WO2005105307A1

WO2005105307A1 - Furnace for heat of catalysts and method of operating the furnace

Info

Publication number: WO2005105307A1
Application number: PCT/NO2005/000144
Authority: WO
Inventors: David Waller; William Clark
Original assignee: Yara International Asa
Priority date: 2004-05-03
Filing date: 2005-05-02
Publication date: 2005-11-10
Also published as: NO20041805L; NO20041805D0; NO320969B1

Abstract

Furnace for thermal treatment of a catalyst material. The furnace chamber is gas fired. It comprises means (10) for heating of a gas, arranged below a support plate (17) adapted to hold the catalyst material to be heat treated, and means for recirculation of gas within the furnace.

Description

Furnace for heat treatment of catalysts and method of operating the furnace

The invention concerns a furnace for heat treatment of catalysts and a method of operating the furnace in order to obtain strong porous metal oxide catalysts.

When designing real industrial catalysts, in the form of pellets or extrudates, an important parameter is the porosity with the catalyst. This is because, for fast and moderately fast reactions, the observed rate of the reaction may be dependant on not just the reaction between the reactant and the catalyst surface, but also by the rate at which reactants are transported into the bulk of the catalyst and products are transported to the exterior of the catalyst. To achieve control over the gas transport properties, the pore volume and pore size within the catalyst should be optimised for the particular application.

To produce a catalyst with the desired pore volume and pore size, a pore-forming material is introduced prior to for example spray drying, which is removed during the thermal treatment. The space occupied by the pore former, becomes the pore. A wide range of materials may be used as pore formers. Organic material such as starches, cellulose, and polymers are commonly used. However, inorganic materials such as ammonium nitrate may also be incorporated. The key points of the pore former are that it should be insoluble in the liquid processing media; it should create pores of the correct size; it should not leave undesirable residue after removal; it should be a low cost and readily available material.

Conventional furnaces used for catalyst production are in the simplest version a sealed metal box that is normally externally heated. In such a furnace the temperature control is poor. The system reacts slowly to an increase or decrease in temperature.

The object of the invention is to obtain a furnace by which it is possible to obtain a controlled thermal treatment of the material. It is beneficial if the thermal treatment is carried out in a conventional, low cost furnace.

These and other objects of the invention are obtained with the furnace and method as described below. The invention is further characterised by the patent claims.

The invention thus concerns a furnace for thermal treatment of a catalyst material where the furnace chamber has a lower gas inlet and an upper gas outlet and comprises means for heating of the gas. This is arranged below a support plate adapted to hold the catalyst material to be heat-treated and which directs the gas flow through the catalyst material. The furnace also contains a means for recirculation of the gas within the furnace. The inlet and outlet are equipped with valves. The furnace chamber consists of two half parts arranged vertically. It is preferred that each half part is hemispherical as vacuum may be applied to the furnace. The upper part is adapted to be lifted up and moved away from the lower part. The heating means preferably is a heater cartridge that could be electric or gas fired. The means for recirculation comprises preferably a gas recirculation fan, recirculation baffles and gas recirculation valves. The furnace has external water-cooling and a gas spreader manifold. The support plate is solid and has perforations where baskets with catalyst material is placed.

The invention also includes a method of operating the furnace where the catalyst particles containing a pore former are introduced into the furnace, the furnace closed and back filled with an inert gas with reduced oxygen concentration. The preferred gas used is nitrogen with 0.1-2 % oxygen; alternatively air is used with a high enough content of natural gas to combust oxygen till a preferred level. The gas is heated within the furnace and passes through the catalyst bed and out of the furnace so that the decomposition products of the pore former is removed. Preferably the gas is heated up to maximum 300- 400°C. Thereafter, the gas atmosphere is changed to air, the furnace is closed or partly closed and gas is allowed to flow from the upper chamber to the lower chamber and the gas is recirculated within the furnace while heating to a temperature high enough to sinter the particles, preferably 950-1000°C. Finally the catalyst particles are cooled by cold air and removed from the furnace.

