Boiler air heater

Boiler air heater

 

1. Introduction

The boiler air heater generally includes two parts: the heater body and the matching automatic control device.

1.1. Application

Boiler air heater is a kind of boiler auxiliary equipment which uses steam as heat source to heat air. It is mainly used in power plant boilers. Figure 26-1 shows the boiler air heater system.

The basic function of the air heater is to use the steam extraction of the steam turbine to heat the inlet air of the boiler, convey the heated air into the air preheater, and then improve the wall temperature of the cold end by increasing the inlet air temperature of the air preheater, so as to prevent low-temperature corrosion. Therefore, the air heater is necessary for the boiler; at the same time, due to the role of steam extraction and heat recovery, the air heater may also play a role in reducing coal consumption.

1.2. Model meaning

1.2.1. Type of air heater.

GN LCB – 1.2 / 300 – 350

GN LCB -- GN refers to boiler heater; L or W indicates vertical or horizontal arrangement; G or C or X respectively indicates that the connection between heat transfer pipe fittings and heater shell is fixed type, drawer type or rotary type; B or S indicates that the arrangement structure of heat transfer tube bundle is parallel type or serpentine type

1.2 --- steam (or water) side design pressure (MPa)

300 -- design temperature

350 --- heat exchange area

1.2.2. Model of automatic control device matched with air heater.

ZDC - 1AS

ZDC -- automatic control device of air heater

1AS-1 or 2 represents DCS system calculation and control or electric actuator local calculation and control respectively; A or B or C represents Shanghai control valve or Germany Samson control valve or other specified control valve respectively; S or Y refers to electric actuator or other specified actuator imported from Shanghai PS technology

1.2.3. Structural features

1.2.3.1. Structural form. It can be seen from the above that the heater can be roughly divided into vertical and horizontal forms.

1.2.3.1.1. Vertical (see figure 26-2). When the air heater is arranged in the horizontal air duct, it should be designed as vertical.

1.2.3.1.2. Horizontal (see figure 26-3). When the air heater is arranged in the vertical air duct, it should be designed as horizontal.

1.2.3.2. Heat exchange elements of air heater. The heat exchange element is the key part of the air heater, and its heat exchange capacity must be guaranteed. At present, fin tube is often used as heat exchange element of air heater.

1.4. Technical level

Because there are some problems in the design, manufacture and operation of the heater, the problems of leakage, ash blockage and water hammer often occur in the actual operation of the air heater.

SPERI has been developing and improving the air heater since 1987. For example, on the basis of the traditional heater body equipment and combined with modern control technology, SPERI creatively developed the drainage side regulation technology (the technology has obtained the national patent), so that the products of the Institute have developed into a mature product series, and the users have reached hundreds of home appliance factories. The regulating technology of the body and drain side of the air heater has the following characteristics:

1.4.1. Features of boiler heater body.

1.4.1.1. The air heater adopts a complete drawer structure. The frame of the air heater is directly welded with the air duct. The heat transfer tube bundle can be drawn out from the side (steam inlet side). Therefore, the maintenance and operation are very convenient and can be completely sealed when it is in place after maintenance. The conventional air heater is connected with the air duct flange, and the original seal cannot be maintained with the air duct after maintenance.

1.4.1.2. The frame of air heater adopts channel steel structure, which can effectively reduce the vibration caused by the increase of air duct resistance; the conventional connection between angle steel flange and air duct is too thin and easy to cause vibration.

1.4.1.3. The heat exchange element of the air heater can be completely absorbed in the body, so as to avoid the leakage of the heater caused by the uneven expansion due to the different temperature difference between the pipe banks. The thermal expansion can not be considered at the steam inlet and drainage outlet. The conventional heater adopts the expansion mode of drain side, and the thermal expansion must be considered at the interface.

1.4.1.4. The steam inlet and drain outlet of the air heater are arranged on the same side to ensure that the drain header is condensate and the steam header is steam. Meanwhile, the water hammer and noise caused by water hammer are avoided, thus the space required for pipeline layout can be effectively utilized.

1.4.2. Features and economy of automatic control device of air heater:

1.4.2.1 the drain side automatic control technology of air heater is a patented technology of SPERI.

1.4.2.2. The automatic control device of air heater can effectively offset the influence of environmental temperature change, and control the metal wall temperature of cold end at air inlet end of boiler air preheater to 73 ℃ constant temperature (adjustable by users), so as to dynamically control low-temperature corrosion of boiler.

1.4.2.3. With the increase of the ambient temperature, the temperature rise of the air heater decreases and the steam consumption decreases. According to the annual operation of 2000 weighted calculation, one unit can save hundreds of thousands of yuan or even millions of yuan in one year (it will be different according to the requirements of units and technical parameters).

1.4.2.4. With the increase of the ambient temperature, the output of the air heater automatically decreases, and the outlet air temperature of the air heater remains unchanged. Therefore, the exhaust gas temperature of the boiler will not increase with the increase of the ambient temperature, thus effectively improving the efficiency of the steel furnace.

1.4.2.5. Steam side control is adopted for conventional air heater (including imported unit), which has high investment cost and can not be adjusted in actual operation.

