REVIEW OF PIRA NON-WOOD FIBRE CONFERENCE

Author

Neil Hunt

Company

Mondi Kraft Felixton Mill, Private Bax X05, Felixton, 3875, South Africa

email

Neil_Hunt@mondi.co.za

Keywords

non-wood, paper, pulp, digester, black liquor, technology

ABSTRACT

This paper presents a brief overview of the proceedings of the Pira conference entitled "Cost effectively Manufacturing Paper & PaperBoard From Non-Wood Fibre & Crop Residues". The advantaged and disadvantages of non-wood fibre sourced is discussed and some non-wood species are compared.  Developments in technology for handling non-wood fibre sources are presented, as are some of the current non-wood initiatives that were highlighted during the conference.

INTRODUCTION

Approximately 60 delegates and speakers from around the world attended the Pira conference entitled "Cost effectively Manufacturing Paper & PaperBoard From Non-Wood Fibre & Crop Residues".  Apart from highlighting the advantages and disadvantages of non wood fibres, the papers presented dealt with various non-wood species that are being used for pulp and paper manufacture, and with various technologies being developed for preparing, digesting, bleaching and treating black liquor in non-wood pulp systems. The use of non-wood fibres to enhance wood and waste based paper properties and innovative business strategies for establishing non-wood paper manufacturing businesses were also presented.

ADVANTAGES AND DISADVANTAGES OF NON-WOOD FIBRES

Specific and general advantages and disadvantages sited during the conference for using non-wood fibres included:

1. Short growth seasons
Non-wood species used in paper making grow to maturity within a short time relative to wood species.  Hemp can be harvested within three to four months while larger14 species like Kenaf require only three years15.  This is advantageous in that the crop returns profits for the grower quickly and crop size can be adjusted at relatively short notice. The disadvantage is that these crops are more susceptible than trees to abnormalities in seasonal weather patterns such as droughts and floods. Another disadvantage is that the harvesting season may be short, requiring storage of the harvested crop over a number of months, to support continuous pulp production, exposing the crop to decay if not properly preserved3,14.

2. Use of waste fibre
Crop residue fibres such as bagasse, straw and cotton liners carry the greatest advantage in that the growing and reaping costs are carried by the primary industry.  The cost of fibre collection then remains the only responsibility of the paper industry A notable except is bagasse where the sugar industry carries this cost also. However, bagasse usually carries a cost related to the calorific value of coal required to replace bagasse that would otherwise be burnt to supply energy to the sugar mill4.

3. Low cooking and refining energy
Non-wood fibre sources are usually supplied to the pulp digester in smaller size fractions than wood chips, and they have weaker inter-fibre lignin deposits, resulting in lower cooking energy requirements1,6.  For example bagasse and straw will cook within 10 to 15 minutes4

It has also been found that most non-wood fibres require less refining energy to achieve the same freeness drops as in wood pulps3.

4. Lower cooking and bleaching chemical requirement
It is also reported that the cooking chemical and bleaching chemical requirements for non-wood species are lower than for wood fibres3,6,11.

5. Technological input
Traditionally the paper industry has focussed on wood as the only significant source of paper fibre. This is partly due to the dependence on wood in the countries in which most technological development has taken place. There has also been a reluctance to invest in alternatives due to the costs involved and lack of urgency in developing non-wood paper technology1

One of the reasons non-wood fibres are viewed with scepticism is the lack of success of some trials that have been run using wood based technology to process non-wood fibres. However, the potential to correct the problems encountered is highlighted by the fact that over the past 30 years eucalyptus was grown from being regarded as a poor quality fibre source to being a premier fibre source due to adaptation of technology to suit the fibre1. Could the same happen with non-woods if enough backing was given to technological development?

NON-WOOD SPECIES

Specific species discussed and their advantages, disadvantages, technologies available and paper uses are briefly summarised in Table 1.

