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Discussing the performance of the Andritz DTVG technology are Suzano’s team (left to right): Marcos Abdalla, Project Coordinator for both installations, Mario Hiroshi Ito, Project Engineer, Marcos Pessotta, Recovery and Utilities Coordinator, and José Alexandre de Morais, Suzano’s Manager of Pulp Production, Recovery and Utilities.
This is a story of two Suzanos – the city and the company.Suzano, the city, is 45 km from São Paulo in Brazil. With its 270,000 inhabitants, and the 360,000 population of nearby Mogi das Cruzes, the cities encircle a large integrated pulp and paper mill.
Suzano, the company, owns the mill. The mill is one of four that Suzano Papel e Celulose owns in Brazil. Suzano is one of South America’s largest integrated pulp and paper producers. It was, in fact, the first company to utilize 100% eucalyptus for the production of printing and writing grades.
The city and the company are intertwined. “Most people who work here, live here,” says José Alexandre de Morais, Manager of Pulp Production, Recovery, and Utilities. “I also live near here with my family. The reason the mill can survive in this location is that we work very closely with the local community.”
Tough on TRSThe location of the mill close to the cities of Suzano and Mogi is part of the reason for the strict TRS permit limits, according to Isaias Shimura, a Process Engineer in the Recovery and Utilities department. Total Reduced Sulfur (TRS) is a measure of the total concentration of bad-smelling sulfur compounds released when pulp is cooked, washed, evaporated, or when the spent cooking liquor is burned for chemical and energy recovery.
“TRS gases are the source of the pulp mill odor,” Shimura says. “It’s what our neighbors refer to when they talk about the smell of the mill. To be good neighbors, we have to do everything possible to eliminate the bad smells.”
The main sources of TRS are the digesters, the evaporators, the lime kiln, the incinerator, and the recovery boilers. According to Shimura, TRS is currently measured at five points: the two lime kilns, the incinerator, and the two recovery boilers.
“We have been on a step-by-step program to address each source of TRS over the years, since we are located in the city,” Shimura says. As part of the upgrade program, Andritz retrofitted one of Suzano’s kilns and the recausticizing plant in 2002-2003. This included the installation of a new slaker, two reactors, and retrofitting the kiln with Sector Coolers and an LMD section.
Removing the last of the odors“Prior to 2005, the biggest remaining odor was coming from the dissolving tanks of our two recovery boilers” says Mario Hiroshi Ito, Project Engineer at Suzano.
The smallest recovery boiler, a Götaverken model built in 1973, burns 860 tds/d of black liquor. The CBC (Mitsubishi) boiler was installed in 1987 and burns 1540 tds/d.
Shimura explains, “After combustion, the black liquor turns into molten ash that collects in the bottom of the recovery furnace. This molten ash (smelt) flows into a dissolving tank. The smelt is mixed with weak white liquor from the recausticizing plant.”
“Typically, the vent stack from the dissolving tank is a major TRS emissions point,” explains João Guilherme Heinz Cruz, an Andritz Service Engineer for recovery boilers and evaporators. “The concentration of TRS emissions from a dissolving tank vent stack can be five to ten times higher than in the recovery boiler’s flue gases. The vent stack is also a significant source of particulate emissions.”
“That smell is not acceptable to our community,” Ito says. We knew we would have to stop venting the gases to the atmosphere and close the system.”
Burning instead of ventingMost dissolving tank emissions are controlled by wet gas scrubbers, where the TRS is washed from the gases before they are vented to the atmosphere. In Suzano’s case, since the mill did not wish to vent gases from the dissolving tank into the atmosphere, the decision was to go with Andritz technology for burning the gases in the recovery boiler.
“The Andritz Dissolving Tank Vent Gas (DTVG) system solves the odor and particulate problems in a unique way,” Cruz explains. “Rather than try to scrub the TRS from the dissolving tank gases and then vent them, we condensate the moisture out of the gases so they can be used in the recovery boiler. Today, it is very common to feed the gases from the dissolving tank to the recovery boiler as part of the combustion air. This has many advantages, including oxidizing the TRS compounds in the recovery furnace and eliminating particulate coming from the vent stack.”
“Andritz has very good technology and the equipment is high quality,” Morais says. “We checked Andritz’s references in this area and were satisfied that they could do the job.”
In the DTVG system, vent gases from the dissolving tank are cooled and washed in the scrubber. Gas enters the lower section of the scrubber vessel and passes through stainless steel packing material and a direct-contact heat transfer surface. The packing material is kept wet with water that is circulated through a heat exchanger. A significant portion of the gas condenses when it passes through the packing material. Excess water is returned to the smelt dissolving tank.
Before leaving the scrubber vessel, the cooled gas passes through a demister to remove water droplets from the gas. From the scrubber, the gases are transported by a fan to the tertiary air system of the recovery boiler.
In order to keep the gas ducts dry and the gas/air temperature high, fresh make-up air is heated and mixed with the cool vent gases.
“This technology eliminates the need for scrubbing chemicals, reduces the chances of plugging the scrubber, and also can recover wasted thermal energy,” Cruz says. “It is an effective and less costly solution.”
First success leads to follow-on projectIn early 2005, Suzano contracted with Andritz to install the first DTVG system on the older, smaller Götaverken boiler (installed in 1973). Andritz delivered the project on a modified EPC basis, according to Morais, with Suzano providing the civil works and instrumentation.
“The project was completed on schedule and the overall performance has been very good,” Morais says. “The flows, temperatures, and burning of the gases in the recovery boiler have been no problem for us.”
Before the first project was fully commissioned in November 2005, Suzano asked Andritz to retrofit the second recovery boiler (the CBC unit installed in 1987).
For this installation, Suzano wanted to retain as much equipment as possible, so the existing fans and heat exchangers were included in the Andritz DTVG design. Additional heat exchangers were installed by Andritz to handle the capacity for circulating and cooling waters.
In the first quarter of 2006, the basic engineering was completed for the project. During the scheduled boiler shutdown in July, Andritz did as much as possible to prepare the tie-ins to the existing boiler systems. In early October, construction started. Twenty days later, the DTVG system was started up. Everything was operational by November 2006.
Suzano Papel e CeluloseEighty-three years ago, Leon Feffer began investing in the pulp and paper industry in Brazil. Eventually, he sold all his assets to build a paper mill near São Paulo. Feffer took the name of the town, Suzano, to become the name for his company. In the 1950’s, Suzano became a pioneer in the development of eucalyptus pulp and was the first to use this fiber for printing and writing grades.
Today, the Suzano Group is still majority-owned by the Feffer family. The Group is active in Pulp & Paper and Petrochemical sectors. Suzano Papel e Celulose has revenues of about US$ 1.42 billion and production capacity of 640,000 tons of pulp and 1,080,000 tons of paper. It produces coated papers, uncoated papers, paperboard, and bleached eucalyptus kraft pulp.
With the addition of a second pulp line at its Murcuri mill (to be completed in 2007), Suzano will increase its production of pulp by one million tonnes per year. Andritz is providing the woodyard and a 3160 t/d fiberline (washing, screening, and bleaching systems) on an EPC basis for the Murcuri project.
Suzano has embarked on a unique program, the Beekeeping Development Program, to offer jobs and income generation through honey production in the regions near the company’s plantations. It turns out that eucalyptus flowers are excellent for beekeeping. Suzano trains local residents and provides the materials (hives, protective clothing, and other materials). Beekeeping is one of 40 such programs developed by Suzano which reach out to 630,000 people.
