Boiler and automation - effective combination at the largest biomass power plant
Alholmens Kraft in Pietarsaari, Finland, which is the world’s largest biomass power plant, has been in commercial operation already for about 15 years. The company highlights the combination of Valmet’s circulating fluidized bed (CFB) boiler and Valmet DNA automation to operate the huge plant.
The biomass power plant has been in use since January 2002. Many international guests who have visited the plant have become convinced about the operation and technology which is in use. Alholmens Kraft has also won several international awards for its sustainable energy production, since the plant is a good model for sustainable business. The plant delivers 215 MWe of electricity on the open market to the Nordic countries and 60 MWth of district heating to the inhabitants in the city of Pietarsaari as well as 100 MWth of process steam to the UPM pulp mill at the same site. The steam capacity of the plant is 550 MW.
Changing electricity market redesigns business
Since the startup of the plant, the energy business has changed dramatically. The prices of electricity have fallen, so the management has had to carefully consider when to use the AK2 biomass boiler. If there has not been sufficient need for electricity, the smaller AK1 boiler, also a Valmet boiler, will be used.
Sami Lassila, Production Supervisor, knows both the boiler and automation since the very beginning. He has also seen the change in the energy business. “It is very challenging for the whole plant to have frequently starts and stops. Even in those demanding conditions, Valmet’s technology has met the requirements. Sometimes, the plant has to be started to full capacity within a few hours,” he explains.
Valmet DNA provides detailed technical descriptions about how to start and stop the operation. The meaning of a good functioning automation system then becomes easily apparent through the quick changes that are possible. “The plant is large in size and very complicated. There are plenty of conveyors around and many types of fuels are in use. To master all these, a reliable system is required.”
In the control room, four operators run the process. Sami can follow the process even from his office.
Caption: Control room at Alholmens Kraft
Fuel flexibility requires expertise
The design of the plant allows fuel flexibility. Today, besides the biomass, sometimes also burnable waste known as recovered fuel (REF) and coal are incinerated so the raw material can be very diverse.
“The boiler makes it possible to burn several raw materials in a mix. Also, the automation system reacts immediately to the changing combustion circumstances. For instance, coal does not have much moisture, whereas the moisture content of bark can be up to 60–65%. With Valmet DNA, this is not a problem,” Sami states.
Sami Lassila explains: “The live steam parameters are high compared with the normal parameters of bio-fuel boilers. The pressure of the boiler is 165 bar and the temperature of the steam is 545 °C. This leads to a very good efficiency for the plant.”
The emissions – including sulphur oxides (SOx), nitrogen oxides (NOx) and carbon monoxide (CO) – are followed continuously with the help of Valmet DNA. For instance, limestone or ammonia will be added to keep the SO2 and NOx values within specific limits. Alholmens Kraft is able to keep the emission values low because of the optimal combustion conditions.
Quick startup for commercial operation
In 2002, when the big AK2 boiler was started, Sami Lassila worked as a shift manager. In his mind, the time spent with skillful project people who worked successfully as a team is still impressive. “We made tests on how quickly it was possible to change the operation of the boiler, and we reached a record time of 10 MW in a minute,” says Sami proudly.
When asked about the benefits of having the boiler and automation from the same supplier, Sami replies: “There are several benefits. All the parties know each other, and it is easy to find the right person responsible for each technical detail. The planning time for the plant is shorter, because you do not have go through all the features with the boiler supplier and then again with a separate automation supplier. The information is transferred easily. Therefore, even the startup can be finalized quicker.”
Björn Åkerlund,Managing Director, joined the company later. He confirms, “Valmet is certainly one of the core suppliers of technology and automation in the field. I can understand that the information is transferred quicker between all the parties when the entire delivery comes from the same company.”
Valmet’s multifuel boiler and automation work well together
To make everything work smoothly, of course, people are key. Alholmens Kraft has the professionals needed to run the process. Plus, Valmet’s experts are close by to support them.
For more information:
ari.kokko at valmet.com