JPS61134521A - Method and device for thermally treating flue gas and combustion air from boiler furnace - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and an apparatus for the heat treatment of flue gas from a boiler furnace, the flue gas being connected in series for the heat treatment of combustion air to be fed to the boiler furnace. combined 2
f! flue gas treatment plant. The flue gas is at a higher temperature in the second flue gas treatment plant than in the first flue gas treatment plant.

Flue gas treatment plants contain flue gas contaminants.
This is a plant for reducing the amount of The first flue gas treatment plant may be a flue gas sulfurizer and the second plant may be a NOx removal plant.

If the flue gas from the boiler furnace were discharged freely into the atmosphere, the nitrogen oxides contained in the flue gas would pollute the air. In order to reduce the above pollution, plants have been developed to remove some of the NOx contained in the flue gas. Such NOx removal plants are generally plants that catalytically remove the content of nitrogen oxides (NOx), and are also called selective catalytic reduction (SCR) plants, and are used in air preheaters in thermal power plants. placed in front of. This is because the NOx removal plant has maximum effectiveness at the temperature of the flue gas entering the air preheater.

In the SCR process, nitrogen oxides are reacted with NH3 fed to the flue gas in the presence of a catalyst.

Many problems arise with coal or oil fired power plants.

Depending on the composition of the M-fuel, most of the sulfur contained in the fuel is converted to SO3.

The activity of the catalyst is not limited to reactions with NH3+ and NOx, but also catalyzes SO2 to 503. The NH3 supplied to the flue gas reacts with the SO2 catalyst to produce various salts. These accumulate in liquid form in addition to the sticky ash particles primarily in the air preheater at temperatures below about 250°C, especially below 230°C.

The resulting buildup causes clogging and pressure loss. Similarly, small deposits may land on the catalyst and render it inactive.

Fine ash can also erode the catalyst, reducing its mechanical stability to a limit. Fine ash also clogs the honeycomb structure of the catalyst. There is also the risk that the catalyst will be gradually destroyed by the alkaline components of the ash, especially potassium compounds.

Catalyst clogging can be avoided by using catalysts with ceramic supports. However, such catalysts are bulky, expensive and susceptible to mechanical stress. Additionally, a soot blower is sometimes required to clean the catalyst.

Vanadium bentoxide is one of the most effective catalysts for NOx removal, but it also has high activity in converting 502 to SO3. Other known catalysts convert less than 1% of the S02 content to S(h), but with low NO
It only has x removal activity.

In an attempt to avoid the above problems it has been proposed to install a NOx removal plant after the flue gas desulphurizer, followed by an air preheater. The gas is at a relatively low temperature and must therefore be heated to a temperature sufficient for reaction within the NOx removal plant.This heating may be done by a heat exchanger7, which is supplied with steam. Yes, however, such heating involves additional energy consumption and thus increases operating costs.

It is an object of the present invention to provide a method and apparatus for the heat treatment of flue gas coming from a boiler furnace and passing through two flue gas treatment plants coupled in series, in which the flue gas is , a higher temperature in the second flue gas treatment plant than in the first flue gas treatment plant;
for the heat treatment of the combustion air to be supplied to the boiler furnace, and in this method and apparatus the external energy supply is not required or the external energy supply is minimized.

According to the invention, a method of the first-mentioned type is characterized in that the heat extracted from the flue gas is used for reheating the flue gas and for preheating the air.

A further feature of the invention is that the flue gas is heated at a temperature sufficient for catalytic removal of NOx, preferably from 130° to 45°C.
in the range of 0°C, preferably 160° to 380°C, e.g. 2
It is heated to a temperature ranging from 00° to 300°C.

Within the scope of the invention, the flue gas is reheated in one or more stages, preferably in two or three stages.

Also within the scope of the invention, the air is preheated in one or more stages, preferably in two or three stages.

Similarly, within the scope of the invention, from the flue gas
1 The extracted heat is first used to preheat the air in the last air preheating stage at a high temperature and then used to reheat the flue gas at a lower temperature. As a result, the combustion air is optimally heated at high temperatures and the purge gas is reheated to a sufficiently high temperature for NOx removal.

