Abstract: This paper introduces in detail the performance characteristics and various economics of the positive-pressure direct-blowing pulverizing system of the medium-speed coal mill cold primary fan and the positive-pressure direct-blowing pulverizing system of the double-inlet double-outlet ball mill. According to the actual situation of 2×1000MW thermal power project in Zouxian Power Plant, combined with the trend of increasing marketization of coal burning, it puts forward scientific and reasonable choices, which will play a reference role in the selection of other thermal power engineering milling systems.

Key words: mill; positive pressure direct-blowing pulverizing system; intermediate storage silo feeding system; medium grinding speed

0 overview

Huadian International Zouxian Power Plant is a modern large-scale pit power station. It was built in 1983 and has a total installed capacity of 4540 MW (4×335 MW+2×600 MW+2×1000 MW). The boiler of 2×1000 MW ultra-supercritical thermal power unit is highly efficient. Critical parameters variable pressure DC furnace, primary reheating, balanced ventilation, open layout above the operating layer, solid slag discharge, all steel frame, full suspension structure ∏ type boiler. As an important auxiliary equipment of the unit, the coal mill's configuration will directly affect the safety and economy of the unit.

1 unit burning coal type and coal mill type

The design of the 2×1000MW ultra-supercritical thermal power unit of Zouxian Power Plant is based on the use of local bituminous coal (ie, the blended coal of Yankuang Group and Jibei Mining), which has high volatile content and is easy to grind (see Table 1). Designed coal type dry ash-free volatiles Vdaf = 39%, is a bituminous coal, high volatile, easy to burn, is very beneficial for boiler ignition, but also easy to spontaneous combustion, shooting. The selection of the milling system will place very stringent requirements. According to the GB/T7562-1998 classification of coal grindability, it can be known that when the HGI of coal is 40~60, it is difficult to grind coal. The coal quality of this project is HGI=64, which is not a coal that is difficult to grind.

For the pulverizing system burning bituminous coal, there are generally four choices in China, namely, the gas ball feeding system of the intermediate storage bin of the steel ball mill, the direct-blowing pulverizing system of the single-input single-out steel ball mill, Speed coal mill cold primary fan positive pressure direct-blowing pulverizing system and double-inlet double-out steel ball coal mill cold primary fan positive pressure direct-blowing pulverizing system. The gas ball feeding system of the intermediate storage bin of steel ball mill is not suitable for bituminous coal with Vdaf=(27~40)%. Because of the high volatile content of such bituminous coal, there is a hidden danger of spontaneous combustion explosion in the powder deposits in all stages of the middle storage system. Threatening the safety of the unit, and the system is complex, the power consumption is high, and the floor space is large. Therefore, the design of this project is not used. The direct-injection pulverizing system of the single-input single-out steel ball mill lacks successful application experience on large-scale units. To avoid risks, this project design will not be used; for medium-speed coal mill cold primary fan positive pressure direct-blowing pulverizing system and double-inlet double-out steel ball coal mill cold primary fan positive pressure direct-blowing pulverizing system According to the characteristics of the unit design coal and milling system, the most economical and reasonable choice should be made.

Comparison of configuration features of 2 medium-speed grinding and double-inlet double-out steel ball mill cold primary fan positive pressure direct-blowing pulverizing system

2.1 Domestic manufacturing status and characteristics of medium speed coal mill

At present, the medium-speed coal mills used in large-scale coal-fired power stations in the world can be roughly divided into three categories: HP (alternative products for RP mills), bowl-type medium-speed mills, MPS-type roller-type medium-speed mills, and MBF-type rolls. Medium speed grinding.

The HP type bowl type medium speed coal mill was developed by ABB-CE in the mid-1980s and is a replacement for the RP type medium speed mill. After the introduction of the RP series medium-speed grinding technology from ABB-CE in 1981, Shanghai Heavy Machinery Factory introduced the HP series medium-speed grinding technology from ABB-CE in 1989, and has already achieved the performance of many HP-type coal mills. , has accumulated a wealth of experience in manufacturing. The HP1103 medium speed coal mill has been ordered by Tuoketuo Power Plant and Baosteel and is in the production stage.

