JPS6287724A - Burning method of tube type furnace - Google Patents

Abstract

PURPOSE:To be able to save energy and reduce environmental pollution while heat efficiency is improved by circulating and supplying burnt exhaust gas as burning gas in such a way that burnt exhaust gas taken out is mixed with gas containing high concentration oxygen and oxygen concentration of a mixture is made the same as that in the air. CONSTITUTION:Heating tubes 2 are installed in the mainbody 1 of a furnace and heated fluid L is introduced into the tubes 2 and heated fluid L is heated by the burning of fuel F via the tubes 2. From upstream of damper 5 placed in an exhaust gas path 4 at least a part of burnt exhaust gas Gw is taken out, and a circulation path 6 which circulates and supplies exhaust being taken out as burning gas G for fuel F along with fuel F into a burning device is installed. A supply pipe 9 is connected to the path 6 from a device 7 which is able to supply pure oxygen and/or gas containing high concentration oxygen and air A0 enriched in oxygen as pure oxygen and/or gas containing high concentration oxygen is supplied and mixed with burnt exhaust gas Gw in the path 6 and the mixture is supplied to the burning device as exhaust gas G for burning.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a combustion method for a tube heating furnace, and particularly to a combustion method for a tube heating furnace that can save energy and reduce environmental pollution. It is related to.

[Prior art]

In the conventional tube-type heating furnace commonly used, a heating tube 2 is arranged inside the heating furnace body 1, as shown in the first conventional example in FIG. 4, and a fluid to be heated is placed in the heating tube 2. The fuel F and combustion air A are combusted in a combustion device, the fluid to be heated is heated through the heating pipe 2, and the combustion exhaust gas is discharged as indicated by the arrow G-.

Therefore, when heating a fluid to be heated at, for example, 300° C. to 320° C. in the heating tube 2 of this tube heating furnace, the amount of heat required for heating is 10×10 6 kcal/Hr.

This absorbed heat amount is appropriated by the combustion heat amount of the fuel F. Also,
Fuel F is combusted with combustion air A, and the generated combustion exhaust gas Gw is higher than the inlet temperature of the heated fluid stream, and in this conventional example, it is dissipated into the atmosphere as combustion exhaust gas Gw of 350 ° C.
This results in heat loss, and this loss of heat occupies a large proportion of the combustion heat.

Other heat loss is radiated into the atmosphere from the furnace wall of the heating furnace body 1, but it is very small compared to the heat radiated from the combustion exhaust gas Gw.

Therefore, it is extremely important for energy saving to reduce the amount of combustion heat by minimizing the amount of heat dissipated from the combustion exhaust gas Gw.

Next, the second conventional example shown in FIG. 5 shows an energy-saving combustion method that improves the combustion method of the tube heating furnace in the first conventional example shown in FIG. A is heat exchanged with combustion exhaust gas G- through an air preheater 8,
The combustion exhaust gas Gw is cooled from 350°C to 150°C, and this amount of heat is recovered by raising the temperature of the combustion air A and circulated to the heating furnace body 1 for effective utilization, thereby reducing heat loss and reducing the amount of combustion heat. This is aimed at reducing the amount of water used.

Furthermore, the third and fourth conventional examples in FIG. In the conversion membrane equipment 3, atmospheric air A is converted into oxygen-enriched air A using an oxygen-enriched membrane that allows oxygen to pass through it well. and nitrogen-enriched air AN.

Generally, a certain amount of oxygen is required to burn fuel F, and when air is used as combustion gas G&4, air contains 21% oxygen, so the amount of oxygen required is This means that 110.21 times the amount of air is required.

Oxygen in the air does not play a role in combustion, so 79% of the supplied air is from atmospheric temperature to
In the conventional example shown in Fig. 5, the temperature was 350°C, and in the second conventional example shown in Fig. 5, it was 15°C.
This means that it is heated to 0°C and wasted into the atmosphere.

Therefore, in the third and fourth conventional examples shown in FIG. 6, the energy saving of the tube heating furnace is achieved by reducing the proportion of gases other than oxygen that do not contribute to combustion.

In other words, an oxygen enrichment membrane facility 3 using an oxygen enrichment membrane, the technology of which has been significantly developed in recent years, is installed, and combustion air with a high oxygen concentration is created there.
. is supplied to the fuel I and the combustion device of the heating furnace main body 1 and burned.

Note that the third conventional example is oxygen-enriched air A containing 25% oxygen, and the fourth conventional example is oxygen-enriched air A containing 28% oxygen.

This is an example of improvement when creating each.

Naturally, it is clear that by combining the third and fourth conventional examples and the second conventional example, it is possible to increase the degree of improvement in thermal efficiency and the like.

Next, when methane is burned as fuel F at an excess oxygen rate of 10% in combustion air A, the composition of the combustion exhaust gas Cw becomes as shown in the table below with Molχ.

