CN111322634A - Air preheating system coupled with rotary preheater and tubular preheater - Google Patents

Abstract

The invention relates to the field of air preheating of boiler systems, and discloses an air preheating system in which a rotary preheater and a tubular preheater are coupled. Type preheater, rotary preheater is used to heat the air at the outlet of the tubular preheater, tubular preheater is used to heat the inlet air of the inlet of the rotary preheater, the tubular preheater is designed in sub-modules, each module It is set as a divided area where the heat exchange process can be independently controlled, and each divided area is provided with a dry burning hot flue gas/hot air introduction interface, which can independently perform dry burning with a temperature of over 232°C. The invention can completely solve the problems of ammonium hydrogen sulfate clogging and low-temperature corrosion of the rotary air preheater, runs smoothly, and is suitable for the new design or reconstruction of the boiler preheating system.

Description

Air preheating system coupled with rotary preheater and tubular preheater

technical field

The present invention relates to air preheating of boilers, especially an air preheating system which can prevent NH ₄ HSO ₄ (ammonium hydrogen sulfate) deposition in a rotary preheater.

Background technique

For large coal-fired boilers, it is conventional to arrange a rotary preheater after the economizer/SCR to heat the supply air of the boiler, so as to reduce the exhaust gas temperature of the boiler and improve the efficiency of the boiler. Generally, in order to improve boiler efficiency, the exhaust gas temperature is generally designed to be relatively low.

But for boilers equipped with SCR devices, the excess ammonia injection will react with _SO3 in the flue gas to form ammonium hydrogen sulfate. Ammonium hydrogen sulfate is solid below 149℃, liquid between 149℃～232℃, decomposes and volatilizes from liquid above 232℃, and decomposes into NH ₃ +SO ₃ +H ₂ O. In boiler design, the exhaust gas temperature is generally 120-130 °C, and the cold end of the rotary preheater is in the solid phase range _of ammonium hydrogen sulfate. Excessive ammonia injection reacts with SO3 in the flue gas to form ammonium hydrogen sulfate, which will adhere to the rotary On the heat exchange element of the cold end of the preheater, the heat exchange capacity of the preheater is reduced, and the corrosion of the cold end is intensified. Especially for the boilers burning high-sulfur coal, the problem of ammonium hydrogen sulfate deposition and blockage is particularly serious.

In order to reduce the risk of corrosion at the cold end of the rotary preheater and clogging with ammonium bisulfate, various solutions are mentioned in the prior art. For example, the Chinese invention patent application with the publication number of CN107191963A "a rotary air preheater and the method for preventing clogging of ammonium hydrogen sulfate in the rotary air preheater", which is provided at the cold end of the preheater and can introduce preheating The flue gas injection device connected to the high-temperature fan of the high-temperature flue gas at the hot end of the preheater can increase the inlet air temperature of the preheater, thereby increasing the comprehensive temperature of the cold end of the preheater, and limiting the ammonium hydrogen sulfate deposition zone to the lower part of the cold end of the air preheater. , and then use the steam soot blower to blow it off; the online air preheater blockage is effectively relieved. However, the increase in the inlet air temperature of the preheater will bring about an increase in the exhaust gas temperature, which will affect the subsequent dust collector, and cannot completely solve the risk of ammonium bisulfate clogging at the cold end, especially for boilers burning high-sulfur coal, ammonium bisulfate deposits The problem of clogging is particularly serious.

The Chinese invention patent application with publication number CN107642793A "System and Method for Preventing Ammonium Bisulfate from Blocking Air Preheater after SCR Denitration Transformation" proposes a solution to cancel the heating surface of the cold section of the rotary air preheater, and use the waste heat of the flue gas. After the further utilization of the dust collector is changed, the primary air heater and the secondary air heater are added to assist the air preheater to achieve air temperature adjustment. In this scheme, the dust collector works at a higher temperature and can withstand greater 's test.

The Chinese invention patent application with publication number CN106765288A "a graded heat exchange system for a rotary air preheater of a power station boiler" is to install a heat pipe heat exchanger after the rotary air preheater, and the high temperature flue gas of the rotary air preheater is installed. The outlet smoke temperature is 200℃～220℃, heat pipe heat exchanger, heat pipe cold end liquid storage tank is set at the end of cold end pipe row, hot end inlet distributor is set at the inlet of hot end pipe row, cold end liquid storage tank and hot end The volume pump and the volume pump outlet regulating valve are set between the inlet distributors; the cooling water inlet regulating valve is set at the cold end cooling water inlet, and the cold end cooling water cooling channel is independently set at the cold end of the heat pipe heat exchanger, and the cold end cooling water flows through the heat pipe for heat exchange After the independent heat exchange channel of the cold end is heated up, it enters the boiler feed water system or heating system; a temperature measurement device is set on the wall surface of the hot end pipe, and the temperature signal transmission device is transmitted to the heat pipe heat exchanger operation control system to adjust the outlet of the positive displacement pump. The valve and the cooling water inlet regulating valve are adjusted to adjust the medium flow rate and cooling water flow in the heat exchange tube of the heat pipe heat exchanger to ensure that the wall temperature of the hot end tube remains constant. This solution can basically solve the problem of ammonium bisulfate clogging of the rotary air preheater, and the working temperature of the back-end equipment such as the dust collector is not high, but the heat pipe heat exchangers it is equipped with may still be blocked by ammonium bisulfate, which needs to be shut down for cleaning. .

The above technologies are based on increasing the temperature of the flue gas at the outlet of the rotary air preheater to prevent the condensation of ammonium hydrogen sulfate and avoid the cleaning and maintenance of the rotary air preheater with complex structure, but only increase the inlet air of the rotary preheater. The temperature of the rotary preheater slows down the cold end corrosion of the rotary preheater, but the blockage and deposition of the rotary ammonium hydrogen sulfate cannot be completely removed. Moreover, after raising the flue gas temperature at the outlet of the rotary air preheater, how to adapt to various working conditions, how to make the subsequent dust collectors and other equipment work normally, how to comprehensively utilize the existing equipment of the boiler and the remaining heat, etc. After careful consideration, it is not complete and needs to be improved.

Announced on November 22, 2019, the Chinese utility model patent with the announcement number CN209672379U "a tube box type air preheater", the tube box type air preheater is mainly suitable for boilers with small unit capacity, except for 300MW circulating flow In addition to the use of tubular air preheaters, chemical bed boiler air preheaters are rarely used in pulverized coal boilers of 300MW and above. The utility model aims to improve the structure of the tubular preheater itself to realize the simultaneous strengthening of the heat exchange inside and outside the tube of the heat exchange tube, so that the tubular preheater is applied to units of 300MW and above.

Is it possible to design an air preheating device that not only has the advantages of high heat exchange efficiency of a rotary preheater, but also has the advantages of self-cleaning of a tubular preheater?

SUMMARY OF THE INVENTION

In order to completely solve the problems of corrosion of the cold end of the rotary preheater and blockage of ammonium hydrogen sulfate, the technical problem to be solved by the present invention is to provide an air preheating system coupled with the rotary preheater and the tubular preheater. On the basis of the existing technology, according to the physical properties of ammonium hydrogen sulfate, an air preheating system that is easy to maintain online and adapt to various working conditions, especially suitable for high-power boiler units burning high-sulfur coal, is formed. .

The technical solution adopted by the present invention to solve the technical problem is as follows: an air preheating system coupled with a rotary preheater and a tubular preheater includes a rotary preheater and a tubular preheater for heat exchange between flue gas and air. Heater, the rotary preheater is used to heat the air at the outlet of the tubular preheater, and the tubular preheater is used to heat the inlet air of the inlet of the rotary preheater. The tubular preheater is designed in sub-modules, and each module is set to The heat exchange process can be independently controlled in divided areas, and each divided area is provided with a dry burning hot flue gas/hot air introduction interface, which can independently carry out dry burning with a temperature above 232°C.

In this technical solution, the rotary preheater is arranged in the middle and high flue temperature area of the economizer/SCR outlet, and the tubular preheater is arranged in the low flue temperature area. After the flue gas of the boiler system comes out of the economizer/SCR, the After passing through the rotary preheater and the tubular preheater, it enters the dust collector. After the primary air and secondary air of the system come out from the primary fan/supplier, they pass through the tubular preheater and the rotary preheater in turn and then enter the boiler. . The flue gas temperature split point in the design of the rotary preheater and the tubular preheater should ensure that the crystallization of ammonium hydrogen sulfate does not occur in the low temperature section of the rotary preheater, that is, the outlet flue temperature of the rotary preheater is greater than 149 °C, Therefore, the coupled air preheating system can completely remove the deposition of ammonium hydrogen sulfate in the rotary preheater and the occurrence of low-temperature corrosion at the cold end; when dry burning is performed, the tube wall temperature of the modular tubular preheater reaches above 232 °C, which can be The ammonium bisulfate volatilizes, and the ammonium bisulfate deposited on the tubular preheater can be removed online. Therefore, the present invention not only prevents the ammonium bisulfate deposition on the rotary preheater, but also can remove the tubular Ammonium bisulfate deposited on the preheater.

The air preheating system can reasonably adjust the area of the rotary preheater and the tubular preheater according to the on-site space and the sulfur content of the coal used, and the area of the tubular preheater can be appropriately increased to reduce the emissions. and the optimal combination of rotary and tubular preheater areas can be determined by calculation to ensure that the heat exchange element of the rotary preheater is above the corrosion temperature, and no ammonium hydrogen sulfate deposition occurs, especially suitable for Large units that burn high-sulfur coal.

Further, each module of the tubular preheater is a separate tube box, corresponding to each of its tube boxes, the air flowing through the tubular preheater is divided by the cold air closing baffle and then flows to each divided area one by one, and the cold air is closed. The baffle is used to cut off the air at the inlet of each tubular preheater; the flue gas flowing through the tubular preheater is divided by the flue gas closing baffle and then flows to each divided area one by one, and the flue gas closing baffle is used to cut off the air. The flue gas at the inlet of the tube box of each tubular preheater; the flue gas goes inside or outside the tube of the tubular preheater. The smoke/air of each segment does not communicate with the smoke/air of the adjacent segment. The number of modular header boxes that need to be divided is reasonably determined according to the parameters of the unit, and it is usually recommended to be at least 4 or more, so that when one or two of the divided areas are dry-fired separately, the stable operation of the entire system will be more affected. Small.

In order to realize the separate regulation of heat exchange in each of the divided regions, and at the same time take into account the economy, the numbers of the cold air closing baffles and the flue gas closing baffles are the same as the number of the tubular preheater tube boxes. It is not necessary to set more than two baffles for each divided area to control the flow of smoke or air.

In order to realize the independent control of the heat exchange between the flue gas and the air in each of the divided regions, the cold air closing baffle and the flue gas closing baffle are provided with independently controlled electric or pneumatic actuators.

According to specific parameters, the tubular preheater can be selected as a light-tube heat exchanger or a finned heat exchanger, and the tubular preheater can be arranged horizontally or vertically.

Further, the cold air closing baffle is arranged between the primary fan/supply fan and the tubular preheater, and the dry burning hot flue gas/heating flue gas is arranged between the flue gas closing baffle and the tube box of the tubular preheater. The hot air is introduced into the interface. The cold air from the primary fan/supply fan first passes through the tubular preheater for heat exchange, and then enters the rotary preheater for heat exchange; the cold air from the primary fan/supply fan can enter the tubular preheater for heat exchange respectively , and then enter the rotary preheater, or can be combined into the tubular preheater, and then enter the rotary preheater.

The dry burning hot flue gas/hot air introduction interface is connected to the inlet or outlet of the rotary preheater through the dry burning hot flue gas/hot air duct, and the dry burning hot flue gas/hot air duct is provided with corresponding control division areas The dry burning hot flue gas/hot air closes the baffle, the dry burning hot flue gas comes from the flue gas at the inlet of the rotary preheater, and the dry burning hot air comes from the hot air at the outlet of the rotary preheater.

