JPH0252799B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to heat transfer and boiler construction techniques. More particularly, the present invention provides a plurality of air passages interconnected in series to an air supply source using connecting air pipes and connected to a first air passage located initially in the direction of air flow. and a bypass air pipe serving to communicate the air supply pipe to the connecting air pipe via a mixer disposed within the connecting air pipe, each of the air passages being heated. formed by a bundle of heat transfer tubes made for the passage of gas, for air high temperature preheating of a portion of the air supplied to the tube area of the bundle of heat transfer tubes of said first air passage; The present invention relates to a multi-air passage type corrosion-resistant air preheater in which the air supply pipe incorporates a device.

The present invention can be most advantageously used in steam boilers, furnaces, and other equipment in which sulfur-containing fuels are burned, and in which the outlet gas vigorously discharged in the air preheater of these equipment heats cold air. useful for.

In air preheaters, where there is usually more than one air passage to the air supply, the area of the first air passage to which cold air is supplied has a temperature that is lower than that of the outlet gas around the tube. It is subject to severe corrosion caused by pseudo-condensation of sulfuric acid vapor onto the relatively cold tube walls, which depends on the temperature of the air flowing through the tube. Since the first air passage of the air preheater is used as the path for the coldest gas and the coldest air is directed to its outer surface, the temperature of the tube wall is lower in the first air passage and the temperature of the tube wall is lower. In some areas the temperature of the tube wall is below the dew point of the water vapor in the flue gas containing sulfuric acid vapor. As a result, sulfuric acid condenses on the tube wall in various concentrations, severely corroding the metal and causing deposits in the tube due to the accumulation of ash.

Corrosion of the tube of the air preheater can result in partial failure of the tube, allowing air to enter the gas from the tube area. Thus, the capacity of the blower fan and smoke evacuator needs to be increased to obtain the required amount of air for the boiler or furnace at the air preheater outlet. This leads to excessive energy consumption. This increased energy consumption is also due to the increased suction on the gas flow due to sedimentation and blockage in the tube.

In addition, the air preheater tube is corroded, depleting the capacity of the blower fan and smoke evacuator, resulting in reduced boiler and furnace output, and ultimately the damaged air preheater tube. The boiler or furnace will be shut down for replacement.

In the field of boiler technology, corrosion-resistant air preheaters [prepared by LBKrol and NI Rozengauz, and in 1976 by Energiya of Moscow]
Convection elements of powerful boiler equipment (Konvektivnyie elementy, moschnykh
page 132-133 of ``kotelnykh agregatov''
-3 and 4-4] is well known. This prior art tubular air preheater is provided with a device for air preheating, such as a hot air heater, in which preheated air is supplied to the tubular shape of the first air passage. In such an air preheater, the preheated air flows outside the tube of the first air passage, inside of which a relatively cold outlet gas passes, so that the temperature of the tube wall is lower than in a normal air preheater. expensive. In this case, since the wall temperature is higher than the dew point of water vapor in the outlet gas, there is no pseudo-condensation of water, and as a result, there is no corrosion of the tube or accumulation within the tube.

This air preheater has the disadvantage that the temperature rise of the outlet gas leaving the air preheater caused by the air preheater reduces the efficiency of the boiler in which it is placed. Such air preheaters are therefore used by boiler manufacturers when burning low sulfur fuels where air preheating is sufficient at low temperatures, ie characterized by a low dew point of the water vapor in the outlet gas. High temperature air preheaters are required when burning high sulfur fuels. However, this is achieved with an unacceptably high temperature of the outlet gas and no increase in the heating area that would allow the outlet gas to be noticeably cooled. In this case, the air preheater described above cannot be used.

Also known in the art is a multi-air passage corrosion resistant air preheater according to US Pat. No. 4,243,096.

The air preheater has a plurality of air passages connected in series using connecting air pipes to an air supply source. Each air passage is formed by a bundle of heat transfer tubes designed for the passage of heated gases. The air preheater is provided with an air supply pipe which is connected to the first air channel arranged in the direction of the air flow. In this air supply pipe,
A device for high-temperature air preheating is mounted for heating a portion of the air supplied to the tube area of the bundle of heat transfer tubes in the first air passage. Upstream of the device for air high-temperature preheating, viewed in the direction of the air flow, at least one bypass air pipe is connected to the air supply pipe, which bypass air pipe connects the air supply pipe to the air supply pipe via a mixer arranged in the air pipe. It serves to communicate with the connecting air pipe.

In this latter prior art air preheater, only a small portion of the air supplied to said first air passage undergoes high temperature preheating in a specific device such as an air heater, while the remaining portion Cold air enters the connecting air tube and a mixture of preheated and cooled air at a temperature that ensures a tube wall temperature above the dew point of water vapor in the outlet gas is supplied to the air passage downstream of the air preheater. Ru. As a result, each air passage in the air preheater is supplied with air that is preheated to a high temperature that ensures a tube temperature above the dew point of the water vapor in the outlet gas, causing precipitation in the tube and corrosion of the tube. do not have.

However, despite the high temperature preheating of the air supplied to the first air passage, the equilibrium temperature of the air supplied to the air preheater from the air heater and the bypass air pipe is quite low and the average of the air preheater The temperature head, or average temperature drop, remains high. As a result, the outlet gas can be cooled considerably and this known air preheater does not require a large increase in heating surface to reduce the temperature of the outlet gas.

This latter prior art air preheater includes a plurality of bypass air pipes to increase the average temperature head by reducing the portion of air preheated to a higher temperature that is supplied to the first air passage. It has the disadvantage that it needs to be installed. Each of the bypass air pipes connects an air supply pipe to a respective downstream connecting air pipe via a respective mixer mounted within the connecting air pipe. This generally complicates the arrangement and construction of the air preheater and reduces the reliability of its operation in that the number of mixers in the connecting air pipes increases. Furthermore, the structure of arranging multiple bypass air pipes allows a significant portion of the heating surface of the air preheater to be covered by air poles (a portion of which flows through the As a result, the overall efficiency of the air preheater is reduced.

The present invention overcomes the drawbacks of the known air preheaters mentioned above and provides easy and reliable operation by providing low temperature preheating of cold air and by a specific method of connecting the bypass air pipe to the air supply pipe. It is an object of the present invention to provide a multi-bypass type corrosion-resistant air preheater in which the efficiency of the air preheater is increased.

It is an object of the invention to provide an air preheater according to the invention with a device for low temperature preheating of air placed in the air supply pipe upstream of the device for high temperature preheating of air, viewed in the direction of the air flow, and with one bypass air channel. is achieved by means of a device connected to the air supply pipe between the device for air low-temperature preheating and the device for air high-temperature preheating.

Such a configuration of the air preheater of the present invention helps increase the flow rate of air supplied to the connecting air pipe via the bypass air pipe and reduces the flow rate of air supplied to the first air passage. will occur. The feature of this air preheater is that the air heated in the first air passage is mixed in the mixer with an increased amount of air sent by the bypass, and the air heated by the device for low temperature preheating is heated by the bypass. It consists in the fact that provision is made to bring the temperature of the mixed air at the inlet of the second air duct to the desired temperature by increasing the temperature of the air being fed. As a result, even in an air preheater where air heated to a high temperature is sent at a low flow rate, it is sufficient to provide one bypass air pipe in most cases.

Due to the arrangement of only one mixer, the air preheater disclosed herein is extremely simple and reliable in design and overall device. At the same time, the efficiency of the air preheater of the present invention increases because a small amount of air heated to a high temperature is supplied to the air preheater, and as a result, the equilibrium temperature of the air supplied to the air preheater is rather low. The air preheater is then characterized by a relatively high average temperature head. In addition, all of the air flows over a large portion of the heating surface of the air preheater while some air flows over a small portion of the heating surface contained in the first air passage, thereby A high heat transfer coefficient can be obtained.

An example of the implementation of the present invention will be described in detail below with reference to the accompanying drawings.

