Equipment for Treating Black Liquor Pollution in Papermaking

Introduction to Comprehensive Resource Utilization Technology for Black Liquor in Papermaking:

This technology is suitable for the comprehensive treatment of black liquor pollution in papermaking enterprises using wood, bamboo, grass, and reed pulp. It involves extracting, concentrating, and purifying the black liquor through sulfonation reactions, followed by spray evaporation drying to produce lignosulfonate products (specifically, wood calcium, which is highly sought after in industries such as concrete admixtures). This technology truly transforms black liquor from waste into a valuable resource. It aligns with national industrial policies aimed at gradually achieving clean production and sustainable development, effectively unifying economic, environmental, and social benefits.

The high-efficiency, energy-saving horizontal spray film evaporation technology and equipment incorporate the features of internationally advanced horizontal spray evaporation technology. By employing operating conditions that prevent scaling on heat transfer tubes and utilizing specially developed, cost-effective defoamers and descaling agents, the system performs washing, descaling, and defoaming operations simultaneously during the evaporation process (without interrupting production). The production line itself generates no new pollution, achieving “zero” emissions.

This technology was originally researched and developed to address the challenges of evaporating straw pulp waste liquid. Straw pulp waste liquid is characterized by high viscosity, high silica content, and a tendency to foam. Due to interference from silica, fine fibers, foreign cells, and polysaccharides, scaling frequently occurs, resulting in extremely poor evaporation performance. Since the waste liquid contains a large amount of fatty acid soap, it tends to form significant amounts of foam during evaporation, which adversely affects evaporation efficiency and operational processes. Consequently, the evaporation and concentration of straw pulp waste liquid has become one of the world’s most challenging problems.

Our plant undertook this research project. Through the application of spatial evaporation technology to concentrate pulping waste liquids—such as those from alkali-processed rice straw pulp, alkali-processed wheat straw pulp, SFP-AQ-processed wheat straw pulp, and sub-ammonium-processed bagasse pulp—as well as solutions of chemical products, we have achieved this by regulating parameters such as the subcooling temperature difference to suppress boiling of the evaporating liquid on the heat transfer tubes. This effectively controls the formation of silica scale and foaming, thereby reducing equipment corrosion. The evaporation intensity for straw pulp waste liquids reaches 18.86–33.50 kg/m²h, while that for the aforementioned chemical product solutions reaches 35.5–54.7 kg/m²h. Compared to the most advanced plate-type evaporators currently available in China (with an evaporation intensity of 8–12 kg/m²·h), the spatial evaporator developed by our plant achieves more than double the performance. In other words, when evaporating the same volume of water, the spatial evaporator requires half the evaporation area of a plate-type evaporator. Based on a pulp mill with an annual production capacity of 1.5–2.0 million tons and an evaporation rate of 25 tons of water per hour, each evaporation station saves approximately 1.5 million yuan in equipment investment. Combined with features such as easy descaling and reduced corrosion, this technology demonstrates its superiority in the safe and efficient treatment of grass pulp waste liquid. This project has passed expert acceptance. The attending experts concluded that the evaporator developed by our plant features high evaporation intensity and a high heat transfer coefficient, with its evaporation intensity for treating grass pulp waste liquid reaching internationally leading levels.

Typical Project Case: Jinyuan Lignin Processing Plant in Huaihua County, Hunan Province – 15 tons/day

Through collaborative efforts between Changzhou Mingxing Drying Equipment Co., Ltd., the Institute of Forest Chemical Industry at the Chinese Academy of Forestry Sciences, and Nanjing Forestry University, a method for the resource utilization of black liquor has been developed. This involves separating the solid and liquid components of black liquor to produce dry lignosulfonate powder. This technology is characterized by its high technological sophistication, advanced engineering, simple process flow, and low investment requirements. Furthermore, the recovered lignosulfonate has a wide range of applications and offers significant economic benefits. Upon completion, the project will not only convert paper-making black liquor into a marketable product but also ensure that there are no wastewater discharge outlets within the project area, thereby eliminating secondary pollution and achieving excellent pollution control results. This project delivers both significant environmental and economic benefits.

Recently, the large-scale spray dryer for alkali lignin with a water evaporation capacity of 1,800 kg/h, manufactured by Mingxing Drying, along with the complete set of horizontal coal-fired hot air furnace equipment produced by our factory, successfully passed its trial run at the Tongdao Lignin Processing Plant in Huaihua, Hunan, achieving full production capacity and meeting all standards. Even more encouraging is that the hot-air furnace produced by our factory demonstrates excellent performance and stable temperatures when using firewood as fuel. This measure saves 3,000 yuan in fuel costs per shift, representing significant economic value.

Calcium lignosulfonate (commonly abbreviated as CLS) is a multi-component, high-molecular-weight anionic surfactant. It appears as a brownish-yellow powder with a slight aromatic odor. Its molecular weight typically ranges from 800 to 10,000, and it exhibits strong dispersing, binding, and chelating properties. Currently, calcium lignosulfonate is widely used as a cement water-reducing agent, pesticide suspension agent, ceramic body strengthener, water-coal slurry dispersant, leather tanning agent, refractory binder, and carbon black granulation agent. It is extensively utilized across various industries and is highly favored by users.

Appearance: Brownish-yellow powder

Lignin Content: ≥50–65%

Water-Insoluble Matter: ≤0.5–1.5%

pH: 4.0–6.0

Moisture Content: ≤8%

Water-Insoluble Matter: ≤1.0%

Reducible matter: 7–13%

Applications of Lignin:

1. As a concrete water-reducing agent: When added at 0.25–0.3% of the cement content, it can reduce water consumption by 10–14% or more, improve concrete workability, and enhance project quality. When used in summer, it can inhibit slump loss and is generally blended with high-efficiency water-reducing agents.

2. As a mineral binder: In the smelting industry, mixing calcium lignosulfonate with mineral powder to form pellets, which are then dried and placed in a kiln, can significantly improve smelting recovery rates.

3. Refractory Materials: When manufacturing refractory bricks and tiles, using calcium lignosulfonate as a dispersant and binder significantly improves workability and provides beneficial effects such as water reduction, strength enhancement, and crack prevention.

4. Ceramics: When used in ceramic products, calcium lignosulfonate reduces carbon content, increases green body strength, reduces the amount of plastic clay required, improves slurry flowability, increases the yield rate by 70–90%, and reduces sintering time from 70 minutes to 40 minutes.

5. As a feed binder, it improves palatability for livestock and poultry, enhances pellet strength, reduces the amount of fine powder in feed, minimizes powder return rates, and lowers costs. Die wear is reduced, and production capacity increases by 10–20%. The permitted addition level in feed in the United States and Canada is 4.0%.

6. Other Applications: Calcium lignosulfonate can also be used as a refining aid, in foundry applications, for processing wettable powder pesticides, in briquette pressing, as a flotation agent in mining and mineral processing, for road, soil, and dust control, as a filler in leather tanning, and in carbon black granulation.