As desired by the Cess Committee the outcome of the following completed Cess Funded Projects will be presented in workshop proposed to be held in May 2011, at New Delhi

Cess Project on "Data for Amendment in stiffness specifications for different Paper Grades under BIS Standards"

Stiffness has become an important parameter for most of paper grades. Bending stiffness is necessary for good runnability on the printing presses and converting machines. A uniform tensile stiffness over the width of the paper web is for instance a condition for good register. During post-treatment in the bindery, the folding machines usually require a certain bending stiffness for good convertibility. In photo copying machine proper stiffness is necessary for proper functioning. Paper products like corrugated fibre board boxes are manufactured from materials which have a marked stiffness towards tensile and compression forces. Modern liquid packages, cartons etc. are further examples of a paper usage which would be impossible without the considerable bending stiffness of the material. Overall stiffness has become an important parameter for most of paper grades.

Bureau of Indian Standards has prescribed different values for cover paper, photocopier paper, coated board and straw board. Different terminology has been used in different standards and there is no uniformity in prescribed methods of testing and ways of expressing the results. Stiffness measurement has become a confused concept according to the procedure prescribed in different BIS standards. The nomenclature used in these standards is not as per International Standards. The test method prescribed is no longer relevant. There is no uniformity in specified values. This is posing lot of problem to Paper manufacturers and traders dealing in national and international market. Detailed studies were carried out on different papers viz. cover paper, coated board, straw board and photocopier papers using L & W stiffness tester (bending stiffness type) and Taber tester. Based on the results of above study following values are recommended for adoption in different BIS standard.

For photocopier paper which is normally in grammage range of 70 to 80 g/m2, instead of specifying Bending stiffness index, the stiffness in Taber unit or millinewton should be prescribed.

Summary :
The effluent generated in Pulp & Paper industry is treated to reduce the COD, TDS and other parameters to conform to the pollution control board norms. Many mills in India have started opting for pollution minimisation at source and switched over to environment friendly process technologies such as Oxygen-De-Lignification (ODL) and Elemental chlorine free (ECF) bleaching to reduce pollution load instead of end-of-pipe treatment, which is not sustainable both environmentally and economically.

However, colour, COD and inorganic TDS are a major source of pollution, which are generated even in the modern bleaching process however to significantly lesser level as the lignin entering the bleaching section is reduced by 40 -50% by ODL to about 1.5% of residual lignin and subsequently the Elemental Chlorine addition is reduced by 2.6 times by replacing elemental chlorine with Chlorine-dioxide having higher oxidation potential.

1. The Pilot Plant was commissioned on 12.7.2009.

2. The trials with Eop effluent shows that colour and COD reduction to the level of 80 to 85 % in the first ten days. The rate of COD reduction was 0.68 mg of COD / gm of activated carbon in the FACCO reactor of CLRI design.

3. Due to the high sodium content (1200 ppm) and viscous nature of the effluent caused saturation of the catalyst in FACCO process, the reduction has decreased in the subsequent trials to 40 to 50 %; COD reduction -36 mg/gm of carbon.

4. Ferrate dosage was increased to 100 ppm and the COD reduction improved to 55%

5. When the flow rate was optimised at 600 to 800 lit/hr and Fenton added to EOP filtrate there was an improvement in the reduction of color & COD to 60 %.

6. Pre-treated Eop filtrate with FACCO process is processed through UF/RO/Nano membrane system helped in segregation of Calcium and Sodium as envisaged and recovery of good quality RO water. However, TNPL has opted for recycling the extraction filtrate through ODL stage and currently discharging the acid bleach filtrate.

7. Acid filtrate of bleach plant was treated with lime soda process to neutralise the effluent, which also reduced the COD and hardness along with colloidal silica. This process generates lime sludge that can go into lime cycle. The filtrate primarily contains sulphate, chloride and COD. The COD is further reduced using anaerobic and aerobic process. This biologically treated filtrate is passed through NF system to separate the chlorides and sulphates. The NF concentrate primarily contains sulphate with minor contaminants such as chlorides which can partially substitute saltcake requirement in SRP line.

8. Based on these concepts TNPL is trying to validate the process to close the bleach loop.

On-line Digester Monitoring and Control of Kappa Number in Indian Pulp & Paper Mills

Executive Summary
Growing demands for improved quality, increasing global competition and stringent environmental and safety regulations have emphasized the need for chemical industries to rely on model based technologies for optimization and control. Model Predictive Control (MPC) has emerged as one of the powerful control algorithms which predicts future output behavior from dynamic model and on-line measurements of the plant. The work under this CESS funded project focuses on the development of a mathematical model of Pandia Digester and online kappa measurement system based on this model which will work on the feed back of soft sensors (pH, conductivity and temperature) from the Pandia digester. Pandia digester is a horizontal continuous digester used in pulp and paper industry for the cooking of non-wood fibers. A kinetic model for delignification of wheat straw has been adopted from literature and it was also further validated by laboratory studies at Central Pulp and Paper Research Institute (CPPRI).

Since this model was not complete for incorporation in the system, we have augmented it by using data corresponding to wood and modified it in order to predict exit Kappa number based on experimental data provided by CPPRI, Saharanpur. With suitable assumptions, a dynamic model has been derived based on first principles and is simulated in MAT LAB(R).

Steady state profiles have been obtained and parametric sensitivity analysis has been performed on the model. As the model for continuous digester is non-linear, Extended Kalman Filter technique has been used for state estimation. Input disturbance modeling has been done to account for steady state sets observed due to parameter mismatches.

For development of the model, design data of the digester was collected from one wheat straw based mill alongwith the operational parameters. It was then validated by running the program with the input values of the mill data and the outputs were compared with the operational values from the mills. Necessary correction factors were used to match the program out put with the mill results. The results have shown that the kappa variation pattern can be observed with the feed back from the mill. The system developed in the study has capabilities to accept the online temperature, pH and conductivity of the black liquor from the digester at different points and predict the online kappa number, alkali profile at different points along the digester tube length. The system for the insertion of the probes at appropriate position is required to be designed by the supplier to effectively monitor the online kappa with the developed software.

For Further Details Regarding Projects Please Contact :

Dr. R. M. Mathur,
Director, CPPRI
Member Secretary (DCPPAI),
Central Pulp and Paper Research Institute,
Email : info@cppri.org.in, director@cppri.org.in

CPPRI Base Office
10. Birbal Road, New Delhi - 110014 (India)
Phone : (011) - 24315400
Fax : (011) - 2431 5401
Email : cppri@yahoo.com
Contact Person: Dr. Kawaljeet Singh (Sc E I & officer In charge)