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(11) | EP 0 094 098 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | High temperature cyclone separator for gasification system |
| (57) In a cyclone separator for use in a carbonaceous material gasification system a porous
inner shell (24) is disposed in an outer shell (22) and is cooled by transpiration
of a cooling gas flowing through the inner shell (24) into the inner shell cavity
(36) into which gas containing carbonaceous particulate material is discharged through
a tangential inlet (26) for separation of the particulate material from the gas. |
[0001] This invention relates to gasification of carbonaceous materials, and more particularly to apparatus for removal of entrained particles from the product gas of fluidized bed gasification reactors.
[0002] In reactors for the gasification of carbonaceous materials, such as coal, a combustible product gas is produced, as well as solid waste products such as agglomerated ash. In an experimental Process Development Unit (PDU) fluidized bed gasification reactor being operated for the United States Government, particulate coal is injected through one of a number of concentric tubes extending upwardly into the center of a vertical bed- containing pressure vessel. Fluidization occurs in the upper sections.
[0003] In the PDU fluidized bed gasification reactor, the product gas from gasified coal contains a significant amount of entrained particles, a large percentage of which is molten at the gasifier exit temperatures of between 930°C and 1040°C, typically approximately 980°C. These particles, which are of varying chemical composition, will stick both to metallic and non-metallic surfaces regardless of the angle of incidence of the gas flow to the surface, as the gas flows from the gasifier exit. It has been demonstrated that eventually flow passages will plug with solidified material, and the efficiency of the cyclone separator will fall correspondingly.
[0004] Present information in technical papers and from experimental data obtained from PDU operations indicate that deposition of these molten particles as they exit from the gasifier will not occur if either of the two following conditions are maintained:
(a) The gas temperature does not exceed 705°C.
(b) The surfaces through which the gas passes or on which it is allowed to impact are metallic and are maintained at less than 260°C at the gas/metal interface.
[0005] Condition (a) has been achieved by water spray quench, but this method is not energy efficient for certain operations.
[0006] Condition (b) has been achieved by water cooling of an uninsulated metal plate, but erosion of the plate has been significant and the pressure differential across the plate necessitates special precautions.
[0007] It is thus the principal object of the present invention to provide gasifier systems with cyclone separators which will not have significant entrained particle deposition and which will not require a reduction in the raw gas temperature in order to permit operation over long periods without repair or maintenance work.
[0008] With this object in view, the present invention resides in a cyclone separator for separating entrained particles from a first gas, comprising an outer shell, first gas tangential inletting means for introducing said first gas into said interior plenum, axial gas discharge means for removing said first gas from said interior plenum, and particle discharge means for discharging said particles from said interior plenum, characterized in that a foraminous inner shell is disposed within said outer shell in spaced relationship therefrom so as to define a cavity between said inner shell and said outer shell, said inner shell further defining an interior plenum, and that second gas inletting means are associated with said outer shell for introducing a second gas into said cavity at a higher pressure than said first gas, said second gas being forced through foraminous inner shell into said interior plenum.
[0009] The invention will become more readily apparent from the following description, of a preferred embodiment thereof shown, by way of example only, in the accompanying drawings, in which:
Figure 1 is a cross sectional view of a cyclone separator,
Figure 2 is a plan view taken along the line 2-2 of Figure 1, and
Figures 3 and 4 show, in cross-section, wall sections of the cyclone.
[0010] A cyclone separator 20 as shown in Figures 1 and 2 comprises an outer shell 22, a porous inner shell 24 disposed within the outer shell 22, a product gas inlet 26, tangentially disposed through the outer shell 22 and the inner shell 24, a product gas outlet 28 disposed through the outer shell 22 and the inner shell 24, at the top of the cyclone separator 20, a particle outlet 30 disposed through the outer shell 22 and the inner shell 24, at the bottom of the cyclone separator 20 and a cooling gas inlet 32 disposed through the outer shell 22. A cavity 34 is formed between the inner shell 24 and the outer shell 22, and an interior plenum 36 is formed inside the inner shell 24. The porous or foraminous inner shell 24 can be made of a corrosion resistant material such as Inconel or a refractory ceramic. One embodiment may be an inherently porous material such as refractory ceramic, while another may be a metal with a plurality of holes for passage of the gas through the metal.
[0011] The cyclone separator 20 operates as follows. A gas containing entrained particles, such as the product gas from a carbonaceous material gasifier system which contains molten and solid entrained particles, enters the interior plenum 36 tangentially through the product gas inlet 26. As the gas spins around the interior plenum 36, the entrained particles impinge against the inner shell 24. Eventually the entrained particles' velocity falls and the particles fall to the bottom of the interior plenum 36, where they are discharged through the particle outlet 30.
