JPH0459892A - Combustion improver for solid fuel - Google Patents

Abstract

PURPOSE:To provide a combustion improver for solid fuel such as coal and petroleum coke, composed of hydrated ferric oxide particles having the shape of bamboo grass leaf with ultrafine stripe structure and effective in suppressing the generation of unburnt material and improving the dust collection efficiency. CONSTITUTION:The objective combustion improver is composed of hydrated ferric oxide particles having an ultrafine stripe structure and exhibiting the shape of bamboo grass leaf having a major diameter of 0.2-1.0mum and an aspect ratio (major diameter/minor diameter) of 3-10. The particle can be produced by mixing an aqueous solution of a ferrous salt with >=1 equivalent (based on the ferrous salt) of an alkali metal carbonate to obtain FeCO3 and oxidizing the FeCO3 by introducing an oxygen-containing gas into the aqueous solution containing FeCO3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a combustion improver for use in solid fuels such as coal and petroleum coke.

[Conventional technology]

In recent years, solid fuels such as coal and petroleum coke have come into widespread use as alternative fuels to petroleum. But coal,
Petroleum coke has less volatile content than liquid fuels such as heavy oil, so it has poor combustibility, so it is used in finely ground form as boiler fuel. Even so, the unburned content reaches several to ten-odd percent, so in petroleum coke boilers with particularly low volatile content, methods of co-firing heavy oil or gas are used, but this is cumbersome to operate, and The situation is economically unsatisfactory because high-value fuel is used.

One of the ways to reduce the amount of fuel oil and gas used for combustion support is to apply combustion improvers, and it is well known that they are effective in suppressing unburned substances. Cu, Co, and Ni have long been used as combustion improvers.

There are heavy metals such as Mn and Pe, alkali metal compounds such as Na, and alkaline earth metal compounds such as Ca and Ba, but these days they are particularly inexpensive and have little effect on the activity of the denitrification catalyst. Since then, iron-based combustion improvers have attracted attention and are now commercially available.

There are two types of iron-based combustion improvers: oil-soluble and water-soluble.

Typical oil-soluble substances include iron naphthenate and iron octylate, which are used by mixing them with liquid fuels such as heavy oil. On the other hand, water-soluble ones are used by impregnating solid fuels such as coal and coke.

[Problem to be solved by the invention]

When using combustion aids such as coal and coke, when co-firing heavy oil, the method is to add an oil-soluble combustion aid to the heavy oil, but when co-firing gas, it is difficult to add it to the gas. Usually, water-soluble combustion improvers are impregnated and mixed with coal or coke. However, iron-based water-soluble combustion improvers have the following problems, which hinder their practical application.

(1) When iron salts used as raw materials for combustion improvers, such as iron sulfate, iron chloride, iron nitrate, and iron acetate, are made into aqueous solutions, they hydrolyze to pH
Becomes acidic below 3 and corrodes equipment materials.

(2) When neutralized by adding alkali, iron hydroxide precipitates, making it difficult to supply a fixed amount using a pump.

(3) Iron chloride generates corrosive gases such as HCI and C12 when burned, iron nitrate generates NOx, and iron sulfate generates S
Causes O□ generation.

(4) Due to solubility, a large amount of water is required, which increases the tank capacity of the combustion improver.

In addition, iron-based oil-soluble combustion improvers are not only expensive themselves, but also often generate sludge when mixed with heavy oil, which can cause fatal troubles in boiler operation, such as the closure of heavy oil line strainers or heavy oil burners. There are cases where In order to avoid the above-mentioned problems, attempts have been made to inject iron-based combustion improvers in powder form, and the present inventors have previously developed iron oxides and/or iron oxides and alkali metal compounds or alkaline earth metal compounds as combustion improvers. We have discovered and provided a method for using the powder mixture.

(Japanese Unexamined Patent Publication No. 62-190288) The present invention further develops the previously proposed invention, improves iron oxide as a combustion improver, and provides a highly efficient combustion improver.

[Means to solve the problem]

In line with the above objectives, the present inventors conducted various studies in order to obtain a more efficient combustion improver, and as a result, it was found that hydrated ferric oxide particles having a bamboo leaf-like ultrafine structure are extremely excellent as a combustion improver for solid fuels. This discovery led to the completion of the present invention.

That is, the present invention has a striped ultrafine structure, has a major axis diameter of 0.2 to 1.0 μm, and has an axial ratio (major axis diameter/minor axis diameter) of 3 to 1.
This is a combustion improver for solid fuels made of hydrated ferric oxide particles in the shape of a bamboo leaf.

[Effect]

Long axis diameter 0.2 having the striped ultrafine structure of the present invention
Hydrous ferric oxide particles with a bamboo leaf shape of ~1.0 μm and an axial ratio (major axis diameter/minor axis diameter) of 3 to 10 have a highly dispersed contact with the solid fuel because the particles themselves are fine. Carbon oxidation is performed efficiently.

In other words, this feature is due to the fact that the hydrous ferric oxide particles specified in the present invention have a striped ultrafine structure with a major axis diameter of 0.
．． 2 to 1.0 μm and axial ratio (major axis diameter/short axis diameter) 3 to 10
Because the particles are shaped like bamboo leaves, they have an extremely large specific surface area, and because they are shaped like bamboo leaves and are rounded, the particles stick together and rarely overlap, resulting in a high porosity and a high porosity. This is due to the high contact efficiency with oxygen required for

The major axis diameter of the hydrous ferric oxide fine particles used in the present invention, which has a streak-like ultrafine structure, is specified as 0.2 to 1.0 μm, and the axial ratio (major axis diameter/minor axis diameter) is specified as 0.2 to 1.0 μm. ) 3 to 1O is specified because particles with a major axis diameter of more than 1.0 μm will have a small specific surface area, which is inappropriate, and particles with a major axis diameter of less than 0.2 μm are too fine, resulting in agglomeration between particles. This is because it is not desirable.

In addition, particles with an axial ratio of less than 3 will have a smaller bamboo leaf-like characteristic with a striped ultrafine structure, while particles with an axial ratio of more than 10 will have an undesirable shape that approaches a needle-like shape. It is.

Next, a method for manufacturing the hydrous ferric oxide particles used in the present invention will be described, which can be easily obtained by the following manufacturing method.

That is, an alkali carbonate of 1 equivalent or more relative to the ferrous salt is added to a ferrous salt aqueous solution and reacted to obtain Fe["Ds, and an oxygen-containing gas is bubbled through the obtained FeCD5-containing aqueous solution. Obtained by oxidation reaction. In the above production method, the ferrous salt aqueous solution is a ferrous sulfate aqueous solution, ferrous chloride aqueous solution, etc. When adding an alkali carbonate to the ferrous salt aqueous solution to obtain pecks , alkali hydroxide may be used in combination with alkali carbonate.As the alkali carbonate, sodium carbonate, potassium carbonate, ammonium hydrogen carbonate, etc. may be used alone or in combination with alkali hydroxide. Sodium hydroxide, potassium hydroxide, ammonium hydroxide, etc. are used as the alkali.

Further, in some cases, the oxidation reaction may be carried out after aging in a non-oxidizing atmosphere.

The pH of the solution during the oxidation reaction is 7-11. If the pH is less than 7 or more than 11, it is impossible to obtain hydrated ferric oxide particles having a bamboo leaf shape. In addition, if the temperature during the oxidation reaction is less than 30°C, it will not be possible to obtain hydrated ferric oxide particles with a bamboo leaf shape, and if it exceeds 80°C, granular black starch will be mixed in. The temperature during the oxidation reaction should be set at 30-80°C. The oxidation means is carried out by passing an oxygen-containing gas (for example, air) into the liquid, and is preferably carried out while stirring using the ventilation gas or mechanical operation. The oxidation reaction product is washed with water to remove by-product salts and obtain hydrous ferric oxide particles.

The hydrated ferric oxide particles thus obtained may be dried and used as a powder and mixed with a solid fuel, or may be used in the form of a slurry without being dried.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to Examples.

[Example 1] A 3.53 mol/1 Na2CL aqueous solution 201 was placed in a reaction vessel, and then a 1 mol# Fe50* aqueous solution 3 was added.
01 was added and mixed to obtain FeCO3 at a temperature of 40°C. An oxidation reaction was carried out by passing air at a rate of 150 l/min into the resulting aqueous solution containing PeCL at a temperature of 40° C. for 4 hours to generate yellowish brown precipitated particles. Note that the PL of the reaction solution during air ventilation was 9.6.

The generated yellow-brown starch particles are filtered and washed with water at room temperature.
It was dried and ground to obtain 2.61 kg of yellowish brown particle powder (a).

As a result of Xa-fraction, it was confirmed that the obtained yellowish brown particles were hydrated ferric oxide. In addition, □ This fine powder was examined using an electron microscope and a mirror photograph (magnification 15) as shown in the first order.
．． 0,000 times), the average value of the long axis diameter is 0.25 μm, the uniaxial ratio (major axis diameter/short axis diameter) is 8, and the specific surface area is 106 m''/g. It was confirmed that the particles were composed of hydrated ferric oxide particles.