According to a further feature of the invention, the heat extracted from the flue gas is used to preheat the combustion air in a first air preheating stage at a low temperature and the heat previously extracted from the flue gas is used at a low temperature. used to preheat the air and reheat the flue gases. The heat may be supplied by a regenerative heat exchanger, such as a rotary gas preheater, or by a switched regenerative heating column, or by a transfer heat exchanger connected by an interleaved heat exchange medium cycle, or by a heat vibrator. The arrangement ensures that the heat contained in the flue gas before the first flue gas treatment plant is utilized in an improved manner. If the first flue gas treatment plant consists of a flue gas desulphurizer, the water consumption of the flue gas desulphurizer is reduced, since evaporation increases and the purified gas has a lower moisture content. This is because it will nurture.

The reheating of the flue gas in all stages before the last of the flue gas reheat stages preferably takes place in an absorption system.

According to a further feature of the invention, the reheating of the flue gas in all flue gas reheating stages before the last stage is performed in the first
This takes place in an M-thermal heat exchanger with a heat exchanger between the flue gas to be fed to the flue gas treatment plant and the flue gas discharged from said plant. Preheating in all flue gas preheating stages up to the last stage preferably takes place in a steam-fed heat exchanger. According to yet another characteristic of the invention, the air is removed in every preheating stage before the last air preheating stage by absorption of heat released in an absorption device and/or from a second flue gas treatment plant. It is preheated by heat exchange with the discharged flue gas.

In a first embodiment of the apparatus for carrying out the method according to the invention, a first
The flue gas treatment plant is preceded by a primary flow path of the first heat exchanger with a secondary flow path communicating with the primary flow path of the second heat exchanger. The second heat exchanger is used to reheat the purified flue gas discharged from the first flue gas treatment plant and has a primary flow in communication between the first and second flue gas treatment plants. has a road. The secondary flow path of the first heat exchanger communicates with the primary flow path of the third heat exchanger, which also preheats the air. It is also characterized in that the heat may alternatively be transferred by means of a heat vibrator arrangement.

A second embodiment of the apparatus for carrying out the method according to the invention provides that a first flue gas treatment plant containing hot flue gas from a boiler furnace is preceded by a regenerative heater; The outlet is in communication with the NOx removal plant via the regenerative heater, and the air preheater is heated by heat extracted from the purified flue gas discharged from the NOx removal plant. and a gas preheater is preferably in communication between the first flue gas treatment plant and the regenerative heater.

In a third embodiment of the apparatus, a fourth heat exchanger has a primary flow path connecting the first heat exchanger and a first flue gas treatment plant, and a fifth heat exchanger for preheating the air. An air preheater having a secondary flow path in communication with the flow path and preheating the combustion air is in communication between the third and fifth heat exchangers and in communication with an outlet of the NOx removal plant and the -NOx Heated by the purified flue gas discharged from the removal plant.

A fourth embodiment of the device according to the invention provides that the first flue gas treatment plant for receiving hot flue gas from a boiler furnace has at least one air preheating heat exchanger and at least one air preheating heat exchanger.
(characterized in that it is preceded by a heat exchanger for reheating the flue gas of Il; the outlet of said first flue gas treatment plant communicates with a NOx removal plant; and the air preheater is in communication with said NOx removal plant. and is heated by purified flue gas discharged from the NOx removal plant.

A number of benefits are provided by the method and apparatus of the present invention. For gas-fired power plants where the flue gas does not contain natural gas or 302, it is possible to use catalysts with optimal surface areas, weights and active substances, since the active substances only need to be treated on the surface. , manufacturing costs are greatly reduced. As a result, problems with contamination or catalyst deactivation are minimized and catalyst life can be greatly increased. It is further ensured that there is no NH3 in the fine ash or in the final product of the flue gas desulfurizer such as gypsum or in the sewage from the flue gas desulfurizer.

Further features, details and advantages of the invention will be explained in more detail with reference to the drawings, in which five exemplary embodiments are shown, in which similar units and blocks have been given the same reference numerals.

In Figure 1, a first embodiment is shown in which hot flue gases (2) from a boiler furnace 1) are fed to a heat resistant heat transfer fluid (4) such as oil.
into the primary flow path of the heat exchanger (3), which has a secondary flow path containing. The flue gas (2) passes from the heat exchanger (3) through the Opsin electrostatic precipitator (5) to the flue gas treatment plant (6).
), the plant may consist of a flue gas desulfurization unit. The cooled purified flue gas (7) is then heated to 90-110°C in a steam absorber (8). This is described in Austrian patent publication mA 6432/83. In the absorber, the purified flue gas contacts an absorbent that absorbs water vapor from the purified flue gas. This absorption has an exothermic effect, resulting in the temperature increase of the purified flue gas.

