DG rotary air preheater

DG rotary air preheater 

 

1. Introduction

1.1. Purpose

It is mainly used for boiler in power plant.

1.2. Model meaning

LAP****/####

LAP -- Ljungstrom Air Preheater

****----The diameter of air preheater (mm) shall be determined according to engineering requirements

####---------Height of heat exchange element (mm), determined according to engineering requirements

1.3. Structural features

1.3.1. The form of air top heater. Three common air preheaters are shown in Fig. 4-1 - Fig. 4-3

1.3.1.1. Air and flue gas flow through two separate sectors of the air preheater.

1.3.1.2. Tri-section type. An air preheater is divided into three sectors (primary fan zone, secondary fan zone and flue gas sector).

1.3.1.3. Quarter-section type: an air preheater is divided into four sectors (primary fan zone, two secondary fan zone and flue gas sector).

1.3.2. Structure of air preheater. The structure of air preheater is shown in Fig. 4-4 (for example, tri-section).

The rotor is supported by a thrust bearing in the center of the lower beam and a guide bearing in the center of the upper beam, and is in a nine sided shell; the upper beam and the lower beam are respectively connected with the shell, and the shell is located on the steel frame. The electric drive device is installed on the drive side shell and drives the rotor to rotate through the shroud pin teeth.

When the flue gas flows through the rotor, the flue gas will release heat to the heat storage element, and the flue gas temperature will decrease; when the heat exchange element rotates to the air side, the heat will be released to the air, and the air temperature will rise. In this way, the heat exchange between flue gas and air is realized.

In order to prevent the air from leaking to the flue gas side, radial, axial and bypass sealing devices are respectively set in the radial direction, axial direction and circumferential direction of the rotor upper and lower end radius direction, outer axis direction and circumferential direction. In addition, the rotor central cylinder sealing device and static sealing device are also provided. The sealing system is shown in Fig. 4-5

1.3.3. Heat exchange elements of air preheater. DG has introduced more than 20 series of boards from CE company. Figure 4-6 and figure 4-7 show the commonly used Du and NF plate types, and the DUF plate type shown in Figure 4-8 is the special cold section heat exchanger plate type for denitration air top heat exchanger independently developed by DG.

1.3.3.1. DU plate type. This type of plate is specially used in the hot end of air preheater. It has the best heat exchange performance and can make the flue gas produce turbulent flow in the element. It can prolong the time of flue gas in the element as much as possible to get more heat. For a certain amount of heat exchange, the amount of components required is the least.

1.3.3.2. NF plate type. This plate type is mainly used in the cold end of conventional air preheater, which is generally large corrugated plate type, which makes ash discharge easier, and can prevent corrosion in low temperature section and effectively prevent cold end blockage of air preheater.

1.3.3.3. DUF board type. This plate type is specially designed for denitration air preheater, with high heat transfer efficiency and low resistance characteristics. It can be used in the cold end of air preheater to effectively prevent the blockage of ammonium bisulfate.

1.3.4. Sealing control. The DG seal control system is a double seal and adjustable gap system. The so-called double sealing system means that each sector plate has at least two radial and axial sealing plates at any time when the rotor is rotating to form two seals. The double sealing technology can effectively reduce the direct air leakage of air preheater.

When the air preheater is running in hot state, the mushroom shape deformation will occur, which will lead to the change of the original sealing interface. The seal clearance control system can automatically track and control the hot deformation of the rotor. With the change of the clearance, the system automatically lifts the sector plate to minimize the seal clearance.

In addition to using the gap automatic tracking system at the hot end of the air preheater with large deformation to maintain a small sealing clearance, the principle of minimum sealing clearance during hot operation should also be followed for the cold end sealing clearance reservation.

1.3.5. Air leakage control system of air preheater. Each hot end sector plate is equipped with a set of gap measuring device and a set of fan-shaped plate lifting mechanism. The sensor continuously measures the distance between the sector plate and the flange surface of the air preheater rotor (sealing clearance), and compares the measured value of the gap with the set value for adjustment. The setting range of seal clearance setting value is 0 ~ 9mm, and the resolution is 0.1mm.