The MPS type roller type medium speed coal mill was first developed by the German DBW company in the 1950s. In 1985, Shenyang Heavy Machinery Factory introduced the manufacturing technology of MPS series 190, 225 and 255 from DBW Company of Germany. The MPS type coal mill manufactured by it has been applied in many domestic power plants. Heavily has built the largest medium-speed grinding MPS450 (grinding limestone) in China, and also manufactured more than 70 MPS265, MPS315, MPS360, MPS375 medium speed grinding (mostly used in cement plants), so design and manufacture MPS280 medium speed coal mill Technically reliable.

In addition, Beijing Electric Power Equipment Factory also introduced MPS225 manufacturing technology and MPS grinding serial design core technology from DBW Company in Germany in 1985, and developed its own product ZGM series coal mill through development, and also applied in domestic power plants. .

The MBF type roller type medium speed coal mill was developed by the US company FOSTERWHEELER in 1975. The MBF coal mill basically retains the advantages of the MPS coal mill: the larger diameter of the grinding roller and the longer grinding life of the grinding roller. At present, there is no manufacturer in China that produces this type of coal mill. In view of the actual situation of the localization equipment to be adopted in this project, it will not be described here.

In February 2003, Changchun Power Generation Equipment Factory introduced the proprietary technology of Germany's BABCOCK MPS-HP-II type coal mill. This technology is the third generation of German MPS mill and is the latest technology in Germany.

The coal-type mechanism of the HP type medium speed mill and the MPS type medium speed mill is roughly the same, that is, the raw coal is crushed mainly by the extrusion between the grinding roller and the bowl liner. HP type grinding and MPS type grinding represent two different genres and styles in the field of medium speed coal mills. In the competitive market environment, the two complement each other, constantly improve and perfect, and have many structures and working principles. Similarities also have their own characteristics.

The similarities:

1) The coal mill adopts variable loading. The output of the coal mill can be adjusted automatically and anytime, anywhere. When the unit is peak-shaving, the frequent start of the coal mill is avoided, and the operation is convenient. Conducive to extending the life of wear parts, energy saving 20;

2) The operation reliability is relatively poor compared to the steel ball coal mill, and the operation and maintenance workload is large, and the equipment needs a coal mill;

3) The transmission uses a planetary gear reducer. The reducer has the characteristics of small volume, light weight, large carrying capacity, high efficiency, stable operation, etc.; the grinding roller and the bowl liner have no direct metal contact, can start and stop with no load, and the starting torque is small, and the grinding wheel is in the bowl when the machine is stopped. Save coal for easy cleaning;

5) The output of the coal mill is controlled by the coal feeder and the primary air volume, and the response to the boiler load is slow;

6) The wind coal is relatively high, and the fineness of the coal powder should not be controlled at low load, which is unfavorable for the stable combustion of the boiler. At full load, the ratio of wind to coal is about 2, and at low load, the ratio of wind to coal is higher. In addition, the high ratio of wind to coal makes the resistance of the primary air system increase, increasing the energy consumption of the primary fan;

7) Applicability to coal types, the two types of coal mills are basically the same. Suitable for low-abrasive (scouring wear index Ke<5), low ash, medium and high volatiles, bituminous coal with less than <25, HGI>40, sub-bituminous coal and lean coal; three pieces in coal (wood blocks, stones and iron) Block) is sensitive and easy to wear. Not suitable for grinding high hardness, high moisture and low volatile coal.

The difference is:

1) The shape of the grinding roller and the grinding disc are different. The HP type grinding roller is a roller cone type, the structure volume is small, the wear resistant material volume is also small, and the grinding roller has a short service life. The grinding roller of the MPS mill is a roller type, the diameter of the grinding roller is large, the structure volume is large, the volume of the wear-resistant material is also large, the grinding roller can be used for turning the roller, and the service life is long;

2) The structure of the HP type coal mill is relatively simple, the volume of the machine is small, the vibration of the machine body is large, the resistance of the body is small, and the displacement of the stone coal is small. The structure of the MPS type coal mill is relatively complicated, the volume of the machine is large, the vibration of the machine body is small, the resistance of the body is large, and the displacement of the stone coal is large;

3) The automatic variable loading device is different. The HP type coal mill adopts an external spring loading device, which has a simple structure, convenient maintenance and low cost. MPS type coal mill adopts hydraulic accumulator variable loading technology;

4) HP type coal mill grinding roller can be turned over and over, so that the roller replacement can be carried out directly on the machine, reducing downtime. The MPS type coal mill grinding roller can also be lifted for inspection, but the inspection time is relatively longer.

Looking at the manufacturing and use of the above two medium-speed coal mills in China, MPS medium-speed grinding and HP-type medium-speed grinding can be applied to the coal quality data of this project design coal, so in the technical and economic comparison of this project The medium-speed grinding system is based on the HP medium-speed coal mill.

2.2 Domestic manufacturing status and characteristics of double-inlet and double-out steel ball mill

There are many manufacturers of double-inlet and double-out steel ball mills in the world, among which three are: ALSTOM in France, FOSTERWHEELER in the US and SVEDALA in Switzerland. The three coal mills have their own characteristics, but the principle of coal grinding is the same, that is, grinding by mutual collision and mutual entanglement between steel balls and coal.

In 1988, Shenyang Heavy Machinery Factory introduced all the design, manufacture, inspection and testing techniques of BBD3448, BBD3854, BBD4060, BBD4366, BBD4760 and BBD4772 six kinds of double-inlet and double-out steel ball coal mills from ALSTOM, France. At present, BBD4060, BBD4062, BBD4760 and other products produced by it have been used in many power plants at home and abroad, and have accumulated rich experience in manufacturing.

In 1995, Shanghai Heavy Machinery Factory also introduced the full set of BBD series double-inlet and double-out steel ball mills from ALSTOM in France, and cooperated with ALSTOM to manufacture the BBD4360 coal mill for export. Currently, it has signed 12 contracts with Changshu Power Plant. At the end of the year, it provided 4 units and accumulated a certain amount of experience in manufacturing.

The characteristics of the double-inlet and double-out steel ball mill are very significant:

1) High continuous operation rate, few operation and maintenance work, no need for equipment coal mill;

2) This type of coal mill can achieve non-stop ball addition to the wearing parts of the steel ball;

3) The life of the auger blades is 2 to 3 years, and the life of the cylinder liner

6 to 8 years, the replacement of the spiral blade and the cylinder liner can be carried out during the maintenance of the boiler, and the inspection and maintenance cost of the coal mill is very low;

4) The response speed is fast within a wide load range. The mill stores a large amount of coal, and the output of the coal mill is adjusted by the primary air volume, so that the mill responds to the boiler load speed quickly;

5) The ratio of wind to coal is low. The low ratio of wind to coal is determined by the structure of the mill itself. The low ratio of wind to coal makes the concentration of pulverized coal increase in the primary air, and the fineness increases at low load, which is conducive to stable combustion of the boiler at low load and reduce fuel consumption;

6) The output and fineness are stable. The adjustment of the output is determined by the primary air volume. Once the air volume is unchanged, the output will be stable. The control of the output and the control of the coal level in the coal mill are independent of each other, and the amount of coal in the mill is not affected by the increase in output. The fineness of pulverized coal is usually determined by the amount of steel balls of the mill. As long as the amount of steel balls is constant, the fineness is stable;

7) Coal has a wide range of applications and is not susceptible to foreign matter. Applicable to all kinds of coal quality, for hard and high abrasive fuels, can meet the service life requirements by improving the damaged parts (liner, steel ball) materials;

8) Great flexibility. The double-inlet and double-out steel ball coal mill can realize three working conditions of double-input and double-out, single-input double-out or semi-grinding according to boiler load requirements, which brings great convenience to users in practical application;

9) High availability. In the case of single-side coal plugging or one coal feeder failure, the double-inlet and double-out steel ball mill can reduce coal output by one side and the output of coal is small, and the coal in the cylinder can be maintained for 15 minutes. Powder demand. Therefore, the availability of double-inlet and double-out coal mills is very high, and the information provided by FW Company can be as high as 99.28;

10) The power consumption of the coal mill is higher than that of the medium speed mill, so the operating cost is high.

