By: Thomas Hägglund & Greger Kåll, Wärtsilä, Finland.
Power plant owners and operators worldwide are seeking ever swifter deliveries of new generating capacity and demanding that suppliers minimize costs and increase efficiency. A packaged power plant based on large oil or gas engines as prime movers promises to satisfy the essential needs of power producers by providing these benefits and many more.
PowerCube is a pre-designed, fully standardized power plant that is delivered fully factory tested
The concept of packaged power plants is nothing new. In fact, many are in use today that provide much needed power in a wide variety of situations. Wärtsilä of Finland now promises a large packaged power system that brings with it an extensive range of power-business and environmental benefits. Its recently introduced PowerCube is a pre-designed, fully standardized power plant that is delivered fully factory tested. With a minimum of installation work, it can be up and running in a short time. PowerCube’s high level of prefabrication before delivery allows quick installation because it needs little construction and engineering work in its erection, which also reduces costs and ensures consistent quality throughout.
The operation of the power unit also benefits from the standardized modular design because the engine technology is fully proven and validated in a number of installations. PowerCube also makes diagnostics and troubleshooting easier, which has benefits in all areas of plant operation and maintenance. The standardization of the power plant also means that spare parts for all of the unit’s components have high availability.
The construction, engineering and commissioning phases of small power plants are often as labour intensive as they are for much larger plants. So the specific investment costs per kilowatt of small and medium-sized plants are often higher than those of large power plants.
Cost ratios work in favour of large facilities because power plants normally require project-specific designs, engineering and project management. These necessary disciplines have a higher impact on the overall specific costs of a small project than a large one. Additionally, economies of scale do not act in favour of small, one-off projects, either in procuring equipment or in the site works. What has been needed for some time to allow economical and speedy delivery, and to reduce the operational costs of a small or medium-sized power plant is a fully standardized and optimized plant that is totally modular. PowerCube is exactly this. It is available in two fuel-efficient versions, the GasCube and the OilCube, both single-engine 9 MW units that have all the components and auxiliaries needed for a complete power production plant. PowerCube will give power producers and users a pre-engineered turnkey power plant in a competitive cost and timing framework. This total package will improve life-cycle costs and the internal rate of return of energy development projects.
PowerCubes bring environmental benefits with them. Each plant’s radiator coolers are on the roof of the plant structure to reduce the structure’s overall footprint on the local environment and improve heat dissipation. This design also reduces the amount of piping used and decreases the time needed for assembly work at site. It also means that the radiators do not need separate supports or foundations, so the amount of infrastructure that the plant requires is reduced, as are the number of interfaces during on-site assembly. In the GasCube package, the exhaust silencer and stack is also integrated and supported on the same foundation.
The ready availability of clean water is a global concern. PowerCube’s cooling system design is an advantage if the power plant is to be located in remote regions far from a ready water supply. The system consumes no water because it has a closed circuit that needs only initial filling, as does the maintenance cooling tank. Most power plants use vast amounts of water for cooling, and large plants such as those based on steam turbines experience problems related to water consumption, especially if the power plant is in a region that suffers from seasonal droughts.
PowerCubes also have low auxiliary power consumption and derating. Their internal auxiliary power consumption has been minimized through the reduction of the parasitic power needs of equipment such as ventilation and cooling fans. This results in the GasCube having a typical net electrical efficiency, after deduction of auxiliary consumption, of more than 44 per cent. Derating is a major concern in extreme ambient conditions, especially in the case of a gas turbine operating in a hot country. The GasCube based on the Wärtsilä 20V34SG gas engine is efficient when it comes to derating, which usually begins at about 35 °C. This, in combination with efficient closed-loop cooling, provides a competitive edge in the market.
PowerCube radiator coolers use low-speed fans, which reduce internal power consumption. Although these are more expensive, they have the benefit of reducing noise from the radiators. The optimized single-circuit cooling system ensures full power output at high ambient temperatures compared with other technologies. The GasCube power plant consists of a single building in which the engine and generator are on a common base frame.
The unit’s air module, charge air silencers, exhaust gas system and an auxiliary module are all connected to the generating set. All of the plant auxiliaries are inside or on the module itself. The auxiliary module includes the gas regulating ramp, the cooling system, the instrument air system, the engine pre-heater and the maintenance-water pump. The only major components not in the auxiliary unit are the starting compressor, starting air bottle and the maintenance-water tank, which are installed next to the auxiliary module.
Oil fired generation
The OilCube uses heavy fuel oil (HFO) with a maximum viscosity of 500 cSt/50 °C. Use of HFO means that the plant needs additional equipment for fuel treatment. Large power plants usually employ steam to heat HFO, but this is expensive in single-engine installations, so in the OilCube the fuel is partly heated by cooling water from the high circuit of the plant’s engine, and partly by electrical heaters. Wärtsilä based its decision to use this combined fuel heating system on extensive life-cycle cost calculations that showed clearly that the lowest cost of generation would be achieved with the chosen technology in single-unit plants, such as the OilCube. These supplementary electrical heaters are necessary but they only slightly increase auxiliary power consumption, and special efforts were made to keep this additional internal consumption down to a minimum.
A major feature of the PowerCubes are their integrated radiator coolers on the roof
The OilCube has a net electrical efficiency of about 43 per cent, which is only slightly less than a power plant that uses steam heating for fuel conditioning. A key innovation in the OilCube is the modular HFO fuel-treatment system, which includes separators. The system is totally integrated into the auxiliary module. There are two full-flow HFO separators, included for full redundancy.
A small intermediate fuel tank has also been included in the fuel treatment module. This eliminates the need for large fuel treatment tanks that would need to be fabricated on-site, resulting in large savings with regard to on-site infrastructure.
Both the GasCube and the OilCube use a low-voltage electrical system that includes a programmable logic controller and a panel-mounted Wärtsilä Operator Interface System (WOIS). This eliminates the need for a separate control room. The control panel in the engine hall can be connected remotely to a central control room. This means that the plant can be monitored and operated remotely from the power plant owner’s control systems, or by using additional WOIS workstations, the final positioning of which can be freely chosen within or outside the structure. For example, the electrical distribution system and an optional WOIS station can be installed in the owner’s facilities or installed in a separate building.
With the PowerCube concept, owners and operators know exactly what they get. Installation is fast and easy, thus guaranteeing a reliable project schedule. At the same time, the size of the power plant can be increased easily by employing more PowerCubes.
The technical risks and problems that arise with project-specific designs are diminished and possible delays in delivery schedules are minimized. These significant reductions in risk mitigation are distinct advantages when potential owners are seeking project financing.
The many user benefits of the PowerCube make it now much easier for prospective power producers to enter the power generation business with small and medium-sized power projects. Equally important, it is now much easier for existing power producers to expand their power operations.