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Efficient Fibre Recovery through Poly Disc Filter & Quality Process Water for Recirculation

Description

The process water from paper machine, passing through the poly disc filter via side hill screen, results in recovery of valuable fibres to be reused. This case study depicts how treating of overflow with coagulating chemicals such as Delfloc-5310 (Polyelectrolyte Polymer) reduces the TSS, results in improved recirculation of water.

Implementing Industry

Best Paper Mill, Unit 1 located in Vapi Industrial Estate, produces Kraft Grade Paper with present capacity of about 160 TPD by using local and imported waste paper as raw material. The industry is medium scale with an annual turnover about Rs. 130 Crores.

Implemented technology / technique

BEFORE:

  • The surplus process water flow mainly from machine area was directly fed to the “Save All” via Side hill screen. The side hill screen generates high levels of residual fibre content as the fibre recovery is not efficient. 

  • The under flow from Save-All was diverted to ‘Sludge Holding Tank” contained for post dewatering in centrifuge, while the overflow with high TSS (>400 mg/lit) was recycled back to process for reprocessing of fibre (internally and via “Save All” system) to various production steps. This leads to the reduction in strength of the fibre as well as increased reprocessing cost.

  • The presence of fibre in recirculating streams also results in problem of biofouling and unnecessary increase TSS in the filtrate.

  • The quality of recirculation water was checked for COD and if it exceeded 5000 mg/litre, then certain quantity was purged to downstream biological treatment system, to avoid potential effect on product quality.

AFTER:

  • Under this intervention it was decided to pass the surplus process water from the machine area through a “Poly Disc Filter“ the after side hill screen, in the process flow. This is expected to recover about 0.5% fibre (based on 160 TPD capacity) from water process stream and reuse it into the process. 

  • The filtrate from poly disc filters to be stored in a new tank with a capacity 100 m3 per day. Where Delfloc 5310 is introduced as a “Coagulant” through an online dosing system.

  • The dosed water is transferred to the existing Save-All where the coagulant will adsorb the remaining fibres & fines (TSS) from the water, the flocs generated settles at the bottom of the Save-All. The overflow from Save-All (TSS<100 mg/litre) is recirculated to the process plant which will also eliminate the biofouling within process water and the underflow goes to the sludge dewatering system through centrifuge.

Economic benefits

The capital cost incurred in the process was Rs. 150,00,000 and the estimated savings was of Rs.36,00,000 per annum giving a payback period of in 4 years.

Contact details 

Mr. D.B.Ashar (G.M.); best.ashar@gmail.com