In the above table, carbon dioxide gas CO2 and water 020 are inevitably generated with the combustion of fuel F, and oxygen 0□ is the theoretically necessary amount of 110χ to completely burn fuel F.
This is an excess of 10% of the amount supplied.

On the other hand, nitrogen N2 does not contribute to combustion and therefore is 79% N2 contained in the air, which requires extra fuel F.

Next, in the second conventional example shown in FIG. 5, although exhaust heat is recovered up to 150° C., there is still room to reduce the combustion exhaust gas G by 72.1%. However, there is still room for significant improvement by reducing the combustion exhaust gas Gw released into the atmosphere to 1/3.6.

In addition, in the third and fourth conventional examples shown in FIG. 6, the oxygen concentration is set to 25% and 28%, respectively, by using the oxygen enrichment membrane equipment 3. Since the system supplies air containing 72% N2, the proportion of N2 released into the atmosphere is reduced and the amount of combustion exhaust gas is reduced.

In this method, in addition to using the oxygen enrichment membrane equipment 3, for example, a device that generates excess pure oxygen generated in a nitrogen generation plant or a gas containing high-density oxygen is used. This has the advantage of saving energy in a tube heating furnace.

However, for this method, 25% and 2%, respectively.
At an oxygen concentration of 8%, the flame temperature is 300°C and 5°C, respectively.
00°C, which necessitates upgrading the materials of the furnace wall of the heating furnace body 1, burner quills, burner chips, etc., which not only increases equipment costs, but also increases the flame temperature. NOx increases rapidly, causing environmental pollution problems.

[Purpose of the invention]

The present invention has been made to solve the problems of each of the conventional examples, and provides a combustion method for a tube heating furnace that can improve thermal efficiency, save energy, and reduce environmental pollution. It is intended to.

[Structure of the invention]

The combustion method for a tube-type heating furnace of the present invention includes circulating and supplying at least a part of the combustion exhaust gas from the tube-type heating furnace as a combustion gas for fuel in the tube-type heating furnace, and adding it to the circulated combustion exhaust gas. It is constructed by supplying and mixing pure oxygen and/or gas containing a high concentration of oxygen.In other words, the outline is that combustion exhaust gas released into the atmosphere from a tube heating furnace is taken out and pure oxygen is extracted. Alternatively, the mixed gas is mixed with a gas containing a high concentration of oxygen, the oxygen concentration in the mixed gas is made to be the same as the oxygen concentration in the atmosphere, and the mixture is circulated and supplied as combustion gas for fuel of the tube heating furnace. That is.

〔Example〕

The present invention will be described in detail below with reference to the drawings, but the same parts or portions are used in each of the embodiments shown in FIGS. 1 and 2 and the conventional examples shown in FIGS. 4, 5, and 6. Indicated by the same number or symbol.

First, in the tube heating furnace of Example 1 shown in FIG. A heated fluid stream is introduced, and the heated fluid stream is heated through the heating pipe 2 by combustion of the fuel F. In the present invention, the damper 5 provided in the exhaust gas passage 4 for the combustion exhaust gas Gs after combustion is heated. A circulation path 6 is provided in which at least a portion of the combustion exhaust gas Gh is taken out from the front, and is circulated and supplied to the combustion apparatus together with the fuel F as a combustion gas G for the fuel F. In addition, the above combustion exhaust gas G
The extraction position of the combustion exhaust gas Gw from the circulation path 6 is not limited to the position in front of the damper 5 of the first embodiment, but may be any position on the way to the exhaust gas passage 4 of the heating furnace main body 1. It's okay.

Next, a supply pipe 9 is connected to this circulation path 6 from equipment 7 that can supply pure oxygen and/or gas containing a high concentration of oxygen, and the combustion exhaust gas Gw in this circulation path 6 is supplied with the above pure oxygen and Or oxygen-enriched air AO, which is a gas containing oxygen at a high concentration, is supplied, mixed, and supplied as combustion gas G to the combustion device.

As the equipment 7, the conventional oxygen enrichment membrane equipment 3 shown in FIG. Any kind of equipment such as supply equipment may be used.

In the first embodiment shown in FIG. 1 having the above configuration, the oxygen concentration of the combustion gas G entering the combustion apparatus is similar to that of the atmosphere, so that the drawbacks of the third and fourth conventional examples shown in FIG. 6 can be solved. In addition, in the combustion exhaust gas Gw released from the heating furnace main body l to the atmosphere, components other than oxygen components in the combustion gas G taken in from outside the heating furnace system and supplied to the combustion device are reduced compared to the atmosphere. 2 in Figure 5.
This eliminates the dissatisfaction with the conventional example.

For example, compared to when the atmosphere is taken in as combustion air A, when pure oxygen is taken in as combustion gas G, the N2 component in the table showing the composition of the combustion exhaust gas G- is reduced, and The combustion exhaust gas Gh to be released is (1,
0-0,721)/1.0 = 1.0/3.6, which is extremely small, resulting in a large energy-saving effect.

Further, by incorporating a waste heat recovery system such as the air preheater 8 into this embodiment 1'' as in the second conventional example shown in FIG. 5, an even greater energy saving effect can be achieved.

Next, Embodiment 2 shown in FIG. 2 has almost the same structure and function as Embodiment 1 shown in FIG.
Or installation 7 that can supply gas containing high concentration of oxygen
An air preheater 8 having an exhaust gas passage 4 is provided in the middle of the supply pipe 9 from the air A to oxygen-enriched air A such as pure oxygen heated by heat exchange with the combustion exhaust gas Gw. is introduced into the circulation path 6 to improve thermal efficiency.

As described above, in the tube heating furnace of the present invention shown in FIGS. 1 and 2, the amount and temperature of combustion gas passing through the heating furnace main body 1, and the flame temperature are different from those of the conventional example shown in FIG. Since it is almost the same as the second conventional example shown in Fig. 5, there is no need to make any major changes to the equipment, and even if the supply of pure oxygen or oxygen-rich gas is temporarily interrupted, the operation of the tube heating furnace is possible. is possible.

Next, Examples 1 and 2 of the present invention, and the first example. Second. The heating amount, heat loss, combustion heat amount, thermal efficiency, combustion exhaust gas temperature, combustion exhaust gas amount, and saved fuel obtained in each tube heating furnace of the third and fourth conventional examples are shown in the table below. It can also be seen from the table that the thermal efficiency etc. of the tube heating furnace of the present invention is significantly improved over the conventional one, and is suitable for the purpose of energy saving.

(Margins below this page) In addition, Fig. 3 shows Example 1 of the present invention in Fig. 1 with a pure oxygen supply ratio of 100χ when the temperature of the combustion exhaust gas Gw is 350°C, and Fig. 4 in which pure oxygen is not supplied. Regarding the first conventional example, the amount of combustion exhaust gas (Nm'/Hr) is
, and is a diagram showing the thermal efficiency in terms of Te(X). If the present invention is adopted, the combustion exhaust gas IW will be significantly reduced as shown by the curve M, and the thermal efficiency Te (X) will be reduced as shown by the curve N.
It can be confirmed from this diagram that the performance is significantly improved.

[Effects of the Invention] By adopting the combustion method of the present invention in a tube heating furnace, the amount of combustion exhaust gas that was conventionally emitted into the atmosphere can be significantly reduced, and the exhaust heat can be used effectively, resulting in improved thermal efficiency as a heating furnace. It is possible to significantly improve energy efficiency and achieve energy saving effects.

In addition, in the tube-type heating furnace of the present invention, the oxygen concentration of the combustion gas entering the combustion device is similar to that of the atmosphere, so the rise in flame temperature is also the same as in conventional heating furnaces. There is no need to use high-grade materials, so equipment costs do not increase, and NO
There is also no problem of environmental pollution caused by a rapid increase in x.

On the other hand, the combustion method of the present invention can be easily adopted in conventional tube-type heating furnaces without major changes, and even if the supply of pure oxygen etc. is temporarily interrupted, it can be used in the same manner as in conventional heating furnaces. The advantage is that it is possible to drive.

The present invention can be particularly effectively applied to tube heating furnaces installed in areas where surplus oxygen or oxygen-rich gas is easily available, such as in nitrogen generating plants.

[Brief explanation of drawings]

1 and 2 are schematic diagrams of tube-type heating furnaces according to embodiments of the present invention. FIG. 1 is a first embodiment, and FIG. 2 is a second embodiment. FIG. 3 is a diagram comparing the combustion exhaust gas amount and thermal efficiency of the tube heating furnace of Example 1 of FIG. 1 and the first conventional example of FIG. 4. FIG. 4, FIG. 5, and FIG. 6 are schematic system diagrams of tube-type heating furnaces in different conventional examples. 1...Heating furnace body, 2...Heating tube, 3...Oxygen enrichment membrane equipment, 6...Circulation path, 7...Pure oxygen and/or gas containing high concentration of oxygen Equipment that can be supplied, 8
...Air preheater, 9...Supply pipe, G...Combustion gas, G&4...Combustion exhaust gas, Ao...Oxygen-enriched air, F...Fuel.

Claims (1)

[Claims] At least a part of the combustion exhaust gas from the tube heating furnace is circulated and supplied as a combustion gas for the fuel of the tube heating furnace, and the circulated combustion exhaust gas contains pure oxygen and/or oxygen at a high concentration. A combustion method in a tube heating furnace that supplies and mixes gas.