Further, in order to facilitate automatic control, a differential pressure transmitter or a pressure transmitter is set at the inlet and outlet of the flue gas side of the tubular preheater, and the resistance on the flue gas side of the tubular preheater is monitored online. If the flue gas resistance exceeds the set value, it means that the tubular preheater is blocked by ash accumulation or ammonium bisulfate; first put the soot blower into operation for a period of time. It can be preliminarily determined that the tubular preheater is blocked by ammonium hydrogen sulfate. At this time, the dry burning system of the tubular preheater will be put into operation. Dry burning. When dry burning the first group of modules, isolate the inlet flue gas of the first group of tubular preheater modules, isolate the inlet air, open the dry burning hot flue gas/hot air closing baffle, and introduce high temperature hot flue gas/hot air into the first group. One group of tubular preheater modules increases the wall temperature of the modules to volatilize the deposited ammonium hydrogen sulfate; after the dry burning of the first group of modules is completed, close the dry burning hot flue gas/hot air closing baffle, and then open the first set of modules. Set up the module smoke inlet baffle door and air inlet baffle door, restore their heat exchange, and continue the dry burning of the second group of modules in the above manner until all the modules are dry burned. During operation, the dry burning system of the tubular preheater can also be controlled by intermittent operation to prevent the blockage of ammonium hydrogen sulfate, for example, each module is put into operation once per shift.

Further, the rotary preheater is arranged after the economizer/SCR, and the tubular preheater is arranged in the flue between the rotary preheater and the dust collector. This arrangement effectively ensures that the working temperature of the dust collector does not increase substantially, because the tubular preheater can be arranged horizontally or vertically, so the flue can be either a horizontal flue or a vertical flue.

According to the above description, the rotary preheater used in the air preheating system can be either a two-bin preheater or a three-bin preheater.

The beneficial effects of the invention are: the invention is coupled with the tubular preheater, which can completely solve the problems of ammonium hydrogen sulfate clogging and low temperature corrosion of the rotary air preheater, and maintain the flue gas resistance of the rotary air preheater. Within the design range, the rotary preheater can work within the safe operating temperature range for a long time, and the power consumption of the induced draft fan and blower will not increase due to the blockage of ammonium hydrogen sulfate; the hydrogen sulfate of the tubular preheater can be removed online. When the dry burning system of the tubular preheater is put into operation, the exhaust gas temperature entering the dust collector will increase, but the increase is small, so the entire air preheating system can operate safely and stably for a long time. In addition, only the action of the baffle plate is consumed during the operation, and the energy consumption is low, which can save the operation cost compared with the existing solutions such as the steam heater in operation. Compared with the existing scheme of simply modifying the tubular preheater, it has great design flexibility and can adapt to the needs of ultra-supercritical units. The invention is suitable for new design or reconstruction of boiler preheating system.

Description of drawings

FIG. 1 is a schematic diagram of the flow of flue gas and air of the air preheating system of the present invention.

FIG. 2 is a schematic structural diagram of the air preheating system of the present invention.

Marked in the figure: 1- Rotary air preheater; 2- Pipe type preheater; 3- Electrostatic precipitator; 4- Primary fan / blower; 5- Cold air closing baffle; 6- Flue gas closing baffle; 7 - Dry burning hot flue gas/hot air duct; 8- Dry burning hot flue gas/hot air closing baffle; 9 - Dry burning hot flue gas/hot air inlet interface; 10 - Separation plate; 11 - Differential pressure transmitter.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Example:

As shown in Figure 1 and Figure 2, a 300MW coal-fired boiler unit is taken as an example to illustrate.

This project uses high-sulfur coal with a sulfur content of 4%. The air preheating system of the present invention is applied to the unit. The rotary preheater is arranged in the middle and high smoke temperature area of the SCR outlet, and the tubular preheater is arranged in the low smoke temperature area. After the flue gas comes out of the SCR, it passes through the rotary preheater, the tubular preheater, and then enters the dust collector; the primary and secondary air come out from the primary fan/supplier, and then pass through the tubular preheater, Rotary preheater before entering the boiler. The rotary preheater is a three-silo preheater, which is used to heat the air at the outlet of the tubular preheater; the tubular preheater is a light tube heat exchanger, which is used to heat the inlet air at the inlet of the rotary preheater. , the flue gas goes outside the pipe, the air goes inside the pipe, and the flue gas differential pressure transmitter is installed at the inlet and outlet of the flue gas side of the tubular preheater.

