Note: Descriptions are shown in the official language in which they were submitted.
CA 02203533 1997-04-23
WO 96/14917 PCT/GB95/02624
P~FSSURE AND Tl~MPERATUT~F SWrNG ADSORPTION AND T~ PERATURE
SWING ~DSORPTION.
The present invention relates to a method of sep~d~ g cornponents from a gaseous mixture
by use of temperature swing adsorption and, more particularly, ples~ule and temperature
swing adsorption. and to an improved method and ~p~dllls for enabling regeneration of
adsorbent m~tt?ri~l.s in one or more beds for use in gas filtration. Particularly the present
invention is concerned with filtering volatile cont~min~nt.s from oxygen and/or nitrogen
co~ i"g gas mixtures such as air.
Pressure swing adsorption processes are suited to air sep~d~ions involving light gases~ but
not those involving high boiling point components which are strongly adsorbed to the filter
bed (see applicant's copending application reference UK 94 22833.5). This limitation can be
overcome by using a combination of ~ule~u~c; and tenl~;ldlule swing, as provided using a
S:~Ule and tt:lllp~ldLu,e swing adsorber (PTSA) bed, using an a~roplldle adsorbent
inventory. where the temperature swing serves to desorb the high boiling point collll~ol~lll~.
The use of a combined pressure and tell,p~ u~e adsorption stage will minimi.~e the size of
the filter bed. A temperature swing adsorption system is however feasible when power and
other limitations prevent the use of a colllpl~s~or device. A filter bed based on lelnl.e~dLu~e
swing adsorption (TSA) alone will however be larger than one based on a combination of
~l~s~e and t~ d~
The present hlvt;lllC~li have rletPrmin~cl that heating systems to be employed in a PTSA bed
or TSA bed for use in such method should possess most or all of the following
characteristics: compactness to allow ,nin;...~l size of adsorber bed; non-intrusiveness in the
bed interior giving it the ability to be snow-storm filled; axial positioning to enable layered
adsorbents to be used in a single bed whilst preventing fluidisation; intrinsic safety for
prevention of bed ovPrhP~ting and therm~l ageing; the ability l:o heat and cool in consi~tçnt
and reproducible manner to give long term stability;
CA 02203533 1997-04-23
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low thermal mass allowing rapid and efficient heating and cooling- efficient andhomogeneous axial and radial. transfer to minimi~e regeneration period such as to generate a
rectangular heating and cooling profile and economical power consumption allowing
flexible deployment of the system in mobile equipments.
There are a number of methods available for generating the telnl)eldlul~ swing but many of
these suffer from one or more limitations. Fx~mples of methods excluded from practical
study include microwave systems and direct electrical heating of the adsorber bed.
Microwave systems would require a generator and waveguide and would heat the bed in a
highly localised fashion. j~tt?ri~l.c of construction, including the adsorber beds and the
adsorbents would be limited by the constraints associated with the use of microwaves
resulting in the risk of thermal degradation and combustion of the adsorbents being high.
Heat transfer within the bed would rely on h~ ,d"icle conduction and would therefore be
inefficient.
Direct electrical heating would suffer from some of the above limitations including
combustion hazards associated with the use of live electrical currents, including current
leakage, and the need for stringent electrical isolation of the adsorber beds would increase
the complexity of the equipment. In addition the use of this system would limit the choice of
adsorbent.
Although both techniques are non-intrusive their use would constrain adsorbent choice. The
present inventors have now provided a method for heating such PTSA beds that allows use
of commercially available heaters and does not limit the adsorbent in this manner.
Thus in a first aspect of the present invention there is provided a method of heating a
prt;S~Ulc: and telllpt;ldLule swing adsorption gas filtration bed unit, or tellll~eldlule swing
adsorption gas filtration bed unit, compri~inp locating a heating means within the bed
housing characterised in that the heating means acts to heat gas passing into the bed or a
layer thereof in the purge direction and uses the heated air to heat the adsorbent material.
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The purge direction will be understood to be the direction of gas flow used when the bed is
being regenerated and will conventionally be counter to the flow direction when the bed is
being used to separate cont~min~nt or other components desired to be separated from a gas
to be treated.
In a l~lcÇ~ d embodiment of this aspect of the present invention the method employs a
number of layers of adsorbent m~terial within the filtration bed housing and positions a
heating means U~ ,dlll, with respect to the purge flow direction, of each of these layers.
Most preferably the heating means are used to separate different adsorbent layers positioned
within a single plcs~ufe and temperature swing adsorber bed unit, or lenlpcldLulc swing
adsorber bed unit, such as the multilayer bed units that are the subject matter of the
applicant's copending application UK 94 22833.5).
In this manner the ~ ucld~llre selected for regeneration of a particular adsorbent material
may be m~tchPcl more closely to its particular characteristics, particularly with regard to its
thPrm~i degradation characteristics and the amount of heat required to purge a particular
colllpol1ent from a particular layer at a given ~llCS:iUlC.
.
Particularly ~rcf~llcd heaters for the purpose of hPating the gas as it enters each layer of a
bed are provided in the form of disc shaped heater units located within divider elements
which may be used for ~up~o~ g and in turn being supported by the adsorbent of an
cent adsorbent m~tPri~l layers. Suitable such heater units are Curie point heaters such as
those provided by Domnick Hunter Filters UK, (these being collv~;lliently located in
batteries of three heater elements each) or any other arrangement including batteries
co~ i"g six or more such discs, or elements of dirrelclll shape.
r~ The heaters are controlled, in the ~ulci~,llcd design, using a microprocessor device (there
being no need to monitor bed t~lllp~ldLulc). The microprocessor device allows rapid control
of the bed heaters including the provision of sequential shutdown in order to minimi~e
cooling periods required and thus return the bed to operational condition as soon as possible.
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The electrical connections to the heater batteries and sensors may conveniently be provided
entering through the ends of the bed, as will be seen in the Example below. The electrical
connections can also be made through the walls of the housing, the housing may also be of
different configuration, e.g. circular, and may use a different heater battery construction
containing six or more curie point elements, which themselves may be of different shape.
The particular use of batteries of air heaters placed within transverse elements to divide a
bed into layers allows placement of heaters at any desired position within the bed. The
preferred Curie point heaters are of honeycomb construction and provide direct gas heating
during passage of gas through the bed with gas temperature controlled by the composition
of the heater element.
In US-A-3 193 985 a regenerable dehumidifier and operal:ing process therefor aredescribed. A vapour laden gas is dehumidified by passage through a bed of granular
adsorbent material and the bed is then regenerated by passing first hot then cold moisture
containing gas through the bed. The gas is heated by heating means mounted near the
outlet side of the bed.
The present invention will now be described further by way of illustration only by reference
to the following non-limiting Figures and Example. Further embodiments falling within the
scope of the claims will occur to those skilled in the art in the light of these.
FIGURES
Figure 1: shows a section view of (1a) a conductive coil heated bed and (1b) the coil used
as a comparative example.
Figure 2: shows temperature profiles obtained using the heater coil of Figure 1 from
thermocouples placed in the bed core or adjacent the housing wall.
Figure 3: shows (3a) elevation section and cross section (3b) through a comparative
example rod and vane heated bed.
Figure 4: shows temperature profiles obtained using the rod and vane heater of Figure 2
obtained from lower manifold temperature.
AMENDED Sf~EET
IPE~/EP
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Figure ~a shows a plan view and an elevation of a 3 element Curie point heater showing its
dimensions. Figure 5b shows a divider element in which the heater of figure 5a is placed
during operation.
Figure 6 shows the arrangement of four heater units of Figure ~ within a vertically oriented
bed such as to divide it into four layers.
Figure 7 shows te~llp~ldLLIre profiles obtained within a bed of zeolite using a 38.5 dm3 fill at
airflow rate 3120 dm3 min~l at the thermocouples Al to A6 of Figure 6.
EXAMPL}~ l: Curie point air heater ~ressure and temperature swin~ adsorber unit.
Curie point heaters (three elements per battery, see figure 5) and housings were supplied by
Domnick Hunter Filters Ltd, UK. Referring to figure 6, four b~tt~rie~ l - 4, each
independently controlled via a microprocessor keypad timing device, were located axially
within a 3 8.5dm3 bed of zeolite, electrical connection being nnade by thin (2mm) in~ terl
wires which passed along the adsorber bed to corulectors introduced into an upper manifold
via gas tight ducts. The upper and lower manifolds, which formed an integr~l part of the bed
housing, also contained the valving arrangement. Each e~em~71t was of honeycomb
construction and provided direct air heating during passage oi`gas along the column of the
bed unit. Gas temperature was controlled by the composition of the heating element and was
approximately 180-210C. Power consumption was ap~lvx;...~tely 2kW (eight three element
blocks occupying 10% ofthe housing volume). Typical in-bed t~ ~c profiles duringheating and cooling measured using thermocouples shown at positions Al to A6 are shown
in Figure 7 with a gas flow of air at 3120 dm3 min~~. In obtain;ng these the heater b~ttt?~ies
were ~vitched offsequentially.
Countercurrent puf~e flow applied during regeneration was varied with higher flowrates
reducing bed telll~ ldlules and thus c~ ing more power to be consumed. The te~ e~
profile for the Curie point air heater bed of the invention should be colllpaled with those
obtained using a conductive coil heater (Figure l) and a rod and vane heater (Figure 3).
CA 02203~33 l997-04-23
W O96/14917 PCT/GB95/02624
The conductive coil heated bed use.d a conductive coil electrically connected through the bed
housing base with a thermocouple placed close to the element. The element occupied 13%
of the housing interior v olume and the heater provided 0.6kW to the adsorbent v ariable by
increasing or decreasing applied current. The valving arrangement for process control was
positioned remote from the housing and typical in-bed tempt;laLulcs measured using
thermocouples placed radially and axially are shown in Figure 2 (0.5 dm3 activated carbon
fill product airflow 55 dm3 min~'.
The conductive rod and vane heaters and housings utilise vane heating via an electric rod
inserted centrally along the bed length with t~ eldlu~e control achieved via a remote
current control device. Power consurnption did not exceed 4.4kW. The rod and vane
arrangement occupied approx. 22% of the housing volume. Typical in-bed telllpeld~UlC
profiles during heating and cooling obtained using thermocouples at sampling points SP0-
SP5 shown in Figure 3 are shown in Figure 4 (6.8 dm3 zeolite fill, airflow rate 1400 dm3
min~'). The valving arrangement for process control was positioned remote from the
housing.