 

2. Main technical parameters

Main technical parameters of air heater are shown in table 26-1

Table 26-1 main technical parameters of air heater

Unit capacity	Air type	Heating air volume	Air duct size	Air temperature rise	Heat transfer area	Air resistance	Thickness
MW		(kg/h)	(mm×mm)	℃	(m2)	(Pa)	(mm)
125	Primary air	appa. 18 000	appa. 1000×1500	22~56	60~140	150~400	350~700
	Secondary air	appa. 200 000	appa. 1800×2400	22~56	150~350	150~400	350~700
200	Primary air	appa. 150 000	appa. 1500-2200	22~56	110~270	150~400	350~700
	Secondary air	appa. 335 000	appa. 2400×3000	22~56	240~560	150~400	350~700
300	Primary air	appa. 225 000	1800x2700	22~56	180～420	150~400	250~700
	Secondary air	appa. 508 00a0	3000×3500	22~56	380～880	150~400	350~700
600	Primary air	appa. 412 000	appa. 2800～3200	22~56	310～720	150~400	350~700
	Secondary air	appa. 980 000	appa. 4000×5300	22~56	730～700	150~400	350~700

 

3. Selection method

The user shall provide the following data to facilitate the design and calculation of the manufacturer.

3.1. Performance parameters

The following parameters are required:

3.1.1. The arrangement of the heater, such as in the horizontal duct or in the vertical duct.

3.1.2. The number of air heaters and boilers for a boiler.

3.1.3. The air volume entering the heater.

3.1.4. Air temperature at inlet and outlet of air heater.

3.1.5. Dimension of air duct interface for installation of air heater.

3.1.6. Steam temperature and pressure for heating air.

3.1.7. Air side resistance requirements.

3.2. Parameters not required

If the user can provide the following parameters, it will be convenient for the manufacturer to design and select the type:

3.2.1. Local climatic conditions, such as earthquake intensity, precipitation, extreme temperature, etc.

3.2.2. Composition of coal used in boiler.

3.3. Supply requirements

3.3.1. Any special material requirements for a part of the heater, especially for the heat exchange tube, such as steel aluminum composite pipe or high frequency welded pipe, SS304 or 20C steel for base pipe, and the size of fin spacing, etc.

3.3.2. Any additional requirements related to measurement and control instruments, such as pneumatic or electric control valve, and corresponding manufacturer brand requirements.

3.3.3. Special requirements for surface protection and paint packaging.

3.3.4. Requirements for technical documents provided at the time of delivery.

 

4. Scope of supply and order requirements

4.1. Scope of supply (typical scope of supply can be increased or decreased according to different requirements of users)

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

4.1.1. Plant and equipment:

4.1.1.1. Heater body. The primary air heater body and secondary air heater body; in addition, depending on the user's requirements, sometimes it is necessary to provide equipment interface (steam side, water side) companion flange, counter flange, bolt, nut gasket and other accessories.

4.1.1.2. Matching automatic control device. The contents of automatic control device are shown in table 26-2.

Table 26-2 contents of automatic control device

No.	Name	Specification and model	Quantity
1	Regulating valve and parts	It can be determined according to the specific requirements of users
2	A complete set of control software for patent rights
3	Inlet air temperature resistance of air preheater
4	Flue gas temperature resistance at air preheater outlet
5	Drain temperature thermal resistance of air heater
6	Inlet steam pressure transmitter of air heater

4.1.1.3. Drain tank. Drain tank is not necessary equipment, whether to provide drain tank depends on user's requirements.

4.1.1.4. Spare parts. The spare parts are not required by the user, but depend on the spare parts provided by the user.

4.1.2. Documents:

4.1.2.1. Cooperate with engineering data.

4.1.2.2. Certificate.

4.1.2.3. Operation and maintenance instructions.

4.2. Specification of air heater

4.2.1. Overview. The function of the air heater is to use the steam extraction of the steam turbine to heat the inlet air of the boiler, convey the heated air into the air preheater, and then improve the wall temperature of the cold end by increasing the inlet air temperature of the air preheater, so as to prevent low-temperature corrosion. The air heater shall be designed to work stably and continuously under the environment of power plant.

4.2.1.1. The supplier shall comprehensively evaluate the design of the air heater, and consider the worst operating conditions and the most important economic factors, so as to optimize the design and select the appropriate model.

4.2.1.2) the supplier shall provide a tender in accordance with the specification, which shall detail and provide the information required in the inquiry so that the tender can be correctly evaluated.

4.2.2. Heat transfer performance. The supplier shall provide calculation data to prove that the designed heater can meet the heat exchange requirements put forward by users, especially under the worst conditions. The calculation method and heat exchange elements should be guaranteed by good operation records.

4.2.3. Equipment maintenance. The design of the air heater shall minimize the need for regular maintenance of the equipment, and shall be designed to be convenient for maintenance. Meanwhile, the spare parts and maintenance time for each overhaul shall be specified.

4.2.4. Reliability. The supplier shall provide the feasibility and reliability of the air heater in the tender document, and especially point out any measures that can improve the heat exchange performance, economic and energy-saving effect of the air heater.

4.2.5. Mechanical design:

4.2.5.1. Materials. The selected materials shall adapt to the working environment, and the materials of main components shall be listed in the tender document.

4.2.5.2. Standards. The material, manufacturing process and paint of the heater shall comply with relevant national standards.

4.3. Technical specifications

4.3.1. Operating conditions. To explain whether the heater is installed in the horizontal or vertical air duct, it is also necessary to provide the air duct size of the heater, the air temperature at the inlet and outlet of the heater, the heating air volume of each heater, and the heating steam parameters.

4.3.2. Technical requirements:

4.3.2.1. The user shall specify the requirements for the air side resistance of the heater.

4.3.2.2. The user needs to explain the material requirements for the important parts of the heater, which can also be decided by the supplier, such as the material used for the heat exchange tube.

4.3.2.3. The user shall explain the relevant requirements for the supporting automatic control device: ① whether the supplier needs to provide control strategy, calculation formula, I / O list, P & ID system diagram, etc. ② Whether the regulating valve adopts foreign or domestic products, whether there are requirements for specific brands. ③ The supplier is required to ensure that the performance index is the error between the actual operating wall temperature and the required control wall temperature.

4.3.2.4. Other problems that users need to explain, such as paint and packaging requirements.