JPH04297708A - catalytic combustion device - Google Patents

Abstract

PURPOSE:To provide a catalyst combustion apparatus, in which a problem, in which heating efficiency is lowerd largly due to the deterioration of burning characteristics, is solved and stable heating efficiency can be maintained for a prolonged time, in the catalyst combustion apparatus used for heating, drying, etc. CONSTITUTION:The relationship of the sectional areas of communicating holes 8 in a catalyst layer 7 and thickness in the direction of a flow is set at sufficient ratios is response to each catalyst layer 7. When the sectional areas of the communicating holes 8 are represented by (s) and the thickness of the direction of the flow by (t), t/s=7(mm<-1>) or more is to be held. By this, the deterioration of burning characteristics is inhibited, and stable heating efficiency is maintained for a prolonged time, thus conducting extremely effective heating, drying, etc.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation heating type catalytic combustion device used for heating, space heating, drying, etc.

0002

[Prior Art] A so-called premix catalyst that performs flameless catalytic combustion on the surface of liquid fuel such as kerosene or gaseous fuel such as city gas that is mixed with air and then brought into contact with a catalyst for oxidation reaction. Various combustion devices have been proposed in the past, mainly for use with gaseous fuels, and some of them have been put into practical use.

0003

In catalytic combustion, fuel (for example, kerosene) premixed with air undergoes a rapid oxidation reaction in the catalyst layer, generating carbon dioxide and water vapor along with reaction heat. The catalytic reaction here is initially concentrated near the upstream surface of the catalyst layer, and the reaction heat is transferred forward by radiation from the catalyst layer through a heat ray transmitter placed opposite to the front surface. It is supplied and used for purposes such as heating and space heating. However, since the catalyst layer is concentrated in the vicinity of the upstream surface and is continuously used at high temperatures and in an oxidized state, catalyst deterioration in this vicinity tends to progress.

As a result, the catalytic activity gradually decreases on the upstream side, and at the same time the central position of the catalytic reaction shifts from the upstream side to the downstream side, the upstream surface temperature also decreases. In addition, the shift of the catalytic reaction center position downstream means that the effective thickness of the catalyst layer in the flow direction becomes shorter, and therefore the combustion characteristics of catalytic combustion (CO/CO2
, HC/CO2) gradually worsens.

[0005] Therefore, as the central position of the catalytic reaction shifts from the upstream side to the downstream side, the radiant heat that was provided to the front through the heat ray transmitting body decreases, and the heating efficiency is greatly reduced. issues, as well as combustion characteristics (CO/
There was also the problem that CO2, HC/CO2) also deteriorated.

The present invention is intended to solve the above-mentioned conventional problems, and an object thereof is to provide a catalytic combustion device that can suppress deterioration of combustion characteristics and maintain stable heating and heating efficiency for a long period of time.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a catalyst layer having a large number of communication holes provided downstream of a fuel and air mixing chamber, and a catalyst layer provided on the upstream surface of the catalyst layer. It has a heat ray transmitting body disposed facing each other and an exhaust port provided on the downstream side of the catalyst layer, and if the cross-sectional area of the communication hole in the catalyst layer is s and the thickness in the flow direction is t, then t/ s=7(m
m-1) or more.

[0008]

[Effect] In a catalytic combustion device, deterioration progresses on the upstream side of the catalyst layer, the center position of the catalytic reaction shifts from the upstream side of the catalyst layer to the downstream side, and the effective thickness of the catalyst layer in the flow direction becomes shorter. When this happens, combustion cannot be completed in the catalyst layer and a small amount of CO and HC are emitted. However, according to the present invention, since the relationship between the cross-sectional area of the communication hole of the catalyst layer and the thickness in the flow direction is set to a predetermined ratio or more, the center position of the catalytic reaction is slightly shifted from the upstream side to the downstream side. It becomes possible to maintain the combustion characteristics in a good state even if the temperature shifts to a certain extent.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a cross-sectional view of main parts showing the overall configuration of a catalytic combustion device according to an embodiment of the present invention. In the figure, 1 is a fuel tank, 2 is a fuel pump, 3 is a fan for blowing air, and 4 is a mixing chamber. An auxiliary flame port 5 is provided at the outlet of the mixing chamber 4, and an ignition electrode 6 is disposed near the auxiliary flame port 5. Above the auxiliary flame port 5, a catalyst layer 7 in which a Pt/Pd active component is supported on a honeycomb-shaped ceramic flat plate with a large number of communication holes 8 is provided upright, and the catalyst layer 7 faces the upstream surface (front surface) thereof. A heat ray transmitting body 9 is arranged. 10 is an exhaust port.

