JPS6133437Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a flue that is exhaust equipment for a combustion furnace that heats, for example, steel pieces.

Generally, when subjecting steel billets, blooms, slabs, etc. to a rolling process, it is necessary to heat the steel billets to a required temperature suitable for rolling. A continuous heating furnace is used. In such a heating furnace, fuel such as by-product gas and heavy oil is mixed with air and blown into the furnace through a burner for combustion, but the furnace is equipped with exhaust equipment to discharge combustion exhaust gas. Continuously installed.

FIG. 3 shows a typical example of exhaust equipment connected to a heating furnace. In the figure, 5 is a heating furnace, 6 is an exhaust gas flue connected to the charging port side end of the heating furnace 5, and 7 is an exhaust gas flue connected to the heating furnace 5. A heat exchange device (requioperator) 8 is installed in the middle of the flue 6, and a chimney 8 is connected to the end of the flue 6. The gas used to heat the material in the furnace becomes high-temperature exhaust gas and is sent into the flue 6, where it is exchanged with the air supplied by the air blower 9 in the requilifier 7, and after its temperature is lowered, it is sent into the chimney 8. is discharged from. The air heated in the recuperator 7 is used as preheated air for a burner 10 provided in the furnace.

However, in the heat exchange device 7 installed in the flue 6, heat transfer from the combustion exhaust gas to the heat exchange device is mainly performed by convection heat transfer, and therefore the heat transfer efficiency is generally considered to be low. For this reason, the temperature of the exhaust gas passing through the heat exchanger does not drop that much, which poses problems in terms of heat transfer efficiency, and the flue lining material after the heat exchanger must also be made of a relatively high-quality refractory.

In view of the above-mentioned current situation, the present invention aims to improve the heat transfer efficiency of the heat exchange device, and also reduces the temperature of the combustion exhaust gas after passing through the heat exchange device, thereby reducing the heat load on the flue. The purpose is to provide a path. However, the flue of the combustion furnace of the present invention to achieve the purpose of leverage is
A breathable solid wall is installed on the downstream side of the heat exchange device installed in the exhaust gas flue, and the breathable solid wall is used as an exhaust gas outlet path, and the radiant heat from the breathable solid wall when the gas passes through the heat exchange device. In addition to receiving heat from the air permeable solid wall, the exhaust gas temperature on the downstream side of the permeable solid wall is lowered, and the material of the flue lining material can be reduced.

Note that the breathable solid wall here refers to a porous material that has good air permeability and moderate pressure loss.Metallic materials include foamed metal, sintered metal, etc., and refractory materials include porous SIC, alumina ball bonding, etc. There is something.

Before explaining the content of the present invention, we will explain the principle behind the above-mentioned breathable solids in the well-known document "White Diameter Mechanical", April 14, 1980, "Improving the Fuel Consumption Rate of Furnaces by 60% Using Radiant Energy of Solids" (Ryozo Echigo). The following is an explanation based on Mr.

In Figure 1, the cross section of the combustion furnace flue (x = x ₁
~ x ₂ ) Consider the heat balance when a breathable solid wall is installed.

Working gas (combustion gas) at the flue entrance (x=O)
Enthalpy ρ ₀ CpToUo (where ρ: working gas density, Cp: specific heat of working gas, T: temperature,
In the case of steady heating, if there is no permeable solid, heat loss through the furnace wall Lw and exhaust gas loss ρeCpTeUe
It becomes. On the other hand, if there is a breathable solid, it will be heated by the working gas and emit strong radiant energy to the surroundings. (The density of the emitted radiant energy is generally much higher in solids than in gases.) Here, the optical thickness of the breathable solid layer in the flow direction τ
If ₀ is selected appropriately and care is taken to ensure that the pressure loss does not become excessive, this system has the following characteristics.

(1) The working gas undergoes a very large enthalpy drop as it traverses the layer of breathable solids, significantly lowering the exhaust gas temperature.

(2) The energy corresponding to the enthalpy drop is emitted as radiant energy from the breathable solid layer, but the main part is directed upstream of the working gas and is absorbed by the working gas in the upstream area to heat the heated object and increase the temperature. You can prevent it from falling and use it effectively.

(3) The flow resistance (pressure loss) in the breathable solid layer is on the order of a few mmAq, and does not pose an obstacle to furnace operation, but rather optimizes the gas flow in the furnace (flow distribution).

(4) The thickness (dimensions) of the breathable solid layer is determined by the material and geometric configuration (filling ratio, average pore diameter), and is actually about 10 mm.

In general, this type of breathable solid is porous, so the heat transfer phenomenon between the breathable solid and the passing gas is approximately similar to the heat transfer in a packed bed of granular material, and the equivalent diameter of the breathable solid is 0.1 to 0.01. If it is about mm, it is 10 ³ to ^{10 4} Kcal/m ²
Since a large convective heat transfer coefficient of h° C. can be obtained, the surface temperature of the gas-permeable solid wall on the gas inlet side is heated almost instantaneously to near the gas temperature.

The temperature of the working gas will therefore drop rapidly as it flows across the permeable solid.

