Rauma five years later: a new look at a world class pulp mill: after five years of operation, Metsa-Botnia's Rauma mill remains a leader in environmentally efficient operations.

Conceived in the early 1990s, Metsa-Botnia's pulp mill in Rauma, Finland, reflects the environmental concerns of that time. The owners decided to build the mill to produce only totally chlorine free (TCF) pulp to address enviromnental pressures of the day and to benefit from the premium price that TCF kraft commanded at the time.

Today, most observers see TCF and elemental chlorine free (ECF) technology as environmental equals, and there is no price premium for TCT. Both Metsa-Botnia and Sodra (the world's largest TCF kraft producer) have selected ECF technology for recently designed fiberlines, although their large TCF fiberlines continue to operate with no plans for changing them. These new ECF fiberlines use extended cooking and two-stage oxygen delignification to minimize the amount of bleaching required, which leads to very low chlorine dioxide use by North American standards. One could consider them to be a compromise between the ECF and TCF technology extant when the debate was at its height in the mid-1990s.

MILL PROCESSES

During a visit in June, mill manager Kaija Pehu-Lehtohen and public relations manager Leena Salminen gave me a tour of the Rauma mill. Because of its location--300 miles further north than any mill in Canada--all systems except the chip piles and a few bleach towers are enclosed in a single building, with only two stacks of any size protruding from the roofs.

Fiberline

The fiberline begins with on-site debarking and chipping, as well as receiving facilities for sawmill chips. Bark is transported to a nearby paper mill for use as fuel,

Cooking takes place in a set of 10 batch digesters, each having 400 [m.sup.3] capacity, using the Metso SuperBatch[R] technology, which is operated with a discharge kappa number of 20. Like all parts of the mill, the pulping system is highly automated.

After cooking, knots are removed for re-cooking. The pulp is washed in a single-stage Metso press, then screened, washed again in a second press and a DD washer.

The two-stage OD system reduces the kappa number of the pulp to 8 (60% delignification), and is followed by further washing and high-density storage.

The mill bleaches to three specifications, all softwood, and in approximately equal quantities. The brightness targets are 88 ISO, 85 ISO and 78 ISO. The latter is primarily used for reinforcing pulp in the adjacent lightweight coated (LWC) groundwood mill.

The bleaching sequence is (OO) (ZQ) (PP) (ZQ) (PP). Filtrate from all alkaline stage washers is recovered counter currently and sent on through the brown stock washers. Acid filtrates are discharged to the wastewater treatment system.

Recovery

In the recovery system, a single seven-effect evaporator raises the concentration of the black liquor to 78% for firing, explained Reijo Kiuru, utilities superintendent. The final stage is a concentrator, which is followed by pressurized storage to keep the temperature of the liquor sufficiently high to compensate for the extreme viscosity of such high concentration liquor.

The evaporator condensate is used for washing bleached pulp, so it must be consistently clean. Conductivity is monitored, and is normally about 100 micromho/cm. If the conductivity exceeds 400 micromho/cm, the condensate is diverted to the effluent treatment system. The total duration of diversions is only a few hours per year, Kiuru noted.

The mill initially overcame problems with calcium deposition in the second effect of the evaporator--similar to those reported by other mills using the SuperBatch[R] process--by installing a black liquor heat treatment system. A slight modification of the cooking procedure later eliminated the problem and the need for the heat treatment system.

The recovery boiler is conventional in principle, but very large, burning 3200 tons/day black liquor solids (7.1 million lbs./day) to produce 120 kg/sec steam (slightly under 1 million lb./hr) at 92 bars, 490[degrees]C.

Due to the highly efficient recovery of pulping and bleaching chemicals, the mill has to take somewhat unusual measures to minimize sulfidity. Tall oil is partly acidulated by adding carbon dioxide to minimize sulfuric acid addition. The exhaust gases from the lime kiln's precipitator are scrubbed with caustic to control S[O.sub.2] emissions, and the scrubber underflow is sold to a GTMP mill., instead of being recovered within the Rauma mill cycle.