Next, to explain its operation in detail, the fuel (kerosene) supplied from the fuel pump 2 and the air supplied from the fan 3 are vaporized in the mixing chamber 4 and are sufficiently premixed to be discharged from the upper part. It is sent to the auxiliary flame outlet 5. At the time of ignition, it is first ignited by the ignition electrode 6 at the auxiliary flame port 5,
At this point, flame combustion begins. The high temperature exhaust gas flows to the upper part and raises the temperature of the catalyst layer 7. The catalyst layer 7 is burnt for a predetermined period of time.
When the temperature has risen to a sufficient temperature, the fuel supply is temporarily stopped, the flame of the auxiliary flame port 5 is extinguished, and then the fuel supply is started again. At this time, the premixture that has left the mixing chamber 4 reaches the catalyst layer 7 that stands upright above, but since the temperature here has been sufficiently raised, catalytic combustion occurs mainly on the upstream (front) surface, and It flows through the hole 8 to the downstream side (rear side). Also, the catalyst layer 7
Part of the reaction heat generated on the upstream surface of the heat ray transmitter 9 passes through the heat ray transmitter 9, and another part heats the heat ray transmitter 9 and is dissipated to the front as secondary radiation from here, causing heating. It is used for heating, heating, etc.

(Example 1) Thicknesses of 5.0 mm, 7.5 mm, and 10 mm mainly composed of silica, alumina, and titania
, 15mm honeycomb ceramics (150□mm,
400 cells/inch2, ref thickness 0.15mm) B
aO・Al2O3・CeO2 powder (specific surface area 120m2
/g) Wash coat made by adding 1000 g, 100 g of a binder with an alumina content of 10 wt%, 85 g of aluminum nitrate nonahydrate, 1300 g of water, and 5 g and 4 g of a dinitrodiammine platinum aqueous solution and a dinitrodiammine palladium aqueous solution in terms of Pt and Pd, respectively. 23g and 34g of slurry, respectively.
45g, 68g coated catalytic combustion catalyst A (t/s = approximately 4.4), B (t/s = approximately 6.7), C (t/s = approximately 8
．． 8), D (t/s=about 13.3) was used to prepare the catalyst layer 7.

(Example 2) Thickness of 7.5 mm, 10 mm, 15 mm, mainly composed of silica, alumina, and titania.
20mm honeycomb ceramics (150□mm, 3
Catalytic combustion catalyst E (t/s = approximately 5.4) coated with 30 g, 40 g, 60 g, and 80 g of washcoat slurry prepared in the same manner as in Example 1 on 00 cells/inch2, reflux thickness 0.25 mm, respectively. F(t/s=approx. 7.2
), G (t/s=about 10.8), H (t/s=about 14.
4) was used to prepare the catalyst layer 7. (Example 3) Thickness 10mm mainly composed of silica, alumina, and titania
, 15mm, 20mm honeycomb ceramics (15
0□mm, 200 cells/inch2, ref thickness 0.30
Catalytic combustion catalysts I (t/s = approximately 4.7) and J (t/s = approximately 7
．． 0), K (t/s=approximately 9.4) to prepare the catalyst layer 7.

Using the catalyst layer 7 thus obtained, a continuous life test of a catalytic combustion device using kerosene as fuel was conducted. Combustion conditions are air-fuel ratio (air/fuel) 1.8, combustion amount 2
It was set to 200kcal/h. (Table 1) Initial and 5000
The combustion characteristics after h are shown.

