Study On The Effect Of Black Liquor Extraction On The Residual Pollution

Paper industry is one of the most important basic industries related to the social and economic development and national demand.At present,China has become the world's paper production,consumption and import and export,but the amount of water consumption is big and high pollution load is high.Papermaking wastewater emissions accounts for about 10% of total industrial wastewater emissions,second only to the chemical industry,iron and steel industry,causing great pollution to the environment.The focus of pollution control and governance is at the traditional end but ignore the pollution transfer and contribution of incomplete extraction of black liquor in the papermaking industry.Pinus koraiensis was used as material with alkaline cooking.Firstly,chemical composition was characterized and the content of liquid phase lignin was studied.The three-stage adverse current washing method and downstream washing method were adopted to wash the black liquor out of the pulp.The relationship between liquid phase lignin,CODCr and BOD5 in black liquor and slurry consistency under the conditions of countercurrent extraction were studied.The relationship between residual liquid phase lignin,residual CODCr and residual BOD5 and extraction rate of black liquor under the conditions of counter stream were studied.It is of great scientific significance and universal practical value to recognize and locate the pollution of pulping process.Firstly,chemical composition was characterized and the content of liquid phase lignin was studied.The results showed that the content of CODCr and BOD5 is very high,which shows that black liquor contains a lot of dissolved organic matter.The value of BOD5/ CODCr is 0.25 below the level of good biodegradability value,which shows that there is a certain amount of organic matter in the black liquor which can inhibit the microorganism.The black liquor was brown in color and dark in color,which shows that black liquor contains a lot of chromophore and chromophore groups.The analysis of IR,UV spectra and GC-MS showed that the organic compounds contained benzene,carbonyl,hydroxyl and ether groups.The relative content of aromatic compounds was 76.84%.The results showed that in DNS solvent system,there is a good linear relationship between the dissolved lignin absorbance at 530 nm and dissolved lignin quality.According to the linear relationship,it can be used for liquid phase lignin quantitative analysis.Secondly,the relationship between the extraction rate of black liquor and the concentration of black liquor under the conditions of downstream extraction was studied.Under the conditions of extraction countercurrent extraction,the relationship between the extraction rate of black liquor and the slurry consistency and the relationship between cleanliness and the slurry consistency were studied.The results show that the black liquor extraction by countercurrent extraction is higher than that by downstream extraction.The higher the slurry consistency,black liquor extraction rate is higher.When the slurry concentration was 35%,the extraction rate of black liquor by downstream extraction was only 83.29%.The extraction rate of black liquor by countercurrent extraction was up to 98.47%.There was a good linear relationship between the slurry consistency and the extraction rate of black liquor under the conditions of countercurrent extraction.Through the analysis of residual alkali in black liquor by countercurrent extraction,in terms of water consumption,the 35% slurry was adopted to extract black liquor.It can reduce water consumption.At the same time,it increased the alkali recovery efficiency and reduced the residual pollutants,which was beneficial to the subsequent bleaching process.Thirdly,the relationship between the extraction of black liquor by countercurrent extraction and the concentration of lignin in the black liquor and the black liquor extraction ratio and residual liquid phase lignin were studied.The results show that with the increase of the concentration of the slurry,after the forth-step extraction the content of extracted liquid phase lignin increased from 474 kg/t to 500.5 kg/t.The residual liquid phase lignin in pulp decreased from 32 kg/t to 5.5 kg/t.There was a linear relationship between the extraction rate of black liquor and the residual liquid phase lignin content in the pulp.With the increase of slurry consistency,it can reduce the amount of residual liquid phase lignin brought the bleaching process and reduce the amount of bleaching agent and AOX.In addition,the relationship between the slurry consistency and CODCr,BOD5 of extracted black liquor by countercurrent extraction and the relationship between the residual CODCr,residual BOD5 and the extraction rate of black liquor were studied.The results show that with the increase of slurry consistency,after the fourth-step extraction,the amount of extracted CODCr increased from 2011 kg/t to 2091 kg/t.The residual CODCr in pulp decreased from 131 kg/t to 51 kg/t.The extraction rate of black liquor and residual CODCr in the pulp was a function of three times(Y = 3157-91.94 X + 0.91X2-0.00298X3 R2 = 0.999).The residual BOD5 in pulp decreased from 12.54 kg/t to 4.5 kg/t.The extraction rate of black liquor and residual BOD5 in the pulp was a function of two times(Y = 106.98-2.09 X + 0.01X2 R2 = 0.999).Increasing the slurry consistency can reduce the extraction times and also get the same extraction effect.Therefore,water consumption decreased.The extraction rate of black liquor had great influence on residual CODCr and BOD5.