PPI (PULP & PAPER INTERNATIONAL) MAGAZINE: Biomass burns brightly

Smurfit Kappa's Piteå mill in Sweden has added a new biomass boiler and turbine generator to increase energy self-sufficiency and cut costs

June 2007
By Graeme Rodden, Editorial Director, Magazines

With a capacity of 700,000 tonnes/ yr of brown and whitetop linerboard, Smurfit Kappa's Piteå mill daily produces a paper web that would stretch from the town in northern Sweden to Brussels.

However, it was not production that brought people to Piteå in late March, rather the startup of the mill's new biofuel boiler. Fittingly, the official inauguration was held in association with the Solander Symposium on biorefining. With an expenditure of Euro 85 million ($115 million), it is the largest investment made in the mill since startup in 1961.

As well as the new Hybex bubbling fluidized bed (BFB) boiler from Metso Power, the project included a new fuel handling system from Raumaster for purchased biomass and a Siemens turbine generator (model SST-PAC-300 axial).

There are myriad reasons why Smurfit Kappa opted for the new boiler. First, the old power boiler was built as a recovery boiler and installed in 1963. It was converted to burn fuel oil in 1973 and then to biomass in 1978. It has been shut down but will remain as a modified low-pressure backup.

Also, with the old boiler, it would have been difficult for the mill to continue producing at full capacity

Smurfit Kappa PitePiteå mill is now up to 47% self-sufficient in electrical energy

Reducing the energy bill

The benefits of the new equipment are increased mill uptime, a reduction in the amount of fuel oil needed (30,000 m3/yr), increased power production (80 GWh), lower emissions (NOx and dust) and an improved work environment. The lower energy bill will help enhance the mill's competitiveness.

The mill uses both purchased biofuel (30%) and that produced in-house from the woodyard, which consumes almost 1.5 million m3/yr of roundwood for its pulping processes (along with 650,000 m3/yr of purchased softwood chips). The mill produces 470,000 m3/yr of biofuel and buys an additional 465,000 m3/yr.

The new Raumaster system was installed to handle the purchased biofuel. After delivery (capacity of 600 m3/hr), it is screened for metals and other large contaminants. There are two silos: a 5,000 m3-one for sawdust and peat; and a smaller one, 2,500 m3, for larger material such as bark, branches and treetops.

The system includes a granulator that can handle wood from demolished buildings and trees that are not suitable for pulp.

At first, Smurfit Kappa expects to use mostly bark and sawdust to feed the boiler but the use of fuel such as branches and treetops will increase. The fuel is mixed and delivered to the boiler via a 243-m long conveyor. The boiler can also burn biosludge at 30% solids content.

As it approaches the boiler, the fuel feed is split into two lines, on opposite sides of the boiler. Each line is then split into two, so there are four feed ports in all. The floor of the boiler is approximately 80 m2 with a layer of sand that is fluidized with primary air (850°C). The fluidized layer is about 1 m thick.

The biomass boiler can produce 50 kg/sec of steam at 12 Mpa pressure at 520°C. The boiler's stack is 93 m high. Near the top, there is an emission control/monitoring station. A bag filtration system is used to clean the gases before they are emitted from the stack. There are a total of 1,960 bag filters in seven baghouses. Each bag filter is 11 m long. Lime is also injected into the flue gas to destroy acid.

Along with the boiler, Metso Power also supplied the flue gas cleaning system, baghouse, electrical works, field instruments and the distributed control system (DCS).

The pressurized steam is sent to the new Siemens turbine-generator (G3). The generator also takes steam from the recovery boiler at 5.8 Mpa. The mill had two older radial turbines but has now shut down the oldest one, which was installed in 1962.

The boiler/turbine project necessitated a rebuild of the mill's steam net with 2.6 km of new piping having to be laid.

Extraction steam is at 2.7 Mpa pressure while back pressure steam is 1.1 Mpa. The steam is used for the mill's evaporators as well as the pulping process and paper machine dryers. The energy output can range from 3-26 MW. With its two turbines, the mill can now be up to 47% energy (electricity) self-sufficient.

Helping the town

Low value thermal energy that cannot be used by the mill is delivered in the form of hot water to Piteå's energy utility. It is used for district heating and meets 95% of the town's heating network needs.

Pulp and paper first

From its pulping processes, the mill also produces 20,000 kg/yr of tall oil, which can be an important and valuable furnish for the making of biodiesel. Speaking at the opening ceremony, mill manager Tore Persson discussed some of the products that can be derived from forest residues: tall oil, turpentine, energy for district heating, chemicals, biodiesel, methane/ dimethyl ether (DME) and "green" electricity. However, he stressed that the important thing is for the fiber to be used first for the production of pulp and paper. Then, this paper/board can be recycled up to four to six times and society still obtains the value as paper products before the energy value will be used.

Also speaking at the inauguration, the CEO of Smurfit Kappa's paper division, Alain Baudant, said the Piteå mill is a flagship of the company and the biomass boiler is another important milestone for it. Although the project had been started before the merger between Smurfit and Kappa, he called it a beacon for the company.