The invention will be further explained with reference to the accompanying Figures 1 - 2, wherein

Figure 1 A) shows a closed furnace B) shows an open furnace C) shows a furnace with the upper part lifted away

Figure 2 A) shows a vertical section through the furnace with containers for the catalyst B) shows a detail of the base of the furnace C) shows a horizontal section of the furnace with support plate with perforations for the baskets holding the catalyst Figure 1 shows the chamber of the furnace 1 consisting of two hemispherical halves 2,3. The furnace is mounted on a hydraulic lift frame 4. Hinged "U-clamps" 5 attached to the flanges facilitate rapid locking and unlocking of the chamber. The furnace is equipped with gas distribution system 6 and a vacuum pump 7 and valve 8 . The furnace has an outlet 9 equipped with a valve (not shown on the figure). The upper half of the furnace may be lifted as shown is Figure 1 B and moved away from the lower half as shown in Figure 1 C, to give free access for loading and unloading the furnace.

Figure 2 A shows a vertical section through the furnace. The lower half contains the gas distribution system 6 and heating element cartridge 10. The heater cartridge could be electric or gas fired. All connections and feed-throughs for power, thermocouples, gas injection and the gas-recirculating fan 11 are located in the lower half of the furnace. A gas spreader manifold 12 and recirculation baffle 13 is also arranged in the lower part of the furnace to force the gas to circulate through the whole area of the catalyst bed.

Sealing of the flange14 is by one or more elastomer O-rings 15. If more than one O-ring is used, the narrow space between O-rings may be flushed with a small quantity of nitrogen to ensure no air leakage into the chamber.

Both halves of the chamber are insulated with low thermal mass ceramic fibre insulation and water-cooled on the outside to enhance rapid cool down times.

The product is contained in containers, trays or baskets 16, which are perforated at the base to allow gas transport through the bed of catalyst pellets held in them. They are placed on a support plate 17 directly above the heating element cartridge. The support plate has perforations where the baskets with catalyst is placed, allowing gas transport only through the baskets. The containers, trays or baskets could have any shape, but are shown cylindrical on the drawing. In the furnace, the trays are stacked 2-high. Figure 2 B shows a detail of the base of the furnace with an air operated gas-recirculating valve 18. These valves are also shown in Figure 2C.

Principal of Operation

Metal oxide catalyst pellets containing a pore former are loaded into heat resistant baskets 16 and placed in the furnace chamber. The chamber is closed and evacuated and back-filled with nitrogen, several times. This ensures firstly that air is removed at the beginning of the thermal treatment. It is also a check on the integrity of the O-ring seals between the two halves of the chamber. Stage 1. Removal of pore forming and organic phases

Nitrogen, containing a controlled amount of air (to give an oxygen concentration between 0.1 and 2%, depending on the stage of the thermal treatment), passes into the lower half of the chamber. The incoming gas is directed by the gas spreaders through the heater cartridge. The gas is heated by the heater cartridge and passes through the catalyst beds. The temperature of the gas is controlled, and thus the temperature of the beds is controlled. During this stage, the temperature of the gas is raised in several stages, to a maximum of 300 to 400°C. The flow of gas through the bed, firstly removes the decomposition products of the pore-forming and organic phases. Secondly, to some extent, the heat generated by the exothermic oxidation of the organic materials is transported out of the bed. This method of heating the catalyst, gives the best temperature uniformity, and the best control over the exotherm. The temperature in the catalyst beds may be controlled by a combination of both temperature and oxygen partial pressure.

Stage 2. Sintering of the catalyst

Once all the organic phases are removed from the pellets, the configuration of the furnace is changed. Firstly, the atmosphere is changed to air. The exit valve on the vent pipe 9 of the upper half of the chamber is closed (or partly closed), and the recirculation plates 17 are lifted to allow gas to flow from the upper chamber into the lower chamber, where it is heated and recirculated through the catalyst beds utilising the recirculation fan 1. A reduced flow of air may be supplied to the furnace to oxidise the residual carbon, in which case the exit valve is partly opened. Again the catalyst pellets are heated by the flow of hot gas through the beds. The temperature is raised to approximately 950 to 1000°C, to allow sintering of the pellets to take place.

