|Title of Invention||
"DIRECTIONAL NOZZLE AIR DISTRIBUTOR FOR FLUIDIZED BED"
|Abstract||The invention relates to improved air distributor for fluidized bed wherein a directional nozzle air distributor (15) for fluidized bed operation wherein a multiplicity of directional air nozzles (7 A) are welded on the bed plate (3) in several directions (13) to achieve directional air flow, the top end of the nozzle (7A) being bent at an angle (8) with respect to the base plate (3), the bend angle (8) lying between 95° and 130°, the bent outer surface of the nozzle being provided with hard facing (6) to reduce erosion, said nozzles (7A) being welded in rows (12) on the bed plate (3) so that the rows are offset from one another and the pitch (11) between the nozzles being maintained between 50 mm and 200 mm.|
|Full Text||Background and Prior Art:
A directional nozzle air distributor for fluidized bed in order to achieve maximum heat transfer in combustion, or for oxidation or drying in a chemical processes. The fluidized bed basically consists of a perforated metal plate called bed on which bed material such as crushed refractory or sand or similar suitable material is placed. A fluid, which is hot air, is then pushed through the perforations by means of an air distributor.
In the existing practice, "bubble cap air distributor" is employed. In this, numerous short pipes are welded on the perforations on the bed. These pipes are sealed on top and have holes on their surface near the top. The hot air is forced through these holes to mix with the bed material. This is termed fluidization.
This practice however has some severe drawbacks, notably -
i) Each bubble cap air nozzle has several orifices to create the required air pressure drop, which is essential to achieve good fluidization across the entire area. Radial drilling of these orifices on the nozzle demands very elaborate and accurate manufacturing process which imparts high cost to the product.
ii) The material of these nozzles being alloys of special steel or stainless steel, close drilling of holes leads to increased failure, which makes the manufacture very slow besides further pushing up the cost.
iii) As the hot air delivery is from top end of the nozzle, it becomes difficult to activate the large sized particles which tend to settle towards the bottom. These particles ultimately render fluidization ineffective.
The present invention overcomes the above disadvantages of the prior art.
Description and objects of invention;
The present invention uses a novel directional air delivery nozzle which does not have any holes on the body and yet achieves desired fluidization. The cost of manufacture as well as time taken to manufacture go remarkably down.
Objects of the invention:
According to one objective of the present invention there is provided an improved air distributor in the fluidized bed for uniform distribution of air to achieve good mixing of the bed particles to improve bed reactivity.
A further objective of the invention is to promote uniform heat transfer over the entire cross section of the fluidized bed which is normally not achieved in the prior art.
Yet another objective of the present invention is to dispense with the onerous task of drilling multiple orifices on each of the numerous air distribution nozzles to make their manufacture cheaper and quicker.
Yet another objective is to direct the larger bed particles towards the ash drain point so that clogging of wind box and defluidization is avoided.
According to the present invention there is provided a directional nozzle air distributor for fluidized bed wherein a multiolicity of directional air nozzles are welded on the bedplate in several directions to
achieve directional airflow, the top end of the nozzle being bent at an
angle with respect to the bottom cotton plate, the bend angle lying between
95° and 130°, the bent outer surface of the nozzle being provided with hard
facing to reduce erosion, said nozzles being welded in rows on the plate
so that the rows are offset from one another and the pitch between the
nozzles being maintained between 40 mm and 120 mm.
The invention will now be described with reference to the following accompanying drawings, which depict one embodiment of the invention, and is not limiting in which -
Figure 1 shows a typical bubble cap nozzle as per prior art. Figure 2 shows the directional nozzle as per invention.
Figure 3 shows the plan of the distributor plate with directional nozzles fitted.
The bubble cap nozzle (1A) has small perforations (1) drilled on the circumference. The first row of holes are drilled at sufficient height from the bottom plate (3X to retain bed material (4) so as to insulate the nozzle from "the hot temperature prevailing during combustion. The total height (2) of the nozzle is in the range 250-300 mm.
The directional air nozzle (7A) as per invention is made of pipe (7)
the top end of which is_bent at an angle (8) between 95° and 130° to the
bottom with bottom plate (3). This ensures that the bed material
particles do riot enter back through the nozzle tip during shut down. Particles upto 6.0 mm in diameter are particularly susceptible to this back-flow. The outlet bend angle of the invention nozzle eliminates the possibility of reverse flow of the bed material to the wind box.
The inner diameter (9) the invented nozzle is vital in determination of the velocity of the air which must be right to achieve good fluidization across entire cross section of the fluidized bed.
The air nozzle material (10) has to withstand high temperature during fluidization and should not itself react with the Usually special alloy steels or special grade stainless steel is used for this. The height (5) of the nozzle tip from the bottom plate (3) is also critical in ensuring proper fluidization. The height (5) lies in the range 50 mm -300 mm. A plurality of nozzles (7A) are fixed on the distributor plate (15) in different directions (13) and with varying pitch (11). Since they are installed in close proximity, each is affected by the high velocity hot air discharge from the neighbouring nozzles. The bent portion of the nozzle is affected most. To protect the nozzle from erosion and increase nozzle life, hard surfacing (6) is provided on the outer surface of the bent top of every nozzle.
The nozzles (7A) are welded on to the distributor plate (15) with a pitch (11) which varies between 40 mm and 120 mm. The nozzles are mounted in rows (12) which are offset in such a way that the discharge of one row is not directed on to the adjacent row to minimize erosion.
Further, the direction (13) of all the nozzles is oriented towards the ash drain point (14) to direct the larger and heavier particles towards the drain point. This feature of the invention reduces the chance of defluidization due to accumulation of particles and clogging.
1. A directional nozzle air distributor (15) for fluidized bed wherein a multiplicity of directional air nozzles (7A) are welded on the be~1 plate (3) in several directions (13) to achieve directional air flow, the top end of the nozzle (7A) being bent at an angle (8) with respect to the bIs~ plate (3k, the bend angie (8) lying between 9~ and 1300 the bent uter surface of the nozzle being provided with hard facing (6) to reduce er0sion, said nozzles (7A) being welded in rows (12) on the~' plate
so tIiat the rows are offset from one anothet and the pitcbXl 1) between the nozzles. being maintained betw~eti mm and 200 mm
2. A directional nozzle air distributor (15) as claimed in Claim 1 wherein the material (10) of the nozzle (7A) is either alloy steel or special stainless steel to withstand very high temperature.
A directional nozzle air distributor (15) as claimed in ('1dm 1 wherein the height (5) of the lower tip of nozzle (7A) from the bottom plate (3) is in the range between 50 mm and 300 mm.
4. A directional nozzle air distributor for fluidized bed
hereinbefore described and illustrated in the accompanying drawings.
|Indian Patent Application Number||55/DEL/2001|
|PG Journal Number||17/2008|
|Date of Filing||23-Jan-2001|
|Name of Patentee||BHARAT HEAVY ELECTRICALS LIMITED|
|Applicant Address||BHEL HOUSE SIRI FORT, NEW DELHI 110049, INDIA.|
|PCT International Classification Number||F23C 10/00|
|PCT International Application Number||N/A|
|PCT International Filing date|