Batch pulping systems are used when 100% defibering is required, or when extra time is needed for the addition of chemicals or heat, such as in deinking or mixed waste applications. A specific amount of dry furnish and water are added to the pulper, and mixed until defibering or the desired chemical reaction is complete. Then the entire contents of the tub are discharged to the dump chest.
Batch pulpers range in size from 2 ft. to 25 ft. in diameter (up to 2400 cu. Ft. stock volume) with capacities ranging to 32,000 pounds of dry furnish per batch. Typical batch times are 30-45 minutes, depending on the furnish. Sizing of the tub volume depends on the total production rate.
Batch pulper tubs are typically round, with deflection vanes installed to direct the flow from the rotor down into the recirculating vortex. The action in the tub is critical to performance, as this is how the stock is wetted out and forced into the rotor for defibering.
For operation up to 8% consistency, pulpers are equipped with a Vokes or Powr-Savr rotor. With the addition of a Mid-Con turbine, consistencies up to 10% are possible. Helico pulper rotors are used for high consistency operation up to 18%.
There are two choices for detrashing any batch type pulper: either a Batch Scavenger or a Hydrapurge III extractor/detrasher. The Scavenger is used for lower tonnage systems where it is less important to segregate heavy from light contaminants. The Hydrapurge with a Selectpurge screening drum is used in those instances where it is more important to achieve a separation between light and heavy contaminants.
Continuous operation is used in high tonnage systems that require stock defibering only to the extent that it can be extracted through a given hole size. Alternate pulper designs are available, depending on the application and type of furnish. Included are continuous pulpers with standard round tub design and Model DR Hydrapulper fitted with a D style tub and raised R rotor.
Continuous pulpers range in typical sizes from 12 ft to 27 ft. in diameter (up to 5200 cu. Ft. stock volume) with capacities up to 1400 tons per day. New designs are available on demand to achieve higher production rates.
The Model D increases Hydrapulper capacity by improving bale submergence. The large bales (typically of OCC and mixed waste furnishes) tend to float and spin in a round tub pulper, taking excessive time to wet out and submerge. The D tub design increases the turbulence in the tub, causing the bale to submerge rapidly. Its bowed D wall disrupts the circular flow pattern of a round tub, displacing the vortex and creating a strong hydraulic nip to submerge the bale.
The raised R rotor design has the rotor, extraction bedplate and extraction chamber mounted above the flat bottom of the Hydrapulper tub. By doing so, a trough is created around the rotor to direct heavy debris into a junk removal device. This reduces rotor contact with contaminants, increasing both rotor and bedplate life. It also prevents the rag rope from riding on top of the rotor, thus eliminating damage to both the rope and the rotor.
All continuous Hydrapulper designs feature under-rotor extraction through a bedplate with holes that are extended beyond the outer diameter of the rotor. The rotor vane design ensures plug-free operation of the bedplate. The leading flat vane is angled downward to maximize defibering and pump-through while the trailing edge is profiled to lift undefibered stock and contaminants from the holes.
Auxiliary detrashing equipment includes the automatic ragger and rope cutter, along with one of two continuous detrashing devices. For low tonnage applications, the Continuous Scavenger detrasher is used. It effectively removes junk from a continuous pulper by treating a sidestream flow and recirculating back into the pulper tub. For high tonnage systems, the Hydrapurge II/Selectpurge detrashing system is used to effectively remove trash from the pulper tub and, at the same time, increase downstream production rates. Heavyweight contaminants are removed from the pulper tub by the trashwell and grapple hoist. Lightweight contaminants are removed via a side stream flow to the Hydrapurge II, where useable fiber is extracted and sent downstream and lightweight contaminants are separated and sent to the Selectpurge for removal and thickening.
Typical applications of continuous pulping are for OCC/Mixed Waste recycled fiber systems making medium or linerboard (D type), or for virgin pulp bale defibering (round type).
Kadant Black Clawson Inc., 605 Clark Street, Middletown, OH 45042. Tel: 513-424-7400; Fax: 513-424-1747.