APPARATUS FOR ON-LINE CONTINUOUS CHLORINE ANALYSIS IN TURBID
WATER AND PROCESS STREAMS
Cross-Reference to Related Applications
Not Applicable.
Statement Regarding Federally Sponsored Research or Development
Not Applicable.
Background of the Invention
The present invention relates generally to methods of, and apparatus for accurately
monitoring the amount of biocides and particular oxidants present in a given water volume.
Oxidants such as sodium hypochlorite arid other halogen-based compositions (including but not
limited to Actibrom, BCDMH, and Siabrex) are frequently used to control the growth of
microbial organisms and other biological deposit formations in water and industrial processes.
Efficient and effective use of these compositions however requires that proper concentrations be
maintained. This is best achie ved by use of an online system that provides real time up to date
concentration information.
One on-line method of monitoring the concentrations in water involves
determining the amount of total halogen and free halogen residuals. This can be accomplished by
a number of commercially available devices using various techniques. The HACH CLI 7
measures free and total chlorine using eolorlmetric method and N,N~diethyl-p-phenylen©diamine
(DPD) indicator reagent. Unfortunately, the use of such eolorlmetric and indicator reagents is
limited to water systems with low solids and with turbidity values below 5 nephelometric
turbidity units (NTU). Paper process water typically has a solids content ranging from 0.1to 0.5%
even in the most clarified parts of the process, which greatly exceeds the limitations of available
technology.
Another method is Oxidation-Reduction Potential (ORP). ORP however only
gives an indirect measurement of oxidant concentration. Also because ORP is affected by factors
other than just halogen concentration, under certain circumstances, and in particular in highly
turbid environments li is inaccurate.
Yet another method is Amperometric measurements. Amperometric
measurements use a conductive element sensor (typically having a copper and platinum or gold
electrode). A small amount of potential is applied to the sensor electrodes. An electric charge is
then generated by the chemical reduction of the oxidant. The resulting charge is in direct linear
proportion to the amount of residual halogen present in the sample. Amperometric measurements
however require membrane caps, which rapidly become fouled when continuously used in many
industrial processes. As a result, Amperometric measurements are only of limited practical use.
it is therefore useful and desirable to provide methods and apparatus to better
detect the concentration of oxidants in water samples. The art described in this section is not
intended to constitute an admission that any patent, publication or other information referred to
herein is "Prior Art" with respect to this invention, unless specifically designated as such in
addition, this section should not be construed to mean that a search has been made or that no
other pertinent information as defined in 37 CFR § i .56(a) exists.
Brief Summary of the Invention
At least one embodiment of the invention is directed to a method of accurately
detecting the presence and concentration of an oxidant in a turbid water sample, the method
comprising the steps of: I) passing the water through a filter array, the filter array comprises at
least one filter constructed and arranged to remove turbidity inducing material but not oxidant
from the water sample, 2) then passing the filter array filtered water to an oxidant monitor that
would not be able to accurately measure the oxidant concentration if the water had not been so
filtered, and 3) returning from the monitor a measurement of the concentration.
The filter array may comprise at least two filters, the filters in series with each
other relative to the downstream flow of the water. At least one less-downstream filter may be
constructed and arranged to filter larger and coarser turbidity inducing material than at least one
more-downstream filter. The filter array may comprise a fii!er-band type filter. The filter array
may comprise a filter, which is constructed and arranged to rotate, the rotation preventing the
accumulation and plugging of the filter by continuous contact with turbidity inducing material.
The oxidant may be halogen based and may be sodium hypochlorite. The monitor
may determine the oxidant concentration by using an algorithm relying upon determining the
amount of total halogen and free halogen residuals. The flow rate through the filter array may be
adjusted by diverting some of the water into a side spillway so the remaining sample flow is
compatible with the time interval needed by the monitor to measure the concentration.
The method may further comprise the step of intermittently passing high
concentrations of oxidant to the monitor where the monitor is constructed and arranged to
thereafter not indicate that the measured oxidant amounts are measured oxidant amounts until
one item has occurred selected from the list consisting of: the measured oxidant concentration is
no greater than 0-40% of the measured amount before the high concentration was passed through,
a predetermined time has passed, a predetermined multiple of the time interval of the analyzer has
passed, and any combination thereof. The high concentrations of oxidant may reduce fouling of
at least one item selected from the monitor, the pumps, the hoses, and any combination thereof.