Table 1: Non-Wood fibre species

Fibre

Advantages

Disadvantages

Technologies

Uses

Bagasse4

 

Short grow time

1 year rotation.

Waste fibre source

Requires depithing. 

Well developed pulp technologies available

Most paper types

Hemp3,14

 

Rapid growth 8-10 ft in four months

Requires decortication and retting. Perceptual problem due to drug association.

Long fibre wraps round equipment.

Well-developed pulp technologies available. Drug free variety available.

Cigarette paper, strength additive to waste paper, light weight papers

Kenaf15,16

High yield 21.3 mt/ha in 3 years. 

Duel source: 57% long bast fibre, 41% short core fibre, therefore bark and core separation required.

Excellent papers have been made using existing technology.

Wide range due to variety of fibres.

Wheat straw3,5,11

Short grow time

1 year rotation.

Waste fibre source

Problems with black liquor treatment.

Perceptual problems

Well-developed pulp technologies available. Successful work on black liquor done.

Most paper types

Linseed Flex 17

Byproduct of linseed industry. Low cooking and TMP refining energy.  Similar cost to hard wood in Canada ($60/ton)

Needs decortication before cooking.

Lower brightness than wood after TMP

Well documented as beneficial in blends with wood pulps. Processing technology is understood.

Used in wood pulp blends to improve strength.

Perenial Grasses 8

Fast growing. Environmentally friendly

Not established. High ash.

 

Potential supplement to hardwood.

Arundo donax10

Fast growth- 5m tall in 6 months.  30 BDT/ha/year

Can be used in hard wood pulping mill as alternative.

Developing acceptance in the industry.

Can use same technology as hardwood pulping.

As for hardwoods

 


TECHNOLOGICAL DEVELOPMENTS

Technological developments and their application in non-wood pulping discussed at the conference included:

1. Extrusion Pulping2,7
Clextral (France) has developed tin-screw, or Bivis, extruders for digesting, washing and developing fibre properties. The Bivis machine has two matching and co-rotating screws that intermesh with each other.  The screw shafts are splined so that various screw configurations can be mounted at different parts of the screw. In this way it is possible to have various effects in a single process.  The screw housing splits on the horizontal plane and can be fitted with port for introduction or extraction of gasses and liquids. 

In a Bivis used for, cooking the cooking liquor and steam can be introduced close to the fibre feed side, and black liquor can be extracted close to the discharge side.  During cooking mechanical energy is applied to the pulp at the same time as chemical energy resulting in a partially refined pulp. 

In pulp washing applications a number of counter current wash stages are possible as the wash liquor can be injected and extracted a number of times along the length of the screws.

Clextral Bivis machines come in the range shown in Table 2:

Table 2: Clextral Bivis range

 

Minimum

Maximum

Capacity

2 kg/h

15 ton/h

Motor power

2 kW

2000 kW

Screw diameter

21 mm

240 mm

AF-QPS are also developing Bivis technology for the Bioregional MiniMill project as discussed later.

2. Chempolis® and Natural Pulping 6,19
Chempolis OY (Finland) and Natural Pulping (Germany) are developing pulping processes using formic acid as a cooking agent or solvent. Cooking is done at atmospheric or slightly elevated pressures at 80 to 95 oC. Since cooking is in an acidic medium, silica does not dissolve into the black liquor, circumventing the usual problems associated with silica in non-wood pulping. Chemical recovery is simply achieved by distillation with no need for chemical make up as formic acid is generated during cooking. The process yields pulp of superior brightness and strength than equivalent kraft pulps.

3. TCF bleaching of Flex and Hemp13
TCF bleaching trials using EDTA to control metals, tetra acetyl ethylene diamine (TAED) as a peroxide activator and ultrasound to assist with lignin displacement and liquor penetration produced pulp with comparable brightness, and improved pulp viscosity, to CEH bleached hemp and flax pulps. TAED is already in use in the paper industry in Scandinavia and South Africa.

