JPS62123296A - Exhaust gas heat exchanging method - Google Patents

Abstract

PURPOSE:To enable stable recovery of heat from high temperature corrosive atmosphere exhaust gas, containing sodium sulfate and sodium carbonate, or potassium sulfate in a sodium recovery boiler for a long time, by a method wherein heat transfer tubes made of Ti or a heat transfer tubes made of a Ti based alloy, e.g., Ti-Pd, are used. CONSTITUTION:Exhaust gas, e.g., SOX, H2S and HCl, produced resulting from analysis of black liquid and partial combustion and containing sodium sulfate and sodium carbonate, or dust, e.g., potassium sulfate, is introduced to a heat exchanger 4. A heat transfer tube bundle 9, spanned between two headers 10 and 11 of a heat exchanger, is formed with heat transfer tubes, made of Ti or a Ti radical alloy, e.g., Ti-Pd, and this constitution results in remarkable prevention of the occurrence of usual corrosion by SOX and H2S through the presence of sodium sulfate and sodium carbonate or potassium sulfate, and in the possibility to use the heat transfer tube for a long time. Further, this constitution can reduce gap corrosion, occurring at a gap between the tubes and the two headers 10, 11 or a support plate 12 when steam is condensed on the surface of the heat transfer tube on the low temperature side, corrosion, occurring as a result of condensate producing an HCl solution, and corrosion on the high temperature side due to the use of a heat transfer tube made of Ti based alloy, e.g., Ti-Pd, and permits decrease of a rise in a price.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is used to recover waste heat in a soda recovery boiler during paper and pulp manufacturing, and to recover waste heat from high-temperature corrosive atmosphere exhaust gas containing sodium sulfate, soda carbonate, or potassium sulfate for a long period of time. The present invention relates to a heat exchange method that can perform stable heat recovery over a long period of time.

[Conventional technology]

Generally, in paper and valve manufacturing, wood chips are heated in a digester with a cooking liquor consisting of caustic soda and soda sulfide, and then separated into pulp and black liquor, but this black liquor contains many organic substances and In order to recover the valuable components, it is concentrated in a multi-effect canister and then burned in a soda recovery boiler, recovering the waste heat as well as the valuable components.

[Problem that the invention seeks to solve]

However, since black liquor contains sulfates, chlorides, etc., corrosion of the heat exchanger tubes of soda recovery boilers was unavoidable. That is, the temperature of combustion exhaust gas is usually 150
℃ to 200℃, and if the heat retained in this exhaust gas is recovered and used, it is possible to save energy during combustion, but the exhaust gas contains corrosive gases such as SOx, ICE, and 11S. When the temperature becomes low, Ilz SOx,
) Since IC1 and the like are dissolved in condensed water, there is a problem in that in order to recover heat from the exhaust gas, a material that is resistant to corrosion by HzSO+ and HCl must be used.

For this reason, conventional exhaust gas heat recovery equipment uses heat transfer tubes such as double-lead tubes that are resistant to 1125O4 (lead itself is not strong, so the surface of the pipe is coated with lead, such as stainless steel), or glass tubes. was used.

However, the former lead has disadvantages such as lack of corrosion resistance against I11 aqueous solution and alkaline water, lack of creep resistance at temperatures above 170°C, and heavy weight.
Further, the latter glass tube has problems such as low strength and heavy weight.

The present invention is applicable to such SOx, 1Icj' and Hls
The present invention provides a corrosion-resistant and practical exhaust gas heat exchange method in a high-temperature exhaust gas atmosphere containing sodium sulfate, sodium carbonate, or potassium sulfate in addition to corrosive gases such as.

(Means for Solving the Problem and Actions/Effects) Through experiments, the present inventors found that SOx, IIc, which is a corrosive gas,
The progress of corrosion of metal materials, which are almost unusable in β atmosphere, is significantly suppressed by the presence of black liquor combustion dust containing sodium sulfate, soda carbonate, or potassium sulfate. In the base alloy material, it was confirmed that the degree of corrosion was further reduced by the presence of sodium sulfate and sodium carbonate or potassium sulfate.

