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Howden centrifugal fan

key word:Heat exchange element

Category:


Product description

Howden centrifugal fan

 

1. Equipment introduction

1.1. Purpose

Centrifugal fan is the most widely used large industrial fan. Since Howden began to manufacture centrifugal fans in the 19th century, the development of centrifugal fans has experienced more than 100 years. Due to the advantages of wide load coverage, good wear resistance and corrosion resistance, high reliability and good design flexibility, centrifugal fans are widely used in air supply and induced draft sites with harsh conditions such as mine, metallurgy, petrochemical, cement, papermaking and power station. Although axial flow fan and mixed flow fan are also developing continuously, centrifugal fan is still the main equipment for power station boiler, especially circulating fluidized bed boiler. Figure 11-1 shows the application of centrifugal fan in thermal power plant.

Howden centrifugal fan has a large number of impeller blade forms, each product is designed according to the specific parameters of customers: therefore, Howden can ensure that each fan has high efficiency and high reliability to meet the needs of different working conditions. In the thermal power plant, although the fan is an auxiliary equipment, it is indispensable and irreplaceable for the power production. Therefore, the reliable operation of fans is an essential condition for thermal power production; the efficiency of fans (reflected in the shaft power of fans) directly affects the cost of power generation, and high reliability and high efficiency are the direct targets of fans in power stations.

1.2. Model meaning

There are many types of Howden centrifugal fan, each model has a clear application purpose. According to the needs of customers and combined with the site conditions, Howden fan has achieved the optimal design from blade form, inlet mode to air conditioning mechanism.

The model and significance of Howden centrifugal fan are as follows:

L3N 3750 0208 D B L 6T

L3N-- Fan impeller/design type of impeller

3750 -- standard diameter of impeller

0208 --- adjustment coefficient of fan diameter and width

D -- number of suction ports (D for double inhalation, S for single inhalation)

B --- inlet type (B is inlet box, O is open type)

L --- adjustment mode (L is inlet box guide vane regulation, V is inlet diameter guide vane adjustment)

6T --- support form (6T is double support, 4T is cantilever support; T is normal curve, F is no negative deviation curve)

1.3. Characteristics of Howden centrifugal fan

1.3.1. Overall structure. The fan is composed of several parts, any one of which may affect the performance of the fan. However, the concept of fan performance (mainly in efficiency) of various fan manufacturers is different. Some manufacturers (such as Howden) put forward the overall efficiency of the fan, that is, the comprehensive efficiency including the rotating parts and static parts; some manufacturers did not include some internal losses of the fan, such as the loss of the inlet box, when providing the efficiency of the fan. In this case, the actual efficiency of the whole fan will be far lower than the efficiency proposed by the manufacturer. No matter what kind of expression, the shaft power of the fan can truly reflect the comprehensive performance of the fan. Therefore, for customers, the most direct reflection of the overall performance of the fan is the shaft power of the fan.

The overall structure of Howden centrifugal fan is shown in Fig. 11-2.

Among them, the main shaft, impeller and coupling of the fan are all rotating parts, and the bearing is the supporting structure of these parts. They are the key parts of the fan, and their performance is directly related to the safety and reliability of the fan operation. The blade form and impeller structure are the important factors to determine the output parameters of the fan, and their reasonable design is the premise to ensure the efficient operation of the fan.

The casing, inlet box, inlet regulating device and collector are non rotating parts, which are usually called static parts. The structure and aerodynamic characteristics of static parts are directly related to the performance of the fan. It is an indispensable part of the fan, and its performance will affect the overall performance of the fan.

1.3.2. Wide performance range. Howden centrifugal fans have many impeller / blade forms (see Figure 11-3), which can meet various pressure and flow requirements. Due to the variety of forms, Howden can choose the most suitable impeller for the specific parameters of customers, which is the fundamental factor for Howden fans to maintain relatively high efficiency in various applications. The maximum flow rate of Howden centrifugal fan can reach 1000m3 / s, and the maximum single-stage head can reach 60kpa; according to the needs of customers, Howden fan can also have good performance of high temperature resistance and wear resistance.

