Bamboo paper making in China has a long history. Bamboo fibre morphology and chemical composition have special characteristics. The average fibre length is long, and the microstructure of the fibre cell wall is special, beating in the strength of the pulp development performance is good, giving the bleached pulp good optical properties: high opacity and light scattering coefficient. Bamboo raw material lignin content (about 23% to 32%) is higher, determining its pulp cooking with higher alkali and sulfide (sulfide generally 20% to 25%), close to coniferous wood; raw materials, hemicellulose and silicon content is higher, but also to the pulp washing, black liquor evaporation and concentration equipment system normal operation has brought some difficulties. Nevertheless, bamboo raw material is not a good raw material for paper making.
Future bamboo medium and large-scale chemical pulp mill bleaching system, will basically use TCF or ECF bleaching process. Generally speaking, combined with the depth of delignification and oxygen delignification of pulping, the use of TCF or ECF bleaching technology, according to the number of different bleaching sections, bamboo pulp can be bleached to 88% ~ 90% ISO whiteness.
Comparison of bamboo ECF and TCF bleaching
Due to the high lignin content of bamboo, it needs to be combined with deep delignification and oxygen delignification technologies to control the Kappa value of the slurry entering ECF and TCF (recommended <10), using Eop enhanced two-stage ECF bleaching sequence, acid pretreatment or Eop two-stage TCF bleaching sequence, all of which can bleach sulphated bamboo pulp to a high whiteness level of 88% ISO.
The bleaching performance of different raw materials of bamboo varies greatly, Kappa to 11 ~ 16 or so, even with two-stage bleaching ECF and TCF, the pulp can only achieve 79% to 85% whiteness level.
Compared with TCF bamboo pulp, ECF bleached bamboo pulp has less bleaching loss and higher viscosity, which can generally reach more than 800ml/g. But even the improved modern TCF bleached bamboo pulp, viscosity can only reach 700ml/g. ECF and TCF bleached pulp quality is an indisputable fact, but the comprehensive consideration of the quality of the pulp, investment and operating costs, bamboo pulp bleaching using ECF bleaching or TCF bleaching, has not yet been concluded. Different enterprise decision makers use different processes. But from the future development trend, bamboo pulp ECF and TCF bleaching will co-exist for a long time.
Supporters of ECF bleaching technology believe that ECF bleached pulp has better pulp quality, with the use of fewer chemicals, high bleaching efficiency, while the equipment system is mature and stable operating performance. However, advocates of TCF bleaching technology argue that TCF bleaching technology has the advantages of less wastewater discharge from the bleaching plant, low anti-corrosion requirements for the equipment, and low investment. Sulphate bamboo pulp TCF chlorine-free bleaching production line adopts semi-closed bleaching system, bleaching plant wastewater emissions can be controlled at 5 to 10m3/t pulp. Wastewater from (PO) section is sent to oxygen delignification section for use, and wastewater from O section is supplied to sieve washing section for use, and finally enters into alkali recovery.Acidic wastewater from Q section enters into external wastewater treatment system. Due to the bleaching without chlorine, the chemicals are non-corrosive, the bleaching equipment does not need to use titanium and special stainless steel, ordinary stainless steel can be used, so the investment cost is low. Compared with the TCF pulp production line, ECF pulp production line investment costs to be 20% to 25% higher, with the pulp production line investment is also 10% to 15% higher, the investment in the chemical recovery system is also larger, and the operation is more complex.
In short, bamboo pulp TCF and ECF bleaching production of high whiteness 88% to 90% fully bleached bamboo pulp is feasible. Pulping should be used in depth delignification technology, oxygen delignification before bleaching, control of the pulp into the bleaching system Kappa value, bleaching using bleaching process with three or four bleaching sequences. Suggested ECF bleaching sequence for bamboo pulp is OD(EOP)D(PO), OD(EOP)DP; L-ECF bleaching sequence is OD(EOP)Q(PO); TCF bleaching sequence is Eop(ZQ)(PO)(PO), O(ZQ)(PO)(ZQ)(PO). As the chemical composition (especially lignin content) and fibre morphology vary greatly among different varieties of bamboo, a systematic study should be conducted on the pulping and papermaking performance of different bamboo varieties before the construction of the plant to provide guidance for the development of reasonable process routes and conditions.
Post time: Sep-14-2024
