JPS59219601A - High-pressure chemical recovery boiler - 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 high pressure chemical recovery boiler. In particular, it is intended to prevent corrosion of the bottom and side walls of the combustion chamber in the reduction zone formed at the bottom of the boiler furnace.

This type of chemical recovery boiler supplies pulp cooking waste liquid (hereinafter referred to as "black liquor") to the combustion chamber of the boiler furnace using a spray gun, and while drying it, it is deposited as smelt at the bottom of the combustion chamber in a high-temperature atmosphere. By burning the material, the inorganic chemicals in the black liquor are completely reduced and Na2S and Na
2 CO3 is recovered and the heat of combustion is used to generate steam, which is used for power generation to cover the on-site electricity, and the steam is also supplied as steam for processes and other equipment.

In this case, corrosive compounds such as CI and NaS are generated from the smelt in a high-temperature reducing atmosphere.

This is a cause of corrosion of water-cooled wall pipes.The higher the temperature, the faster the corrosion rate tends to be, resulting in high epoxy, and when the surface temperature of water-cooled wall pipes becomes high, this corrosion is more likely to occur than before. Countermeasures are important.

In the unlikely event that this corrosion progresses and the water pipe breaks and water enters the smelt, an explosion may occur and is dangerous. Furthermore, if the fins that connect the water pipes corrode and the smelt inside leaks to the outside, there is a risk of an explosion and an unexpected accident for workers. If such a situation were to occur, the boiler would have to be shut down, and the supply of steam would become impossible during the long repair period, which would necessitate a complete shutdown of not only the on-site power supply but also the entire plant. This was extremely important and was pointed out as a solution to the corrosion problem.

To give an overview of the high-pressure chemical recovery boiler shown in FIG. 1, black liquor is supplied to the combustion chamber 1 in the lower part of the boiler furnace by a spray gun B. The supplied black liquor is dried by combustion heat and falls to the bottom as smelt 4 to be deposited. The pile of solids that formed this smelt 4 burns at the bottom.

An air nozzle 2 for blowing combustion air is provided around the combustion chamber 1, and a high-temperature reducing atmosphere region 7 is maintained below the air nozzle 2.

Therefore, the smelt 4 is held in a high temperature reducing atmosphere,
As a result, the Na2S and Na2CQ contained in the smelt 4 are recovered, and the combustion of the new solids supplied to the upper part of the smelt 4 is suitably continued.

On the other hand, in the side wall 5 and bottom section 6, which are made up of water-cooled tube walls of the combustion chamber 1, the water tubes 8 are connected to each other by fins 9 to form a membrane panel, as shown in FIG. A stud 10 is installed in the water pipe 8 inside the furnace, and a refractory material 11 held by the stud 10 is provided.
The outside of the furnace is a heat insulating material 12 with a casing 16 fixed to its surface.
covered by.

The water-cooled pipe wall, which constitutes the entire side wall and bottom of a conventional combustion chamber, had a structure as shown in FIG.

In other words, if the refractory material falls off or cracks due to stud corrosion or thermal shock, use CI, Na,
The compound No. 5 enters from that location and corrodes the water pipe 8 and fins 9. To prevent this, the outer surfaces of the water tubes 8 are coated with stainless steel 14 as shown in FIG.
There is a method of forming a membrane panel by joining them together on both sides of the fins 90 made of mild steel or stainless steel. However, with this membrane panel, corrosion of the water pipes 8 themselves can be avoided, but when mild steel is used for the fins 9, There is a disadvantage that corrosion of the fins 9 is likely to proceed, and smelt may leak from this portion, which is dangerous.

In order to eliminate this drawback, there is a method of using stainless steel for the fins 9, but this method also has the following drawbacks.

The wall thickness of the water pipe 8 is 6.5 to 4 in order to maintain pressure resistance.
．． Use a material with a thickness of 5 layers, and a stainless steel material with a thickness of 1 layer.
The coating of 4 is about 1.6'w, which is very thin compared to the wall thickness of water pipe 8.
I use a material with a thickness of about .

Therefore, thermal expansion is controlled by the material of the water tube 8. This means that the coefficient of thermal expansion of the material of the water tube 8 and the stainless steel of the fin 9 are greatly different, which creates a difference in thermal expansion between the water tube 8 and the fin 9, which places a large stress on the joint. This may cause cracks to occur in the water pipe 8.

The present invention has been made in view of the problems of the prior art described above, and uses a new device to eliminate the difference in thermal expansion between the water tube and the fins, and is extremely effective in preventing corrosion at the bottom of the combustion chamber. The aim is to provide a high-pressure chemical recovery boiler.

The first configuration of the present invention is that, in the combustion chamber of a high-pressure chemical recovery boiler, the side walls and bottom of the water tubes, which are in the reducing atmosphere formed in the combustion chamber, are entirely coated with stainless steel, and the water tubes are covered with mild steel. It is characterized by being formed by a membrane/panel joined on both sides of a fin made of clad steel made of a composite material of stainless steel. The side wall and bottom part in the reducing atmosphere formed are characterized by being formed by a membrane panel in which the outer surface of a finned tube is covered with stainless steel, and the fins of the finned tube are butted and welded.

The present invention will be explained below with reference to embodiments shown in FIGS. 4, 5, and 6.

4 and 5, first, the fin 9 shown in FIG. 4 is a composite material with stainless steel 15 pasted on one side of the base material 16, and the fin 9 shown in FIG. Made of wood. In addition, both water pipes 8 are made of stainless steel 14 on the pipe surface.
is covered.

Is the base material 16 the same thermal expansion coefficient as the material of the water tube 8?
Or this stainless steel 14 which uses mild steel with not much difference.
A membrane panel may be formed by joining the water pipe 8 coated with NALFIN 9 made of the composite material by welding.

In this way, the water tube 8 is cooled by the fluid in the water tube 8, and at the same time, the fins 9 are also cooled to approximately the same temperature by heat conduction. In this case, the water tube 8 and the fins 9 will depend on the material properties of the water tube 8 and the base material 1 on the fin 9 during thermal expansion.
However, by selecting the materials of the two, the difference in expansion can be made approximately equal, so that the generation of stress at the joint becomes no problem.

Figure 6 shows another example of the actual JJ value, in which a finned tube is used as the water tube, and the outer surface of the finned tube 8' is made of stainless steel.
4' is coated. This coated fin bamboo tube 8
The fins 9' of the fins 9' are fixed to each other by butt welding to form a membrane panel.

In the case of this embodiment, the finned tube 8' and the fins 9' are under the same conditions, which are completely suitable for thermal expansion.

Therefore, the stress generated at the joint between the two is similar and low.

In the case of this embodiment, the refractory material 11 is
Even if the stainless steel 14, 14' (see FIG. 2) falls off or cracks occur, corrosion of the water pipes 8, 8' and fins 9, 9' can be reliably prevented by the coated stainless steel 14, 14'.

According to the present invention configured as detailed above, since the membrane panel is formed by selecting the materials of the water tubes and the fins and combining them so that they have approximately the same conditions for thermal expansion, the water tubes and the fins are The stress generated at the joints is suppressed, and there is no risk of the water pipes becoming cracked or damaged.

In addition, since the surfaces of the water tube and fins are coated with stainless steel,
It is an industrially significant invention, as it can prevent corrosion and eliminate dangers such as explosions.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing the combustion chamber at the bottom of the furnace of a chemical recovery boiler, Figure 2 is an enlarged detailed sectional view of the water-cooled pipe wall structure in Figure 1,
Fig. 6 is a partially enlarged sectional view of a conventional water cooling pipe wall, Figs. 4 and 5 show an embodiment of the present invention, and Fig. 4 is a membrane panel in which stainless steel is pasted on one side of the base material of the fin. FIG. 5 is a partial cross-sectional view of a membrane panel in which stainless steel is pasted on both sides of the base material of the fin, and FIG. 6 is a partial cross-sectional view showing another embodiment. In the figure, 1 is a combustion chamber, 5 is a side wall, 6 is a bottom, 7 is a reducing surrounding area, 8 is a water pipe, 8' is a finned tube, 9.9' is a fin, 14, 14', 15, 15' is stainless steel and non-resistance. Patent applicant: Kawasaki Heavy Industries, Ltd.

Claims (2)

[Claims] (1) In the combustion chamber of a high-pressure chemical recovery boiler, the side walls and bottom of the reducing atmosphere formed in the combustion chamber are covered with stainless steel, and the water tubes are made of a composite material of mild steel and stainless steel. A high-pressure chemical recovery boiler characterized by being formed of membrane panels joined on both sides of fins made of clad steel. (2) In the combustion chamber of a high-pressure chemical recovery boiler, the outer surface of the finned tube is coated with stainless steel, and the fins of the finned tube are butt welded to the side wall and bottom part in the reducing atmosphere formed in the combustion chamber. A high-pressure chemical recovery boiler characterized by being formed from a membrane panel.