Cost advantages on a grand scale

Water consumption largest lever

10 liters: This is the amount of water consumed in the pro­duc­tion of a single DIN A4 sheet of paper, ac­cord­ing to the German Water Pro­tec­tion As­so­ci­a­tion (Vere­ini­gung Deutscher Gewässer­schutz), (source: http://​vdg.​durstige-​gueter.​de/​das_​projekt.​html). De­sign­ing pro­duc­tion plants and com­po­nents in an optimal, process-ori­ented manner offers a great lever for reducing water con­sump­tion. Sealing tech­nol­ogy in this context plays an im­por­tant role.

The decisive factor is the op­er­a­tion of a seal in Nonflow mode. To explain: Double me­chan­i­cal seals in pulp pumps of the pulp and paper industry are usually supplied with fresh water from an open barrier fluid circuit. Fresh water is con­tin­u­ously supplied to the seal as a barrier fluid. This is pres­sur­ized to prevent product leakage to the at­mos­phere and serves to lu­bri­cate and cool the sealing system. After passing through, the water is drained off. In Nonflow op­er­a­tion, on the other hand, the water cir­cu­lates in a closed system.

This type of closed system usually consists of pipes, valves and a storage tank. It also includes mea­sur­ing and control devices for mon­i­tor­ing the tem­per­a­ture, buffer pressure and flow rate. Water is filled in once and remains in the system, shut off by the valves, through­out the entire service life of the seal. Only a neg­li­gi­bly small amount of fresh water is fed from the pro­duc­tion plant's water network to com­pen­sate for the leakage. Since the pressure in the water network is gen­er­ally higher than the product pressure, it is also suitable as buffer pressure.

Compared to con­ven­tional double me­chan­i­cal seals, the seal systems designed for the Nonflow op­er­at­ing mode have ad­di­tional bores and spiral grooves inside the housing. This allows the barrier fluid to cir­cu­late inside the seal between the product side and the at­mos­phere side. The fric­tional heat is con­ducted to the product side and the cooled sealing water flows back from the product side to the at­mos­phere side, driven by the rotary motion of the shaft. The seal acts like a heat ex­changer. The typ­i­cally oblig­a­tory ther­mosiphon con­tainer for dual action me­chan­i­cal seals is not required.

Selecting optimum materials

The ma­te­ri­als also play an im­por­tant role for seals that are operated in Nonflow mode. While con­ven­tional seal face pairings consist of carbon material and stain­less steel, the com­bi­na­tion of carbon material and silicon carbide enables improved sliding behavior and lower friction losses. This also reduces the overall tem­per­a­ture de­vel­op­ment due to friction in the seal.

Benefit I: Enormous reduction in water consumption

The ad­van­tages of Nonflow op­er­a­tion are obvious: Water con­sump­tion is reduced to a fraction of the quantity normally required. Assuming, for example, a mag­ni­tude of 30 seal units, the con­sump­tion is as follows:

• Packings: 10 l per minute / 142,560 m3 per year
• Mechanical seal standard mode: 4 l per minute / 57,024 m3 per year
• Mechanical seal Nonflow: 0.000152828 l per minute / 2.25 m3 per year

Benefit II: Cost advantages for plant operators

As well as eco­log­i­cal benefits, the re­source-sav­ing op­er­at­ing mode also involves economic ad­van­tages for paper pro­duc­ers. As a result, the annual water saving cor­re­sponds to a cost re­duc­tion of around 2,000 euros per pump. There is great po­ten­tial in this: Paper mills with pumps equipped with Nonflow seals can save up to six-fig­ure cubic meters of water each year. KotkaMills in Southern Finland is a good example of this: Here, 41 pumps were retro­fit­ted with Nonflow tech­nol­ogy. The annual con­sump­tion for the seal supply since then has been reduced by 181,000 cubic meters.

Benefit III: Less contamination, increased service life

A further ad­van­tage is that Nonflow seals are less sus­cep­ti­ble to con­t­a­m­i­na­tion. The water enters the seal housing once. After the line is sealed off, it is present sta­t­i­cally. This elim­i­nates the need for large amounts of flowing water - and thus also the entry of dirt par­ti­cles which grad­u­ally ac­cu­mu­late in the seal. In a worst case scenario, the dirt par­ti­cles could block the seal, given the con­sid­er­able amounts of dirt that ac­cu­mu­late during op­er­a­tion. For example, 10 ppm of solids over the course of the year equals 19 kilo­grams of dirt. A Nonflow seal will not allow this amount to pass through. This in­creases their service life by a factor of 3.

Result

Double me­chan­i­cal seals are suc­cess­fully used in Nonflow op­er­a­tion by many com­pa­nies world­wide. One key area is the paper and pulp industry in Finland. In addition, Nonflow tech­nol­ogy can also be used in the phar­ma­ceu­ti­cal, chemical and food in­dus­tries. The benefits for plant op­er­a­tors are apparent. Nonflow seals have proven them­selves many times over. The sig­nif­i­cant re­duc­tion in water con­sump­tion and con­t­a­m­i­na­tion and the re­sult­ing increase in the average op­er­at­ing life of the seals achieves sig­nif­i­cant cost benefits. The prospects for seals with Nonflow tech­nol­ogy are promis­ing: The de­ter­mined op­er­at­ing con­di­tions allow the use of cor­re­spond­ing systems for an es­ti­mated 80 percent of rotating shafts in pro­duc­tion fa­cil­i­ties in almost all in­dus­tries.