Note: Descriptions are shown in the official language in which they were submitted.
208~.061
FLUID TREATMENT APPARATU5, HEAT EXCHANGER
AND METHOD OF FORMING A~ INSULATED TUBULAR
BACKGROU~D OF THE IN~ENTIO~
Field of the Invention
This invention relates to an improved insulated
tubular and heat exchanger and a continuous fluid treatment
apparatus such as may be used in down-hole wet oxidation of
fluid waste streams, including municipal sludge.
Description of the Prior Art
Above ground wet oxidation systems have been in use
for several years with limited success for the treatment o$
municipal sludge received from a sewage treatment process.
The above-ground wet oxidation systems use high surface
pressure and heat to initiate the wet oxidation reaction,
however, the apparatus is not energy efficient, the system is
subject to failure and results in only partial oxidation of
the sludge; see for example, U.S. Patent No. 2l665~249 of
Zimmermann and U.S. Patent No. 2,932,613 of Huesler, et al.
The above ground wet oxidation ~rocesses have not therefore
replaced the traditional methods of treating municipal sludge,
which includes settling, dewatering, drying, incineration and
the like.
Various vertical or down-hole fluid treatment
systems have been proposed by the prior art but are used only
in very limited applications. A down hole fluid treatmen~
sys~em utilizes ~er~ical pipes which generally extend
downwardly into the ground from a control station. The fluid
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to be treated is pumped into the vertical reactor pipes and
the fluid head creates a pressure which assists in the desired
fluid process or reaction. In the processes used ~o date, the
reaction requires additional heat which may be added by
electrical resistance coils or heated fluid which circulates
in a heat exchanger. Air or other gases may be added to the
fluid being treated to assist in the reaction.
Although several prior art patents propose a
vertical well wet oxidation reaction system for treatment of
municipal sludge or other fluid waste streams, the processes
and apparatus disclosed in these patents have not been
successful; see for example U.S. Patent No. 3,449,247. As
recognized by these prior art patents, the pressure created by
the fluid head is dependent upon the length of the reactor.
Thus, it is theoretically possible to fully oxidize municipal
sludge at a depth of approximately one mile provided the
concentration of the oxidizable material in the municipal
sludge is balanced against the oxygen available in the air
injected into the system. To the applicant's knowledge,
however, no one has been successful in building a down-hole
wet oxidation system for municipal sludge except the assignee
of the present invention.
United States Patent No. 4,272,383 of Dr. McGrew,
entitled "Method and Apparat~s for Effecting Subsurface,
Controlled, Accelerated Chemical Reactionsn, assigned to the
assignee of the present invention, discloses the principles of
the first successful down-hole wet oxidation reaction system
for municipal sludge which is now ~perating on an e~perimental
basis in Longmont, Colorad~. The apparatus disclosed in the
McGrew patent includes a series of generally concentric tele-
~2~
scopically nested pipes or tubes wherein diluted municipalsludge is preferably received in the inner pipe and flows
downwardly to a reaction zone adjacent the bottom of the pipe
and recirculated upwardly through a second pipe/ which
surrounds the inner pipe, following ~he reaction. Compressed
air is injected into the downwardly flowing sludge preferably
in the form of Taylor-type gas bubbles. In the McGrew patent,
the temperature of the reaction is controlled by a heat
exchanger jacket which surrounds the inner concentric pipes
wherein heated oil or other heat exchange fluid is pumped into
the jacket to control the temperature of the reac~ion zone.
The fluid treatment apparatus of this invention
preferably utilizes a centrally located heat exchanger wherein
the fluid to be treated is contained within recircula~ing
pipes which surround the heat exchanger, resulting in better
control of the temperature of the reaction zone and more
efficient heating of the fluid to be treated. The center
downcomer pipe of the heat exchanger is preferably an
insulated tubular which comprises two concentric pipes or
tubes telescopically nested in spaced relation wherein the
space between the tubes is sealed and preferably filled with
an inert gas. As will be understood, the pipes and insulated
tubular used in the fluid treatment apparatus of this inven-
tion comprises a series of pipes interco~nected in a vertical
string to accommodate the length of the overall fluid treat-
ment apparatus. Insulated tubulars have been used in the oil
well industry and other industries for several years to
transfer heated fluids and gases. As set forth hereinbelow,
however, ~he fluid treatment apparatus of this invention
requires localizing the hea~ as much 2S possible in the
reaction zone located adjacent the bottom of the pipes. The
heated oil or other heat transfer fluid is received at the top
of the apparatus or ground level. Thus, radial heat losses
through the insulated tubular to the r~-irculated heat
transfer fluid must be minimized. It has now been found that
a substantial heat loss results from atomic hydrogen
permeation into the space be~ween the tubes of the insulated
tubular which recombines to form gaseous hydrogen. There is
therefore a need to develop an improved insulated tubular
which inhibits hydrogen permeation to improve the insulation
qualities of the insulated tubular which results in an
improved heat exchanger and fluid treatment apparatus of the
type disclosed herein.