[Comparative Example] 0.68 mol/1 FeS'Oa aqueous solution 801 was placed in a reaction vessel, and then 4. '3-2 mo1/'J Na1L aqueous solution 101 was added and mixed, and then temperature 4
The reaction was carried out at 0℃ for 4 hours while passing electricity at a rate of 13'0'''1:,/min, and the yellow color □
Starch grains were produced, ,・'4'. Note that the p″H of the reaction solution during air ventilation is 5.
It was 8-4.0. '.1 The yellow-brown starch particles produced were filtered, washed with water, and dried and ground to obtain 1.83 kg of yellow-brown starch powder (c). As a result of X-ray diffraction, it was confirmed that the powder particles were hydrated ferric oxide, and the crystals had an average major axis diameter of 0.3 as shown in the electron micrograph shown in Figure 2 (magnification: 100,000 times).
It was confirmed that it was hydrated ferric oxide having a needle-like structure with an axial ratio (major axis diameter/minor axis diameter) of 10 μm. Further, when the specific surface area was measured, it was 95 mF/g.

[Example 2] Hydrous ferric oxide (a) with a bamboo leaf-like ultrafine structure obtained in Example 1 and hydrous ferric oxide (a) with a needle-like structure obtained in Comparative Example
6) and ferric oxide (which is generally commercially available as a reagent)
100 ppm of each of FeJs) was added to petroleum coke fine powder.
was added and evaluated through combustion experiments.

Figure 3 shows a conceptual diagram of the combustion experiment equipment. In Fig. 3, 1 is an electrically heated combustion furnace, 2 is a coal or coke powder feeder, 3 is secondary air for combustion, 4 is secondary air for combustion, 5 is a cyclone for collecting combustion ash, and 6 is an exhaust gas suction fan. , 7 is a chimney, 8 is an exhaust gas measurement line, and 9 is a combustion burner.

The suction fan 6 is activated to cause finely pulverized petroleum coke to fall from the quantitative feeder 2, and is sprayed by the combustion burner 9 into the electric furnace 1 which has been heated to a predetermined temperature together with the secondary combustion air 3. At the same time, secondary combustion air 4 is introduced into the furnace 1 to adjust excess O2 in the combustion exhaust gas to a range of 2 to 6%.

00 in combustion exhaust gas. Once the concentration was controlled to a predetermined level, a certain amount of the exhaust gas was sampled from the exhaust gas measurement line 8, and the soot dust concentration was measured and unburned carbon was analyzed using the circular filter paper method.

The combustion experiment was conducted under the following conditions.

Set temperature in electric furnace 1300℃ Combustion amount 2kg/h Primary air temperature Room temperature secondary air temperature 250℃ Excess 0.2~6% Table 1 shows the amount of unburned carbon in the exhaust gas when burned at an excess of 0.24%. It was measured and expressed as the unburned carbon amount ratio when no combustion improver was added as 100.

Table 1 [Example 3] Bamboo leaf-shaped hydrated ferric oxide (a), needle-shaped hydrated ferric oxide (Co., Ltd.), and commercially available ferric oxide were added to fine coal powder using the same equipment and under the same conditions as in Example 2. The results of combustion by adding 200 ppm of (Fe203) and changing the excess 02 to 2.4.6% are shown in the fourth column.
Shown in the figure. As a result, it was found that the mixture containing bamboo leaf-shaped hydrated ferric oxide particles contained less unburned carbon in the combustion ash (it was found to be effective as a combustion improver).

〔Effect of the invention〕

When the combustion improver of the present invention is used for solid fuels such as coal and petroleum coke, it has the effect of suppressing the generation of unburned matter and improving dust collection efficiency at the same time.

[Brief explanation of drawings]

Figure 1 shows the hydrous oxidation of a bamboo leaf used in the present invention. Electron micrograph showing the crystal morphology of ferric particles (magnification: 1 jo
2 is an electron micrograph showing the crystal morphology of acicular hydrated ferric oxide particles (10,000 times magnification), and FIG. 3 is the concept of the combustion experiment apparatus used to confirm the effects of the present invention. 4 are graphs showing results for proving the effects of an embodiment of the present invention.

Claims (1)

[Claims] Long axis diameter 0.2 to 1.0 with a striped ultrafine structure
A combustion improver for solid fuel, characterized by comprising hydrous ferric oxide particles having a bamboo leaf shape and an axial ratio (major axis diameter/minor axis diameter) of 3 to 10 in μm.