Advantages and disadvantages in the process of engineering design of China's coal preparation technology

1. The optional test data is incomplete and lacks representativeness.

The development of the coal preparation process based on the lack of representative screening of floating and sinking data is misleading to the design and the consequences are serious.

Therefore, the newly issued "Code for Design of Coal Washing Engineering" 5.1.6 (compulsory provisions in boldface) clearly requires that "feasibility studies and preliminary design must review the representativeness of screening and floating test data. When screening, floating and sinking When the representativeness of the test data is insufficient, it should be adjusted according to the regulations to make it close to the actual production." This is one of the most important changes to the new and old specifications. This requires that the borrowing data must be reasonably adjusted in conjunction with the conditions of the minefield and the mining technology used in the mine to increase the representativeness of the data.

At present, China has no uniform standard for the method of adjusting data. It can only be adjusted in accordance with the principles stipulated in 5.1.6 of the Code for Design of Coal Washing Engineering. The provisions of the “Design Specification” for data adjustment are “1 adjustments based on actual production conditions of adjacent coal mines and coal preparation plants. 2 Adjustment according to factors such as coal field geological report, coal mining method, and transportation upgrading method”. When adjusting the data, you need to pay special attention to the following aspects:

(1) Reasonable prediction of the production of raw coal ash;

(2) Reasonable adjustment of the particle size composition of the small kiln raw coal screening data, in view of the use of lump coal or sorting. Therefore, for the classification of thermal coal, the accuracy and representativeness of the particle size composition of raw coal screening data is particularly important.

If the optional analysis or reasonable prediction is not made, the coal preparation plant will encounter many problems in the actual production after the completion, and even the site cannot handle it. Among all the problems, the ash prediction is inaccurate, and the problem of slime water system caused by insufficient consideration of coal slurry treatment capacity is most prominent.

[Case] ​​A coal preparation plant of a coal group in Sichuan Province was designed and contracted by a German company. Due to insufficient selection of raw coal in the design, the coal preparation engineer who presided over the design did not have the coal preparation plant project in Southwest China, and directly used the design experience of the North Coal Preparation Plant for design and equipment selection.

After the completion of the coal preparation plant, the coal slurry water system often brings many problems of production and environmental protection due to the serious shortage of treatment capacity.

One of the main reasons for the serious shortage of processing capacity of the slime water system is that coal in southwestern China is more likely to be muddy than coal in the north, and the amount of secondary coal is also higher. Another reason is that the change of mining mode, at the beginning of the design of the coal preparation plant, the coal mine supporting the coal preparation plant is a high-grade general mining. In the design and construction process of the coal preparation plant, the coal mining method is upgraded to a thin coal seam. Arm mining (comprehensive mechanized mining). After upgrading to fully mechanized mining, the clamping rate of the top and bottom plates is significantly improved. Due to the coal enterprise management system, the two groups of coal mining and coal preparation have little communication, the general contracting price has been fixed, and the general contractor has not immediately adjusted the design plan. Therefore, after the completion of the coal preparation plant, the slime water system frequently has problems due to insufficient capacity.

The coal preparation plant project became the heart disease of the coal group. Since then, the group has never implemented the general contracting project of the coal preparation plant, and the group's top management is biased against modern coal preparation technology.

2. When the coal preparation plant is selected for the second layer of coal, it cannot be handled correctly.

If the raw coal selected by the coal preparation plant comes from multiple mines or multiple coal seams of the same mine (in fact, most designs fall into this category), then it is necessary to consider whether the multi-layer raw coal should be mixed or grouped.

Article 5.1.5 of the “Code for Design of Coal Washing and Selecting Engineering” requires “When the coal seams have the same sorting density, the selectivity, the ash content of the element are large, the difference of the sulfur content of the net coal is large or the coal type is different. , should be separately sorted." At this time, it is most reasonable to take the mining and distribution of the underground, and to divide the storage and separately.

If the coal quality conditions permit the implementation of the mixed selection method, it is also necessary to solve the problem of how to ensure the mixing ratio of each layer of coal. At this time, the best solution is still to take the mining and distribution in the underground, and the ground storage is proportionally matched with coal.

However, it is difficult to achieve sub-mining, sub-transport, and separately lifting in the underground. Generally, mines do not have such conditions. Secondly, it is conceivable to set up a raw coal homogenized coal yard on the ground to ensure that the nature of the selected coal is relatively uniform over a period of time (the length of time depends on the capacity of the coal yard, generally 2 to 3 days). Foreign and domestic coal preparation plants use this method.

[Case] ​​A large difference in coal ash and density between the 4th and 6th layers of the first mining area of ​​a coal mine in the Zhungeer mining area is a major feature of the coal quality of the mine field. "Feasibility Study" recommends taking the form of long-term filling and coal blending. In view of the fact that there is no mining and distribution in the underground, the quantity and quality of the two-layer coal mining are random, and the ground production system has not adopted any coal mixing measures. Therefore, the proportion of coal blended in the 4th and 6th layers of coal determined by the feasibility study is (1:5) There is no guarantee that the method of blending coal into the wash will not be implemented. In fact, the two layers of coal on the 4th and 6th were randomly mixed. Eventually, the sorting process will be difficult to control, and the quality of the products will be unstable after the election.

3. Determine the problems in the coal preparation process

The comparison of the sorting process plan is only for qualitative technical analysis. The various factors related to the sorting process are not fully considered, the quantitative data is lacking, the arguments are not sufficient, and the conclusion is difficult to be convincing.

The newly issued "Code for Design of Coal Washing Engineering" 5.1.7 (compulsory provisions in boldface) clearly stipulates that "the coal preparation method should be based on the nature of raw coal (such as particle size composition, density composition, optionality, floatability, sulfur composition). Relevant factors such as its occurrence characteristics, meteorite lithology, product requirements, sorting efficiency, sales revenue, production cost, and infrastructure investment are determined after technical and economic comparison. The above provisions have qualitative changes than the old "norms", which is one of the most important differences and advances between the new norms and the old ones. The core requirement is to comprehensively consider various factors related to the sorting process based on representative optional data, and determine the sorting process through technical economic quantitative comparison and comprehensive demonstration. The determination of the coal preparation method should not only reflect the principle of maximum yield, but also reflect the principle of maximizing economic benefits.

[Case] ​​In a Hegang mining area in Northeast China, a coking coal preparation plant designed and constructed by a foreign company (1.50 Mt/a) is a two-stage pressurized feed two-product heavy medium cyclone + coarse coal slurry. Spiral sorting machine sorting process. As a result, the coal production rate of the coal preparation plant using the three-product heavy medium cyclone + slime heavy medium cyclone separation process before the selection of the mine is reduced by about 5%. Losing tens of millions of yuan in income a year. It can be described as a typical police example of improper selection of fine coal (including coarse coal slurry) sorting process.

[Case] ​​A coal preparation plant (4.00 Mt/a) in the Yanheng mining area of ​​northern Shaanxi, the coal into the long flame coal. The most important feature of the coal quality of the mine is that the top and bottom plates of most coal seams and the lithology of the sandwich are all mudstones, which are easily disintegrated and easily muddy when exposed to water. The coal preparation process adopts the whole coal washing process, that is, the pre-sludge deliming, 50~1.5mm is divided by two-product heavy medium cyclone with pressure feeding, and the 1.5~0.15mm coarse coal slime is sorted by spiral sorting machine. -0.15mm fine mud is directly recovered by a filter press.

Since the self-test production commissioning, the main coal of the 4-2 coal seam mined in the mine has been washed into the mine. The coal has an average thickness of 200mm mudstone. The main problem is that even when the amount of coal washed is not large (the average actual coal washing amount is less than 1/5 of the designed rated capacity), the washing water quickly becomes black and thick, and the capacity of the slime water system is seriously insufficient. Can not be processed, resulting in the circulating pool liquid level rising and overflowing, driving only a few hours, it can not be produced. The reasons for this are mainly the following two points:

(1) The design uses a pressure-feeding heavy medium cyclone sorting method to produce a large amount of secondary slime. The feed material is strongly impacted by the centrifugal pump blades, and is stirred at a high speed. The mudstone vermiculite contained in the raw coal is muddy. According to the actual measurement, the amount of fine mud entering the concentrator of -0.15mm accounts for 18% of the original coal, which is nearly 3.5 times higher than the original design prediction value of 5.23%. As a result, the capacity of the slime water system is seriously insufficient.