[0012] During operation, a cooling gas, at a pressure greater (typically 0.07 kg/cm2 to 1.05 kg/cm2 greater) than the pressure of the product gas, enters the cavity 34 through the cooling gas inlet 32. This gas moves through the porous inner shell 24 by transpiration through pores or a plurality of fabricated small holes which may be directed generally downward to the center of the plenum 36 and distributed throughout the inner shell 24. The temperature of the cooling gas may be between 24°C and 66°C and typically approximately 38°C, and this gas will cool the inner shell 24 to a temperature of about 204°C.
[0013] The product gas from which a quantity of entrained particles has been removed exits the interior plenum 36 through the raw gas outlet 28.
[0014] Looking now to Figures 3 and 4, transpiration cooling involves the passage of a fluid coolant 40 through a material, by either the use in the porous inner shell 24 of numerous holes 42 or of a material with numerous pores 44. The holes 42 or pores 44 provide a very high ratio of heat transfer area to coolant flow rate. Some of the benefits resulting from the use of transpiration cooling are that 1) entrained particle deposition on the porous inner shell 24 of the cyclone separator 20 is reduced, 2) the temperature of the product gas is not significantly affected and 3) the thickness of the porous inner shell 24 may be reduced.
[0015] The use of transpiration cooling will allow the porous inner shell 24 to be at or near 204°C. As a result, very little deposition of particles will occur.
[0016] Because of the intimate contact of the fluid coolant 40 with the porous inner shell 24, a small volume of fluid coolant 40 is required to achieve the desired cooling effect. Thus the temperature of the product gas is not significantly effected since the addition of a large volume of coolant gas is not necessary.
[0017] Since the porous inner shell 24 is continuously cooled, it is not subjected to extreme thermal stresses and can be made thinner than without the cooling. This reduces the cost and complexity of fabrication, repair or replacement of the porous inner shell 24.
[0018] The specifics of hole size and hole surface density (number of holes per unit surface area of the inner shell 24), or alternatively of material porosity, must be based on the exact cooling characteristics required. Factors such as cyclone separator 20 height and diameter, product gas temperature and particle loading, fluid coolant 40 temperature and flow volume will all effect the amount of cooling capacity required. This in turn will effect the amount of heat transfer area on which the hole sizing and hole surface density, or material porosity is based.
[0019] In the preferred embodiment the fluid coolant 40 used will be product gas which has been processed by cooling and removal of substantially all the entrained particles. The advantage of this method is that there is no chemical change in the product exiting the cyclone separator 20 due to the addition of a cooling gas of another chemical composition.
1. A cyclone separator for separating entrained particles from a first gas, comprising
an outer shell (22), first gas tangential inletting means for introducing said first
gas into said interior plenum, axial gas discharge means for removing said first gas
from said interior plenum, and particle discharge means for discharging said particles
from said interior plenum, characterized in that a foraminous inner shell (24) is
disposed within said outer shell (22) in spaced relationship therefrom so as to define
a cavity (34) between said inner shell (24) and said outer shell (22), said inner
shell (24) further defining an interior plenum (36), and that second gas inletting
means (32) are associated with said outer shell (22) for introducing a second gas
into said cavity (34) at a higher pressure than said first gas, said second gas being
forced through foraminous inner shell (24) into said interior plenum (36).
2. A cyclone separator according to claim 1, characterized in that said first gas
is product gas from a carbonaceous material gasifier system and said particles are
entrained particles from said gasifier system.
3. A cyclone separator according to claim 1 or 2, characterized in that said second
gas comprises a gas at a lower temperature than said first gas.
4. A cyclone separator according to claim 1, 2 or 3, characterized in that said second
gas is a clean gas which contains substantially no particulate matter.
5. A cyclone separator according to any of claims 1 to 4, characterized in that said
second gas is the same kind of gas as said first gas.
6. A cyclone separator according to any of claims 1 to 5, characterized in that the
temperature of said first gas is between 930 and 1040°C and the temperature of said
second gas is between 24 and 66°C.
7. A cyclone separator according to any of claims 1 to 6, characterized in that the
pressure of said second gas exceeds the pressure of said first gas by between 0.07
to 1.05 kg/cm .
8. A cyclone separator according to any of claims 1 to 7, characterized in that said
foraminous material comprises a refractory ceramic material.
9. A cyclone separator according to any of claims 1 to 7, characterized in that said
inner shell has walls provided with a plurality of holes.