ENVIRONMENTALLY FRIENDLY CARBON DIOXIDE

Transcription

1 ENVIRONMENTALLY FRIENDLY PROCESS IMPROVEMENTS USING CARBON DIOXIDE Ann-Charlotte Lotta Jansson, Linde AG, Linde Gas Division Monica Ortiz-Cordova, Linde Canada Limited PaperCon 211 Page 196

2 Introduction Carbon dioxide environmentally friendly process chemical Process improvements Easier to reduce fresh water consumption PaperCon 211 Page 1961

3 Packaging Papers at Neutral/Pseudo-Neutral ph ph control with H 2 SO 4 and/or alum If the furnish contains RCF Local ph shock Unstable ph Increased conductivity Dissolution of CaCO 3 CaCO 3 Ca 2+ + CO 3 2- increased process water hardness PaperCon 211 Page 1962

4 Negative Impact of Dissolved Calcium Ions on Papermaking Ca 2+ agglomerate disturbing substances react with fatty and resin acids forming insoluble Ca-soaps negative effect on the performance of many process chemicals PaperCon 211 Page 1963

5 Effect of Calcium Ions on Rosin Sizing Low calcium hardness is better than total absence of calcium (Lab studies by Farley 1992) High calcium hardness has a negative effect Higher Ca hardness More alum necessary to protect the rosin size PaperCon 211 Page 1964

6 Change in COD and Sulfur Load when Reducing Specific Water Consumption COD dependence on fresh water consumption for mechanical fiber containing printing grades Inorganics have low affinity to fibers accumulate faster than organic substances tration [mg/l]. COD Concen concentration at 2 m³/t]. COD & Sulfate [% of level a 8% 7% 6% 5% 4% 3% 2% 1% % COD Sulfates Specific Water Consumption [m³/ton]. Specific water consumption [m³/t] Source: Möbius (1993) Source: Data from Hermosilla et.al. (21) PaperCon 211 Page 1965

7 Improved Pulp Washing with Carbon Dioxide Patented method Reduces carry-over from the fiber line to the paper machine and/or Reduces the wash water usage Other possible benefits are - increased runnability and capacity - reduced effluent load - reduced maintenance cost - reduced defoamer consumption PaperCon 211 Page 1966

8 Carbon Dioxide-Based Applications for Papermaking Patented methods BasedonCO 2 only or on a combination of CO 2 and NaOH Dissolution of CaCO 3 can be significantly reduced or completely avoided Improved ph stability Applications based on the use of carbon dioxide only, such as CODIP and GRAFICO will hereafter be referred to as the CO 2 method PaperCon 211 Page 1967

9 Carbon Dioxide-based Applications Prevent Dissolution of Calcium Carbonate No ph shock at the addition point Increased concentration of carbonates ph stabilization Acid neutralization: HCO 3- + H + H 2 CO 3 Base neutralization: HCO 3- + OH - H 2 O + CO 3 2- dness [ppm CaCO 3 ] Total har CaCO (s) Ca 2+ (aq) + CO (aq) Ks.p(CaCO 3 )= [Ca 2+ ][ CO 3 2- ] Ks.p(CaCO 3 )= [Ca 2+ ][ CO CO 3 2- (added)] Coated broke - reference Coated broke - with ADALKA 6, 6,5 7, 7,5 8, 8,5 ph PaperCon 211 Page 1968

10 Lower Conductivity When Using the CO 2 Method Newsprint machine (DIP) Kraftliner machine (UBKP+RCF) Condu uctivity [µs/c cm] Grade A Grade B Grade A Grade B H2SO4 CO2 method m]. Condu uctivity [µs/c Sulfuric acid CO2 method and less alum PaperCon 211 Page 1969

11 Less Pitch Deposits When Using the CO 2 Method ph shocks and high concentrations of dissolved calcium can trigger deposition i of pitch Process Unbleached Kraft, RCF, Rosin sizing Problem Ca-resinate deposits Carbon dioxide based solution Change from using H 2 SO 4 and alum to using the CO2 method and less alum Results Significantly reduced process water hardness Equipment remains clean PaperCon 211 Page 197

12 Dissolved and Entrained Carbon Dioxide Generated from Dissolution of CaCO 3 Disso olved CO 2 [g/l] Dissolved CO 2 Entrained ta edco 2 5, 5,5 6, 6,5 7, 7,5 8, ph Entrain ned CO 2 [% v/v]. Source: Redrawn from Grist & Canty (26) PaperCon 211 Page 1971

13 Big Bubbles are Difficult to Dissolve The mass transfer equation: N = k k1 a (C* - C) ]N 6 e area a [m²] liter gas 5 4 where 3 N = absorbed gas per unit time 2 k 1 a = mass transfer coefficient = gas / liquid interfacial area per unit volume C* = saturation concentration of the gas in the liquid phase C = gas concentration in the liquid phase Surface per Bubble diameter [mm] For bubbles a = 6/d The mass transfer rate is slower for larger bubbles PaperCon 211 Page 1972

14 Reduced Amount of Entrained Gas When Using the CO 2 Method on a Kraftliner Machine Kraftliner mill using UBKP and OCC trained gas [%]. En Entrained gas [%] Defoamer [l/min] 4, 16 3,5 14 3, ,5 1 2, 8 1, , 4,5 2, Sulfuric acid CO2 method and less alum on [l/min]. Defoa amer additi PaperCon 211 Page 1973

15 Environmental Benefits of Using the CO 2 Method Reduced conductivity Lower process water hardness Stable ph - Improved efficiency of process chemicals - Easier to further close the water circuit - Possibility of running the process at higher ph without t generating calcium-resinate deposits - Improved efficiency of rosin sizing Easier to control the Na/S balance in closed Kraft mills PaperCon 211 Page 1974

16 Thank You for Your Attention PaperCon 211 Page 1975

17 References 1. Möbius C. H., Abwasser der Papier- und Zellstoffindustrie. Biologische Reinigung von Abwässern aus der Erzeugung von Papier und Zellstoff, 3rd Edition, November 22, revised December 29, Augsburg, Germany 2. Hermosilla D., Ordoñez R., Blanco A., San Pío I., Rodríguez L., Sustainable water use in graphic paper production, Mid-term Aquafit4use Conference, June, 21, Oveido, Spain 3. Farley C. E., Influence of dissolved ions on alum cationicity under alkaline papermaking conditions, Tappi Journal, November 1992, pp McLean D.S., Vercoe D., Stack K.R., Richardson D., The colloidal pka of lipophilic extractives commonly found in Pinus radiata, Appita J. Vol 58, No 5, 25, pp Bokström M., Kontola P., Improvement of pulp washing by addition of carbon dioxide, id TAPPI Pulping Conference Östberg, G. M. K., Öhrn M. I., Kvist E. U., Use of carbon dioxide in the production of sulphate pulp, 5th International Conference on New Available Techniques, The World Pulp and Paper Week, June 4-7, 1996, Stockholm, Sweden. 7. Jansson A-C., Carbon Dioxide based applications for optimization of Calcium Carbonate containing papermaking processes, TAPPI Papercon Grist S. R., Canty R. J., Carbon dioxide in pulp/paper p p p mill stocks: fix or fizz?, 6th Appita Annual Conference and Exhibition, Melbourne, Australia, 3-5 April 26, Proceedings PaperCon 211 Page 1976