(2) When the mudstone vermiculite is cemented, it is not easy to settle, and the pressure filtration effect is deteriorated. The area of ​​the thickener and filter press which are conventionally selected is obviously insufficient, the fine mud is not recovered in time, and a large amount of accumulation in the washing water leads to circulation. The water quickly turns black and thickens, and the circulating pool level rises and overflows.

Later, I had to “reinforce the sheep” and build a filter press workshop. On the basis of the original 3 filter presses (300m2/set), we added 6 additional filter presses (400m2/set), and the filter press area increased more than twice. Increase investment by nearly 15 million yuan.

These are all negative cases, mainly because of improper selection of coal preparation methods. In addition, the case also shows that the lithology of meteorite has a great influence on the choice of coal method.

For this kind of raw coal containing a large amount of muddy vermiculite, the “pre-drainage” is a widely used and mature application process. There are two kinds of pre-drainage processes in China, heavy medium shallow trough and moving sieve jig.

Remarks: There is no discussion of process adaptability here. Each type of raw coal has different adaptation processes. It is not “a fresh trick, eating all over the sky”. There is no best coal preparation process, only the most suitable coal preparation process!

The pre-drainage process can remove large mudstone vermiculite from the system as early as possible, which is very beneficial to the subsequent main selection process and slime water system. The effective sorting granularity of the heavy medium shallow trough is generally 13mm-200mm in the technical specification. Some manufacturers even say that the minimum sorting lower limit is 6mm in the propaganda. In fact, these are misleading. From the actual operating experience, only when the selected particle size ≥ 25mm, the heavy medium shallow groove has a better sorting effect.

In Australia and South Africa, the mainstream process for pre-drainage is “selective crushers ”.

When it comes to selective crushers, most of China's coal-mining colleagues will sneer at it and think that China's technology that has been eliminated for 10 years can be used in mining technology developed countries like Australia. actually not.

The selective crushers used in Australia and South Africa are exactly the same as the ones that were eliminated 10 years ago in China, but the effects and adaptability of the equipment are completely different. The selective crusher is very successful in the coal preparation pre-discharging process in Australia and South Africa, and the equipment failure rate is low. The maintenance cost is lower than that of the moving sieve jig and the heavy medium shallow tank, and the operation is also simple.

The main reason is the difference in coal quality between Australian raw coal and Chinese raw coal. At present, only the mines of Jincheng Anthracite Group and some mines in Ningxia are suitable for the pre-discharge process, and the coal quality in other areas is not suitable. In addition, it is the processing and manufacturing details of the equipment. When asked why the price difference between the devices is so large, the simple analogy that I often do is that both Xiali and Mercedes can go on the road. What difference do you say? There is no detailed discussion here.

4. Problems in the sorting process of the moving sieve jig

At present, there are many pre-sorting and sorting processes for moving sieve jigs, but the reasonable conditions for adopting the process often lack in-depth analysis. For example, it is reasonable to ask whether the proportion of meteorites in the feed of the moving sieve jig is reasonable. In the case of a small amount of vermiculite, the moving sieve jig is blindly pre-discharged. In addition, many design institutes are moving the screen. Adding a buffer tank in front of the jig, resulting in an increase in the rate of the feed, so that the sieve jig can not work properly.

[Case] ​​A coal preparation plant (6.00Mt/a) in Shenfu Mining Area (South District) of Shaanxi Province, "Possibility" uses a moving sieve jig to pre-drain. The ore content of the original coal gangue is generally small, and the content of the strontium is less, and the content of vermiculite in the +50mm raw coal only accounts for less than 9%. The use of a moving sieve jig is not reasonable. Because the raw coal containing too little strontium is driven by a moving sieve jig, it is not conducive to the full play of the processing capacity of the moving sieve jig. This will result in a corresponding increase in the number of moving sieve jigs.

[Case] ​​A coal preparation plant in Shanxi Lu'an mining area adopts the dynamic sieve jig pre-discharge process, but a buffer tank is added before the moving sieve jig, which increases the limit rate in the feed and makes the sieve jigging. The machine does not work properly.

5. Problems in the design of two or more media systems

If large-scale heavy medium coal preparation plant arranges more than two independent production systems, some designs combine some parts of the medium system (such as rare tank and magnetic separator) in the two production systems because of the tight space of the plant. It is unreasonable to treat a device to reduce the number of devices. In order to improve the accuracy of medium density and flow control, it is necessary to maintain the independence of the media system of each production system.