The water sample may be water from a paper mill process stream. The turbidity inducing
material may be selected from the list consisting of; cellulose fibers, mineral fillers, property
enhancing polymers, sizing agents, wood chips, and any combination thereof.
Additional features and advantages are described herein, and will be apparent
from, the following Detailed Description
Brief Description of the Drawings
A detailed description of the invention is hereafter described with specific
reference being made to the drawings in which:
FIG. 1 is a schematic drawing of the analyzer system.
Detailed Description of the Invention
For purposes of this application the definition of these terms is as follows:
"Fouling" means the undesirable presence of or deposition of any organic or
inorganic material in the water or on a surface.
"Monitor" means a device constructed and arranged to measure at least one
physical or chemical characteristic and to output a signal or display in response to thai
measurement.
In the event that the above definitions or a description stated elsewhere in this
application is inconsistent with a meaning (explicit or implicit) which is commonly used, in a
dictionary, or stated in a source incorporated by reference into this application, the application
and the claim terms in particular are understood to be construed according to the definition or
description in this application, and not according to the common definition, dictionary definition,
or the definition that was incorporated by reference. In light of the above, in the event that a term
can only be understood if it is construed by a dictionary, if the term is defined by the Kirk-Othmer
Encyclopedia of Chemical TecJwology, 5th Edition, (2005), (Published by Wiley, John & Sons,
Inc.) this definition shall control how the te rm is to be denned in the claims.
Referring now to FIG.1 it is shown that at least one embodiment is a method and
apparatus (i) for accurately determining the amount of oxidant in a volume of water. The water
flows from a source (2) and undergoes multiple pre-filtering processes prior to analysis by a prior
art oxidant analyzer or a "doctrine of equivalents" equivalent. The pre-filtering is accomplished
by passing the water through a filter array (4), The water may flow under due to the effects of
one or more pumps (3). The pre-filtering removes materials that would otherwise foul the
analyzer (6) or which would render the measurement inaccurate, At the same time the prefiltering
is done in a manner that does not alter the oxidant content of a sample so the oxidant
sample is truly representative of the water volume being analyzed.
In at least one embodiment the water source is a volume of process water from a
paper mill. Such process water is typically highly turbid and contains large amounts of cellulose
and other fibers, paper and wood solids, fillers, minerals, and various property enhancing
additives, ail of which overwhelm and make impossible accurate and/or long term analysis of the
oxidant content of the process water. This in turn makes the addition of oxidants "blind" and is
therefore either too much and needlessly wasteful (and possibly toxic) or too little and not
sufficiently effective.
In at least one embodiment the pre-filtratton is accomplished by the use of one or
more bandfilters. Bandfilters are known in the art as a filter apparatus that allows the liquid to
always pass through a clean filtering material. This cleanliness is achieved because the band
itself is a Song strip that is constantly pulled (nmch like the tape in a cassette tape) across an
aperture through which the liquid flows. Because it is pulled, the same given filtering surface is
only in contact with the liquid for a short period of time and does not have time for significant
fouling to occur. Commonly bandfilters are at least in part held in place against the aperture by a
pressure gradient pulling the band in the same direction as the liquid flow. In at least one
embodiment this gradient is caused by a pump (5) downstream from the filter (4), Often the band
is in a loop that Includes a cleaning stage the same section of band will cycle past the aperture
again and again, but because it is constantly cleaned, the effect is a perpetually clean filter surface
through which the liquid flows.
ID at least one embodiment a bandfilter passes the aperture at a rate of between 0.5
1 cm per minute to 11 ran per hour. In at least one embodiment the bandfilter is constructed and
arranged to he used with liquids
In a t least one embodiment, the liquids that pass through the bandfilter do not
exceed 2% (meaning 2% fibers and most/all of the remaining 98% is water),
in at least one embodiment the bandfilter is rotated and is continuously washed so turbidityinducing
materials do not clog up the- filter.
