RU2309991C2 - Fuel combustion method in heating furnace and heating furnace for performing the same - Google Patents

Abstract

FIELD: heating furnaces used in metallurgy and machine engineering for heating metal before plastic working of it and heat treatment of metal.

SUBSTANCE: method of fuel combustion in heating furnace comprises steps of after-burning non-complete combustion products due to supplying high-speed highly twisted flow of oxidizing agent under high pressure into after-burning apparatus in the form of single-line (with suppressed gas feed) flat-flame radiation burner where in the result of high twisting vortex is destructed and significant evacuation degree is created. It provides supply of non-complete combustion products into after-burning zone. First stage of after-burning is realized in torch propagating along surface of heated metal at value of oxidizing agent consumption factor 0.48 -0.55 and at concentration degree of air with oxygen 0.35 -0.45. Heating furnace includes burners arranged in its lateral wall for full preliminary mixing of fuel gas with oxidizing agent for creating said torch. After-burning apparatuses are arranged in roof and(or) in lateral walls of furnace and they are in the form of single-line flat-flame radiation burners.

EFFECT: suppression of metal oxidation process, small bursts of nitrogen oxides to atmosphere, rational consumption of fuel in heating furnace.

13 cl, 2 dwg

Description

The present invention relates to fuel furnaces intended for heating metal before pressure treatment or for heat treatment of metal and metal products. It can be both continuous kilns, for example methodical, and periodic kilns.

One of the most significant drawbacks of many of these furnaces is the high waste of metal, which amounts to about 2% or more. This means that, for example, for a large methodical furnace with a capacity of 200 t / h, metal losses are enormous - about 30 thousand tons per year.

Another important problem associated with the operation of fuel heating furnaces is the very significant emissions of one of the most dangerous types of atmospheric pollutants - nitrogen oxides. Reducing these emissions can provide obvious environmental and economic effects. There is the possibility at the same time, by carrying out the same measures, to solve both of these problems and, in addition, to obtain significant fuel economy.

We are talking about the method of operation of the furnace, which is based on the well-known two-stage technology of fuel combustion and which is as follows.

At the first stage of the process in the area of the working space of the furnace where there is a danger of oxidation of the metal surface, the fuel is burned with a lack of oxidizer. If at the same time low values of the oxidizing agent consumption coefficient are used in the combustion process, it may be necessary to heat it to high temperatures or to use sufficiently high degrees of oxygen enrichment in the air.

In the second stage, the afterburning of incomplete combustion products formed in the first stage is carried out, so that the total oxidizer consumption coefficient is not less than 1.05. In this case, of course, the afterburning heat must also be transferred to the heated metal.

Known methodical furnace for direct non-oxidative heating of metal, in which the air used for primary combustion is heated to 600-800 ° C in a metal recuperator. For the afterburning of products of incomplete combustion, a secondary air supply is provided under the arch of the furnace and on the hearth. The secondary air supply is dispersed along the length and width of the furnace by supplying it in small streams (AS USSR No. 141881).

However, heating the air to such high temperatures in a metal recuperator requires the use of expensive heat-resistant metal for its manufacture. To achieve an acceptable calorimetric temperature in the combustion zone at the first stage of the two-stage combustion process, it is reasonable to use not high-temperature air heating, but its enrichment with oxygen. This will, firstly, reduce the cost of heating nitrogen (these costs are of the same order as the heat consumption for heating the metal), and secondly, reduce NO _x emissions by reducing the nitrogen content in the air. In addition, the supply of a secondary oxidizer under the arch and under the furnace in small streams cannot provide a rational scheme for the movement of gases in the furnace, that is, the movement of products of incomplete combustion in the afterburning region, guaranteeing efficient and complete afterburning of products of incomplete combustion, as well as intensive transfer of heat released when burning fuel, to the heated metal.

A known method of heating metal in a methodical furnace (French patent 2785668. PROCEDE DE CHAUFFAGE D'UN FOUR A CHARGEMENT CONTINU NOTAMMENT POUR PRODUITS SIDERURGIQUES, ET FOUR DE CHAUFFAGE A CHARGEMENT CONTINU / LE GOUEFFLEC GERARD // PUBL. 05.12.00. the fact that in the heating zones of a continuous furnace, fuel is burned with an oxidizer consumption coefficient of 0.95-0.99, and in the method zone, jet afterburning of products of incomplete combustion with oxygen is carried out. Air or oxygen-rich blast is used as an oxidizing agent in heating zones.

