Liquid purification or separation – Processes – Ion exchange or selective sorption
Reexamination Certificate
2001-10-25
2004-03-16
Barry, Chester T. (Department: 1724)
Liquid purification or separation
Processes
Ion exchange or selective sorption
C210S688000, C210S739000, C210S277000, C210S279000, C210S912000
Reexamination Certificate
active
06706195
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to ion exchange systems for removing arsenic from water. More particularly it relates to fixed bed ion exchange systems for removing arsenic which are configured to yield the flexibility and efficiency of moving bed systems.
BACKGROUND AND STATE OF THE ART
Ion exchange is a chemical process often used to separate certain contaminant substances from a drinking water supply containing a mixture of several other harmless dissolved substances. For example, common ground water used for drinking water will contain substances such as the ionic forms of calcium, magnesium, sulfate, chloride and bicarbonate. In many cases, the water may also contain contaminants that are known to be detrimental to health. Such ionic substances as nitrite, nitrate, arsenic, antimony, fluoride, selenate, chromate, perchlorate and other similar harmful substances are often found. It is desirable to separate out the contaminants harmful to health by treating the water with an ion exchange system. There is a special interest in removing arsenic to very low levels.
Ion exchange processing systems range in production capacity from 50 gallons per day (GPD), such as is used in home water softeners and water purification devices, to very large plants having a capacity of several million gallons per day (50 to 100 million GPD) for centralized treatment of a public water supply.
Various equipment configurations or systems of vessels, plumbing and valves are used to apply the ion exchange process to the above purpose of treating a water supply to remove undesirable substances. For example, one prior art system is shown in
FIG. 1
as system
100
. This system is referred to as a single “fixed bed” design. The water to be treated is pumped from line
10
through a vessel
12
containing a bed
14
of ion exchange resin. Purified water is removed via line
16
. Note that the word “single” indicates that all process streams flow through the vessel
12
only once before continuing flow. Also the term “fixed bed” indicates that all ion exchange vessels are fixed in their positions.) During operation, there is no visible change in the positioning of the vessels or piping or any other component, only the internals of the valves change as they go from open to closed. (In contrast, when a moving bed system is in operation the position of the vessels and piping change and a multiport valve remains in a fixed position.
The vessel
12
containing the bed
14
is equipped with about eight to eleven different valves which control which process stream passes through the ion exchange bed. These are large full capacity valves capable of handling 50 to 100 percent of the peak flow rate through the plant. Practical flows of 500 to 1000 gallons per minute or more capacity for valve passage are not uncommon. By selecting the proper set of valves to be opened or closed either manually or by electronic controls, the flow of water to be treated by being passed through the vessel
12
and resin bed
14
can be stopped when the resin bed is exhausted. Control valve operations allow a sequence of process steps to be executed involving rinsing, regenerating and back washing and declassification (if required) to restore the adsorptive capacity of the resin. This sequence of steps produces a quantity of waste water that contains waste salt materials. This quantity of waste water is discarded. In
FIG. 1
regenerant solution, such as brine, is shown supplied via line
18
and removed via line
20
and rinse liquid is shown being supplied via line
22
and removed via line
24
.
Use of a single fixed bed of the prior art is also similar to a batch operation in that the flow of treated water is stopped completely while the resin goes through the resin regeneration steps. If an uninterrupted flow of treated water is desired, at least two fixed bed units must be used in parallel. Each bed is operated as above. After the first bed is exhausted, the bed is taken off line and regenerated while the second bed is placed into operation.
In general, a fixed bed system is comprised of as few vessels as is economically possible from the cost equipment point of view. Keeping the number of vessels to a minimum also reduces the number of large valves to be maintained or replaced. It also simplifies the valve control system with fewer valves to operate. It is customary therefore for plant designers to minimize the number of vessels to keep the number of valves to a minimum.
There are disadvantages, however, because larger vessels and large valves are required. To maintain or replace vessels or valves on a twelve foot diameter vessel, two or three men are required with the aid of heavy equipment lifting devices. Operation and maintenance costs will rise when first equipment costs are low because of large vessels. A popular design of a fixed bed system uses three vessels. Twenty four to thirty three large valves must be operated and maintained on such a system.
With a fixed bed system it is also often required to declassify the resin bed after regeneration. This step requires time and process water and produces additional waste water. The present invention eliminates this step.
Another prior art ion exchange system is known as a moving bed system or as a “merry-go-round” design. In this system the ion exchange resin is contained in several small vessels containing only an inlet port and an outlet port. Multiport valves communicate with these ports and control which process stream flows through each vessel.
FIG. 2
depicts such a system as
200
. These systems eliminate the use of large vessels and the subsequent high maintenance and replacement costs. In these systems multiple vessels
12
, such as eighteen vessels numbered 1 through 18 are mounted on a circular platform
26
near the perimeter of a platform that slowly rotates while the system is in operation. The vessels
12
are each coupled through a line
32
to an upper multiport valve
28
and through a line
34
to lower multiport valve
30
. Valves
28
and
30
can be combined or separate as shown.
The multiport valves are constructed with fixed (in and out) ports corresponding in position to the (in and out) ports of the ion exchange vessels which rotate part. The types of process streams flowing through the various vessels is controlled by the multiport valves
26
and
28
and is dependant on the position of the vessel on the circular platform. Consequently, as the platform rotates, the process stream entering and leaving any of the vessels changes according to a predetermined and difficult to alter process flow, set by the multiport valves.
Returning to
FIG. 2
, the system
200
shown therein has eighteen discreet vessels
12
and eighteen discreet positions for a vessel on the circular, rotating platform
26
. The rotation of the platform physically moves each vessel from one position to the next position with all eighteen vessels moving simultaneously. The multiport valves
26
and
28
are positioned in the center of the rotating platform. The main process streams of treated water, regenerant, and rinse are first fed to the central multiport valves that then select the appropriate process stream for each position into which a vessel can be placed.
For example, a single vessel physically moves from position to position as shown in
FIG. 2
When a given vessel is in positions
4
through
18
on the merry-go-round, it is fed untreated water from line
10
through valve
26
and line
30
which it purifies and discharge via line
32
, valve
28
and line
16
. As the vessel moves from position
4
through to
18
it continues in water treatment service but at each successive step the resin becomes more and more loaded with contaminant until it is virtually exhausted in position
18
. When the vessel is moved into positions
1
through
2
, a brine stream enters the vessel via line
22
, valve
28
and line
32
to regenerate the resin by displacing contaminant off of it. Spent regenerant is removed via line
34
, valve
30
and line
24
. When the vess
Guter Gerald A.
Jensen Peter L.
Ziol Dan
Barry Chester T.
Swiss Law Group LLC
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