As shown in FIG. 1, the air preheater of the present invention includes four air passages 1, 1, 2, and 4 interconnected in series to an air supply source using connecting air lines or connecting air pipes 5.
2, 3 and 4. Each of the air passages 1, 2, 3 and 4 is formed by a bundle of heat transfer tubes 6 designed for the passage of heated gases. The first air passage 1 is connected to an air supply line, i.e. an air supply pipe 7, which is connected to a direct contact heat exchanger 9 [compiled by SIMochan, Energia, Leningrad in 1977]. Aerodynamic Calculation of Boiler Equipment (Standardization Method) (Aerodinamicheskii raschot) published by (Energiya)
kotel′nykh us tanovok (normativnyi matod)”
A device 8 for high-temperature preheating of a portion of the air is provided.

The heated air is passed from a hot air line or hot air pipe 12 connected to the fourth air passage 4 of the air preheater to a recirculating air line or recirculating air pipe 11 to a heat exchanger 9 using a fan 10. Supplied. In the air preheater disclosed herein,
The device includes a hot air heater (prepared by LBKrol and NI Rozengauz) placed in the air supply pipe 7 upstream of the heat exchanger 9 as seen in the direction of the air flow. , Energiya in Moscow in 1976
Convection elements of powerful boiler equipment (konvektivnyie, elementy, moschnykh) published by
page 132-133 of ``kotelnykh agregatov''
A device 13 for low-temperature heating of air is provided. The bypass air line or bypass air pipe 14 communicates with the air supply pipe 7 at one end and with the connecting air pipe 5 containing the mixer 15 at the other end. A control valve 16 is provided within this bypass air pipe 14 .
One end of the bypass air pipe 14 is connected to the air supply pipe 7 between the heat exchanger 9 and the air bass heating device 13, and the other end is connected to the mixer 15.
Air is supplied to the air supply pipe 7 using a blower fan 17.

The air preheater according to the invention operates as follows. The heated gas passing through the heat transfer tube 6 is fed from the first passage 1 towards the fourth passage 4 and vice versa from the fourth passage to the first passage. This heat transfer tube 6 heats the air passing through the area in which the tube is located, and the gas within the tube 6 is cooled. All of the cold air supplied to the air preheater via the air supply pipe 7 using the blower fan 17 is first supplied to the air preheater at a temperature of 30°C or higher, for example 50°C or higher.
The air is supplied to a low temperature preheating device 13 at 70°C. A portion of the air preheated to 50-70° C. then enters the direct bond heat exchanger 9, while the other air passes through the bypass air pipe 14 to the mixer 15. Air heated in the heat exchanger 9 to a high temperature, for example 100 DEG -150 DEG C., is fed to a tube region consisting of a bundle of heat transfer tubes 6 in the first air passage 1 of the air preheater. In this tube zone, the air is heated by the heating gas, which in turn is cooled to 130 DEG C. to 180 DEG C. Due to the high temperature of the air supplied to said tube zone, the temperature of the metal forming the tubes 6 is higher than the dew point of the water vapor in the flue gas. Therefore, no ash buildup or corrosion occurs in the heat transfer tube 6. 1st
The air heated in the air passage 1 is transferred to the connecting air pipe 5.
The air is heated to 50 to 70°C by the mixer 15 placed on the connecting air pipe 5, and evenly mixed with the remaining air supplied to the mixer 15 from the bypass air pipe 14. Ru. Control valve 1
6, the ratio between the flow rate of air supplied to the first air passage 1 and the flow rate of air supplied into the bypass air pipe 14 is determined such that the temperature of the mixed air in the connecting air pipe 5 is The temperature is set so that the heat transfer tube 6 of the second air passage 2 does not corrode. Thus, all the air is heated while
air passage 3 and fourth air passage 4 and then leaves the air preheater via hot air pipe 12. Since only one bypass air pipe 14 and only one mixer 15 are provided, the construction of the air preheater and associated equipment is simple and provides reliable, corrosion-free operation.

