1. A screening apparatus for screening pulp suspensions, comprising:
a housing,
a tubular screen basket dividing the interior of the housing into a central chamber and an outer substantially annular chamber, the screen basket including at least two separate tubular screen sections,
an inlet member for supplying a suspension to be screened into one of the central chamber and outer chamber,
an accept outlet member for discharging a developed accept fraction of the suspension that has passed through the screen basket,
a reject outlet member for discharging a developed reject fraction of the suspension,
a rotor arranged in the housing for providing pressure and suction pulses in the suspension to be screened along the screen basket, and
dilution means for supplying diluting liquid to one of the central chamber or outer chamber, the dilution means including at least one annular element axially interconnecting the two tubular screen sections and forming a tubular dilution liquid compartment extending at least substantially around the screen basket, the annular element forming a plurality of dilution liquid ejection passages between the dilution liquid compartment and one of the central chamber and outer chamber.
2. A screening apparatus according to claim 1, wherein one of the accept outlet member and reject outlet member forms an outlet passage from the outer chamber, and the dilution means comprises at least one dilution liquid supply conduit extending through the outlet passage to the annular element, to supply dilution liquid from outside the housing to the dilution liquid compartment.
3. A screening apparatus according to claim 2, further comprising an outlet pipe releasably connected to the outlet member that forms said outlet passage, wherein the dilution liquid supply conduit extends from outside the housing through the wall of the outlet pipe into the outlet passage.
4. A screening apparatus according to claim 1, wherein the dilution means comprises first and second dilution liquid supply conduits connected to the annular element at different places thereon.
5. A screening apparatus according to claim 1, wherein the tubular dilution liquid compartment extends in a closed loop around the central chamber, and the dilution liquid supply conduit is arranged to direct the dilution liquid into the dilution liquid compartment such that the dilution liquid flows in one direction along said closed loop.
6. A screening apparatus according to claim 4, wherein the tubular dilution liquid compartment extends in a closed loop around the central chamber, and the first and second dilution liquid supply conduits are arranged to direct the dilution liquid into the dilution liquid compartment such that the dilution liquid flows in one direction along said closed loop.
7. A screen basket comprising.
a tubular mantle wall provided with screen holes and including at least two separate tubular wall sections, and
dilution means for supplying dilution liquid to one of the inside and outside of the tubular mantle wall, the dilution means including at least one annular element axially interconnecting the two tubular wall sections of the mantle wall and forming a tubular dilution liquid compartment extending at least substantially around the tubular mantle wall,
wherein the annular element forms a plurality of dilution liquid ejection passages between the dilution liquid compartment and one of the inside and outside of the screen basket.
8. A screen basket according to claim 7, wherein the ejection passages have circular cross-sections.
9. A screen basket according to claim 7, wherein the ejection passages take the shape of slots.
10. A screen basket according to claim 7, wherein the tubular dilution liquid compartment has a rectangular cross-section.
11. A screen basket according to claims 7, wherein the dilution means comprises first and second dilution liquid supply inlets on the annular element positioned at different places thereon.
12. A screen basket according to claims 7, wherein the tubular dilution liquid compartment extends in a closed loop around the tubular mantle wall.
13. A method of screening a pulp suspension by the use of a screening apparatus having a tubular screen basket, the method comprises:
feeding the suspension to be screened to one of the external side and internal side of the screen basket,
screening the suspension along a primary screening section of the screen basket to obtain a primary accept fraction that passes through the screen basket and a primary reject fraction that is prevented from passing through the screen basket,
supplying a flow of dilution liquid to dilute the primary reject fraction,
screening the diluted primary reject fraction along a secondary screening section of the screen basket to obtain a secondary accept fraction that passes through the screen basket and a secondary reject fraction that is prevented from passing through the screen basket,
discharging the secondary reject fraction from the screen basket,
combining the primary and secondary accept fractions to form a common final accept fraction, and
controlling the flow of dilution liquid being supplied in response to the consistency and flow of the suspension being fed to the screen basket and the consistency and flow of the secondary reject fraction being discharged from the screen basket, so that the consistency of the primary reject fraction entering the secondary screening section becomes substantially the same as the consistency of the suspension being fed to the screen basket.
14. A method according to claim 13, wherein the suspension to be screened is fed into the internal side of the screen basket and is screened so that the primary reject fraction develops inside the screen basket, whereby the flow of dilution liquid is supplied to the inside of the screen basket and the secondary reject fraction develops inside the screen basket.
15. A method according to claim 13 or 14, further comprising supplying the flow of dilution liquid in the form of jets having a velocity in the range of 2-10 ms, preferably 4-8 ms.
16. A method of screening a pulp suspension by the use of a screening apparatus having a tubular screen basket with perforations, the method comprises:
feeding the suspension to be screened to one of the external side and internal side of the screen basket,
screening the suspension along a primary screening section of the screen basket to obtain a primary accept fraction that passes through the screen basket and a primary reject fraction that is prevented from passing through the screen basket,
supplying a first flow of dilution liquid to dilute the primary reject fraction,
screening the diluted primary reject fraction along a secondary screening section of the screen basket to obtain a secondary accept fraction that passes through the screen basket and a secondary reject fraction that is prevented from passing through the screen basket,
supplying a second flow of dilution liquid to dilute the secondary reject fraction,
screening the diluted secondary reject fraction along a tertiary screening section of the screen basket to obtain a tertiary accept fraction that passes through the screen basket and a tertiary reject fraction that is prevented from passing through the screen basket,
discharging the tertiary reject fraction from the screen basket,
combining the primary, secondary and tertiary accept fractions to form a common final accept fraction, and
controlling the first and second, respectively, flow of dilution liquid being supplied to the screen basket in response to the consistency and flow of the suspension being fed to the screen basket and the consistency and flow of the tertiary reject fraction being discharged from the screen basket, so that the consistency of the primary reject fraction entering the secondary screening section and the consistency of the secondary reject fraction entering the tertiary screening section, respectively, becomes substantially the same as the consistency of the suspension being fed to the screen basket.
17. A method according to claim 16, wherein the suspension to be screened is fed into the internal side of the screen basket and is screened so that the primary reject fraction develops inside the screen basket, whereby the first and second flows of dilution liquid are supplied to the inside of the screen basket and the secondary and tertiary reject fractions develop inside the screen basket.
18. A method according to claim 16, further comprising supplying the first and second flows of dilution liquid in the form of jets having a velocity in the range of 2-10 ms, preferably 4-8 ms.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A fuel cell system, comprising:
a fuel cell stack in a hot zone, the fuel cell stack comprising a plurality of fuel cells and a plurality of interconnects; and
a module comprising a plurality of bypass elements, the module attached to the fuel cell stack and located in the hot zone,
wherein:
at least one of the plurality of bypass elements is electrically connected to at least two of the plurality of interconnects so as to bypass at least one of the plurality of fuel cells located between the interconnects;
each of the plurality of interconnects comprise at least one recess;
the bypass module comprise at least one protrusion; and
the bypass module is attached to the fuel cell stack by inserting the at least one protrusion into the at least one recess.