JPS6133438Y2 - - Google Patents

Description

[Detailed explanation of the idea]

The present invention relates to a heat exchange device for exhaust heat recovery using a breathable solid, and particularly to a heat exchange device suitable for preventing dew condensation at the outlet of a heating fluid (primary fluid) and reducing the heat transfer area. The exhaust heat recovery heat exchanger is composed of a primary fluid as a heating fluid, a secondary fluid as a heated fluid, and a heat transfer area, and effectively transfers the sensible heat of the primary fluid flowing in at a relatively low temperature to the secondary fluid. It is something that is communicated. At this time, the temperature of the primary fluid after a certain heat transfer area is The primary fluid may reach its dew point around the heat transfer pipe near the secondary fluid inlet. The primary fluid contains S, which is harmful to heat transfer pipes, and when the dew point is reached, H ₂ SO ₄ is produced, and this SO _4-2 ion causes corrosion of heat transfer pipes. Furthermore, in order to recover primary fluid sensible heat as effectively as possible, the heat transfer area is usually designed to be maximized, and in this case, the primary fluid outlet temperature is further reduced, resulting in a repeating vicious cycle of corrosion. There is. In other words, at present, while increasing the heat transfer area for the purpose of improving thermal efficiency, preventing corrosion due to the acid dew point at the primary fluid outlet is a major issue. Corrosion has become an important design issue. The purpose of this invention is to install a breathable solid to prevent acid dew point corrosion of the primary fluid containing harmful components, which is seen in conventional equipment, and to make more effective use of the sensible heat on the outlet side of the primary fluid. It is something. The main purpose is to irradiate the primary fluid outlet sensible heat (recovered as radiant heat) recovered by this air-permeable solid installation to the secondary fluid inlet heat transfer pipe to raise the temperature of the pipe. Further objectives include improving the thermal efficiency of the entire equipment, reducing the heat transfer area, and reducing equipment costs. Note that the breathable solid wall here refers to a porous material that has good air permeability and moderate pressure loss.
There are foamed metals, sintered metals, etc., and refractory materials such as porous SiC and alumina ball composites. Before explaining the content of the present invention, we will explain the principle behind the above-mentioned air permeable solids in the well-known document "Nichisai Mechanical" 1980, 4, 14 "Improving the fuel consumption rate of furnaces by 60% using radiant energy of solids". (Mr. Ryozo Echigo) is explained below. In Figure 1, a cross section with a combustion furnace flue (X=
Consider the heat balance when a breathable solid wall is installed between X ₁ and _{X 2} ). Working gas (combustion gas) at the flue entrance (X=0)
The enthalpy of ρoCpToUo (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
becomes. On the other hand, if there is a breathable solid, it will be heated by the working gas and emitted into the surroundings as strong radiant energy. (The density of emitted radiant energy is generally much higher in solids than in gases.) Here, the optical thickness τ ₀ of the air-permeable solid layer in the flow direction is appropriately selected, and the pressure loss is not excessive. Considering this, 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 of it is directed upstream of the working gas and is absorbed by the working gas in the upstream area to heat the heated object and become effective. Available. 3. The flow resistance (pressure loss) in the breathable solid layer is on the order of several mmAq, which does not impede the operation of the furnace, but rather optimizes the flow of gas 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 size) 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 powder and granules, 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. is obtained, the surface temperature of the gas-permeable solid wall on the gas inlet side is heated almost instantaneously to near the gas temperature. Therefore, the temperature of the working gas will drop rapidly as it flows across the breathable solid. On the other hand, when there is a sharp temperature gradient in the X-axis direction as shown in Figure 2, the propagation of radiant energy within this layer only needs to be considered in the X-axis direction; It can be ignored (referred to as one-dimensional propagation approximation). The transport of radiant energy within this layer is determined by a complex process of absorption, scattering, and re-emission.
The injection energy depends on the local temperature. The radiant energy emitted downstream from the hot section is cut off by the layer of breathable solid, so that the main part of the radiant energy emitted from this entire layer is directed in the opposite direction to the flow. This tendency becomes stronger as the temperature drop increases. This invention reduces the sensible heat on the primary fluid outlet side to radiant heat by installing the above-mentioned air permeable solid on the outlet side of the exhaust heat recovery type heat exchanger, and irradiates it to the surrounding area with the secondary fluid inlet pipe. This prevents the acid dew point corrosion that was previously seen in the surrounding area. First, the configuration and functions of conventional equipment will be explained (see Figure 3). The primary fluid 1 as a heating fluid flows into the heat exchanger 2 in a wide temperature range. In some exhaust heat recovery equipment, this primary fluid 1 has a temperature range of 250 to 300°C. The primary fluid 1 that has flowed into the heat exchanger 2 exchanges heat with a heat transfer pipe 4 installed inside the heat exchanger 3. In the heat transfer pipe 4, a low boiling point fluid is used as a secondary fluid to improve thermal efficiency (for example, Freon, Therm S, etc.). The primary fluid that has undergone predetermined heat exchange reaches the heat exchanger outlet 5 and flows into the exhaust gas pipe 6. At the heat exchanger outlet 5, the secondary fluid 7 is at about 100°C.
