Drying and gas or vapor contact with solids – Apparatus – With means to treat gas or vapor
Reexamination Certificate
2001-06-01
2003-03-04
Esquivel, Denise L. (Department: 3749)
Drying and gas or vapor contact with solids
Apparatus
With means to treat gas or vapor
C034S074000, C034S130000, C096S125000, C096S130000
Reexamination Certificate
active
06526674
ABSTRACT:
The present invention relates to a gas dryer which includes a drying drum containing an adsorbent material, and, in particular, to such a dryer in which a primary gas is dried using the adsorbent material and in which a secondary gas is used to regenerate the adsorbent material.
A drum dryer which can be used in a compressed gas system comprises a housing and a quantity of an adsorbent material within the housing by which fluid in the gas to be dried (the primary gas flow) can be adsorbed. The fluid can be aqueous (especially water) or non-aqueous. It will generally be entrained in the primary gas flow in gaseous form (for example as a vapour), although it can be entrained in liquid form (for example as droplets). The adsorbent material can be regenerated for reuse by means of a secondary gas flow which is supplied to the drum to flow over the adsorbent material which is loaded with adsorbed fluid (generally liquid). The secondary gas flow is usually in the opposite direction to the primary gas flow. Such dryers are particularly used in compressed air processes as dehumidifiers to remove vapour from a compressed gas stream which has been cooled after compression stages. The secondary gas flow which is used to regenerate the adsorbent material can be compressed air at elevated temperature as a result of the compression stage, which is fed through the adsorbent material so as to regenerate it.
An example of a drum dryer is disclosed in U.S. Pat. No. 5,385,603, in which an adsorbent material is arranged in on the surface of a cylindrical drum which is arranged to rotate around its longitudinal axis. The adsorbent material can be define a plurality of parallel channels for gas to flow over the surface of the drum, in a direction that is parallel to the drum axis. The drum and the housing between them can provide partitions by which the housing can be divided into different regions for gas to flow through the drum. One of the regions can be for the primary gas flow in which the adsorbent material adsorbs entrained fluid, and the other of the regions can be for the countercurrent secondary gas flow, which is used to regenerate the adsorbent material by desorbing adsorbed fluid. The drum is driven rotationally by a motor positioned at one end of the axis of rotation. The axis is only supported transversely at the end from which it is driven. The dryer has a system of seals located around the periphery of the drum between the drum and the housing, to keep the primary and secondary gas flows separate. Frictional forces between the drum and the housing can place significant load on the motor by which the drum is made to rotate.
The present invention provides a gas dryer in which gas is introduced into the dryer housing into the space between the internal wall of the housing and the external surface of the drum, to flow in that space to the drum gas inlet.
Accordingly, in one aspect, the invention provides a gas dryer comprising a drying drum which is arranged for a gas to flow through it to be dried from a first end of the drum to its opposite second end, a housing in which the drum is located with a space around the drum between the internal wall of the housing and the external surface of the drum, and a housing inlet for the gas to be dried through which gas can be directed into the said space, to flow in the space to the first end of the drum where it can be admitted into the drum for drying.
The dryer of the invention has the advantage that the flow of the gas in the space between the housing and the drum can provide primary separation of liquid that is entrained to flow with the gas prior to admission of the gas into the drum. This enables the separated liquid to be collected before the gas is admitted to the drum and has the advantage that the adsorbent material in the drum is not exposed to the liquid. Separation is enabled as a result of the surface area that is provided on the housing wall for collection (including condensation) of entrained liquid and vapour. This primary separation facilitates regeneration of the adsorbent material in the drum.
Preferably, the inlet for the gas that is to be treated, and the path that the gas flows along between the inlet and being admitted to the drying drum is such that the gas flows in a generally tangential direction relative to the drum axis. This increases the length of the path along which the gas flows. The centripetal forces to which the gas and any entrained liquid are exposed during tangential flow around the dryer drum encourages primary separation of any entrained liquid from the primary gas flow. Preferably, the inlet is configured to direct the gas into the space for substantially tangential flow, rather than being directed straight at the surface of the drum in the housing. For example, the inlet can be formed as a port in the wall of the housing with the axis of the port arranged generally tangentially with respect to the annular space between the housing and the drum.
Preferably, the cross-section of at least one, especially both, of the drum and the housing is substantially circular. This has the advantage of encouraging smooth flow of the gas in the annular space. It is particularly preferred that the cross-section of the annular space be substantially constant around the dryer. Smooth tangential flow of gas in the space between the housing and the dryer can encourage separation of the gas and liquid entrained therewith. A preferred drying drum has a circular cylindrical shape.
An advantage of introducing the gas that is to be treated into the space between the drum and the housing is that it the pressure of the gas can be reduced as it enters the space. This can give rise to a reduction in the temperature of the gas. This can facilitate condensation of any vapour that is present in the gas flow, which can then separate from the gas flow. It can be preferred for the gas to enter the space through an injector so that there is a localised reduction in gas pressure at the housing inlet. The reduced pressure in the space and the resulting reduction in gas flow velocity ensures that reentrainment of deposited liquid is minimised.
Preferably, the external surface of the drum is provided by a metal jacket. This can facilitate loss of heat from the dryer, in turn facilitating condensation of liquid from the gas that is to be treated as it flows in the annular space between the drum and the housing.
Preferably, the ratio of the distance from the inlet to the first end of the drum to the overall length of the drum is at least about 0.25, preferably at least about 0.45.
The dryer will generally include a drain through which collected liquid can drain from the housing. Preferably, the drain is located towards the first end of the drum, and includes a partition at the first end of the drum which defines a primary gas chamber that communicates with the primary region of the drum, and a secondary gas chamber that communicates with the secondary region of the drum, the dryer including a seal by which a pressure differential between the primary and secondary gas chambers can be substantially maintained. A suitable seal might be provided by two sealing surfaces in moving contact with one another, for example in the form of a bearing seal.
In another aspect, the invention provides a dryer in which the drying drum has a primary region for the primary gas to flow through it in which liquid in the gas is adsorbed by the drum as it flows from a first end of the drum to its opposite second end, and a secondary region for a secondary gas to flow through to regenerate the drum by displacing adsorbed liquid, the drum including a drain at a first end of the housing for removing liquid from the housing, and a partition at the first end of the drum which defines a primary gas chamber that communicates with the primary region of the drum, and a secondary gas chamber that communicates with the secondary region of the drum, the dryer including a liquid trap into which liquid in the primary chamber drains, the partition extending into the trap so that, wh
Billiet Colin Thomas
Fielding Robert Michael
Sienack Desideratus Julius
Domnick Hunter Limited
Esquivel Denise L.
Maginot Moore & Bowman
O'Malley Kathryn S.
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