1061 PHARANDE et al: ENERGY OPTIMIZATION IN INTEGRATED PULP AND PAPER MILLS Journal of Scientific & Industrial Research Vol. 70, December 2011, pp. 1061-1069 *Author for correspondence E-mail: vilaspharande@gmail.com Energy optimization in integrated pulp and paper mills with recourse to environmental benefits V A Pharande 1 *, S R Asthana 2 , D R Saini 2 and S N Kaul 3 1 Bharati Vidyapeeth Deemed University College of Engineering, Pune, India 2 CSIR-National Chemical laboratory (NCL), Pune 411 008, India 3 CSIR-National Environmental Engineering Research Institute (NEERI), Nagpur 440 020, India Received 24 June 2011; revised 30 September 2011; accepted 11 October 2011 This study focuses on energy optimization in evaporator and digester of integrated pulp and paper mills in India, and recommends application of 7 effects/plates evaporator in place of 5 effects/plates normally used. Steam economy resulting from this modification is definitely more than 7. Pinch technology is found suitable for optimization of controlled parameters in the digester. Using recommendations, total energy savings was observed in West Coast Paper Mill (11.74%) and Star Paper Mill (12.97%). Environmental benefits that will accrue in terms of reductions in emissions are: SPM, 46464-48664 TPA; SO 2 , 1045 kg/annum; H 2 S, 55,020 kg/annum; and CO 2 , 13612 TPA. Keywords : Air emissions, Digester, Evaporator, Pinch technology, Steam economy Introduction Pulp and paper (P&P) sector holds sixth position in Indian energy intensive industries. Energy cost is 15% of manufacturing cost and 10% of annual turnover and accounts for 4.2% of total fuels consumed in manufacturing sector 1 . In P&P production, 75-80% of energy requirement is being used as process heat and 15-25% as electrical power 1 . Indian P&P mills have 20% energy saving potential and 7% of steam saving potential from total steam consumption. P&P studies 2 reveal that pulping in digester, drying in evaporator and pressing in paper making machines are more energy intensive processes. Major factors affecting energy consumption of evaporator are type of evaporator, number of stages and steam economy achieved. Pinch technology 3 reduces energy consumption in manufacturing processes like pulping in digester by control of various parameters (quality of raw material, seasonal effect, conc. of white liquor (WL), optimum digester temperature, etc.). This study suggests possible retrofit attachment to existing evaporators in integrated P&P mills and can be useful to all evaporator-based industries (distillery, dye industries, textile industries etc.). Mathematical Modeling for Energy Conservation and Environmental Benefits Multi Effect Flat Falling Film Evaporator Modeling is carried out in steps for falling film single lamella type evaporator to optimize mass flow rate, dry solids content and wall temperature for enhancing heat transfer coefficient of evaporator. Firstly, ß level model is developed followed by final level model. This model is then validated using plant data and results are obtained. Introducing dimensionless variables [mass flow rate G * {black liquor (BL) mass flow rate/ initial BL mass flow rate}, dry solids content X * (BL dry solids content/ initial BL dry solids content), space coordinate along the plate Z * (space coordinate along the plate / plate length), velocity along the plate V * (flow velocity along the plate / friction velocity at initial conditions), time t * ,0 * f tV t L = , evaporated water flow rate W* (evaporated water mass flow rate / initial conditions evaporated water mass flow rate), and dimensionless variable 0 0 LW G h = for development of partial differential equations for total mass flow rate for BL and dry solid content, respectively] are presented as (δG * / δt * ) + V z * (δG * / δz * ) = – W * η V z * …(1)