JPH0227871Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a wet flue gas desulfurization device, and more particularly to a wet flue gas desulfurization device that can prevent clogging by slurry in a slurry communication pipe.

[Background of the idea]

In recent years, as the demand for power generation has increased, boilers that use fossil fuels as their main fuel have become larger, and the influence of power generation boilers on air pollution is also increasing.

Emission regulations for sulfur oxides (SO _x ), which account for a large proportion of the pollutants that increase air pollution, are becoming stricter year by year. Under these circumstances, Japan's power generation industry, which has used oil as its main fuel since the second oil shock, is now switching to coal, which is cheaper and has ample supply.

However, as boilers have become larger, boilers have been started and stopped repeatedly on a daily basis (DSS operation) in order to frequently change load according to power generation demand in order to reduce power generation costs.

As a feature of recent electricity demand, as nuclear power generation grows, the difference between maximum and minimum loads also increases.
There is a trend to shift boilers for thermal power generation from base load to load adjustment, and these boilers are operated at variable pressure by changing the pressure according to the load.
By using a variable pressure boiler that operates in a so-called supercritical pressure region at full load and in a subcritical pressure region at partial load, the power generation efficiency at partial load can be improved by several percent.

However, because DSS operation is frequently performed on a daily basis and the load is varied, the amount of exhaust gas fluctuates due to the load variation, for example, 1/4, 1/2, etc.
At partial loads such as 3/4 loads, it is not possible to reduce the SO _x value below the target.

For example, wet flue gas desulfurization equipment installed at thermal power plants, etc. uses an absorbent slurry containing calcium carbonate (CaCO ₃ ), calcium hydroxide [Ca(OH ₂ )], or calcium oxide (CaO) as an absorbent. Using slurry, SO _x in exhaust gas from boilers etc.
The most common method is to absorb calcium sulfite, oxidize the resulting calcium sulfite, and recover it as calcium sulfate, that is, gypsum.

A schematic system diagram of a conventional wet flue gas desulfurization apparatus using this limestone or lime is shown in FIG.

In FIG. 4, exhaust gas 2 from a boiler 1 is pressurized in an inlet flue 3 by a desulfurizing ventilator 4, cooled by heat exchange with the treated gas by a gas heater 5, and then exits from an outlet flue 6 into wet exhaust gas. It is introduced into the cooling tower 7 of the desulfurization equipment.

After the cooling tower 7 is cooled to a saturation temperature through gas-liquid contact with the circulating fluid supplied from the cooling tower circulation tank 8 by the cooling tower circulation pump 9, and the dust contained in the exhaust gas 2 is removed, It is sent to the absorption tower 10. In some cases, a mist eliminator 11 may be installed to remove mist in the exhaust gas 2 sent to the absorption tower 10.

In the absorption tower 10, _SO
After the mist is absorbed and removed, the entrained mist is removed in the demister 15 to become a processing gas, and this processing gas passes through the mist eliminator 17 in the flue 16 and is heated by the exhaust gas 2 in the gas heater 5 to prevent white smoke. released into the atmosphere.

On the other hand, the slurry branched from the circulation line of the cooling tower circulation pump 9 is supplied to the reaction tank 18, where sulfuric acid 19 is added to adjust the pH to facilitate oxidation. and is oxidized using air 22 as a medium to become gypsum slurry. Here, it is necessary to keep the air amount constant, the pressure inside the oxidation tower 21 constant, and the slurry level inside the oxidation tower 21 constant so that it can easily become oxidized gypsum slurry.

The gypsum slurry is sent from the oxidation tower 21 to the gypsum concentration tank 25 via a slurry communication pipe 24 having an oxidation tower level control valve 23, where it is separated into supernatant leakage water and concentrated gypsum slurry. .

Leakage water is transferred to leakage water connection pipe 26 and leakage water tank 2.
7. The leakage water is blown down to wastewater treatment equipment through the leakage pump 28 or reused as make-up water for the limestone slurry tank 29, etc.

On the other hand, the gypsum slurry concentrated in the gypsum concentration tank 25 is supplied to the centrifuge 32 via a gypsum slurry tank 30 and a centrifuge supply pump 31. The centrifugal separator 32 dehydrates and separates the water into gypsum 33 and waste water 34, and the gypsum is used as a raw material for cement, boards, etc. Further, the wastewater 34 is sent to the absorption tower circulation tank 12 via a centrifugal separator drainage tank 35 and a centrifugal separator drainage pump 36, and is reused as crystals to prevent scaling in the desulfurization equipment.

Limestone slurry, which serves as an absorbent for desulfurizing SO ₂ , is mixed with limestone powder 37 and leakage water from leakage water pump 28 to form limestone slurry, which is supplied to absorption tower circulation tank 12 by limestone slurry tank 29 and limestone slurry pump 38. Ru.

The above is an explanation of a general system of a wet flue gas desulfurization apparatus, and the level control of the oxidation tower 21 was performed as follows.

FIG. 5 is a level control system diagram of the oxidation tower 21. 4 and 5, 23 is an oxidation tower level control valve, 24 is a slurry connection pipe, 39 is an oxidation tower level detector, 40 is an oxidation tower level controller, 41 is an actual level signal, 42 is a setting signal, 4
3 is a deviation signal.

In such a structure, in order to keep the level of the gypsum slurry in the oxidation tower 21 constant so that it can be easily converted into gypsum in the oxidation tower 21, the level is set by the oxidation tower level controller 40 and the oxidation tower level is adjusted. The measured level signal 41 from the detector 39 and the set signal 42 were compared, and the oxidation tower level control valve 23 was opened and closed based on the deviation signal 43 from the oxidation tower level controller 40.

That is, in order to keep the level in the oxidation tower 21 constant, the slurry flow rate from the reaction liquid pump 20 to the oxidation tower 21 is adjusted from the oxidation tower level control valve 23 to the slurry connection pipe 24 to the gypsum concentration tank 25.
It was being discharged to.

However, as mentioned above, when DSS operation is performed on the boiler 1 and the load is low, the reaction liquid pump 20
The amount of slurry flowing into the oxidation tower 21 is reduced, and therefore the amount of slurry flowing out into the slurry communication pipe 24 is also reduced. For this purpose, the slurry connection pipe 24
The slurry flow rate in the slurry becomes low flow rate and low flow rate, and solids in the slurry flow into the slurry connecting pipe 24.
Eventually, the slurry communication pipe 24 becomes clogged, forcing the operation of the wet flue gas desulfurization equipment to be stopped.

[Purpose of invention]

In order to eliminate such conventional drawbacks, the present invention
The purpose of the present invention is to provide a wet flue gas desulfurization device that can prevent clogging of slurry communication piping even when the inflow and outflow of gypsum slurry decreases during low loads and can be operated continuously.

[Summary of the idea]

In order to achieve the above-mentioned purpose, the present invention provides a leakage water recirculation pipe with a leakage water flow rate control valve between the leakage water tank and the slurry connection pipe, thereby reducing the slurry flow rate in the slurry connection pipe. In this case, the control is to increase the leakage water from the leakage water recirculation piping.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

Fig. 1 is a schematic system diagram of the wet flue gas desulfurization equipment according to the embodiment of the present invention, Fig. 2 is a control system diagram at the oxidation tower level, and Fig. 3 is the opening and closing of valves in the control system diagram of Fig. 2. It is a figure explaining a state.

In FIGS. 1 to 3, numerals 1 to 43 indicate the same parts as the conventional ones.

44 is the slurry connection pipe 24 and the leakage water tank 2
7, 45 is a leakage water flow control valve provided in the leakage water recirculation pipe 44, 46 is an arithmetic unit with bias, and 47 is a leakage water flow control valve 45.
This is a control signal that causes a reverse response.

In such a structure, the flow rate of gypsum slurry in the slurry connecting pipe 24 decreases when the load is low, so in the present invention, as shown in FIG.
A leakage water recirculation pipe 44 having a leakage water flow rate adjustment valve 45 is provided at the outlet of the oxidation tower level adjustment valve 23.

In other words, when the slurry flow rate in the slurry communication pipe 24 decreases during low load, the leakage water flows from the leakage tank 27 to the slurry communication pipe 24 via the leakage water flow control valve 45 and the leakage water recirculation pipe 44. The water flow rate is increased to prevent solid matter from accumulating in the slurry communication pipe 24 by leaking water.

By increasing the leakage water flow rate from the leakage water recirculation pipe 44 in this way, it is possible to prevent solid matter from depositing in the slurry connection pipe 24. Moreover, since the leakage water is used to prevent deposition, industrial water The amount of (fresh water) used can be reduced.

Figure 2 is a control system diagram of the oxidation tower level, and Figure 3 is the control system diagram of the oxidation tower level control valve 2 according to the control system diagram of Figure 2.
3 and a characteristic curve diagram of the leakage water flow rate control valve 45.

In FIG. 2, the oxidation tower level control valve 23 is opened and closed by the deviation signal 43 from the oxidation tower level controller 40, but the leakage water flow rate control valve 45 is operated separately from the oxidation tower level control valve 23. Arithmetic unit with bias 4
It is controlled by a control signal 47 from 6 with an inverse characteristic.

Straight line A in FIG. 3 shows the opening degree characteristic of the oxidation tower level control valve 23, and straight line B shows the opening degree characteristic of the leakage water flow rate control valve 45.

For example, as shown by straight line A in Fig. 3, when the opening degree of the oxidation tower level control valve 23 decreases from point C to point D, the slurry flow rate in the slurry communication pipe 24 decreases, so that the leakage water The flow control valve 45 is controlled to open from point E to point F, indicated by straight line B in FIG. 3, to increase the flow rate of leaked water from leaked water recirculation pipe 44 to slurry communication pipe 24.

By controlling the leakage water flow rate control valve 45 and the oxidation tower level control valve 23 with opposite characteristics in this way, the opening degree of the oxidation tower level control valve 23 is small, and the oxidation tower level control valve 23 is controlled with opposite characteristics.
When the amount of outflow from 1 is small, leakage water control valve 4
To increase the amount of leaked water supplied by increasing the opening degree of the valve No. 5, to keep the flow rate and flow velocity in the slurry connecting pipe 24 almost constant, and to prevent accumulation and sedimentation of slurry in the slurry connecting pipe 24. Can be done.

In addition, when the valve opening degree of the oxidation tower level control valve 23 is large, the leakage water control valve 45 is closed to reduce the flow rate of leakage water, contrary to the previous method.

In this way, by adjusting the leakage water flow rate from the leakage water recirculation pipe 44 according to the slurry flow rate to the slurry communication pipe 24, the slurry communication pipe 24
Canal occlusion within the body can be prevented.

[Effect of idea]

This invention provides a leakage water recirculation pipe with a leakage water flow rate control valve between the leakage water tank and the slurry connection pipe, and when the slurry flow rate in the slurry connection pipe decreases, the leakage water recirculation pipe is connected to the slurry connection pipe. control to increase leakage water, so even if DSS operation is performed, slurry deposition and accumulation in the slurry connection piping can be prevented, and the wet desulfurization equipment can be operated continuously even with load fluctuations. Can be done.

[Brief explanation of the drawing]

Figures 1 to 3 relate to embodiments of the present invention; Figure 1 is a schematic system diagram of a wet flue gas desulfurization equipment; Figure 2 is a control system diagram at the oxidation tower level in Figure 1;
The figure shows the opening and closing characteristics of the valve in the control system diagram of Figure 2. Figures 4 and 5 show the conventional wet flue gas desulfurization equipment. Figure 4 shows the schematic system of the wet flue gas desulfurization equipment. 5 is a control system diagram at the oxidation tower level in FIG. 4. 21... Oxidation tower, 23... Oxidation tower level control valve, 24... Slurry connection piping, 25... Gypsum concentration tank, 26... Leakage water connection piping, 27... Leakage water tank, 44... Leakage Excess water recirculation piping, 45...
Leakage water flow control valve.

Claims (1)

[Scope of utility model registration request] In a wet flue gas desulfurization system in which an oxidation tower and a gypsum concentration tank are connected by a slurry connection pipe having an oxidation tower level control valve, and a gypsum concentration tank and a leakage water tank are connected by a leakage water connection pipe, the leakage water is A leakage water recirculation pipe with a leakage water flow control valve is installed between the tank and the slurry connection pipe, and when the amount of slurry water in the slurry connection pipe decreases, leakage water from the leakage water recirculation pipe is increased. A wet flue gas desulfurization device characterized in that it is controlled so as to