For this corrosion test, test pieces of various metal materials were
λSO+ 60% water solution (A? night) and! +, So
A solution (solution B) in which 50% black liquor combustion dust was added to 50% aqueous solution with a concentration of 60%, and a solution (solution C) in which 29% black liquor combustion dust was added to a 71% aqueous solution with a JSO+ 60% concentration. Furthermore, a solution prepared by adding 29% of a mixture of sodium sulfate and potassium sulfate to a 71% aqueous solution of 112s0460% (
D) and the amount of corrosion at temperatures of 80°C and 100°C was determined.

As a result, the corrosion ff1 (+u/Y) after 25 hours was as shown in the table below.

Margin below C] Here, among the above test pieces, the rTi-Pd alloy crack test piece is Ti-Pd ASTM grade 7, and r Tii Te, 2. ) Peace” is Ti
ASTM grade 2.

The results of these corrosion experiments show that Ti and Ti-based alloys are considerably corroded by an aqueous solution of sulfuric acid, but when black liquor combustion dust containing lithium sulfate and soda carbonate is added to this aqueous sulfuric acid solution, It was found that the amount of corrosion was significantly reduced when sodium sulfate and potassium sulfate were added (solutions B and C) and when sodium sulfate and potassium sulfate were added (solution D).

Therefore, the present invention provides Tit! as an exhaust gas heat exchange device in a high temperature exhaust gas atmosphere containing sodium sulfate and sodium carbonate or potassium sulfate. Ti heat exchanger tube or Ti-Pd etc.
It is proposed to use heat exchanger tubes made of base alloys.

In other words, Ti-based alloys such as Ti-based alloys and Ti-Pd burn and decompose black liquor to recover inorganic substances as soda carbonate and soda sulfide, and when recovering the heat produced by combustion of organic substances as steam, Even if the material contains corrosive components such as SOx and Has, the progress of corrosion is significantly suppressed by the presence of sodium sulfate, soda carbonate, or potassium sulfate, as shown in the above experiment. For exhaust gas heat exchangers that were too large to be put into practical use,
By adopting a Ti-tone heat exchanger tube or a heat exchanger tube made of a Ti-based alloy such as Ti-Pd, the progression of corrosion of the heat exchanger tube in a sulfuric acid environment is delayed, and the life of the equipment is extended much longer than in the conventional case. It can be kept for a long time.

However, Ti-based alloys such as Ti-Pd
As can be seen from the corrosion test of the i-Pd alloy test l-piece, its corrosion resistance at high temperatures is worse than that of Ti.

On the other hand, Ti has better corrosion resistance against exhaust gases containing sodium sulfate, soda carbonate, or potassium sulfate than Ti-based alloys such as Ti-Pd, even at high temperatures, and is considerably more expensive than Ti-based alloys. There is, but Ti is II
Cjl! In the case of a solution containing Corrosion that occurs in the gap between the support plate and the support plate is likely to occur, and corrosion resistance against Hi is poor even in exhaust gas containing sodium sulfate, soda carbonate, or potassium sulfate. On the contrary, Ti-Pd alloys have II(l
The corrosion resistance in solutions containing Ti is superior to that of Ti,
The inventors have learned from experience that corrosive gases such as SOx and HC
It was confirmed that the corrosion resistance and crevice corrosion resistance were superior to that of Ti even in a condensed atmosphere of ρ.

Therefore, the heat exchanger tube at χ and e used for heat recovery is T
Setting iff1 means that when water condenses on the surface of the heat exchanger tubes on the low temperature side of the heat exchanger tube group, this condensed water contains Ill! in the exhaust gas. Due to the dissolution of
]' There is a possibility that crevice corrosion may occur in the heat exchanger tube made of i5, and
by F! One meal becomes big.

Other inventions have addressed this problem in that 3! In the case of recovery, it is proposed to use a heat exchanger tube made of Ti on the high temperature side and a heat exchanger tube made of Ti-based alloy such as Ti-r'd on the low temperature side.

With this configuration, the upper bound of the value associated with the use of heat exchanger tubes made of a Ti-based alloy such as Ti-Pd as all heat exchanger tubes for heat recovery can be reduced to Only T
While this can be avoided by using heat exchanger tubes made of Ti-based alloys such as i-Pd, all heat exchanger tubes are
, crevice corrosion on the low temperature side due to the use of 5 tubes and lIC7! corrosion can be reduced by using a Ti-based alloy heat exchanger tube such as Ti-Pd only for the heat exchanger tube on the high temperature side, and by using a Til heat exchanger tube for the heat exchanger tube on the high temperature side. Therefore, corrosion caused by exhaust gas on the high temperature side can be reduced.

