CA1080211A

CA1080211A - Method for operating a hot blast stove

Info

Publication number: CA1080211A
Application number: CA201,650A
Authority: CA
Inventors: Masaru Higashi
Original assignee: Nippon Mining Co Ltd
Current assignee: Nippon Mining Holdings Inc; Eneos Corp
Priority date: 1973-06-12
Filing date: 1974-06-04
Publication date: 1980-06-24
Also published as: JPS5014506A; PH10883A; US3902844A

Abstract

ABSTRACT OF THE DISCLOSURE
A method for operating a hot blast stove in which a combustion gas of a sulfur-containing fuel is passed through a regenerator to heat up the regenerator and air subsequently is blown through the regenerator and is heated by heat-exchange with the heat built up in the regenerator, the improvement comprising preheating the air to a temperature above the acid dew point of the combustion gas whereby corrosion of the regenerator by sulfur is prevented.

Description

108Vi~ll BACKGROUND OF THE INVENTION
1. Field of the Invention This invention relates to a method for operating a hot blast stove in which a sulfur-containing fuel is burned, with the heat of the combustion gas being stored in a regenerator, and with the air to be heated by the regenerator being brought into contact with the regenerator for heat exchange. More specifically, this invention relates to a method for operating a hot blast stove without causing corrosion of the regenerator structure.