For final heating of the purified flue gas, the gas is passed through a heat exchanger (9
) is forced to pass through the secondary flow path. The heat exchanger (9) has a primary flow path that communicates with the secondary flow path of the heat exchanger (3). The reheated purified flue gas (7) is fed to the NOx removal plant αl. In the regenerative air preheater (11), the heat contained in the purified flue gas discharged from the NOx removal plant α1 is transferred to the combustion air (12), which air was previously heated in the absorber (8). ) is preheated inside. The purified flue gas discharged from the air preheater (11) is sent to the chimney (13).
) into the atmosphere. A branched stream of combustion air (12) discharged from the air preheater (11) is fed to the absorber (8) and supplies it with the energy required for withdrawal.

The cooled air discharged from the absorber (8) is passed through the blower (
14) and mixed with the combustion air (12) for feeding the air preheater (11). Combustion air (12
), the air is forced through the secondary flow path of the heat exchanger (15), which communicates in series with the secondary flow path of the heat exchanger (3). It has a primary flow path. The heat transfer fluid (4) is sent to the heat exchanger (3) by a pump (16), which pumps the heat transfer fluid through the heat exchanger (15) and from the heat exchanger (3). Vessel (9
).

The heat absorber (8) shown in Figure 1 may be omitted if the heat exchangers (3) and (9) have suitable dimensions and if the hot flue gas has a suitable heat content. You may, in that case,
The purified flue gas discharged from the flue gas desulphurization device (6) is reheated only in the heat exchanger (9).

The purified flue gas entering the NOx removal plant is preferably 1
The temperature is from 30 to 450°C, preferably from 160 to 380°C, for example from 200 to 300°C.

To facilitate understanding of the temperatures at the flue gas service inlet and outlet, let us discuss an example of oil and combustion air used as transfer fluids.

For example, the hot flue gas (2) leaving the boiler furnace (1) is at a temperature of 370°C and heats the oil in the heat exchanger (3) from a population temperature of 130 to 350°C. Heat exchanger(
The flue gas (2) discharged from 3) is at a temperature of 150°C and enters a flue gas desulphurization device (6), which discharges the flue gas at a temperature of 60°C. The cooled purified flue gas (7) is in a steam absorber (8) about 1
Heated to 10°C.

The oil (4) heated in heat exchanger a (3) first flows to heat exchanger (15) where it is used for the final heating of the combustion air to about 325°C. The oil (4) leaving the heat exchanger (15) is at a temperature of 320° C. and at that temperature it enters the heat exchanger (9) in which it collects the purified flue gas (7) discharged from the steam absorber. ) is heated to 300°C.

At that temperature, the purified flue gas is removed from the NOx removal plant αl.
Enter. The oil (4) leaving the heat exchanger a (9) is at a temperature of 130°C and at this temperature it is pumped by the pump (16) into the heat exchanger (
3).

The combustion air (12) is preheated to approximately 90°C by the heat generated by the absorption of water vapor and heated to 270°C in the air preheater (11) and heated to 270°C in the heat exchanger (15).
1 to a final temperature of 325°C.

The purified flue gas (7) leaving the NOx removal plant is about 3
00℃, and the air preheater (11
), the purified flue gas is heated to 130°C by this preheater.
Leaves at a temperature of The gas then escapes through the chimney. The high outlet temperature ensures very good diffusion of residual contaminants, which are present in the flue gas only in small amounts.

A second embodiment is shown in FIG. 2, which is very similar to the embodiment shown in FIG. Heat exchanger 13), (91.

(15) is replaced by a regenerative heater (17), which has three chambers and may for example be a three-chamber Ljungström gas preheater. Flue gas and air channels must be arranged in the preheater in the correct order: flue gas from the boiler furnace, combustion air, flue gas from the NOx removal plant, in this order. ensures that the gas stream is at the correct temperature and that gas leakage from the raw gas flow path to the purge gas flow path is negligible.

