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Paper Waste

Hiller machines provide world-class standards of high-performance decanter centrifuges for a variety of Pulp & Paper industry applications. The Hiller decanter centrifuge series has been developed for maximum cake dryness at high throughputs with significantly reduced polymer consumption. Hiller has supplied many machines into the Pulp & Paper industry for the following applications:

  • Primary sludge (fiber sludge) dewatering (effluent treatment plant)
  • Biological sludge dewatering (effluent treatment plant)
  • Mixed sludge dewatering (effluent treatment plant)
  • Hydroxide (chemical precipitation) sludge dewatering
  • Coatings sludge dewatering
  • De-Inking sludge dewatering
  • Colour wastewater treatment
  • Water treatment before recycling (closed loop) into used paper processing (removal of solids and of some dissolved matter)
  • Clarification of production wastewater directly from tissue / paper machines

The benefits of Hiller decanters in Pulp & Paper industry are unmatched due to our unique ability to adapt our standard range of DP machines to the specific task and plant making Hiller decanters an ideal solution and perfectly suited for each project. Such specialized adaptions and features can include:

  • Close clearance scroll/bowl design for slippery sludges (e.g. de-inking sludge)
  • Hydraulic scroll drive for primary or mixed sludge dewatering which are not susceptible to mechanical damage due to chattering (a conveying problem in the decanter due to the fibers which introduce high levels of vibrations into the scroll drive and can quickly destroy gearboxes)
  • Special mechanism and design features that help clear sticky solids from the decanter solids casing (for example coating sludges)
  • Large number of different and optional wear protection systems and materials of construction to account for product abrasiveness and corrosivity

There are several common Pulp & Paper Mill applications within the paper mill and paper making process where the Hiller DecaPress decanter centrifuge is well designed to cost effectively provide solutions for liquid / solids separation and sludge dewatering:

  1. De ink sludge dewatering producing stackable cakes discharged between 30 and 50%
  2. Paper machine effluent producing stackable cakes discharged between 35 and 55%
  3. Paper coating effluent producing stackable cakes discharged between 50 and 60%
  4. Activated sludge dewatering by thickening from 0.8% to 10% dry solids, which can then be mixed with the primary sludge for disposal or dewatering up to 25% dry solids

The activated sludge dewatering is of special interest because typical belt presses or screw presses have difficulty dewatering sludge containing surplus activated sludge. The centrifuge will dewater activated sludge and will often work without the use of polymer, resulting in very low operating costs.

For many years the belt press and the screw press have been the standard sludge dewatering devices in the paper industry. However the environmental legislation of recent years has forced many mills to install secondary or biological treatment for the wastewater in order to reduce trade effluent charges by reducing COD levels.

The addition of surplus biological sludge to the primary sludges for dewatering has been problematic for the belt press and the screw press. The centrifuge is establishing itself as an ideal piece of equipment to process this mixture, and in other applications previously thought problematic. Several machines have been successfully installed on a variety of applications these paper mill applications.

There are several unique features that enable the centrifuge to process slurries or sludges more effectively than other equipment in a typical paper mill per the following:

  1. The centrifuge is a continuous process
  2. The centrifuge process can be almost completely automated
  3. The floor space required by the centrifuge is comparatively small (A machine to process 200-gpm will fit into a 14’L x 5’W space) and the centrifuge can often be installed outside
  4. The centrifuge range is very diverse and feed rates from 50 to 500-gpm can be accommodated with a single machine
  5. The centrifuge does not require belt washing and therefore spray bars or nozzles which minimizes water consumption
  6. Routine maintenance is comparatively low
  7. Some paper and / or paper board products are able to use very short fibers that are normally lost with the wet end backwater, but the centrifuge is able to recover these materials and thicken them to a degree that enables recycling of the material back into the paper stock, which provides the double benefit of reducing materials wasted to effluent and increasing product yield

Biological sludge dewatering: The construction of a new biological treatment plant on many sites has necessitated the need for dewatering the bacteriological sludge produced by the aeration tank. Most operate the centrifuge when the level in the tank reaches a predetermined level pumping a proportion of the liquid through a centrifuge. The sludge with an approximate consistency of 0.6% dry solids is mixed with a polyelectrolyte solution to promote flocculation and this is then fed through the centrifuge which typically produces a dry stackable solids content of the discharged sludge at approximately 18% to 20%.