The impeller / blade forms of Howden fan are mainly organic wing blade, backward curved arc plate blade, backward curved straight plate blade, etc. each blade form has a series of product models. The brief introduction is as follows:

① Wing shaped blade. This type of blade was invented by Howden more than 50 years ago. It has good mechanical strength and high aerodynamic efficiency. It is very suitable for applications with large flow rate and small head. The fan is widely used in various industries of mine ventilation, process cooling air supply and boiler induced air system.

② Back curved arc plate blade. Howden has developed a series of backward curved arc plate blades. The fans of each blade have the characteristics of high efficiency, compactness and wear resistance. Due to its many advantages, the fan is widely used in metallurgy, cement, paper industry and other extremely harsh conditions, but also suitable for power plant boiler primary air, secondary air and other places with high head requirements

③ Back curved straight blade. The blades of this series have the advantages of simple structure, wear resistance, easy maintenance, and not easy to deposit ash, so they are widely used in the occasions of induced air and exhaust air under bad working conditions.

In addition, Howden has developed radial blade, forward curved arc plate blade and backward curved radial inclined blade. These blades have the advantages of high strength, strong abrasion resistance, and not easy to deposit ash

1.3.3. Set up a good regulatory performance. Howden fan has good control performance. The fan itself can be equipped with inlet box guide vane regulating baffle or inlet diameter guide vane adjusting device (see Fig. 11-4). Generally, the fan adopts the inlet box regulating baffle plate to adjust; the regulating baffle is installed at the inlet of the fan inlet box, and the opening angle of the baffle blade is controlled by the actuator to adjust the fan flow. Similarly, the angle of the guide vane is controlled by the actuator to achieve the purpose of regulating the flow. But different from the inlet baffle, the inlet diameter guide vane is installed near the impeller inlet, which makes the whole fan more compact, thus saving the space on site. This is a very reasonable layout for the renovation project with extremely limited space.

Due to the inherent characteristics of centrifugal fan. When the guide vane is used to regulate the fan, the efficiency under partial load is always lower than that under full load, and the smaller the opening angle of the guide vane (i.e., the smaller the load), the lower the efficiency. Therefore, for the same fan, the efficiency of inlet box guide vane regulation is higher than that of inlet diameter guide vane regulation at full load; However, the efficiency of inlet box guide vane is lower than that of inlet diameter guide vane at low load (i.e. the opening of splitter is smaller).

In addition, the fan load can be adjusted by regulating the speed of the fan. Because the speed of the fan is adjusted to avoid the air loss when the inlet box guide vane or the inlet diameter guide vane is small angle, the fan can always be in high-efficiency operation state. For example, the use of hydraulic coupling, variable-speed motor, variable-speed steam turbine, etc., can achieve the adjustment of fan speed. The hydraulic coupling itself has the advantages of isolating shaft vibration, stable starting and convenient clutch. However, due to the existence of transmission loss and slip loss, the effect of hydraulic coupling used in fan energy saving is not ideal.

At present, there are two types of variable speed motor, namely, two speed motor and variable frequency motor. If the fan is driven by a two speed motor, the temporary high-speed operation of large load and low-speed operation of small load can be realized, so as to achieve the purpose of saving energy at low-speed and small load compared with single speed fan. However, because there are only two rotating speeds, the capacity of fan regulation by variable speed is quite limited, and the corresponding energy saving effect is also limited. Compared with this, the adjustable performance of variable frequency motor is very strong. As long as it is within the speed range of frequency converter and variable frequency motor, any fan speed can be realized. Therefore, the fan can operate efficiently at all operating points. However, the initial investment of frequency converter is very large, the cost recovery cycle is long, and the frequency converter itself is also a power consumption equipment, its operation and maintenance need a considerable cost.