SUMMARY OF THE INVENTION
As described, the heat exchanger and insulated
tubular of this invention is particularly, although not
exclusivelyl adapted to utilization in a fluid treatment
apparatus for continuous treatment of fluid waste at elevated
temperatures and pressures, such as down-hole fluid treatment
apparatus including wet oxidation of municipal sludge and
other fluid wastes. The preferred heat exchanger includes an
elongated insulated tubular preferably having an open end
which is generally concentric with and telescopically nested
in a second pipe preferably baving a closed end adjacent the
open end of the surrounding pipe to communicate with the
insulated tubular. The insulated tubular includes a first
inner tube and a second outer tube which is preferably
generally concentric with and surrounds the first tube in
sp~ced relation. The space between the first and second tubes
is preferably sealed and filled with an inert gas, such as
arg~n, helium or xenon. The heat transfer fluid such as oil
3~)7
is received in the first inner tube of the insulated tubul~r
preferably at an elevated temperature. The heat transfer
fluid then flows through the insulated tubular until adjacent
the lower extent of the heat exchanger when the heat transfer
is concentrated and returns through the annular space between
the outer tube of the insulated tubular an~ the downcomer pipe
containing fluid and oxidizing gas for heating and recircula-tion.
In the most preferred embodiment of the heat
exchanger, the insulated tubular includes a hydrogen
permeation barrier on the inner and outer surfaces of both
tubes of the insula~ed tubular. The hydrogen permeation
barrier is prefera~ly formed by coa~ing the inner and outer
surfaces of the tubes with aluminum, nickel or copper. The
permeation barrier reduces the flow of Atomic hydrogen int~
the space between the first and secQnd tubes of the insulated
tubular, thereby reducing heat losses from the hot transfer
fluid in the center tube of the insulated tubular to the
returning heat transfer fluid in the annular region whose
inner surface is the outer surface of the insulated tubular.
When the heat exchanger of this invention is submerged in a
fluid, the heat transfer is concentrated in a reaction zone
located adjacent the end of the heat exchanger, which is
particularly advantageous in ~he down-hole fluid treatment
apparatus of this invention. The elongated fluid heat
exchanger is then surr~unded by circulation pipes containing
the fluid to be treated. The circulation pipes include a
first pipe which telescopically surrounds the outer pipe of
the heat exchanger in spaced relation which receives the fluid
to be treated in contact with the outer pipe of the heat
exchanger. A second pipe generally cDncentric With and sur-
rounding the firs~ pipe receives the treated fluido The fluid
to be ~reated, ~uch as municipal slud~e or other fluid waste
~Z~3~3V~7
is received between the outer pipe of the heat exchanger and
the first pipe of the fluid circulation pipes. The fluid to
be treated flows through the first pipe in contact with the
heat exchanger and recirculates through the second outermost
pipe. In this embodiment, the fluid treatment apparatus thus
creates a fluid reaction æone adjacent the end of the fluid
circulation pipes.