However, as mentioned above, the use of jet afterburning is not a successful solution to the problem, since it does not provide complete mixing of the furnace gases with oxygen, and can also lead to undesirable contact with the heated metal. In addition, the given values of the oxidizing agent coefficient do not provide sufficient protection of the surface of the heated metal from oxidation and effectively suppress the formation of nitrogen oxides. Finally, the afterburning of products of incomplete combustion in the methodological zone leads to an increase in temperature in this zone, which can lead to too rapid heating of the metal, causing the danger of disruption of the metal continuity, as well as to an undesirable increase in the temperature of the flue gases at the outlet of the furnace, i.e. heat and thermal pollution.

Calculations show that when the oxidizer consumption coefficient is 0.75-0.8, the metal burn is reduced by approximately 60-70% for thermal furnaces and by 20-25% for high-temperature heating (for example, methodical) furnaces of rolling production, and implemented by the indicated method two-stage combustion of fuel allows to reduce emissions of nitrogen oxides by an order of magnitude. At the same time, the use of moderate, up to 35-45%, oxygen enrichment degrees of the air supplied for fuel combustion at the first stage gives a fuel economy of 10-15% and provides a sufficient content of combustible components in incomplete combustion products to organize efficient afterburning.

However, in the scientific and technical literature there is evidence that, at the indicated values of the oxidizing coefficient, the metal surface is covered with a thin film of wustite (FeO), which is difficult to remove during rolling, which can lead to an increase in rejects in the rolled metal. In this regard, it is rational to reduce the oxidizer consumption coefficient to 0.48-0.55.

A method is proposed for burning fuel in heating and thermal furnaces, which consists in the fact that at the first stage of fuel combustion this process is carried out in a flat, i.e. a torch propagating directly along the metal surface formed by a burner with complete preliminary mixing of fuel and an oxidizer with oxidizer consumption coefficient values ranging from 0.48 to 0.55. At the same time, oxygen enriched air at an enrichment degree of 0.35-0.45 is used as an oxidizing agent in the first stage.

The indicated limits for the change in the coefficient of consumption of the oxidizing agent are justified by the following considerations. When the oxidizer consumption coefficient is less than 0.48, intense soot emission occurs due to oxidative pyrolysis of hydrocarbons, which makes it almost impossible to burn products of incomplete combustion in the second stage, i.e. in the methodical zone of the furnace. When the value of the oxidizer consumption coefficient is greater than 0.55, the protection of the metal from oxidation is not effective enough.

A heating furnace is provided for implementing the above method of burning fuel. On one of its side walls there are burners for the complete preliminary mixing of combustible gas with an oxidizing agent, creating a spreading torch spreading directly along the surface of the heated metal, and on its arch there are afterburners in the form of single-wire plane-flame radiation burners. Reburning devices in the form of single-wire flat flame radiation burners can also be located on the side walls of the furnace.

The invention is illustrated by drawings, where in Fig.1 shows a cross section of a heating furnace with a afterburner installed on the arch. In figure 2. shows a cross section of the furnace, and the afterburner is located on the side wall.

The invention is implemented as follows: burners 3 full preliminary mixing are located on one of the side walls of the furnace 2, and products 5 of incomplete combustion move to the opposite wall, transferring heat to the metal 1 due to radiation heat transfer and convective heat transfer. In addition, they create a protective gas-dynamic layer on the surface of the metal 1, preventing the direct contact of the products of complete combustion with the heated metal 1.

Having reached the walls of the furnace 2, products of incomplete combustion rise upward along it to the roof. On the arch are devices 4 designed for afterburning products of incomplete combustion 5.

Afterburners 4 can also be installed on the side walls of the furnace, as shown in FIG.