On the other hand, the propagation of radiant energy within this layer is shown in Figure 2.
When there is a steep temperature gradient in the x-axis direction, as in
Only the x-axis direction needs to be considered, and transport in a plane perpendicular to the x-axis can be ignored (referred to as one-dimensional propagation approximation). The transport of radiant energy within this layer is absorbed,
It is determined by a complex process of scattering and re-emission, and the emitted energy is determined by the local temperature. Radiant energy emitted downstream from the hot section is blocked by the layer of breathable solid, so that the bulk of the radiant energy emitted from this entire layer is directed against the flow. This tendency becomes stronger as the temperature drop increases.

In order to utilize the radiant energy of the above-mentioned breathable solid, the present invention provides a breathable solid wall on the downstream side of the heat exchange device installed in the flue, and the form factor of the heat exchange device element and the breathable solid wall is It has been discovered that the heat transfer efficiency of the heat exchange device can be greatly improved by devising ways to increase the value.

The present invention will be explained below based on embodiments shown in the drawings.

FIG. 4 is a cross section showing an example of the present invention, and 1
2 is a flue wall, and 2 is an element of a heat exchange device disposed within the flue, through which air, for example, can freely flow. Reference numeral 3 indicates a permeable solid wall installed near the element 2 and on the downstream side and side of the exhaust gas flow direction in the flue, and 4 indicates the flow of combustion exhaust gas. When the downstream side of the element 2 is surrounded by the air permeable solid wall 3, the exhaust gas discharged from the combustion furnace and flowing through the flue 1 passes through the element 2 part as shown by the arrow 4 and passes through the air permeable solid wall 3. pass. Due to the above-mentioned properties of the breathable solid, the surface of the breathable solid wall 3 in contact with the exhaust gas instantaneously reaches the same temperature as the exhaust gas, and emits radiant heat in the opposite direction to the gas flow, which is received by the element 2. The air within the element 2 is heated by the exhaust gas flowing from upstream and the radiant heat from the air-permeable solid wall 3 to raise its temperature, and is used as preheating air for the burner of the combustion furnace. On the other hand, the exhaust gas that has passed through the breathable solid wall 3 has a reduced temperature and is discharged from the chimney through the damper.

Note that the elements of the heat exchange device are preferably arranged in a staggered manner in consideration of heat transfer efficiency. Further, the flue wall after the installation of the permeable solid wall 3 is different from the upstream side, and since the exhaust gas temperature is significantly lowered, the flue wall may have a simple structure, such as only an iron skin, and its diameter may be narrowed down.

FIG. 5 shows another embodiment, in which the elements 2 of the heat exchange device are arranged in multiple rows in the flue axis direction,
3 Breathable solid walls in multiple stages downstream of each row
is arranged. Every time the high-temperature exhaust gas passes through the plurality of rows of breathable solid walls 3, it generates radiant heat toward the rear (upstream side) thereof, and the heat is received by the element 2. In the structure shown in Fig. 5, the permeable solid walls 3 are installed at multiple stages in the gas flow direction.
Very efficient heat transfer.

Furthermore, FIG. 6 shows another embodiment of the present invention, in which air-permeable solid walls 3 are arranged at intervals along the axial direction of the flue, and heat is heated between the air-permeable solid walls 3. It is constructed by arranging elements 2 of a switching device in a row. In this example, the two elements on the upstream side of the air-permeable solid wall 3 are expected to receive heat through radiant heat, as in the previous example, but the elements on the downstream side are expected to receive heat from the back side of the air-permeable solid wall ( It has a cooling effect on the low temperature side). This is based on the knowledge that if the thickness of the breathable solid is set to a certain value or more, no matter how much the low temperature side is cooled, the temperature on the high temperature side will not change.

As explained above, according to the flue of the combustion furnace of the present invention, since the radiant heat of the permeable solid wall can be utilized, the heat transfer efficiency of the heat exchange device can be greatly improved, and the heat transfer area is the same as that of the conventional one. In this case, a much higher heat transfer efficiency than before can be expected, and when trying to obtain the same heat exchange rate as before, the heat exchange device can be made more compact. Furthermore, according to this invention, the temperature of high-temperature exhaust gas can be significantly lowered after passing through the permeable solid wall, which simplifies the subsequent structure of the flue wall (down material, only an iron shell without refractory lining). There is also the advantage of being able to do so.

[Brief explanation of the drawing]

Figure 1 is a model diagram to explain the principle of the breathable solid used in the present invention, Figure 2 is a schematic diagram showing the emission and attenuation process of radiation in the breathable solid layer, and Figure 3 is a diagram of the combustion heating furnace. FIGS. 4, 5, and 6 are cross-sectional views of the main parts of the flue, each showing an embodiment of the present invention. 1... Flue wall, 2... Heat exchange device (element), 3... Breathable solid wall, 4... Exhaust gas flow,
5... Heating furnace, 6... Flue, 7... Requiperator, 8... Chimney, 9... Air blow, 10...
Burna.

Claims (1)

[Scope of utility model registration request] In a flue that is connected to one end of the combustion furnace and has a heat exchanger installed in the middle, a breathable solid wall is provided downstream of the heat exchanger so that the combustion exhaust gas passes through the breathable solid wall. The flue of a combustion furnace is characterized by: