Executive Summary : | Close to 200 Paper Mills are located along the GANGA basin spread along five states on India. Pulp manufacturing technology is energy and water intensive in nature besides huge consumption of wood as raw materials i.e. through deforest. Above all, this industry produces huge quantity of greenhouse gases (CO2, SO2, NOx, H2S etc.), suspended particulate matters, generate huge mass of solid wastes and discharge contaminated (high pH) water as waste stream. IIT Roorkee, Saharanpur Campus is one of the worst affected institute located within 500m from M/s STAR Paper Mills Ltd., Saharanpur. Every resident remains concerned with the severe harm being done to environment by old Paper mills. In paper mills delignification from wood cheeps are carried out in digesters using white liquor made up of NaOH and Na2S. After cooking of wood pulp and black liquor (BL) are separated. BL is rich in lignin and is used as major source of green energy in Paper mills. Obviously huge quantity of greenhouse gases and suspended particulate matters evolved from these furnaces. In the recovery section of Paper Mills major portion of chemicals are recovered from ash residues of furnace. The ash residues (Na2CO3 and Na2SO4) are converted to NaOH and Na2S by soda ash process and recycled as white liquor, WL. Huge amount of wet solid residues containing CaCO3 (major constituent) is obtained and this is recycled as lime (CaO) after drying and calcination of wet lime. This section of Paper Mills demands huge amount of energy (causing environmental pollution) and it produces large quantity of suspended particulate matters during handling of lime. In the neighboring area of M/s Star Paper Mills Ltd., SRE a huge area (5 sq. km.) have been earmarked as land fill for excess lime. ED application on the green liquor can eliminate soda alkali process, solid waste generation and energy intensive calcination steps and still produce the desired white liquor concentration of NaOH and Na2S. Investigators are developing bipolar membranes (BM) which can treat green liquor and generate distinctly different streams (i) NaOH, (ii) process water and (iii) acid gas mixtures CO2, H?S . H2S gas can be separated from the gas mixtures and proportionately added to NaOH to achieve Na2S : NaOH balance of white liquor, WL. CO? may be used for pH adjustment of process streams. Another modification in process flow diagram is made after surface modification of anion exchange membrane (AEM). In this scheme direct conversion of GL to white liquor of different dilutions are achieved. PI and his team have technology to fabricate ED setups where indigenous Bipolar membranes are used to convert acid, alkali and process water from strong electrolytes. This technology is needed to be used for recovery of white liquor from green liquor. |
