JPH05337329A - Method for saving water supply to wet-type desulfurization device - Google Patents

Abstract

PURPOSE:To save water supply to an absorption device by reducing moisture drained into an area outside a system as an entrained one in treated discharged smoke. CONSTITUTION:At least, part of an absorbent based on a calcium absorbent is extracted from an absorption system loop 8, and the extracted absorbent is introduced into an indirect cooling-type heat exchanger 9. After cooling the absorbent using a coolant, the absorbent is returned to the absorption system loop to lower the temperature of an absorption liquid slurry supplied to a gas/ liquid contact part. Further, an exhaust smoke is washed by the absorption liquid slurry at a low temperature and the temperature of the exhaust smoke after washing is maintained at the adiabatic cooling saturation temperature level of the exhaust smoke before washing.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for saving make-up water to a wet desulfurization unit, and more particularly to a calcium based flue gas absorbent slurry in a wet flue gas desulfurization method.
(Hereinafter referred to as absorption liquid slurry) is taken out from the absorption system loop, cooled without scaling and trouble, and then returned to the absorption system loop to lower the temperature of the absorption liquid slurry supplied to the gas-liquid contact part of the absorption liquid loop. , The temperature of the treated flue gas leaving the gas-liquid contact part is kept lower than the saturation temperature of the flue gas before desulfurization (hereinafter referred to as untreated flue gas) supplied to the absorption system loop, and the content in the treated flue gas is maintained. It relates to a method of significantly reducing water.

[0002]

2. Description of the Related Art As a wet flue gas desulfurization method, a method of cleaning flue gas with an absorbing liquid slurry is currently widely used worldwide. This method removes the sulfurous acid gas (SO ₂ ) in the flue gas after humidifying and cooling the flue gas, or by directly introducing it to the absorption tower and washing it with the absorbent liquid slurry. Insulation of flue gas (hereinafter referred to as untreated flue gas) that is supplied to the cooling unit (hereinafter referred to as gas-liquid contact part where untreated flue gas is washed with the absorbent liquid slurry) before contact with the absorbent liquid slurry The temperature becomes around the saturation temperature, and in the case of coal-fired smoke, the temperature is usually 45 to 55 ° C., and the partial pressure of water corresponding to this temperature is included in the treated smoke and discharged outside the system.

Therefore, it is necessary to supply the moisture difference amount, which is introduced into the system due to untreated flue gas and is discharged outside the system due to treated flue gas, to the humidification / cooling section as make-up water. there were.
Table 1 shows the water content difference between the untreated smoke and the treated smoke. In order to eliminate the disadvantage of high consumption of makeup water, the rational use of water and drainage system for the entire power plant has been used to reduce the amount of makeup water.

On the other hand, a dry desulfurization method, a semi-dry desulfurization method, etc. have been studied. The wet flue gas desulfurization method has been the world's most popular due to its excellent characteristics, that is, high desulfurization rate, load followability and reliability. It has been adopted as a mainstream process. It is conceivable to provide a cooling unit at a place other than the present invention in the desulfurization device as another method for saving makeup water, but this causes a problem because draft loss of the flue increases.

The amount of make-up water to the humidification cooling part (contact part with the absorbing liquid slurry) occupying the whole of the present commercial thermal power plant in Japan is such that the heat recovery of the untreated flue gas introduced into the desulfurization device is carried out, By installing the gas / gas heater used to reheat the treated flue gas, the temperature of the untreated flue gas introduced into the humidification / cooling section could be reduced to 100 ° C to 90 ° C.
As a secondary effect, we were able to save about 30% of make-up water, but the amount of make-up water reached about 70% of the total amount of water used by the power plant during normal operation, making it an industrial water source like rainwater sources like Japan. Even in countries where it is difficult to obtain makeup water, it will be difficult to secure a construction site for large coal-fired thermal power plants in response to the recent economic expansion and the expansion of power demand supported by private demand for electricity. Is becoming a factor.

