for easy and rapid maintenance. Built-in electronically controlled components will ensure that all cylinders stay within the operating window, avoiding knocking and misfiring. This eliminates unnecessary load reductions and shut-downs. The Wärtsilä 18V32DF is designed to give the same output whether it is running on natural gas or on LFO.
The lean burn concept
The 18V32DF engine operates on the lean burn principle: the mixture of air and gas in the cylinder has more air than is needed for complete combustion. Lean combustion reduces peak temperatures and therefore NOx emissions. Efficiency is increased and higher output is reached while avoiding knocking. Combustion of the lean air-fuel mixture is initiated by injecting a small amount of LFO (pilot fuel) into the cylinder. The pilot fuel is ignited in a conventional diesel process, providing a high-energy ignition source for the main charge. To obtain the best efficiency and lowest emissions, every cylinder is individually controlled to ensure operation at the correct air:fuel ratio and with the correct amount and timing of pilot fuel injection.
Wärtsilä and Sampol signed an agreement for construction of the 33 MW cogen plant in mid-2003. Handover of the new plant will take place in July 2004
In the Wärtsilä 18V32DF engine, the air:fuel ratio is very high (typically 2.2) and is uniform throughout the cylinders. Maximum temperatures and subsequent NOx formation are therefore low, since the same specific heat quantity released by combustion is used to heat up a large mass of air. Benefiting from this unique feature of the lean burn principle, the NOx emissions from the Wärtsilä 18V32DF are extremely low, complying with the most stringent of existing legislation. The engine is optimized for operation with 500 mg/Nm3 (five per cent O2), 1.3 g/kWh NOx in gas mode.
The 18V32DF can be started in both gas and diesel mode. In gas mode the engine is started only with pilot fuel injection. When combustion has stabilized in every cylinder, gas admission is activated. This procedure ensures safe and reliable starting. When running the engine in gas mode, the pilot fuel amount is less than one per cent of full load fuel consumption. The pilot fuel amount is controlled by the engine control system.
The fuel oil supply on the engine is divided into two separate systems, one for full load LFO operation and one for the pilot fuel system for gas operation. The pilot fuel is first fed to a pump unit, including duplex filters, pressure regulator and the electrically driven radial piston-type pilot pump. The pilot pump raises the pilot fuel pressure to approximately 1000 bar. The fuel is then distributed through a common pipe system to the injection valves in the cylinder heads. Timing and duration of the pilot fuel injection are electronically controlled. The backup fuel is fed to a normal camshaft-driven injection pump. From the injection pump the high-pressure fuel goes to a spring-loaded injection valve of standard diesel engine design.