Recovered Fiber Pulping

Globally there is an increasing trend of using recovered paper as a feedstock in pulp production. In some parts of the world, recovered fiber utilization rates are rather high – for example, in Europe, average utilization rate is 48.4% (BREF, 2010. p. 473). There are many mills that rely exclusively on recovered paper and most mills make use of some fraction of recovered paper in their production. It should be noted that the maintenance of the fibre cycle relies on the feed of a certain amount of primary fibres to ensure the strength and other properties of the paper to be produced.

In stock preparation using recovered fibers, used fibers are pulped, purified and optionally de-inked. Depending on the paper grade and the type of furnish used, a wide variety of recovered paper processing systems can be applied – combining similar processes differently to fullfil specific tasks. Generally, these can be in two main categories:

  • processes with exclusively mechanical cleaning, i.e. without deinking comprising products like Testliner, corrugating medium, uncoated board and carton board;
  • processes with mechanical cleaning and deinking comprising products like newsprint, tissue, printing and copy paper, magazine papers, coated board and carton board.

In a typical processing system, recovered paper is put into a pulper together with hot water or white water (water from paper machine) and pulped with mechanical and hydraulic agitation resulting in disintegration into fibres. For processes with deinking, chemicals such as surfactants and NaOH can sometimes be added as pulping additives. Low consistency (4-6% dry solids), high consistency (15-20% dry solids) and drum pulpers are the three main types of pulpers and there are batch and continuous types. Contaminants and clusters are removed by mechanical means during pulping.

For further removal of mechanical impurities hydrocyclones and screens are used. Depending on the furnish quality to be achieved, recovered paper processing also includes fractionators, dispergers or refiners.A fractionator separates the pulp into two fractions rendering it possible to treat short and long fibres of the pulp slurry in different manners. The energy demanding process of disperging can be performed in order to achieve improved fibre-to-fibre bonding (better strength characteristics) in the paper produced and to reduce visible dirty specks in size. A stock preparation plant for the processing of recovered paper can be optionally equipped with refiners to improve optical and strength characteristics of the paper. Refining is associated with a substantial energy demand. An example arrangement for a stock preparation plant for processing recovered paper for two-ply Testliner is shown in the figure below (BREF, 2010. pp.474-475).

Although the actual energy demand varies depending on the extent and types of contamination and final pulp yields, pulp production from recovered and secondary materials is usually less energy intensive. Examples of typical energy consumption levels taken for real cases for stock preparation of different paper grades is given in table below (BREF, 2010. p. 486).

Energy consumption levels for stock preparation of different paper grades (BREF, 2010. p. 486)
  Packaging Paper Newsprint Lowweight coated/Supercalendered Tissuepaperandmarketpulp
Recovered paper quality Sorted mixed paper and boards, recovered paper from stores Deinkable recovered paper (old newsprint and old magazines) Deinkable recovered paper (old newsprint and old magazines) Deinkable recovered paper (old newsprint + magazines); wood- free office recovered paper
Electricity consumption (kWh/t) 150 -250 300 – 420 400 – 500 400 – 500
Thermal energy consumption (MJ/t) 0 (heating may be required if dispersing is applied) 450 – 900
(= 0.2-0.4 tsteam/t)
650 – 1100
(= 0.3-0.5 tsteam/t)
650 – 1100
(= 0.3-0.5 tsteam/t)

Recovered Fiber PulpingSchematic

Recovered Fiber PulpingTechnologies & Measures

Technology or MeasureEnergy Savings PotentialCO2 Emission Reduction Potential Based on LiteratureCostsDevelopment Status
Increased Use of Recycled PulpUse of recovered pulp can reduce energy consumption by 10 to 13 GJ/t-pulp (IEA, 2012. p.35)) US flag The production of one ton of recycled pulp is estimated, on average, to consume 6.3 to 11.6 GJ less energy compared to chemical pulp and 6.3 to 10.6 GJ/t less as compared to mechanical pulp. (Kramer et al., 2009. p. 27)US flag Studies estimate the construction costs of recycled pulp processing capacity at around $485/ton of pulp. Depending on the price of waste paper versus virgin pulp this may result in up to $73.9 per ton of pulp in operations and maintenance cost savings (Kramer et al.2009. p. 97). Commercial
XTREME CleanerThis technique reduces the enegy consumption by 50% of as compared to the conventional dispersion systems.The technology saves between $3,500 - $11,000 per day by using low-grade furnish.Commercial
Using Drum PulpersA study suggests that if a vat type pulper is replaced with a continuous drum pulper in de-inking operations, energy consumption reduction by over 25% can be achieved. (Kramer et al. 2009. p. 97) Energy consumption can be reduced by 10 kWh/t-pulp as compared to a batch pulper (NCASI, 2001. p131)