As described, the fluid treatment apparatus of this
invention is particularly suitable for continuous ~reatment of
fluid waste including municipal sludge and contaminated fluid
waste at elevated temperatures and pressures. Where the fluid
treatment apparatus is utilized to treat municipal sludge and
other waste by wet oxidation, the fluid treatment apparatus
comprises a plurality of elongated generally concentric and
telescopically nested pipes which extend vertically into the
ground as much as a mile or more in depth. The central
insulated tubular, which receives the hot heat transfer fluid,
preferably has an open end and the cuter pipe of the heat
exchanger preferably has a closed end adjacent the open end of
the insulated tubular providing communication with the
insulated tubular and continuous flow of the heat transfer
fluid. The first pipe of the fluid circulation pipes, which
surrounds the outer pipe of the heat exchanger, also has an
open end and the outermost pipe may also have a closed end
which communicates with the open end of the fluid circulation
pipes~ providing continuous circulation of the fluid to be
treated. The heated reaction zone is thus located adjacent
the bottom of the fluid circulation pipes and the pressure of
the fluid head in the circulation pipes assures fluid reaction
of the fluid waste at elevated temperatures and pressures in
the reaction zone.
3~
In the most preferred embodiment of the heat
exchanger and fluid treatment apparatus of th.s invention, the
hydrogen diffusion barrier is a diffusion coa~ing of aluminum
on the inner and outer surfaces of the concentric tubes of the
insulated tubular, forming a surface "coating" of an iron-
aluminum alloy. The iron-aluminum alloy coating has been
found to be particularly effective in preventing diffusion o
atomic hydrogen into the sealed space between the tubes. The
diffusion barrier may also be formed by electroplating copper
or preferably nickel on the surfaces of the tubes. As
described, the diffusion of atomic hydrogen into the sealed
space between the tubes of the insulated tubular results in an
increased thermal conductivity and resultant increased radial
heat losses from the heat transfer fluid flowing through the
insulated tubular to the recirculating heat transfer fluid in
the second outer pipe of the heat exchanger.
The method of forming an insulated tubular for use
in a heat exchanger apparatus, as described, thus includes
forming the telescopically nestable tubes/ forming a hydrogen
permeation barrier coating on the exterior and interior
surfaces of the tubes and assembling the tubes in nested,
concentric, telescopically spaced relation and sealing the
space between the tubes. The space between the tubes is then
evacuated and preferably filled with an inert gas~ In the
most preferred method of forming the insulated tubular of this
invention, the hydrogen permeation barrier coating is formed
by diffusion coating the interior and exterior surfaces of the
tubes with aluminum, forming an iron-aluminum alloy on the
surfaces. ~s described, the hydrogen permeation barrier may
also be formed by electroplating the surfaces with nickel or
o~
the barrier may also be formed by electroplating copper on the
surfaces.
Other advantages and meritorious features of this
invention will be more fully understood from the following
description of the preferred embodiments, the appended claims,
and the drawings, a brief description of which followsO
.~24''3~
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic illus~ration of a preferred
embodiment of the continuous fluid treatment apparatus of this
invention; and
Figure 2 is a cross-sectional view of the lower
portion of the fluid treatment apparatus shown in Figure 1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
AND METHOD OF THIS INVENTION
The continuous fluid treatment apparatus 20
illustrated in the drawings is a vertical down hole fluid
reaction apparatus suitable for treatment of various
contaminated fluid wastes including wet oxidation treatment of
municipal sludge. As disclosed in the above-referenced McGrew
patent, the fluid treatment apparatus comprises a plurality of
generally concentric and telescopically nested pipes which
extend vertically into the ground. In a treatment apparatus
for wet oxidation of municipal sludge, for example, the pipes
may extend approximately one mile into the ground creating a
very substantial pressure head. It will be understood, how-
ever, that the length of the pipes will depend upon the fluid
being treated and the desired fluid reaction. The fluid
treatment apparatus of this invention may also be used in
various conversion reactions wherein a solid particulate is
suspended in the circulating fluid. Further, the pipes or
tubes are generally not continuous. Each pipe comprises a
plurality ~f sections which are interconnected in serial
alignment in a string, similar to the pipes in an oil well.
In a typical municipal sludge wet oxidation application, the
.~1.. ~ A'~ ) t;~
length of each pipe section is 40 fee~ long, the total length
is about 5,200 feet and the flow rate of the fluid being
treated is abou~ 80 to 400 gallons per minut~
In the disclosed preferred embodiment of the fluid
treatment apparatus of this inven~ion, the fluid heat
exchanger 22 is located at the cen~er of the concentric pipes
of the fluid treatment apparatus. The first or innermost pipe
of the heat exchanger is an insulated tubular 24 having an
open end 26. As described more fully hereinbelow, the
insulated tubular reduces radial heat transfer from the
downflowing heated heat transfer fluid in the insulated
tubular to the recirculating upwardly flowing heat transfer
fluid in the second pipe 28. As shown, the first pipe or
insulated tubular 24 is generally concentric with and tele-
scopically nested in second pipe 28 and the second pipe has a
closed end 30 adjacent the open end 26 of the insulated
tubular. The fluid to be treated is then circulated around
the heat exchanger 22, as now described.
A third pipe 32, which is the first pipe of the
outer fluid circulation piping, surrounds the heat exchanger
22 in generally concentric spaced telescopic relation. The
third pipe 32 ~as an open end 34 adjacent the closed end 30 of
the fluid heat exchanger. A fourth pipe 36 surrounds the
third pipe 32 in generally concentric spaced telescopic
relation and includes a closed end 38 adjacent the open end 34
of the third pipe 32. The fluid to be treated is circulated
downwardly through pipe 32 in contact with the second pipe 28
of the heat exchanger 22 and the trea~ed fluid then flows
through the open end 34 of the third pipe 32 and upwardly
through the fourth pipe 38 in contact with the outer surface
3~0~
of the third pipe 32~ As described in ~he above-referenced
McGrew patent~ the fluid treatment apparatus creates a
reaction zone adjacent the bottom of the apparatus wherein the
fluid to be treated is reacted under heat and pressure. A
principal object of the present invention is to concentrate
the heat transferred from the heat exchanger to the fluid
circulating in pipe 32 to the lower reaction ~one, and reduce
radial heat transfer, particularly in the upper portion of
the heat transfer apparatus.
Figure 1 illustrates schematically the above-ground
component~ utilized in the fluid treatment apparatus and
process~ The heat transfer fluid, such as oil, is stored in a
reservoir tank 40. The oil is heated in a heater 42, such as
a conventional gas fired heater. The oil is pumped by pump 44
from reservoir40 through line 46 to heater 42 and the rate of
flow is controlled by valve 52. The heated oil is then
transferred through line 48 and the rate of flow is controlled
by valve 50. Where the fluid reaction is exothermic, such as
a wet oxidation reaction, cooling of the reaction zone may be
required where the heat of reaction exceeds the preferred
temperature in the reaction zone. Thus, the disclosed
apparatus includes a heat exchanger 54 where the oil may be
cooled. The oil from reservoir 40 may be pumped through line
56 to the heat exchanger 54 by pump 57. The flow is
controlled by line 62. The cooler oil is then discharged
through line 58 and valve 60 to the supply line 48 of the
fluid treatment apparatus.
Normally heated oil is then supplied through line 4B
into the top of the insulated tubular 24. ~s best shown in
Figure 2, the h~ated oil then flows downwardly through the
insulated tubular as shown by arrow 70. The oil then flows
out of the open end 26 of the insulated tubular and the oil is
recirculated upwardly through pipe 28 in contact with the
tubular, as shown by arrow 72. The oil or o~her heat transfer
fluid is then disch~rged from the top of pipe 28 through line
74, back to reservoir 40 through valve 76.
The fluid to be treated, such as contaminated
industrial fluids, municipal sewage or the like is supplied to
the top of pipe 32 and circulates arouna the heat exchanger 22
as described. As shown in Figure 1, the fluid to be treated
is stored in reservoir tank 80~ As described in the above
referenced McGrew patent, the fluid treatment apparatus is
particularly suitable for treatment of municipal sludge
received from a conventional municipal wastewater treatment
plant. The sludge is received through line 82 and the flow is
controlled by line 84. The fluid sludge is then delivered to
the apparatus through line 86 and valve 88. The fluid sludge
is preferably diluted with liquid effluent from municipal
wastewater treatment plant delivered through line 90 and
valve 92. The fluid sludge is preferably diluted ~o control
the percentage of oxidizable material delivered to the fluid
treatment apparatus. The diluted fluid sludge, fluid waste or
other fluid to be treated then flows downwardly through pipe
32 in contact with the outer wall 28 of the heat exchanger 22
as shown by arrows 94. As clescribed, pipe 32 has an open end
34 and the treated fluid then flows upwardly through the outer
pipe 36 for discharge from the fluid treatment apparatus. As
shown in Figure 1, the treated fluid is discharged from pipe
36 through line 98 to tank 100. Where the apparatus is used
for wet oxidation of fluid sludge, tank 100 is preferably a
settling tank where the substantially inert ash is separated
12
38U~7
from the water. The ash may be drawn off through line 102 and
the rate of flow is controlled by valve 104.
In a wet oxidation reactor, the supernatant may be
drawn off through line 106 and used as a diluent in the
process. As shown in Figure 1, the supernatant is drawn off
through line 106 and delivered to line 8S which communicates
with pipe 32. The rate of flow and dilution is controlled by
valve 108. As described in the above-referenced McGrew
patent, air is injected into the down-flowing sludge in wet
oxidation of municipal sludge and other waste materials. The
air is preferably injected into the down flowing stream of the
fluid to be treated below the ground level 39 in the form of
Taylor-type bubbles. It will also be understood that other
fluid reactions may require other gases dependent upon the
desired reaction. The disclosed apparatus therefore includes
an air compressor 110 and the compressed air is delivered to
the downward flowing fluid to be treated in pipe 32 below
ground level by line 112 and the flow is controlled by valve
114. 110 may also be a pump delivering any gas required by
the reaction occurring in the fluid treatment apparatus of
his invention.
As described, the fluid treatment apparatus of this
invention is primarily intended to treat fluid waste at
elevated temperatures and pressures. The pressure is provided
by the fluid head and the temperature is provided by the heat
of reaction where the reaction is exothermic and the heat
exchanger 22. In a typical wet oxidation reaction of
municipal sludge, the bottom hole temperature is approximately
~00 degrees Fahrenheit. Thus, the oil delivered to the second
or outer pipe 28 of the heat exchanger should be in excess of
13
)7
500 degrees Fahrenheit. In a typical wet oxidation reaction,
the oil will be delivered to the inlet of the insulated
tubular 24 at a temperature of about 700 degrees Fahrenheit.
The oil or other heat transfer fluid then flows downwardly to
te open end 26 of the insulated tubular, where it is delivered
to the outer pipe 28 of the heat exchanger at a temperature of
about 525 to 550 degrees Fahrenheit The fluid then flows
upwardly through pipe 28 as shown by arrow 72 of Figur~ 2 and
heats the down-flowing fluid to be treated which contacts the
outer surface of pipe 28 in pipe 32. The temperature of the
oil at the top exit of the pipe 28 is about 150 degrees
Fahrenheit~ As described, the fluid reaction occurs in a
reaction zone where temperature of the down flowing fluid
exceeds 350 degrees Fahrenheit. The preferred embodiment of
the fluid treatment apparatus therefore utilizes an insulated
tubular 24 to reduce the radial heat transfer from the down-
flowing heat transfer fluid in the insulated tubular 24 to the
cooler heat transfer fluid in line 28. The details of the
insulated tubular 24 are disclosed in Figure 2. The insulated
tubular includes an inner tube 120 having outer and inner
surfaces 122 and 124, respectively, and an outer tube 126
having outer and inner surfaces 128 and 130, respectively.
The inner tube 120 is preferably concentric with and tele-
scopically nested within the outer tube 126 in spaced rela-
tion. The space 132 between the tubes is fixed and sealed
with a sealing ring 134 which may be welded or otherwise
secured in the space between the tubes. The space between the
tubes is then evacuated and filled with an inert gas such as
argon, helium and xenon. The inert gas has a low thermal
conductivity, reducing the radial heat transfer through the
space 132 between the tubes 120 and 126.
14
`3~
The heat transfer across the space 132 between the
tubes is defined by the following equation:
Q = kA t/ r
wherein Q is the heat transferred in btu per hour, k is the
~hermal conductivity, A is the area for heat transfer/ t/~
r is the radical temperature gradient. In the wet oxidation
apparatus operating experimentally at Longmont, Colorado, the
inner tube 120 has an inside diameter of two inches and an
outside diameter of 2 3/8 inches~ The ou~er tube 126 has an
inside diameter of three inches and an outside diameter of 3
1/2 inches. Thus, ~`~ r is 5/3 inch. In the example above,
I t at the top of the heat exchanger is 550 degrees Fahrenheit
1700 degrees F. - 150 degrees F.). Thus, the temperature
gradient is substantial and substantial radial heat transfer
will occur in the upper portion of the fluid treatment
apparatus unless the inner pipe 24 is well insulated.
The use of an insulated tubular 24 hasresulted in a
substantial decrease in radial heat losses, however, the
insulating qualities have decreased with time. It has now
been discovered that the reduction in the insulating qualities
of the insulated tubular is due at least in part to the
permeation of atomic hydrogen through the walls of the
insulated tubular into the space 132 between the tubes.
Atomîc hydrogen is able to permeate the interstices of the
metal tubes 120 and 126 into the space 132 between the tubes.
The atomic hydrogen then combines to form hydrogen gas which
cannot esrape through the walls. The hydrogen gas then
accumulates in the space 132 between the tubes, increasing the
thermal conductivity of the gas. As described above, the
space between the walls is filled with an inert gas. The
insulated ~ubular o this invention therefore includes a
hydrogen permeation barrier which reduces the flow of atomic
hydrogen into the space between the tubes.
The most preferred hydrogen permeation barrier
comprises a diffusion coating of aluminum on the inner and
outer surfaces of both tubes, 124, 126, 128 and 130. The
tubes are preferably formed of steel, such that the diffusion
coating is an iron-aluminum alloy. Aluminum diffusion
coatings are commonly applied to steel furnace tubes and the
like to improve corrosion resistance and furnace life by a
process known as "Alonizingn. In the Alonizing process, the
pipe is packed externally and internally with aluminum and
alumina powder and placed in a furnace at about 1700 degrees
Fahrenheit for three to four days. The coating is very hard
and does not interfere with welding. It has now been
discovered that an Alonized aluminum-iron diffusion coating
substantially reduces atomic hydrogen diffusion.
The hydrogen diffusion barrier coating may also be
formed by electroplating nickel on the interior and exterior
surfaces of the tubes. The electroplated nickel coating also
provides an excellent atomic hydrogen diffusion barrier, not
quite as good as the Alonized surfaces. Finally, the hydrogen
diffusion barrier may be formed by electroplating copper on
the surfaces of the tubes, however, copper will interfere with
welding and may adversely affect the strength properties of
the tubes. Where the surface is electroplated with nickel or
copper, the thickness of the coating should be approximately
O.OOlmm. Comparing bare steel with a hydrogen permeation
~arrier coated insulated tubular, the coated insulated tubular
had a hydrogen permeation rate reduced by a factor of about
1000. Comparing Alonized steel with a nickel pla~ed steel,
16
38(~7
the permeation rate was reduced by a factor of about 10.
Thus, the most preferred embodiments includes a hydrogen
diffusion barrier formed by diffusion coating of aluminum,
forming an iron-aluminum alloy. The hydrogen diffusion
barrier substantially reduces degradation of the insulating
qualities of the insulated tubular.
The method of forming an insulated tubular thus
includes forming telescopically nestable steel tubes,
preferably seamless tubes as shown at 120 and 126 in Figure 2.
A hydrogen permeation barrier coating is then formed on the
tubes, preferably on the exterior and interior surfaces of
both tubes. The tubes are then assembled in nested concentric
telescopically spaced relation as shown in Figure 2 and the
space between the tubes is sealed as by sealing ring 134. The
space 132 between the tubes is then evacuated and the space is
filled with an inert gas, such as neon, argon or xenon. The
resultant insulated tubular is not as subject to insulation
degradation because the barrier reduces the permeation of
atomic hydrogen, as described.
Having described the preferred embodiment of the
heat exchanger, continuous fluid treatment apparatus and
method of forming an insulated tubular of this inv~ntion, it
will be understood that various modifications may be made to
the inventions disclosed herein within the purview of the
appended claims. As described, the heat exchanger and fluid
treatment apparatus of this invention may be used in various
applications, however, the inventions are particularly adapted
for use in vertical tube or deep well reaction apparatus such
as may be used for wet oxidation of municipal sludge. The
apparatus may, however, be used for treatment of various
Q~7
contaminated or waste fluids or contaminated solid waste
suspended in a fluid. The apparatus may also be used to treat
or convert various materials in a fluid reaction requiring
elevated temperatures and pressures. Having described the
preferred embodiments of the heat exchanger, continuous fluid
treatment apparatus and method of this invention, I now claim
the invention as follows:
