As the name suggests the recovery section was installed to recover the cooking chemicals from the Black liquor received from the Brown Stock Washing section. Although, this section is much cost-intensive it needs to be installed to avoid the use of 100% fresh cooking chemicals. As the losses in the Brown Stock Washing is 8-12%, the requirement of the fresh chemicals will be only 8-12%.
The main subheads in the Recovery plant are,
The Black Liquor received from Brown Stock Washing Section is having a concentration of 0.8- 1.5% depending upon the use of Raw Material. The Concentration of Black Liquor is increased to 25-30% in the evaporator section. There are different types of evaporators being used in the paper industry depending upon the quality of Black Liquor. These are Long Tube Vertical evaporators, Falling Film Evaporators, Natural Circulation Evaporators, etc.
The most common evaporator being used in the paper industry are Falling Film Evaporators which are having advantages over Long Tube Vertical Evaporators, which are as follows.
The basic concept of this system is the use of fluidized bed technique for the treatment of black liquor received from Multiple Effect Evaporator to recover the Pulping chemicals as well as to reduce the pollution load on the environment. The Low-Temperature Incinerator is used in the paper mill, where the Black Liquor solids are less than 300 tons per day.
IN LTI, The solids in the liquid waste containing heat energy are amenable. The advantage of LTI is,
The system consists of mainly
The Semi Concentrated Black Liquor from the evaporator is fed to Venturi Scrubber, which works on the Direct Contact Evaporator. The Concentration of Black Liquor is increased to 45%. This Black Liquor is fed to LTI- where the Temp. Is around 600-700 Deg. C is maintained. The water in the Black Liquor is evaporated & the solids are converted to Soda Ash.
The Soda Ash produced is withdrawn from the side of the reactor at a controlled rate by a variable speed Rotary Valve. The Soda Ash is conveyed through Water Cooled Screw Conveyor before being stored in a Silo.
The Soda Ash (NA2CO3) produced in the LTI- is further treated with milk of lime (Ca(OH)2) to get Caustic Soda (NaOH) which is used in the Digester for the Cooking of the Raw Material & the Calcium Carbonate (CaCO3) produced is either used as Landfills or sold to Cement Industry.
The Major Equipment in Recaustisicing Section is as below.
Category
Stock PreparationSub Category
White Waste/Mix WasteCompany Presentation
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