In the past, sulfidity has exceeded 45%, but this caused plugging in the boiler bank or the recovery furnace. With sulfidity in the range 40% to 45%, the boiler runs from one annual inspection to the next without water washing.

Energy

The mill's only source of steam and electricity is the recovery boiler, which burns oil only on startup. A back-pressure/extraction turbine is used to generate power, and about 20% of the steam is sold to the adjacent UPM-Kymmene paper mill. All electricity used in the mill, including that necessary for manufacture of oxygen and ozone for bleaching, is generated on site, and approximately 20% of the power produced is sold. Power consumption is very low. Most pumps use variable speed drives to avoid the loss of energy inherent in control valves, and chips are handled by mechanical conveyor rather than pneumatically.

The production of steam is high due to efficient recovery of the non-fibrous fraction of wood (note low COD loss discussed below), and the practice of firing a modern boiler with liquor at 78% concentration. The use of the very high-pressure boiler of course contributes the high production of electricity.

Any difference in yield between the TCF process and conventional ECF pulp will contribute to high-energy production. The Metsa-Botnia environmental report shows that the Rauma mill uses 2% more wood per ton of pulp than the Joutseno mill. While this is not a rigorous measure of yield, it supports the widespread assumption that the overall process yield of a TCF process is one to two percentage points below that of an efficient ECF process. With today's energy prices, much of the additional cost of wood is compensated by energy recovery. All five of Metsa-Botnia's mills sell electricity, while burning oil only in lime kilns. Pehu-Lehtonen believes this is common to most Finnish kraft mills. Metsa-Botnia mills average 122% energy self sufficiency burning bark and black liquor. Rauma is unique in that it operates at that level of self sufficiency and also sells all bark. These calculations ignore the oil consumed in the lime kiln, which is also true in some, but not all, statements on energy self sufficiency in the kraft pulp industry. Typically, the heat requirement of an efficient lime kiln is about 10% of the heat produced by Rauma's recovery boiler, so that even if the kiln is included, the mill energy balance is still positive.

As a net seller of energy, the mill benefits from today's increasing energy prices. It is difficult to avoid correlating this excellent energy balance with the fact that the Finnish kraft production is expanding, and the industry reports a healthy return on investment, while the U.S. industry is reducing pulp production and reeling under high energy prices. The Finnish experience shows that there is a technological fix to the problem of high energy prices, although the scale of projects undertaken in Finland over the past 10 years, and reported frequently by TAPPI, demonstrates that the "fix" is neither low-capital nor rapid.

Water consumption

The Rauma mill was designed for very low water consumption and effluent discharge, but water use has increased to the point where the current discharge rate is approximately 16 [m.sup.3]/ton pulp. Operation at very low discharge flows was found to create problems with scale, but the present discharge is not considered the minimum practical level, with a generous water supply, and an effluent discharge that is very low relative to the permit and to world norms, there is currently no pressure on the mill to reduce water consumption.

Effluent treatment

Effluent is mixed with the wastewaters from the adjacent paper mill and treated in a combined activated sludge treatment (AST) plant. Discharges, based on the untreated mill effluent characteristics, by applying the average removal in the AST are shown in Table 1. Discharges allowed under the mill permit are expressed in tons/day, but the estimated equivalent in kg/ton pulp are shown to facilitate comparison with other mills. The permit refers to maximum monthly average, whereas the actual discharge data shown are the average for 2000.

The extremely low COD discharge of 2.3 kg/ton pulp is a reflection on the efficient recovery of residuals from pulping and bleaching, mad also demonstrates very good control of accidental losses. The COD discharge of North American mills ranges from 7 kg/ton (at AlPac) to about 150 kg/ton. Effluent treatment sludge is burned.