The biological sludge dewatering is of special interest because belt presses and / or screw presses typically have difficulty dewatering sludge containing surplus activated sludge. It is common in some mills to add fiber to effluent as a sweetener, in order to make existing equipment function properly. This can be a very costly exercise. The centrifuge will naturally dewater activated sludge and will often work without the use of polymer resulting in very lower operating costs.

Dewatering sludge from the primary settling tank: Prior to most centrifuge installations, paper mills normally employ belt type presses to dewater the primary effluent sludge. There is often concern about the time required to service belt presses and the risk of presses becoming unserviceable. The use of a centrifuge is considered a more durable mechanical solution plus the centrifuge typically dewaters factory effluent to a standard greater than that of the existing belt presses. The centrifuge repeatedly provided the following benefits in several installations:

  1. The centrifuge produced cakes on average 8 points better than belt presses.
  2. As a result, the centrifuge produced 16.5 tons less wet cake per 24hrs-operation for a higher capacity flow rate of sludge than the belt press.
  3. Centrate produced while using a polymer as flocculent was on average 104 ppm, and 185ppm on average without polymer.
  4. Performance is often suitable over a wide range of bowl speeds and pool depths, with little change to either cake dryness or centrate quality for maximum versatility and ease of use.

Dewatering effluent to produce an easily transportable product: Usually it is desirable and / or a requirement that thickened effluent from the paper mill is dewatered on site, producing a stackable solids discharge which can be easily transported to landfill. A centrifuge typically dewaters the thickened effluent (around 0.5% ds) at site producing a dry to the touch crumbly discharge at between 50% and 58% dry solids.

Best results were achieved without the additional use of polyelectrolyte and the centrifuge running at a force of 3000xG. Feed to the centrifuge with this application commonly varies both in the nature of solids and in concentration, 0.38% to 1.3% dws. Centrate quality is typically controlled within a range of 0.8 ppm to 11.6 ppm suspended solids, and is achievable because the conveyor speed in a Hiller machine will automatically respond to changes in feed concentration to maintain maximum cake dryness and separation performance even when the machine is unattended.

Solids recovery (from “white water”): A trial was performed at the mill to establish to what degree the centrifuge would clarify the effluent being produced by the paper machine, with a view to re-using the recovered materials in the mill. In this case there is no real need to produce the solids as a dry cake but more of a pasty texture so that it can be pumped. The automated conveyor speed control made sure the machine delivered consistent solids concentration from the decanter and to the recycle pump.

One of the products from the mill uses Titanium Dioxide as filler, which costs over $2,400 per ton. The mill wanted to recover some of this material to reduce its cost, and to reduce the load on its effluent plant. A secondary objective was to evaluate the centrifuge performance and ability to dewater the solids into a crumbly consistency for times when the effluent was to be treated as waste and taken off site in hoppers. The results were acceptable to the mill and led directly to the installation of a Hiller DP45 decanting centrifuge.

Other Hiller Activity: We also have a number of machines running on de-ink sludge. Hiller is actively exploring other possible applications in the paper industry as well as pursuing these more established processes.

Hiller also offers more than just a very well performing decanter:

  • Full support for development and optimization of treatment processes via laboratory tests as well as pilot testing on site in full scale
  • Customizing of decanter design to best suit untypical or difficult products and / or offer more flexibility for treatment of different products with the same machine
  • Easy-to-maintain decanter design
  • Best available after-sales support focused on long-lasting customer relationships, from trouble-shooting on site to high quality repairs
  • Replacement rotors to maintain decanter operation on site while the original rotor is being overhauled
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