JPH0776601B2 - Soda recovery boiler - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a soda recovery boiler which is capable of maximizing the output of a power plant while reducing boiler corrosion.

2. Description of the Related Art In recent years, there has been a remarkable tendency toward energy saving and high efficiency in steam power plants, and even in the soda recovery boiler, which is the main power source of paper pulp mills, there is a tendency toward high pressure and high temperature. It is the current situation that it is difficult to raise the temperature and pressure to the next level due to the high humidity corrosion of furnace tubes and superheated tubes due to corrosion.

In other words, the conventional steam condition for the superheater outlet of the soda recovery boiler was pressure 65 Kg / cm ² g and temperature 450 ° C or less, but recently pressure 100 Kg / cm ² g and temperature 500 ° C have become common. The trend of the times is coming, and recently, we have taken a step further, and in order to save energy and improve efficiency, pressure 120 Kg / cm ² g, temperature 540
The needs of customers who desire steam conditions of ° C are increasing.

However, in the soda recovery boiler, due to the peculiar cause (smelt corrosion) of the soda recovery boiler, in the general boiler
Even the highest grade SUS steel pipe, which can be expected to have a life of about 10 years even at a steam temperature of 540 to 569 ℃, has a steam temperature of 480 ℃ for only 5 years. In addition, even materials that could handle steam conditions up to a pressure of 100 Kg / cm ² g and a temperature of 500 ° C (special pipes such as 25Cr steel pipes) will have a useful life under the steam conditions of a pressure of 120 Kg / cm ² g and a temperature of 540 ° C. There is a problem, and it is the current situation that practical application is difficult unless new materials are developed in the future.

3 and 4 show two different conventional examples, FIG. 3 is a system diagram of a conventional example without a low-pressure turbine, and FIG. 4 is a system diagram of a conventional example with a low-pressure turbine.

In these figures, the soda recovery boiler 01 is equipped with a superheater 02, the high-temperature and high-pressure steam superheated by this superheater is guided to a high-pressure turbine 04, and the low-pressure low-temperature steam exiting this high-pressure turbine is the third In the figure, it is supplied to the process for miscellaneous use in the factory, and in FIG. 4, it is introduced to the low pressure turbine 05. In addition, 06 is a generator.

In the soda recovery boiler 01, the residual water in the black liquor having a concentration of 65 to 70% charged into the furnace is first evaporated to burn the solid matter. Then, sodium sulfate contained in the solid matter is reduced to sodium sulfide, taken out as "smelt" from the furnace bottom, and the chemicals are collected, but sulfur sulfide in the gas and Na ₂ SO ₄ contained in the dust are collected. , NaCl, K, etc. cause corrosion in the superheater 02.

When NaCl and K are present, the melting point of ash, which is usually 600 ° C to 700 ° C, is greatly lowered to near 530 ° C to 550 ° C, and the progress of corrosion becomes remarkable. Therefore, in the soda recovery boiler, keeping the steam condition at the superheater outlet below 500 ° C is the best way to prevent corrosion.

FIG. 2 shows the relationship between the metal temperature of the superheater tube and the corrosion amount in the soda recovery boiler. From FIG. 2, it can be understood that the steam temperature at the outlet of the superheater is a very important factor in the soda recovery boiler, and how difficult it is to raise the temperature as a problem peculiar to the soda recovery boiler. In particular, comparing the amount of corrosion when the soda temperature of the superheater pipe is 500 ° C. and the amount of corrosion when the soda temperature is 550 ° C., the amount of corrosion is about 1/5 at 500 ° C. Therefore, in the soda recovery boiler, keeping the steam temperature at the superheater outlet as low as possible is the best way to prevent corrosion. In addition, FIG. 2 shows the test results of the SUS-321HTB steel pipe.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In a plan to improve efficiency of a power plant including a soda recovery boiler, low pressure and low temperature (for example,
30-70Kg / cm ² g × 350-450 ℃) If you have a steam turbine with a high pressure and high temperature soda recovery boiler and a high pressure turbine to increase the efficiency as a high temperature and high pressure power plant system, the existing low pressure and low temperature If we try to obtain high power generation output while matching the exhaust gas of the high-pressure turbine to the steam condition of the turbine, the steam condition of the new soda recovery boiler will have to be made extremely high, resulting in the corrosion problem of the soda recovery boiler. .

On the other hand, if the steam condition of the soda recovery boiler is lowered to the extent that corrosion does not occur, the output of the high pressure turbine will be small, and the advantage of installing a high temperature and high pressure power plant will be lost.

The present invention has been made in order to solve the problems of the conventional art, and an object thereof is to reduce the corrosion of the soda recovery boiler and maximize the output of the power generation plant.

