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Side by side
A new ANDRITZ Bio Boiler and new recovery boiler sit side-by-side in the same building at ENCE Navia mill.
The Navia mill, on the Costa Verde of Spain, was once known as CEASA (Celulosas de Asturias S.A.), and is now owned by the ENCE Group. It has been the focus of major activity – and major investment in the last months.
When completed, ENCE claims that Navia will be the most efficient pulp mill in Europe, with a production capacity increase from 300,000 to 500,000 t/a and 550,000 MWh/a of electrical energy generated from renewable sources. That represents 76 MW of biomass renewable energy.
Papermakers and energymakers“Not only are the side-by-side boilers efficient from a construction standpoint,” says Eduardo Garcia, Mill Director for ENCE Navia, “but they improve our ROI by generating green energy for sale to the grid. This is a new business area for us.”
The project design started about five years ago. “Originally, we were very conservative,” Garcia says. “But then we had a change in the company development strategy. By combining our expertise in green electricity generation with traditional papermaking, our target for energy production increased significantly.”
First BioBoilerThe batch cooking process was replaced by continuous. And, ENCE decided to increase the pressure of the mill’s steam, which meant replacing the boilers and turbines completely.
“The negotiation for the boilers was tough since it was the first major package to be contracted,” Garcia says. “ANDRITZ had good references for their recovery boilers, but did not yet have a reference for their biomass boiler. On our side, we are quite experienced with the technology. We have been fighting with euca bark for several years, which is a difficult fuel. We evaluated the ANDRITZ technology and were confident that it would be successful.”
The ANDRITZ BioBoiler is based upon bubbling fluidized bed (BFB) technology, which is the preferred technology for burning biomass. It has a membrane-walled, single drum structure.
The key component is the furnace floor, for which ANDRITZ developed an advanced construction to enable the use of the most challenging fuels.
Florentino Lopez was ENCE’s Project Manager for the Recovery Island upgrade. “We had a very tight schedule,” he says. “The contract was signed in January 2007 and the BioBoiler started up in November 2008.” There was no problem with the boiler, but the mill had to wait for the delivery of the turbines before the BioBoiler boiler could be started on time.
Lopez notes that the ANDRITZ boiler operates at 120 bars pressure and the steam flow is 120 t/h. “Not the biggest, but this is a large boiler,” he says.
The boiler has been operating well since November 2008. “Its performance depends upon the quality of the biomass, which is difficult to control,” Lopez says. “About 40% of the fuel is bark from the mill and the other 60% is procured on the outside. It was difficult to check the quality, and we had some issues with large stones, oversize bark, etc.”
Lopez estimates that at full capacity, the BioBoiler will burn about 400,000 t/a of biomass. “About half the energy we produce at the mill is consumed here, and the other half is available to the national grid,” he says. “This is a significant revenue opportunity for us.”
Fully recoveredANDRITZ was also selected to supply the chemical recovery boiler, the evaporation plant, and the ash recrystallization system (ARC) for removing corrosive chlorine and potassium from the boiler ash.
The recovery boiler is rated at 1,800 tds/d and has the flexibility to handle the full production increase in the mill. It operates at 93 bar pressure and a temperature of 485º C. Incoming black liquor is 75% dry solids (without ash). “Putting the two boilers in the same structure was the best solution from the technical and economical point of view,” Lopez says. “We have a common feedwater system, common continuous blowdown, common condensate tank, etc.”
A major mill shutdown began on January 19, 2009. When the mill came back up on March 1, 2009 the recovery island was complete and running, according to Lopez.
But it wasn’t that simple.
The big liftThe e vaporation project was challenging because ENCE wanted to reuse some of the existing equipment. As is often the case, the existing equipment was not in the right location, according to Jeff Brown, ANDRITZ’s Project Manager for the evaporation plant.
“All of the new equipment was installed and commissioned at the end of 2008,” Brown says. Then, Brown and his team had to wait until the January shutdown to relocate the existing equipment and put everything together.
Relocation required a 750 t crane. “Only one vendor in Spain had a rental crane capable of making the lifts,” Brown says. “The crane lifts were exciting.” The major lifts took just two days – two evaporator bodies, a stripping column, and a large surface condenser. “It went like clockwork,” Brown exclaims. “It couldn’t have gone any better.”
“Because of the tight schedule, we needed site people who could be firm and get things done,” Lopez says. “The ANDRITZ team had these people, yet they were open and professional the entire time.”
“The project team for evaporators and boilers at ANDRITZ has done excellent work,” says Cesar Morante, Project Director for ENCE Navia. “They knew what was required and worked independently to get the job done. They are very professional and efficient.”
World-class install – world-class dryingUnlike other areas where equipment could be pre-erected prior to the January 2009 shutdown, the drying line did not have that luxury. “That is one of the major reasons that we chose ANDRITZ,” Morante says. “Eighty to ninety percent of the work had to be done during the shutdown period, requiring a well-planned approach. We had good experience with ANDRITZ’s on-site erection services in the past.”
According to Morante, the existing drying line was essentially an ANDRITZ design from when ANDRITZ did a modernization at Navia in 2002. “We have been very satisfied with the performance of the line,” Morante says. “The machine is quite reliable and the production guarantees were fulfilled.”
The new line will be capable of world re-cord guaranteed specific production (guaranteed tonnes produced per each meter width of the machine). Design capacity is 1,600 t/d (400 tonnes per working meter guaranteed specific production). The highest guaranteed specific production so far is 375 t/m at Aracruz Celulose in Brazil. Since the rebuild, Navia has achieved 1,594 admt/d production and further work is being done to optimize the process.
“Our relationship with ANDRITZ has been quite good throughout the drying line project,” Morante says. “They fulfilled the requirements during the shutdown without delay. That was quite important. Their erection experience and the coordination of new equipment into the existing equipment has been superior.”
Commissioning on the runOne major challenge for ENCE was that due to the short shutdown period, there was very little time to fully test the systems after modifications were made. “The starting of the new equipment was more or less on schedule,” Garcia says. “The retrofits, however, were quite complex, and we had limited time to fine-tune. Basically, we had to commission equipment while we were running it.
“Still, there are no issues with the overall design, and the mill is balanced. There are only small problems and fine-tuning to be done. Our goal to produce consistently and at steady-state – and we are quite confident.”