Similar to variable frequency motor, steam turbine can also realize variable speed regulation in a wide range. When the shaft power of the fan is large and there is abundant steam source in the plant where the fan is installed, it is a good choice to use steam turbine drive. For example, many manufacturers in petrochemical industry choose this configuration.

If the fan adopts variable speed regulation, the shafting analysis of fan and driving equipment is more important. Howden can perform a complete shafting analysis to ensure the safety of the fan shafting regardless of the drive equipment selected.

The performance curve of centrifugal fan with different regulating devices is shown in Figure 11-5

1.3.4. High efficiency and high reliability. Howden centrifugal fans have always been known for their high efficiency and reliability. Due to the needs of production industry, users may face various difficult parameters and harsh working conditions, but they can always find the best solution in Howden's rich models. After determining the model, Howden will carry out the selection calculation and specific design according to the customer's parameters, so as to obtain the most matching impeller diameter, the most appropriate diameter and width correction factor, and other appropriate configuration. The fan designed in this way naturally has high efficiency and high reliability.

For example, for the induced draft fan of power station, according to its parameter characteristics and medium characteristics, firstly, it is determined that the fan with wing blade or back curved arc plate is more suitable; secondly, the model size with the highest efficiency is calculated according to the specific parameters, and then the final type selection can be obtained according to the user requirements and site conditions, such as Z9B 2357.00.02 SBL6T, 985rpm, After the final model selection is determined, the design engineer will carry out the impeller stress analysis, shafting analysis, casing strength analysis, etc., and specifically implement the calculation and model of other components, such as coupling, bearing, actuator, etc.

Consistent with precise design is Howden's advanced manufacturing process and efficient quality management mechanism. Howden is equipped with advanced processing and welding equipment and complete manufacturing process. Its products have passed the Lloyd's ISO 9000 certification, which is the certification of the top organization in quality management. The overall efficiency of Howden centrifugal fan is as high as 87%. In terms of reliability, the Drax power station in the UK is equipped with a Howden fan, which has no accident in continuous operation for 19920h, and the reliability is as high as 99.66%; while the Howden fan operating in the British Ratch-liffe power station has no accident after 23816h continuous operation, with the reliability of 99.70%.

At present, with the development of industrial production process, the flow rate of gas to be transported is increasing, and the pressure head is also required to be higher, which means that the capacity of centrifugal fan to transport gas must be continuously enhanced. In order to meet the new requirements, Howden introduced the most advanced FEA technology (computer finite element analysis) and CFD Technology (computer-aided fluid dynamics design) into the development and design of fans (see Figure 11-6). The use of advanced technology further ensures the high efficiency and reliability of Howden fan.

1.3.5. Design flexibility. Howden centrifugal fan has good design flexibility and can provide the most effective solution according to the specific needs of users. The inlet and outlet of Howden centrifugal fan can be at any angle; the impeller of the fan can be added with special protective material plate; the fan in cold zone is equipped with bearing oil pool heating device; the inlet pipe or outlet pipe of the fan can be equipped with muffler, gas heater, etc. (see Fig. 11-7). In short, Howden can always provide flexible and effective solutions for the needs of customers. For example, Howden can make the following design for impeller protection:

1.3.5.1. Add lightweight partial lining plate to induced draft fan impeller of power station.

1.3.5.2. The impeller of sintering fan in iron and steel industry is provided with bolt on lining plate which is easy to replace.

1.3.5.3. Add high temperature resistant composite wear-resistant lining plate to the high-temperature fan at the cement kiln tail.

1.3.6. Professional installation. The installation of centrifugal fan is very important. Improper installation will cause excessive vibration, bearing temperature is too high, which will lead to bearing damage, shaft or coupling fracture and other malignant accidents. Therefore, the installation of centrifugal fan must be carried out under the guidance of professionals, so that the whole process can be well controlled. Figure 11-8 shows the professional installation of Howden centrifugal fan.