In this case, the absorber (8) shown in the first diagram is replaced by the gas preheater (18).
), which was supplied with steam bled from a turbine. This gas preheater (18)
may be replaced by conventional rotary gas preheaters or other regenerative heaters, in which the heat is distributed between the flue gas to be supplied to the flue gas desulphurizer (6) and the smoke discharged from it. The road gas is exchanged between. In this embodiment, the gas preheater (18) can also be used if the regenerative heater (17) is of suitable size or if the hot flue gas has a suitable heat content. May be omitted.

The third embodiment shown in Figure 3 is also highly similar to the first embodiment. The absorber (8) was omitted and a heat exchanger was provided, which was used to conduct the flue gas to be fed to the flue gas desulphurization device (6) and a heat exchanger (19) for air preheating. It consists of a heat exchanger (20) for guiding combustion air to be supplied to the combustion chamber (11). A heat transfer fluid is circulated through the heat exchangers (19) and 20) by a pump (22). They are interconnected by a tubing system (21).

1.2 and 3. In the second and third embodiments, the NOx removal plant αω is equipped with a heat exchanger (9
) or a regenerative heater (17)' on the other hand and an air preheater (
11). Alternatively, the NOx removal device is configured such that if the heat exchange area is formed by the catalyst,
It can also be integrated into the heat exchanger (9) or air preheater (11).

In FIGS. 4 and 5 only the heat exchanger next to the boiler furnace (11) is shown. The remaining units are designed and interconnected in the same way as in FIG. 1 or 3.

According to the fourth embodiment of FIG. 4, a heat transfer type heat exchanger is provided, which includes a heat exchanger (23) for conducting flue gases and a heat exchanger for conducting combustion air.

The heat exchangers (23) and (24) are interconnected by a pipe system (25), through which a heat transfer fluid is circulated by a pump (26).
') corresponds to the heat exchanger (3) shown in the first figure.

Heat exchanger (3') is correspondingly connected to heat exchanger a (9) of FIG.

In the fifth embodiment of FIG. 5, a regenerative heat exchanger is provided, which has a rotary air preheater (27) in the flue gas flow path of the preheater for heat exchange! fl(3')
are connected, which correspond to the heat exchanger (9) shown in the first diagram. The transfer heat exchanger consisting of heat exchangers (3') and (9) may be replaced by a regenerative heat exchanger system, for example a rotary gas preheater.

[Brief explanation of the drawing]

Figure 1 is a block diagram of the first embodiment, Figure 2 is a block diagram of the second embodiment, Figure 3 is a block diagram of the third embodiment, and Figures 4 and 5 are flue gas according to the present invention. It is a figure which shows two different Examples of a preheating means, respectively. (1) is the boiler furnace, (2) is the hot flue gas, (3) is the first heat exchanger, (4 is the heat transfer fluid, (5) is the desulfurization device, (7
) is purified flue gas, (9) is the second heat exchanger, α is NO
x removal blunt, (11) is air preheater, (12) is combustion air, (15) is third heat exchanger, (I7) is regenerative heater, (1st) is gas preheater, (27) is a rotary air heater. Day g, 4 Fig, 5 = 109

Claims (1)

[Claims] 1. A method for heat treating flue gas sent from a boiler furnace through two flue gas treatment plants connected in series and combustion air to be supplied to the boiler furnace, comprising: , the heat extracted from the flue gas reheats the flue gas in a heat treatment method in which the flue gas is at a higher temperature in a second flue gas treatment plant than in a first flue gas treatment plant. A method for heat treatment of flue gas and combustion air from a boiler furnace, characterized in that it is used for heating and preheating the air. 2. A method for heat treatment of flue gas and combustion air from a boiler furnace as claimed in claim 1, in which the flue gas is heated to a temperature sufficient for catalytic removal of NOx, preferably 13
A process for heat treatment of flue gas and combustion air from a boiler furnace, characterized in that it is reheated to a temperature in the range from 0 to 450°C, suitably from 160 to 380°C. 3. A method for heat treatment of flue gas and combustion air from a boiler furnace according to claim 1, characterized in that the flue gas is reheated in one or more stages, preferably in two or three stages. A method for heat treatment of flue gas and combustion air from a boiler furnace. 4. A method for heat treatment of flue gas and combustion air from a boiler furnace according to claim 1, characterized in that the air is preheated in one or more stages, preferably in two or three stages. Method for heat treatment of flue gas and combustion air from. 5. A method for heat treatment of flue gas and combustion air from a boiler furnace as claimed in claim 4, wherein the heat extracted from the flue gas is first preheated at a final air preheating stage at a high temperature. and then used for reheating the flue gas at a lower temperature. 6. A method for heat treatment of flue gas and combustion air from a boiler furnace as claimed in claim 4, in which heat is extracted from the flue gas at an elevated temperature and preheats the air and regenerates the flue gas. Flue gas and combustion air from a boiler furnace, characterized in that the heat extracted from the flue gas is then used to preheat the combustion air in a first air preheating stage. heat treatment method. 7. The method for heat treatment of flue gas and combustion air from a boiler furnace according to claim 3, wherein the flue gas is reheated by an absorption device in all flue gas preheating stages before the final stage. A method for heat treatment of flue gas and combustion air from a boiler furnace, characterized in that: 8. In the method for heat treatment of flue gas and combustion air from a boiler furnace according to claim 3, in all the flue gas reheating stages before the final stage, the flue gas is heated by a regenerative heater. A flue from a boiler furnace, characterized in that it is reheated by a heat exchanger between the flue gas to be supplied to a first flue gas treatment plant and the flue gas discharged from said plant. Method for heat treatment of gas and combustion air. 9. In the method for heat treatment of flue gas and combustion air from a boiler furnace according to claim 3, the flue gas is supplied with steam in all flue gas reheating stages before the final stage. A method for heat treatment of flue gas and combustion air from a boiler furnace, characterized in that the flue gas and combustion air are reheated in a heat transfer heater. 10. In the method for heat treatment of flue gas and combustion air from a boiler furnace as claimed in claim 4, in all air preheating stages before the final stage, the air is heated by the heat released in the absorption device. and/or a method for heat treatment of flue gas and combustion air from a boiler furnace, characterized in that the flue gas and combustion air are preheated by heat exchange with the flue gas discharged from the second flue gas treatment plant. 11. A method for heat treating flue gas sent from a boiler furnace through two serially connected flue gas treatment plants and combustion air to be supplied to the boiler furnace, comprising:
The flue gas is at a higher temperature in the second flue gas treatment plant than the first flue gas treatment plant, and the heat extracted from the flue gas reheats the flue gas and In an apparatus for carrying out a method for heat treatment of flue gas and combustion air from a boiler furnace, characterized in that it is used for preheating air, the flue gas treatment plant containing the hot flue gas from the boiler furnace comprises: one of the second heat exchangers preceded by a primary flow path of the first heat exchanger, the first heat exchanger for reheating the purified flue gas discharged from the first flue gas treatment plant; a secondary flow path communicating with the secondary flow path, a second heat exchanger having a secondary flow path communicating between the first and second flue gas treatment plants; A device for heat treating flue gas and combustion air from a boiler furnace, characterized in that the passage communicates with the primary passage of a third heat exchanger for preheating the air. 12. The apparatus for heat treating flue gas and combustion air from a boiler furnace as set forth in claim 11, wherein the secondary flow path of the first heat exchanger is connected to the second and third heat exchangers. two of the first heat exchanger are in series communication with the primary flow path;
A device for heat treating flue gas and combustion air from a boiler furnace, characterized in that the heat transfer fluid discharged from the secondary flow path is first led to the primary flow path of the third heat exchanger. 13. In the apparatus for heat treating flue gas and combustion air from a boiler furnace according to claim 11, a water vapor absorption device for preheating the combustion air to be supplied to the third heat exchanger, Flue gas and combustion from a boiler furnace, characterized in that the flue gas flow path is in communication between the first flue gas treatment plant and the secondary flow path of the second heat exchanger. A device that heat-treats air. 14. In the apparatus for heat treating flue gas and combustion air from a boiler furnace according to claim 11, the secondary flow path of the third heat exchanger is an air preheater for preheating the combustion air. and a primary flow path of the third heat exchanger is communicated with an outlet of the NOx removal plant, so that the third heat exchanger is heated by the purified flue gas discharged from the NOx removal plant. A device for heat treating flue gas and combustion air from a boiler furnace, characterized by: 15. A method for heat treating flue gas sent from a boiler furnace through two serially connected flue gas treatment plants and combustion air to be supplied to the boiler furnace, comprising:
The flue gas is at a higher temperature in the second flue gas treatment plant than the first flue gas treatment plant, and the heat extracted from the flue gas reheats the flue gas and In an apparatus for carrying out a method for heat treatment of flue gases and combustion air from a boiler furnace, characterized in that it is used for preheating air, a first flue for receiving hot flue gases from the boiler furnace. A gas treatment plant is preceded by a regenerative heater, the outlet of the first flue gas treatment plant communicates via the regenerative heater with a NOx treatment plant, and an air preheater is connected to the NOx removal plant. An apparatus for heat treating flue gas and combustion air from a boiler furnace, characterized in that the apparatus is in communication with the outlet and heated by purified flue gas discharged from the NOx treatment plant. 16. An apparatus for heat treating flue gas and combustion air from a boiler furnace as set forth in claim 15, wherein a gas preheater is communicated between the first flue gas treatment plant and the regenerative heater. An apparatus for heat treating flue gas and combustion air from a boiler furnace, characterized in that: 17. In the apparatus for heat treating flue gas and combustion air from a boiler furnace as set forth in claim 15, the outlet of the air preheater communicates with the boiler furnace via the regenerative heater. An apparatus for heat treating flue gas and combustion air from a boiler furnace, characterized by: 18. The apparatus for heat treating flue gas and combustion air from a boiler furnace according to claim 15, wherein the regenerative heater is a Ljungström preheater. Equipment for heat treating gas and combustion air. 19. In the apparatus for heat treating flue gas and combustion air from a boiler furnace according to claim 11, the fourth
a primary flow path of a heat exchanger is in communication between the primary flow path of the first heat exchanger and the flue gas treatment plant and directs air;
The air preheater for preheating the combustion air is a NOx removal plant. The primary flow path communicated with the outlet of the third and fourth heat exchangers.
a secondary flow path communicated between the secondary flow paths, and the NOx
A device for heat treating flue gas and combustion air from a boiler furnace, characterized in that it is heated by purified flue gas discharged from a removal plant. 20. A method for heat treating flue gas sent from a boiler furnace through two serially connected flue gas treatment plants and combustion air to be supplied to the boiler furnace, comprising:
The flue gas is at a higher temperature in the second flue gas treatment plant than the first flue gas treatment plant, and the heat extracted from the flue gas reheats the flue gas and In an apparatus for carrying out a method for heat treatment of flue gases and combustion air from a boiler furnace, characterized in that it is used for preheating air, a first flue for receiving hot flue gases from the boiler furnace. an outlet of the first flue gas treatment plant, the gas treatment plant being preceded by at least one air preheating heat exchanger primary flow path and at least one flue gas reheating heat exchanger; is NO
a flue gas from a boiler furnace, characterized in that the air preheater is in communication with an outlet of the NOx removal plant and is heated by the purified flue gas discharged from the NOx removal plant; A device that heat-treats combustion air. 21. A device for heat treating flue gas and combustion air from a boiler furnace according to claim 11, wherein the first flue gas treatment plant is a flue gas desulfurization device. equipment for heat treating flue gas and combustion air from 22. A device for heat treating flue gas and combustion air from a boiler furnace according to any one of claims 14, 15, 19 and 20, wherein the NOx removal plant and the air preheater are compact. A device for heat treating flue gas and combustion air from a boiler furnace, characterized in that it is combined into a unit. 23. A device for heat treating flue gas and combustion air from a boiler furnace according to claim 19 or 20, in which the NOx removal plant and the second heat exchanger are combined into a compact unit. An apparatus for heat treating flue gas and combustion air from a boiler furnace, characterized in that: 24. A device for heat treating flue gas and combustion air from a boiler furnace according to any one of claims 14, 19 and 20, comprising the second heat exchanger, the NOx removal plant and the air 1. A device for heat treating flue gas and combustion air from a boiler furnace, characterized in that a preheater is combined into a compact unit and the flue gas channels are connected in series in this order. 25. An apparatus for heat treating flue gas and combustion air from a boiler furnace according to claim 22 or 24, wherein at least one of the second heat exchanger and the air preheater is configured to heat a catalyst containing heat. Apparatus for heat treating flue gas and combustion air from a boiler furnace, characterized in that it has a flue gas flow path delimited by an exchange surface.