JPH03151024A - Method for preventing trouble due to sulfuric acid in waste combustion gas - Google Patents

Abstract

PURPOSE:To remarkably reduce flocculation, to enhance scattering into the waste fossil fuel combustion gas and to compeletly preventing trouble due to sulfuric acid in the waste gas by coating the surfaces of the grains of MgO and CaO with a specified liq. organosilicic compd. CONSTITUTION:A liq. organosilicic compd. (its amt. controlled to 0.2-2.0wt.% based on MgO or a mixture of MgO and CaO) such as dimethylhydropolysiloxane and methylmethoxypolysiloxane is brought into contact with the grains of MgO and CaO (the content controlled to <=30wt.%) and chemically adsorbed on the surfaces of the grains. Consequently, the grains are coated with the monomolecular layer of the organosilicic compd. When the coated grains are scattered in the waste fossil fuel combustion gas, the flocculation of the grains is remarkably reduced, the fluidity is increased, the movement as the single grain is facilitated, and the scattering property is remarkably enhanced. As a result, trouble due to the sulfuric acid in the waste gas is completely prevented.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention provides a method for applying finely powdered MgO or a mixture of MgO and CaO, which has particularly increased fluidity and scattering properties, to the combustion exhaust of sulfur-containing fossil fuels such as boilers. This invention relates to a method for preventing damage caused by sulfuric acid in flue gas by adding it into smoke and scattering it.

[Conventional technology]

Hazards caused by sulfuric acid in flue gas include falling of acidic soot from chimneys, corrosion of flues, and functional deterioration of electrostatic precipitators and air heaters due to adhesion of acidic soot.

It is known that the basic cause of these problems is that soot particles adsorb sulfuric acid and become sticky.

[Problem to be solved by the invention]

In particular, acidic soot is also called acid smut or snow fume, and soot that has adsorbed sulfuric acid adheres to the inner wall of the chimney, grows and separates, and falls in the form of snowflakes. Since this is a strong acid, if it falls on it, it will harm all substances, so effective prevention methods are an urgent issue.

Conventionally, as methods for preventing these sulfuric acid injuries, (1) M
Attempts have been made to add fine particles of g(oH)s into the fuel as an oil slurry, and to add powdered MgO or CaO into the flue.

However, in method (1), approximately 50% of the added MgO
% by weight remains in the furnace, resulting in poor efficiency.If the amount added is increased, the adhesion of MgO will impede the heat conduction of the heat transfer part in the furnace, so the minimum amount added is necessary to protect the heat transfer part in the furnace. are forced to stay. (The addition of powder in step 2 is Mg.
Both O and CaO have strong aggregation properties, and when they are supplied quantitatively from the bottom of the storage tank using a screw feeder or the like, the supply often idles due to the so-called bridging phenomenon, making continuous addition difficult.

In addition, even if bridging prevention measures are taken and it is added for a certain period of time, since it is a cohesive powder, the flying percentage in the form of single particles is incomplete, and for this reason, it only partially neutralizes sulfuric acid, and the effect is poor, so it is not widely used. is the current situation.

[Means to solve the problem]

The present invention uses a specific liquid organosilicon compound to
By mixing and agitating the particle surface of O and caO with a ball mill or ribbon blender, etc., and coating the particle surface, the agglomeration property is significantly reduced, and the dispersion into fossil fuel flue gas is dramatically increased. This is due to the discovery that sulfuric acid damage can be completely prevented.

The composition constituting the present invention includes a liquid organosilicon compound,
It consists of MgO or a mixture of MgO and CaO, and as the organosilicon compound, dimethylhydrogen polysiloxane (hereinafter referred to as p-x) and methylmethoxypolysiloxane (hereinafter referred to as p-2) are most suitable. These organosilicon compounds are chemisorbed onto the particle surfaces by contact with LigO and CaO particles, and these particles are footed by a monomolecular layer of the organosilicon compound. f MgO and CaO particles coated with a mechanical compound have significantly reduced cohesiveness between particles, increasing fluidity and making it easier to act as a single particle, resulting in a dramatic increase in scatterability. It was confirmed that

The amount of the organosilicon compound used in the present invention is Mg
0.2% by weight for O or a mixture of MgO and CaO
It is effective from 2.0% to 2.0%. A particularly suitable range is 0.8
% to 1.5%. If it is less than 0.2%, there will be almost no practical effect, which is not preferable.

Moreover, if it exceeds 2%, the organosilicon compound will be present as an unadsorbed liquid, which will rather reduce fluidity and dispersibility, which is not preferable.

MgO, that is, magnesium oxide, which is the main component used in the present invention, is also known as magnesha, and the components of commercially available industrial products vary, with products obtained from seawater and bittern (A) and products obtained from magnesite ore (B). There is a large difference in MgO purity, but Mgo + (1!ao = 65
% or more, there is no problem in using other contained inorganic substances in the present invention. Especially if 3102 is in a fine particle state,
It is effective in preventing caking of the composition, and its content up to about 15% by weight is permissible. Table 1 shows the main components of commercially available magnesha.

Table 1 MgO0ILO5ift FeIOSJido% Weight% Weight% Weight% (A) 9 4.5 0.9 1.2
0.0 5(B) 8 5.2 1.8
4.1 0.6 Calcium oxide, also known as CaOIIJ, is cheap and commercially available in large quantities as quicklime, and industrial products usually contain 95% by weight or more, and the average particle size is 40%.
The thickness is approximately 50 μm, which is a suitable range for the constituent composition of the present invention.

When using a mixture of MgO and CaO, the content of CaO is preferably 30% by weight or less based on the total of MgO and CaO, and a preferable range is 10% by weight or less.

In general, the reaction rate for neutralizing sulfuric acid is faster with CaO than with MgO, but hard crystals of 0aSO+, which are insoluble in water, adhere to the surrounding area and are difficult to remove by washing during periodic repairs. is limited. On the other hand, the reaction rate of MgO to neutralize sulfuric acid is inferior to that of CaO, but after neutralization MgO
Since 5O< is water-soluble, it has the advantage of being easily removed by washing with water.

Therefore, the content of CaO is preferably set to 30% by weight or less of Oao in consideration of the possibility of removing it by washing with water later.

〔Example〕

The present invention will be explained below with reference to Examples.

Example 1 Powder 100 consisting of magnesium oxide with an average particle size of 3.5 μm and calcium oxide with an average particle size of 45 μm in the proportions shown in Table 1 was prepared. After adding P-1 and/or P-2 in the proportions shown in Table 1, the P-1 and/or P-2 were stirred in a ball mill for 5 minutes to obtain P-1.
1 and/or p-2 treated powders were obtained. The obtained treated powdery material 501i' was fixed to a vibrator and put into a V-shaped glass funnel which was being vibrated under certain conditions, and the flow time was measured. The size of the glass funnel was as follows. Angle 60 degrees V
Table 2 shows the measurement results of the flow time for the shape, inner diameter of the foot of 11 m, and length of 110 m.

The percentages in the table are by weight.

Table 2 MgOCaO Other components P-I P-2 Flow time %%%%% seconds 95 2 3-- 15095 2
3 0.2 3095
2 3 0.5 59
5 2 3 1.0
295 2 3 1.5 -
295 2 3 2.0 -
395 2 3
0.5 595 2 3
1.0 295 2 3
1.5 295 2 3
0.5 0.5 195 2
3 07 0.7 180
15 5 0.5 0.5
165 30 5 0.5 0.5
160 35 5 0.5
0.5 1 As is clear from the results in Table 2,
The flow time of the powdered material treated with an appropriate amount of p-1 and/or P-2 is only 1 second, whereas the flow time of the untreated material is 150 seconds. In particular, it was confirmed that the combined use of P-1 and/or P-2 was more effective than treatment with either alone.

Furthermore, when the amount of P-1 and/or p-2 added is 2% by weight or more, the flow time tends to increase, and the practically preferred range is 0.2% to 2.0% by weight. It is. A particularly effective addition amount was 0.8% to 1.5% by weight.

This dramatic change in flow time is caused by P-1 and/or P
It is presumed that this is because the particles coated with -2 lost their cohesiveness and the single particles became able to move freely, and the scatterability into the gas also increased dramatically.

Example 2 The thoroughly mixed and stirred composition shown in Table 3 [however, no organosilicon compound was added to (C) and P-1 was added to (D)] was poured into a flue during boiler operation. was added to the water and its scattering property was measured. The area of the flue is: 2.5 rrLX 1.9
m N length: 26 WL N gas amount: 1.5 million rr
t/1 hour, inlet temperature: 160°C.

The amount of the composition added was 10% by weight of the soot amount, and the method of adding the composition was to continuously add a fixed amount of the composition, and immediately after dropping, the composition was forcibly dispersed with pressurized air.

Add it from the top near the flue entrance in this way, and add it for 20 minutes.
Soot was collected from the center of the flue downstream m by isometric suction, and the amount of MgO in the medium was measured. The results are shown in Table 3. The percentages in the table are by weight.

Table 3 Mg0 0aO Other components % in P-1 collection medium
% % % Mg0%(c) 96
1.5 2.5 1.2(D)
96 1.5 2.5 1.6
9.1 From the results in Table 3, there is clearly a large difference in the percentage of MgO in the abstraction medium, and untreated composition (C) does not reach the collection point due to poor scattering properties and most of the It is assumed that the water settled during the process. In such a case, there is little possibility that the additive composition will reach the inside of the chimney by scattering, and prevention of acidic media generated on the inner wall of the chimney cannot be expected at all.

In contrast, in composition (D), most of the particles reached the collection point, and it was confirmed that the scattering property was dramatically increased.

Example 3 The composition (D) in Table 3 was added to the boiler flue (same as in Example 2) during combustion operation of 0 heavy oil (S = 1.2 to 1.4%) in the same manner as in Example 2. 6% by weight of the soot amount was continuously added and the effect of preventing acidic medium drop was measured. 107F from Tsubotsu! Wooden boards measuring 1 m x 1 m were placed at four separate locations on the ground, north, south, east, and west, and the total number of acidic soot that fell at the four locations within 24 hours was measured.

The results are shown in Table 4.

Table 4 Number of days elapsed after addition Total number of descending acid groups 0
26 3 21 10 5 20 2 30 1 As seen in the results in Table 4, the acidic medium drop almost disappeared 30 days after the addition, and a remarkable preventive drop was confirmed.

Example 4 In the same manner as in Example 2, the compositions shown in Table 5 were added to the inlet of the electrostatic precipitator of the same boiler in operation to test for increasing the efficiency of the precipitator. The percentages in the table are by weight. The amount of the composition added was 5% by weight of the measured soot amount.

MgOCaOP-I P-2 % % % % (E) 6
6 2B 0.7 0.7ff)
60 35 0.7 0.7 As a result of continuous addition for about 6 months, the collection performance of the V collector increased and the composition (
E) and (F) In both cases, an average efficiency increase of 5% was confirmed. Sulfuric acid adsorbed on soot particles causes MgO, C
It is neutralized by aO, the adhesion force decreases, and II! This is presumed to be the result of accelerated departure from the poles.

In the case of composition (10), hard deposits of 0aSC+4 were deposited around the electrode fixing part, and it was difficult to remove the fine details by washing with water.Composition (10) also had this tendency. However, it was judged that there was no practical problem.

The test results revealed that a CaO content of up to 30% by weight in the composition is practically safe.

Example 5 In the same manner as in Example 2, 4% by weight of the measured soot amount as shown in Table 3 (D
) was added and tested for approximately 6 months. As a result, an increase in efficiency of about 3% was observed. According to the observation at the time of stopping, the amount of soot attached was significantly reduced compared to when no additive was added, and it was easy to remove by washing with water.

〔Effect of the invention〕

As is clear from the data of each example described above, MgO
Alternatively, the acidic soot removal efficiency can be improved by adding an organosilicon compound to the mixture of MgO and CaO.

Claims (4)

[Claims] (1) Finely powdered MgO or a mixture of MgO and CaO, in which a small amount of a liquid organosilicon compound is added and stirred to increase fluidity and dispersion, is added to and dispersed in the flue gas from fossil fuel combustion. How to prevent damage caused by sulfuric acid inside. (2) Claim 1 wherein the organosilicon compound is dimethylhydrogen polysiloxane and/or methylmethoxypolysiloxane.
Method described. (3) The amount of organic silicon compound added is Mg
The method according to claim 1, wherein the amount is 0.2% by weight or more and 2.0% by weight or less based on the total amount of O or MgO and CaO. (4) The method according to claim 1, wherein in the mixture of MgO and CaO, CaO accounts for 30% by weight or less.