Personal View: Embracing Super Cyclones: Eight Perspectives on Phasing out Shallow Troughs!

Writing this article, I feel somewhat disheartened. It pains me to see enthusiasts of shallow troughs potentially hurt. Nevertheless, I must be straightforward in stating: the era of shallow troughs in coal washing is coming to a close.

1. Granularity Range of Separation

Presently, the introduction of intelligent X-ray water-free sorter to improve workers' environments encounters little controversy in the coal preparation process. The effective granularity range of shallow troughs overlaps significantly with that of intelligent water-free selection. Intelligent X-ray water-free selection is well-established for lump coal above 50mm. In fact, to my knowledge, HOT Company has already lowered its XRT Intelligent Ore Sorter lower limit for separation to 12 mm. On the other hand, the super cyclones leave no doubt in separating coal below 50mm. For instance, the S-GHMC440 cyclone (with a diameter of 1000) can handle feed sizes of up to 120mm at minimum, and the S-GHMC650 cyclone (with a diameter of 1200) can handle feed sizes of at least 145mm at minimum. Thus, the granularity coverage of super cyclones is exceptionally wide.

As intelligent X-ray water-free selection and super cyclone technologies mature, the advantages of shallow troughs are gradually replaced by these two methods. Moreover, the shortcomings of shallow troughs are compensated for by super cyclones. Positioned between the two, shallow troughs are gradually being phased out, rendering their technology obsolete.

2. Complexity of Systems

Shallow troughs require full-width feeding, necessitate coordination with desliming screens?and scrapers, and involve multiple supporting systems. With desliming screens, water spraying becomes imperative. If using recirculating water, subsequent equipment such as grading cyclones, concentrators, and recirculation pumps must be scaled up, resulting in a large coal slurry system. Alternatively, using magnetic tail water spraying adds additional links such as multiple dilution pumps or magnetic tail pumps, increasing the number of coal slurry transports. While shallow troughs may have low power consumption, when factoring in the associated equipment and comparing with super cyclones, their power consumption is not necessarily lower.

In contrast, super cyclones require belt conveyor head feeding, eliminating the need for fabric spreading and desliming. They have no moving parts, making their layout extremely simple. Furthermore, they eliminate the desliming process, directly sending magnetic tails to grading equipment. Consequently, with fewer equipment, simpler processes, fewer points of failure, energy efficiency and effectiveness become inevitable. Even a layperson can draw such conclusions.

3. Adaptability to Coal Quality Variation

For shallow troughs, once the raw coal contains high ash or moisture content, production becomes highly passive. High ash content, especially in fine coal, necessitates lowering the separation threshold to maintain the calorific value of the blend. In such cases of high ash and moisture content, block and fine coal separation screens are prone to blockage, leading to decreased separation efficiency. The fine coal carried by the screens is detrimental to shallow trough systems. Even if there is excess capacity in shallow trough processing, the inability to lower the separation threshold renders this excess capacity futile.

In contrast, super cyclones do not suffer from such shortcomings. Even if separation efficiency decreases in block and fine coal separation screens, the presence of fine coal in the super cyclones poses no significant harm. By leaving some margin for the cyclones, their advantages become evident. They compensate for the inadequacy of block and fine coal separation screen processing capacity, complementing each other perfectly.

From this perspective, cyclones and separation screens are complementary, whereas shallow troughs and separation screens are incompatible. As fine coal content increases, lowering the separation threshold is necessary, requiring a reduction in separation screen aperture. However, separation screens require a significant throughput, leading to decreased efficiency, posing a dilemma for separation screens. Shallow troughs, on the other hand, cannot select fine coal, highlighting their obvious shortcomings.

4. Gangue Sorting Capability

Super cyclones, when paired with large secondary cyclones behind intelligent dry selection, handle gangue variability with ease, making the combination flawless. Even without intelligent dry selection, a single large secondary cyclone set up demonstrates unquestionable gangue sorting capability. Consequently, shallow troughs lose their advantages.

Furthermore, when discussing gangue sorting capability, it is essential to consider the gangue system's handling capacity fluctuations. Relying solely on shallow troughs is insufficient. The processing capacity of gangue screens is also crucial. As long as the entire system is well-coordinated, there are no major issues. Choosing similar-sized gangue screens, replacing shallow troughs with cyclones, and proper matching pose no problems.