6. The problem of high media consumption in heavy media sorting

Media consumption is an important technical and economic indicator for heavy media separation and is the main factor affecting the production cost of coal preparation plants. Reducing the dielectric loss is one of the key points in the design of heavy-duty sorting process. "Coal washing design specification" Section 5.3.9 mandatory provision that "the magnetic iron ore sorting technology consumption per ton of coal should meet the following requirements: Lump: <0.8kg; mixed coal, fine coal : <2.0kg". However, many designs are often ineffective after being put into production, and the consumption is too large. Most of them are larger than 2kg or even 3~5kg. In Guizhou, where the degree of muddy is serious, there is more than 8kg.

The factors affecting the mediation index are multi-faceted and must be considered comprehensively, and comprehensive technical measures can be taken to receive good results. These technical measures include:

(1) Reasonably select the area of ​​the sieve and the gap of the sieve hole (the qualified section is 0.5mm, the thin section and the curved sieve are 0.75~1.0mm, if the material under the sieve is finally floated, it should not be more than 0.5mm) Screening and running;

(2) In addition to the pre-desorption of the curved screen, the de-screening screen must be provided with qualified medium sections to minimize the amount of medium to be removed from the thinning section to reduce the loss caused by the medium purification;

(3) Try to avoid double-layer de-screening. Many designs are designed in a heavy-duty sorting system using a two-layer stripping screen to combine the functions of product stripping and grading into one double-layer screen. Although there are advantages such as simplification and convenient arrangement, there is also a disadvantage that the efficiency of lower layer screening is not high, which will increase the dielectric consumption;

(4) Before the material is removed into the sieve, a uniforming facility (such as a curved sieve and a uniform tank) is added to make the material uniformly screened to improve the desorption efficiency;

(5) Increasing the pressure head of the descreening water spray and ensuring sufficient water spray volume (small water volume, high pressure head) to reduce the amount of medium carried away by the material on the screen;

(6) The high-gradient magnetic separator is used to recover the medium, and the magnetic separation efficiency is as high as about 9.9%, which can effectively reduce the medium consumption;

(7) Strictly control the feeding amount of the magnetic separator (100 m3/h·m) to ensure a reasonable feed concentration (15% to 25%, optimal value 20%) to ensure the magnetic material in the magnetic separator. The content does not exceed the allowable value (18.5 t / h · m). In order to keep the magnetic separator operating conditions and magnetic separation efficiency in an optimal state, it is very important to reduce the dielectric consumption. The concentration of the incoming slurry (ie, the dilute medium) depends not only on the amount of water discharged from the sieve, but also on the presence or absence of pre-de-sludge. Therefore, the formulation and calculation of the process should be considered in conjunction with the selection of the magnetic separator;

(8) Reasonable choice of additional media. In order to ensure the timely replenishment of the medium, the processing capacity of the Lieutenant Magnetic Separator should be reserved for a certain affluence or a dedicated magnetic separator for purification and supplementation of new media.

7, process equipment selection common problems

The selection of process equipment is wrong, and the adverse consequences can only be gradually exposed after the coal preparation plant is completed and put into production. Because, once the project is completed, the space and area of ​​the plant have been fixed, and it is very difficult to make up for the mistakes in correcting the equipment selection. Regardless of economic losses, it is very difficult to implement only technical changes in equipment. If we accept the fait accompli, it will cause insurmountable passiveness and trouble to the production management of the coal preparation plant, and even leave a lasting regret. No matter how good the design, the process is advanced and perfect; in the end, it depends on the long-term stability of the equipment, and it can be reflected in normal operation. In recent years, the heavy-duty coal preparation plant that was designed and put into production has not had many problems in the process flow. Most of the problems exposed are caused by mistakes in equipment selection.

So far, the problem of equipment selection has existed in the design of almost every coal preparation plant in China; the difference in the size of the problem.

The "habit" of mistakes in the selection of such equipment, if it is in the international project, or this attitude, the cost will be very heavy enough to make the design unit or the general contracting company bankrupt.

[Case] ​​South Africa's famous mining engineering technology provider BATEMAN, because of a project mistake, not only lost tens of millions of dollars in EPCM costs (engineering design + project management contract), and was claimed by the owner. Directly led to delisting from the stock market, the last stagnation, fell to the result of low-cost acquisition by competitors.

