Abstract: This article provides an in-depth exploration of the technical comparison between natural gas-heated single-layer and multi-layer belt dryers in the roasting and drying process of nuts such as peanuts. A systematic analysis is conducted across five dimensions: product output, drying speed, roasting quality, equipment price, and drying airflow direction, providing a scientific basis for enterprise equipment selection.
Nut roasting, a flavor magic spanning millennia. From ancient people slowly roasting over fires to modern automated production lines with precise temperature control, the interplay of heat and time has always been central to developing the mellow aroma of nuts and achieving a crispy texture. Today, in an era that values both green development and efficiency, roasting processes using clean natural gas as a heat source are driving a profound transformation in the nut-processing industry. Among them, single-layer and multi-layer belt dryers, as mainstream continuous drying equipment, are like two craftsmen with unique skills, playing a game of chess across the multi-dimensional board of output, speed, quality, cost, and thermal energy management, jointly shaping the backbone and flavor of the modern nut industry. This article presents a comparative analysis of these two types of equipment for nut roasting and drying, using natural gas as the heat source, and examines their technical characteristics and business logic.
I. Foundation: The Symphony of Natural Gas Heat Source and Belt Drying Principle
Before commencing the comparison, it is essential to understand the common stage background: the basic principles of the natural gas heat source and belt drying.
The advantages of natural gas as a heat source lie in its cleanliness, high efficiency, and precise temperature control. Its combustion primarily produces carbon dioxide and water vapor, thereby avoiding potential odor pollution from sulfur compounds, smoke, and dust that may arise from coal or biomass fuels, thereby preserving the pure, original aroma of nuts such as peanuts. Its high calorific value and rapid response characteristics enable the heating system to achieve more precise temperature control, which is crucial for key stages in the roasting process, such as the Maillard reaction and caramelization, which form flavor and color.
A belt dryer is a continuous-operating device that uniformly distributes material on a moving mesh belt or chain plate and allows it to exchange heat with a hot medium (e.g., hot air) as it passes through the chamber, thereby removing moisture. Material conveyance is stable, heating is relatively uniform, and automation and scale production are straightforward. When this principle combines with the clean hot air produced by natural gas combustion, it forms the core unit for improving quality and efficiency in modern nut roasting.
Schematic Diagram of Belt Dryer Working Principle
Single-Layer Belt Dryer
Material passes through the drying chamber in a single layer; hot air is typically blown vertically from above or below.
Multi-Layer Belt Dryer
Material passes through the drying chamber layer by layer; hot air can be directed in multiple directions and across multiple zones.
Figure 1: Comparative Schematic Diagram of Single-Layer and Multi-Layer Belt Dryer Working Principles
II. Multi-Dimensional Comparison: Analysis of the Advantages and Disadvantages of Single-Layer vs. Multi-Layer Belt Dryers
1. Product Output: The Divide Between Spatial Game and Economies of Scale
| Comparison Dimension | Single-Layer Belt Dryer | Multi-Layer Belt Dryer |
| Working Principle | Production capacity intuitively depends on the width and length of the single belt (i.e., the drying area) and the allowable material bed thickness on the belt. | The core advantage lies in the revolutionary improvement of space utilization. By stacking the drying area vertically (commonly 3-12 layers). |
| Output Characteristics | Significantly increasing output usually requires a substantial increase in equipment length or width. The former results in a linear increase in factory floor space, whereas the latter may be constrained by technical bottlenecks, such as the uniformity of hot-air distribution. | Within nearly the same factory floor area, the effective drying area can be multiplied. This means that under equal floor space conditions, the theoretical output of a multi-layer machine far exceeds that of a single-layer machine. |
| Suitable Scenarios | More suitable for occasions where output requirements are not extreme, or where factory layout is spacious. | For processing enterprises with high land costs or limited factory space, multi-layer machines are a more intensive choice for achieving large-scale continuous production. |
Summary: In the dimension of output/floor area ratio, multi-layer belt dryers hold a significant advantage and are a powerful tool for intensive, large-scale production. Single-layer machines are more suitable for scenarios in which output requirements are not extreme or the factory layout is spacious.
2. Drying and Roasting Speed: The Trade-off Between Time and Uniformity
Roasting speed is not necessarily the determinant of quality; it must match the temperature, humidity, and flow velocity of the hot air, as well as the nuts’ heat- and mass-transfer characteristics, to ensure uniform roasting and consistent doneness.
| Comparison Dimension | Single-Layer Belt Dryer | Multi-Layer Belt Dryer |
| Drying Process | The material undergoes only one pass through the drying zone; the process is simple. Hot air is usually blown vertically from above the material (or from both above and below), penetrating the material bed. | The material passes through layer by layer, resulting in a long total drying time, but the overall equipment length is shortened. The control of its roasting speed is more complex but also has greater potential. |
| Advantages | Being single-layer, the hot air flow path is relatively direct, and airflow organization can be designed to be quite uniform, resulting in good consistency in the heating history of different parts of the material. | Different temperature and humidity parameters can be set for different floors, simulating a more optimized “roasting curve.” This ability for zoned precision temperature control can theoretically optimize the roasting process. |
| Disadvantages | If one wants to further increase speed (shorten drying time), it often requires raising the hot air temperature or speed, which may increase the risk of the surface being over-roasted or even charred while the interior remains under-roasted. | Material may tumble or pile during inter-layer transfer; if not designed properly, this can affect heating uniformity; hot air between layers may interfere with each other, placing extremely high demands on the airflow distribution system design. |
Summary: In terms of precise control and process optimization potential of the drying/roasting process, a well-designed multi-layer belt dryer holds the advantage. The single-layer machine is more reliable due to its operational simplicity and basic assurance of heating uniformity.