In at least one embodiment there is only one filter. In at least one embodiment
two or more filters are positioned in aeries with each other relative to the flow path of the water.
The multiple serially positioned filters remove ever-increasing proportions of the turbidity
inducing materials from the water sample,
In at least one embodiment the filters are so effective at reducing the effects of
turbidity inducing materials that process waters having a solids content as high at 6% can
effectively be measured. In at least one embodiment the one or more filters are arranged to
remove the turbidity inducing materials from a sample thai is from 2-4% solids.
In at least one embodiment the analyzer (6) downstream from the filters is a
HACH CL17 analyzer.
In at least one embodiment the flow rate of the water samples through the one or
more filters are constructed and arranged to match the optimal flow rate for the analyzer. For
example in the HACH CL17, the analyzer measures residuals at 3-mmute intervals and the flow
rate is adjusted to accommodate that rate. In at least one embodiment if the flow rate of the water
samples exceeds the measuring rate of the analyzer, a portion of the water sample is diverted
down a spillway (7) and the remainder is the optimal amount which is passed on to the analyzer,
In this way a flow rate that is greater than the interval rat e of the analyzer can provide accurate
readings. En at least one embodiment the spillway is constructed and arranged to always assurethat
liquid passes into the analyzer at a fixed rate,
hi at least one embodiment a cleaning cycle is available to the system. The
cleaning cycle allows one or more of the sensor, hoses, pumps, filters, etc. . . to be maintained in a
clean state. As various parts of the system continuously receive potentially infested water,
microbial slimes may accumulate along various surfaces that contact with this Infested water. In
at least one embodiment the cleaning cycle can he achieved by diverting the process flow water
away from one or more portions of the system and instead introducing a liquid stream that is
highly concentrated with oxidant or other biocide.
in at least one embodiment concentrated sodium hypochlorite (or another oxidant
or biocide) is introduced to at least one portion of the system and it cleans that portion. In at least
one embodiment, concentrated sodium hypochlorite (or another oxidant or biocide) is introduced
to at least one portion of the system, and the introduced sodium hypochlorite (or another oxidant
or biocide) continues on to subsequent downstream portions of the system and cleans those
downstream portions. This allows one insertion of a chemical to accomplish effective cleaning of
multiple portions of the system. In at least one embodiment the concentrated sodium
hypochlorite (or another oxidant or biocide) is introduced into a process stream which is
upstream of at least one of the pre-filtering steps. In at least one embodiment the sodium
hypochlorite (or another oxidant or biocide) (8) is introduced by its own pump (9),
In at least one embodiment the sample water pump (3), post filter pump (5), and
the cleaning cycle pump (9) are coordinated to run at the same time with different flow rates. In
at least one embodiment the sample water pump (3) runs at &flow rate of between 75 to 250
times as great as the post filter pump (5). in at least one embodiment the cleaning cycle pump (9)
runs at a flow rate of between 3 * 10-7 to 6 * 10-7 times more slowly than the sample water pump
(3), Irs an exemplary embodiment the sample- water pump (3) runs at a rate of 1 liter per minute,
the post filter pump (5) runs at 5-10 ml per minute, and the cleaning cycle pump (9) runs at a rate
of 30 ml per 12 hours.
Even after this slime-removing stream is no longer flowing through the sensor,
much higher oxidant concentrations may persist for a while. In at least one embodiment the
sensor (or process control equipment that is in communication with the sensor) is designed to
reject as inaccurate oxidant readings until after either a time interval which is a multiple of the
time interval of the sensor or until the detected oxidant levels are hack down to close to what they
were (for example within 0% - 50% of what they were) before the cleaning cycle was initiated.
In at least one embodiment the time interval is between 1 and ? minutes long.
At least one possible example of the cleaning process is as follows: The cleaning
cycle pump (9) pumps hypochlorite (and/or another oxidant or hiockle) to clean some or all of the
hoses and the analyzer (6), As a result the analyzer detects chlorine levels are higher than typical
(for example > 5ppm). After a communication with the process control system for the apparatus
(1), the apparatus switches into a static state for an interval of time (for example 30 minutes).