It is sent from pipe 8 and passes through heat transfer pipe 9. Since the primary fluid 1 around the heat transfer pipe 9 has already finished releasing heat, the temperature has dropped to about 150°C. When the primary fluid in this state comes into contact with the heat transfer pipe 9 at approximately 100° C., the temperature of the primary fluid further decreases. The primary fluid 1 contains S as a harmful component, and the dew point of this fluid is about 100°C. Therefore, when the temperature of the primary fluid whose temperature has been lowered by contact with the heat transfer pipe 9 falls below 100° C., the water vapor in the primary fluid becomes saturated water vapor, and if the temperature continues further, dew condensation occurs. FIG. 4 shows the temperature drop characteristics in the counterflow type heat exchanger 2. In Figure 4, T ₁ is the primary fluid 1
T ₂ is the temperature of the primary fluid 1 at the heat exchanger outlet 5, T ₁ ' is the temperature of the secondary fluid 7 at the heat exchanger inlet heat transfer pipe 9, and
T ₂ ' indicates the temperature of the secondary fluid 7 at the heat exchanger outlet 25. In this figure, thermal efficiency (that is, temperature efficiency φ) is expressed as φT ₁ −T ₂ /T ₁ −T ₁ ′, and in order to improve this thermal efficiency, T ₂
It is important to lower the The drop in T ₂ therefore has the risk of inducing dew condensation around the heat transfer pipe 9. Therefore, while it is necessary to increase the heat transfer area (the contact area with the primary fluid 1 ensured by the heat transfer pipes 9 and 4) to increase the thermal efficiency of the equipment, this also promotes a decrease in T ₂ However, acid corrosion of the heat transfer pipe 9 due to dew condensation is promoted. The configuration of the heat exchange device of the present invention will be explained based on FIG. 5. The heat exchanger 12 in FIG. 5 is a counter-flow type having a structure similar to that in FIG. 3, and the primary fluid (heating fluid) 11 is supplied from the heat exchanger inlet, and
4 through the exhaust gas pipe 16. A heat transfer pipe 13 is provided inside the container through which the primary fluid 11 passes.
A secondary fluid (heated fluid) 17 is introduced from the inlet pipe 18, and the outlet pipe 20
is discharged from. In the present invention, in the heat exchanger described above, a permeable solid wall 15 is installed near the inlet of the heat transfer pipe 13 at the heat exchanger outlet 14. The air permeable solid wall 15 must be provided at the outlet 15, but it may also be provided at an intermediate position of the heat transfer pipe. As shown in FIG. 8, the air permeable solid wall 15 is included in the primary fluid 11 by having a structure that can be attached to and detached from the inner wall of the heat exchanger using mounting bolts 22 and a removable fixing plate 23. Equipment troubles caused by clogging due to dust etc. can be easily resolved. In addition, in the area on the heat transfer pipe 13 where dew condensation occurs most frequently, the air direction adjusting plate 21 is
5, it is possible to efficiently prevent condensation (see Fig. 7). Furthermore, as shown in FIG. 9, by dividing the breathable solid 15 into a plurality of pieces along a dividing line 24, partial replacement can be made possible. Next, the operation of the present invention will be explained. The primary fluid 11 enters the counterflow heat exchanger 12;
After exchanging heat with the heat transfer pipe 13, it reaches the heat exchanger outlet 14. Here, the gas passes through the newly installed gas permeable solid 15 and exits to the exhaust gas pipe 16. On the other hand, a secondary fluid 17 as a fluid to be heated is sent from an inlet pipe 18, passes through heat transfer pipes 19 and 13, and is supplied to the next system from an outlet pipe 20. A feature of the present invention is the installation of a breathable solid 15, whereby the sensible heat possessed by the primary fluid 11 that has reached the heat exchanger outlet 14 is converted into radiant heat, and this radiant heat heats the heat transfer pipe 19. Conventionally, therefore, the reaching of the acid dew point of the primary fluid 11 induced by this heat transfer pipe 19 is avoided. FIG. 6 shows the temperature characteristics in the case of the present invention. In this figure, T ₁ , T ₂ , T ₁ ′, and T ₂ ′ are the same as the conventional heat exchanger characteristics. T ₁ ″ indicates the temperature of the secondary fluid 17 in the heat transfer pipe 19 in the present invention. By installing the breathable solid 15, the heat transfer pipe 19
is heated, so the secondary fluid temperature rises rapidly, and T ₂ further drops to T ₂ ″. At this time, the temperature efficiency φ is φ=T ₁ −T ₂ ″/T ₁ −T ₁ ′>T ₁ − T ₂ /T
₁ - T ₁ ', which is higher than that of the conventional method. Furthermore, if we adopt the same efficiency as the conventional method,

[Table] Using the same efficiency as the method
Primary fluid outlet treatment when
The temperature T ₂ ″ at the heat exchanger outlet 14 of the primary fluid 11 can be set higher by the increase by installing the breathable solid 15 (increase =
T ₂ −T ₂ ″). This shows that it is possible to reduce the heat transfer area of the heat transfer pipe 13. As described above, according to the present invention, (1) the heat transfer area is the same as the conventional method; Then, primary fluid 1
It is possible to achieve the prevention of dew condensation (1), and it is possible to ensure an improvement in thermal efficiency. (2) If the thermal efficiency is the same as that of the conventional method, a reduction in the heat transfer area and hence a reduction in equipment costs can be achieved. Benefits such as these will be secured.

[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 within the breathable solid layer, and Figure 3 is a diagram of the conventional method for exhaust heat. A schematic side view of a recovery heat exchanger, Figure 4 is a temperature characteristic graph of a conventional heat exchanger,
Fig. 5 is a schematic side view of the present invention, Fig. 6 is a temperature characteristic graph of the present invention, Fig. 7 is a partial side view showing an example of a breathable solid body with a wind direction adjustment plate, and Fig. 8 is a structure for mounting the breathable solid body. FIG. 5 is a detailed view of the section, and FIG. 9 is a front view of the breathable solid. 11...Primary fluid, 12...Counter flow heat exchanger, 13, 19...Heat transfer pipe, 14...Heat exchanger outlet, 15...Breathable solid, 16...Exhaust gas pipe, 17...2 Next fluid, 18... Inlet pipe, 2
0...Outlet pipe, 21...Wind direction adjustment plate, 22...
...Mounting bolt, 23...fixing plate, 24...dividing line.

Claims (1)

[Scope of utility model registration request] In a heat exchange device in which a heat transfer pipe is disposed in a container body through which a heating fluid flows in one direction and a heat transfer pipe through which a heated fluid flows in a direction opposite to the flow of the heating fluid, at least A heat exchange device for waste heat recovery characterized by having a breathable solid wall arranged near the inlet of a heat pipe.