JPS6245691A - Method of modifying combustion dust of low quality fuel derived from petroleum - Google Patents

Abstract

PURPOSE:To suppress the deposition of slag on a heat transfer tube of a boiler or the like through enhancement of collection efficiency of an electric precipitator and reduction of unburned carbon. CONSTITUTION:In the furnace of a boiler or the like which uses a low-quality fuel derived from petroleum (e.g., oil coke or asphalt), at least one of iron and iron compds. having an average particle diameter of 30mu or less is fed in amt. of 10-1,000ppm (in terms of Fe2O3) into the furnace. This enhances the collection efficiency of an electric precipitator, reduces unburned carbon and suppresses the deposition of slag. Examples of the iron or iron compd. include pulverized metallic iron, iron oxides such as FeO and Fe2O3, inorg. iron compds. such as iron sulfate and iron chloride, and iron salts of org. acids such as iron octylate.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for reforming combustion dust in a furnace such as a boiler that uses petroleum-based low-quality fuel, and in particular to improving the dust collection efficiency of an electrostatic precipitator and reducing the amount of unburned carbon. The present invention relates to a method for reducing slag and at the same time suppressing the adhesion of slag to heat exchanger tubes such as boilers.

Conventional technology Since the oil crisis, fuel costs, which account for a large portion of energy costs, have received a lot of attention as the price of heavy oil has skyrocketed, and oil coke and asphalt have come into the spotlight, making them the world's top 7. (Compared to 4 oils, it is cheaper and has a higher calorific value, and can be used by simply modifying existing equipment, so it is expected to grow significantly in the future.

However, even though they are petroleum-based, oil coke and asphalt have slightly different properties. First, considering oil coke, (1) it contains a lot of fixed carbon and has little volatile content, so when it is burnt in a burner, the speed of the stone fire is slow, stable combustion cannot be achieved, and there is a lot of unburned carbon.

In order to improve these combustibility, (increase v 02.■ Oil coke is further crushed and finely divided,
Increase the contact surface 8t with the ■ Atmosphere temperature) -
Shoulder. ■ Improvements to the burner can be considered. (2) leads to a decrease in boiler efficiency and an increase in NOx%S03. ■
However, the capacity of the pulverizer (200 mesh 95φ or more) is limited, and further pulverization requires a large amount of equipment cost.

Regarding ■, if the ambient temperature is increased, NOx
, which leads to an increase in SOx, melting of the boiler slag, and corrosion of the tubes.Instead, efforts are being made to lower the temperature. Although various efforts have been made regarding ■,
This alone cannot improve flammability. In any case, the current situation is that a sufficient solution has not yet been found.

Next, (2) the ash content is about 10 times higher than that of heavy oil, and although the melting point of the ash is relatively high, the ash melts and adheres excessively to the tube. This slag is a sticky slag that cannot be removed with a soot blower, and it will continue to adhere to the screen tube, etc., and eventually the draft inside the furnace will increase rapidly, making operation impossible. In addition, as the amount of adhesion increases, heat absorption inside the furnace deteriorates, leading to an increase in exhaust gas temperature and NOx1S.
Problems such as an increase in OX occur.

Conventionally, there is no good way to deal with these problems, so countermeasures have been taken such as reducing the amount of oil coke relative to heavy oil and operating the boiler at a lower load, but all of these measures have a negative economic impact. The elements were huge.

Next, as for (3) and 7, when the amount of soot and dust increases in relation to (1), it becomes difficult to treat with a dust collector (hereinafter referred to as EF), and the EP processing capacity must be increased to achieve the best rate. In some cases, the value is lower than the standard value of 10 to 10'ΩC1n, and in such cases, the dust collection efficiency decreases. ffi oil-fired boilers (1 to 3 μ) and coal-fired boilers, which have a single-digit fire rate of 4Σ＼ compared to heavy oil-fired boilers. Therefore, oil coke has a lower dust collection performance because its electrical resistivity and particle size change depending on the fuel and combustion conditions. 2 is greatly influenced by them.

Furthermore, asphalt has a high content of vanadium, sulfur, residual carbon, and ash, so high and low temperature corrosion becomes a major problem as well as combustibility and staining of heat transfer surfaces. However, all fuels have the same deterioration in combustibility and dirt on the heat transfer surface.

Despite being a cheap fuel as mentioned above, the current situation is that it is being hindered from being fully utilized due to these major problems.

Conventional combustion improvers include barium, manganese, cerium, copper,
Cobalt and other materials were used, but these were expensive, turned white after combustion, impeded heat absorption in the furnace, and were problematic in terms of pollution. Although this method has been implemented for heavy oil, it has not been realized for oil coke or asphalt due to oil temperature and cost issues.

