NEWS CENTER

Cement dust selection technology and guide


Release time:

Feb 13,2012

Dust collection technology and equipment of 1. cement plant 1. Difficulties in smoke and dust control The main dust emission sources of cement plant are crusher, rotary dryer, vertical dryer, raw mill, powder separator, cement mill, vertical kiln, packaging machine, etc. In addition, the conveying equipment, the top of the warehouse, the bottom of the warehouse, the inlet and outlet, etc. are the dust sources that produce the dust of the post. Among them, the treatment of shaft kiln exhaust gas is more difficult. The smoke and dust control of vertical kilns is mainly difficult in the special working conditions of "wet, eroded and variable" flue gas, not in the large amount of smoke (much smaller than the amount of waste gas at the end of rotary kiln), nor in the high dust concentration (vertical mill and O-sepa separator

Dust collection technology and equipment for 1. cement plant

1. Difficulties in smoke and dust control

The main emission dust source of cement plant is crusher, rotary dryer, vertical dryer, raw mill, powder separator, cement mill, vertical kiln, packaging machine, etc. In addition, the conveying equipment, the top of the warehouse, the bottom of the warehouse, the inlet and outlet, etc. are the dust sources that produce the dust of the post. Among them, the treatment of shaft kiln exhaust gas is more difficult.

The smoke and dust control of vertical kilns is mainly difficult in the special working conditions of "wet, corroded and changed" of flue gas, not in its large amount of flue gas (much smaller than the exhaust gas at the end of rotary kiln), nor in its high dust concentration (the emission concentration of vertical mill and O-sepa classifier is dozens or even hundreds of times higher). "Wet" refers to the flue gas with high moisture content (8% ~ 20%), high dew point temperature (40% ~ 55%), and higher acid dew point temperature; "corrosion" refers to the corrosive flue gas, especially the corrosion of fluoric acid after adding compound mineralizer is particularly strong; "Change" refers to the frequent changes of exhaust gas, dust content (1~30g/Nm3), temperature (45~450 ℃), humidity, dust specific resistance value (109~1012 Ω m) and other parameters with the process operating conditions, large-scale fluctuations.

2. Several existing domestic vertical kiln dust collection technologies

Domestic products can be described as a variety of forms, in addition to the settlement chamber, there are a variety of wet dust, electric dust and bag dust. Wet dust removal includes spray, water shower, water film, ultrasonic, cyclone, self-excitation, water bath, composite type, etc. Electric dust removal includes dry horizontal, vertical, riser rotary umbrella type, wet vertical, hydropower composite type, etc. Bag removal method includes glass fiber bag dust collector (upper and lower air inlets) using reverse blowing to clean dust, low-pressure long bag box pulse dust collector using pulse dust removal, etc. From the perspective of current development, efficient bag and electric dust collection technology is still the mainstream of application.

3. Discussion on several dust collection technologies

①? Water dust removal

The biggest advantage of water dust removal is to adapt to the dark fire combustion process of modern shaft kilns, and has a strong adaptability to the changing working conditions. At the same time, it is not afraid of the adhesion of dust, and has the effect of desulfurization and defluorination. It is relatively simple to make, less investment. However, water dust removal is difficult to reach the standard, and the resistance is high, the water consumption is large, which is easy to cause secondary pollution. The mud solution is very corrosive. Even if the mud returns to the ball plate and forms the enrichment of potassium and sodium, the quality of clinker will be affected. At the same time, the discharged water mist is diffuse and the flue gas is vast. Environmental protection departments in some developed regions have banned their use.

② Dust removal in settling chamber

The advantages of the drop room dust removal are simple structure, the most economical investment, no special management, and the least power consumption. The disadvantage is that only coarse particle dust can be settled, and dust with a particle size of 50 μm or less, which usually accounts for more than 60%, is difficult to capture, and is far from meeting the emission requirements.

③ Water and electric compound dust removal

Because the first-level water dust removal caused by secondary pollution and other ills still exist, and the second-level electric dust removal anti-condensation, corrosion and water mist removal task is arduous, such as a single electric field can not achieve smoke emission.

Dust collection technology and equipment for 2. cement production process

1. CXQM air box pulse bag filter

With the development of energy saving and environmental protection technology, the CXQM air box pulse bag filter is now used to collect dust, which can meet the emission requirements within 50 mg/Nm3 at the outlet. The system is simple, the resistance is small, and the energy consumption is low.

1.1 working principle

When the equipment is working, the dust-containing gas enters the ash hopper from the air inlet. Due to the rapid expansion of the gas volume, some coarse dust particles fall into the ash hopper, while the rest of the dust particles rise into the bag chamber with the air flow. After being filtered by the filter bag, the dust particles are retained outside the filter bag. The purified gas enters the upper box from the filter bag, and then is discharged into the atmosphere through the valve plate hole and exhaust port, thus achieving the purpose of dust collection.

With the continuous filtration, the dust collection resistance also rises. When the resistance reaches a certain value, the dust cleaning controller sends a signal. With the pulse valve sending the high-pressure reverse air flow used for dust cleaning into the bag, the filter bag swells rapidly and produces strong jitter, resulting in dust shaking off outside the filter bag to achieve the purpose of dust cleaning. Since the equipment is divided into several box areas, the above process is carried out box by box. When one box area is cleaned, the remaining box areas are still working normally, ensuring the continuous and normal operation of the equipment. The reason why it can deal with high concentration, the key lies in the fact that the cleaning time required for this strong cleaning is extremely short (only 0.1~0.2 seconds for one injection).

1.2 technical characteristics

(1) No pre-dust collection equipment is required, smoke and dust with a concentration of up to 1000g/Nm3 can be processed at one time, and the discharge is less than 50 mg/Nm3, and the process flow is simple.

(2) There is no need for a blowpipe in the bag room, and it is convenient to change the bag outside the machine.

(3) Embedded elastic bag mouth, good sealing performance.

(4) The number of pulse valves is small, the cleaning intensity is large, and the action is rapid.

(5) The whole machine adopts microcomputer automatic control, and each parameter is easy to adjust.

(6) The service life of the filter bag is more than 2 years.

(7) easy to achieve isolation maintenance, dust collector relative to the host operating rate of 100%.

As a kind of filter type dust removal equipment, bag filter has the advantages of high dust removal efficiency and stability, low equipment cost, simple management, convenient maintenance and so on. It is suitable for collecting all kinds of dust in cement plant and has excellent performance, which can fully meet the requirements of environmental protection.

1.3 the cleaning effect of bag filter determines the quality of bag filter to the greatest extent. At present, the bag type dust collector mainly has the following three cleaning methods:

1.31 mechanical vibration

Mechanical vibration mainly relies on mechanical force to make the filter bag shake and deform, so as to achieve the purpose of cleaning ash. Due to the uneven distribution of mechanical dust removal vibration, the required filtering wind speed is low, and the damage to the filter bag is large, which has been gradually replaced by other dust removal methods.

1.32 anti-blowing dust

Anti-blowing dust cleaning is reverse air flow dust cleaning, which relies on the anti-blower to feed a large amount of low-speed air flow, so that the pressure inside and outside the filter bag is unbalanced, and the filter bag is deformed to achieve the purpose of dust cleaning. The dust removal by reverse blowing can only cause partial deformation of the filter bag, and the deformation position is fixed. The dust layer on the filter bag has certain elasticity, and the filter cake cannot fall off in a large area, so the dust removal is not complete. In addition, the filter bag filtration wind speed in different parts is different, which also causes large local resistance loss of the dust collector, low dust removal strength by reverse blowing, and also limits the filtration wind speed of the dust collector.

1.33 pulse cleaning

Pulse cleaning is the use of the pulse valve to make the compressed air in the instantaneous release of the air explosion, so that the filter bag to produce pulse expansion vibration. The filter bag wall gets a great acceleration, and at the same time, the filter cake on the filter bag is shaken under the action of the reverse air flow. Compared with rapping and back blowing, pulse dust cleaning is a strong dust cleaning. This method has obvious advantages of high dust cleaning intensity, long filter bag life, high dust collection efficiency and high filtration speed.

The CXQM gas box pulse bag dust collector developed by our factory is a new type of high-efficiency bag dust collector developed on the basis of introducing the technology of Fuller Company in the United States, absorbing the technical advantages of similar products in Germany, and combining with the actual situation in China. It integrates the advantages of chamber back blowing and pulse jet bag dust collector, and overcomes the defects of insufficient kinetic energy of chamber back blowing and simultaneous dust cleaning and filtration by pulse jet, expanding the scope of application of bag-type dust removal equipment.