In order to ensure the long-term stable operation of the preheater, the non-contact wear-free method is adopted to measure the air leakage gap in the seal room except the regulating system, and the probe cooling air system is set. The measurement and adjustment of the control system are carried out in real time, and the regulation cycle is the time when the air preheater rotor rotates one cycle. The maintenance period of control system is more than or equal to 4 years.

The air leakage control system of air preheater (see Figure 4-9) adopts the control mode of high-performance PLC Combined with industrial computer. The monitoring and operation interface is intuitive, rich and easy to operate. It can display important information such as gap measurement value, set value, main motor current value of air preheater, equipment operation status and alarm signal.

All analog signals and switching signals are input into PLC, and the control function is completed by PLC with high reliability. The upper computer displays and sets the internal adjustment state of PLC through friendly interface. The PLC and the upper computer are connected by RS232 serial communication, and they monitor each other. When one of them fails, the other will give an alarm and has high reliability.

1.3.5.1. The control functions of PLC are as follows: ① real time acquisition, calculation and processing of air preheater clearance signal, giving the clearance state, sending mechanism ascending and descending actions to adjust the air preheater clearance; ② collecting and calculating the current signal of the main motor in real time, giving the over-current signal and adjusting the over-current; ③ Process the button input signals of local cabinet and program-controlled cabinet and give corresponding action signals; process overload and shutdown input signals and give corresponding action signals; ④ detect abnormal shutdown of air preheater rotor and alarm.

1.3.5.2. The functions of the upper computer are as follows: ① read dynamic gap value and current value from PLC, and display them in bar graph and digital form at corresponding positions on the screen; ② read clearance adjustment, over-current adjustment action signals and program control cabinet button operation signals from PLC, and display them in the form of pictures at corresponding positions on the screen; ③ It can realize the setting of the given value of gap and current, and transmit it to PLC; 4) record the fault every day; 5) display the history curve of gap signal.

1.3.6. Fire alarm system. DG fire alarm system (HSDS) adopts advanced infrared detection technology, which can detect the infrared radiation energy of the air preheater in real time and accurately under the running state of the air preheater, so as to monitor the temperature field distribution inside the air preheater. When the temperature in the air preheater is too high and the radiation of infrared energy exceeds the normal range. The system sends out alarm signals to warn the operating staff to take corresponding measures in the early stage of fire. The whole system adopts advanced measurement and control technology. The practice shows that the system has high reliability under the operating environment of air preheater, and is suitable for the matching use of various capacity of Ljungstrom Air preheater.

The composition of the fire alarm system is shown in Figure 4-10. The system adopts linear moving integral mechanical mechanism, which is composed of power drive mechanism component, chain transmission mechanism, moving position control switch and sensor sheath. The whole machine has good sealing performance and stable operation. The infrared detection protective suit has a jet nozzle, which can blow dust and clean the infrared lens when the whole machine is running.

The electric control part of the system consists of a main control cabinet arranged in the central control room and two local operation boxes arranged locally. The temperature measuring points of the system are arranged with several thermocouples at the upper part of the preheater and two infrared sensors at the lower part of the preheater. The main performance indexes of the system are shown in table 4-1.

Item	performance index	Item	performance index
Measure temperature (℃)	0 ~ 500	Electronic control sampling resolution (mV)	2.4
Working band (μm)	8 ~ 14	Response time of electronic control sampling (μs)	<100
Max.measure target (mm)	φ40	Fire judgment time (s)	<52
Response time of infrared probe (ms)	<300	Baud rate	9600

1.3.7. Driving device of air preheater. The transmission mode of air preheater is divided into national belt drive and center drive.

1.3.7.1. Belt drive mode. The driving motor maintains the rotation of the air preheater by meshing the big gear of the output shaft of the reducer and the shroud pin of the rotor of the air preheater. When the main motor and auxiliary motor are in interlocking operation, one auxiliary motor is used for interlocking operation, and one auxiliary motor is used for interlocking operation. The auxiliary motor can also be replaced by pneumatic motor or DC motor.

1.3.7.2. Central transmission mode. Each reducer is equipped with main motor and auxiliary motor. The main motor adopts the auxiliary power supply, and the auxiliary motor adopts the security power supply. Some projects are also equipped with auxiliary pneumatic motor, and the air preheater reducer adopts three shaft mode. The central driving mode is that each air preheater is equipped with a frequency conversion control cabinet, and the main and auxiliary motors are controlled by separate frequency converters. The main and auxiliary motors are electrically interlocked. When one motor fails, the other will be put into operation automatically. Both the main and auxiliary motors can be used to start the air preheater with variable frequency speed regulation. When the motor runs to the rated speed, the frequency converter is disconnected and the motor is switched to the power frequency power supply.

1.3.8. Soot blower. The soot blower mainly includes steam soot blower, dual medium soot blower and gas pulse soot blower.

1.3.8.1. Steam soot blower. For conventional air preheater, the soot blower is semi telescopic. The soot blower is driven by rack and pinion, which can move along the radial direction to cover the whole heat exchange surface. There are several nozzles on the soot blowing pipe. The number of nozzles depends on the diameter of the rotor. During soot blowing, the soot blower moves slowly and gradually along the radial direction of the rotor until the whole heat exchange surface is covered. The soot blowing medium is 350℃ superheated steam and the pressure is 1.2 ~ 1.5MPa. According to the characteristics of fuel, soot blowing at cold end or soot blowing at both cold and hot ends of air preheater can be adopted.

1.3.8.2. Dual medium soot blower. For denitration air preheater, a common steam valve soot blower is generally set at the upper part of the air preheater, and a double medium soot blower with steam and high pressure water is set at the lower part. High pressure water parameters are generally 10 ~ 20MPa, steam parameters are 1.2 ~ 1.5MPa, 350℃ superheated steam.

1.3.8.3. Gas pulse soot blower. The principle of gas pulse soot blowing technology is that the air and combustible gas are mixed in a special container, and then they are put into the pulse tank. After being ignited by high-frequency ignition, deflagration occurs in the pulse tank, and the volume expands rapidly to generate high-temperature and high-pressure gas, and the dust is removed in the form of chemical energy and shock wave. The gas pulse soot blower is equipped with an independent control system.

1.3.9. Bearing lubricating oil system. Forced lubrication is adopted, and each bearing of air preheater is equipped with a separate lubricating oil station. Double system structure is adopted for guide bearing oil, one for operation and one for standby; single pump structure is adopted for thrust bearing oil station. The oil inlet pipe is connected with the bearing oil inlet pipe to form a half closed oil circulation system. The lubricating oil station has the function of filtering and cooling the bearing lubricating oil, which can prolong the service life of the bearing. The lubricating oil station system consists of oil pump, oil temperature measuring point, mesh type oil filter, tubular oil cooler, bimetal thermometer, pressure gauge, pipeline, valve, flow meter, etc. The cooling water is general industrial water, the pressure is 0.3-0.5mpa, and the cooling water consumption is about 70kg / min.

The control of lubricating oil station can adopt PLC local control and ICs centralized control. When the bearing lubricating oil temperature is 55℃, the oil pump starts; when the oil temperature drops to 45℃, the oil pump stops; when the oil temperature exceeds 70℃, the system sends out an alarm signal of high oil temperature.

1.4. Technical level

As an important part of boiler, air preheater can use a lot of heat energy in waste flue gas to preheat the cold air in the boiler, so as to improve the boiler efficiency and save fuel. Reducing air leakage and preventing corrosion and blockage of air preheater are the most important problems in the development of air preheater.

DG began to develop rotary air preheater in 1960s. In the early 1980s, the company introduced a complete set of design and manufacturing technology of Ljungstrom Air Preheater from CE company in the United States, and strengthened the technical cooperation and development with domestic colleges and universities. The rotary air preheater designed and manufactured by DG has achieved good operation performance and more than 100 air preheaters have been put into operation.

The development of air preheater has experienced the following stages:

1.4.1. The first stage (1960-1985): domestic cooperation and self-development.

1.4.2. The second stage (1982-1983): in order to cooperate with the development of large-scale boiler, the design and manufacturing technology of a complete set of rotary air preheater was introduced from CE company, and the first three compartment rotary air preheater with 300MW unit in Zouxian project was successfully designed and manufactured.

1.4.3. The third stage (1983-2000): through years of digestion and absorption of imported technology and rich field operation experience, the hot end sector plate air leakage control system and infrared fire alarm system were developed.

1.4.4. The fourth stage (2000-2002): a large number of applications of double sealing technology have been successfully used in the 200MW boiler project of Guangdong Hengyun Power Plant and the 300MW boiler project of Guizhou Anshun and their follow-up projects. The air leakage of air preheater is lower than the contract requirements. At the same time, the unique lower center frequency conversion drive technology has been developed and successfully applied to the air preheater of Heshan 300MW boiler and its follow-up projects.

1.4.5. The fifth stage (2002-2006): the first 600MW boiler air preheater in Qinbei, the four compartment air preheater of Qinhuangdao 300MW CFB boiler, the air preheater of 100MW boiler in Zouxian county and the 300MW flue gas heat exchanger (GGH) in Xutang were developed. Combined with the field operation experience, a new type of radial sealing control system at the hot end was developed, and the field input rate was more than 90%.

1.4.6. The sixth stage (from 2006 to the present): the denitration air preheater suitable for the boiler equipped with denitration device is developed, and the new type of DUF plate type is adopted for the cold section heat exchange element. With the development of electronic component technology, the field input rate can reach more than 99% after further optimization of the hot end radial seal control system.

 

2. Main technical parameters

The main technical parameters of air preheater are shown in Fig. 4-11 and table 4-2.

Table 4-2  Main technical parameters of the air preheater  (mm)

Parts dimensions	135MW	200MW	300MW	600MW	1000MW
A	7930	8650	10320	13494	17286
B	9120	9904	12104	15282	19278
C	9830	10544	12222	15396	19432
D	7772	5800	6718	8305	10198
E	0	2275	2756	4343	6236
F	2985	3353	3823	5410	7144
G	0	1430	1727	2794	3810
H	2985	3353	3823	5410	7144
I	7772	8458	10084	13258	17044

 

3. Selection method

3.1. Data required for type selection of air preheater

3.1.1. Flue gas flow direction.

3.1.2. The number of air preheaters matched with one boiler.

3.1.3. Altitude and atmospheric pressure

3.1.4. Fuel composition of boiler.

3.1.5. Mass flow of flue gas population of air preheater

3.1.6. The mass flow at the secondary air outlet of the air preheater, and the mass flow of the primary air outlet of the three compartment air preheater shall also be provided.

3.1.7. Ambient humidity and temperature range and average value.

3.1.8. Flue gas inlet temperature.

3.1.9. Flue gas temperature under the assessment condition.

3.1.10. The temperature of the secondary air at the inlet and the temperature of the primary air at the inlet of the three compartment air preheater shall be provided.

3.1.11. Temperature of primary air entering the pulverizer.

3.1.12. Heating method of inlet air temperature, hot air recirculation or air heater.

3.1.13. Pressure difference between primary and secondary air.

3.1.14. Requirements for air leakage rate.

3.1.15. Boiler simultaneous denitration or reserved denitration.

3.2. Site conditions

3.2.1. Power supply voltage, phase and frequency of power plant.

3.2.2. Temperature and pressure of soot blowing medium in power plant.

3.2.3. Pressure and temperature of water source of power plant.

3.2.4. Compressed air parameters of power plant.

3.3. Scope of supply and requirements

3.3.1. Design and supply limits of air preheater.

3.3.2. Material requirements of air preheater.

3.3.3. Type and quantity of soot blowers.

3.3.4. Types and requirements of driving device.

3.3.5. Transportation and packaging requirements.

3.3.6. Other special requirements.

 

4. Selection examples

4.1. Material of air preheater for typical coal fired boiler

The material of air preheater of typical coal-fired boiler is shown in table 4-3 for reference only.

Table 4-3 material of air preheater for typical coal fired boiler

Item	Material	Item	Material
Heating element of hot layer	High quality low-carbon steel	Center drum and short shaft	42CrMoA、45
Heating element of cold layer	Low alloy corrosion resistant cordon steel or enamel components	Up and down beam	Low carbon steel
Housing	Low carbon steel	Bearing support	QT500-5、ZG230-450
Modular basket	Low carbon steel	Sealing sheet	Low alloy corrosion resistant Corden steel

4.2. Air preheater matching example of typical 600MW unit

See table 4-4 for working medium parameters of air preheater of 600MW unit.

Table 4-4

Item	Flow (kg/s)	Temperature （℃）	Item	Flow (kg/s)	Temperature （℃）
Flue gas at inlet	680	379	Primary air entering the mill	110	298
Secondary air entering the boiler	522	350	Ambient temperature	___	20

4.2.1. Heat exchange area of each air preheater: 109686m²

4.2.2. Net weight of each air preheater: 666000 kg.

4.2.3. Rotation direction of rotor: flue gas - secondary air - primary air.

4.2.4. Air preheater model: LAP13494 / 1900.

4.2.5. Quantity of air preheater: 2 sets.

 

5. Scope of supply and ordering instructions

5.1. Scope of supply (standard scope, which can be deleted according to the needs of users)

The scope of supply includes product design, procurement, manufacturing, factory testing, installation and commissioning drawings and operation and maintenance manual.

5.1.1. Plant and equipment:

5.1.1.1. Rotary air preheater body.

5.1.1.2. Driving device and turning gear.

5.1.1.3. Metal outer guard plate

5.1.1.4. Lubricating oil system (including oil pipeline).

5.1.1.5. Soot blower.

5.1.1.6. Fire fighting and cleaning equipment.

5.1.1.7. Temperature measuring components.

5.1.1.8. Automatic clearance control device.

5.1.1.9. Fire alarm device.

5.1.1.10. Shutdown alarm device.

5.1.1.11. Special tools.

5.1.2. Supply boundary:

Wind side. From the inlet flange of air preheater to the outlet flange of air preheater.

Smoke side. From the inlet flue flange of air preheater to the outlet flue flange of air preheater.

5.1.2.3. Connection point between air preheater support and boiler steel frame of power plant, including connecting bolts.

5.1.2.4. Steam pipe flange of soot blower (including matching flange and accessories).

5.1.2.5. Fire fighting and cleaning pipe flange stop (including matching flange and accessories).

5.1.2.6. All motor power supply parameters.

5.1.2.7. Junction box of bearing oil temperature measuring element of air preheater.

5.1.2.8. Bearing cooling water interface.

5.1.2.9. Compressed air interface.

5.2. Technical specification for air preheater

5.2.1. The supplier shall evaluate the design of various air preheaters, and select the most suitable model considering the operating conditions and the most important economic factors.

5.2.2. Heat exchange elements.

5.2.3. Type and quantity of soot blowers.

5.2.4. Type of driving device.

5.2.5. Type of bearing.

5.2.6. Air leakage performance (within 1 year / after 1 year).

5.2.7. The air preheater shall be protected from low temperature corrosion and blockage,

5.2.8. Fire monitoring and fire fighting.

5.2.9. Equipment overhaul and maintenance requirements.

5.2.10. Form of thermal insulation and outer guard board.

5.2.11. Control and instrumentation.