US flag For a 300 t/d capacity plant, CO2 reductions due to reduced power demand are estimated to be 1055 t CO2/y. (NCASI, 2001. p.131)

Costs of a continuous drum or dry pulper will be higher than those of batch equipment with equivalent capacity. US flag For a 300 t/d capacity plant , annual savings are estimated to be around $37 000 [2001 dollars] (NCASI, 2001. p.131)Commercial
Heat Recovery from De-inking EffluentUS flag  For a mill in the US having effluent streams at 49 °C and flow rate of 2.7 m3/min, the installation of a heat exchanger to recover heat and generate warm filtered shower for the mill's paper machines is estimated to reduce boiler fuel consumption by 39 000 GJ/y. US flag  Fuels savings for the boiler are estimated at $125,000/y. Capital costs had been $375,000 with a payback period of around 3 years.Commercial
Fractionation of Recycled Fiber11 to 13% reductions in electricity consumption, and up to 40% reduction in thermal energy can be achieved.Capital reduction of 13 to 22% can be achieved compared to traditional de-inked pulp (DIP) lines. Commercial
Electrohydraulic Contaminant RemovalImproved sticky removal, floatation and clarification may lead to direct energy consumption reductions of 10 to 15% in contaminant removal and cleaning equipment (Kramer et al., 2009. p. 111).Demonstration
Upgrading of Stock Preparations Plants with Decreased Electricity Consumption and EmissionsThe option one results in energy consumption in the range 45 kWh/tonne and 95 kWh/tonne. The second option consumes between 75 kWh/tonne and 175 kWh/tonne.The investment and operational costs of option two are higher than that of option one. Commercial
Incineration of Residues

One ton of rejects (from mills without de-inking) with about 45% water content can substitute 0.7 tons of brown coal in the boiler. in a German plant with 370 000 t/year production capacity, incineration of rejects in a hearth combustion (with a capacity of 28 000 t/year) that is integrated in the power plant of the mill, fossil fuel usage corresponding to 66 000 MWh was reduced.

Because the rejects help substitute coal, and about 50% of solid matter in the rejects are CO2 natural substances, CO2 emissions are reduced.

The investment cost for a co-incineration plant including facilities for reject pretreatment, drying and the gasification chamber for a reject volume flow rate of maximum 3 t/hour is estimated to be around €2.5 million. In Europe, these can provide annual annual savings of €0.6 million, assuming costs for landfilling of €50/t. An additional EUR 0.3 million/yr can be saved through the substitution of brown coal.

Commercial
Recovery of Boiler Ash and CO2 Gas to Produce Recycled Mineral Fibres for Use in PaperProduction of precipitated calcium carbonate (PCC) using boiler ash requires up to 50% less fossil fuels compared to producing CaO from limestone quarry (CaCO3). CO2 emissions are reduced due to reduced fossil fuel use for CaO and due to CO2 being captured from incineration of de-inking residues. Production of precipitated calcium carbonate (PCC) from deinking ash as a raw material is appealing in countries where landfill costs are high as it gives both economic and environmental benefits. Demonstration
Continuous Batch Fibre Recovery System to Processing Recovered Paper in a Complete System

Process is more energy efficient.

Investment costs are low.

Commercial
Secondary Separation Pulper for Pulping Process in Wastepaper Treatment

Japanese flag For a mill with original production capacity of 365 tpd, installation of this technology helped increase capacity to 445 tpd and reduced energy consumption by around 146 800 kWh/year (NEDO, 2008. p.160).

Japanese flag Equipment cost is estimated as ¥90 million. Construction cost is around ¥30 million approximately (NEDO, 2008. p.160). Commercial
Screenable, Pressure-Sensitive Adhesives for EnviroSensitive LabelsN/AThe technology indirectly saves CO2 emissions by increasing the recycling of wider varieties of paper.Commercial

Recovered Fiber Pulping Publications