JPH08112516A - Ceramic filter and method for carrying catalyst - Google Patents

Abstract

PURPOSE: To reduce thermal shock to a ceramic filter, to prevent the breakage of the filter and to improve the reliability of the filter by carrying a TiO2 or Nb2 O5 negative catalyst for combustion on the surfaces of the pores in a ceramic porous body. CONSTITUTION: An alcoholic soln. of Nb or Ti alkoxide is prepd., a porous ceramic filter is immersed in the soln. and a TiO2 or Nb2 O5 negative catalyst for combustion is carried on the surfaces of the pores in the ceramic filter. At the time of back cleaning, unburnt carbon deposited on the surface of the filter is burned with air for back cleaning. This burning is inhibited by the catalyst, the generation of heat is suppressed and thermal shock to the filter is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic filter, and more particularly to a negative combustion catalyst-supporting ceramic filter suitable for separating dust from coal-fired combustion gas.

[0002]

2. Description of the Related Art From the viewpoint of highly efficient use of coal, a pressurized fluidized bed boiler combined cycle power plant with high power generation efficiency has been attracting attention. In a pressurized fluidized bed boiler, a high-temperature dedusting technology is required because it is a system that sends hot coal combustion gas directly to a gas turbine to generate electricity. It is possible to use a multi-stage cyclo, but since the dust collection efficiency is low, there is concern that erosion of gas turbine parts due to scattered dust will occur. In particular, if the dust collection efficiency of the cyclone decreases due to fluctuations in the amount of combustion gas, etc., there is concern that the turbine blades of the gas turbine will be damaged.

From such a viewpoint, recently, there is a document (Cera
mics Bulletin, vol.70, No.9 (1991) 1491) and Asahi Glass Research Report (vol.42, No.1 (1992) 81), ceramic filters capable of high temperature and high efficiency dedusting have attracted attention. ing. This is cordierite, alumina, mullite, S
A filtration layer having micropores of micron to submicron order is provided on the surface of a porous body such as iC. The fine holes provide high dust collection efficiency and solve the problem of gas turbine erosion.

However, the ceramic filter has a problem that it is weak in thermal shock and is easily damaged. In particular, when unburned solid carbon, which is likely to be generated during startup or when operating conditions are changed, is deposited on the filter, the unburned carbon is burned by the air during backwashing and the temperature rises rapidly, causing thermal shock to the ceramic filter. May result in damage.

[0005]

The problem to be solved by the present invention is to alleviate the thermal shock of the ceramics filter. This is intended to prevent damage to the ceramic filter and improve reliability of the ceramic filter.

[0006]

[Means for Solving the Problems] The above problems are caused by TiO ₂
Alternatively, it can be solved by supporting a combustion negative catalyst made of Nb ₂ O ₅ on the ceramic filter layer.

[0007]

[Function] The thermal shock that a high temperature member receives during use causes the growth of minute defects such as cracks and pores existing in the member.
It reduces strength and often destroys parts. In order to prevent this destruction, it is sufficient to reduce the thermal shock received by the member. The thermal shock of the porous ceramics filter for a pressurized fluidized bed boiler is particularly large during backwashing. This is because unburned carbon deposited on the filter surface is burned by backwashing air and the temperature rises rapidly. If the combustion of the deposited carbon on the filter can be suppressed, the generation of heat can be suppressed and the thermal shock received by the filter can be mitigated.

When TiO ₂ and Nb ₂ O ₅ are carried on the filtration surface of the porous ceramic filter, they have a negative catalytic effect on the combustion of carbon, and the combustion of unburned carbon deposited on the filter during air backwashing is carried out. As a result, the temperature rise of the ceramic filter can be prevented from rising rapidly.

[0009]

EXAMPLES A pressurized fluidized bed boiler combined cycle power plant supplies coal combustion gas generated in a pressurized fluidized bed to a gas turbine and rotates the gas turbine to generate electricity. The coal combustion gas in the pressurized fluidized bed has a high temperature of about 800 ° C. and contains a large amount of dust such as several hundred mg / Nm ³ . When coal combustion gas containing dust is sent to the turbine, gas turbine parts are severely eroded. Therefore, it is necessary to remove dust at high temperature and high efficiency.

As a dust removing method, a cyclone or the like has been examined as a candidate, but the dust removing efficiency is not sufficient. The ceramics filter has high dust removal efficiency and is a promising method for removing dust from combined power generation coal bed boiler combined power generation. Although cordierite, alumina, mullite, SiC, etc. have been studied as the material of the ceramics filter, cordierite having a small coefficient of thermal expansion is most preferable as the filter material for the pressurized fluidized bed.