[0006]

The problem to be solved by the present invention is to further greatly reduce the amount of make-up water in a wet flue gas desulfurization apparatus.

[0007]

A method for saving make-up water to a wet desulfurization apparatus according to the present invention is a wet flue gas desulfurization method in which at least a part of an absorbent based on a calcium-based absorbent is absorbed. The temperature was lowered by lowering the temperature of the absorbing liquid slurry which was extracted from the loop and introduced into a heat exchanger of indirect cooling type, cooled by a cooling liquid and then returned to the absorption system loop and supplied to the gas-liquid contact section. It is characterized in that flue gas is washed with the absorbent slurry and the temperature of flue gas after washing is kept below the adiabatic cooling saturation temperature of flue gas before washing.

The present invention will be described below with reference to FIG.
The untreated flue gas 21 is boosted by the flue gas fan 1 and cooled by heat exchange with the treated flue gas obtained in the gas / gas heater 2 as described later. The flue gas temperature at the outlet of the gas / gas heater 2 is
Is a minimum of about 85 ° C for a non-leakage type heat storage rotary heat exchanger, but it is 100-85 ° C depending on the type of gas / gas heater.
(At rated load). The untreated flue gas 22 discharged from the gas / gas heater 2 is subjected to humidifying and cooling in the humidifying / cooling unit 3 by direct contact with the spray of the mother liquor 23 or the absorbing liquid slurry 24, and is absorbed in the absorbing tank 4 as unsaturated flue gas. be introduced. The temperature of this water-saturated untreated flue gas is, as shown in Table 1 below,
When a gas / gas heater is used and the outlet smoke temperature of this heater is approximately 95 ° C and the water-saturated untreated smoke temperature is approximately 47 ° C, the humidification content is approximately 0.023 kg H ₂ O per kg dry gas. is there.

Then, the water-saturated untreated flue gas is blown into the calcium-based absorbent liquid slurry 24 by the blowing pipe 5, and the untreated flue gas and the absorbent liquid slurry 24 are directly contacted with each other. SO ₂ in the absorbent is a calcium-based absorbent in the absorbent slurry, such as CaCO ₃ , Ca (OH)
It reacts with ₂ and is fixed and removed as gypsum. The desulfurized exhaust gas 25 has its mist removed by the mist eliminator 6 and is then heated by the gas / gas heater 7 to a predetermined temperature by heat exchange with untreated flue gas and released into the atmosphere.

What is important in the present invention is that at least a portion of the absorbent slurry 24 is withdrawn from the absorbent loop 8.
This absorbent slurry is cooled to a required temperature below the water saturation temperature of the untreated flue gas 22 in front of the humidification cooling section 3 in an indirect cooling type heat exchanger, for example, the cooler 9, and the cooled absorbent slurry 26 is cooled. (Hereinafter referred to as a cold absorbent slurry) is returned to the absorbent loop 8 and is contained in the treated exhaust gas leaving the absorbent loop 8 by lowering the temperature of the untreated exhaust gas which comes into contact with the absorbent slurry 24. Water content (water content kg / dry gas
(kg) and the amount of water in the untreated flue gas 21 (kg of moisture / kg of dry gas) is maintained at a predetermined value to reduce the amount of water escaping to the outside due to the treated flue gas.

Here, the absorption liquid loop 8 is a system including an absorption tower and an absorption liquid slurry circulation pump in the case of the spray tower type packed tower type which is a portion surrounded by a broken line in FIG. That is, in the present invention, the absorbent slurry may be taken out from any part of the absorbent loop 8 described above, and the cold absorbent slurry may be returned to any part of the absorbent loop 8. FIG. 1 shows, as an example thereof, the absorption liquid slurry 24 taken out from the bottom of the absorption tank 4, cooled by the cooling liquid 28 in the cooler 9, and the obtained cold absorption liquid slurry 26 is returned to the gas-liquid contact portion of the absorption tank 4. The case is shown.

