This page describes the major differences between RDH and DDS.   [中文]

DDS versus RDH

The DDS cooking system is an enhanced design of the RDH cooking system.  The modifications create more stable temperatures and residue chemicals in the tank farm, less channeling in the digester, and more efficient pulp discharge to ensure lower kappa variation, more consistent production rates, and highly automated cooking operations with minimum operator intervention.  This superior design has addressed these performance concerns by better piping configurations, better heat exchanger design and most importantly, through the use of modern process control techniques (Advanced Process Control).

Tank Farm Temperatures

The DDS tank farm produces a higher temperature accumulators with better temperature segregation.  The higher temperatures at the beginning of the cooking cycle remove and strip out of the digester substantial amounts of byproducts to allow for a lower alkali charge later in the cooking cycle which thereby producing less fiber damage.  This is also the reason that the DDS is able to cook bamboo with other woods and produce quality fiber.

Proprietary Advanced Process Control

Digester Discharge

Displacement batch digesters are not pressurized after the cooking is completed due to the displacing of the hot spent cooking liquors to the tank farm.  Therefore, the pulp in the digester can not be 'blown' or flashed to a blow tank similar to conventional batch digesters because most of the energy has been displaced to the tank farm.  The technique used to empty the digester is to pump the contents from the digester.  However, as the level of the digester decreases the NPSH_available decreases, the pulp consistency varies and the tendency for high consistency pulp clumps creates a constantly varying suction environment to the discharge pump.  The DDS control system has minimized these challenges with 'fuzzy logic control (FLC)'.

Tank Farm Management

The tank farm is used to store chemical and thermal energy contained in the hot spent cooking liquors for reuse.  The tank farm serves the digesters, which need to produce pulp without disruption.  The DDS cooking system uses 'model predictive control (MPC)' to predict the levels in the tank farm which are used to make adjustments to the flows between the tankage as well as to the digester scheduler.

Digester Channeling

The flow of liquid in the digester must remain in a 'plug flow' profile with an interface zone between the different fluids as thin as possible.  The DDS^TM cooking system uses 'multi-variable control (MVC)' to maintain plug flow inside the digester.

Piping Techniques

Digester Discharge

The DDS cooking system has minimized suction head variations to the discharge pump by using new piping configurations.

Temperature Variations

The DDS cooking system uses various piping connections for liquor segregation to minimize temperature variations in the accumulators.

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