Prepared by: Jalak Patel ( ) Pranay Patel ( ) Kuldip Maniya ( ) Kiran Patel ( ) Yash Patel ( ) Guided by: Jyoti Verma Chemical Department

 White liquor. ◦ Fresh pulping liquor for the kraft process containing NaOH, Na 2 S, and a variety of impurities.  Black liquor. ◦ The waste liquor from the kraft pulping process. Contains most of the original inorganic components (most in different forms) and a high concentration of dissolved organics.  Green liquor. ◦ Partially recovered kraft liquor (intermediate liquor in recovery sequence). 2

This is a very simplified diagram. There are several steps between each box. We will discuss this whole sequence in depth in a later lecture. Digester White Liquor Black Liquor Recovery Furnace Lime Kilm Green Liquor

 The kraft process (also known as kraft pulping or sulfate process) is a process for conversion of wood into wood pulp consisting of almost pure cellulose fibers. It entails treatment of wood chips with a mixture of sodium hydroxide and sodium sulfide, known as white liquor, that breaks the bonds that link lignin to the cellulose.

Kraft Process

 Wood pulp for sack paper is made from softwood by the kraft process. The long fibers provide the paper its strength and wet strength chemicals are added to even further improve the strength. Both white and brown grades are made. Sack paper is then produced on a paper machine from the wood pulp. The paper is microcrepped to give porosity and elasticity. Microcrepping is done by drying with loose draws allowing it to shrink. This causes the paper to elongate 4% in the machine direction and 10% in the cross direction without breaking Machine direction elongation can be further improved by pressing between very elastic cylinders causing more microcrepping. The paper may be coated with polyethylene (PE) to ensure an effective barrier against moisture, greaseand bacteria. A paper sack can be made of several layers of sack paper depending on the toughness needed. Manufacturing Process

Kraft paper is produced on paper machines with moderate machine speeds. The raw material is normally softwood pulp from the kraft process. Maintaining a high effective sulfur ratio or sulfidity is important for the highest possible strength using the kraft process. The kraft process can use a wider range of fiber sources than most other pulping processes. All types of wood, including very resinous types like southern pine, and non-wood species like bamboo and kenaf can be used in the kraft process.

 The majority of the chemicals used in the pulping process are recoverable for use in further pulping operations  Large amounts of energy are produced in the recovery boilers during the recovery process  The Kraft process can pulp pine trees

Various byproducts containing hydrogen sulfide, methyl mercaptan, dimethyl sulfide, dimethyl disulfide, and other volatile sulfurcompounds are the cause of the malodorous air emissions characteristic for pulp mills utilizing the kraft process. The sulfur dioxide emissions of the kraft pulp mills are much lower than sulfur dioxide emissions from sulfite mills The wastewater effluent can also be a major source of pollution, containing lignins from the trees, high biological oxygen demand(BOD) and dissolved organic carbon (DOC), along with alcohols, chlorates, heavy metals, and chelating agents.

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