[0014]

[Table 1] Figures 2 and 3 are graphs of the results shown in Table 1, with Figure 2 showing the CO/CO2 characteristics and Figure 3 showing the HC/CO2 characteristics. As is clear from the figure, t/s=7(mm-1
) It can be seen that the above catalytic combustion apparatus maintains excellent combustion characteristics even after 5000 hours. On the other hand, in a catalytic combustion device using a catalyst layer with an insufficient ratio between the cross-sectional area of the communicating holes and the thickness in the flow direction, the HC/CO2
The deterioration of characteristics had become remarkable.

Regarding catalyst G, the combustion characteristics were further measured after 8000 hours. As a result, CO/CO2 (×10-5
) = 4, HC/CO2 (x10-5) = 5, which was good. However, when measuring the temperature distribution in the thickness direction of the catalyst layer 7,
As shown in Figure 4, the temperature peak position is about 2.
The temperature shifted to the downstream side by 5 mm, and the temperature on the upstream side decreased by about 70°C. This means that heating efficiency due to radiation from the surface of the catalyst layer 7 is decreasing over time.

Therefore, if the central position of combustion has shifted to the downstream side, even if the combustion characteristics of the catalyst layer 7 have not deteriorated, it is assumed that the catalyst layer 7 has reached the end of its life without being used any further. It is desirable to make a judgment and replace the catalyst layer 7 (the limit temperature for the upstream temperature to be lowered from the initial stage is determined depending on the conditions of use). It is necessary to make the ratio of the cross-sectional area of the communication hole 8 to the thickness in the flow direction sufficiently large, but as time passes, the upstream side of the catalyst layer 7 deteriorates and the surface temperature of the catalyst layer decreases. Rather than increasing the ratio of the cross-sectional area of the communicating hole 8 to the thickness in the flow direction, it is thought that setting t/s to about 7 to 12 (mm-1) is an efficient way to utilize the catalyst layer 7. It will be done.

As described above, according to the above embodiment, the catalyst layer 7
When the cross-sectional area of the communicating hole 8 is s and the thickness in the flow direction is t, by setting t/s = about 7 to 12 (mm-1), the combustion characteristics, especially the combustion characteristics during long-term continuous use, can be improved. This has the effect of improving.

[0018]

Effects of the Invention As is clear from the above embodiments, the present invention comprises a catalyst layer provided downstream of a fuel and air mixing chamber and having a large number of communication holes, and a catalyst layer that faces the upstream surface of the catalyst layer. ,
It has a heat ray transmitting body disposed and an exhaust port provided on the downstream side of the catalyst layer, where s is the cross-sectional area of the communication hole in the catalyst layer, and t is the thickness in the flow direction, t/s=7 (mm-1) or more, it is possible to suppress deterioration of combustion characteristics and perform stable heating, heating, drying, etc. for a long time.

[Brief explanation of the drawing]

[Fig. 1] A cross-sectional side view of essential parts showing the overall configuration of a catalytic combustion device in an embodiment of the present invention.

[Fig. 2] Combustion characteristics (CO/C
Characteristic diagram showing the results of measuring O2)

[Fig. 3] Combustion characteristics (HC/C
Characteristic diagram showing the results of measuring O2)

[Fig. 4] Air-fuel ratio 1.8 in the catalytic combustion device of one embodiment
, a characteristic diagram showing the temperature distribution in the thickness direction of the catalyst layer when combustion is performed at a combustion rate of 2200 kcal/h.

[Explanation of symbols]

4 Mixing chamber 7 Catalyst layer 8 Communication hole 9 Heat ray transmitter 10 Exhaust port

Claims (1)

[Claims] 1. A catalyst layer provided downstream of a fuel and air mixing chamber and having a large number of communication holes; a heat ray transmitter disposed opposite to an upstream surface of the catalyst layer; and a catalyst layer. and an exhaust port provided on the downstream side of the catalyst layer, where s is the cross-sectional area of the communication hole in the catalyst layer, and t is the thickness in the flow direction, t
A catalytic combustion device characterized in that /s=7 (mm-1) or more.