JPH0699698B2 - Solid fuel combustion method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for burning solid fuel, and more specifically,
The present invention relates to a method of burning solid fuel for the purpose of suppressing unburned solid fuel content in a coal-fired boiler and a petroleum coke-fired boiler and improving dust collection efficiency by an electric dust collector.

[Conventional technology]

In recent years, solid fuels such as coal and petroleum coke have been widely used as alternative oil fuels. However, since coal and petroleum coke have less volatile content than liquid fuels such as heavy oil, they have poor combustibility and are used as finely pulverized boiler fuel, but the unburned content is still a few percent to a dozen percent. In order to reach the target, boilers that use petroleum coke as fuel have no choice but to use heavy oil or gas fuel for auxiliary combustion, which is unsatisfactory not only in terms of operation and operation but also in economic efficiency.

One of the methods to reduce the amount of heavy oil and gas used for combustion support is the application of combustion support, which has long been used as a combustion support material such as Cu, Co, Ni, Mn, Fe.
Heavy metals such as, alkali metal compounds such as K and Na, Ca and Ba
It is well known that alkaline earth metal compounds and the like are used, but recently, iron-based combustion improvers have attracted attention and are commercially available because they are particularly inexpensive and have little influence on the activity of the denitration catalyst. ing.

There are two types of iron-based combustion improvers, oil-soluble and water-soluble, and typical oil-soluble ones include iron naphthenate and iron octylate, which are used by mixing with liquid fuel such as heavy oil. On the other hand, water-soluble materials are used by impregnating and mixing with solid fuels such as coal and coke.

[Problems to be solved by the invention]

In using combustion aids such as coal and coke, in the case of heavy oil mixed combustion, a method of adding an oil-soluble auxiliary combustion agent to heavy oil is adopted, but in the case of gas mixed combustion, addition to gas is difficult,
Usually, a water-soluble burner is used by impregnating and mixing coal and coke.

However, iron-based water-soluble burners have the following problems:
It is impeding practical application.

1. Iron salt as a raw material for combustion improver, ie, iron sulfate, iron chloride, iron nitrate,
When complexed iron is hydrolyzed into an aqueous solution, it will have a pH of 3
It becomes the following acidity and corrodes equipment materials.

2. When alkali is added to neutralize, iron hydroxide precipitates and it is difficult to supply a fixed amount by a pump.

3. Iron chloride produces corrosive gases such as Cl ₂ and HCl upon combustion, and iron nitrate causes NO _x .

4. A large amount of water is required due to the solubility, and the capacity of the combustion improver tank increases.

In addition, iron-based oil-soluble burners are themselves expensive and often produce sludge when mixed with heavy oil, causing fatal troubles in boiler operation such as clogging of heavy oil line strainers or heavy oil burners. There is a case.

The present invention seeks to provide a solid fuel combustion method which does not have the drawbacks of the prior art methods described above.

[Means for solving problems]

The present invention, when applying an aqueous solution of an iron salt as a solid fuel combustor, stabilizes iron as a complex ion to solubilize iron even at a pH of 5 or more, and is safe against corrosion and has a maximum combustor effect. The present invention provides a new method of using a combustion improver that can be exhibited to the limit.

That is, the present invention is a solid fuel characterized by adding an iron complex ion-forming substance to an aqueous iron salt solution, and then impregnating or mixing the solid fuel with a combustion improver obtained by neutralizing the iron complex ion to near neutrality and then burning the solid fuel. It is the burning method.

[Action]

An iron complex ion-forming substance such as citric acid is added to the iron salt aqueous solution to form an iron complex ion, and then a neutralizing agent such as NaOH or NH ₄ OH is added to make the region stable to corrosion, that is, pH 5 or more. The target combustion improver can be obtained by adding a small amount of a surfactant to this in order to enhance the effect of impregnation into the solid fuel.

By impregnating and mixing the above-mentioned combustion improver into coal, coke, etc., as compared with the case where no combustion improver is used, the unburned content is halved, and the amount of fuel used for combustion increase can be reduced.
At the same time, the dust collection efficiency of the electrostatic precipitator could be significantly improved as compared with the case where no combustion improver was added.

As an iron complex ion forming agent, in addition to citric acid, tartaric acid, complex acid soda, oxalic acid, triethanolamine, ethylenediaminetetraacetic acid, etc. are present, but citric acid is the most effective in inhibiting iron hydroxide precipitation.

The surfactant is used to enhance the effect of impregnating the combustion improver into the solid fuel, and an anionic type is preferable, and 1 wt% or less in the combustion improver gives a sufficient effect, but it is wettable to water. Good fuel is not necessarily needed.

The amount of citric acid required to prevent the precipitation of iron hydroxide and form iron complex ions varies depending on the type of neutralizing agent.Equivalent moles of iron ion in NaOH and iron ion in NH ₄ OH are 0.3 moles or more of iron ion. Sufficiently, but all other complex ion formation requires equimolar or more.

〔Example〕

 Embodiments of the present invention will be described with reference to the drawings.

Example 1 FIG. 1 is a conceptual diagram of a petroleum coke boiler. The coke thrown into the raw material hopper 1 is crushed by the crusher 2 to 95% of 200 mesh and is conveyed by the air supplied by the blower 3 and injected into the boiler 4. Further, heavy oil or gas for supporting combustion is supplied from 5 and 6, respectively, and is mixed and burned with coke in the furnace.

In this experiment, the test was conducted under the following conditions.

Evaporation rate 85t / h, Economizer outlet O ₂ 4% Fuel coke 5t / h, Gas for combustion support (gas consisting of H ₂ , CO, CH ₄ ) 2100Nm ³ / h Storage of combustion support agent in supply tank 7 and coke by pump The powder was quantitatively supplied as Fe ₂ O _{3 in a} weight ratio of 100 ppm.

As shown in Table 1, the unburned content is 12.7 g / Nm ³ when the combustion improver is not added, while the unburned content is 5 g / Nm ³ or less in all cases where the combustion improver is added. And it was able to be greatly reduced. Further, the one to which 1% of the surfactant was added exhibited a better effect of reducing unburned components.

Further, the results obtained by adding the combustion improver were improved in the dust collection efficiency by the electric dust collector, as compared with the case where no combustion improver was added.

Example 2 1 / of the Fe content in a ferric sulfate 10% aqueous solution was previously prepared.
2 equivalents of citric acid was added, and an aqueous solution of a combustion improver neutralized to pH 6 with NH ₄ OH water was added to petroleum coke fine powder at any ratio,
The results of combustion with 4% excess O ₂ are shown in FIG. According to this, the addition of 100 ppm of Fe ₂ O ₃ reduced the amount of unburned carbon in the exhaust gas by half, and the combustion promoting effect was clearly shown by the addition of the combustion improver. It doesn't change much.

Example 3 The result of burning by adding 100 ppm of Fe ₂ O ₃ as an Fe ₂ O ₃ powder to an aqueous solution of a combustion improver prepared by the same method as in Example 1
As shown in the figure. According to this, the amount of unburned carbon in the combustion ash decreases with the increase of the excess O ₂ amount even without addition, but the amount of unburned carbon does not increase regardless of the excess O ₂ amount when the aqueous solution of the combustion improver is added. It was reduced to 1/2 compared to the one without additives.

〔The invention's effect〕

INDUSTRIAL APPLICABILITY As described in detail above, the present invention uses citric acid as a means for solving the problem of material corrosion that has been a factor of impeding practical use when using an aqueous solution of iron salt as a burner for solid fuel such as coal and coke It is possible to improve the dust collection efficiency without impairing the function as a combustion improver by adding and neutralizing the iron complex ion-forming agent, and according to the present invention, the iron salt aqueous solution is used as a combustion improver. It has been put to practical use as a new technology that is extremely effective in industry.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a combustion improver test device used to confirm the effect of the present invention, and FIGS. 2 and 3 are graphs demonstrating the effect of the embodiment of the present invention.

Front page continued (72) Inventor Arihiko Sorata 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Mitsubishi Heavy Industries, Ltd. Hiroshima Shipyard (72) Inventor Toshihiko Furumoto 4-6 Kannon-shinmachi, Nishi-ku, Hiroshima Prefecture No.22 Ryomei Giken Co., Ltd.

Claims (1)

[Claims] 1. A solid characterized in that an iron complex ion-forming substance is added to an aqueous solution of an iron salt, and then a neutralizing agent obtained by neutralizing the iron complex ion is impregnated into or mixed with a solid fuel and then burned. How to burn fuel.