3. Roasting Quality: The Contest of Flavor, Color, and Integrity
Roasting quality is the lifeline of nut products, involving color uniformity, crispness, flavor development, and breakage rate.
| Comparison Dimension | Single-Layer Belt Dryer | Multi-Layer Belt Dryer |
| Uniformity | Since the material undergoes only a unidirectional roasting process with relatively constant parameters, and hot air distribution is easy to make uniform, the produced nuts often exhibit stable uniformity within the batch. | Roasting quality harbors both potential and risk. Any uneven hot air or temperature loss of control in one layer will lead to quality issues for the material on that layer, which are difficult to compensate for in subsequent layers. |
| Flavor Development | Overall color is consistent, less prone to local over-darkening or over-lightening. As long as parameters are set appropriately, it can well exhibit the natural flavor of nuts. | The advantage lies in the ability to more scientifically guide the Maillard reaction through zonal control, potentially developing a richer, more layered flavor profile. |
| Breakage Rate | The simple and direct process also reduces the risk of physical damage to nuts (especially materials like peanuts that may shed skin or break) caused by mechanical handling. | Inter-layer transfer devices (such as hoppers, diverters) if poorly designed, can easily cause nut collisions and friction, leading to increased breakage rates, surface scratches, and affecting product appearance. |
Summary: For traditional high-quality products pursuing stability, uniformity, and low breakage rates, the single-layer belt dryer is a lower-risk choice. For enterprises aiming to develop distinctive flavors and optimal texture through precise processes and possessing strong process debugging and equipment management capabilities, the multi-layer belt dryer offers a higher-quality ceiling.
4. Equipment Price and Operating Costs: The Choice Between Initial Investment and Long-Term Efficiency
| Cost Type | Single-Layer Belt Dryer | Multi-Layer Belt Dryer |
| Initial Investment | Simple structure, relatively low manufacturing cost. | Complex structure, including multi-layer conveyor systems, inter-layer material transfer systems, independent or interconnected hot air circulation and distribution systems for each layer, etc. Therefore, its manufacturing cost and purchase price are usually much higher than a single-layer belt dryer designed for equivalent capacity. |
| Energy Consumption Cost | Thermal energy utilization efficiency is relatively low; a large amount of hot air is discharged after one pass (although it can be improved through partial waste heat recovery). | Great potential in comprehensive thermal energy utilization: the warm, high-humidity gas discharged from upper layers can be treated and used as a supplement for lower layers or the same layer’s circulating air, achieving cascaded use of thermal energy. The natural gas consumption per unit product is usually significantly lower than that of single-layer machines. |
| Maintenance Cost | Simple structure, fewer failure points, easy and low-cost maintenance. | With more moving parts, inter-layer transfer mechanisms are prone to wear; the hot air system is complex; maintenance frequency and difficulty are higher; and maintenance requires a more professional technical team, resulting in higher maintenance costs. |
Summary: In terms of investment, the single-layer machine is superior; in terms of long-term operating energy consumption, an efficient multi-layer machine may surpass it. Enterprises need to conduct comprehensive analyses based on their financial situation, capacity planning, and expectations regarding long-term energy costs.
5. Drying Airflow Movement Direction: The Artistic Core of Thermal Energy Management
Airflow direction directly determines the efficiency and uniformity of hot-air contact with the material, as well as the utilization of thermal energy, and is central to equipment design.
| Airflow Type | Single-Layer Belt Dryer | Multi-Layer Belt Dryer |
| Airflow Patterns | Vertical Through-Flow: Hot air passes vertically through the material bed; high heat and mass transfer efficiency. Horizontal Circulation: Hot air flows horizontally above or below the material; good uniformity. Cross-Flow: Air direction alternates, helping to improve uniformity. | Independent Circulation per Layer: Each layer has independent fans, heaters, and ducts; parameters can be controlled independently. Overall Circulation, Counter-Current: The hottest, driest fresh hot air enters from the bottom layer and flows upward layer by layer. Cross-Flow, Compound Flow: Combining multiple airflow patterns to achieve optimal thermal efficiency. |
| Design Characteristics | Airflow path is simple, easy to control and optimize. | Airflow design is a complex systems engineering task, offering diverse possibilities, but the challenge lies in preventing short-circuiting between layers and ensuring uniform airflow within each layer. |
| Energy Efficiency Performance | High heat transfer efficiency, but thermal energy is used once; overall energy efficiency has room for improvement. | In an overall counter-current design, thermal efficiency is highest. The hot air closely matches the moisture content gradient of the material, and the driving forces for heat and mass transfer remain relatively balanced throughout the process. |
Summary: In terms of the complexity of airflow organization and the potential for comprehensive thermal energy utilization, multi-layer belt dryers demonstrate a higher technical level and energy-saving ceiling. The airflow design of single-layer machines emphasizes reliability, efficiency, and ease of achieving uniformity.
