Two industrial sites at opposite ends of Italy are home to highly efficient CHP installations based on reciprocating engines burning a combination of fuels from natural gas, through oils, to liquid bio-fuel. Wärtsilä’s Marco Golinelli describes the two very different installations.
The first Wärtsilä 50DF dual-fuel engine installed in Italy has now been operating at the Fantoni combined heat and power (CHP) plant for more than 6000 hours. Meanwhile, in Pisticci the first Italian plant to use a Wärtsilä gas engine and the first combined cycle, re-powering plant combining three different generating technologies is operational.
These two Italian projects demonstrate how internal combustion engines can be applied in generating electricity and heat with high efficiency and low emissions.
THE FANTONI CHP PLANT
Fantoni, an Italian board manufacturer located in northeast Italy, has become a pioneer in Italy’s energy business. In 2009 it became the first company in Italy to install a Wärtsilä power plant based on the Wärtsilä 50DF engine, and the power plant’s capabilities are proving to be ideal for supplying the heat and power needed in the furniture manufacturing process.
Twelve months ago, the company had four engines generating some 16 MW. To discontinue the use of some of its older energy plants, Fantoni began operation of a new power plant at the Osoppo site in August 2009.
In addition to this being the first installation of a Wärtsilä 50DF engine in Italy, the location of the Osoppo plant presents interesting opportunities.
Proximity to the Wärtsilä factory in Trieste opens up the potential for using the plant for further engine development. It gives Wärtsilä the opportunity to monitor the plant running under actual conditions and provides important data that will be useful in developing the next generation of the Wärtsilä 50DF.
Generating the company’s own electrical power and heat for drying wood has been the norm at Fantoni for a long time. Since 1996, the company has been using several Wärtsilä engines for CHP plants at other sites.
In 2007 expansion of the cogeneration capability in Osoppo was investigated, and the decision was eventually made to install a Wärtsilä 18V50DF capable of delivering just over 16 MW. The new engine enables the company to maximize its production of electricity and heat using the minimum number of engines.
Wärtsilä supplied the engine, and auxiliaries such as pumps for lube oil and light fuel oil (LFO) pilot fuel, as well as emission control equipment for CO and NOx control.
EFFICIENT AND FLEXIBLE
The heart of the new plant, the Wärtsilä 50DF, is a dual-fuel engine designed to provide high output with fuel
|The Fantoni plant|
The engine is designed to yield the same output regardless of whether it is running on natural gas, LFO or heavy fuel oil (HFO). Providing 50 Hz electrical output at a speed of 500 rpm, the engine has a maximum thermal design efficiency of 45%, higher than that of any other gas engine.
Engine functions are controlled by an advanced automation system that allows optimized operation with each fuel option over a wide range of ambient conditions.
Both gas input and the injection of pilot fuel are electronically controlled, which allows the correct air/fuel ratio to be set for each individual cylinder.
This ensures safe and stable combustion using minimum quantities of pilot fuel. All the combustion parameters are controlled automatically during the engine’s operation.
The Wärtsilä 50DF operates on the lean burn principle: the mixture of air and gas in the cylinder has more air than is needed for complete combustion of the fuel, reducing peak temperatures and consequent NOx emissions. Efficiency is increased and higher output is achieved.
At the Fantoni CHP plant, emissions are further controlled by an SCR (selective catalytic reduction system) that involves injecting urea into exhaust gas and using a catalyst to reduce NOx and CO levels.
|The Pisticci plant|
Heat recovered from both the engine cooling water circuit and the engine exhaust gas is fed directly to the factory’s dryers. As the air required for drying has to be at about 180ºC, air heated by the engine exhaust is mixed with ambient air to achieve the correct temperature. Some heat extracted from the engine exhaust gas is recovered by heating thermal oil which is then used to produce steam.
All electricity generated by the Wärtsilä 50DF is consumed within the factory. With a guaranteed value of 45% for electrical efficiency and the utilization of waste heat, the plant’s overall efficiency is 85% or more.
BENEFITS OF CHP
The performance has been confirmed, and in compliance with the local NOx emission limit of 200 mg/Nm3 (at 5% O2) and CO limits of 170 mg/Nm3 has been achieved.