Therefore, design engineers must attach great importance to the importance of process equipment selection in the design of coal preparation plants.

8. Mistakes in equipment selection are mainly reflected in the following two aspects:

(1) Uncertainty about the performance and features of the equipment; in order to unilaterally pursue the specification and model uniformity, the selection is not too large or too small, which deviates more than the reference indicators provided by the Code, and some deviate by several times.

[Case] ​​The general contracting of the main washing system of a coal preparation plant in the Juye mining area of ​​Shandong Province was carried out. The de-screening type adopts a horizontal linear vibrating screen. Although it is feasible, because the horizontal linear vibrating screen is used for de-intermediation, its processing capacity per unit area is small (3~4t/m2), so the general sieve area selection specification is larger. The large-area horizontal linear vibrating screen has poor rigidity and is easy to break the beam. For the decoupling of -50mm blended coal products, it is more suitable to use banana sieves with relatively large processing capacity per unit area (5~6t/m2) and strong structural rigidity.

The area of ​​fine coal de-screening is 4×22 m2, and its processing capacity per unit area has reached 6t/m2, which is nearly double the “norm” indicator, indicating that the selection area is nearly doubled. The medium and smear de-screening is consistent with the specifications of the fine coal de-screening type, and the selection area is too large. The processing capacity per unit area is less than 2t/m2, which is much lower than the “norm” indicator. The medium and sputum decontamination screening area is too large, and it will also bring about the disadvantages of excessive filtration and excessive water injection, resulting in a low magnetic separator input concentration, which affects the magnetic separation efficiency. Equipment selection does not have to deliberately pursue the unification of specifications and models, resulting in unnecessary investment waste, especially for engineering general contracting projects.

[Case] ​​Some designs are not reasonable for the use of banana sieves for the off-screening of block coal heavy-duty sorting products.

[Case] ​​The profound lessons of the economic losses caused by the general contracting of a heavy-duty cyclone feed pump in a coal preparation plant in Shaanxi Hengheng Mining Area must be carefully absorbed.

[Case] ​​A lot of process design, the principle of dewatering and recycling separately using coarse and fine coal slurry is reasonable. However, for the fine coal slurry with a particle size of less than 0.15 mm, the pressure filter is used for dehydration recovery, but there is a problem that the filter cake has large moisture, low dehydration efficiency, and the treatment capacity is doubled, and the design should be treated with caution.

(2) One-sided pursuit of the introduction of equipment, should give priority to domestic technology clearance equipment.

[Case] ​​It is not advertising to Jingjin Group. If the filter press selection continues to adopt foreign brands, it must be a local tyrant.

9. Problems in process layout

1) Many design institutes do not have a coal storage yard and a raw coal buffer tank when the surface of the ground production system is laid out. The main wellhead lifting equipment is directly connected to the coal preparation plant production system. This is not in line with the provisions of Articles 3.2.1 and 3.2.3 of the newly-designed Code for Design of Coal Washing Engineering. There are also a series of drawbacks:

(1) Direct connection, so that the hourly capacity of the production system of the coal preparation plant must be the same as that of the main well lifting equipment, and in order to ensure the safety of the main well, the production system of the coal preparation plant needs equipment system, which will inevitably result in huge investment. waste.

(2) Any equipment in the production system of the coal preparation plant fails. Due to the closed relationship of the coal flow system, the main shaft lifting equipment (belt conveyor) will be stopped. If the main shaft lifting equipment is a winch, it will definitely bring great harm to mine production.

2) At present, the design of the main plant of the coal preparation plant is often called a modular arrangement. But in fact, most of the main plant design is not a true modular structure, let alone modular process layout.

Special Flip Clock

This kind of special Flip Clocks shown on our official website are the hot selling product in our factory. We provide the good quality and competitive price to our customers and try our best to make customers please. We have many interesting kinds of flip clock, and some of them are never seen in the world. Such as bike flip clock and TV flip clock and so on. Besides, we also provide the classic style flip clocks for daily sell.

Retro Modern Auto Flip Clock;Retro Mechanical Flip Clock;Flip Wall Clocks;Large Flip Clock Wall;Flip Numbers Alarm Clock

Guangzhou Huan Yu Clocking Technologies Co., Ltd. , https://www.mk-times.com