A widely used method is to inject NH3 into the EP inlet to prevent corrosion in the flue. NH3 gas reacts with SO3 to form Nf(4)2So4. EP Ko's ash also (NH4)
2so, the specific resistance increases due to the mixing of (10Ω1
From 10 Ω foil 1 ;) @L but these ammonia ■
It is treated as a deleterious property and is inconvenient to handle. There are problems such as: ■ It is difficult to control the molar ratio of NH3/sO due to acidic ammonium sulfate, etc., and ■ It is not economical, so there is a tendency to reduce its use. Currently, Mg and the like are used together with their anti-corrosion effects, but they have the drawback of whitening the inside of the furnace and poor heat absorption.

As a result of intensive research into means for solving the above-mentioned problems, the present inventors have found that in furnaces such as boilers that use low-quality petroleum fuel, a trace amount of fine particles of iron or iron compounds relative to the fuel can be used. Developed a combustion dust reforming method that improves the dust collection efficiency of the electrostatic precipitator, reduces unburned carbon, and improves the scattering of slag on the heat exchanger tubes in the furnace, thereby suppressing slab adhesion. did.

In the present invention, petroleum-based low-quality fuels include oil coke, asphalt, etc., and furnaces such as boilers, heating furnaces, and kilns that use these fuels are classified as F' e 203, F
Iron oxides such as 'e304 (FeO1Fe20g); inorganic iron compounds such as iron sulfate, iron chloride, iron nitrate; and organic iron compounds such as iron octylate, iron naphthenate, iron stearate, iron acetate, iron formate, iron methacrylate, etc. Contains iron acid salts. In other words, any iron compound that becomes F'e 203 after combustion in the furnace can be used. The amount of iron or iron compound used is appropriately selected in the range of 10 to 10009 F (in terms of Fe203) based on the fuel type and combustion conditions. 10pp
lI) You cannot expect much effect with a small amount, 100 Op.
If the amount of PL is large, the amount of metal in one furnace tends to increase, and at the same time, it is economically disadvantageous. If the particle size of iron or iron compounds is larger than the particle size of dust, its effectiveness will decrease.

It needs to be smaller than the dust particle size. Therefore, in the case of oil coke, the dust particle size is about 15 to 30μ, so the particle size of the iron or iron compound used is 3.
It must be less than 0μ.

The smaller the grain size, the larger the total area, and therefore the greater the effect. The same can be said about asphalt.

Considering the reason why syslag adhesion is suppressed by the present invention, low-purchase fuel dust such as oil coke is 5102
Despite the presence of a large amount of high melting point substances such as , Al2O3, etc., the slag melts and enlarges. However, if Fe 203 is present, V205 reacts in the slag, producing Pe 203 ・V2O5 (860°C), F'e
It is thought that the adhesion of the dust, which is easily scattered, is suppressed by the dust blower installed in the furnace for forming high melting point compounds such as 203.2v20s (855°C). The reason why the collection efficiency of the electrostatic precipitator is improved is that the coexistence of Fe2O3 modifies the specific electrical resistance value of EP ash to 10 to 109 m2. The theoretical reason for this is not clear, but it is thought that Fe2O3, which originally has a high electrical resistance, mixes into the dust shell, increasing the overall resistance of the dust and changing the value to the appropriate value for collection by the dust collector. It will be done. Furthermore, although the theoretical reason for the reduction in unburned carbon is not clear, these effects have been experimentally confirmed.

Next, the present invention will be explained with reference to an illustrated embodiment. Figure 4 shows an example of a boiler that uses oil coke as fuel. A total of 1 oil coke as fuel is collected in hopper 1 and crushed in mill 2 after death.

It is transported by air through line 3 and burned in burner 11 and boiler 10. On the other hand, the iron or iron compound additive from the auxiliary additive tank 4 is passed through the metering pump 5 through the cylinder line 8 and mixed with C heavy oil in the line 9. The mixed fuel and additives are ignited by the burner 12, and burnt in the boiler lo together with the oil coke ignited by the burner 11 to become exhaust gas.

The dust (unburned carbon with a sufficient ash content) generated in the boiler passes through a 15-ton air heater and is collected by an EP 13. Further, the dust adhering to the heat transfer surface is also blown away by the street blower 16, and the dust that cannot be collected, which flies downstream, is discharged into the atmosphere through the chimney 14. In the case of asphalt, the equipment described in 1, 2.3.11 above is not used, and the asphalt is stored in the heavy oil tank 6 and guided to the injection pump via a heater (not shown), and the subsequent steps are the same as above. It's the same.

