JPS5992014A - Desulfurization of waste gas - Google Patents

Abstract

PURPOSE:To adjust a desulfurization factor, by controlling the supply amount of an Mn-compound into a Ca-compound-containing absorbing tower recirculation slurry by detecting the amount to be absorbed into the slurry of O2-gas blown into said slurry. CONSTITUTION:The flow amounts and the SO2-concns. of untreated exhaust gas and desulfurized exhaust gas are detected by detection terminals 2, 4 to calculate an SO2-absorbing amount S. A part of the recirculation slurry of an absorbing tower 3 is guided to an aeration tank 9 and the introducing amount A thereof is detected by a detector 8 while O2-containing gas is blown into the aeration tank 9. The flow amounts and O2-concns. of gases before and after blowing-in are detected by detection terminals 10, 11 to calculate an O2-absorbing amount C. A part of the recirculation slurry is withdrawn out of the system according to mass balance and an outflow amount is detected by a detector 15. When the supply amount of an Mn-compound is adjusted so as to set the value of (200XBXC)/(AXS) to about 5 or less, the control of a desulfurization factor is facilitated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a flue gas desulfurization method, and more specifically to a so-called wet lime/gypsum method for removing 5o2F from combustion flue gas using limestone, slaked lime, dolomite, or other calcium compounds as absorbent raw materials. Devalue method 1-1 (related to good).

In the absorption process of wet lime/gypsum flue gas desulfurization equipment, 5o
Exhaust gas containing 2f and Oa (OH) 2, 0aOO3°caso3H'/2 H20, CaSO4・2 H20
OJ: UZ solubility (7) t' is brought into contact with a slurry containing a calcium compound, and so2. 'l
The SO absorption reaction can be expressed as a general reaction formula: +0a(OH)2→0a803.
%H,O+%H20,-,・(11so2+aaco3
+y2H20-+ caso3-'72H20+0O2
-(21), and the following oxidation reaction also occurs due to Oct'll accumulation in the exhaust gas.

0aSO3,'AH20+%0. +%H20→0aS
O4-2H20 (31) Although the overall reaction formula is simple, the actual reaction mechanism is not as simple as it seems, and involves various dissolved ions such as Oa2+, λ4f2-',
so: , Na”.

so, , H80i, Co3. HCOi, H2
BO3, H2CO,, Ot-, F-.

At", IIX', 820 knee, H+, OH-
There are various chemical factors that affect the desulfurization performance in the absorption process.This fact is still being confirmed based on various studies. It is clear that a variety of desulfurization methods are being developed. The influence of trace components on desulfurization performance is often not understood.Among the trace 1% components, one that is relatively well known is IF: SO2 in combustion exhaust gas.
In addition, there are NO, ammonia compounds, halogen compounds, dust, etc. Oa (OH) 2 and caco 3 used as absorbents for S02 are prepared from naturally occurring limestone and dolomite, so aluminum compounds, Contains impurities such as silicon compounds, iron compounds, and manganese compounds. Furthermore, it is no secret that the make-up water, which is essential in the wet method, also contains impurities.

In the process of conducting detailed research into the effects of these various components on desulfurization performance, the present inventors discovered that manganese compounds have a specific effect on desulfurization performance, and in completing the present invention. The present invention is a method for desulfurization treatment by bringing the exhaust gas into contact with a slurry containing 802% total calcium compounds, in which a part of the slurry is introduced into an aeration tank, and oxygen is introduced into the slurry in the aeration tank. This oxygen absorption 1. This flue gas desulfurization method is characterized by supplying a manganese compound to the slurry that is brought into contact with the exhaust gas and adjusting the desulfurization lid by detecting this.

Figure 1 shows that the desulfurization rate when desulfurization treatment is carried out by contacting a gas containing 200 ppm of 5o2j with a slurry containing calcium compounds depends on the manganese compound concentration (Mn) in the slurry.
The changes depending on mf/l) are all illustrated based on the results found by the present inventors.

As is clear from FIG. 1, when the manganese concentration increases, the desulfurization rate decreases and then increases in a specific manner. Therefore, when adjusting the desulfurization rate to sl' by changing the manganese concentration, It has been found that it is necessary to perform the exact opposite operation of increasing or decreasing the manganese 0 degrees at point (1) or point (11) in FIG.

The manganese concentration is in a very small concentration range of 1 mW/1 to 1000 mV/l, which is much lower than the calcium compound concentration in the slurry, which is about 10 to 20 wt%. Since instantaneous measurement is not possible, a means of predicting the manganese concentration is required in order to operate a wet flue gas desulfurization equipment. This is due to the fact that the concentration of manganese is predicted by the correlation line 0) in Figure 2. A part of the slurry being served is introduced into an aeration tank, a gas containing oxygen is blown into the slurry in the aeration tank, and the amount of oxygen absorbed in the aeration tank is detected using an oxygen gas meter and a gas flow meter. It was discovered that the amount of oxygen absorbed has a simple correlation with the manganese concentration in the slurry. Therefore, once the calibration curve of the correlation line (B) in Figure 2 is created, all that is left is to adjust the aeration tank. Manganese concentration can be predicted by the amount of oxygen absorbed at

The amount of oxygen absorbed can be easily and continuously detected by using a commercially available oxygen gas meter and gas flow meter and calculating the difference in the amount of oxygen between the inlet gas and the outlet gas of the aeration tank.

It is explained based on the chemical reaction equation (3) above that the amount of oxygen absorbed in the aeration cell is related to the sulfite concentration in the slurry, but as the manganese concentration in the slurry increases When SO2 is absorbed into the slurry in the absorption process, the oxidation reaction of equation (3) by oxygen in the exhaust gas is also promoted, and the sulfite concentration in the slurry decreases. It is thought that the amount of absorption will decrease.

Manganese compounds have long been well known as catalysts that promote oxidation reactions, and it is also described in known literature that manganese compounds are fully supplied to the absorption process in the wet vapor dehydration method to fully promote gypsum production through oxidation. However, it is completely unknown that there is a phenomenon characteristic to the desulfurization rate as shown in Figure 1.

The present invention utilizes the method of adjusting the manganese concentration to adjust the desulfurization rate based on the phenomenon shown in FIG. 1, and the prediction of the manganese concentration in the slurry as shown in FIG. This method is characterized in that it is carried out by detecting oxygen absorption 1j in the tank.

When the correlation line between oxygen absorption and manganese concentration shown in Figure 2 (B1) is combined with the correlation line between desulfurization rate and manganese concentration in Figure 1, the result in the aeration tank is as shown in Figure 2 (A). A correlation line between oxygen absorption-IT and 802 (JU degree) in the exhaust gas at the exit of the absorption process can be obtained. It can be seen that the highest desulfurization rate can be obtained with a lower SO concentration. Therefore, it is possible to know the desulfurization performance in the absorption process just by detecting the oxygen absorption level in the aeration tank. , the amount of oxygen absorbed can be adjusted by adjusting the manganese concentration in the slurry based on the correlation shown in Figure 2 (B). It was found that by adjusting the manganese concentration so that the number of moles is about 5 moles or less, it is possible to operate on the left side of the peak in Figure 2 (A). Gas absorption amount is approximately 5 (mol/h
) is 0, which corresponds to approximately 5 moles of SO in the absorption process and the absorption amount.In other words, in order to fully adjust the desulfurization rate in the absorption process, it is necessary to introduce slurry from the absorption process to the aeration tank in a steady state. A (t/b) in the aeration tank, the amount of oxygen gas absorbed in the aeration tank 't C (mol/h), and the 802 absorption in the absorption process fj3', f: S in the steady state. (m
o]/h), and the slurry flow rate tJJ extracted from the system from the absorption process is B (t/h l) in a steady state. We experimentally discovered that the first
Operation is possible only on the side (II) in the figure, and it is possible to prevent the operation from entering the side (1).

An embodiment of the present invention including the above-mentioned stoichiometric relationship shown in FIG. 5 will be described below by way of an example.

Example 1 In Fig. 5, the exhaust gas 1 of about 2000 m3N/kl containing about 1600 ppm SO2 is
2 It enters the absorption tower 5 through a duct having a detection end 2 for detecting the degree of absorption, and after being brought into contact with a slurry containing a calcium compound and subjected to desulfurization treatment, it passes through a duct having an SO□ concentration detection end 4 to the absorption tower. go out from Detection end 2 and 4
The SO2 absorption 'hLB (mol/h) can be determined in the SO2 absorption amount detector 5 having a function of calculating the signal. In the absorption tower 5, a slurry containing a calcium compound that can be used as an 802 absorbent such as aaco3 or ca (OH) 2 in an amount of y is supplied to the Hso2 absorber from a line 6, and a large amount of the slurry is passed through the absorption tower circulation pump 7. It's circulating. A portion of this absorption tower circulation slurry is led to an aeration tank 9 via a flow rate detector 8 . In the ventilation 'm9, gas containing oxygen gas is blown into the slurry in the tank through the entire line 11 having a detection end 10 for detecting the gas flow rate and 020 degrees, and the remaining gas is used to detect the gas flow rate and 02 concentration. It is discharged through a line 15 having all the detection ends 12 for detection. Oxygen gas absorption i 0 (
mol/h) f can be determined0Also, since absorbent is supplied from line 6 in proportion to the amount of S02 absorbed,
According to the mass balance, a part of the circulating slurry in the absorption tower is extracted from the absorption tower while the flow rate detector 15 detects the entire stream-1Ii. (1/h), the above-mentioned p value of B (mol/h), C (mo], /b) is multiplied by (200XBXC)/(AXSJ O
The value is found.

In the example, manganese 6ir acid is supplied from line 16,
Figure 1 shows the desorption (jf ratio) under steady state pressure when operating with various manganese concentrations in the circulating slurry of the absorption tower.
A correlation diagram with the amount of oxygen gas absorbed in the aeration tank (0 (mol/h)) is shown in FIG.

When the lowest desulfurization rate in Figure 1 is set to 1, the manganese concentration is approximately 40 mV/l, and
It corresponds to the case where becomes the highest, and (200XBXO)/(
AXS) is about 5 (about 5 mol%) and 7 (. Therefore, (
The desulfurization rate improves even if the value of 200
It is preferable to carry out the absorption operation in the region below FiS, that is, in the region where the desulfurization rate improves as C decreases, since it is easier to adjust the supply amount of the manganese compound and has the advantage of making it easier to control the desulfurization rate. That is, when adjusting the Mn concentration, in the area to the right of the peak in Figure 2 (A) where the scale is thin, as is clear from Figure 2 (A1. This causes large changes in the gas absorption amount and the 5O2a degree in the exhaust gas at the outlet of the absorption process, making operation difficult.On the other hand, in the region to the left of the peak in Figure 2 (A), the Mn 6 degree adjustment is relatively rough and continuous. For example, 5 Ina degree 10 mW/
The change in the concentration of l (i.e., the error in addition adjustment is t o tn?
/ This is true if there is. ), peak right 1t!
It can be seen that at L, the outlet SO2 fluctuates by about 1100 pp, but on the left side of the peak, the outlet SO2 does not fluctuate by about 20 ppm L. Therefore, when controlling ``81'', it is easier to operate if it can be treated as ``ft''.

Embodiment 2 FIG. 4 shows the case where a gas containing oxygen gas is blown into the absorption tower circulation slurry through the line 11. If the oxygen gas concentration contained in the slurry is detected 711 by the detection end 12 at 020 degrees, the absorption tower circulation The slurry pipe could be used as a substitute for the aeration tank. Even in the second embodiment in which the aeration tank as shown in FIG. 5 was not provided, the effects of the present invention could be achieved in exactly the same way as in the first embodiment.

Furthermore, as can be inferred from Fig. 4, the amount of absorbed oxygen gas can be detected in any part of the circulating slurry of the absorption tower, such as the slurry inside the absorption tower or the slurry in the lower tank of the absorption tower. It goes without saying that it is not limited to Figure 40

[Brief explanation of the drawing]

Figure 1 is a diagram showing a specific phase diagram of desulfurization rate and manganese concentration in slurry, which is the basis for proposing the present invention, and Figure 2 is the amount of oxygen gas absorbed in the aeration cell used in the method of the present invention. Figures 5 and 4 are diagrams showing one embodiment of the present invention. Agent Ryo Hagiwara - 8C Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] In a method of desulfurizing exhaust gas containing 5o24 by contacting it with an absorption tower circulating slurry containing calcium compounds in an absorption tower, a gas containing oxygen gas is blown into the slurry, and the oxygen gas in the gas is introduced into the slurry. A flue gas desulfurization method characterized in that the supply fk of the manganese compound into the slurry that is brought into contact with the exhaust gas is controlled by detecting the absorption fif, and the desulfurization 1° is adjusted.