4. NACO pulping 11
This process uses NaCO3, Oxygen and NaOH in a specialised and patented digester called a Turbopulper. Delignification is through reaction with oxygen in a NaCO3 solution with NaOH acting as an activation and makeup chemical. The Turbopulper has a perforated plate and rotor arrangement in the base that selects cooked fibre out of the reactor.  Typically two turbopulpers are used in series operating at 6-7 bar pressure, pulp consistency of 8%.

Because oxygen is the delignifying agent the pulp has a high brightness (50% ISO) and is easily bleached by one stage of peroxide to 80% ISO, or ozone to 90% ISO.

Chemical recovery is similar to that in soda chemical recovery but requires a support fuel.  Green liquor from the recovery plant contains silica that is removed by treating the liquor with lime. No Caustisization is required as the system is dependent of NaCO3, not NaOH.

5. Black liquor treatment methods

    a. Lignin Precipitation System (Granit S.A. Switzerland)18

    Black liquor is treated with acids to precipitate the lignin that is then sold as a commodity. This system does not offer chemical recovery or process steam but this is compensated for by the sale of the lignin. Unfortunately the effluent liquor COD is only reduced by about 50% and still contains the cooking elements.

    b. Wet Oxidation (Granit S.A. Switzerland)18

    Wet Oxidation involves the reaction of the black liquor, with oxygen or air, in the liquid phase at high temperature and pressure.  Process steam is generated and cooking chemicals are recovered after filtering and recaustisising the effluent liquor.  No evaporation is required prior to wet oxidation thus eliminating the problem of silica scale formation on evaporators.

    c. Black liquor treatment by AF-QPS for the MiniMill project5

    AF-QPS is working on a chemical recovery system for the Bioreginal MiniMill project. The system is based on fluidised bed technology that is precisely controlled at relatively low temperatures to avoid the agglomeration problems usually experienced with fluidised bed reactors. A secondary fluidised bed reactor is used for lime calcining.

    d. Conox (not presented at the conference but included for interest)

    Conox of Finland has developed a Chemical recovery boiler that incorporates desilication, recaustisisation and steam generation.

INNOVATIVE APPROACHES

1. BioRegional MiniMill5
BioRegional is a UK based environmental organisation that focuses on the use of local resources to meet local needs. Their MiniMill project is an attempt to develop small-scale pulp mills that can use locally available fibre sources, such as wheat straw, to produce pulp on a sustainable and environmentally friendly basis. They are aiming at a production range of between 10 and 100 BDTPD. The technological development is primarily through AF-QPS and focuses on the use of twin-screw extruder systems for cooking and washing the pulp.  As mentioned earlier AF-QPS is also developing a chemical recovery system for the MiniMill. 

2. Vision Papers16
Vision Papers, USA, is a paper manufacturer with a difference. Having secured a supply of kenaf from local farmers they approach pulp mills that have spare capacity to pulp the kenaf to agreed specifications.  The pulp is than taken to paper machines with spare capacity and used to manufacture a variety of printing grade papers that are sold for specialty publications. 

3. Kenaf Society15
The kenaf society of the USA focuses on developing and popularising the use of kenaf for a variety of fibre related industries including the paper industry.

4. Tree (Impromptu presentation –no paper available)
Tree is a religious organisation that worships nature. Since Tree uses the tree as a symbol through which to worship nature, they actively advocate the use of hemp as a substitute for wood in paper manufacture in the USA. 

