WO1989006268A1

WO1989006268A1 - Composition reducing slag crustation in boiler furnaces and emission of sulfur

Info

Publication number: WO1989006268A1
Application number: PCT/HU1988/000085
Authority: WO
Inventors: György VÁMOS; G. Béla WENCZEL; Zoltán SÜDI; László Barta; György SCHAMSCHULA; Györgyné SCHAMSCHULA; József Kovács; Tamás Kovács; Józsefné KOVÁCS
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-12-28
Filing date: 1988-12-27
Publication date: 1989-07-13
Anticipated expiration: 1990-06-28
Also published as: HU200361B; HUT48671A

Abstract

The present invention relates to a composition reducing slag crustation in boiler furnace and emission of sulfur, which composition consists of a mixture of ammonium sulfate, magnesium chloride, a fly ash fraction and oil. This composition can be fed into the furnace chamber in an amount of 0,1-5 % calculated on the total mass of ashes in the coal.

Description

Composition reducing slag crustation in boiler furnaces and emission of sulfur

Field of the invention The present invention relates to a composition reduc¬ ing slag crustation in boiler furnaces - firing devices - and emission of sulfur and to application of this composition as well.

Prior art

Problems coming from slag crustations formed on heat¬ ing surfaces of firing devices are well known. Heat transfer decreases with thickening of the slag layer and as a consequenc of this temperature of the furnace chamber will be increased, what makes formation of a slag crustation more probable.

Boiler is to be stopped so that the slag layer would be re¬ moved, what means a hard physical work. This causes a break¬ down and the restarting is expensive.

Firing devices working with solid fuels considerably pollute the environment. SO and NO being present in flue gases combine with water in the atmosphere and significantly damage the nature in form of acid rains. Temperature-rise in furnace chamber caused by slag crustation enhances formation of NO therefore in a given case unfavourable processes may be strengthened by one another.

Consequently pollution of environment and slag crusta¬ tion are connected with each other, therefore for their eli¬ mination there is a need for measures influencing both processes. Studying the mechanism of slag crustation it can be concluded that fusability of the forming fly ash increases with decreasing of the grain size, because surface deforming stress increases with decreasing of the grain size. Therefore all firing processes are accompanied, at least moderate¬ ly, with a slag crustation.

For the elimination of slag crustation in addition to the usual mechanical methods, e.g. water jet blusting or removal by tools, there are known chemical methods as well. The great advantage of the chemical methods to the mechanical methods is that they are suitable for a conti¬ nuous cleaning and operation of the boiler is not to be stopped. According to the Hungarian Patent No. 133 077 sodium chloride and calcium sulfate and according to the Hungarian Patent No. 166 853 ammonium hydrogen sulfate, sodium chloride and graphite are used to reduce slag crustation. However, the known methods are unsuitable to elimin- ate the harmf l emission of sulfur or even it is increased by them, moreover their application is uneconomical.

Disclosure of the invention

It has been found that a composition containing 25-55% ammonium sulfate, 20-40% magnesium chloride, 5-55% fly ash fraction with a high specific surface and 1-2% oil calculated on the total dry mass of the composition is excellently suitable to reduce slag crustation in boiler furnaces and in addition to hinder emission of sulfur preventing its damaging effect on the environment. (The percents indicated are always percents by weight.)

A composition of the present invention contains 25-55%, prefarably 30-45% ammonium sulfate, 20-40%, pre¬ ferably 25-35%, suitably about 30% magnesium chloride (this one e.g. in form of a saturated solution in water) calculated on the total mass of the composition.

Essential ingredient of the composition of this invention is the fly ash fraction with a high specific surface, amount of which is ranging from 5 to 55%, pre¬ ferably from 10 to 40% calculated on the total mass of the composition. The "high specific surface" expression means

2 a specific surface of 5-30 m /g or higher, a specific sur-

2 face of about 30 m /g is preferable. The fly ash fraction contains CaO+Na₂0+K₂0+MgO+Si0₂+Al₂0₃+Fe₂0 as ingredients, its alkali content, what can be expressed by the molar ratio of (CaO+Na₂0+K₂0+MgO) : (Si0₂+Al₂0-+Fe₂0-) , is very important, and this molar ratio is ranging from 1,2 to 2,8. A high alkali content, namely a¹ molar ratio of about 2,2 to 2,8, moreover a CaO content of at least 45 wt% are preferred.

Role of the oil in the composition is actually to prevent dusting of the composition, so its selection is not of critical importance. The composition of the present invention may be in form of a powder or a granulate depending on the intended application. With respect to applicability a granulate is preferred. A granulate can be prepared according to known processes by means of suitable equipments. A composition of the present invention can be pre¬ pared by simple mixing of the ingredients making a homo¬ geneous mixture.

The present invention relates also to the applica¬ tion of the compositions mentioned above, the very essence of this application is that the composition may be fed into the furnace chamber in an amount of about 0,1-5% calculated on the total mass of ashes in the coal.

The advantageous effect of a composition of the present invention is based probably on it that ammonium sulfate sublimates in the surface chamber with a temperature of 1100-1200°C and immediately condenses in the boiler tubes with a relatively lower temperature. Thus submicronic molten flue-dust particles, which appear at the beginning of slag crustation, will be contacted at first with this substance. With advancement of the slag crustation tem¬ perature of the slag layer increases, what is accompanied by decomposition of the ammonium sulfate, and this process makes loose the slag layer or removes it respectively. Magnesium chloride fed together with ammonium sulfate part¬ ly melts and partly evaporates at the temperature of the furnace chamber. Therefore reacting with the sulfur dioxide it forms magnesium sulfate decreasing thus the emission of sulfur. At the temperature of the furnace chamber fly ash fraction absorbs sulfur oxides, and as a result of this surface reaction it will be transformed to calcium sulfate additionally reducing the emission of sulfur.

The following examples are intended to illustrate the present invention in details.

Example 1

45 wt% ammonium sulfate and 30 wt% magnesium chloride were admixed with 25 wt% fine fly ash and then granulated with 2 wt% oil. The so obtained mixture was fed into the pulverizing mill before the coal preheater of a boiler with a capacity of 40 t/h powdered fuel firing. Ash content of the coal burned in the boiler was 35% calculated on the total mass of fuel, and sulfur content was 4,5% calculated on the total mass of ashes. To this coal was given the above mixture in an amount of 0,5% calculated on the total mass of ashes. Results of measurements obtained within a half of a year period showed that^'slag crustation in boiler ceased completely and emission of sulfur could be reduced by 45%.

Example 2

55 wt% ammonium sulfate and 25 wt% magnesium chloride were admixed with 20 wt% fine fly ash and then granulated with 3 wt% oil. The so obtained mixture was fed into a boiler with a capacity of 95 t/h powdered fuel firing. Ash content of the coal was 40% calculated on the total mass, sulfur content was 3,7 % calculated on the total mass of ashes. Feeding this mixture in an amount of 5% calculated on the total mass of ashes emission of sulfur reduced by 50% and no slag crustation appeared.

Claims

1. A composition reducing slag crustation in boiler furnace and emission of sulfur characterised in that it contains 25-55% ammonium sulfate, 20-40% magnesium chloride, 5-55% fly ash fraction with a high specific surface and 1-2% oil calculated on the total mass of the composition.

2. A composition according to claim 1 characterized in that magnesium chloride is contained in form of a solu- tio .

3. A composition according to claim 1 or 2 characterized in that the fly ash fraction has a specific surface of

2 5-30 m /g or higher.

4. A composition according to any of the claims 1 to 3 characterized in that the fly ash fraction contains

CaO+Na₂0+ ₂0+MgO+SiO +Al₂0₃+Fe₂0₃ as ingredients.

5. A composition according to claim 4 characterized in that the molar ratio of (CaO+Na₂O+K₂0+Mg0) to (Si0₂+ +Al₂0₃+Fe₂0₃) in the fly ash fraction is ranging from 1 ,2 to 2,8 and the CaO content is suitably at least 45%.

6. A composition according to any of the claims 1 to 5 characterized in that it is in form of a granulate.

7. Process for reduction of slag crustation in boiler furnace and emission of sulfur characterized in that a composition according to any of the claims 1 to 6 ±s fed into the furnace chamber in an amount ranging from 0 , 1 to 5% calculated on the total mass of ashes in the burned coal.