When a ceramics filter is used to remove dust, dust accumulates on the filter surface during filtration. If the dust accumulates on the surface of the filter, the differential pressure increases, so it is necessary to periodically remove the accumulated dust from the surface. This is done by instantaneously supplying air from the opposite direction once every few minutes.

The unburned carbon content in the accumulated dust is very small during normal load operation, but increases during start-up or load change. When dust containing a large amount of unburned carbon is deposited on the filter, when backwashing air is supplied, the unburned carbon rapidly burns and the surface temperature of the filter is about 800 ° C, which is the normal operating temperature in a short time. To about 1200 ° C.

Due to the rapid rise of the surface temperature, thermal shock is generated in the ceramics filter. When this is repeated, minute defects in the ceramic filter or internal defects such as pores grow and become large cracks, resulting in deterioration of the strength of the filter or destruction. In order to prevent mechanical deterioration such as breakage, it is only necessary to reduce the temperature difference that the members receive and reduce the thermal shock.

When a ceramics filter is used for dust separation for a pressurized fluidized bed boiler combined cycle power plant, thermal shock is caused by rapid combustion of unburned carbon deposited on the surface of the ceramics filter during backwashing. Therefore, if the combustion of the accumulated unburned carbon on the filter during backwashing can be suppressed, the thermal shock received by the filter can be alleviated by suppressing the amount of heat generated.

Example 1 Graphite is an example of solid carbon, and α-Al ₂ O is an example of a ceramic filter material.
₃ (average particle size 0.6 μm), solid carbon combustion negative catalyst candidate materials BaO (average particle size 0.3 μm), MgO (average particle size 0.7 μm), Nb ₂ O ₅ (average particle size 0.6 μm) , SiO
₂ (average particle size 0.4 μm) and TiO ₂ (average particle size 0.6
μm) was selected and the solid carbon combustion catalytic activity of these candidates was investigated.

Α-Al ₂ O for 60 mol% of graphite
30 mol% of _{3 and} 10 mol% of the candidate material were mixed, and the mixed powder was subjected to thermal analysis using a differential thermal analyzer (DTA), and the weight loss starting point was defined as the combustion starting temperature. Activity of the negative catalyst, a combustion start temperature of the mixed powder of graphite + α-Al ₂ O _3, qualitatively defined by the difference between the combustion start temperature of the mixed powder of the catalyst + graphite + α-Al ₂ O _3. The larger this value in the negative side, the greater the solid carbon combustion negative catalyst activity of the catalyst.

When the combustion starting temperature of only graphite was first measured, the combustion starting temperature was 630 ° C. The combustion starting temperature of the mixed powder of graphite and α-Al ₂ O ₃ was 573 ° C. Compared with the combustion start temperature of graphite alone, the solid carbon combustion catalytic activity of α-Al ₂ O ₃ is 5
It was 7 ° C. α-Al ₂ O ₃ has a solid carbon combustion catalytic effect and may promote combustion of deposited carbon during backwashing and increase thermal shock on the filter.

Subsequently, the candidate materials BaO, MgO, Nb ₂
O ₅ , SiO ₂ and TiO ₂ are mixed with graphite and α-Al ₂
The negative catalyst activity of these candidate materials was measured by mixing with O ₃ . The results are shown in Table 1.

[0019]

[Table 1]

When the combustion catalyst candidate materials are added, the catalytic activity has a negative value, so it is understood that all of these candidate materials have a negative combustion catalytic action. But Ba
The negative catalytic activity of O, MgO, and SiO ₂ is low, and TiO ₂
And that of Nb ₂ O ₅ is high. Therefore, TiO ₂ and Nb ₂ O ₅ are preferable as the solid carbon combustion negative catalyst.

Example 2 To 100 parts by weight of crystallized cordierite powder having an average particle diameter of 1 μm, 300 parts by weight of ethyl alcohol and 3 parts by weight of polyvinyl butyral as a binder were added and mixed in a ball mill for 24 hours. The obtained slurry was spray granulated with a spray dryer to obtain granulated powder. The granulated powder was molded with a mold, calcined at 800 ° C. for 2 hours, and then sintered at 1300 ° C. for 30 minutes to obtain a porous ceramics sintered body having a porosity of 15%. The cordierite porous impregnated with _{Ti (OCH (CH 3) 2} ) 4 5wt% ethyl alcohol solution was heated to ethyl alcohol solution is evaporated. Then, it was fired at 1000 ° C. for 1 hour to obtain a TiO ₂ catalyst-supporting ceramic filter.
The surface of the obtained ceramic filter is TEM and SEM.
/ EDM was used for observation and analysis. TiO ₂ having an average particle size of about 0.35 μm was dispersed on the surface. This confirmed that the TiO ₂ carbon combustion negative catalyst was carried on the surface of the cordierite filter.

