JPH0739913B2 - Honeycomb heat storage - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a large number of honeycomb-shaped streams.
The present invention relates to a heat storage body having a passage . More specifically, the present invention relates to an exhaust heat recovery system of a combustion device such as a heat storage type radiant tube burner or a heat storage type open frame burner (a direct fire type heat storage type burner). The present invention relates to a honeycomb heat storage body suitable for use in repeating a cycle (hereinafter referred to as high cycle heat storage). still,
In the present specification, the term "honeycomb shape" includes not only the original hexagonal holes but also the number of square and triangular holes. In addition, cells are used for many partition walls (cell walls).
Therefore, the flow path that penetrates the partitioned heat storage body in the longitudinal direction is defined.
To taste.

[0002]

2. Description of the Related Art In recent years, a technique for preheating combustion air has been developed in order to recover a considerable amount of heat from waste gas and improve thermal efficiency. For example, although not shown, burners each having a heat storage body are provided at both ends of the radiant tube, and these burners are alternately burned to discharge the combustion gas through the burner-side heat storage body which is not burned, and the heat storage body stores the heat. A heat storage type radiant tube burner that preheats combustion air using the heat of the generated combustion gas is provided (Industrial heating Vol. 23, NO. 6, P71 published by Japan Industrial Reactor Association).

Such alternating combustion type radiant tube
As a conventional heat storage body used in a heat storage system that uses sensible heat such as used in a burner device, a heat storage brick used in an industrial furnace such as iron making or a ceramic industry, or a metal heat storage material is generally known. It As the heat storage bricks, those having a thickness of about 6 cm are arranged in a lattice and stacked and used, and as the heat storage material made of metal, pure iron or the like having a thickness of 2 to 3 cm is used. In recent years, it has been considered to use a ceramic sphere such as an alumina ball as a heat storage body.

[0004]

However, in the case of the heat storage brick, the heat storage-heat radiation cycle of several tens of minutes to one hour is repeated, and the rate of heat input and output becomes slow, the average temperature decreases, and the thermal efficiency deteriorates. Become. That is, since the capacity of the heat storage body is large, a sufficiently long time is required for sufficient heat storage and sufficient heat dissipation. Therefore, it is not suitable for high cycle heat storage in which a heat storage-heat radiation cycle is repeated in a short time of 20 to 60 seconds. Further, in the case of the metal heat storage material, the heat storage-heat radiation cycle can be repeated in units of minutes, but it is not suitable for use with oxidizing gas such as combustion exhaust gas. Also, 1
Even in the case of a high temperature combustion gas of about 000 ° C or higher, it cannot be used due to heat resistance.

Therefore, as a result of various studies, the present inventor has considered forming a honeycomb cylindrical body having a large specific surface area by using a ceramic which is inert to combustion gas and has excellent heat resistance. Conventionally, ceramics having such a form have been used to reduce NOx in exhaust gas of automobiles .
There is a catalytic ceramic for.

However, the primary purpose of this ceramic for catalyst is to obtain a large surface area in order to support as much catalyst as possible. For this reason, the cell wall thickness of the honeycomb is made as thin as possible to make the pitch finer. Usually, it is formed thin until it reaches the limit of the manufacturing technology. However, such a configuration has a problem that ventilation resistance increases. In the case of an automobile engine having a high pressure ratio, this is not a serious problem, but in a combustion device such as a burner, an increase in pressure loss cannot be ignored, and it is unsuitable as a heat storage body for a combustion device. On the other hand, in order to reduce the ventilation resistance, if the pitch is increased and the air permeability is improved without changing the cell wall thickness, the heat storage capacity decreases. Therefore, simply diverting the automotive catalyst ceramic as a heat storage body is not suitable as a heat storage body for a combustion device. As described above, the conventional heat storage body has a compact size, a small ventilation resistance, and a reasonably large heat storage capacity and heat transfer surface area, that is, it is difficult to obtain a honeycomb heat storage body suitable as a heat storage body of a combustion device. It was

An object of the present invention is to provide a honeycomb-shaped heat storage body suitable as a heat storage body for a combustion device.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the inventors of the present invention have made various studies and found the following.
Came to.

That is, used in such an exhaust heat recovery system
A high-performance heat storage body, in other words, an optimal one
The conditions as are shown in (A) to (D) of FIG. 4, for example.
Assuming such a honeycomb heat storage body, it is as follows.
It In addition, in (A)-(D) of FIG. 4, D is a heat storage body.
Outer diameter, L is the length of the heat storage body, P is the cell pitch of the heat storage body (cell
(The distance between the vertical center of gravity and the center of gravity), T is the cell wall thickness of the heat storage body
Now, A is an empty cylinder cross-sectional area of the heat storage body. Large Vc / V, that is, heat storage in a limited volume
It has a large capacity . Compact size and large quantity
This is so that heat can be stored. Where V is heat storage
The empty cylinder volume of the body, Vc is the heat storage volume of the heat storage body (which contributes to heat storage
True volume). Large At / V, that is, transmission per unit empty cylinder volume
The hot surface area is large. The speed to store a certain amount of heat
The larger the heat transfer surface area, the faster
It becomes a high response. As a result, high cycle heat storage is realized.
Be done. This is because it is preferable that heat can flow in and out quickly. The ventilation resistance ΔP per unit empty cylinder cross-sectional area is small.
It The above conditions are triangular or hexagonal even if the cell shape is not square.
It is also valid for polygons.

[0010] Therefore, honeycomb-shaped heat storage member of the present invention, the following equation f = {(Vc / V) × (At / V) × (1 / ΔP)} = (1-β) β 3 where, beta = Opening rate of heat storage body β = (P−T) ² / P ² P = cell pitch of heat storage body (distance between center of gravity perpendicular to cell wall and cell wall)
Separation) T = P and T are set in a range in which f obtained by the cell wall thickness of the heat storage body shows a maximum value or a value in the vicinity thereof.

In the heat storage body of the present invention, P and T are
The P / T ratio is in the range of 5 to 10, more preferably about 7.5.
It is set to be.

[0012]

[Action] For example, assuming a honeycomb ceramics structure as shown in (A) and (B) in FIG. 4, in cell units
The open ratio beta of the heat storage body when considered, β = (P-T) 2 / P 2 and can Wath table. Therefore, the above-mentioned heat storage volume ratio Vc / V is Vc / V = 1-β. Also, the heat transfer surface area ratio per unit empty cylinder volume
At / V is

[Number 1] ^{At / V = 40 (P-} T) / P 2 (cm 2 / cm 3) α (P-T) / P 2 = {1 / (P-T)} β and ing. Here, since 40 is a constant, it is omitted for convenience of explanation.
I am In addition, At is a heat transfer surface area.

The pressure loss ΔP is expressed by ΔP = λ · (γ / 2g) · v ² · L / de. Here, λ: friction coefficient γ: specific weight of fluid (kg / m ³ ) v: flow velocity of fluid (m / sec) g: acceleration of gravity (9.8 m / sec ² ) de: equivalent diameter of cell (mm) Is. The flow velocity v of the fluid is v = G / 3600A _R where G: flow rate of the fluid (m ³ / H) A _R : cell cross-sectional area of the heat storage body (m ² ) cell cross-sectional area A _R of the heat storage body is A _R = expressed by βA. Also, the cell equivalent diameter de of the heat storage body is

[Equation 2] Can be expressed as Here, since 4 / π is a constant, the expression
Omitted to simplify opening. Therefore, the pressure loss ΔP
The expression is expanded as follows.

[0014] First, the reciprocal 1 / [Delta] P of the honeycomb pressure drop per unit position length

[Equation 3] Becomes Therefore , by substituting the fluid velocity v into the above equation, the reciprocal 1 / ΔP of the pressure loss of the heat storage body per unit flow rate is

(4) 1 / ΔP∝ (A _R ) ² · de = (βA) ² · de . Therefore, the reciprocal 1 / ΔP of the pressure drop of the heat storage body per unit empty cylinder cross section is

[Equation 5] 1 / ΔP ∝ β ² · de ∝ β ² (P-T) And 1 / ΔP can be expressed as β ² (P−T). still,
Equivalent diameter is a cell of one cell with arbitrary cross-sectional shape
(Channel) The diameter of a circular channel with a cross-sectional area equal to the cross-sectional area
I mean. Therefore, the equivalent diameter de is
Therefore, it will be different, and the hexagonal section shown in FIG.
In case of face,

[Equation 6] Therefore, in the case of the triangle shown in FIG.

[Equation 7] Becomes However, in either case, the constant part is
Therefore, 1 / ΔP is β ² (P−T)
Can be represented.

And, it is most suitable as a honeycomb heat storage body.
Is considered to be when all of the above three conditions are maximum.
Be done. Therefore, as an evaluation formula for evaluating the condition of the high-performance honeycomb heat storage body , f = {(Vc / V) x (At / V) x (1 / ∆P)} = (1-β) x (β / P- T) × (P−T) β ² = (1−β) β ³ is obtained. Here, as a result of calculating f with respect to the value of (P / T) (see the graph in FIG. 1), it can be seen that f shows the maximum value when P / T = 7.5. Therefore, when the value of T, that is, the cell wall thickness is determined, a pitch 7.5 times that value is optimal for the heat storage honeycomb. Also, the P / T ratio is 5
Within the range of -10, the conditions close to the optimum conditions
Obtainable.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of the present invention will be described in detail below with reference to the embodiments shown in the drawings.

[0017] shown in FIG. 4 (A) and (B) or ceramics
1 shows a schematic structure of a honeycomb-shaped heat storage body made of The honeycomb ceramics 2, characterized by the relationship between cell wall thickness T of the cell pitch P and the honeycomb of the honeycomb, as a heat storage body
Does not have any particular characteristics in the overall shape or cell shape. For example, it is limited to mainly described to Rugakore by way of example ceramic honeycomb regenerator cylindrical shape having cells 2a square in myriad longitudinal direction shown in (B) of FIG. 4 in this embodiment Not a thing. In this honeycomb ceramic, the ratio P / T of the cell pitch P and the cell wall thickness T
Is an evaluation formula of the following formula f = {(Vc / V) × (At / V) × (1 / ΔP)} = (1−β) β ³ where β = opening ratio of the heat storage body β = (P−T ) ² / P ² P = cell pitch of the heat storage body (center of gravity C, C perpendicular to the cell wall W)
(Distance between) T = P and T are set in a range where f obtained by the cell wall thickness of the heat storage body shows a maximum value or a value in the vicinity thereof. For example, in FIG. 4
As is clear from the graph of FIG. 1, which shows the result of obtaining the relationship between the cell pitch and the cell wall thickness for the honeycomb heat storage bodies of (A) and (B) , f is the maximum when P / T is 7.5. It turns out that it shows a value. Therefore, when the cell wall thickness T is determined, it is optimal for the heat storage honeycomb to have a pitch of about 7.5 times that. Also, the P / T ratio is in the range of 5 to 10.
Even when setting P and T in the
You can get something good.

On the other hand, the cell wall thickness T suitable as a honeycomb heat storage body for a combustion apparatus has an optimum maximum cell wall thickness for each switching time. For example, when the switching time is long, q increases almost proportionally as the cell wall thickness T increases. However, when the switching time is short, when the cell wall thickness T becomes a certain amount or more, q increases even further. It will not increase. This is because when the cell wall thickness T is large in a short time, the heat does not sufficiently penetrate into the interior and is not released. As is clear from FIG. 3 showing the result of calculation from the viewpoint of heat storage efficiency, it was found that there is a relationship between the switching time and the cell wall thickness as shown in Table 1 for a constant heat storage efficiency . Further , as is clear from FIG. 2 showing the heat storage capacity and the size of the heat transfer surface area with respect to the relationship between the cell pitch and the cell wall thickness, if the pressure loss is neglected, the ratio x between the cell pitch P and the cell wall thickness T When (= P / T) is about 2, both the heat storage capacity and the heat transfer surface area are maximized. However, in this case, it is not suitable for use in a system for recovering heat from exhaust gas of a combustion device such as a burner whose pressure loss cannot be ignored. Then, for example, assuming a honeycomb-shaped heat storage body that is switched for 40 seconds, a suitable cell wall thickness T is 1.6 mm to 2.4 mm, and more preferably about 1.76 mm as is clear from Table 1. Then, the preferable cell wall pitch P is 13.2 m.
m. When such cell wall thickness and cell pitch are set, the honeycomb heat storage body becomes large in a state where all of the heat storage capacity, the heat transfer surface area, and the air permeability are balanced. Further, it is considered that a cell wall thickness of 1 mm or less is not preferable as a heat storage body of a burner device as described in Example 1 described later, but it is considered that a cell wall thickness exceeding 1 mm is preferable.

[0019]

[Table 1] Relationship between cell wall thickness and switching time Switching time Thermal storage efficiency (%) (SEC) 99 98 97 97 96 20 0.8514 1.0031 1.1084 1.2012 30 1.3251 1.5356 1.6811 1.8019 40 1.7647 2.0341 2.2291 2.3839 50 2.2043 2.5139 2.7368 2.9164 6000 2.6223 2.9783 3.2353 3.4520 70 3.0031 3.4118 3.7121 3.9474 80 3.3963 3.8421 4.1734 4.4334 90 3.7771 4.2632 4.6130 4.8916

In consideration of these, there is a correlation between the cell wall thickness T of the honeycomb cerax and the switching time, and it is high if the wall thickness T is set in the range of 0.004 to 0.006 mm / sec. The heat storage efficiency can minimize the increase in ventilation resistance.

Here, as the cell shape of the honeycomb ceramics, the quadrangular shape shown in the figure can be cited as one of the preferable shapes because it is easy to manufacture, but it is not particularly limited thereto. For example, as shown in FIG.
A honeycomb heat storage body having a large number of prismatic cells 2a, and FIG.
For the triangular honeycomb heat storage body shown in (D) of
However, the above-mentioned evaluation formula is applicable. P and P in this case
And T have the relationship shown in the figure, but both are equivalent cell diameters.
Expression showing pressure loss ΔP only by different constant part in
Is the same as 1 / ΔP is represented by β ² (P−T)
Evaluation formula can be used. Further, as the honeycomb ceramic, for example, one manufactured by extrusion molding using cordierite, mullite or the like as a material can be cited as one preferable example.

Example 1 FIG. 5 shows an example of a heat storage type radiant tube burner apparatus using the honeycomb heat storage body of the present invention. This heat storage type radiant tube burner device is a radiant tube 1
A burner 3A, 3B respectively installed at both ends thereof, a heat storage body 2 provided in a burner shell 5 of each burner 3A, 3B, a burner air supply system 9 and a combustion gas exhaust gas. From a four-way valve 8 that is selectively connected to the system 10, a three-way valve 7 and a pilot burner 6 that selectively connect a fuel supply system 13 to each of the burners 3A and 3B to supply fuel to one of the burners. It is configured. Burner 3A,
3B alternately burns and discharges the combustion gas from the other unburned burner side through the heat storage body 2,
Combustion air is preheated and supplied to the burner on the burning side through the heat storage body 2.

The heat storage body 2 is for recovering and storing the sensible heat of the combustion gas that has passed through the radiant tube 1. Generally, the honeycomb is made of a material that does not react with the combustion gas or adversely affect the combustion air. It is preferable to use ceramics and the like. The heat storage body 2 has a burner gun 4 penetrating through the center thereof. The heat storage body 2 is installed upstream of the ejection port of the burner gun 4, for example, inside the burner shell 5 so as to surround the burner gun 4, or outside the burner shell 5 in some cases. Of course, the heat storage body 2 may not be housed in the burner shell 5 but may be arranged outside the burner shell 5 in a cylindrical shape. As the heat storage body 2, for example, a honeycomb body having a square hole formed by extrusion molding using cordierite, mullite, or the like as a material can be cited as one preferable example. The relationship between the cell wall thickness T and the cell wall pitch P of this honeycomb is P / T of 5 to 10,
It is preferably set to 6 to 8, and most preferably about 7.5.

A combustion air supply system 9 and a combustion gas exhaust system 10 are connected to the burner shell 5 of both burners 3A and 3B via a four-way valve 8, and the operation of the four-way valve 8 causes the combustion air supply system 9 to operate. The combustion air supplied from the forced air blower 11 is supplied to either one of the two burners 3A and 3B for combustion, and this combustion gas is stored in the heat storage body 2 of the other burner.
After that, the exhaust blower 12 is provided to attract and exhaust the air. The flow of the combustion air and the combustion gas is switched by a timer (not shown) for a certain period of time, for example, 2
It is performed every 0 seconds to 90 seconds, preferably every 20 seconds to 60 seconds, and most preferably every 40 seconds, or the temperature of the combustion gas passing through the heat storage body 2 is measured by a thermo sensor (not shown), and this is a predetermined temperature. Will be performed when.

[0025]

As is apparent from the above description, the honeycomb heat storage body of the present invention has the following formula: f = {(Vc / V) × (At / V) × (1 / ΔP)} = (1-β) Since P and T are set in a range in which f obtained by β ³ shows a maximum value or a value in the vicinity thereof, a honeycomb heat storage having a large heat storage capacity and heat transfer surface area and a small ventilation resistance
And the body can be obtained suitable regenerator.

[Brief description of drawings]

FIG. 1 f for explaining a honeycomb heat storage body of the present invention
It is a graph which shows the relationship between a value, a cell wall thickness, and a pitch.

FIG. 2 is a graph showing the relationship between cell pitch and cell wall thickness in a honeycomb for a heat storage type burner system.

FIG. 3 is a graph showing the effect of switching time on the relationship between heat storage efficiency and cell wall thickness.

[4] (A) is a perspective view showing an example of appearance of the honeycomb regenerator, (B) is an enlarged view showing the relationship between the cell walls and the cell pitch of the honeycomb regenerator rectangular cells, (C) is six Square cell
The relationship between the cell wall and the cell pitch of the honeycomb heat storage body of
(D) is a cell of a honeycomb-shaped heat storage body with triangular cells.
FIG. 7 is an enlarged view showing the relationship between the wall and the cell pitch .

FIG. 5 is a schematic diagram showing an example of an exhaust heat recovery system applied to a honeycomb heat storage body.

[Explanation of symbols]

Vertical center of gravity between the distance in 2 honeycomb regenerator P honeycomb cell pitch (cell walls
Separation) T Honeycomb cell wall thickness C Cell center of gravity W Cell wall 2a Cell

Claims (3)

[Claims] 1. In a heat storage body having a large number of honeycomb-shaped flow paths , the following expression f = {(Vc / V) × (At / V) × (1 / ΔP)} = (1-β) β ³ , Β = opening ratio of heat storage body β = (P−T) ² / P ² P = cell pitch of heat storage body (distance between center of gravity perpendicular to cell wall
Separation) T = Honeycomb-shaped heat storage body, wherein P and T are set within a range in which f obtained by the cell wall thickness of the heat storage body shows a maximum value or a value in the vicinity thereof. 2. The honeycomb heat storage body according to claim 1, wherein the P / T ratio is in the range of 5 to 10 . 3. A honeycomb regenerator according to claim 1, wherein the P / T ratio is set at about 7.5.