1.4 promotion and application

The dust collector has been widely used in more than 3000 discharge points such as vertical mill, powder separator, rotary dryer, raw meal mill, cement mill, vertical dryer, packaging machine, crusher, etc.

2. Blowback air bag dust collector

Blow-back air bag dust collector is an internal filter type, which is a weak ash removal. Each time a room is blown back for 10-20 seconds, it can only deal with smoke and dust of conventional concentration. The usual advantage is that the price is cheaper, but it is now gradually eliminated.

3. Vertical, horizontal and wide pole distance electrostatic precipitator

(1) Basic structure

The product consists of 6 parts: ① electric field body; ② lock air ash unloading device; ③ exhaust system; ④ vibration dust cleaning system; ⑤ high voltage silicon rectifier transformer; ⑥ electrical control system.

(2) Working principle

Under the negative pressure of the induced draft fan, the dust-containing gas enters the wind box of the dust collector through the air inlet pipe, and then passes through the cyclone device to form a rotating air flow running along the direction of the electric field. Under the action of collision and centrifugal force, the large particle dust is separated from the gas and falls into the ash hopper, and the fine powder enters the electric field with the swirling gas.

(3) Promotion and application

The dust collector has a good effect on the dust collection of dryer, raw mill, crusher and other equipment.

(4) Existing problems

In the large emission concentration is not suitable, the dust specific resistance is greatly affected, and the dust removal effect is affected by many factors.

Suggested Technology and Equipment for Dust Collection in 2. Vertical Kiln

1. CXIY cylindrical shaft kiln bag dust collection

Due to the high dust removal efficiency of the bag filter, to adapt to the wide range of dust concentration, and is not affected by the dust specific resistance, the use of bag filter for machine kiln flue gas treatment has become the choice of most cement production plants. Usually, as long as the design and selection are reasonable and the production is defect-free, the bag filter can meet the emission requirement of <50mg/Nm3. At present, LFEF is widely used in the market, such as upper inlet air blowback, lower inlet air blowback and injection pulse filter, but most of them have defects such as large investment, many failure points and short filter bag life, which are difficult to popularize.

The successful development of CXIY cylindrical vertical kiln bag filter solves the problems of unreasonable structure, large investment, high operating cost, poor bag sealing, short life, "paste bag", uneven airflow and other problems in the existing bag filter, which has good results.

Development and Research of 1.1 CXIY Cylindrical Vertical Kiln Bag Filter

CXIY bag filter is a new type of bag filter based on the traditional anti-blowing dust collector, according to the characteristics of the kiln flue gas, bold innovation, research and design. The dust collector in the design process mainly considers the following points:

① Design of process system

In order to reduce the air leakage of the system and reduce the resistance, in the process design, the dust collector adopts primary dust removal, and the fan is arranged on the top of the kiln room as much as possible to facilitate maintenance.

② Selection of working temperature

Since the flue gas temperature is generally between 45-250 ℃ during normal operation of the shaft kiln, the maximum working temperature of the designed dust collector is less than or equal to 200 ℃. In case of abnormal kiln conditions and high temperature, the temperature can be adjusted by mixing cold air into the air inlet.

③ Structural design

Due to the high position of the air outlet point of the vertical kiln, the CXIY dust collector adopts the top air inlet in the design, and the central air pipe is introduced into the lower part, eliminating the traditional upper plate and moving the center of gravity of the equipment down. In addition, the structural design also considers a series of measures such as thermal deformation compensation and corrosion protection, especially the use of cylindrical structure, so that the equipment covers an area greatly reduced, suitable for the narrow site of the old line transformation. Because the cylindrical structure is evenly and reasonably stressed and has less consumables, the cost is relatively low.

④ Filter material selection

Using EWF550-RH glass fiber bulky yarn filter material, the filter material adopts RH formula, and uses non-silicone hydrophobic agent to organically unify hydrophobic, wear-resistant, folding, anti-corrosion and other properties through a specific process. It has the advantages of high temperature resistance, corrosion resistance, condensation resistance, easy ash removal, dimensional stability, high strength, moderate price, etc. It can be used for a long time at 280 ℃, and the instantaneous high temperature can reach 300 ℃. It is an ideal filter material for vertical kiln dust collector.

⑤ Choose reasonable wind speed

The filtering wind speed not only determines the volume of the dust collector, but also has a decisive influence on the dust removal efficiency, resistance, dust removal effect and service life of the equipment. The allowable filtering wind speed of glass fiber bulk yarn is 0.6 m/min. In order to ensure the long-term stable, high-efficiency and low-resistance operation of the dust collector, the filtering wind speed of the CXIY dust collector is determined to be 0.5 m/min.

⑥ Improve the fixing method of filter bag

Using clamps instead of ropes, the filter bag is fixed more firmly and the sealing effect is better, thereby reducing the failure of bag dropping and improving the dust collection efficiency. The use of elastic hanging devices can well maintain the shape of the filter bag and reduce the wear of the filter bag., Extend the service life of the filter bag.

⑦ Anti-condensation design

Due to the high dew point of the vertical kiln flue gas, 100mm silicon cotton is used for insulation in the intake pipe, shell, ash hopper and other parts of the dust collector to reduce the heat dissipation of the shell and improve the heat storage capacity of the equipment. In addition, clean air is used to reduce condensation caused by temperature difference between inside and outside. The actual use effect shows that the best use temperature of the dust collector is between 65-260 ℃, and it can be used normally at 60 ℃. For lower kiln temperature, a small amount of hot air can be mixed in front of the flue gas dust collector by using a hot blast stove to increase the inlet temperature of the dust collector without affecting the normal operation of the shaft kiln. The inlet temperature of the dust collector can also be increased by reducing the moisture content, controlling the thickness of the wet material layer, operating behind closed doors, and appropriately increasing the amount of coal blending.

⑧ Microcomputer control system

The advantages and disadvantages of the control mechanism have a great impact on the normal operation of the equipment. CXIY's microcomputer control system adopts Siemens PLC programmable controller to control the blowback and work according to the predetermined program. The control system also adds an over-temperature sound control system to remind the operator to adjust in time when abnormal flue gas temperature occurs.

Reducing moving parts

In order to simplify the operation and reduce the failure rate, CXIY kiln bag filter adopts the lifting switching valve to replace the original air outlet and back blowing butterfly valve, which greatly simplifies the cleaning procedure and reduces the failure rate. And multiple chambers share an ash hopper and an ash discharge valve. In this way, only eight valves are used for the whole dust collector.

Equipment maintenance is simple, good working environment.

The working principle of 1.2 equipment

① Pre-separation

The dust-containing gas discharged from the shaft kiln enters the air inlet main pipe in the center of the dust collector through the flue, and evenly enters each filter chamber of the dust collector from above the dust hopper under the negative pressure generated by the induced draft fan of the dust removal system. Coarse particles in the dust-containing flue gas directly fall into the dust hopper due to the blocking of the deflector and its own gravity, and dust pre-separation is implemented.

② Filtration

The dust-containing gas enters the filter bag, and the dust is retained on the inner surface of the filter bag. The dust-containing gas is purified by the filter bag, and the purified gas enters the filter chamber, and then passes through the three-way switching valve exhaust channel and the air outlet pipe, and is discharged into the atmosphere by the exhaust fan.

③ Dust cleaning and automatic control

After the dust collector runs for a period of time, the dust trapped on the inner surface of the filter bag thickens, and the running resistance of the dust collector rises. When it increases to a certain value, the filter bag needs to be cleaned. At this time, the microcomputer instructs the lifting switch valve to close the exhaust channel, and at the same time opens the back blowing pipe. Under the action of the back blower (the direction is opposite to the original airflow direction), the original expanded filter bag is compressed and deformed, remove the dust attached to the inner surface of the filter bag, and the dust will fall into the ash hopper and be discharged through the ash discharge valve. The whole ash cleaning process is carried out in turn in separate rooms without affecting the normal operation of the dust collector.

Examples of 1.3 Equipment Applications

After the successful development of CXIY vertical kiln bag filter, due to its unique advantages, it was quickly recognized by users. The products have been used in Jiangsu, Guangdong, Hebei, Guizhou, Sichuan, Chongqing, Jiangxi, Shandong, Ningxia, Hunan and other places, and have achieved good results.

