JPS5942236B2 - Corrosion prevention method and equipment used for heat exchange of gas containing condensable corrosive components - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for preventing corrosion of heat exchangers in heat exchange of gases containing corrosive components that can condense.

During the last millennium, a large number of sulfuric acid plants have been designed and constructed based on the multi-stage contact/multi-stage absorption principle.

In this chemical process, a gas stream containing sulfur dioxide and oxygen is subjected to an intercooling operation to remove the heat generated from the reaction that converts the large amount of sulfur dioxide contained in the gas stream to sulfur trioxide. It goes through a multi-stage catalytic conversion process.

The gas is then sent to an intermediate absorption step where the formed sulfur trioxide is absorbed from the gas stream.

As the absorbent, sulfuric acid with a concentration of about 98 to 99% is usually used.

Some processes use hot sulfuric acid absorbers to provide a portion of the heat required to reheat the residual gas stream destined for the second conversion step to the catalytic reaction initiation temperature.

The residual gas stream, now at the catalytic reaction initiation temperature, is introduced into a subsequent catalytic catalytic step to convert residual sulfur dioxide to sulfur trioxide for absorption prior to discharging the gas stream to the atmosphere.

Because multiple stages of conversion and absorption steps are used,
The total conversion rate that can be achieved is very high.

For example, the conversion rate of sulfur dioxide to sulfur trioxide is 99.9
% or more.

Problems arise in equipment maintenance and in the piping section leading from the intermediate absorber back to the so-called cold heat exchanger or other heat exchanger combination in order to preheat the gas stream to its introduction temperature to the next catalytic conversion step.

Acid mist exists in the gas flow, and the sulfuric acid that had previously evaporated condenses, resulting in severe corrosion of the piping, and when the sulfuric acid condensation and acid mist remover does not work satisfactorily. The inlet end of the heat exchanger is also corroded due to condensation of acid mist.

Since the gas stream leaving the intermediate absorber is in equilibrium with the acid used in the intermediate absorber, the gas stream contains free sulfuric acid;
This sulfuric acid condenses on cold metal surfaces below the dew point of sulfuric acid, causing severe corrosion problems.

Furthermore, if the process air or process gas is insufficiently dried, the sulfur trioxide subsequently produced during the process may react with water vapor, resulting in the formation of sulfuric acid mist.

Free particles of acid mist, present in aerosol form, coalesce due to flow disturbances in the piping towards the cold heat exchanger and then adhere to the internal surfaces of the heat exchanger, causing further corrosion problems.

Many sulfuric acid plants based on multi-stage contact/multi-stage absorption principles encounter serious corrosion problems, for example in pipework and in cold heat exchangers, and some are completely destroyed after 6 to 9 months of use. It is known that it can be damaged.

For this reason, equipment losses and lost time required for equipment replacement are large.

Practical solutions to these problems have not yet been presented.

The present invention provides a method for disposing a baffle plate in the outer body of the heat exchanger at a position near the tube sheet on the inlet side of the relatively cold gas flow, and the baffle plate is disposed adjacent to the tube sheet by the hot gas flow. Corrosion is prevented by providing a hot zone above the condensation temperature of the corrosive components in the cold gas stream.

The invention also provides a modified process for the production of sulfuric acid known as a multi-stage contact/multi-stage absorption system.

That is, in addition to the corrosion prevention method in the heat exchanger described above, the present invention also provides a method for preventing corrosion in the heat exchanger in the production process of sulfuric acid or fuming sulfuric acid. Maintaining the sulfuric acid in the gas phase by introducing sufficient external heat from a corrosive heating medium into the piping to maintain the temperature of the gas stream above the dew point of the sulfuric acid being carried by the gas stream. to prevent sulfuric acid from condensing on the piping surface.

According to the present invention, the heat exchanger itself is installed in high temperature areas where gas does not flow or where gas hardly flows in order to prevent sulfuric acid and collected acid mist from condensing on the soil and prevent surface corrosion. By providing this, it is possible to prevent sulfuric acid and acid mist from depositing inside the heat exchanger itself.

The invention also prevents corrosion in a multi-stage contact/multi-stage absorption sulfuric acid production plant and extends the life span of the equipment used to convey the gas stream from the intermediate absorber to at least one heat exchanger by a thousand to several thousand meters. It can be increased by a year or more.

Corrosion in the piping leading the gas from the intermediate absorber used in the process to the next heat exchanger used to preheat the catalyst to the catalytic reaction initiation temperature can be caused by sulfuric acid or sulfur trioxide contained in the process gas stream. This can be prevented by providing sufficient external heating to the piping to maintain the process gas stream temperature above the dew point of water and water.

The present invention will be explained below based on a typical example of a multi-stage contact/multi-stage absorption sulfuric acid plant.

After passing the gas stream containing sulfur dioxide and oxygen through multiple catalytic conversion steps with intercooling placed in the middle of each step, an intermediate absorber containing 98-99% sulfuric acid as the absorbent A gas stream is passed through the tower.

Following intermediate absorption to remove the sulfur trioxide produced, the gas stream is sent to a gas-to-gas heat exchanger to convert all or a portion of the gas stream into one or more catalytic conversion steps. Preheat to the reaction initiation temperature required to convert residual sulfur dioxide to sulfur trioxide.

This operation is performed prior to absorbing the sulfur trioxide generated from residual sulfur dioxide in the gas stream in the final absorption step.

A plant with a production capacity of about 1200 tons per day, in which, following intermediate absorption, all or part of the gas stream is reheated to the catalytic reaction initiation temperature and introduced into the next catalytic catalytic step. The case of a plant in which piping is provided between a gas-to-gas heat exchanger and the intermediate absorber will be described.

The piping in a plant of this size is usually about 2 m in diameter (6.5 m in diameter).
The external heat transfer area, which suffers convective and radiant heat losses, measures approximately 121 m'' (1300 square feet).

Under normal operating conditions, the process gas flow ducted from the intermediate absorber is approximately 1930771”/
(68,000 standard cubic feet/minute) or about 151
300 kg/hour (333,000 pounds/hour).

The standard exit temperature of the gas stream leaving the intermediate absorber is approximately 82.2
°C (180'F), ambient temperature is 0 °C (below 32), wind speed perpendicular to the pipe is 8 kg/hour (5 miles/hour),
The specific heat of the gas stream is approximately 0.13 kcal/kg (0.24
B T U/lb), the process gas flow will be at least about 2.2 mm, depending on other weather conditions such as cloudy weather, daylight, or late night.
℃ (4V) or more.

In this case, the estimated heat loss from the process piping itself is approximately 662 kcal/hr/m (244 BT
80,200 kcal/hour (318,000 BUT/hour) for a total duct length of 20 meters (65 feet).

The gas stream leaving the intermediate absorption column is of course in equilibrium with the sulfuric acid absorbent.

From vapor phase data of vapor in equilibrium with sulfuric acid, 98
．． For an absorber containing 6% H2SO4, when the gas in the duct is cooled to about 2.2°C (4y), the vapor pressure of sulfuric acid drops from 0.04 mm to about 0.035 mm of mercury.

This corresponds to a partial pressure drop of 0.005 mm of mercury for sulfuric acid vapor.

Heat loss occurs in two ways.

One is the reduction in the sensing temperature of the gas due to cooling of the process gas stream, and the other is the release of the latent heat of condensation of sulfuric acid as it condenses in the gas stream and changes from the gas phase to the liquid phase. It is the amount of heat.

Under these conditions, approximately 3.06 kg/hour (6
, 75 pounds/hour) of sulfuric acid is condensed from the gas phase to the liquid phase.

The sulfuric acid condenses into droplets and coalesces into sulfuric acid liquid, which accumulates on the cold ducts and metal surfaces of the heat exchanger.

If condensed at this rate, the annual amount would be approximately 24.5) n(27).
tons of acid condenses and accumulates inside ducts or gas-to-gas heat exchangers.

This acid must be heated above the boiling point, reevaporated into the gas phase, or removed from the drain manifold.

If acid formation is left unchecked, first of all about 98.
Liquid sulfuric acid with a concentration of 6% will come into contact with the metal surface.

Based on the known corrosion curve for carbon steel, a common material used for pipework and heat exchanger tubular construction, in Plato sulfuric acid, this concentration, i.e. 149°C of 98.6% sulfuric acid.
(3ooy) corrosion rate is 5.08mm (2
00 mils) and the pipework and heat exchanger tubes are short-term, i.e., under normal plant operating conditions for pipes and pipework with standard wall thicknesses of 3.4 to 3.05 mm (134 to 120 mils). This results in an account that will only last for about 6 to 8 months.

In order to overcome the problem of corrosion that occurs as a result of condensation of sulfuric acid, in the embodiment shown in the drawings 1, a gas pipe is provided on the outer periphery of the piping section 10 leading from the intermediate absorber (not shown) to the gas-to-gas heat exchanger 12. A heat source is provided that is capable of transferring heat to the gas stream in an amount sufficient to maintain the stream at a temperature above the dew point of the sulfuric acid.

As shown, the heat source consists of a spaced helical array of tubes 14 or preferably spaced longitudinal tubes disposed circumferentially along their entire length in the same orientation as the piping section 10; Steam via Dowthe
rm) or a similar non-corrosive heat transfer medium.

Between the tubes 14 there is a space 16 which is heated by the liquid transmission flowing through the tubes 14 .

A reinforcement layer 18 is provided to support the gas space 16, typically an air gap between the outer insulator 20 and the tubes 14 to reduce the amount of heat required by the system, and the gas space between the tubes 14 is A thermal gradient is provided so that the space is always at a high temperature and heat flows into the gas flow passing through the piping section 10.

Generally speaking, the amount of heat delivered through tube 14 will increase the air gap 16 between tube 14 and insulator 20 by at least 55.6 to 11.1.1 degrees C. above the average temperature of the gas stream. (
The temperature must be maintained at an elevated temperature of 100-200° C. or more to ensure that sufficient heat is transferred from the external heat source to the internal surfaces of the ducts carrying the process gas stream to prevent the sulfuric acid from condensing.

The method of arranging a jacket around the piping section instead of the tube 14 is not a preferred method.

This is because, in the event of a leak in the internal ducts, the fluid heating medium will enter the gas of the sulfuric acid plant and contaminate it.

The duct 10 and the heat exchanger 12 are maintained at a temperature above the dew point of sulfuric acid by applying means to allow heat to flow into the gas stream at an intermediate portion between the intermediate absorption tower and the heat exchanger 12. Corrosion due to sulfuric acid condensation can be eliminated in both cases.

Therefore, the life of the expensive and essential equipment involved in the operation of the multi-stage contact/multi-stage absorption sulfuric acid production process can be extended.

Although the heating system surrounding the duct 10 prevents condensation during steady operation, condensation of sulfuric acid or sulfite compounds can occur under overload conditions.

This type of condition occurs during start-up or when the duct heating system itself malfunctions.

As a precautionary measure, a weir 19 is provided around the duct 10 just before the heat exchanger 12 to collect the condensates flowing through the duct 10 and prevent them from entering the heat exchanger 12.

By providing a drain 21 with a valve 23 in combination with the weir 19, the collected acid and to be removed from the duct 10 can be drawn off through the mouth of the coin 21.

The drain 21 also serves as a means for monitoring the gas flowing through the duct 10.

When the valve 23 is opened during operation, if gas comes out, it can be confirmed that the inner surface of the piping section is dry and there is no condensate.

If liquid comes out, it indicates that condensation has occurred and the duct needs to be heated further to prevent condensation, or that it is under an overload condition.

Other significant problems associated with corrosion problems in piping and heat exchangers are the condensation and collection of sulfuric acid and the condensation of acid mist that occur on the surfaces of the heat exchangers.

The acid mist is present in the form of an aerosol of fine sulfuric acid particles and passes through a mist eliminator or equivalent device with the intermediate absorber effluent.

It is also part of the present invention to provide an improved gas-to-gas heat exchanger whose construction avoids sulfuric acid and sulfuric acid mist droplet aggregation or dripping that avoids sulfuric acid aggregation/deposition and corrosion of the heat exchanger surfaces.

A typical gas-to-gas heat exchanger consists of an inlet head with a gas inlet and an outlet head with a gas outlet.

These heads are connected to each other, for example by tubes or spaced plates.

The tube is surrounded by an outer body and has a gas inlet and a gas outlet, so that the gas flow flowing through the tube can be heated or cooled by the gas flow flowing through the tube within the outer body. There is.

Typical of these gas-to-gas heat exchangers are shell-and-tube heat exchangers and plate-to-plate heat exchangers.

In many processes, such as multi-stage contact/multi-stage absorption processes, the gas stream to be heated can condense on the surfaces of the heat exchanger, especially on the surfaces where the gas stream enters the heat exchanger. Contains ingredients.

As mentioned above, one example of such a gas stream is the gas stream returning from an intermediate absorber.

FIG. 1 shows a case in which a relatively cold gas stream from an intermediate absorber flows through the shell side of heat exchanger 12 and exchanges heat with hot gas flowing through heat exchanger tubes 30 from a catalytic conversion step. shows.

In the case shown in FIG. 2, the relatively cool gas stream from the intermediate absorber flows through tubes 30 of heat exchanger 12 and heats the hot gas flowing through the shell side of heat exchanger 12 from the catalytic conversion process. Make an exchange.

In either case, the heat exchanger 12 is connected to the outer body 22
and an inlet 24 for gas entering from one or more conversion stages before or after intermediate absorption, and an inlet head for either gas from the conversion process or gas from the intermediate absorber. 26 and an upper transverse tube plate 28 from which tubes 30 extend vertically.

Lower transverse tube plate 32 to which the tubes are connected by flares
, which forms an outlet head 34 through which the gas exits via tube 40 to another heat exchanger or catalytic conversion process.

In the case shown in Figure 1, when only one heat exchanger was used to reheat to the catalytic reaction initiation temperature, the intermediate absorber returned at approximately 82.2°C (180'''F'). While flowing through passage 36, the gas is heated on the shell side of heat exchanger 12 and exits through passage 38 to the next conversion step at approximately 438°C (below 820°C).

When multiple heat exchangers are used, the gas flow exits at a lower temperature because the heat exchange area is smaller.

The gas stream delivered from the catalytic conversion step at about 510-621° C. (below 950-1150° C.) transfers heat to the gas from the intermediate absorber through the tubes 30 of heat exchanger 12 to achieve the usual desired catalytic contact. The reaction initiation temperature is about 4
The temperature will be 38°C (820″F).

Since the temperature of the gas stream entering the heat exchanger 12 from the intermediate absorber may be below the condensation temperature of the sulfuric acid in the system, the accompanying sulfuric acid mist may be caused by flow turbulence, etc.
0 and cross tube sheets 32 and begin to corrode.

To eliminate this possibility, according to the invention, a perforated intermediate baffle plate 42 is provided.

The baffle plate 42 maintains a gas-free zone 44 between the baffle plate and the transverse tube sheet 32.

Due to the hot gas flow flowing through the tube 30, the area without gas flow is above the condensation temperature of the sulfuric acid mist, i.e. about 343°.
c (650y) or higher.