1.3.7. Convenient and quick on-site maintenance. Due to Howden's unique design, centrifugal fans require very little maintenance. At present, as long as the load of the rotor is optimized reasonably, and the best bearing and bearing box with reasonable design are selected, the lubricating oil station can be exempted, and even the cooling water is not required; The bearing can still keep good operation condition under natural cooling condition, and the design life of bearing is far beyond the requirements of JB / T 4358-2008 "Centrifugal Fan of Power Plant Boiler". Figure 11-9 shows the maintenance free design of centrifugal fan.

For the general purpose of the power station fan, under normal circumstances, as long as regular inspection of the bearing oil level, if necessary, change the lubricating oil. Even in the overhaul of power station, the maintenance work of Howden fan is very little; under normal conditions, only the shaft seal and lubricant of fan need to be replaced.

1.3.8. Shaft power and operating cost of wind turbine. With the increasing attention to environmental issues and the increasingly stringent requirements of the state in energy conservation and emission reduction, the power generation cost of power stations is becoming more and more important. Howden wind turbine can reduce the power consumption in the process of power generation, thus reducing the cost of power generation, thus producing good economic and social benefits.

For example, for a centrifugal fan with a certain parameter at the same location, the shaft power of one fan is 2800KW, while that of another is 3077kw. If the fan is in full load operation, the fan with small shaft power will save 3077-2800 = 277kw. If the annual operation time is 6000h, the electricity charge is calculated as 0.4 Yuan / kW · h), the annual cost saving is 277 × 6000 × 0.4 = 664800 Yuan, that is about 665000 Yuan.

Even if the fan is always in partial load operation, the energy saving characteristics of the fan with small shaft power is very obvious. For the above example, when the fan is in partial load operation, the shaft power of the fan with small shaft power is 140kW less than that of the fan with large shaft power, and the cost can be saved in one year: 140 × 6000 × 0.4 = 336000 Yuan, that is 336000 Yuan.

From the above example, it can be seen that the use of efficient centrifugal fan is a good means of energy conservation and emission reduction, and also an effective way to reduce the cost of power generation. Even in the stage of engineering design bidding, users can draw this conclusion by comparing the shaft power of fans.

1.4. Working principle

When the impeller of the centrifugal fan rotates, the air flow is "dragged" by the blades to rotate; at the same time, due to the centrifugal force, the air flow will accelerate to fly out along the radial direction. The working principle of centrifugal fan is shown in Fig. 11-10.

The airflow enters the impeller along the axial direction, and then flies out along the radial direction after passing through the impeller. Therefore, in order to collect the air flow, the casing of centrifugal fan must be designed as volute.

Due to the difference of working characteristics, generally speaking, the pressure head produced by centrifugal fan is higher than that of axial flow fan and mixed flow fan.

 

2. Main technical parameters

When purchasing centrifugal fans, users should provide the following parameters:

2.1. Local atmospheric pressure or altitude.

2.2. Working environment temperature of fan.

2.3. Fan inlet pressure (absolute pressure or relative pressure).

2.4. Medium flow at fan inlet (actual flow or standard flow).

2.5. Medium density at fan inlet (actual density or standard density).

2.6. Medium temperature at fan inlet.

2.7. Total pressure rise or static pressure rise of fan.

2.8. Dust content of fan medium.

In addition, if the medium is corrosive or toxic, the user should also be clear, so that the fan designer can take relevant measures.

 

3. Equipment appearance and structural dimensions

As Howden large centrifugal fans are all designed according to the specific parameters of customers, the sizes of fans provided by Howden to each customer are different. The outline structure of Howden centrifugal fans is shown in Fig. 11-11 and Fig. 11-12.

 

4. Selection method

Howden fan selection adopts computer technology, so it can give the fan selection as quickly as possible after receiving the customer's parameters, and each model selection can be accurate.

4.1. Selection example of 300MW CFB fan

The selection parameters of typical 300MW CFB fan are shown in table 1L-1.