2. Description of the Prior Art It is customary to introduce a hot blast into a smelting furnace in order to smelt ores. Various methods are available to generate heat for the hot blast. Generally, however, prior techniques have employed a method in which an iron blast furnace gas is used, or a method in which a fuel is burned and the sensible heat of the exhaust gas is utilized. The sensible heat of the exhaust gas is stored generally in a heat-receiving device con-structed of bricks, by passing the exhaust gas through the heat-receiving device. This heat-receiving device is generally called a regenerator. In operation, when the temperature of the regener-~ator has reached a fixed levelx~the flow of the combustion gasis stopped, and then air is blown in an opposite direction to the combustion gas flow, so that air is heated with the heat stored in the regenerator. As a result of this operation air is heated to a fixed temperature and usually, all of this equipment is called a hot blast stove.
Thus, in a hot blast stove operation, a fuel is burned in a combustion furnace which is separate from a regenerator, and then, the combustion gas is passed through the regenerator 1080Z~l 1 to transfer the he~t of the combustion gas to the regenerator, with the combustion gas being passed through the regenerator for about 30 to 55 minutes to achieve a wall temperature of about 250 to 350C. Then, in order to use the stored heat for a desired purpose, air at room temperature is introduced into the regenera-tor generally from the side of the outlet of the combustion gas from the regenerator and is brought into contact with the regen-erator to recover the heat as hot blast. In this case, the temperature of the section of the regenerator near the air inlet of the regenerator drops to about 50C.
However, in such a method for operating a hot blast stove, a sulfur free heat~source is required. When the sulfur content of the fuel is less than 0.2%, SO3 which is a main cause of corrosion is scarcely formed, and therefore, no consideration on the corrosion of the stove due to the sulfur is needed. How-ever, when the sulfur content is higher, corrosion of the regenerator in contact with the combustion gas occurs, and the regenerator can be damaged or destroyed.
It is said that when a heavy oil containing 2~ of sulfur is used as a fuel, the amount of corrosion of a steel material in general, for example, is 10 to 50 mg/dm2Hr. If the lifetime of a hot blast stove can be calculated on this basis, a hot blast stove should be renewed every eight years when it is operated in the conventional method. This is about half of the inherent lifetime. Generally speaking, the inherent lifetime of a hot blast stove is about 15 years. In order to avoid this, fuels containing large ~uantities of sulfur have not been employed as a heat source.
SUMMARY OF THE INVENTION
.
Accordingly, it is an object of this invention to remove 1080Zll 1 these defects of the conventional methods, and to provide a method for operating a hot blast stove which permits the use of a fuel having a high sulfur content which could not be used previously.
The present invention provides a method for operating a hot blast stove of the type in which a combustion gas of a sulfur-containing fuel is passed through a regenerator and the regenerator heated up, followed by the blowing of air through the regenerator to heat the air using the heat built up in the regen-era-tor, comprising perheating the air to be blown through the regenerator to a temperature above the acid dew point of the combustion gas prior to blowing the air through the regenerator.
DETAILED DESCRIPTION OF THE INVENTION
According to this process, the hot blast stove is operated so that the temperature of every part of the regenerator is not below the acid dew point of the combustion gas. In order to achieve this, the air to be blown for about 35 to 60 minutes through the regenerator, generally at 500 to 650 Nm3/min, for producing the hot blast is pre-heated to a temperature above the acid dew point, preferably at least about 50C above the acid dew point, so that upon blowing the pre-heated air through the regen-erator,the temperature of the regenerator is maintained always at a temperature above the acid dew point.
The range of acid dew point of the exhaust gas cannot be unequivocably defined. The acid dew point is dependent upon the sulfur content of the fuel, and the water content in the exhaust gas. Therefore, the heating temperature for the blast air is determined by the fuel used. Generally, a pre-heating temperature of about 200C to about 250C is sufficient. The pre-heating of the air blast can be by any known method, but a 1080;~11 1 method for heating using steam, or a method of heating by circu-lating a part of the high temperature hot blast is preferred.
The following example illustrates the method of this invention more specifically. Unless otherwise indicated all parts, and percents are by weight.
EXAMPLE
A hot blast stove which was used to provide a feed hot blast to a smelting furnace for smelting a copper ore and which had a regenerating capacity of 6,700,000 Kcal per hour was used. A heavy oil containing 2~ of sulfur was burned at a rate of 1,000 liters per hour, and the burning was stopped when the temperature of the brick at the outlet of the combustion exhaust gas of the hot stove reached 350C. After regeneration, using a heat exchanger separately provided, air was pre-heated to 200C
with superheated steam, and then fed to the hot blast stove at a rate of 500 Nm3 per minute. The supply of the blast was stopped when the hot blast temperature fed to the smelting fur-nace could not be maintained at 900C, and the operation was switched over to one for regeneration. The time required for regeneration was about 55 minutes, and the time for supplying the hot blast was about 60 minutes. These operations were repeated alternately. After a lapse of about 6 months, scarcely any appreciable corrosion or damage of the stove was observed.
Since the damage of the regenerator by corrosion can be prevented by operating the hot blast stove in accordance with the method of this invention, fuels having a slightly higher sulfur content, e.g., up to about 3% and higher as desired, can also be utilized. Thus, use of such a higher sulfur content has not been possible with prior approaches as set forth above. The shortened lifetime of the stove, estimated at about 8 years in - , .

-` 1080;~11 1 the conventional method, can be obviated. Rather since the pre-heating of air to be supplied also causes a decrease ln the periodical change in thermal expansion, it is expected that the brick collapsing of the hot blast stove due to thermal stresses on the brick can be prolonged.
Furthermore, because of the air pre-heating, the regenerator can be heated to the desired temperature even if the combustion time is shorter than in conventional method.
While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a method for operating a hot blast stove in which a combustion gas of a sulphur-containing fuel is passed through a regenerator to transfer the heat of the combustion gas to the regenerator, and air subsequently blown through the regenerator is heated using the heat stored in the regenerator, the improve-ment herein is such that the air is pre-heated, before passing through the regenerator, to a temperature above the acid dew point of the combustion gas wherein the condensation of corrosive acid is prevented from occuring within the generator.

2. The method of claim 1, wherein said pre-heating is to a temperature of at least about 200°C.

3. The method of claim 1 or 2 wherein the air is preheated using steam.

4. The method of claim 1 or 2 wherein the air is preheated by recirculating a portion of the air passed through the regener-ator, and now heated, and mixing it with air yet to enter the regenerator.

5. The method as claimed in claim 1 or 2 wherein the combustion gas and the air are alternately passed through the regenerator.