The tubular preheater is divided into 24 modules, each module is a separate tube box, and the design of each tube box ensures that the flue gas/air does not enter the adjacent tube boxes; the inlet smoke of the tubular preheater is The duct is divided into 24 areas by the flue gas partition plate. The number of divided areas is the same as the number of tube boxes of the tubular preheater. Each divided area corresponds to a tubular preheater tube box, and the entrance of each divided area is A flue gas closing baffle is set, and a dry burning hot air introduction interface is set between each flue gas closing baffle and the tube box of the tubular preheater, and a dry burning hot air duct is introduced into each area from the interface, and the There is also a dry-burning hot air closing baffle on the pipeline. During dry-burning, the baffle is opened to introduce the hot air from the outlet of the rotary air preheater; the inlet air of the tubular preheater is also divided into 24 areas, each of which is divided. Corresponding to a tube preheater tube box, a cold air closing baffle is set at the entrance of each segmented area. In this way, the smoke closing baffle and the cold air closing baffle can be used to control whether the separate pipe box is put into use for heat exchange, and the hot air closing baffle can be used to control whether to introduce dry burning hot air to the area where the pipe box is located. Do dry roasting.

In actual operation, the resistance on the flue gas side of the tubular preheater is monitored online by the flue gas differential pressure transmitter. If the monitored flue gas resistance exceeds the set value, it means that the tubular preheater has ash or hydrogen sulfate. Ammonium blockage; after the soot blower is put into operation for a period of time, if the flue gas side resistance of the tubular preheater still exceeds the set value, it can be preliminarily determined that the tubular preheater is blocked by ammonium hydrogen sulfate; The flue gas closing baffle and the cold air closing baffle corresponding to the module, suspend the flue gas-air heat exchange of the module, open the dry burning hot air closing baffle, and introduce part of the hot air from the outlet of the rotary air preheater into the divided area (introduced into the divided area). The air volume is about 1% of the total air volume of the boiler), that is, the dry burning system of the corresponding module of the tubular preheater is put into operation. Since the temperature of the hot air is above 290 ℃, the hydrogen sulfate can be accumulated on the wall of the tubular preheater. The ammonium is volatilized and turned into gas, and after the dry burning is completed, the flue gas closing baffle and the cold air closing baffle are opened and discharged with the flue gas, which can effectively remove the blockage of ammonium hydrogen sulfate in the tubular preheater. When the dry burning system of the tubular preheater is put into operation, the dry burning is carried out according to the modules and regions; after the dry burning of the first group of modules is completed, the dry burning hot air is closed to close the baffle door, and then the flue gas inlet corresponding to the first group of modules is opened. baffles and air inlet baffles, dry-fire the second group of modules, and do this until every block found to be blocked has been dry-fired. After calculation, when the dry burning system is put into operation, the temperature of the exhaust gas entering the dust collector will increase by 1 to 2 °C, which will not adversely affect the subsequent dust removal equipment.

In addition, the tubular preheater can also be controlled by intermittently operating the dry firing system of each module, thereby preventing clogging.

The calculated value of the flue gas temperature of the air preheating system is shown in Table 1 below.

Table 1 Calculated value of flue air temperature of air preheating system

Note: BMCR means the maximum continuous output condition of the boiler; THA means the guaranteed heat consumption condition of the unit.

It can be seen that after the implementation of the patented system, the inlet air temperature and outlet smoke temperature of the rotary preheater have been greatly improved, and the safety of the rotary preheater is guaranteed.

The invention transfers the ammonium hydrogen sulfate deposition phenomenon from the rotary preheater to the tubular preheater by combining the rotary preheater and the tubular preheater, and combines the characteristics of the tubular preheater to carry out Zoned dry burning, and at the same time, the high temperature flue gas at the inlet of the combined rotary preheater or the high temperature air at the outlet is used as the heat source for dry burning, which realizes the optimal combination and rational utilization of boiler equipment. Because the area of the rotary preheater and the tubular preheater can be adjusted reasonably according to the site space and the sulfur content of the coal used, and the area of the tubular preheater can be appropriately increased to reduce the exhaust gas temperature; Through calculation, the optimal combination of rotary and tubular preheater area is determined to ensure that the heat exchange element of the rotary preheater is above the corrosion temperature, and no ammonium bisulfate deposition occurs. It has considerable design flexibility and excellent ease of maintenance.

Claims (10)

1. An air preheating system coupled with a rotary preheater and a tubular preheater, including a rotary preheater, characterized in that it also includes a tubular preheater for heat exchange between flue gas and air, and a rotary preheater The heater is used to heat the air at the outlet of the tubular preheater, and the tubular preheater is used to heat the inlet air of the inlet of the rotary preheater. Independently controlled segmented areas, each segmented area is provided with a dry burning hot flue gas/hot air introduction interface, which can independently perform dry burning with a temperature above 232°C. 2. The air preheating system coupled with the rotary preheater and the tubular preheater according to claim 1, is characterized in that: each module of the tubular preheater is a separate tube box, corresponding to each of its In the tube box, the air flowing through the tube preheater is divided by the cold air closing baffle and then flows to each divided area one by one. The cold air closing baffle is used to cut off the air at the inlet of each tube preheater tube box; The flue gas of the preheater is divided by the flue gas closing baffle and then flows to each divided area one by one, and the flue gas closing baffle is used to cut off the flue gas at the entrance of each tubular preheater tube box; At the same time, each tubular preheater module is provided with a flue gas/air dividing plate, so that the flue gas/air of each divided area does not communicate with the flue gas/air of the adjacent divided area. 3. The air preheating system coupled with the rotary preheater and the tubular preheater according to claim 2, wherein the number of the cold air closing baffles and the flue gas closing baffles is the same as that of the pipes Type preheater tube number. 4. The air preheating system coupled with the rotary preheater and the tubular preheater according to claim 2, wherein the cold air closing baffle and the flue gas closing baffle are all provided with independently controlled electric or Pneumatic actuator. 5. The air preheating system coupled with the rotary preheater and the tubular preheater according to claim 2, is characterized in that: the tubular preheater is a light tube type heat exchanger or a finned heat exchange The tubular preheater can be arranged horizontally or vertically. 6. The air preheating system coupled with the rotary preheater and the tubular preheater according to claim 2, wherein the cold air closing baffle is arranged between the primary fan/blower and the tubular preheater. The dry-burning hot flue gas/hot air introduction interface is set between the flue gas closing baffle and the tube box of the tubular preheater. 7. The air preheating system coupled with a rotary preheater and a tubular preheater according to any one of claims 1 to 6, characterized in that: the dry burning hot flue gas/hot air introduction interface The dry-burning hot flue gas/hot air duct is connected to the inlet or outlet of the rotary preheater, and the dry-burning hot flue gas/hot air duct is provided with a dry-burning hot flue gas/hot air closing baffle for controlling each segmented area. , The dry burning hot flue gas comes from the flue gas at the inlet of the rotary preheater, and the dry burning hot air comes from the hot air at the outlet of the rotary preheater. 8. The air preheating system in which the rotary preheater and the tubular preheater are coupled according to any one of claims 1 to 6, wherein the tubular preheater has a flue gas side inlet. The outlet is provided with a differential pressure transmitter or a pressure transmitter. 9. The air preheating system coupled with a rotary preheater and a tubular preheater according to any one of claims 1 to 6, wherein the rotary preheater is arranged in an economizer After the preheater/SCR, the tubular preheater is arranged in the flue between the rotary preheater and the dust collector, and the flue is a horizontal flue or a vertical flue. 10 . The air preheating system coupled with a rotary preheater and a tubular preheater according to any one of claims 1 to 6 , wherein the rotary preheater is a two-division bin. 11 . Preheater or three bin preheater.

Images