The fact that a small portion of the air supplied to the air preheater is preheated to a high temperature ensures a low equilibrium inlet temperature of the air preheater and therefore a high temperature head in the air preheater, while the Having all the air flow around a large portion of the heating surface provides a high heat transfer coefficient in the air preheater. These two features contribute to high efficiency of the air preheater.

In the embodiment, the air low temperature preheating device 13
The combination of high temperature air preheating in and low temperature air preheating in direct contact heat exchanger 9 serves to increase the efficiency of the air preheater, since the two air preheats are performed using the most efficient techniques. Thus, for example, low-temperature preheating is carried out using the heat obtained by extraction of low-pressure steam in the turbine, and high-temperature preheating is carried out using circulating hot air of moderate temperature and already controlled. be exposed.

As part of the steam turbine equipment and the first
Under operating conditions of air preheating operating at a moderate temperature of the air supplied to the pipe area of the air passage, for example 100-120°C, a device 8 for high temperature air preheating is withdrawn from the turbine (not shown). Advantageously, it is constructed as a surface heat exchanger 18 (FIG. 2) heated by low-pressure steam. This air preheater operates in a similar manner to the air preheater described above.

The corrosion-resistant air preheater with multiple air passages in accordance with the present invention provides continuous, reliable, corrosion- and deposit-free operation under conditions of high concentration sulfur gas flow within the multiple heat transfer tubes. can. To date, this type of air preheater has been in operation for a long time. In addition, the air preheater disclosed herein is capable of cooling the gas exiting the boiler to a temperature of only 30 to 40 degrees Celsius above the temperature of the air supplied to the first air passage. Even if the air is heated to 150°C and supplied to the first passage, the temperature of the gas at the outlet is maintained at about 180°C. The air preheater according to the present invention helps increase the efficiency of a steam turbine system because it uses the heat of the low pressure steam drawn from the turbine in the system for high temperature air preheating.

Thus, for example, high sulfur content coal was used.
Using the air preheater of the present invention in a 300 MW steam turbine increases the efficiency of the system by 0.6%.

[Brief explanation of the drawing]

FIG. 1 is an illustration of a four-air passage corrosion-resistant air preheater according to the invention, with a device for high-temperature air preheating made, for example, as a direct contact heat exchanger; FIG. 1 is an illustration of a four-air channel corrosion-resistant air preheater according to the invention, with a device for high temperature air preheating, for example made as a surface heat exchanger; FIG. 1, 2, 3, 4... Air passage, 5... Connecting air pipe, 6... Heat transfer tube, 7... Air supply pipe to the pipe area, 8... Device for air high temperature preheating, 9, 18...
... Heat exchanger, 10 ... Fan, 11 ... Recirculation air pipe, 12 ... Hot air pipe, 13 ... Air low temperature preheating device, 14 ... Bypass air pipe, 15 ... Mixer, 16 ... Control Valve, 17...Blower fan.

Claims (1)

[Claims] 1. A plurality of air passages 1, 2, 3, 4 interconnected in series to an air supply source using connecting air pipes 5.
, an air supply pipe 7 connected to the first air passage 1 arranged first in the direction of the air flow, and a mixer 15 placed in the connecting air pipe 5 to the air supply pipe 7 . 7 to the connecting air pipe 5;
Each of said air passages is formed by a bundle of heat transfer tubes 6 designed for the passage of a heated gas, which is supplied to the tube area of said bundle of heat transfer tubes 6 of said first air passage 1. In the multi-air passage type corrosion-resistant air preheater in which the air supply pipe 7 incorporates a device 8 for high-temperature preheating of air for a part of the air, the device 8 for high-temperature preheating of air is installed as viewed in the direction of air flow.
An air low-temperature preheating device 13 is provided in the air supply pipe 7 upstream of the air supply pipe 7 , and a bypass air pipe 14 is provided between the air high-temperature preheating device 8 and the air low-temperature preheating device 13 . A multi-air passage type corrosion-resistant air preheater characterized by being connected to.