JPH021523B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas absorption tower, and more particularly to a spray type gas absorption tower suitable for absorbing sulfur dioxide in exhaust gas.

Conventionally, tower types used for gas absorption and gas cleaning operations include the perforated plate type, the rutling (sometimes saddle) filling type, and the spray type. In cases where crystals such as calcium sulfate are formed as a by-product of the absorption reaction, such as in the so-called limestone slurry desulfurization method, in which sulfur dioxide and other substances in exhaust gas are absorbed using a calcium carbonate suspension, perforated plate methods and filling methods are recommended. In the absorption tower, gypsum scale forms, adheres, and grows on the perforated plates, Rutsch rings, etc. where the reaction proceeds. This scale problem in perforated plate type and packed type absorption towers is the biggest drawback of the wet desulfurization process, and in flue gas desulfurization equipment that contains a high concentration of sulfur dioxide, the scale is completely removed when the equipment is shut down once or twice a year. This avoids blockage and prevents a decrease in desulfurization efficiency and absorption efficiency.

On the other hand, with the recent revival of lime-fired power generation, the concentration of sulfur dioxide in flue gas is increasing, and scale problems in flue gas desulfurization equipment are predicted to increase rapidly. Spray tower structures that cause fewer problems are being adopted. In the spray method, the reaction site for producing crystals is the particle surface of the spray droplets, and is the space within the tower through which the absorbed gas flows, either opposite to or accompanied by the flow.

Therefore, the key points in tower design to improve the efficiency of the absorption reaction within the spray tower are the selection of a spray nozzle that sprays fine particles and the appropriate layout of the spray header to ensure uniform spray distribution. .

FIG. 1 shows an example of a typical wet flue gas desulfurization process flow sheet. The main equipment of the process is a cooling bench tower 2 and an absorption tower 9 at the gas inlet. The exhaust gas passes through the inlet gas duct 1 in the direction of the arrow, enters the cooling bench lily tower 2, is sent from the cooling liquid circulation tank 6 by the pump 5, passes through the piping 4, and is sprayed from the cooling spray 3, which lowers the temperature of the exhaust gas. , and the soot and dust in the gas is primarily removed. The coolant that has undergone gas cooling is returned to the circulation tank 6 from the bottom of the cooling tower 2, and the coolant entrained in the gas is collected by a demister 7 and returned to the circulation tank 6 through a return pipe 8. .

Spray nozzles 10 are provided in multiple stages in the absorption tower 9, and absorption liquid is sent from a circulation tank 13 to the spray nozzle 10 through a pipe 12 by a pump 14, and the sprayed cooling liquid accumulates at the bottom of the tower and is transferred to the circulation tank. will be returned to. The gas cooled in the cooling tower 2 enters the absorption tower 9 from the lower side and rises, comes into gas-liquid contact with the sprayed absorption liquid in countercurrent, and a desulfurization reaction (SO ₂ absorption reaction) proceeds. The gas that has completed the desulfurization reaction is discharged from the tower 9 in the direction of the arrow. 11 is a demister that collects the absorption liquid. In addition, in the absorption liquid circulation tank 13,
An absorbent tank 15, supply pump 16, and piping 17 are attached as an absorbent make-up and PH control system. Although the spray absorption tower 9 is often hollow, it may also have a perforated plate structure.

To give an example of the specifications of spray absorption towers that have been constructed in the past or are currently under construction, the diameter of the tower is 15mφ, and the number of spray nozzles is approximately 100 per spray header stage.
5 to 6 stages of spray headers are arranged with a spray stage interval of 1.5 to 2 m, and the liquid-gas ratio (L/G) is 20/N.
There is a sulfur dioxide absorption tower of less than ^m3 .

There are two types of absorption liquid spray nozzles used in spray absorption towers: a hollow cone type that exhibits a bell-shaped spray pattern, and a full cone type that exhibits a brush-like spray pattern. Spray absorption towers that have been constructed or are currently being constructed include:
All of the above-mentioned nozzles are of the same type and have the same specifications.

FIG. 2 shows an example of the spray particle size distribution when the spinal pressure of the hollow cone nozzle is 1 Kg/cm ³ G. As seen in FIG. 2, the average particle size is 1000 to 1100μ, with a normal distribution between 100 and 2500μ. In addition, when the spinal pressure is increased to 3 to 5 kg/cm ³ G or the spray hole diameter is decreased, the peak of the particle size distribution decreases.
500 to 300μ, and changes to a fine particle distribution form. Conversely, when spinal pressure is lowered, the particle size distribution peaks at 1500.
~2000μ, resulting in a coarse grain (large grain size) distribution type.

FIG. 3 shows the specific surface area ratio of the sprayed particles having the particle size distribution shown in FIG. As can be seen from FIG. 3, if the particle size distribution is biased toward fine particles, the surface area will increase dramatically, and if the distribution is biased toward coarse particles, it will decrease dramatically. Therefore, the rate of gas absorption reaction that progresses on the surface of the droplet largely depends on the particle size and number of droplets. The droplet size and number of droplets here are highly dependent on the nozzle supply spine pressure. This supplied spinal pressure is directly proportional to the pump power requirement; doubling the spinal pressure requires doubling the pump drive motor power requirement. In order to keep the column filled with fine particles, it is extremely uneconomical to install spray nozzles for fine particle atomization with high feed pressures in view of the power requirements of this pump.

On the other hand, according to the inventor's experiments, when droplets as shown in Fig. 2 are sprayed into the absorption tower, (a) Fine particles of 100 to 500μ are sprayed from the nozzle of the spray header in the upper stage of the tower. (b) The large droplets of 500 to 2,500μ sprayed from the nozzle of the spray header at the bottom of the tower flow into the gas. It became clear that the water was flowing backwards and immediately falling to the bottom of the tower. Since the reaction site in the spray tower is the droplet surface, the liquid particles (a) and (b) described above do not contribute to improving the absorption efficiency and result in a loss of spray power.

FIG. 4 shows part of the results of experiments conducted by the present inventor. Figure 4 shows a flow rate of 2 to 3 from the bottom of the tower to the top.
It shows the movement behavior of particles of each particle size in a gas passing at m/s. That is, particles with a particle size of 500 μm or less rise together with the gas, and particles with a particle size of 800 μm or more fall in a straight line against the gas flow.

An object of the present invention is to provide a gas absorption tower that eliminates the above-mentioned drawbacks of the prior art and can obtain high gas absorption efficiency without increasing the spray power.

The gas absorption tower according to the present invention has a plurality of spray stages having a plurality of spray nozzles that spray absorption liquid, and in the gas absorption tower in which gas is introduced from the bottom of the tower and discharged from the top, the spray stage has an average particle size of diameter
It consists of an upper stage spray that sprays droplets with an average particle size of 800 to 1500μ, a middle stage spray that sprays droplets with an average particle size of 500 to 800μ, and a lower stage spray that sprays droplets with an average particle size of 100 to 500μ, and each of the above stages. A gas concentration detector is provided at the gas inlet to the gas absorption tower, and when the detector detects a set high concentration, all of the flow rate regulation valves are opened. It is characterized by comprising a control means that outputs a signal and sequentially closes the flow rate control valves of the sprays in each stage from the side where the average particle size of the droplets is large to the side where the average particle size of the droplets changes as the concentration changes from high concentration to low concentration. That is.

The inventor has reached the following conclusions (i) and (ii) based on the experimental results shown in FIG. 4.

(i) Particles with a particle size of 500 μm or less will accompany the gas and rise, so they must be sprayed upstream of the gas stream in order to obtain a long residence time in the column and extend the connection time with the gas. .

(ii) Particles with a particle size of 800μ or more flow downstream in a straight line against the gas flow, so they must be sprayed from the nozzle of the spray header as high as possible in the column.

Now, in order to satisfy conditions (i) and (ii) above while keeping the required pump power constant and the spray pressure constant,
It is necessary to take the following actions.

(i) The upper spray header is equipped with a nozzle with a large nozzle hole diameter that sprays particles with an average particle size of 800 to 1500μ.

(ii) Spray header in the middle has an average particle size of 500~
Install a nozzle that sprays 800μ particles.

(iii) The lower spray header is equipped with a nozzle that sprays fine particles with a minimum nozzle hole diameter and an average particle size of around 100 to 500 microns to form a fine particle spray zone at the bottom of the tower.

In particular, it is necessary to spray particles having an average particle size of 800 μm or more exclusively from the nozzles of the upper spray headers, without spraying them from the nozzles of the middle or lower spray headers as much as possible.

On the other hand, considering power saving and high efficiency operation, it is possible to increase or decrease the absorption liquid circulation throughout the tower according to the gas flow rate at the tower inlet, and also to control the above-mentioned upper, middle, and lower stages of spraying according to the concentration of the absorbed gas. It goes without saying that it is essential to control the amount of spray for each group. For example, when absorbing a low concentration of gas, the upper spray header group is stopped, and only the middle and lower stages have a fine particle atmosphere with a high specific surface area, and are operated with low pump power to ensure high absorption efficiency.
In the case of conventional spray nozzle groups of the same type, if the absorption liquid circulation amount is controlled, the spray characteristics will change suddenly, making low power, high absorption rate operation (throttle operation) impossible.

FIG. 5 shows a flow sheet of an embodiment of the gas absorption tower of the present invention. Gas is introduced from the inlet 18,
The absorption liquid is discharged from the outlet 19, and the absorption liquid in the absorption liquid circulation tank 13 is sent to the spray header through the pipe 12 by the pump 14, and the spray liquid is sent from the bottom of the column to the tank 13.
It is exactly the same as in the case in FIG. 1 that the absorbent tank 15 and other attached equipment are provided.

In this device, the spray stages, that is, the spray headers, are roughly divided into three groups: an upper spray 20, a middle spray 21, and a lower spray 22, which are connected to the piping 12 via flow rate control valves 20A, 21A, and 22A, respectively. There is. Spray 20,2 for each stage
Spray nozzles 20B, 21B, and 22B for spraying coarse particles (800 to 1500 microns), fine particles (500 to 800 microns), and fine particles (100 to 500 microns) are attached to 1 and 22, respectively. A gas flow rate sensor 2 is installed at the gas inlet 18.
3 and a gas concentration detector 24 are provided. The absorption liquid pipe 12 is provided with a control valve 25, and the control valve 25 is controlled by a control means (not shown) in response to a signal from the gas flow rate detector 23. Further, the signal from the gas concentration detector 24 is sent to the control means 26,
The control means 26 controls the flow control valves 20A, 21A, and 22A of the spray headers at each stage.

Particle size sprayed from the lower spray nozzle 22B
After the fine particles of 500 μm or less absorb gas at the lower part of the tower, they rise to the upper part of the tower, become larger particles due to collision, adhesion, etc., and fall, and some of them are captured by the demister 11. Fine particles have a large specific surface area and a long residence time in the column, so they perform effective absorption. In addition, the particle size sprayed from the upper spray nozzle 20B
Coarse particles of 800μ or more are sprayed in the upper stage, so they remain in the tower for a relatively long time, and when they fall, they collide with the top of the header, header support frame, etc. in various parts of the tower, and are cleaned, that is, scaled. Heading towards the bottom of the tower. In this way, there is no waste in droplet behavior within the column, and high absorption efficiency can be obtained.

Further, when the signal from the gas concentration detector 24 at the inlet 18 indicates a low gas concentration, the control means 26 closes the control valve 20A of the upper spray header 20 to pump the absorbent liquid to the upper spray header 20. stop operating. Therefore, the absorption tower is filled with only a fine particle atmosphere with a high specific surface area from the middle and lower nozzles 21B and 22B, and is operated with low pump power (small number of pumps) to ensure high absorption efficiency without waste. . When the gas concentration further decreases, the control valve 21A of the middle stage spray 21 is also closed, and the operation of the pump supplying the absorption liquid to the middle stage spray header 21 is stopped.

As described above, in the gas absorption tower according to the present invention, a spray nozzle for spraying coarse particles (800μ or more) is attached to the upper spray, and if necessary, fine particles (500 to 800μ) are sprayed to the middle spray and fine particles (500 to 800μ) are sprayed to the lower spray. Since a spray nozzle that sprays 100 to 500μ) is installed, the residence time of each particle in the column is extended, effective gas absorption can be performed, and high absorption efficiency can be achieved. This allows the pump supply pressure of the absorption liquid to be lowered, and since the pump power is also directly proportional to this, it is possible to save 3 to 5% of the power with the same absorption efficiency. Furthermore, depending on the gas concentration, the flow rate for each spray at each stage changes from spraying droplets with a large average particle size to spraying small droplets as the gas concentration changes from high concentration to low concentration. Since the spray is sequentially narrowed and appropriately controlled in the direction of the spray, it is possible to achieve high absorption efficiency at all times with appropriate power savings. In addition, control such as throttling the control valve (25 in FIG. 5 in the embodiment) is performed simultaneously with the sequential flow rate adjustment control for each spray at each stage, based on the signal from the gas flow rate detector regarding the gas flow rate. It is possible to respond to changes in flow rate and gas concentration from various angles, and from this point of view, further power savings and high absorption efficiency can be achieved.

[Brief explanation of drawings]

Figure 1 is a flow sheet of a typical conventional wet flue gas desulfurization process, Figure 2 is a particle size distribution diagram of atomized particles from a typical spray nozzle, and Figure 3 shows the specific surface area ratio of the particles in Figure 2. 4 is a diagram showing the flight behavior of droplets in the tower, and FIG. 5 is a flow sheet of an embodiment of the gas absorption tower of the present invention. 2...Cooling Benchelli tower, 9...Absorption tower, 10
... Spray nozzle, 13 ... Absorption liquid circulation tank,
20, 21, 22... Upper stage, middle stage, lower stage spray header, 20A, 21A, 22A... Upper stage, middle stage,
Lower stage flow control valve, 20B, 21B, 22B...Upper stage, middle stage, lower stage spray nozzle, 23...Gas flow rate detector, 24...Gas concentration detector, 25...Flow rate control valve, 26...Automatic control means.

Claims (1)

[Claims] 1. In a gas absorption tower that has multiple spray stages with a plurality of spray nozzles that spray absorption liquid, and gas is introduced from the bottom of the tower and discharged from the top, the spray stage is configured to spray droplets with an average particle size of 800 to 1500μ. It consists of an upper stage spray that sprays liquid, a middle stage spray that sprays droplets with an average particle size of 500 to 800μ, and a lower stage spray that sprays droplets with an average particle size of 100 to 500μ, and the flow rate is adjusted for each spray in each stage. It has a gas concentration detector and a gas flow rate detector at the gas inlet to the gas absorption tower, and the output signal from the gas flow rate detector In addition to controlling the opening and closing of the other control valves, when the gas concentration detector detects a preset high concentration, it outputs a signal to open all of the flow rate control valves, and changes from high concentration to low concentration. A gas absorption tower characterized by comprising a control means for sequentially closing the flow rate control valves of the sprays in each stage from the side where the average particle size of the droplets is large to the side where the average particle size of the droplets is small.