Black Liquor is a waste generated during cellulose production at tree mills that produce paper. At present, it is used to recover cooking chemicals and produce high-pressure steams which are necessary in the pulping and papermaking processes. It comprises a variety of substances like lignin, hemicellulose, NaOH (sodium hydroxide), and Na2S (sodium sulfide). The biofuel can be made using the lignin compound present in the black liquor.
However, as per the IEA report, black liquor as an energy source has a bright future ahead since it is considered one of the top five most essential energy sources on Earth!
Black Liquor Properties
The basic properties are:
- Basis of Evaporation Equipment Design: Optimizes the design based on heat transfer, material characteristics as well and processes.
- Impact of Changes in Liquor Cycle Chemistry: Regular control of deviation of design value is vital for ensuring evaporators’ performance.
- Viscosity: It affects motion and heat conduction; and increases at higher solid contents and temperatures.
- Boiling Point Rise: With rising boiling temperatures during evaporation and influenced by chemical composition and concentration, the equipment must cope.
Also See: What are Renewable Energy Resources?
Black Liquor Thermal Properties
1. Thermal Conductivity Correlation:
Black liquor thermal conductivity is modeled with a correlation in terms of ± 4%k, W/m°C -0.58 +1.44×10-3 (T°C) -3.35×10-3 (%S). With uncertainty about three, this equation gives an accurate value for the thermal conductivity at any given temperature about solids (%) content.
2. Specific Heat (Cp):
It has a non-uniform specific heat denoted as Cp, which changes based on the solids content and temperature. Such variation varies from 2700 – 3900 J/kg/°C or 0.65 – 0.95 Btu/lbm/°F. This understanding becomes essential during thermal transfers of black liquors.
3. Heat of Vaporization:
The heat of vapor is -2325 kJ/kg or 1000 Btu/lb. The presence of this parameter is critical in process design and optimization related to evaporation of black liquor which enables determination of the amount of energy needed during this phase transition.
Also see: What is Biomass?
Black Liquor Produced By Paper Industry
This substance contains huge amounts of suspended solids, organic pollutants, and poisonous compounds leading to severe pollution when released directly into the nearby water source. The main hazards are:
- The presence of paper industry wastes with excess fiber, pigment, and inorganic salt in the water body gives it a dark black color and a foul peculiar smell.
- The black liquor found in paper industry wastes with high concentrations of organic contaminants has a high biochemical oxygen demand (BOD) of 5000~40000g/L.
- The extruded black liquor used in the pulping process has a high concentration of lignin. Complete utilization of lignin sulfonate product in the form of black liquor for papermaking.
- As a raw material, concentrated, sulfonated, and dusted black liquor is utilized comprehensively in the production of lignosulfonate products.
- For ecologic safety and natural harmony in development, papermaking black liquor is converted into lignin products through comprehensive utilization, which reduces ecological impact.
Also Read: What are E-fuels?
Why Papermaking Makes Black Liquid?
The reason, behind the existence of liquor in the papermaking process, is due to the discharge of three types of water.
- The first one is the waste liquid generated during pulping and cooking commonly known as papermaking liquor.
- The second type is the water used for washing, selecting, and rinsing the pulp after separating it from the liquor also referred to as water.
- Lastly, there is the water on the paper machine that can be treated and reused.
Among these waters, middle water constitutes more than 10% of the amount left after extracting black liquor. However, it’s important to note that 90% of pollutants discharged by the plant come from black liquor emissions. Consequently, these emissions become a source of pollution, in paper mills.
The composition of liquor is altered during the editing process. When it comes to materials used in papermaking, like straw they contain cellulose, lignin, and hemicellulose (glycans). Only cellulose ( 40%) is utilized for making paper while 25% comes from wood. 18% consists of hemicellulose and xylose along with potassium, nitrogen, phosphorus, and other elements that are discarded with the liquor. The black liquor contains substances such as lignin and hemicellulose, such as xylose, potassium, nitrogen, and phosphorus that have significant industrial and agricultural applications.
Also read: What is Renewable Fuel Standard (RFS)?