Atmospheric emissions

The mill's total emissions are low, as could be expected in a modern, energy efficient operation. However, there have been some problems with local odor. The data presented in the annual report suggest that the extent of odor perception is similar to that of the better U.S. mills, but not as low as in the very best performing U.S. installations. However, there are no standardized ways of comparing the odor impact of mills. The mill has successfully reduced odor perception substantially since start-up.

The measured and permitted atmospheric emissions are shown in Table 2, with the permitted values converted to equivalent kg/ton pulp.

Environmental policy

The mill operates in compliance with ISO 14001, and has a policy of practicing the best available techniques for environmental protection and resource conservation. The full policy is presented, in English, on their web site at www.metsabotnia.com/content.asp?path=825;923. The company's environmental report is also available on the web-site.

THE PEOPLE SIDE OF RAUMA

Metsa-Botnia's pulp mill in Rauma, Finland, has been in operation since 1996, and is still the most recent greenfield pulp mill built in Europe--or North America--although a few new fiberlines have been constructed in older mills on both sides of the Atlantic.

The Rauma mill in one of five kraft mills in the Metsa-Botnia company, which is owned 47% by UPM-Kymmene, 47% by M-real (formerly known as Metsa-Serla), and 6% by Metsaliitto Osuoskunta, which is a cooperative of small forest owners.

Upon arriving at Rauma, you are impressed by the immense size of the installation, and the comparatively small size of the employee parking lot. The 1700 tons/day fiberline is very large by U.S. standards, although this scale of operations is becoming relatively common overseas. The small parking lot is explained by the fact that only about 200 people work at the mill, including approximately 30 full-time contract maintenance staff, with a shift crew of just 15 operators.

The company policy is to have corporate specialists in fields such as environmental control resident at the mills, although they perform functions traditionally associated with head office staff. Kaija Pehu-Lehtonen, Rauma's mill manager, advises that there are only about 20 staff in the company's head office. For a company operating five major kraft mills, and sales of approximately U$$ 1.2 billion, this is an amazingly Jew head count, although marketing is a separate function. Based on data in the Metsa-Botnia annual report, is seems that sales are over U$$ 500,000 per employee.

All staff members have desks in one large, totally open office, without even portable partitions. Pehu-Lehtonen's desk is identical to the others, with nothing visible to distinguish her workplace from that of a secretary or maintenance planner. She was appointed director of the Rauma mill in April 2001, having been production manager at the Joutseno pulp mill since 1997.

Overall, the management style at Metsa-Botnia emphasizes the importance of people over technology, despite the firm's track record of investing very aggressively in the most advanced technology available. Their 2000 environmental report states "Automation cannot replace people. On the contrary, the importance of know-how gets highlighted when automation gets more refined." The report also shows that each employee receives about 5 days training every year and that there is a profit sharing plan for employees that added 6% to salaries in 2000.

The return on capital employed (ROCE) in 2000 was 41%, and the average ROCE for 1996-2000 was 16%, according to the Metsa-Botnia annual report available through http://www.metsabotnia.com/main_eng.asp?path=825.

--Nell McCubbin

Table 1: Effluent discharges

                                   Average   Permit
                                   2000

Flow               [m.sup.3]/ton   15.5
Suspended solids   kg/ton           0.47
COD                kg/ton           2.3      22
BO[D.sub.7]        kg/ton           0.055     2.5
Total phosphorus   kg/ton           0.002     0.03
Total nitrogen     kg/ton           0.019
AOX                kg/ton           <.01

Note: BO[D.sub.5] discharge is about 15% less than the BO[D.sub.7]
value measured

Table 2: Atmospheric emissions and solid waste
discharge, kg/ton pulp

                           Average 2000   Permit

S[O.sub.2]                     0.31        1.0
TRS                            0.027       0.062
NOx                            1.35
C[O.sub.2] (fossil fuel)       0.10
C[O.sub.2] (biofuel)           2.22
Particulate                    0.48

Solid waste                   25.70

About the author: Neil McCubbin is principal of N. McCubbin Consultants Inc,, Foster, Quebec, Canada; Contact him by email at: [e-mail]