φ3.0 × 11 vertical kiln originally adopted LFEF vertical kiln dust collector. Due to unreasonable design, since the dust collector was put into operation, the air inlet is uneven and the bag is often burned. The filter bag is replaced only once in more than two months, and the dust emission often exceeds the standard. The factory dismantled the original dust collector in February 2002 and replaced it with a CXIY-3.0 dust collector. After it was put into operation, it has been running synchronously with the main engine. After being tested by the environmental protection department, its dust inlet concentration is 12.3g/m3 and its emission concentration is only 48 mg/m3. Use more than a year, after many checks, has been trouble-free operation. The economic analysis of the plant is as follows:

(1) The installed capacity of the system is 83KW, and the actual consumption is about 65KW. The annual production is calculated on the basis of 300 days. The electricity charge is calculated on the basis of 0.4 yuan/degree, reducing the electricity consumption by 187200 yuan.

4 × 10-9 = 4990t

According to the 70 yuan per ton of dust, the benefit is increased by 4990 × 70=349300 yuan.

(5) The salary of the personnel shall be increased by 15000 yuan/year.

(6) Annual economic increase and decrease 34.93 18.72-3.5-5-1.5=436500 yuan

After adding CXIY shaft kiln dust collector in this way, after deducting all expenses, it can also increase 436500 yuan.

2. Electric dust removal

Electric dust removal is also a high-efficiency dust collection equipment, its biggest advantage is low resistance (<250Pa) and stable. The disadvantage is that the efficiency is greatly affected by the dust specific resistance value, there are accidental emissions, and with the passage of running time, the efficiency is mostly declining. The dry electrostatic precipitator with good performance can achieve smokeless and dust-free emissions in normal weather, which is favored by some owners. Electric dust removal mainly solves the problem of anti-corrosion, adaptation to changeable working conditions and high-voltage insulator condensation and creepage.

Transformation of 4. Dust Precipitator and Centralized Dust Removal of Dispersed Dust Point

1. Transformation of dust collector

The original dust collector shell can still be used, but the internal structure is not good

Use or need to increase the amount of filtered air and other reasons, can be used to leave the shell method for transformation.

2. Centralized dust removal of scattered dust spots

In cement production, there are dust spots all over the whole line from crushing, drying, grinding and burning to packaging. For example, crusher discharge port, warehouse top, warehouse bottom, inlet and outlet, packaging machine, belt conveyor transfer place, elevator entrance or equipment discharge port, etc.

For these scattered dust spots, it is necessary to set the air hood exhaust with appropriate size and height, and the air speed at the suction inlet is> 1 m/s, which can ensure the standard of post concentration ≤ 6mg/m3. There are two specific governance programs:

(1) For those with concentrated dust spots in the workshop, multi-branch suction pipes are used to connect centralized dust collection. The design of the air duct must conform to the principle of reasonable air volume distribution. Sometimes it is necessary to set a regulating valve on the branch pipe with small resistance to adjust the air volume distribution. The dust collector outlet is placed outside the workshop or on the roof to ensure clean air in the workshop. CXQM air box pulse bag dust collector and stand-alone bag dust collector can be used as dust collector.

(2) In addition, for scattered dust spots outside the workshop, it is recommended to use stand-alone dust collection and local treatment. Using CXQM air box pulse single bag dust collector, can realize online dust removal, no moving parts, reliable and continuous high efficiency.

Dust Concentration of Main Dust Source Points in 5. Cement Plant and Selection of Supporting Dust Collector

6. closing remarks

The pollution control of enterprises should be implemented in the whole process of production. The national standard GB4915-1996 that there are detailed regulations on the smoke (or dust), sulfur dioxide, nitrogen oxides (NO2) and fluoride (total fluorine) of air pollution from production equipment, and with the increase of environmental protection efforts, the standards will only become more and more stringent. Each enterprise must choose the proper dust removal equipment according to the existing equipment and dust spots. If the selection is improper, not only will the waste be serious, but also the dust collection will be ineffective and even affect the whole production process. Through the operation of the entire production line dust removal equipment, modern kiln enterprises will also become pollution-free production enterprises.