In mid-2012 the Finnish forest industry major Metsä Group fired-up a new 48 MW biomass gasification plant at its Metsä Fibre Joutseno pulp mill. A year later it started the world’s largest MOXY process at the same mill. The result is that the Joutseno pulp mill has increased its production capacity with the same volume wood and become the first carbon-neutral mill of its kind in Finland.
– One key goal for our company is to make all our mills carbon dioxide-neutral, said Risto Joronen Vice President for Metsä Fibre Oy, the pulp division of Metsä Group, when Bioenergy International paid a visit to Joutseno last November. Metsä Fibre is one of Europe’s largest pulp manufacturers producing a total of over 2.46 million tonnes of softwood and birch pulp at its four mills. With an annual production capacity of 690 000 tonnes softwood pulp the Joutseno mill is Metsä Fibre’s largest. It is also the world’s largest single-line softwood pulp mill.
The Metsä Group are no strangers to using bioenergy either. According to the 2012 sustainability report, Metsä Group consumed a total of 29 TWh of energy. Bioenergy, including purchased heat and electricity, made up two-thirds or 66 percent of this total. Wood-based fuels in own energy production accounted for 83 percent.
Environmental and economic drivers
– The Joutseno mill was a good place to start. Similar development is underway at our other three mills in Finland, said Joronen who is also mill manager for the Metsä Fibre Joutseno mill.
The lime kiln was the only part of the process that was still using fossil gas as fuel. With the new biomass gasifier, the mill became the first carbon neutral mill of its kind in Finland.
Joutseno does indeed seem a fitting place to start. Located 20 km north of Lappeenranta, the town of Joutseno is aptly named- it literally means “Pulp”. It has a long history of pulp mills thanks to its strategic location in the Bothnia-Karelia region, the Metsä Fibre mill can be traced back to 1909.
Co-located on the same site is another Metsä Group mill commissioned in 2002, almost a century later. This mill belongs to the Metsä Board division and produces 290 000 tonnes per annum of bleached chemical-thermo-mechanical pulp (CTMP) for the division’s own board and paper mills. Both mills share the log receiving, debarking, chipping and handling infrastructure.
– The motivation for doing this is both environmental and economic. We wanted to replace fossil gas with a very low-cost renewable fuel source. The availability of low-cost bark biomass here at the Joutseno site was a key driver for us in selecting gasification technology as we had no bark boiler, explained Joronen.
Previously all the bark, a combination of pine, spruce and birch with a moisture content of 50 – 60 percent, was sold to a local combined heat and power (CHP) plant. The gasifier uses around 175 000 tonnes of bark per annum.
Turnkey CFB from Andritz
The project was designed to replace all the fossil gas needed for fuelling the 600 tonnes per day capacity lime kiln with sustainable biomass. Andritz Oy, the Finnish subsidiary of the Austrian company, proposed a complete 48 MWth gasification plant and was subsequently awarded the contract. The scope of delivery included the biomass feedstock handling systems with receiving pocket and bark screen, a belt dryer and feeding conveyor to the gasifier, ash handling, the gasifier, auxiliary systems and a replacement burner for the lime kiln.
– This was a complete delivery from the foundations up, commented Kari Salo, CEO of Carbona and a gasification technology specialist. Andritz acquired full ownership of Carbona Oy in 2010 and the company operates as a subsidiary under Andritz Pulp & Paper division.
The feed system conveys roughly 22 tonnes per hour of P45 sized wet bark to the belt dryer distributing it evenly across the 8 m wide belt. Using the residual hot water and low-pressure steam from the mill, the air in the dryer is heated indirectly via heat exchangers to about 95°C. The dryer has an evaporation capacity of up to 12 tonnes per hour and the bark coming out has a moisture content of 15 percent. This means that the feedstock feed to the gasifier is approximately 11 tonnes per hour.
The gasifier itself is a 48 MW atmospheric air blown Circulating Fluidized Bed (CFB) reactor type, a state-of-the art technology typically used in the forest industry for gasification of forest fuels such as bark. The gasifier operates at about 750-800° C. The turbulent intermixing in the fluidized bed compensates for fuel quality fluctuations, accommodating low-grade fuels with variable moisture and ash content. The management of nitrous oxides (NOx) and sulphur oxides (SOx) is easily accomplished without adding post-combustion cleaning equipment.
– It’s a proven technology, Andritz CFB gasifiers have been in operation since the 1980’s. The technology has been upgraded over the years to satisfy today’s demands for reliability and efficiency, said Salo.
The plant fired up during 2012 and some modifications were made to the bark sizing equipment and belt dryer feeding system. The main challenge now is to improve the utilization of secondary heat in the bark dryer. The economics can be further improved by using more of the hot water from the bleach plant instead of the more costly low-pressure steam.
The gasifier itself has been performing as expected and Joronen was comfortable from the outset that it was not a risk.
– Although it is the critical item in the plant in terms of production, we were quite comfortable with Andritz’s experience and knowledge. This mill site has lots of equipment from them and an on-going service contract, he said revealing that it was the kiln burner that was perceived as a potential risk. The producer gas from the gasifier burns differently and is supplied in larger volumes than the fossil gas. After start-up, there are no worries about its continued performance.
– This is a new kind of fuel for our lime kiln and there are new things to learn about maximizing the secondary heat from our bleaching line. We didn’t have much experience about these things. But we are fast learners! he said.
The other big unknown at the outset was if and how the non-process elements (NPEs) in the gasifier gas would affect the lime quality or the entire chemical recovery loop.
– The chemicals in a modern mill, including inorganics, are recirculated over and over, Joronen explained. These could build up and cause a dead load in the system. We didn’t know for sure if the small proportions of ash formed during gasification would cause us problems. Our lime is a slightly different colour now but the quality is the same. For the NPEs, we just open up the loop a bit and everything seems to be in balance, said Joronen.
A glance at a chart showing operations before and after the change from fossil gas to gasifier producer gas reveal virtually no change in lime kiln operations. Production rates, temperatures, and residual carbonates are almost identical.
– We replaced fossil gas with green energy from a very low-cost fuel source. We can say that under normal operations we are reducing CO2 emissions by about 200 tonnes per day or 72,000 tonnes per year making us the first carbon-neutral pulp mill. On top of that, we are realizing a short pay-back time on the investment. It was a smart move for us and will appear even smarter as energy prices rise in the future, concluded a notably pleased Risto Joronen.
In a separate project, Andritz installed a white liquor sulfide-to-polysulfide conversion (MOXY) plant. The process enables the mill to improve certain qualities, increase its fibre yield and reduce recovery boiler loading. It the largest single MOXY unit in operation worldwide.
Metsä Fibre Joutseno pulp mill
Mill type: Single-line ECF bleached softwood pulp
Capacity: 670,000 tonnes/year
Grades: Pulp for wood-fibre printing papers (SC and LWC) and for high-quality coated printing and speciality papers
Export share: 70%
Wood consumption: 3.5 million m³ annually
Energy self-sufficiency: 100% heat & 192% power, carbon-neutral Installed technology
Andritz fuel receiving & sizing equipment
Capacity: 22 tonnes/hour P45 softwood & birch bark (50 – 60 % mc)
Andritz BDS belt dryer
Evaporation capacity: 12 tonnes/hour to 15 % mc, 12 MW @ 950C
Heat source: 12 MW cooling of mill filtrates & low pressure steam
Andritz Carbona CFB gasifier
Capacity: 48 MW uses c. 11 tonnes/hour P45 bark @ 15 % mc
Output: Producer gas 750-8000C @ 7 kg/second