As a result, (the durability of the heat tube can be further improved,
It can be provided at low cost.

〔Example〕

Figure 1 is a flow sheet of a soda recovery boiler. A reduced black liquor containing 50 to 50% solids is introduced into the soda recovery boiler 2 through pipe 1 and is injected, and the black droplets are dried in a suspended state by the combustion exhaust gas. It falls while receiving the char, and reaches the bottom of the furnace in a state called char, where only the solid content remains. At this time, if the particle size is small, the non-primary particles will be carried away as fly ash in the exhaust gas, causing dust problems, and if the particle size is too large, it will reach the bottom of the hearth in an insufficiently dry state, resulting in drying of the hearth. temperature drops,
It is important to maintain an appropriate particle size because combustion becomes unstable and the soda reduction rate decreases. Furthermore, in order to reduce sodium sulfate, a special operation is required so that there is insufficient air near the hearth and excess air in the upper part of the furnace.

The organic content of the black liquor burned in this way becomes the heat produced by combustion, the boiler feed water introduced from the pump 3 is supplied to the boiler 2 via the heat exchanger 4, and the generated steam is sent out from the pipe 5 to a predetermined location. After the dust is removed from the combustion exhaust gas by the electric collecting unit 6, it passes through the blower 7 and enters the heat exchanger 11, which heats the boiler feed water, which is then cooled and released into the atmosphere from the chimney 8.

In the above equipment, the concentrated black liquor is combusted and decomposed in the soda recovery boiler, and the inorganic components are recovered as soda carbonate and soda sulfide, and the heat produced by combustion of the organic components is recovered as steam. S containing das 1- such as sodium sulfate and sodium carbonate or potassium sulfate by combustion
Ox, Has and IIc/! The exhaust gases such as the above are introduced into the heat exchanger 4.

In the heat exchanger 4, the heat exchanger tube bundle 9 installed between the tube plates 10 and 11 is configured to have a large number of Tie heat exchanger tubes, or is made of a Ti base such as Ti-Pd. By configuring a large number of alloy heat exchanger tubes,
SOx,H! The normal corrosion caused by S is further significantly inhibited by the presence of sodium sulfate and sodium carbonate or potassium sulfate, and the
The use of heat exchanger tubes made of i-based alloys, together with the presence of dust containing sodium sulfate, sodium carbonate, or potassium sulfate, which are effective in preventing corrosion, enables long-term use. Note that reference numeral 12 in the figure indicates a support plate that supports the middle portion of each heat exchanger tube.

In another embodiment, the heat exchanger tube bundle 9 in the F1 exchanger 4 is replaced with the heat exchanger tube bundle 9 in the heat exchanger 4 as shown in FIG.
The heat exchanger tube bundle 9a on the high temperature side near the exhaust gas inlet 4a and the heat exchanger tube bundle 9b on the low temperature side near the exhaust gas outlet 4b are divided, and each heat exchanger tube in the heat exchanger tube bundle 9a on the high temperature side is made of Ti. Each of the heat exchanger tubes in the heat exchanger tube bundle 9b on the low temperature side is constructed of a Ti-based alloy heat exchanger tube such as Ti-Pd.

With this configuration, it is possible to avoid the increase in price associated with using Ti-based alloy heat exchanger tubes such as Ti-Pd for all the heat exchanger tubes in the heat exchanger tube bundle 9, and it is possible to avoid the increase in price due to the use of Ti-based alloy heat exchanger tubes such as Ti-Pd. While it is possible to reduce crevice corrosion that occurs in the gap between both tube sheets 10.11 and the support IFi 12 when steam condenses on the surface of the heat tube, and corrosion that occurs when this condensed water becomes 11Cβ melt, Corrosion on the high temperature side can be reduced by using Ti-based alloy heat exchanger tubes such as Ti-r'd for all the heat exchanger tubes in the heat exchanger tube bundle.

In addition, by using Tip as the support plate and tube machine for the heat exchanger tube bundle 9a on the high temperature side, and using a Ti base alloy such as Ti-Pd as the support plate and tube machine for the heat exchanger tube bundle 9b on the low temperature side, the price can be increased. It is possible to further reduce the corrosion resistance, and also improve the corrosion resistance of the support plate and the blue sky.

[Brief explanation of drawings]

The figures show an embodiment of the present invention; FIG. 1 is a flow sheet thereof, FIG. 2 is a longitudinal sectional front view of a heat exchanger, and FIG. 3 is a longitudinal sectional front view of a heat exchanger according to another embodiment. 1...Pipe, 2...Soda recovery boiler, 3...
・Pump, heat exchanger, 5...pipe, 6...electric dust collector, 7...blower, 8...chimney, 9...
Heat exchanger tube bundle, 9a...High temperature side heat exchanger tube bundle, 9b...
Low temperature side heat exchanger tube bundle. Patent Applicant Sasakura Kikai Fusakusho Co., Ltd. Tetoku 7 Zoshi Seisho” (Spontaneous) 1 June 5, 1985 Commissioner of the Patent Office Michi Uga rIB Tono 1, $171 Indication Special Shop No. 1988-107861 2. Name of the invention Exhaust gas heat exchange method 3. Relationship with the case of the person making the amendment
6-7-5 Goheijima, Nishiyodo-ku, Osaka City Name: 'r! 1 Kuramaki Seisakusho Specification Book 6, Contents of the amendment? l1li official manuscript (spontaneous) June 30, 1985 Tokushi Shou 61-107861 No. 2, title of the invention Exhaust gas heat exchange method 3, relationship with the amendment case Patent Issue Person Address
6-7-5 Goheijima, Nishiyodo-ku, Osaka City Name: Sasakura Machinery Works Co., Ltd. Specification Document 6, Contents of Amendment (1), Specification originally attached to the application, page 11, line 6, “Dust collector " should be corrected to "dust collector." (2), same as above, add the following sentence after page 13, line 13. [In addition, since the present invention is an exhaust gas heat exchange method using a Ti or Ti-based alloy heat exchanger tube in a high-temperature exhaust gas atmosphere containing sodium sulfate and soda carbonate, the outer surface of the heat exchanger tube is used as a heat exchanger tube of a heat exchanger. By using a double tube made of Ti or Tt-based alloy and having a steel tube or stainless steel tube on the inner surface, high temperature exhaust gas may be supplied to the outer surface of the heat transfer tube and boiler feed water to the inner surface. This has the advantage that all of the heat exchanger tubes are superior in strength to Ti or Ti-based alloys, and the heat exchanger tubes can be produced at low cost. (3), same as above, page 13, line 20, ``dust collector'' is corrected to ``dust collector''.

Claims (9)

[Claims] (1) An exhaust gas heat exchange method characterized by using a heat exchanger tube made of Ti or a heat exchanger tube made of a Ti-based alloy in a high-temperature exhaust gas atmosphere containing sodium sulfate and soda carbonate. (2) The exhaust gas heat exchange method according to claim 1, wherein the high-temperature exhaust gas atmosphere is exhaust gas from a soda recovery boiler for paper manufacturing. (3) The exhaust gas heat exchange method according to claim 1, wherein the heat exchanger tube made of a Ti-based alloy is a heat exchanger tube made of a Ti-Pd alloy. (4) An exhaust gas heat exchange method characterized by using a heat exchanger tube made of Ti or a heat exchanger tube made of a Ti-based alloy in a high-temperature exhaust gas atmosphere containing sodium sulfate and potassium sulfate. (5) The exhaust gas heat exchange method according to claim 4, wherein the high-temperature exhaust gas atmosphere is exhaust gas from a soda recovery boiler for paper manufacturing. (6) The exhaust gas heat exchange method according to claim 4, wherein the heat exchanger tube made of a Ti-based alloy is a heat exchanger tube made of a Ti-Pd alloy. (7) In a high-temperature exhaust gas atmosphere containing sodium sulfate, soda carbonate, or potassium sulfate, Ti is placed on the high-temperature side.
An exhaust gas heat exchange method characterized in that a heat exchanger tube made of a Ti-based alloy is used on the low temperature side. (8) The exhaust gas heat exchange method according to claim 7, wherein the high-temperature exhaust gas atmosphere is exhaust gas from a soda recovery boiler for paper manufacturing. (9) The exhaust gas heat exchange method according to claim 4, wherein the heat exchanger tube made of a Ti-based alloy is a heat exchanger tube made of a Ti-Pd alloy.