Any sulfuric acid mist that condenses from the gas stream falls through the opening in the baffle plate 42 into the area 44, which is hot enough to evaporate back into the gas stream, preventing the sulfuric acid mist from falling and entraining, and Corrosion problems of heat exchangers associated with heat exchangers can be prevented.

The combination of the gas-free zone 44 and the duct 10 transfers pressure heat to the gas stream to keep the sulfuric acid in the gas stream in gaseous form at all times, so that it condenses on the tubes 30 and on the transverse tube sheet 32. It can prevent corrosion and eliminate corrosion problems.

In the case shown in FIG. 2, the gas stream flows from the head 26 through the inlet tube 30, enters the flow passage 24 and flows through the shell side of the heat exchanger.
It exchanges heat with the gas stream 'F) from the head 34 via a channel 40 to a further heat absorber or heat exchanger at approximately the same temperature as above.

In this example, since the tubes 30 are attached perpendicularly to the transverse tubesheet 28 by flares, recesses are created on the tubesheet 28 where sulfuric acid or acid mist can collect and condense.

There is also the possibility of accumulation and condensation on the walls of the inlet head 26.

To avoid this, approximately 416-454°C (780°C
The presence of the baffle plate 42 allows a portion of the gas flow exiting from the conversion process (from 55 oy to 55 oy) to be routed through an externally branched channel 48 or an equivalent internally branched bypass (not shown). It flows into the no-flow area 44.

The amount of gas flowed into section 44 by bypass is approximately 3 to 20% of the total gas flow.

A portion 43 of baffle plate 42 may be removable and configured to allow gas from the hot converter to flow across baffle plate 30 to outlet 46 .

Even with this configuration, the effect of maintaining the walls of tube 30, tube sheet 28, and head 26 at a temperature sufficient to prevent condensation of sulfuric acid and acid mist is the same.

By doing so, the upper part of the tube 30 and more importantly the adjacent walls of the tubesheet 28 and head 26 can be effectively kept above the condensation temperature of the sulfuric acid and acid mist that falls onto these surfaces. The prone sulfuric acid and acid mist can be evaporated back into the gas stream coming from the intermediate absorber.

Corrosion of the tubesheet 28, tubes 30 and adjacent walls of the head 26 is thus avoided.

As shown in FIG. 2, it is preferable to insulate the entire heat exchanger to help prevent corrosion problems from occurring.

In the example shown in Figure 2, the evaporation of the sulfuric acid and acid mist and return to the gas stream takes place indirectly, whereas the
In the case shown, the reboiling of the acid mist and its return to the gas stream takes place directly.

In either case, however, a high temperature zone is provided to increase the temperature of that portion of the heat exchanger to eliminate the usual corrosive condensate due to sulfuric acid condensation or acid mist collection.

In the case of a plate-to-root heat exchanger, a baffle plate corresponding to baffle plate 42 is placed between the plates, but its position is on the side of the plate opposite to the side of the plate communicating with the head.

In summary, a fundamental improvement to gas-to-gas heat exchangers is that by flowing a hot process gas, e.g. The point is that a zone is provided inside the heat exchanger to prevent corrosion of the heat exchanger surface due to condensation or aggregation of these corrosive components.

Preferred embodiments of the present invention are listed below.

(a) the relatively cold gas stream is the effluent stream from a sulfur trioxide absorber in a multistage contact/multistage absorption sulfuric acid production process and contains at least condensable sulfuric acid, and the hot gas stream is an effluent stream containing at least condensable sulfuric acid; , a gaseous stream emanating from a process of converting sulfur dioxide to sulfur trioxide.

(b) A method in which external heat is supplied by flowing a fluid heating medium through a row of tubes arranged at intervals in contact with the piping section, the tubes having a reinforcing layer and an external insulating layer. A method according to the patent, characterized in that a gas space in the middle of said tube is heated by a stream of fluid heating medium surrounded by said tube and flowing through said tube.