The TiO ₂ negative catalyst-supported cordierite porous sintered body thus obtained was incorporated as a ceramics filter into a small simulated tester, and a dusting test was conducted while measuring the surface temperature. Average surface temperature during normal operation is 805
However, the surface temperature rose to a maximum of 984 ° C during backwashing. After repeating the cycle of normal operation → backwashing → normal operation 100 times, a part of the TiO ₂ negative catalyst-carrying filter tested was cut out and the strength was evaluated. The 4-point bending strength decreased from 90 MPa before the cycle to 83 MPa, and a strength decrease of about 10% was observed. After 1000 cycles, the ceramic filter was not damaged and the 4-point bending strength was 81 MPa.
Met.

As a comparative example, a dust removal experiment was conducted while measuring the surface temperature by incorporating a cordierite porous sintered body having no porosity of 15% as a filter into a small-sized test apparatus. The surface temperature of the filter during normal operation was 807 ° C on average, but the maximum surface temperature was 12 when backwashing.
Raised to 15 ° C. After repeating the cycle of normal operation → backwash → normal operation 100 times, a part of the cordierite filter tested was cut out and the strength was evaluated. 4-point bending strength decreased from 90 MPa before cycle to 75 MPa, about 1
A strength decrease of 7% is observed. After 1,000 cycles, the 4-point bending strength decreased to 58 MPa, and a strength decrease of about 36% was observed.

Example 3 α-Al _{2 having} an average particle size of 1 μm
A slurry was prepared by mixing 3 parts by weight of polyvinyl butyral as a binder and 300 parts by weight of ethyl alcohol with 100 parts by weight of O ₃ powder for 24 hours using a ball mill. Then, this slurry was spray-granulated with a spray dryer to obtain α-Al ₂ O ₃ granulated powder. This granulated powder is molded into a mold, calcined at 800 ° C for 2 hours, and then at 1300 ° C for 3 hours.
After sintering for 0 minutes, a sintered body having a porosity of about 20% was obtained. This α
10 ml of Nb (OC ₃ H ₅ ) ₅ 5 wt% ethyl alcohol solution was sprayed per 1 cm ³ of surface area on the porous surface of Al ₂ O ₃ and dried at 200 ° C. for 5 hours in a dryer. Then 1
It was fired at 000 ° C. for 1 hour to obtain a Nb ₂ O ₅ catalyst-supported ceramic filter.

The surface of the porous sintered body thus obtained was observed and analyzed using TEM and SEM / EDM. Nb ₂ O ₅ having an average particle size of about 0.27 μm was dispersed on the surface. This confirmed that the Nb ₂ O ₅ carbon burning negative catalyst was carried on the surface of the α-Al ₂ O ₃ porous sintered body.

The thus obtained Nb ₂ O ₅ negative catalyst-supported α-
The Al ₂ O ₃ porous sintered body was incorporated as a ceramic filter in a small-sized simulated test device, and a dust removal experiment was conducted while measuring the surface temperature. The surface temperature during normal operation was 805 ° C on average, but the surface temperature rose to a maximum of 984 ° C during backwashing. After repeating the cycle of normal operation → backwash → normal operation 100 times, a part of the Nb ₂ O ₅ negative catalyst-carrying filter tested was cut out and the strength was evaluated. The 4-point bending strength decreased from 90 MPa before the cycle to 83 MPa, and a strength decrease of about 10% was observed. After 1,000 cycles, the ceramic filter was not damaged, and the 4-point bending strength was 81 MPa.

As a comparative example, when an α-Al ₂ O ₃ porous sintered body having a porosity of 15% which does not carry a catalyst was tested as a filter, the four-point bending strength was 71MP after 100 cycles.
In a, it decreased to 60 MPa after 1,000 cycles.

[0028]

EFFECTS OF THE INVENTION The carbon burning negative catalyst supporting ceramic filter of the present invention suppresses rapid combustion of dust containing solid carbon deposited on the filter at the time of backwashing and can reduce thermal shock. Due to this effect, strength deterioration can be reduced when the carbon burning negative catalyst-supporting ceramics filter of the present invention is used for separating dust from coal-fired combustion gas.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the number of thermal shock cycles by backwashing and the 4-point bending strength of a filter.

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location B01J 23/20 A 37/02 301 M

Claims (3)

[Claims] 1. A ceramic filter characterized in that a TiO ₂ or Nb ₂ O ₅ combustion negative catalyst is carried on the surface of pores of a ceramic porous body. 2. The method for supporting a catalyst according to claim 1, wherein an alcohol solution of an alkoxide of Nb or Ti is prepared, a porous ceramic filter is immersed in the alcohol solution, and then the mixture is combusted. 3. A method of supporting a catalyst according to claim 1, wherein an alcohol solution of Nb or Ti alkoxide is prepared, sprayed on the filtration surface of the porous ceramic filter, and then calcined.