5. Maximum Processing Capacity per Machine

The largest shallow troughs can handle up to 800t/h. However, they cannot complement raw coal grading screens; instead, they must consider imbalance coefficients. Conversely, the maximum processing capacity of super cyclones is 1300t/h (practical case data for unwashed coking coal), leaving room for imagination if processing only lump coal. Super cyclones exhibit greater adaptability and simpler systems across different-scale coal preparation plants. It is crucial to emphasize that the efficiency of a single system surpasses that of a dual system, not the other way around.

6. Density and Precision of Separation

Due to shallow troughs' inferior separation precision compared to cyclones, gangue loss is usually considered at 1.8g/cm3. Even if the separation density is increased to 1.9g/cm3, gangue loss is difficult to avoid. In contrast, cyclones achieve zero gangue loss in chunk separation, leading the way in separation precision.

Regarding the ease of suspension fluid configuration, shallow troughs require a density of 1.8g/cm3, whereas cyclones have a certain concentration effect. By continuous concentration in the first and second stages, a low-density system of 1.4g/cm3 can achieve high-density gangue rejection at 2.0g/cm3. Pump and pipeline wear are significantly reduced.

7. Environmental Perspective

Opting for shallow troughs leads to compromises due to their lower separation limits. To adjust the calorific value of fine coal, shallow troughs often crush the refined coal to blend with fine coal. Consequently, the gangue in fine coal remains unchanged, causing significant pollution when burned in power plants, especially when the sulfur content in fine gangue is high. This contradicts our pursuit of a cleaner environment. Simultaneously, the reduced high-calorific refined coal results in decreased economic benefits. In contrast, super cyclones with lower selection limits and a bit of margin adjustment easily remove gangue from high-ash fine coal, contributing significantly to environmental preservation.

8. Common Sense

The understanding of shallow troughs is well-established. With sufficient investment, shallow troughs are readily produced. Moreover, Guohua's acquisition of the U.S.-based Dennis Company, which specializes in shallow troughs, further strengthens its position. When an entrepreneur makes such a decision, would they risk their business without confidence?

Many years ago, Mr. Zhao Shuyan proposed the gradual exit of shallow troughs from the market. Like many others, I couldn't accept this view. At that time, there were few applications of super cyclones, limited experience, and various issues during application. Our understanding of them was little, mistaking the advantages of shallow troughs over ordinary cyclones as equivalent to those over super cyclones. It was believed that shallow troughs had strong gangue removal capacity and low power consumption.

However, as our understanding of super cyclones deepened, and with the widespread application of intelligent X-ray water-free selection in the preparation stage, the issue of coal quality variation became prominent, and the shortcomings of shallow trough technology began to emerge. Meanwhile, the increased upper limit of feed particle size and gangue removal capacity of super cyclones, along with reduced energy consumption per ton of coal, and the accumulation of application cases, led to a change in the situation. I now wholeheartedly agree with his view.

Super cyclones have a simple structure and can be easily produced once they are designed. This is no different from shallow troughs. In recent years, the number of manufacturers capable of producing super cyclones has gradually increased. This is not good news for Guohua, but it is beneficial to the entire industry. After all, updating China's coal selection technology is tantamount to saving coal resources.

After the above analysis, if someone still clings to their idealized view of shallow troughs, then they are labeling themselves as backward and stubborn. It's time to wake up.

Unfortunately, few have seen super cyclones, and even fewer possess the technical expertise. Super cyclones cannot exist independently of systems. The main obstacles to the widespread application of super cyclones lie in understanding them, especially for larger models. Choosing a suitable dilute medium pump for a large-scale cyclone is challenging, and traditional slurry pump curves rarely match. This becomes the stumbling block for 90% of designers. Additionally, a critical and challenging aspect is the dense medium system. Identifying the key issues in the event of a problem is difficult, and systemic issues are not easily resolved with one or two adjustments, which also hinders the promotion of super cyclones.

Lastly, a point to supplement: the difference between selecting limp coal and fine coal, and between two-product and three-product cyclones. Selecting lump coal requires lower pressure, meaning it is more energy-efficient, with lower system coal slurry content, making desliming easier. In some cases, the actual power consumption of a combined dilute medium pump can reach 0.6 to 0.7 kWh. When producing two products, the key to separation lies in the secondary stage, whereas in three-product systems, the key lies in the primary stage. Compared to this, super cyclones for three-product separation are much simpler than those for fine coal selection, making the design and production process simpler.

Perhaps those who consider shallow troughs their "dream lover" will criticize me. However, if they are rational, they should thank me for timely loss-cutting, eliminating shallow troughs, and embracing super cyclones.

Contact for more:

Tiffany Chen

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