Wide Operation Range Clinches the Deal on Steam Generator Acquisition

With the experience of a 100 year-old energy producer, Pori Energia Oy produces electricity, district heat and process steam for the Pori region and its surroundings in western Finland. In addition to providing process steam for Boliden Harjavalta’s copper electrolysis, Pori Energia supplies UPM’s Seiku mill and Corenso’s cartong production from its Aittaluoto power plant in the centre of Pori city. In the north of the city, Pori Energia has a joint power plant with local industry. From the plant, electricity and steam are supplied to Sachtleben Pigments Oy.

A few years ago, Pori Energia was facing a decision. A thermal power station supplying process steam for an industry client was nearing its end, and the station’s oil-based steam production was to be replaced with steam produced through renewable energy, mainly wood chips, in a power plant 4.7 kilometres away. What Pori Energia needed was Europe’s longest continuous vacuum steam pipe connected to a transforming station, where the process steam is made with power-plant steam. The steam leaves the Aittaluoto power plant at +205°C. At the transforming station, the heat is transferred to the industrial plant’s pipelines, where the temperature and pressure are lower.

The two-year planning and construction project was completed in December 2012 and Pori Energia started supplying steam for Boliden Harjavalta’s copper electrolysis at the beginning of 2013. After long assessment, a Plate & Shell heat exchanger was chosen for the process. As the main component, Vahterus supplied Pori Energia with a 13 MW steam generator, a condensate receiver and a condenser pre-heater. For an industry traditionally utilising mainly Shell & Tube heat exchangers, the choice required much thought.

‘We made a specified list of the pros and cons and compared the findings’, explains Pori Energia’s construction engineer Ari Aittamäki. ‘One of the most important criteria was the wide operation range of the Vahterus Plate & Shell heat exchanger.’

After the first weeks of production, Aittamäki is satisfied with the results. ‘The minimum load has been reached’, he explains. ‘And even though we’d agreed on a minimum capacity of 30%, we’ve reached even lower figures. All in all, the heat exchanger’s wide operation range and adjustment possibilities are of great importance to us.’

‘Adjustability and the minimum load were the main reasons why we chose the plate heat exchanger’, he adds, ‘and why we were confident about its functionality. Of course, the choice also had to be secure, long-lasting and as maintenance-free as possible. People-made machinery has the tendency to encounter issues sooner or later, but the lifecycles of Vahterus’ units seem credible. Vahterus also offers maintenance service and many things can be fixed within a couple of days.’

Of course, when choices were being made, the lower price of the investment also had a role to play. At the start of the project, Pori Energia also had to think about the possibility of fouling, which could be caused by possible impurities in the circulating fluids. Maintenance solutions were found together with Vahterus.

The steam generator had to be fitted in the old thermal power centre, in a space reserved for the boiler. A compact unit fitted the purpose well. ‘The fact that the installation is lighter and needs less space made the decision easier. Expanding the space would not have been possible’, says Aittamäki.

‘The old boilers will be kept as reserve’, he adds. ‘When heat exchange solutions are made for years ahead, a lot of things can happen in the long run. At all times, we need to ensure supplies to our customers. Our assumption and wish is that the new installation provides us with a long-term solution, functioning for the first 30 years without any further action.’

Around ten similar steam applications already in use

To date, Vahterus has supplied its customers with more than ten similar steam generators that function by the steam-to-steam principle. According to Vahterus’ Customer Service Director Valtteri Haavisto, the applications have worked exceptionally well. For the units supplied to Pori Energia, innovative product development at Vahterus was done according to the customer’s needs. These developments will also be of use to other customers.

‘We cleared out the functions and made the units smaller’, says Haavisto. ‘The condensate’s pre-heaters are now very functional and compact. Moreover, during the project, new solutions to tackle the customer’s challenges with contamination and reparability were developed.’