In the journey of agricultural modernization, key goals include improving fertilizer efficiency, reducing environmental pollution, and promoting sustainable soil development. Humic acid-coated fertilizer is a new, highly effective fertilizer that is gaining widespread attention. The humic acid coating production line is the core equipment for the large-scale production of this fertilizer, and its emergence has brought about many positive impacts on agriculture.

I. Production Line Composition

1. Raw Material Processing System Humic acid is typically sourced from leonardite or weathered coal. The first step of the production line is to process these raw materials. First, a crusher, such as a jaw crusher or hammer crusher, breaks down large lumps of raw coal into smaller particles for further processing. Then, a grinding machine, like a ball mill, grinds the crushed material into a fine powder. This increases the surface area of the humic acid, allowing it to better participate in subsequent reactions and also improving the coating effect.
2. Proportioning and Mixing System This system is responsible for precisely proportioning the various raw materials. Metering equipment, such as an electronic belt scale, accurately weighs the main components, including humic acid, urea, and phosphates, as well as auxiliary materials like binders. These materials are then fed into a mixer, commonly a horizontal ribbon mixer. The mixer ensures all ingredients are thoroughly and uniformly mixed, guaranteeing the stability and consistency of the final product.
3. Core Coating Equipment The coater is the most critical part of the entire production line. A rotary coater is commonly used. In operation, fertilizer granules that have been screened by a sieving machine tumble continuously inside a rotating drum. At the same time, a spray gun system uniformly sprays the prepared humic acid coating solution onto the surface of the granules. By adjusting parameters such as the pressure and flow rate of the spray gun and the rotation speed of the coater, the thickness and uniformity of the coating can be precisely controlled to meet the needs of different products.
4. Drying and Curing Device Coated fertilizer granules contain a certain amount of moisture and need to be dried to cure the coating layer. A rotary dryer is the primary equipment for this function and is widely used. Inside the dryer, hot air has full contact with the fertilizer granules, carrying away the moisture from their surface. The hot air system, consisting of a burner and a fan, provides a stable and appropriately heated airflow to the dryer, which accelerates the drying process and improves production efficiency.
5. Packaging Stage After drying, the fertilizer granules are measured and packaged by an automatic quantitative packaging scale and then sealed by a sealing machine. This prepares them for storage, transport, and distribution in the market.

II. Working Principle

The operation of the humic acid coating production line is based on a series of physical and chemical principles. First, in the raw material processing stage, crushing and grinding increase the specific surface area of the humic acid, enhancing its activity. During the proportioning and mixing, each raw material is precisely proportioned according to the fertilizer formula, and they are fully blended in the mixer to create a uniform coating material.

In the coating stage, the rotation of the coater and the spraying from the gun ensure that the humic acid coating solution adheres evenly to the surface of the fertilizer granules. The binder component in the coating solution allows the humic acid to securely wrap the fertilizer granules. During the subsequent drying process, hot air promotes rapid moisture evaporation, and the coating layer gradually solidifies, bonding tightly with the fertilizer granules. Finally, an off-spec screening process removes unqualified granules to ensure product quality before the packaged product is ready for use.

III. Features

A humic acid coating production line is a specialized production system designed for the processing needs of functional humic acid coatings. Its features center on process adaptability, product quality stability, production efficiency, and environmental requirements.

1. Strong Process Specificity, Adapts to Humic Acid Properties Humic acid has characteristics such as varying water solubility, high viscosity, and sensitivity to temperature. The production line's core components are specifically designed for these traits.
   • Material Pre-treatment Module: It's equipped with a dedicated mixing and dissolving system that uses temperature control (usually 30-50°C) and shear mixing to ensure the humic acid is uniformly blended with auxiliaries (e.g., binders, slow-release agents), preventing clumping or stratification.
   • Spray Parameter Adaptation: It uses an adjustable high-pressure atomizing nozzle to precisely control the droplet size (usually 50-150μm) based on the humic acid solution's concentration (generally 10-30%). This prevents nozzle clogging or coating accumulation due to high viscosity.
2. High Coating Uniformity, Ensures Functional Effectiveness Coating uniformity directly affects key metrics like product slow-release performance and nutrient utilization. The production line uses multi-dimensional controls to achieve efficient coating.
   • Fluidized Bed Coating Technology: It uses a bottom-spray or side-spray fluidized bed structure to make the granules (e.g., fertilizer, seeds) suspended and fluidized by airflow. This allows them to have full contact with the atomized humic acid solution. The single-granule coating thickness deviation can be controlled to within ±5%.
   • Dynamic Monitoring and Adjustment: It integrates online infrared thickness gauges and granule motion sensors to provide real-time feedback on the coating status. The PLC system then automatically adjusts airflow, spray volume, and granule retention time to ensure uniform consistency within each batch.
3. Integrated Functions, Achieves Full-Process Continuous Production The production line integrates multiple stages into a continuous process, which reduces losses during intermediate transfers and improves production efficiency.
   • Integrated Pre-treatment, Coating, and Post-treatment: It forms a closed-loop production system, from humic acid dissolving and granule feeding to coating, drying (hot air temperature 60-80°C to avoid loss of humic acid activity), cooling, and finally screening and packaging. A single line can have an hourly capacity of 0.5-5 tons.
   • Integrated Auxiliary Functions: It is equipped with an automatic feeding system (that uses a liquid level sensor to replenish the solution in real-time) and an automatic off-spec return device, which lowers the cost of manual intervention.
4. Excellent Environmental Performance, Compliant with Green Production Requirements The production line has enhanced environmental design to address potential pollution points during humic acid production (such as volatiles and dust).
   • Waste Gas Recovery and Treatment: The moist and hot exhaust gas from the drying stage is treated by a condensation recovery system to recover humic acid volatiles for reuse. The exhaust gas is then passed through an activated carbon adsorption device before being discharged, achieving a VOCs removal rate of over 90%.
   • Water Recycling: Wastewater from equipment cleaning is filtered through a sedimentation tank and then recycled for the humic acid dissolving process. The water recycling rate is ≥80%, which reduces wastewater discharge.
5. High Degree of Automation, Ensures Production Stability The production line relies on a smart control system to achieve precise parameter control and reduce human error.
   • Full Digital Parameter Control: A human-machine interface can be used to set over 20 key parameters, including temperature, humidity, spray pressure, and fluidization air velocity. The system records real-time operational data, supporting traceability and process optimization.
   • Self-Diagnosis of Faults: Integrated sensors monitor indicators like motor current, equipment pressure, and solution concentration. When an anomaly occurs, it automatically triggers an alarm and a shutdown protection, reducing the risk of equipment damage.
6. Flexible Adaptability, Meets Diverse Needs The production line can be flexibly adjusted according to product type and process requirements to adapt to different application scenarios.
   • Granule Specification Adaptability: By changing the fluidized bed screen plate and adjusting the airflow parameters, it can process granules from 0.5-5mm (e.g., compound fertilizers, rice seeds, lawn fertilizers).
   • Formula Adjustability: It supports multi-component compound coatings of humic acid with amino acids, micro- and macro-elements. By changing the metering pumps and adjusting the mixing ratio, it can quickly switch product formulas.
7. Stable Product Quality, Preserves Core Functions The process controls ensure the preservation of humic acid activity and product physical properties.
   • Activity Preservation Design: The drying stage uses low-temperature hot air circulation to prevent humic acid from carbonizing or having its structure damaged by high temperatures (>80°C), which ensures its biological activity (e.g., soil improvement, root promotion).
   • Coating Strength Assurance: The cooling stage uses a gradual temperature reduction (from 80°C down to room temperature) to reduce cracking of the coating due to thermal expansion and contraction. The damage rate of the coated granules in a durability test (rotary drum method) is <3%.
8. Optimized Energy Consumption, Lowers Operating Costs The energy-saving design reduces the energy consumption per unit of product.
   • Waste Heat Recovery and Utilization: The waste heat from the drying hot air is used by a heat exchanger to preheat fresh air, reducing heating energy consumption by over 30%.
   • Variable Frequency Speed Control Technology: Fans and pumps use variable frequency control to dynamically adjust power based on the production load, which reduces idle energy consumption by 40%.

In summary, the humic acid coating production line achieves efficient, stable, and green production of humic acid products through process adaptation, precise control, functional integration, and environmental optimization, providing technical support for agricultural efficiency and soil improvement.

IV. Application Fields of the Humic Acid Coating Production Line

The humic acid coating production line plays a crucial role in agriculture by scientifically proportioning humic acid with other substances and uniformly coating them on a carrier to form a functional coating. Its application fields mainly include seed treatment, fertilizer production, and customized applications for different crops.

1. Seed Treatment Seed treatment is a critical part of ensuring agricultural production, and the humic acid coating production line excels in this area. Through precise proportioning and uniform coating, the line scientifically integrates and adheres components like humic acid, trace elements, and fungicides to the surface of seeds. This coating has multiple advantages: on one hand, it slowly releases nutrients, providing a continuous and sufficient supply for seed germination and early seedling growth. On the other hand, the coating forms a micro-ecological protective barrier around the seeds, which can effectively resist pathogens and pests in the soil, reducing the probability of disease and insect infestations.

   In practical application, this production line is widely used for treating seeds of major grain crops like corn, rice, and wheat, as well as economic crops like vegetables and flowers. For example, corn seeds treated with a humic acid coating show a significant improvement in germination potential and rate, and the seedlings' resistance to stress is also notably enhanced, laying a solid foundation for subsequent growth and high-quality yields.

2. Fertilizer Production Humic acid, as a high-quality fertilizer additive, has the effect of improving fertilizer utilization and reducing nutrient loss. The humic acid coating production line also plays an important role in fertilizer production. The production line can uniformly coat fertilizer granules with humic acid, creating humic acid-coated fertilizer. This coated fertilizer has excellent slow-release properties; the humic acid layer on its surface can control the release rate of nutrients, allowing them to be slowly released according to the crop's growth needs.

   This feature brings many benefits: it not only improves fertilizer utilization and avoids the waste caused by the rapid release of nutrients from traditional fertilizers, but it also reduces the environmental pollution caused by nutrient loss. In different planting scenarios, humic acid-coated fertilizer can play a good role. In orchards, it can provide continuous nutrient support for fruit tree growth, reducing the frequency of fertilization and improving fruit quality. In tea plantations, it can meet the long-term nutrient needs of tea trees, promoting their growth and development. In farmland, it can provide precise nutrient supply according to the growth cycle of different crops, increasing crop yield.

3. Applications for Different Crops Different crops have different growth habits and nutritional needs, and the humic acid coating production line can provide customized coating treatments for them. The production line can adjust the humic acid coating formula and process based on the crop's characteristics to better meet its growth needs.

   For example, leguminous crops require more phosphorus during their growth. The production line can appropriately increase the phosphorus content in the coating to promote the growth of the root system and nodulation in legumes. Leafy vegetables, on the other hand, need more nitrogen to ensure leaf growth, so the proportion of nitrogen in the coating can be increased accordingly. Through this customized humic acid coating treatment, the line can precisely meet the nutritional needs of different crops at various growth stages, effectively improving crop yield and quality.

V. Key Selection Criteria for a Humic Acid Coating Production Line

In the process of agricultural modernization, humic acid-coated fertilizers are widely used because they can improve nutrient utilization and soil structure. Their production relies on efficient and stable coating production lines. Choosing a suitable humic acid coating production line requires a comprehensive consideration of multiple factors to balance production efficiency, product quality, and long-term economic benefits. Here are the key selection criteria:

1. Capacity Matching and Flexible Expansion The production line's capacity must be precisely matched with your company's actual production needs. First, you need to be clear about your annual capacity plan and single-batch output requirements to avoid production bottlenecks due to insufficient capacity or resource waste due to excessive capacity. A small company can choose a production line with a capacity of 1-5 tons/hour, while a large-scale producer will need a high-capacity configuration of over 10 tons/hour.

   At the same time, you should leave room for flexible expansion. As market demand grows, the production line should have a modular upgrade capability. You should be able to increase capacity by adding coating units or expanding the drying system without needing to replace the entire equipment, which lowers long-term investment costs.

