Black liquor ingredients
1.The straw and other raw materials used in papermaking all contain three parts: cellulose, lignin and hemicellulose (polysaccharides). Papermaking uses only cellulose (about 40%), and about 25% of them are used in papermaking. % Of lignin and about 28% of hemicellulose, xylose, potassium, nitrogen, phosphorus and other substances are discarded with black liquor. The lignin and hemicellulose contained in the black liquor, as well as xylose, potassium, nitrogen, phosphorus and other substances, are of high value in industrial and agricultural production. 3 Ways for paper mills to solve emission pollution.
2.The cause of papermaking black liquor The paper mill discharges three streams of water according to the process. One is the pulping and cooking waste liquid, which is commonly called papermaking black liquor. The second is the washing, selection and bleaching water of the pulp after the separation of the black liquor. The third is papermaking. The white water on the machine can be treated and reused. The middle water is the remaining part of the incomplete black liquor extraction, which should account for less than 10% of the total. The pollutants contained in the black liquor account for more than 90% of the total pollution discharge of the whole plant. Therefore, black liquor discharge is the main source of pollution in paper mills.
system introductio
The tubular falling film evaporator is composed of heating chamber, liquid distribution tray, separation chamber, demister, circulation pipe and outriggers. The heating chamber is composed of tube sheets, heat exchange tubes, partitions, and shells.
The heating steam is sent to the shell side of the heating chamber, and the steam condensate is discharged from the bottom of the heating chamber. The black liquor is sent into the separation chamber, drawn from the separation chamber by the circulating pump, and sent to the liquid distribution pan on the top of the heating chamber through the built-in circulating pipe, and the liquid distribution pan is evenly distributed on the heating tube, and the black liquid flows down the inner wall of the heating tube in a film shape And flow into the separation chamber together with the evaporated secondary steam, the secondary steam is separated from the black liquor in the separation chamber, and is discharged from the upper part of the separation chamber through the demister.
system features
1.Higher heat transfer coefficient
Some of the advantages of falling film design are related to circulation, heat transfer mechanism and secondary steam release. The high heat transfer coefficient of the tubular falling film is due to:
a、The liquid flowing down the heating tube is affected by both the gravity and the secondary steam flow rate, which accelerates the flow rate of the descending liquid.
b、The heating steam condensate flowing down the pipe wall is cut off by the built-in partition of the evaporator, the liquid film on the condensate side becomes thinner, and the thermal resistance is reduced.
c、The wall thickness of the heating tube can be designed to be thinner, which reduces the thermal resistance.
2.High strength and long life
The design provided by the tubular falling film evaporator greatly reduces the welding and stress area compared with the design of the plate falling film evaporator, and reduces the risk of stress corrosion and priority damage at the weld. This tubular design is used in the produced evaporator products, with outstanding strength and longer life. The evaporator is characterized by excellent reliability.
3.Built-in circulation tube
The preheating tubular falling film evaporator circulating tube is set inside the equipment. The advantage of this design is easy piping, management and maintenance. The circulation pipeline is the least. It is composed of the downcomer from the separation chamber to the circulation pump and the return pipe of the circulation pump returning to the preheating section. In addition to reducing investment costs, the preheating falling film evaporator requires heat dissipation and the lift through the circulation pipe. The smallest.
4.Open cloth liquid tray
The flow distribution in the falling film evaporator is very important. The falling film evaporator includes an open liquid distribution tray, which makes it easier for suspended solids and fibers to pass. Each heat exchange tube forms a tube bridge with the corresponding three liquid distribution holes
5.High-efficiency mist eliminator
The mist eliminator in the falling film evaporator is an important element, which determines the COD value of the secondary condensate. The designed defogger has high defogging efficiency, so that the secondary condensate has a clear color and low COD value. The reuse rate of secondary condensate is greatly improved, and the amount of sewage in the factory is reduced.