(c) the fluid heating medium stream flowing through said tube maintains the gas space at a temperature of about 55.6 to about 111.1 degrees Celsius or more above the temperature of the gas stream flowing through said piping section; The method according to item b) above.

(d) A method according to item (b) above, characterized in that the fluid heating medium is water vapor.

(e) A method according to item c) above, characterized in that the fluid heating medium is water vapor.

3. A method according to claim 2, characterized in that (f) the hot zone is heated by indirect heat exchange with a gas stream flowing from the conversion step through the gas-to-gas heat converter.

(g) A method according to claim 2, characterized in that the hot zone is heated directly by the flow of at least a portion of the gas stream flowing through the zone from the conversion step.

(h) The method of item iQg), characterized in that about 3 to 20% of the total gas flow from the conversion step is passed to the hot zone.

(i) the relatively cold gas stream is the effluent stream from a sulfur trioxide absorber in a multi-stage contact/multi-stage absorption sulfuric acid production process and contains at least condensable sulfuric acid; 4. A gas-to-gas heat exchanger according to claim 3, characterized in that the gas stream is a gas stream emanating from a process of converting sulfur dioxide to sulfur trioxide.

(j) the relatively cold gas stream is the effluent stream from the sulfur trioxide absorber in the multi-stage contact/multi-stage absorption sulfuric acid production process and contains at least condensable sulfuric acid, and the hot gas stream is the effluent stream containing at least condensable sulfuric acid; 5. A gas-to-gas heat exchanger according to claim 4, wherein the gas stream exits from a process of converting sulfur dioxide to sulfur trioxide.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of one embodiment of a heat exchanger and piping section according to the present invention, and FIG. 2 is a cross-sectional view showing another embodiment of the heat exchanger and piping section according to the present invention. 10...Duc l, 12...Heat exchanger, 14...Pipe, 16...Space, 18...
... Reinforcement layer, 19 ... Cough, 20 ...
...Insulator, 21...Drain, 22...
...Outer body, 23...Valve, 24...
- Inlet, 26... Inlet head, 28-... Upper transverse tube plate, 30... Tube, 32... Lower transverse tube plate, 34... ...Exit head, 36...
... Passage, 38, 40... Channel, 42...
... Baffle plate, 44 ... Area where gas does not flow, 4
6,48...Flow path.

Claims (1)

