JPS60821A - Wet method for desulfurizing stack gas - Google Patents

Abstract

PURPOSE:To remove impurities such as aluminum and fluorine collected in the system of a wet method desulfurizer of stack gas, and to increase the pH of the whole system by measuring the pH of a supernatant liquid in an apparatus for concentrating a slurry after oxidation, and throwing in slaked lime in accordance with the pH. CONSTITUTION:A slurry absorbent 11, wherein SO2 in a stack gas is adsorbed, is oxidized in an oxidation tower 24, and introduced into a concentration apparatus 30. The pH of a mother liquid 45 overflowing from the concentration apparatus 30 is measured by a pH measuring apparatus 46, and a slaked lime emulsion is thrown into the concentration apparatus 30 in accordance with the pH from a slaked lime supply apparatus 44 through a line mixer 54 to regulate the pH of the mother liquid 45 to 7-8. The impurities such as F<-> and Al<3+> are precipitated by the slaked lime as CaF2 and Al(OH)3, and removed. The mother liquid 45 is circulated into an absorption tower 10. In this way, the deactivation of the slurry adsorbent 11 due to the impurities and the corrosion in the system due to the ions of impurities can be prevented.

Description

Detailed Description of the Invention The present invention is a wet method in which sulfur oxides in exhaust gas such as boiler exhaust gas are absorbed and removed by absorption R, and the absorbed liquid is oxidized and gill-netted, and then solid-liquid separation is performed to recover gypsum. The present invention relates to a flue gas desulfurization method.

In the wet flue gas desulfurization method, the dust in the flue gas is removed in a desulfurization tower, and then introduced into an absorption tower, where it is brought into contact with a slurry absorbent such as lime to remove sulfuric acid compounds in the flue gas, producing a clean On the other hand, the slurry absorption liquid that has absorbed sulfuric acid compounds is acidified in an oxidation tower, and the slurry liquid after one oxidation is concentrated using a sotsu, kuna, etc., and then the concentrated liquid is converted into a solid liquid by a dehydrator. The stone is separated and collected. In this case, some of the supernatant liquid from the thickener is
The remaining 9
The supernatant liquid is then treated with wastewater treatment equipment. In the absorption tower, if the pf (pf) of the slurry absorption liquid is low, calcium hydrogen sulfite [Ca(H8O3)2] is formed, which causes a reverse reaction and generates sulfur dioxide [So2], which reduces the desulfurization rate. , the slurry absorption liquid has a practical pH of 5.
, 0 or more, and if the pH value is high at 6s @, calcium carbonate [Ca CO3] will remain unreacted and excessive Ca content will be required, which is disadvantageous, so the pH should be 60 or less, preferably 58 or less. is desirable.

In this way, the pH control range of the slurry absorption liquid in the absorption tower is narrow, 5.0 to 5.8, but in the oxidation tower, calcium sulfite [Ca5Os] is acidified and gypsum (CaSO4, :l
In order to achieve this, the presence of intermediate VcCa (H8O3)2 is required, and as a result, the lower the pH value, the faster the oxidation occurs, so Ca (H8O3)2 is likely to be generated in the absorption tower at around pH 5.0. It is preferable to drive with

However, the exhaust gas contains impurities such as fluorine and aluminum in fly ash, and if the absorption tower is operated at a pH of around 5.0, the p+I of the slurry liquid exiting the IR tower will be 3.5 or less. When the impurity is dissolved, this 7t is F- in the supernatant of the 7tschner.

At3'' ions exist in the form, and when this supernatant liquid is recycled to the absorption tower as a mother liquid, the activity of the slurry absorption liquid decreases, it becomes difficult to control the pH in the absorption tower, and the impurity ions cause threads. It is easy to corrode.

Furthermore, if the above-mentioned liquid containing the impurities dissolved therein is supplied to the wastewater treatment apparatus after passing through the wastewater treatment apparatus or after passing through a dehydrogenation tower, there is a problem that F-treatment in the wastewater treatment increases.

The purpose of the present invention is to remove the impurities trapped in the system of the wet flue gas desulfurization equipment, to increase the pH of the entire system, and to improve the performance of the desulfurization equipment even when the I)H value of the absorption tower has decreased to about 45. The purpose is to provide a wet flue gas desulfurization method that does not interfere with the operation of the system.

In the present invention, the exhaust gas is brought into a total absorption tower after desulfurization, the exhaust gas is brought into contact with the slurry absorption liquid, and after the contact, the slurry absorption liquid is acid-ratioed and then supplied to a ml condensation device such as a thickener, and then concentrated. In a wet flue gas desulfurization method in which the supernatant liquid of the equipment is supplied to the wastewater treatment equipment and a part of it is supplied to the absorption tower, the supernatant liquid QPH of the concentrator is measured, and depending on the pH value, the supernatant liquid QPH of the concentrator is Slaked lime is supplied as a slaked lime emulsion using the installed line mixer, and F-At” is added to the supernatant liquid of the concentrator.
Impurities dissolved as CaF2゜At(
It is designed to be precipitated as OH)3 and removed from the supernatant liquid.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the accompanying drawings showing an apparatus for carrying out the wet flue gas desulfurization method according to the present invention.

Exhaust gas from a boiler or the like passes through a booster fan 1, a gas-gas heater 2, and is introduced into a dust removal tower 3.

In the dedusting tower 3, the dust in the dust removal tower 3 is sucked by a spray pump 5, and a liquid is injected from a spray nozzle attached to a spray joint pipe 6 to completely remove dust and the like from the exhaust gas. The number 4 is supplied from the dust removal tower 3 to the wastewater treatment device 8 by the pump 7. The exhaust gas that has passed through the desulfurization tower 3 is led to an absorption tower 10 through a duct 9. Absorption 1li1o here
The exhaust gas passing through is sucked from the lower part of the absorption tower 10 by a circulation pump 12 and comes into contact with the slurry absorption liquid 11 which is injected from spray nozzles attached to a number of spray joint pipes 13 provided at the upper part of the tower 10. The 5O2-F slurry in the gas is absorbed and removed by the absorption liquid 11. Injection pipe 13
A mist eliminator 14 is provided at the top of the tower 10.
The mist separated by the mist eliminator 14 is washed with a washing liquid supplied from the raw water supply device 15 or the mother liquor tank 32 through the nozzle 16, and then sent to the column 1.
Return to 0. An exhaust duct 1γ is provided at the top of the tower 10, and the gas is heated through the gas heater 2 and discharged from the chimney 18. The slurry absorption liquid 11 in the absorption tower 10 is supplied from the slurry pit 19 to the tower 10 through a pump 20. Slurry absorbing liquid 11 is placed in the slurry pit 19.
An absorbent such as calcium carbonate or slaked lime is supplied into the slurry pinto 19 from an absorbent supply device 21 via a hopper 22t.

The absorption tower 10 stripes 1 and the absorption liquid 11 are supplied to the oxidation tower 24 by a pump 23. Sulfuric acid is supplied into the oxidation tower 24 from a sulfuric acid supply device 25 by controlling the pH of the oxidation tower outlet liquid, and air is supplied from the lower part of the oxidation tower 24 from an air supply device 26. The air supplied to the oxidation tower 24 undergoes an acid ratio reaction with the slurry absorption liquid supplied from the absorption tower 10,
The remaining gas flows into the duct 9 through the nosoip 27. The liquid acidified in the oxidation tower 24 is circulated by a pump 28, and is supplied to a concentrator 30 such as a thickener via a pipe 29 and a line mixer 54. The supernatant liquid overflowing from the concentrator 30 is supplied to the IP mother liquor tank 32 through the IP Eve 31 . The upper liquid in the mother liquid tank 32 is sent from the pump 33 to the draining device 8 via the pipe 34′f, and a part of it is transferred as the mother liquid to the slurry bit 1 via the pipe 35.
9 and absorption tower 10.

The concentrated liquid in the concentrator 30 is supplied from the pump 36 to the dehydrator supply tank 31, and then from the supply tank 31 to the gypsum dehydrator 39 by the pump 38, where it is centrifugally dehydrated.
The solid content is transferred from the belt conveyor 40 to the gypsum storage tank 41.
Guided to.

The liquid dehydrated by the gypsum dehydrator 39 is drained into a drainage pit 42v.
This is supplied and returned to the concentrator 30 by the pump 43.

A slaked lime supply device 44 that supplies slaked lime, which is strongly alkaline, is connected to the line mixer 54 provided in the acid ratio tower outlet vibe 29. This supply device 44 is the concentrator 30
pH'fr of the mother liquor in the overflow pipe 31: The slaked lime emulsion is supplied to the line mixer 54 according to the pH signal 41 of the PTL measuring device 46 to measure it, and after being mixed with the oxidation tower outlet liquid, it enters the concentrator 30 and is transferred to the mother liquor tank. Mother of 32 g45 P
The l value is controlled to be in the range of 7.0 to 8.0.

In addition, raw water is supplied to the desulfurization tower 3 from the raw water supply device 15 via the guide 48, and from the mother liquor tank 32 to the pump 3.
3. Pipe 49'f: mother liquor is supplied through each pipe. Further, the slurry absorption liquid 11 in the absorption tower 10 is stirred by a stirrer 53.

Next, the present invention will be explained in detail.

The exhaust gas that has been desulfurized through the desulfurization tower 3 is introduced into the absorption tower 10, where it comes into contact with the slurry absorption liquid 11 that is injected from several spray nozzles arranged in the joint pipe 13. Due to the contact, the sulfur compounds in the exhaust gas are absorbed by the slurry absorbing liquid 11, and the desulfurized exhaust gas from the upper part of the absorption tower 10 is heated by the gas-gas heater 2 through the duct 1γ, and then sent out from the chimney 18. Exhausted.

Sulfur thicket f in exhaust gas absorbed by slurry absorption liquid 11
The arsenic reacts with the Ca content in the slurry to become calcium sulfite, which is supplied to the ratio reforming tower 24. In the 17 ratio column 24, the following reaction is carried out by air supplied from the lower part of the oxidation column 24.

In addition, the unreacted absorbent that did not react with the sulfurized product was mixed with gypsum using sulfuric acid.

According to the above reaction, the gas discharged from the ratio column 24 contains a small amount of SO2, so it is returned to the duct 9 via the pipe 2γ.
supply to.

The slurry after oxidation is supplied to the concentrator 30 through the line mixer 54 attached to the pipe 29, where the condensed concentrate is separated into solid and liquid from the supply tank 37 by the gypsum dehydrator 39. It is stored in the storage tank 41 as a general purpose.

The supernatant liquid of the concentrator 30 is supplied to the mother liquor tank 32, a part of which is used as a mother liquor of the slurry absorption liquid 11 of the cough collection tower 1υ, a part of which is supplied to the desulfurization tower 3, and the remaining part is supplied to the wastewater treatment equipment. 8. In this desulfurization equipment, a part of the raw water is supplied from the raw water supply device 15 to the absorption tower 1υ, but most of the liquid content of the slurry absorption liquid 11 is used by circulating the mother liquor 45 in the mother liquor tank 32. Fluorine, aluminum, etc., which are impurities in the exhaust gas, are mixed into the mother liquor 45 and tend to accumulate without being separated.

As mentioned above, the p of the slurry absorption liquid 11 in the absorption tower 10
l (When the value is operated at around 5.0, the oxidized gypsum slurry 1 passed through the oxidation tower 24)-WOPH value tends to decrease to around 35, and the dissolved concentration of aluminum etc. in the above 7 cases increases, At'' and F- are absorbed into the mother liquor 45.If this mother liquor 45'ff is circulated through the slurry pit 19 and the absorber q1o, the activity of the slurry absorbent 1'1 will decrease, and OPH will be removed in the absorption tower 10. The value decreases and its Pl
It becomes difficult to control -1 values.

Furthermore, if the wastewater is supplied to the wastewater treatment device 8, it becomes particularly difficult to remove dissolved fluorine components.

Therefore, the concentrator 3υJ: 9 over-low mother liquor 45
The Pl value of is measured by the PH measuring device 46, and the slaked lime emulsion is charged into the concentrating device 30 through the slaked lime supply device 44 and the sill line mixer 54 according to the Pl value. F-1At3+, which was dissolved by adding the slaked lime emulsion, becomes a solid and precipitates through the following reaction.

2F-10Ca2-*CaF,, ↓ At + 30H-> A7(OH)34 The amount of slaked lime to be added is such that the pH value of the mother liquor 45 overflowing in concentrator #30 is 7.0 to 8.0. Appropriate pH measuring device 4
671> transmit the pi signal 41 to the slaked lime supply device 44,
The amount of slaked lime supplied is controlled by the signal.

The amount of impurities that settle in the 30 yen concentrator is extremely small, and even if they are mixed into 95 gypsum, there will be no problem with the product.

As is clear from the detailed description above, the present invention exhibits the following excellent effects.

(1) Since the liquid mixed with slaked lime is fed into the concentrator using a line mixer, impurities such as aluminum and fluorine dissolved in the liquid can be removed.

(2) The pH of the supernatant liquid of the concentrator is measured and slaked lime is added accordingly, so the pH of the supernatant liquid can be controlled.
Sonf: Even if it is circulated to the absorption tower, it is easy to control the pH within the absorption tower.

(3) Since the supernatant liquid from which impurities have been removed is supplied to the wastewater treatment equipment, the burden of wastewater treatment such as fluorine is reduced.

(4) Even if the absorption tower is operated at a pH value of 50 or less, the slaked lime that enters the concentrator via the line mixer removes impurities and then circulates to the absorption tower as the entire supernatant mother liquor. (5) Since the mother liquor from which all impurities have been removed is circulated to the total absorption tower, no reduction in the activity of the slurry absorption liquid occurs.

(6) Since the absorption tower can be operated near or below Pl-15.0, the ratio treatment can be carried out quickly.

(7) By adding slaked lime, the pH value of the mother liquor can be increased, improving the corrosion resistance of the device.

[Brief explanation of the drawing]

The accompanying drawings are diagrams showing an example of an apparatus for carrying out the present invention. In addition, in the figure, 3 is a desulfurization tower, 10 is an absorption tower, 11 is a slurry absorption liquid, 24 is an oxidation tower, 30 is a concentration device, 32 is a mother liquor tank, 44 is a slaked lime supply device, 46 is a pH measuring device,
54 is a line mixer. Patent applicant: Ishikawajima-Harima Heavy Industries Co., Ltd. Agent: Nobuo Kinuya, patent attorney

Claims (1)

[Claims] After desulfurization, all the exhaust gas is introduced into an absorption tower and brought into contact with the slurry absorption liquid, and after the contact, the slurry absorption liquid is oxidized, and then supplied to a concentration device such as a Ntukuner, and a part of the supernatant liquid of the concentration device is In a wet flue gas desulfurization method in which gas is circulated to the absorption tower, the upper layer liquid OPH of the concentration device is measured, and its PI
Wet type % characterized by adding slaked lime according to J value
formula%