The term "at least a part of the absorption liquid slurry" means a part or a large part of the absorption liquid slurry, and its range is usually expressed by the concept of L / G (l / Nm ³ ). 10 to 70% of the rated load (absorption liquid slurry volume (l
/ hr) / the amount of smoke emitted in the standard state Nm ³ / hr). Seawater is usually used as the cooling liquid 28, and the temperature difference between the outer pipe and the inner pipe of the cooler 9 from the pipe line 17 to the jacket side cooling liquid circulation loop 18 is within a predetermined temperature, and at the inner pipe outlet of the cooler 9. The temperature of the cold absorption liquid 26 is controlled and replenished so that it becomes a constant value, and the cooling loop 18
The excess cooling liquid inside is discharged to the outside of the system from an overflow pipe (not shown) provided on the suction side of the cooling liquid circulation pump 19.

In the calcium-based absorbent slurry of the present invention, the calcium salt is generally in a supersaturated state. Figure 2 shows the solubility of calcium salt (mainly gypsum dihydrate) in the absorbent slurry in water. The calcium salt in the absorbent slurry is mostly CaSO ₄ .2H ₂ O, and the causative agent of scaling is also this dihydrate.

Therefore, the saturation temperature of untreated flue gas is usually 45 to
The temperature is in the range of 55 ° C., and in the process shown in FIG. 1, the absorbing liquid slurry temperature is 42 to 45 ° C., though it varies depending on each case.
It is predicted that when the absorbent slurry is cooled, calcium salts are deposited on the inner wall surface of the inner pipe 9A of the cooler 9 to form scales, and the overall heat transfer coefficient is sharply reduced. However, according to the examination results by the present inventors, the following points were clarified. That is, the inner tube 9A having a smooth surface is used.
Keep the fluid state (flow velocity) of the absorption liquid slurry inside the allowable value or more. A stagnation part that gives the possibility of scale generation in the inner tube 19,
Do not create a swirl generator. Under the above conditions, there is an allowable range in which scale is not formed on the wall surface of the inner pipe 9A due to the temperature difference between the absorbing liquid slurry and the cooling liquid.

By selecting the optimum conditions (1) and (2), it is possible to prevent the scale generation in the inner pipe 9A. Specifically, the flow velocity (Reynolds number) of the absorbing liquid slurry in the cooler 9 in the inner pipe 9A is maintained at a constant flow rate as a rule over the allowable value, and the flow velocity of the cooling liquid is also maintained at a constant flow rate in principle. On the liquid side, the supply temperature to the jacket side is controlled by controlling the ratio of the new cooling liquid supply and the circulating cooling liquid. However, when the cooling load is significantly reduced, the flow velocity inside the pipe (absorption liquid slurry) and outside the pipe (cooling medium) can be reduced within the allowable range.

The absorption liquid slurry flow velocity range in the inner pipe 9A,
Table 2 shows the relationship between the maximum liquid temperature difference allowed between the absorbing liquid slurry and the cooling liquid. An embodiment of the present invention will be shown below with reference to FIG.

[0017]

EXAMPLE FIG. 2 shows a flow diagram of the practical test equipment, and the practical test equipment was installed near the desulfurization absorber in operation. Flow of gas system Untreated flue gas (humidified and cooled) 71 is taken out from the flue and guided to the absorber 42, and the absorbent liquid slurry is supplied from the sparger nozzle 43.
It was jetted out at a predetermined immersion depth position in 72. The untreated flue gas is desulfurized and cooled in the generated foam layer, that is, the gas-liquid contact portion, and the entrained mist is removed as the treated flue gas 73 by removing the entrained mist by the flow velocity reduction in the enlarged portion 44 of the upper part of the absorber. Was discharged to the treated smoke exhaust part 48 of the existing desulfurization absorber 47 via the suction flow meter 46. The amount of untreated flue gas introduced into the absorber 1 was changed by looking at the treated flue gas flow meter 46 by operating a valve on the suction side of the treated flue gas suction fan 45 to correspond to data collection. In addition, since the saturation temperature of the moisture in the untreated flue gas is almost determined by the fuel ratio of coal, the attached moisture content, and the gas / gas heater outlet temperature, in order to change the saturation temperature as a variable, the low pressure steam 74 is replaced by the steam flow meter 49, It was adjusted by operating the valve 50 and was replenished to the untreated smoke introduction line 51 to the absorber 42.