Stage 3. Cooling

After sintering is complete, cold air is forced through the furnace via the gas distribution system 6 and out through the upper chamber vent pipe 9, to increase the rate of cool down of the furnace.

The above method is based on decomposing the organic phases (pore formers and processing aids) by oxidation in a reduced concentration of oxygen. The low oxygen concentration relies on passing nitrogen or an inert gas through the bed, and adding a small quantity of air to the gas feed to give the necessary oxygen concentration.

An alternative approach to reducing oxygen concentration is by consuming oxygen in a flow of air by combusting natural gas or some other hydrocarbon.

To achieve an oxygen concentration of 1% by dilution of air with an inert gas, it is necessary to dilute the air by a factor of 19 (i.e. 1 m³ of air requires 19m³ of nitrogen to produce a gas with 1% oxygen).

Using natural gas to combust air through:

2O₂ + CH₄ → CO₂ + 2H₂O

Therefore, to achieve an oxygen concentration of 1% one would require 0,095 m³ of CH₄ per 1 m³ of air. As it is difficult to control the temperature of a gas flame with so little excess air, the gas burner is only used to control the atmosphere passing through the catalyst bed. The temperature is still controlled by the heating cartridge.

Therefore, the major advantage of this second approach is that a large volume of nitrogen is not required. However, this will only work if the catalyst is not adversely affected by being exposed to CO₂ and water vapour, at the stage when the oxygen concentration needs to be controlled. Some catalysts, such as those containing lanthanum, may have problems. In which case, the nitrogen dilution route is best.

Claims

Patent claims

1. Furnace for thermal treatment of a catalyst material, characterised in that the furnace chamber has a lower gas inlet (6) and an upper gas outlet (9) and comprises means (10) for heating of a gas, arranged below a support plate (17) adapted to hold the catalyst material to be heat treated and which directs the gas flow through the catalyst material, and means (11 , 13, 18) for recirculation of gas within the furnace.

2. Furnace according to claim 1 , characterised in that both the gas inlet (6) and gas outlet (9) is equipped with valves.

3. Furnace according to claim 1 , characterised in that the furnace chamber consists of two half parts (2,3) arranged vertically.

4. Furnace according to claim 3, characterised in that each of the half parts is hemispherical.

5. Furnace according to claim 3, characterised in that the upper part is adapted to be lifted up and moved away from the lower part.

6. Furnace according to claim 1 , characterised in that the heating means is a heater cartridge (10), electric or gas fired.

7. Furnace according to claim 1 , characterised in that the means for gas recirculation comprises a gas recirculation fan (11), recirculation baffles (13) and gas recirculation valves (17).

8. Furnace according to claim 1 , characterised in that the support plate (17) is solid, and has perforations (19) where baskets (16) with catalyst is placed.

9. Furnace according to claim 1 , characterised in that the furnace has a gas spreader manifold (12).

10. Method of operating a furnace according to any of claims 1 -9 characterised in that catalyst particles containing a pore former are introduced into the furnace and the furnace closed, the furnace chamber is evacuated and back filled with an inert gas with reduced oxygen concentration, the gas is heated within the furnace and led through the catalyst bed and out of the furnace, until the decomposition products of the pore former is removed.

11. Method according to claim 10, characterised i n that the method further includes changing gas atmosphere to air, closing or partly closing exit valve and allowing gas flow from upper chamber to lower chamber and recirculating the gas while heating to a temperature high enough to sinter the particles, before finally cooling by cold air and removing the catalyst particles from the furnace

12. Method according to claim 10, characterised in that the gas is heated up to maximum of 300-400°C.

13. Method according to claim 11 , characterised in that to the gas is heated to 950- 1000°C to sinter the particles.

14. Method according to claim 10, characterised in that the gas used is nitrogen with 0.1-2% oxygen.

15. Method according to claim 10, characterised in that the gas used is air with a high enough content of natural gas to combust the oxygen in the air.