5. Current Academic and Research Developments

    a. Finland3

    Finland has a shortage of hardwoods and is intensively looking at non-wood alternative sources of short fibre.  Of particular importance is the use of hemp that produces a substantial crop over the three or four months of warm summer weather.

    b. Canada17

    The Alberta Research Council is actively working on non-wood pulping technology using agricultural residues such as oilseed flax.

    c. United Kingdom

      • BioRegional is developing the MiniMill5
      • Biocomposites Centre is working on Flax and hemp pulping technology13.
      • Hemcor is working on and advocating technology for the use of hemp for paper manufacture14.
      • Apsley Paper Trail initiative is using the Frogmoor mill in cooperation with Cross and Bevan to run trials on various non wood pulp supplements to recycled fibre1.

    d. Australia11

    Arisa Ltd. are in the process of establishing a wheat straw mill in Victoria that will use the NACO process.

    e. USA9,10,15,16

    A number of initiatives already mentioned are gaining momentum in the USA.

    f. Netherlands2,8

    Research into non-wood fibre pulping technologies, and the application of non-wood fibre to enhance wood and recycled paper qualities, is being done through the Agro Technological Research Institute.

CONCLUSION

The conference highlighted that non-wood fibres can be easily and quickly grown and make paper of excellent quality, but that development of technology for handling them has been retarded by the industries focus on wood pulping technologies and conservative attitudes towards new concepts.  Equipment manufacturers seem reluctant to invest in development of machinery technology to handle non-woods especially in countries where wood papermaking is the backbone the economy.

Lack of success with most non-wood initiatives was attributed to attempting to apply wood pulping technology to non-woods resulting in poor pulp quality due to incorrect handling.  This is particularly true for digestion and refining which tend to produce overcooked and over -refined pulps, as the energy required for non-woods is generally lower than for wood processing. Lack of industry financial and management support for non-wood initiatives has also been lacking despite strong technical proof of the potential of non-wood fibres.

However, there are many non-wood based paper mills already producing the full spectrum of paper grades.  There are also a number of initiatives world wide that are actively advancing the cause of non-wood paper making.  Non-Wood fibre is gaining acceptance as a cost effective, quality competitive, and environmentally friendly alternative to wood.

REFERENCES

All papers referred to are from the unpublished proceedings of the Pira conference entitled Cost effectively Manufacturing Paper & PaperBoard From Non-Wood Fibre & Crop Residues (2001).  Proceedings may be obtained direct from Pira by contacting Andre Eagle at email: andrewe@pira.co.uk

1. Dean, W.R., "Non-Wood Fibres, Past Present – and Future."

2. Westenbroek, A.P.H, "Extrusion Pulping of Natural Fibres."

3. Paavilainen, L., "Paper making potential of Non-Wood Fibres."

4. Hunt, N.A., "The Challenges and Rewards of Bagasse Papermaking."

5. Riddlestone, S., "The MiniMill Concept."

6. Rousu, P., "Examining Elements In the design of the Non-Wood Pulping Process."

7. Combette, P., "Introduction of a Non Conventional Pulping Process for the Pulping of Non- Wood Fibres and Crop Residues."

8. Elbersen, H.W., "The Potential of Perennial Biomass Grasses and their Options for Multifunctional Land Use."

9. Woods, J.E., "Bamboo as the Natural Non-Wood Fibre to Use in Place of Wood Pulp."

10. Lewis, M.S., "Arundo donax: A Non-Wood Fibre Source Suitable for Existing Pulp Mils."

11. Paul, D., "The Technical and Logistical Challenges in Establishing a Straw Based Pulp Mill in Australia Using the NaCO Process."

12. Karus, M., "Flex & Hemp For the European Specialty Pulp Industry – A Market Study."

13. Snell, R., "TCF Bleaching of Flax and Hemp Pulps."

14. Hobson, J., "Cannabis Hemp –A Raw Material for the European Paper Industry."

15. Bledsoe, R., & Bledsoe, V., "Kenaf from Seed to Market"

16. Rymsza, T., "Comercial Paper Making with Kenaf."

17. Chute, W., "Pulps From Oil Seed Flax Straw in Mainstream Pulp and Paper Applications."

18. Lora, J.H., "Options for Black Liquor Processing in Non-Wood Pulping."

19. Siegle, S., "An Overview of Non-Wood Pulping Technology."

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