Table 11-1 selection parameters of typical 30omw CFB fan

Fan application Item TB Working condition BMCR Working condition
Primary air fan Inlet air flowm3/s) 79 63
Total pressure rise of fanPa) 28860 22200
Inlet air temperature () 19.8 19.8
Inlet air densitykg/m3) 1.06 1.06
Secondary air fan Inlet air flowm3/s) 98 85
Total pressure rise of fanPa) 15700 11400
Inlet air temperature () 19.8 19.8
Inlet air densitykg/m3) 1.06 1.06

According to the selection parameters of typical 300MW CFB fan, the selection results are shown in table 11-2.

Table 11-2 selection results of typical 300MW CFB fan

Fan application Fan model Speed (r/min) Motor power(kW)
Primary air fan L1 2484 1485 2800
Secondary air fan L3N 1952 1485 2000

 

4.2.600MW CFB fan selection example

The selection parameters of typical 600MW CFB fan are shown in table 11-3.

Table 11-3 selection parameters of typical 600MW CFB fan

Fan application Item TB Working condition BMCR Working condition
Primary air fan Inlet air flowm3/s) 172.6 135.3
Total pressure rise of fanPa) 30200 21400
Inlet air temperature () 17.6 17.6
Inlet air densitykg/m3) 1.16 1.16
Secondary air fan Inlet air flowm3/s) 198.6 154.6
Total pressure rise of fanPa) 13800 10060
Inlet air temperature () 17.6 17.6
Inlet air densitykg/m3) 1.16 I.16

According to the selection parameters of typical 600MW CFB fan, the selection results are shown in table 11-4.

Table 11-4 selection results of typical 600MW CFB fan

Fan application Fan model Speed (r/min) Motor power(kW)
Primary air fan L3N 2330 1490 6100
Secondary air fan L3N 2838 990 3400

 

5. Scope of supply and order requirements

5.1. Scope of supply

The scope of supply of centrifugal fan can be determined according to customer requirements. Normally, the scope of supply includes the fan body and some other accessories. The body part of each fan shall include the following parts:

5.1.1. Rotor (1 set, including fan impeller and shaft).

51..2. Collector (1 single suction fan, 2 double suction fans).

5.1.3. Casing (1 piece).

5.1.4. Intake box (1 single suction fan, 2 double suction fans).

5.1.5. Shaft seal (2 pieces).

5.1.6. Guide vane of fan inlet box (1 set, corresponding to fan suction).

5.1.7. Bearing and bearing box (one for driving end and one for non driving end).

5.1.8. Bearing base (one for drive end and one for non drive end).

5.1.9. Fan bearing vibration and temperature measurement equipment (1 set).

5.1.10. Coupling (1 set, between fan and driven equipment).

5.1.11. Fan regulating door actuator (1 set).

5.1.12. Shield (1 set, covering coupling and shaft).

5.1.13. Anchor bolt (1 set, fixing the casing inlet box and bearing base).

5.1.14. Matching fasteners for fan body assembly.

5.1.15. Fan name plate.

5.1.16. Other components necessary for the operation of the fan itself.

5.1.17. After sales service (including installation guidance and equipment training).

5.1.18. Drawings, installation, operation and maintenance manual.

Among them, the casing and all intake boxes shall be equipped with access doors, and all equipment shall be provided with surface protection (such as painting or greasing).

In addition to the fan body, it can also provide driving equipment (such as motor, steam turbine, hydraulic coupling, etc.), inlet and outlet expansion joint, muffler, transition air duct, etc. according to the user's requirements.

5.2. Order requirements

When ordering fans, users should not only specify the working parameters of the fans, but also point out the basic information of the projects where the fans are supplied (for example, whether they are new projects or renovation projects), and limit the scope of supply (for example, whether to provide complete fan body, plus driving equipment and other auxiliary equipment). If there are requirements for the brand of the purchased parts, it should be clear.

Usually, the user and the supplier will sign a supply agreement (technical agreement), which will specify all the above contents. The supply agreement is the basis of technical exchange between the supplier and the supplier, and also the basis for the supplier to design and supply goods. For the fans of power station, there are ready-made technical agreement templates for reference, and the contents of these templates have covered the basic information that users and suppliers need to hand over.