After the time interval has lapsed, the process control system returns the apparatus back to a
regular state.
While this invention may be embodied in many different forms, there described in
detail herein specific preferred embodiments of the invention. The present disclosure is an
exemplification of the principles of the invention and is not intended to limit the invention to the
particular embodiments illustrated. All patents, patent applications, scientific papers, and any
other referenced materials mentioned herein are incorporated by reference in their entirety.
Furthermore, the invention encompasses any possible combination of some or all of the various
embodiments described herein and incorporated herein,
I he above disclosure is intended to be illustrative and not exhaustive This
description will suggest many variations and alternatives to one of ordinary skill in this art. All
these alternatives and variations are intended to be included within the scope of the claims where
the term "comprising" means "including, but not limited to". Those familiar with the art may
recognize other equivalents to the specific embodiments described herein which equivalents are
also intended to be encompassed by the claims.
Ail ranges and parameters disclosed herein are understood to encompass any and
all subranges subsumed therein, and every number between the endpoims. For example, a stated
range of"l to 10" should be considered to include any and all subranges between (and inclusive
of) the minimum value of 1 and the maximum value of 10; that is, all subranges beginning with a
minimum value of 1 or more, (e.g. 1 to 6.1), and ending with a maximum value of 10 or less,
(e.g. 2 3 to 9.4, 3 to 8, 4 to ?), and finally to each number 1. 2, 3, 4 5, 6, 7, 8, 9, and 10 contained
within the range.
This completes the description of the preferred and alternate embodiments of the
invention. Those skilled in the art may recognize other equivalents to the specific embodiment
described herein which equivalents are intended to be encompassed by the claims attached hereto.
Claims
What is claimed is:
1. A method of accurately detecting the presence and concentration of an oxidant in a turbid
water sample, the method comprising the steps of;
passing the water through a filter array the filter array comprises at least one filter
constructed and arranged to remove turbidity inducing material but not oxidant from the water
sample,
then passing the filter array filtered water to an oxidant monitor that would not be able to
accurately measure the oxidant concentration if the water had not been so filtered,
and returning from the monitor a measurement of the concentration.
2. The method of claim 1 wherein the filter array comprises at least two filters, the filters in
series with each other relative to the downstream flow of the water.
3. The method of claim 2 wherein at least one less-downstream filter is constructed and
arranged to filter larger and coarser turbidity inducing material than at least one moredownstream
filter.
4. The method of claim 1 in which the filter array comprises a filter-band type filter.
5. The method of claim 1 in which the filter array comprises a filter, which is constructed
and arranged to rotate, the rotation preventing the accumulation and plugging of the filter by
continuous contact with turbidity inducing material
6. The method of claim 1 in which the oxi dant is halogen based,
7. The method of claim 1 in which the oxidant is sodium hypochlorite.
8. The method of claim 1 in which the monitor determines the oxidant concentration by
using an algorithm relying upon determining the amount of total halogen and tree halogen
residuals.
9. The method of claim 1 in which the flow rate through the filter array is adjusted by
diverting some of the water into a side spillway so the remaining sample flow is compatible with
the time interval needed by the monitor to measure the concentration.
10, The method of claim 1 further comprising the step of intermittently passing high
conceiitrations of oxidant to the monitor, ike monitor constructed and arranged to thereafter not
indicate that the measured oxidant amounts are measured oxidant amounts until one item has
occurred selected from the list consisting of: the measured oxidant concentration is no greater
than 0-20% of the measured amount before the high concentration was passed through, a
predetermined time has passed, a predetentiiRed multiple of the time interval of the analyzer has
passed, and any combination thereof.
11, The method of claim 10 in which the high concentrations of oxidant reduce fouling of at
least one item selected from the monitor, the pumps, the hoses, and any combination thereof.
12. The method of claim 1 in which the water sample is water from a paper mill process
stream
13. The method of claim 1 in which the turbidity inducing material is selected from the list
consisting of: cellulose fibers, mineral fillers, property enhancing polymers, sizing agents, wood
chips, and any combination thereof.