With the plant located just 100 km from Wärtsilä’s manufacturing facility in Italy, activities to monitor its operation, maximize efficiency and extend intervals between maintenance have been launched – all of which will have a direct impact on the plant economics. With current electricity prices, these plants represent an economically feasible option.
THE PISTICCI COMBINED CYCLE CHP PLANT
Another ‘first’ in Italy is the Pisticci CHP plant in Val Basento, south Italy, it was the first plant in Italy to employ medium-speed Wärtsilä engines running on natural gas, and today the first CHP plant to operate three different generating technologies.
The design configuration consists of four Wärtsilä 18V34SG gas engines producing some 22 MW of electricity and full heat recovery to pre-heat feed water for an existing steam turbine plant. The engines burn natural gas as the area is home to one of Italy’s few commercial deposits of hydrocarbons.
Since start-up in October 1999, the plant has proved that gas engines can be harnessed to steam turbines to produce more electricity than either technology could achieve alone.
ENGINE COMBINED CYCLE WITH RE-POWERING
Wärtsilä engineers chose the radical concept of re-powering the existing unit by employing engines fuelled by natural gas, and using the 400°C exhaust gases to heat water for the existing steam turbine.
Output from the original plant running just two steam turbines totalled 20 MW of electricity plus process steam for the industrial park. The average electrical efficiency achieved by this process was 31% with an overall plant efficiency of 52%.
After the gas engines were connected, one of the steam turbines was shut down. The revised normal operating load then totalled some 30 MW, with 16 MW coming from the new engines, 14 MW generated by the steam turbine and process steam being provided as before.
The electrical-thermal production split changed from 45/55 to 50/50. In the new setup, the plant’s electrical efficiency rose to 37% and overall plant efficiency increased to 58%.
Recycling of the exhaust and cooling circuit heat to preheat feedwater and condensate in the steam plant was achieved by simply placing economizers on the exhaust side of the gas engines and piping the collected heat back to the steam turbine section.
This arrangement reduces the amount of steam that would normally be used to pre-heat feed water in the turbine plant.
This “extra” steam can then be used to generate additional output from the steam turbine or made available to customers who are purchasing process steam. The benefits are a reduction in the amount of fuel used to heat the boiler or more power generated by the turbine section of the plant.
HIGHER ELECTRICAL EFFICIENCY
The additional power generated by the steam turbine means that in terms of efficiency, almost 50% of the energy in the fuel used in the gas engines can be converted into electricity. This is quite a remarkable figure for a small gas engine plant with a simple process connection to a steam turbine.
Achieving such efficiency in a gas turbine combined-cycle power station normally requires a total capacity of at least 100 MW, but has not been reached in smaller facilities like the one at Pisticci before.
|Figure 1. Process diagram for gas engines connected to a steam turbine at Pisticci|
Connecting the two systems with four gas engines and economizers together allows high-pressure hot water to be exchanged for steam, and in this way the electrical efficiency is higher than if a small steam turbine was located after the gas engines. The technology is very advanced, and has already proved itself with more than 60,000 trouble-free running hours.
FLEXIBILITY IN OPERATION
Not only is this solution reliable, it is also flexible: to optimize load handling, the gas engines can be run individually or together with or without the steam plant – and vice versa.
The Pisticci facility can adjust output to match current electricity demand from daytime peaks to lower night-time levels.
A plant consisting of a steam turbine-gas engine combination gives operators the flexibility to operate the turbine at as high a load as possible, maximizing that section’s efficiency. Because gas engines have high part-load efficiency, they can either be run at part load or one or more of them can be disconnected as demand falls. The output from gas engines can also be ramped up quickly as demand rises.
THREE GENERATING TECHNOLOGIES
In 2007, the Pisticci plant was extended once more and three Wärtsilä 18V32 LBF (liquid bio-fuel) engines producing 24 MW were installed, raising total output to 76 MW. As before, full heat recovery to the existing steam turbine was incorporated.
The new engines are running on vegetable oils that comply with Wärtsilä’s technical specifications. This gives both the plant and its customers’ full fuel flexibility. It will be able to generate power using natural gas or vegetable oil or both.
Since 2008 Pisticci Campagna has thus had the world’s only CHP station operating three different generating technologies. The lower level of emissions generated mirrors the technological advances that have been made.
Marco Golinelli is vice president, Wärtsilä Power Plants in Italy.Email: email@example.com
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