Means for Solving the Problems In order to solve the above problems, the present invention is a power plant having a low-pressure low-temperature steam turbine, in a device equipped with a high-pressure high-temperature soda recovery boiler and a high-pressure turbine, in the soda recovery boiler A superheater and a reheater are provided, the high-pressure and high-temperature steam discharged from the superheater is guided to the high-pressure turbine, the low-pressure steam discharged from the high-pressure turbine is returned to the reheater, and the reheated steam is introduced to the low-pressure turbine. It was done like this.

Operation According to the above means, in a power plant having a low-pressure low-temperature steam turbine in an existing line, a high-pressure high-temperature soda recovery boiler and a high-pressure turbine are installed, and a conventional soda recovery boiler is installed in the soda recovery boiler in order to improve the efficiency of the plant. By newly installing a reheater in addition to the superheater, the steam conditions of the soda recovery boiler are kept low within the allowable range for corrosion and corrosion is reduced, while maximizing the output of the high temperature and high pressure power plant including the existing turbine. be able to.

Embodiment Hereinafter, one embodiment of the present invention will be described in detail with reference to FIG.

In FIG. 1, 1 is a soda recovery boiler, 2 is a superheater thereof, 4 is a high-pressure turbine, 5 is a low-pressure turbine, and 6 is a generator, all of which are existing ones. , A soda recovery boiler 1 is additionally provided with a reheater 3 in addition to the conventional superheater 2, and the high-pressure high-temperature steam that has exited the superheater 2 is guided to the high-pressure turbine 4 and the low-pressure steam that has exited the high-pressure turbine 4. Is again returned to the reheater 3, and the reheated steam is introduced into the low pressure turbine 5.

By thus providing the soda recovery boiler 1 with the reheater 3, it is possible to prevent the temperature of the superheater 2 from becoming excessively high and reduce the corrosion of the superheater pipe due to the combustion exhaust gas, which is a problem peculiar to the soda recovery boiler. However, the total output of the power plant (high-pressure turbine output + low-pressure turbine output) can be increased.

As one specific example, the present invention shown in FIG. 1 and the conventional example shown in FIG. 4 are compared as follows.

(I) Superheater outlet steam temperature Conventional example: 505 ° C (assumed metal temperature 530 ° C) Present invention: 485 ° C (assumed metal temperature 510 ° C) Under these conditions, referring to Fig. 2, comparing the amounts of corrosion of the superheater The present invention is about 1/2 the size of the conventional example, and has a great effect on reducing corrosion.

(Ii) Turbine Output conventional: 4290KW + 16460KW = 20750KW (100 %) the invention: 4460KW + 16450KW = 20910KW (101 %) It should be noted that, in the turbine output, shown in FIG. 4 as a conventional example 114Kg / cm ² g × 505 ℃ steam conditions The reason for taking up is
This is because the steam conditions at the inlet of the low-pressure turbine are aligned with those of the present invention in order to match the base for comparison. That is, the high-pressure turbine outlet exhaust condition of the conventional example is to obtain the high-pressure turbine inlet steam condition so as to match the reheat steam condition of the low-pressure turbine inlet of the present invention 64 Kg / cm ² g × 450 ° C, thereby 114 Kg / cm ² It is g × 505 ° C.

In this way, when the low-pressure turbine inlet steam conditions are aligned and the heat input and thermal efficiency of the soda recovery boiler are the same, the boiler outlet steam generation amount is calculated and compared.

As described above, according to the present invention, in a power plant having a low-pressure low-temperature steam turbine in an existing line, a high-pressure high-temperature soda recovery boiler and a high-pressure turbine are installed to improve the efficiency of the plant. By installing a reheater in addition to the conventional superheater in the soda recovery boiler, the steam conditions of the soda recovery boiler are kept low enough to allow corrosion, and corrosion is reduced, while high temperature and high pressure including existing turbines are used. The output of the power plant can be maximized.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing a relationship between a metal temperature of a superheater or the like in a soda recovery boiler and a corrosion amount, and FIGS. 3 and 4 are different from conventional ones. It is a systematic diagram which shows two examples. 1 ... Soda recovery boiler, 2 ... Superheater, 3 ... Reheater, 4 ... High pressure turbine, 5 ... Low pressure turbine, 6 ...
Generator.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuharu Uoyama 5-1-408 Seto, Kanazawa-ku, Yokohama-shi, Kanagawa (56) References JP-A-59-219603 (JP, A)

Claims (1)

[Claims] Claim: What is claimed is: 1. In a power plant having a low-pressure low-temperature steam turbine, a device equipped with a high-pressure high-temperature soda recovery boiler and a high-pressure turbine, the soda recovery boiler is provided with a superheater and a reheater, and the high pressure discharged from the superheater is used. A soda recovery boiler, characterized in that high-temperature steam is guided to a high-pressure turbine, low-pressure steam discharged from the high-pressure turbine is returned to the reheater, and reheated steam is introduced to the low-pressure turbine.