Figure 2 shows the changes in furnace draft and evaporator endotherm before and after addition of iron octylate (70-/oil coke standard, as Fe2O3).As can be seen from this figure, without iron addition, after 20 days, Furnace drafts are rapidly increasing. Also, the heat absorption of the evaporator is significantly reduced due to excessive dust deposition. On the other hand, after the addition of Tetsurishi-Yuan=Hitoi, the value of 0-7 remains almost constant even after about 50 days, and is almost unchanged from the initial value. Heat absorption also remains flat at 70°C. In other words, it can be said that almost no slag is attached. Observing the slag adhesion value in each furnace, the latter was found to have a value of N/3 or less compared to the former.

Table 1 below compares the properties of heavy oil C, asphalt, and oil coke. It can be seen that compared to Q4 oil, oil coke has a very high ash content.

Table 2 following Table 1 shows the addition of iron octylate to oil coke (
'yopps,' oil coke standard, Fe2O2) shows the change in soot and dust concentration before and after and the change in dust collection efficiency.

Before addition, when the evaporation amount and 02 were under the same conditions, and the ftk of oil coke was changed, the soot and dust a degree was 10.8.
j! / Nm" to 3.5 g/N-, and the dust collection efficiency also increased from 81.5% to 9413%.

Add iron under the same conditions as before addition. oil coke 5.7
Comparing with T/H, the EP population dust amount is 10.8
Ji'/Nm3 to 4.6. ? /Nm3 and oil coke 2-3T/H, the dust collection efficiency decreased from 3.57i/Nm to 3.4g/Nm", and the dust collection efficiency was 81.5, respectively.
% increased from 98.1% and 94.3% to 98.8%. The reason for this increase in dust collection efficiency can be easily understood by examining the specific resistance (11t) of the collected EP ash.

Table 2 * Izushi% E PM% 150 mA The following Table 3 shows soot and dust9 before and after addition of iron octylate to asphalt (50pp/asphalt standard, as Fe 203)
It shows the change in temperature and dust collection efficiency.

In Table 3, Figure 3, ``■'' indicates when conducting, and ``■'' indicates when oil coke and heavy oil are co-fired (4:1), which is 103 to 104 Ωcm. Although it is one digit higher than heavy oil-only combustion, it is lower than the EP's appropriate collection value of 105 to 106 Ω, and when iron octylate is added, it increases to 105 to 106 Ω as in line 3.
This has increased the dust collection efficiency. The particle size was also found to be 60% smaller than the 15-30μ before addition. Line 4 is a reference example, and the resistance value in the case of only iron oxide is as high as 1010 to 1011Ω.

The following Table 4 shows the addition of iron octylate to oil coke (70
P1ml/oil coke standard, as Fe2O3)
and addition of iron octylate to asphalt (50 [) 1111
/ Asphalt standard, as F'e203) EP before and after
Each shows changes in ash properties. Before and after adding iron, the iron content increased from 2-1% to 6.5% and from 0.5% to 1.6%, and the unburned carbon increased from 88.0% to 58.0%, and 42%. This has decreased significantly from 8% to 32.2%.

Table 4 In the above example, iron octylate, which is an oil-soluble organic acid iron salt, was used, but metallic iron, Fed, F'eQOH, P'e2
Iron oxides such as 03F'e304 (FeO-Fe203), inorganic iron compounds such as iron sulfate, iron chloride, iron nitrate, and organic acids such as iron naphthenate, iron stearate, iron acetate, formic acid method, iron methacrylate, etc. Regarding iron salts, after combustion, Fe20
3, and therefore, similar results can be obtained if the usage conditions of the present invention are satisfied.

[Brief explanation of drawings]

Figure 1 is a 70-sheet for explaining one embodiment of the present invention, and Figure 2 is a 70-sheet for oil coke.
P (as Fe203) Furnace Dou 7 before and after iron boxing
Figure 3 shows the changes in heat absorption and evaporator heat absorption for various EP ash (
For reference, in the case of only iron oxide without EP ash = 4), the exhaust gas temperature of EP A and the specific electrical resistance value of EP ash (Ω
-(1)). 1 Ni oil coke hopper, 2: Mill, 3.8.9 Ni line, 4: Additive tank, 5: Metering pump, 6: Heavy oil tank, 7: Injection pump, 10: Boiler, 11.12
: Burner, 13: Electrostatic precipitator (EP), 14: Chimney,
15: Air heater, 16: Soot prower. (4 other people) Figure 1

Claims (1)

[Claims] In a furnace such as a boiler that uses petroleum-based low-quality fuel, at least one type of iron or iron compound having an average particle size of 30 μ or less is added to the furnace in an amount equivalent to 10 to 1000 ppm (in terms of Fe_2O_3) based on the fuel. A fuel dust reforming method that improves the dust collection efficiency of an electrostatic precipitator, reduces unburned carbon, and suppresses slag adhesion.