In order to supply oxygen for oxidizing the sulfurous acid gas absorbed in the absorber 42 to sulfuric acid into the absorbing liquid slurry 72, the nozzle 52 for blowing the oxidizing air 75 to the bottom of the absorber 42.
Was installed, and the oxidizing air (humidified) was adjusted and supplied by the flow meter 53 and the valve 54. Absorption liquid slurry system flow The absorption liquid slurry 76 is taken out from the existing desulfurization absorber 47, guided to the absorption liquid slurry pump 55, and the absorption liquid slurry 76 is cooled by the electromagnetic flow loop installed on the discharge side of this pump.
Supply and cool to the inner pipe 57 of 56, and cool absorption liquid slurry 77 to the absorber
Feed 42 into the gas-liquid contact section upper part of the washed raw flue gas in the gas-liquid contact portion, the removal of SO ₂ simultaneously oxidizing the absorption of SO _2,
Cooled. The absorbent slurry 78 after cleaning was returned to the existing desulfurization absorber. Absorption liquid slurry cooling liquid system flow A cooling liquid circulation system countercurrent to the flow of the absorption liquid slurry was installed. That is, the cooling liquid 79 is taken out from the lower side of the sleeve 58 (absorption liquid slurry inlet side) of the cooler 56, is guided to the suction of the cooling liquid circulation pump 59, and the pressurized cooling liquid 80 is supplied to the cooler 56.
A circulation loop was formed so as to supply to the inlet on the upper side (absorption liquid slurry outlet side) of the sleeve side 58. As a general rule, the flow rate of the cooling liquid in this circulation loop is a constant flow rate, and the cooling medium supply temperature of the circulation cooling liquid 80 is such that the new cooling liquid 81 is on the suction side of the cooling liquid circulation pump 59 and the discharge side of this circulation pump 59. It was controlled by supplying a flow rate adjusted by the supply circulation coolant temperature adjusting loop 60 of. By supplying new cooling liquid, excess cooling liquid in this circulation loop system is branched from the outlet on the jacket side of the cooler 56.
61 was started up, and it was made to flow into the drain as an outlet cooling liquid by an overflow 82. Main equipment 1) Absorber 42 A standard untreated flue gas sparger pipe was used as the center. The amount of untreated flue gas blown is from 2000 to 500 Nm ³
/ Hour (wet gas) 2) Cooler 56 The inner tube 57 is a special stainless pipe for seawater heat exchangers of size 1B and 1 1 / 4B. Since the trowel side uses industrial water as the cooling liquid, a gas pipe is applied, and 1B each
2B SGP for the inner tube, 2 1 / 2B SG for the 1 1 / 4B inner tube
P was used. The effective heat transfer length is 2.5m x 4 pieces,
The roughness of the inner surface of the inner tube was G / D = 0.00005 or less.

Test results 1) Test-1 condition (case of inner tube 1B) -Untreated smoke emission condition Water saturation temperature 47.5 ° C Untreated smoke emission (dry basis) Approx. 350 Nm ³ / hr SO ₂ concentration approx. 700 ppm-Absorbing liquid Slurry condition Soluble salt concentration About 6 wt% Seed gypsum about 15 wt% Average 50 μm Slurry specific gravity 1200 kg / m ³ Inlet temperature 43 ℃ Specific heat 880 kcal / m ³ ℃ Absorbing liquid slurry flow rate Varying flow rate ・ Circulating coolant side condition Coolant : Industrial water flow velocity: 2.0m / s (4.3m ³ / hour) New cooling liquid: 15 ℃ Cooler supply temperature: 20 ℃ ・ Treatment flue gas temperature target 40-41 ℃ ・ Method of each test [Absorption Liquid slurry flow velocity, absorption liquid slurry, and cooling liquid temperature difference are fixed] Operating time: 3 hours / fouling of each test, scaling: Temperature data regarding cooling performance deterioration, internal inspection for each test, and visual inspection of scaling of fouling were performed. 2) The result of test-1 is shown in Table 3. 3) Test-2 condition It is the same as the outer test-1 condition that the coolant supply temperature is 15 ° C. The results are shown in Table 4.

[0020]

As described above, according to the present invention, the absorbent slurry is taken out of the system through the absorption system loop, cooled by the cooler and then returned to the absorption system loop. The discharged treated flue gas can be cooled to a predetermined temperature below the adiabatic cooling saturation temperature of the flue gas before cleaning.

Therefore, according to the present invention, it is possible to save the water discharged to the outside of the system in association with the treated flue gas, and to save the make-up water to the absorber. In particular, in the present invention, the scale generation in the cooler of the absorbent slurry, the Reynolds number in the pipe flowing the absorbent slurry (flow velocity), and by maintaining the temperature difference between the absorbent slurry and the cooling liquid in a specific range, It is possible to completely prevent scale generation from the absorbent slurry.

Normally, the water content of flue gas depends on the amount of water adhering to the coal used for combustion, the fuel ratio of coal, or the water injected into the exhaust gas on the upstream side. Then around 0.05kg moisture / 1kg dry gas (about 8vol.
In most cases, the untreated flue gas introduced into the humidification / cooling unit is 100 to 85 ° C (at rated load). In these cases, the saturation temperature after the humidification cooling has the values shown in Table 1.

Then, since the treated flue gas containing the moisture corresponding to the temperature of each humidification cooling section inlet is discharged out of the system per 1 kg of the dried flue gas, the moisture leaving the system by evaporation is shown in Table 5.
As shown in, the difference between the moisture in untreated flue gas in the desulfurization equipment is 0.05 kg moisture / dry gas 1 kg and the moisture in treated flue gas is kg moisture / kg dry gas. Therefore, if it is possible to cool the absorbent slurry so that the treated flue gas is cooled to 40 ° C, the amount of make-up water accompanying evaporation will be reduced to the level of water in the untreated introduced flue gas, depending on the degree of cooling. be able to.

Further, in the present invention, the gas-liquid contact for desulfurization is also used together, and the cooling is performed to reduce the water content in the treated flue gas. Therefore, it is possible to save energy by saving energy. Therefore, the present invention provides a method for solving a problem in the case where the site environment conditions are not met only by the mismatch between the make-up water acquisition and the site environment conditions in the large-scale thermal power plant site environment.

Table 1

Table 2

Table 3

Table 4

Table 5

[Brief description of drawings]

FIG. 1 is a process drawing showing a method of the present invention.

FIG. 2 is a diagram showing the solubility of a calcium salt in an absorbent slurry according to the present invention.

FIG. 3 is a diagram showing an outline of a flow diagram used in an example of the present invention.

[Explanation of symbols]

4 Absorption tank 8 Absorption system loop 9 Cooler

Claims (1)

[Claims] 1. In a wet flue gas desulfurization method, at least a part of an absorbent based on a calcium-based absorbent is extracted from an absorption system loop, introduced into an indirect cooling type heat exchanger, and cooled by a cooling liquid. After that, the temperature of the absorption liquid slurry supplied to the gas-liquid contact portion is returned to the absorption system loop and the temperature of the exhaust gas after cleaning is washed by the absorption liquid slurry whose temperature is lowered before cleaning. A method for saving make-up water to a wet desulfurization device, characterized in that the adiabatic cooling of the flue gas is kept at a saturation temperature or lower.