A fairly simple and effective method of afterburning of products of incomplete combustion of fuel can be implemented by using the well-known phenomenon of vortex decay. This phenomenon consists in the fact that during the flow of a high-speed, strongly swirling gas flow in a cylindrical chamber in the axial region of the latter, a strong vacuum is created, which ensures the suction of the environment from the side of the open end of the chamber. If this end face has the form of a curved ultradiffuser emerging on a plane, as is the case in plane-flame burners, then the flow of gas flowing out of the chamber will propagate along this plane.

Thus, the proposed method of afterburning of products of incomplete combustion is as follows. A high-speed, strongly swirling flow of oxygen or oxygen-enriched air is fed under high pressure to a afterburner, which has the form of a single-wire (with a gas supply plugged), flat-flame (radiation) burner. In the afterburning device due to strong twisting and under the influence of high speeds, the vortex decays and a strong rarefaction is created in the axial region. Under the influence of this rarefaction, furnace gases containing combustible components leak to the afterburner. Some of them enter the burner chamber, where they mix with the oxidizing agent and burn. Gases entering the afterburning zone are also sucked into a flat lay torch, which is formed as a result of the expiration of the swirling flow from the curved diffuser of the afterburning device. As a result of the heat exchange of this flat torch with the refractory surface of the burner stone and the roof or side walls of the furnace, this surface is heated to high temperatures, as is the case with a flat flame radiation burner, which provides intense radiative heat transfer to the metal.

Claims (13)

1. A method of burning fuel in heating and thermal furnaces of non-oxidative heating of metal, including the burning process in two stages: at the first stage of the process, in the area of the furnace working space where there is a high risk of oxidation of the metal surface, the fuel is burned with a lack of oxidizing agent, in the second stage afterburning of products of incomplete combustion using an oxidizing agent, characterized in that the afterburning of products of incomplete combustion is carried out by supplying a high-speed, strongly twisted of a high pressure oxidant stream into dozhigatelnoe device having a single-wire type ploskoplamennoy radiation burner, in which the decay of the vortex and the creation of a strong vacuum, providing supply of incomplete combustion products to afterburning. 2. The method according to claim 1, characterized in that the first stage of fuel combustion is carried out in a plume spreading along the surface of the heated metal. 3. The method according to claim 1 or 2, characterized in that the first stage of combustion is carried out using full pre-mixing burners with an oxidizer consumption coefficient of 0.48 ÷ 0.55 and using oxygen enriched air as an oxidizer. 4. The method according to claim 1 or 2, characterized in that the first stage of combustion is carried out using burners full preliminary mixing at a value of the coefficient of consumption of the oxidizing agent of 0.48 ÷ 0.55 and when used as an oxidizing agent. 5. The method according to claim 1 or 2, characterized in that the first stage of combustion is carried out using burners full preliminary mixing at a value of the coefficient of consumption of the oxidizing agent 0.48 ÷ 0.55 and without preheating the oxidizing agent. 6. The method according to claim 1 or 2, characterized in that the first stage of combustion is carried out using burners of complete preliminary mixing with a value of the coefficient of consumption of the oxidizing agent 0.48 ÷ 0.55 with preheating of the oxidizing agent. 7. The method according to claim 1 or 2, characterized in that the afterburning is carried out using technically pure oxygen. 8. The method according to claim 1 or 2, characterized in that the afterburning is carried out using oxygen-enriched air. 9. The method according to claim 1 or 2, characterized in that the afterburning is carried out using air. 10. A heating furnace for non-oxidative heating of metal, comprising a burner for burning fuel with an oxidizer deficiency and afterburners for afterburning products of incomplete combustion using an oxidizing agent, characterized in that the burner for burning fuel with an oxidizer deficiency is made in the form of pre-mixers of combustible gas with an oxidizing agent, and the afterburning device is made in the form of a single-wire plane-flame radiation burner that realizes the decay of the vortex and with It produces a strong rarefaction in the afterburning area. 11. The heating furnace of claim 10, characterized in that on one of its side walls there are burners for the complete preliminary mixing of the combustible gas with the oxidizing agent, creating a spreading flame that spreads directly along the surface of the heated metal. 12. The heating furnace according to claim 10, characterized in that the afterburners in the form of single-wire plane-flame radiation burners are located on the roof of the furnace. 13. The heating furnace of claim 10, wherein the afterburning devices in the form of single-wire plane-flame radiation burners are located on the side walls of the furnace.

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