Comparison of Technical Performance between 2.3HP Medium Speed Milling System and BBD Type Double Inlet and Double Out Ball Milling System

HP type medium speed grinding system and BBD type double inlet and double outlet steel ball milling system have advantages and disadvantages in technical performance:

1) In the design, HP type medium speed grinding system and BBD type double inlet and double outlet steel ball milling system generally have 6 coal mills (including 6 coal mills of HP type medium speed grinding system) The station is running, 1 set is spare).

2) In terms of working principle, HP1103 medium speed grinding is carried out by rotating bowl-type grinding disc with grooved raceway and three fixed tire-type grinding rolls; and BBD4360 double-input double-out steel ball mill It is carried out by collision and mutual entanglement between the steel ball and the coal.

3) The HP1103 medium speed grinding structure is complicated. The grinding roller is placed inside the coal mill, and the operation requirements are high; the equipment needs to be ground and arranged vertically. The main body of the coal mill has high resistance, and there are many operation and maintenance points. There are lubrication stations, hydraulic stations, grinding roller lubrication, etc., and the operation reliability is slightly poor. Sensitive to “three blocks” (wood blocks, stones and iron blocks), large blocks have an impact on operation. It is suitable for grinding medium-hard and medium-abrasive lean coal and bituminous coal. It has no reserve capacity. It needs to stop immediately after coal breaking, and responds slowly to changes in boiler load. It can be adjusted by changing the output of coal feeder, and it is delayed for more than 10 minutes. Poor fineness of coal powder at low load is unfavorable for stable combustion of the boiler. The output of the coal mill is controlled by the coal feeder and the primary air volume. Each device is self-contained, and the attached equipment is faulty. The standby coal mill needs to be activated. The wear resistance is reduced in the later stage of wear. The power consumption is low, generally 8-9 kWh / ton of coal, but due to the higher resistance of the coal mill, the power of the primary fan motor is high. There are many operation and maintenance points, and the operation reliability is slightly poor. The life of the grinding roller and the grinding disc is generally 8,000 hours. The noise is small, and the noise at 1m from the device is <85dB(A). The coal powder has good uniformity. The weight and floor space of the equipment are smaller than that of the double-inlet and double-out steel ball milling system. The coal mill has good start-up and shutdown performance. The wind coal is relatively high, about 2 at full load, and higher at low load. First, the sum of the energy consumption of the secondary air system is high. The output of coal grinding is ≤95. The wear parts need to be replaced every year, and the continuous operation rate is affected. The maintenance work is large and the technical requirements are high. The quality of the operation and maintenance personnel is relatively high.

3) The double-inlet and double-out steel ball milling system has a simple structure. The inside of the coal mill only needs to be filled with steel balls and has no moving parts. The coal mill body has low resistance, only about 45 of the medium speed coal mill, no need for spare grinding, horizontal arrangement. There are few operation and maintenance points, only one lubrication station needs routine maintenance, and the operation reliability is high. Stones, iron blocks and wooden blocks in raw coal have less impact on operation. It has strong adaptability to coal types and is mainly used for hard and medium hardness coals. It is especially suitable for coals with high volatile content and strong abrasiveness. It also has strong adaptability to high moisture raw coal. Second to the fan coal mill). The reserve capacity is large, and the boiler can still run for 15 minutes after the coal is broken. The coal pulverizer has a large reserve of coal powder and responds quickly to changes in boiler load. It is adjusted by changing the primary air volume, which is suitable for peak shaving of the unit and only delays for 15 seconds. Because the raw coal stays in the cylinder for a long time, the fineness of the coal powder is high, and when the load is low, it is beneficial to the stable combustion of the boiler. The coal mill output is controlled by the primary air volume, and the cylinder coal position is controlled by the coal feeder. Coal mill output control and coal mill coal level control are two sets of control systems. Because it can operate in double inlet and double outlet, single inlet and double outlet, single inlet and single outlet (semi-grinding), even if the auxiliary machine equipment such as individual coal feeder fails, the full-load operation can be guaranteed. But the weight and floor space of the equipment is higher than HP.