Chemical apparatus and process disinfecting – deodorizing – preser – Chemical reactor – Fluidized bed
Reexamination Certificate
1998-10-28
2001-03-06
Knode, Marian C. (Department: 1764)
Chemical apparatus and process disinfecting, deodorizing, preser
Chemical reactor
Fluidized bed
C406S173000
Reexamination Certificate
active
06197266
ABSTRACT:
FIELD OF THE INVENTION
This application is the national phase of international application PCT/BR96/00068 filed Dec. 27, 1996 which designated the U.S.
The present invention relates to a system for sealing the leg of a cyclone for separating out solids from a particulate suspension.
More specifically, the present invention presents on arrangement of valves at the ends of the legs of cyclones to promote improved sealing of the system.
More particularly, the present invention presents a system for sealing the legs of seperation cyclones which are used in fluid catalytic cracking (FCC) processes.
BACKGROUND OF THE INVENTION
In the field of separating out solid particles in gaseous suspension it is customary to use cyclones as the mechanism for separating out the suspended solids. Such cyclones normally have a valve at their ends where the solid material is discharged or, as is more well-known, at the ends of the legs of the cyclones. This valve acts as a sealing element, preventing a gaseous counterflow current towards the inside of the cyclone, which would considerably reduce its separation efficiency. On the other hand, however well the valve is designed, it is mechanically impossible for a single valve to eliminate completely the draw-back of solid particles due to the counterflow of the gaseous current in the interval between the opening and subsequent closing of the valve.
In the specific case of fluid catalytic cracking (FCC) processes, it is known that the internal pressure in the cyclone is always below the pressure of the separating vessel surrounding it, which requires the use of sealing valves at the lower end of the legs of the cyclones.
Next, a critical point, which directly influences the efficiency of the FCC process, is the seal provided by the sealing valves in the cyclone legs. As they have to operate under fairly harsh conditions, such as temperatures in excess of 500° C. and a solids charge rate of the order of 20-50 t/min, these valves do not normally provide a perfect seal, so they permit to some extent the passage of gas from the separating vessel towards the inside of the leg of the cyclone. A flow in excess of 0.5% of the total volume fed into the inlet port of the cyclone causes draw-back of the fine solid particles, which disrupts the operation of the cyclone and thereby reduces its separation efficiency.
As an alternative solution, GB-A-2,272,248 proposes the use of a deadweight valve which provides a virtually total seal through the pressure of a conical section installed between the base of the valve and the seat of the leg of the cyclone.
However, it is important to remember that a small amount of gas passing through the sealing valve, of the order of 0.01 to 0.5% of the total volume fed into the port of the cyclone, is beneficial since it causes fluidification of the solid which will have accumulated in the leg of the cyclone, which promotes its discharge.
In this way, an attempt to prevent the passage of the gas flow through the valve, as proposed by the aforementioned patent, may give rise to the loss of fluidification of the solid which has accumulated in the leg of the cyclone, principally in the second phase of separation when the charge of solids is fairly dilute, e.g. of the order of 0.2 to 7.5 grams of particulate per cubic meter of gas. Under such operating conditions the accumulation of solids, leading to a balance in pressure and resulting discharge of the solids, may require a period in excess of eight hours to effect adequate build-up and, if there is not a minimum flow of gas through the valve, the dense bed of particulates may become “packed down”, with the consequent risk of complete obstruction of the leg of the cyclone and a drop in the efficiency of the cyclone.
OBJECT OF THE INVENTION
The present invention aims to solve these problems involving draw-back of particluates during the opening cycle of the cyclone-leg sealing valve, thus maintaining the high operating efficiency of the cyclone, in a simple, inexpensive and safe manner.
It is a further object of the present invention to provide a system for sealing the legs of separation cyclones used in fluid catalytic cracking (FCC) processes which totally prevents a counterflow of gas towards the inside of the leg of the cyclone with no risk of the dense bed of particulates “packing down”.
SUMMARY Of THE INVENTION
Accordingly the present invention provides a sealing system for the leg of a cyclone for separating out solids in particulate suspension, characterized in that, at the lower end of the leg of the cyclone, there is an arrangement of two or more sealing valves mounted in series with an intermediate solids-accumulation chamber between two successive said sealing valves; in that an upper said valve is intended to promote sealing between the inside of the leg of the cyclone and the inside of the intermediate solids-accumulation chamber; and in that a lower said valve is intended to promote sealing between the inside of the intermediate solids-accumulation chamber and the inside of a separating vessel.
REFERENCES:
patent: 2901331 (1959-08-01), Held et al.
patent: 4246231 (1981-01-01), Figler et al.
patent: 4324563 (1982-04-01), Jones et al.
patent: 4362442 (1982-12-01), Bentzen-Bilkvist et al.
patent: 4871514 (1989-10-01), Ross
patent: 2 212 248 (1989-07-01), None
Cardoso De Melo Guerra Eduardo
Fusco José Mozart
Neves Vieira Valmor
Doroshenk Alexa A.
Knode Marian C.
Nixon & Vanderhye PC
Petroleo Brasileiro S. A.-Petrobras
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