2. Core Coating Effect Indicator Control The coating effect directly determines the quality of the humic acid fertilizer, so you should focus on the following indicators:
   • (1) Coating Uniformity: The production line must be equipped with a precise material conveying and mixing system to ensure the humic acid coating solution is uniformly distributed on the fertilizer granule surface, avoiding overly thick spots or missed areas. You can verify this by observing the color consistency of the coated granules and conducting sample tests to check the film thickness distribution.
   • (2) Film Adhesion: The coating film must be tightly bonded to the fertilizer granules and not easily peel off during transport and storage. The production line's temperature control (e.g., preheating temperature of the coating pan, initial drying temperature) and the intensity of material tumbling are key influencing factors. You should choose equipment with precise temperature control and an adjustable-speed mixing device.
   • (3) Slow-Release Performance Matching: Based on the product's designed slow-release cycle, the production line should be able to precisely control the film's density by adjusting the coating solution concentration, spray volume, and drying time to achieve the target slow-release effect. This can be verified by simulating field tests to measure the fertilizer's nutrient release curve.
3. Equipment Stability and Material Adaptability Humic acid has some corrosiveness, and the production process involves the transportation and handling of powdered and liquid materials. Therefore, equipment stability and material selection are crucial.
   • (1) Core Component Quality: Core components like motors, transmission systems, and control systems should be from reputable brands to ensure stable operation and reduce the frequency of machine failures. You should check the component's warranty period and reliability test reports provided by the equipment manufacturer.
   • (2) Material Corrosion Resistance: Parts that come into contact with the humic acid coating solution and fertilizer granules (e.g., coating pan, conveying pipes, mixing paddles) must be made of corrosion-resistant materials. 304 or 316 stainless steel is a preferred choice to prevent material corrosion from affecting product purity and equipment life.
   • (3) Wear Resistance: For fertilizer granules with a higher hardness, the material-contacting surfaces of the equipment need to be treated for wear resistance, such as by spraying a wear-resistant coating, to reduce wear and deformation from long-term use.
4. Automation and Intelligence Level A highly automated production line can improve production efficiency, lower labor costs, and ensure product quality stability.
   • (1) Smart Control System: It's best to choose a production line equipped with a PLC control system and a human-machine interface. This allows for the precise setting and real-time monitoring of key parameters like temperature, speed, spray volume, and material flow. It also supports a parameter memory function for quick switching between different product formulas.
   • (2) Online Monitoring and Feedback: A production line with functions for online coating thickness detection and real-time granule moisture monitoring can use sensor data feedback to adjust production parameters promptly, which reduces manual inspection errors and improves product pass rates.
   • (3) Automated Linkage: The line should achieve automated linkage between processes such as feeding, coating, drying, cooling, screening, and packaging. This reduces manual intervention, lowers labor intensity, and prevents secondary contamination of materials.
5. Environmental Compliance and Energy Consumption Control With increasingly strict environmental policies, the production line must meet environmental requirements and control energy consumption.
   • (1) Dust Collection and Treatment: It should be equipped with an efficient dust collection system, such as a cyclone separator + bag filter combination, to ensure the dust emission concentration meets national standards (≤10mg/m³), while also reducing raw material waste.
   • (2) Waste Gas Treatment: If the coating solution uses organic solvents, a waste gas condensation recovery device or an activated carbon adsorption system should be installed to prevent volatile organic compounds (VOCs) from exceeding emission limits.
   • (3) Energy Consumption Optimization: Choose a drying system with a waste heat recovery function, such as using the heat from the drying exhaust gas to preheat fresh air. This can reduce heating energy consumption by over 30%. Use variable frequency motors to adjust equipment operating power dynamically, which can lower energy consumption per unit of product. Compare the unit energy consumption indicators (e.g., kWh/ton of product) of different production lines during selection.
6. Total Life-Cycle Cost Calculation In addition to the equipment purchase cost, you need to comprehensively consider the total life-cycle cost.
   • (1) Operating Costs: This includes energy, consumables (e.g., coating nozzles, filter membranes), and labor costs. Prioritize a production line with highly versatile and easily replaceable consumables to reduce long-term costs.
   • (2) Maintenance Costs: Understand the replacement cycle and cost of the equipment's wear parts. Choose a model with a simple structure and easy maintenance to reduce downtime and repair costs.
   • (3) Depreciation Costs: Calculate the average annual depreciation cost based on the equipment's service life (usually 8-10 years) and residual value. Choose a cost-effective piece of equipment.
7. After-Sales Service and Technical Support Assurance Reliable after-sales service is a guarantee for the long-term stable operation of the production line.
   • (1) Installation, Debugging, and Training: The manufacturer should provide professional on-site installation and debugging services and offer systematic training for operators to ensure they master the skills for equipment operation, maintenance, and troubleshooting.
   • (2) Repair Response and Spare Parts Supply: Be clear about the after-sales service response time (e.g., remote guidance within 24 hours, on-site service within 48 hours) and ensure a sufficient supply of key spare parts and fast delivery.
   • (3) Technical Upgrade Support: Find out whether the manufacturer provides long-term technical upgrade services, such as software updates for the control system or guidance on process optimization, to help your company continuously improve production levels.

In conclusion, choosing a humic acid coating production line requires a combination of factors, including your company's scale, product positioning, and environmental requirements. By comprehensively evaluating capacity, quality, cost, and service, you can select the most suitable production line for your needs, laying the foundation for the efficient and high-quality production of humic acid-coated fertilizers.