Comparative Summary
Through a systematic comparison of the five dimensions, it can be seen that single-layer and multi-layer belt dryers each have their own distinct advantages and applicable scenarios:
- Single-Layer Belt Dryers have advantages in equipment investment, operation and maintenance, product quality uniformity, and low breakage rates. They are suitable for medium-scale, multi-variety production, or scenarios with extremely high requirements for product integrity.
- Multi-Layer Belt Dryers excel in space utilization, long-term operating energy efficiency, process optimization potential, and economic feasibility for large-scale production. They are suitable for enterprises with high land costs, significant energy constraints, a focus on large-scale, intensive production, and strong technical management capabilities.
III. The Path to Decision: Application Scenarios and Decision Considerations
There is no absolute superiority or inferiority, only the choice of suitability. Enterprises need to comprehensively consider their own conditions and requirements when making decisions:
Scenarios where Single-Layer Belt Dryers are prioritized:
- Product varieties change frequently, necessitating frequent adjustments to raw materials or process parameters.
- Extremely high requirements for product integrity (low breakage rate), such as high-end whole nuts and coated nuts.
- Limited initial investment budget, ample factory space.
- Medium production scale, no urgent need for extreme energy savings.
- Relatively weak technical force within the enterprise, preferring equipment that is simple to operate and maintain.
Scenarios where Multi-Layer Belt Dryers are prioritized:
- Pursuing large-scale, continuous, intensive production, with high land costs.
- Single or serialized products, stable processes, aiming to create unique product quality through precise process control.
- High long-term energy cost pressure, placing great importance on reducing operating energy consumption.
- Possessing a strong technical team for process R&D and equipment maintenance.
- Having clear sustainable development goals, focusing on improving energy efficiency in the production process.
Decision Recommendation: Enterprises should conduct a detailed return-on-investment (ROI) analysis that accounts for not only equipment procurement costs but also the potential for energy cost savings over 5-10 years. For medium- to large-scale enterprises, a phased implementation strategy can be considered: first, use single-layer equipment to meet current needs, then upgrade to a multi-layer system after market expansion.
IV. Future Outlook: Intelligent Integration and Green Upgrading
With the advancement of Industry 4.0 and the “Dual Carbon” goals, both types of equipment are evolving towards intelligence and greenization. Whether single-layer or multi-layer equipment, integrating technologies such as online moisture monitoring, machine-vision color recognition, adaptive temperature-control systems, digital-twin simulation optimization, efficient waste-heat recovery, and low-NOx combustion has become a key area of development.
Specific trends include:
- Intelligent Control: Real-time optimization of roasting curves through AI algorithms, automatic parameter adjustment based on differences in raw material batches, achieving “one-click optimal roasting.”
- Comprehensive Energy Utilization: Combining heat pump technology, solar auxiliary heating, etc., to further reduce natural gas consumption and build near-zero emission green roasting systems.
- Modular Design: The equipment adopts a modular structure, facilitating flexible expansion to meet capacity requirements and reducing upgrade and renovation costs.
- IoT Integration: Equipment is fully integrated with the Industrial Internet of Things platform, enabling remote monitoring, fault detection, and preventive maintenance.
Future competition will not only be about equipment form but also about the comprehensive competition in process wisdom, energy efficiency, and digital control capabilities.
V. Conclusion
In the mellow journey of nuts like peanuts, single-layer and multi-layer belt dryers use natural gas as the pen and hot air as the ink, outlining different production landscapes. The single-layer machine is like steady, regular script, each stroke clear and reliable, laying a solid foundation for quality; the multi-layer machine is like bold cursive script, free and unrestrained, with endless potential, pursuing a higher realm of efficiency and flavor.
The choice of an enterprise is about finding the optimal balance under its own strategy and resource constraints among scale and flexibility, cost and energy efficiency, stability and excellence. With technological progress and industrial upgrading, the boundaries between the two types of equipment may gradually blur, giving rise to more innovative designs that integrate the advantages of both.
This game about thermal energy and craftsmanship will ultimately push the entire nut-processing industry steadily forward toward a more efficient, higher-quality, and more sustainable future. Regardless of the equipment chosen, the unwavering core values of the nut roasting industry remain:坚守 quality,钻研 the process, and重视 the consumer experience.
Acknowledgements: In the writing of this article, relevant domestic and international technical literature and industry practice cases were referenced. Special thanks are extended to manufacturers of nut-processing equipment, process engineers, and researchers. The views in this article are for reference only; for specific equipment selection, please consult professional institutions based on actual circumstances.