[Scope of Claims] 1. A gas inlet head having a gas inlet, a gas outlet head having a gas outlet, and a first gas inlet head having a gas inlet and a gas outlet communicating with each other, and a first gas inlet head having a gas inlet and a gas outlet head having a gas outlet; a plurality of spaced apart gas flow tubes attached to the tubesheet forming a plurality of flow paths for gas flow and a second gas flow for indirect heat exchange around the gas flow tubes; an outer body surrounding the gas flow tube and having an inlet and an outlet for heating a relatively cold gas stream containing potentially condensable corrosive components by indirect heat exchange with the hot gas stream. In a countercurrent heat exchanger used for raising the temperature of a gas, a baffle plate is disposed within the outer body and near the tube plate on the inlet side of the relatively cold gas flow, A corrosion prevention method characterized by providing a high temperature area adjacent to the tube sheet at a temperature higher than the condensation temperature of the corrosive component. 2 A gas stream containing sulfur dioxide and oxygen is passed through multiple catalytic contacting steps in which the sulfur dioxide is converted to sulfur trioxide, cooled in the middle of the contacting steps to remove the heat due to the exotherm of the reaction, and then the gas stream is The stream is passed through at least one absorption column where it is contacted with at least sulfuric acid to separate the produced sulfur trioxide from the gas stream, and then sent via piping to a gas-to-gas heat exchanger to remove at least a portion of the gas stream. heating the gas stream to a temperature necessary to introduce at least one additional catalyst into a tangential lamp for converting residual sulfur dioxide to sulfur trioxide, prior to discharging the gas stream to the atmosphere; In a multi-stage contact/multi-stage absorption process for producing sulfuric acid or oleum by extracting the sulfur trioxide formed from the gas stream, it passes through pipes closely surrounding the piping section from the absorption tower to the heat exchanger. Sulfuric acid is brought into the vapor phase by introducing external heat from a non-corrosive heating medium into the piping in an amount sufficient to maintain the temperature of the gas stream above the dew point of the sulfuric acid being carried by the gas stream. The gas-to-gas heat exchanger includes a gas inlet head having a gas inlet, a gas outlet head having a gas outlet, and a gas inlet head having a gas outlet. and a plurality of spaced apart gas flow tubes attached to the tube plate communicating between the gas outlet heads to form a plurality of flow paths for a first gas flow therebetween; an outer body surrounding the gas flow tube and having an inlet and an outlet for forming a second gas flow for indirect countercurrent heat exchange around the flow tube; A baffle plate is disposed near the tubesheet on the inlet side of the side gas flow, and the hot side gas flow passing through the heat exchanger causes the high temperature side gas flow adjacent to the tubesheet to reach a high temperature above the condensation temperature of the corrosive components. Corrosion prevention method characterized by the provision of zones. 3. To prevent condensation of potentially corrosive components contained in a relatively cold gas stream from a gas source consisting of: A gas-to-gas counterflow heat exchanger comprising: (a) a gas inlet head having a gas inlet for a hot gas stream; and (b) a relatively cool gas stream cooled by indirect heat exchange. a gas outlet head having a gas outlet for subsequent hot gas flow; (c) a tube for passing a hot gas flow from said gas inlet head to said gas outlet head, said gas inlet head having a gas outlet; and a plurality of spaced apart gas flow tubes communicating with said gas outlet head; (d) an outer shell for indirect heat exchange of a relatively cool gas stream with a hot gas stream flowing through said gas flow tubes; a gas inlet for said relatively cool gas stream located spaced apart from said gas outlet head and a gas outlet located above said gas inlet; an outer body surrounding a plurality of gas flow tubes; (e) a gas inlet for said relatively cool gas flow and said gas outlet head spaced apart from said gas outlet head and said gas flow tubes; a baffle disposed between the baffle and the gas outlet head, the gas zone formed between the baffle and the gas outlet head being controlled by the relatively cool gas stream flowing through the gas flow tube; A heat exchanger comprising: a baffle plate for maintaining the temperature above the condensation temperature of corrosive and condensable components contained in the flow. 4. To prevent condensation of potentially corrosive components contained in a relatively cold gas stream from a gas source consisting of: A gas-to-gas counterflow heat exchanger comprising: (a) a gas inlet head having a first gas inlet for a relatively cold gas stream; and (b) heating by indirect heat exchange with a hot gas stream. (c) a gas outlet head having a first gas outlet for a relatively cool gas flow after the gas has been removed; and (c) a tube for passing a relatively cold gas flow from said gas inlet head to said gas outlet head. a plurality of spaced apart gas flow tubes in communication with the gas inlet head and the gas outlet head; (d) a relatively cool gas flow passing through the gas flow tubes to connect the hot gas stream; an outer body for indirect heat exchange with a second gas inlet for the hot gas flow and a second gas outlet spaced apart from the second gas inlet for the hot gas flow; an outer body surrounding a plurality of gas flow tubes; (e) a second gas inlet for said hot gas flow and said gas inlet head spaced apart from said gas inlet head and said gas flow tubes; a baffle plate disposed between the baffle plate and the gas inlet head, the hot zone formed between the baffle plate and the gas inlet head being connected to the high temperature zone through a bypass pipe; a baffle plate for maintaining above the condensation temperature of corrosive and condensable components contained in the relatively cool gas stream entering through the gas inlet head and the gas flow tube; A heat exchanger characterized by: