Patent Application
20140021141
The invention relates to an arrangement for the addition of chlorine dioxide to a water-carrying pipeline, comprising a cylindrical reaction chamber and two reactant lines which open out into the reaction chamber and via which two reactants can be conveyed separately, from outside the pipeline, into the reaction chamber, the reaction chamber being provided with an exit hole which allows the exit of chlorine dioxide, formed from the reactants in the reaction chamber, into the water carried by the pipeline, and the axis of the exit hole in the service state being oriented in the direction of the longitudinal axis of the pipeline.
An arrangement of this kind is known from U.S. Pat. No. 4,534,952.
Water for industrial and commercial use must be treated so that it is disinfected thoroughly, safely and in an environmental benign way. Cooling or process waters offer ideal conditions for the multiplication of microorganisms, for example. Slime-forming bacteria in particular form so-called biofilms, which are microbiological contaminations which, in cooling water lines, severely disrupt heat transfer and cause corrosion.
A particularly efficient agent for water disinfection on account of its activity against microorganisms is chlorine dioxide (ClO2). It is active across a broad pH range and can be used not only to treat industrial waters such as cooling or process waters, in particular, but can also be used—subject to compliance with appropriately low concentration—in the beverage and food industries as well, in agriculture or in medical technology. A further field of application is in the paper industry, where chlorine dioxide is used to bleach pulp. Lastly, chlorine dioxide also serves for the disinfection of swimming pool water.
The commercial units typical to date for producing chlorine dioxide contain considerable quantities of chlorine dioxide, with all of the attendant risks in the operation of the generating units. The risk derives from the fact that chlorine dioxide is a highly toxic, explosive chemical, which even at low concentrations undergoes explosive decomposition and, in so doing, releases chlorine.
On account of its hazardous nature and low stability, ClO2 is not happily transported or stored, being instead, more preferably, synthesized directly at the site of use, more particularly in the water that is to be treated. In this way, the problem of producing and handling toxic and explosive chlorine dioxide is resolved. Accordingly, a variety of patent specifications disclose chlorine dioxide reactors which generate the ClO2 in situ and supply it immediately to the water to be treated, without further temporary storage. Examples of this kind are found in WO2009/077309, WO2009/077160A1, DE202004005755U1, US2005/0244328A1 and U.S. Pat. No. 4,534,952.
Generation of chlorine dioxide (ClO2) in situ takes place popularly by the chlorite/hydrochloric acid process, in which hydrochloric acid (HCl) is reacted with sodium chlorite (NaClO2) to give ClO2, water (H2O) and sodium chloride (NaCl):
5NaClO2+4HCl->4ClO2+5NaCl+2H2O
An advantage of this process is that there are only two reactants to be conveyed into the reactor, namely hydrochloric acid (HCl) with sodium chlorite (NaClO2). Since both chemicals are in aqueous solution, this is technically no problem, apart from the corrosiveness of these media. Mixed in a reactor, the two reactants undergo immediate and vigorous reaction to give the desired chlorine dioxide (ClO2). The water (H2O) of reaction that is formed, and the water constituents of the reactants supplied in aqueous form, wash the chlorine dioxide in highly concentrated aqueous solution from the reactor, where it becomes diluted with the water to be treated, attaining less hazardous but still biocidal concentrations. A disadvantage of this process is the inevitable formation of sodium chloride (NaCl), which if the solubility limit is exceeded, precipitates in crystalline form and clogs the reactor.
Many reactors known in the patent literature for the generation of chlorine dioxide in situ within the water to be treated are arranged within pipelines which carry the water to be treated. Reactors to be mentioned here include, first of all, those which have a tubular reaction chamber, which extends essentially along the pipeline with the water to be treated, and said water flowing around the reactor. One example of an axial reactor of this kind is found in DE20200400575501. Another example is shown in DE102010027908A1. With these chlorine dioxide reactors, then, the tubular reaction chamber extends along the pipe and discharges the synthesized chlorine dioxide at the distal end of the reactor through an exit opening which is directed in the longitudinal direction of the pipe, in other words in the flow direction of the water to be treated. With axial pipe reactors of this kind, the supplying of the reactants proves to be difficult.
U.S. Pat. No. 4,534,952 discloses a pipe reactor for generating chlorine dioxide, which is arranged in a bend in the pipeline with the water to be treated. In the region where the product exits, the reaction chamber extends likewise axially in the flow direction. Since the shaft runs radially, so to speak, at least sectionally, in the region of the bend in the pipe, the supplying of the reactants into the reaction chamber is easier. A disadvantage of this embodiment is that there are sections of the reaction chamber where ambient air, rather than the water to be treated, flows around the reaction chamber, since the two reactants are still mixed outside the pipeline. This means that in an accident scenario, toxic chlorine dioxide may be released. A construction of this kind is therefore inadvisable on safety grounds.
Known from German published specification DE1203691 is a chlorine dioxide synthesis reactor whose reaction chamber is implemented in the form of a dead water zone on the pipeline. Extending into the dead water zone are two open reactant lines via which the reactants are metered into the dead water for the purpose of synthesizing the chlorine dioxide. Within the dead water, the reactants undergo reaction to form chlorine dioxide, which exits from the dead water zone and is entrained by the drinking water to be treated, which flows in through the pipeline. This embodiment appears unfavourable from the standpoint of fluid dynamics. Moreover, there is a risk of the base of the dead water zone increasingly salting up. Lastly, the reactant lines run radially, unprotected, through the pipeline.
In light of this prior art, the object on which the present invention is based is that of specifying an arrangement for the synthesis of chlorine dioxide in situ within a pipeline that carries the water to be treated, this arrangement exhibiting high operational reliability and properties that are favourable from the standpoint of fluid dynamics.
This object is achieved, surprisingly, in that the reaction chamber is arranged at the distal end of a cylindrical shaft which in the service state is oriented radially to the pipeline and extends at least sectionally into the pipeline, such that the reaction chamber in the service state is located completely within the pipeline, and such that both reactant lines extend from outside the pipeline longitudinally through the shaft toward the reaction chamber.
The invention accordingly provides an arrangement for the addition of chlorine dioxide to a water-carrying pipeline, comprising a cylindrical reaction chamber and two reactant lines which open out into the reaction chamber and via which two reactants can be conveyed separately, from outside the pipeline, into the reaction chamber, the reaction chamber being provided with an exit hole which allows the exit of chlorine dioxide, formed from the reactants in the reaction chamber, into the water carried by the pipeline, and the axis of the exit hole in the service state being oriented in the direction of the longitudinal axis of the pipeline, wherein the reaction chamber is arranged at the distal end of a cylindrical shaft which in the service state is oriented radially to the pipeline and extends at least sectionally into the pipeline, such that the reaction chamber in the service state is located completely within the pipeline, and such that both reactant lines extend from outside the pipeline longitudinally through the shaft toward the reaction chamber.
The invention is therefore notable in particular for the shaft, which is arranged radially to the pipeline and which extends into said pipeline. Within the shaft there is no synthesis of chlorine dioxide; that synthesis takes place exclusively within the reaction chamber which is arranged at the distal end of the shaft. The shaft therefore initially fulfils the function of positioning the reaction chamber within the pipeline, so that in an accident scenario the chlorine dioxide is taken off in dilution by the water carried within the pipeline. Furthermore, the shaft surrounds the two reactant lines, so that the reactants can be neatly conveyed separately from one another into the reaction chamber, only intermixing therein and reacting to form chlorine dioxide. With the arrangement according to the invention, therefore, the chlorine dioxide is always produced within the pipeline. By virtue of its cylindrical form, the shaft has a streamlined shape. Lastly, the shaft protects the reactant lines from damage, thereby further enhancing the safety of the unit.
In one preferred embodiment of the invention, the dimensions of shaft and reaction chamber are such that the axis of the exit hole in the service state extends coaxially with the longitudinal axis of the pipeline. This means that chlorine dioxide exits centrally in the pipeline and thus enables outstanding mixing with the water flowing within the pipeline.
In one preferred embodiment of the invention, the reaction chamber is fastened detachably on the shaft, in particular by means of a screw connection. This permits the simple construction of a sequence of different arrangements with different performance classes, which will be elucidated in more detail later on.
Preferably, the reaction chamber, like the shaft, possesses a cylindrical form, is arranged coaxially with said shaft, and has the same outer diameter as said shaft; accordingly, with the reaction chamber mounted, the cylindrical form of the shaft is continued onto the distal end of the reaction chamber with no changes in cross section. This embodiment results in low hydraulic resistance.
In one preferred embodiment, the reaction chamber not only has a cylindrical outer form but also encloses a cylindrical reaction volume which is in contact with the surroundings exclusively via the two reactant lines and via the exit hole, the two reactant lines opening out at a distance from one another on the proximal end face of the reaction chamber, and the exit hole being made in the shell of the reaction chamber, with the axis of the exit hole being arranged perpendicularly to the axes of the outlets of the reactant lines, but not intersecting these axes.
This design of the reaction chamber leads to outstanding intermixing of the reactants within the reaction chamber, meaning that the reaction proceeds rapidly. The low residence times associated with this permit a small reaction volume, making the reactor less expensive and generating a reduced flow resistance.
In one particularly preferred development, the exit hole should be arranged as close as possible to the outlets of the reactant lines, at least in the proximal half of the reaction volume, when the entire reaction volume enclosed by the reaction chamber is conceptually divided transversely into a distal half and a proximal half.
As already mentioned, during the operation of a chlorine dioxide reactor according to the hydrochloric acid/chlorite process, there is, inherently, co-production of sodium chloride, which under amphorous operational conditions causes the reactor to salt up.
Surprisingly, in operation according to the hydrochloric acid/chlorite process, the arrangement configured in accordance with the invention shows no salt deposits at all if the ratio of the hourly generated mass of chlorine dioxide (M) in grams to the cross section (Q) of the exit hole in mm2 is governed by the following relation:
(30 g/h/mm2)<M/Q<(60 g/h/mm2)
if the hole cross section Q is selected too small in relation to the production volume M (M/Q>60 g/h/mm2), the reaction chamber becomes clogged. If, alternatively, the hole cross section is dimensioned too generously (M/Q<30 g/h/mm2), the water flowing through the pipeline washes out the reaction chamber and, in so doing, flushes out unreacted reactant. The conversion rate of the reaction and hence the efficient use of resources are diminished as a result.
As already mentioned, by combining a shaft with different screw-on reaction chambers, it is possible to set up a sequential construction of arrangements according to the invention, this construction entailing a small number of parts. The invention accordingly further provides a sequential construction comprising at least two arrangements according to the invention, with screw-connected reaction chambers, where the two arrangements have different reaction volumes and their shafts are identical.
Since within the sequential construction it is then necessary only to vary the reaction volume and possibly the cross section of the exit hole as well—the reactant lines can be kept constant—it is appropriate to construct the sequential construction on a uniform shaft, which to vary the conversion performance is combined with different reaction chambers. In this way, the number of parts within the sequential construction is significantly reduced, thereby significantly lowering the production costs. A further possibility is to convert an existing reactor into a higher performance class by changing over the reaction chamber.
The sequential construction preferably has not just two arrangements in two performance classes, but instead a greater number of performance stages, such as four or five, for example.
Additionally provided by the invention, furthermore, is the combination of a water-carrying line with the arrangement according to the invention, where the pipeline has a pipe section within which the pipeline runs linearly and on which the pipeline is provided with a dead water zone which extends radially relative to the pipe section, and into which the shaft of the arrangement has been introduced coaxially, such that the exit hole is located centrally in the pipe section and its axis is turned coaxially with the longitudinal axis of the pipe section. In this united construction of pipeline and reactor, there is no accumulation of salt at the product exit point, and the flow resistance of the shaft protruding into the pipeline, with the reaction chamber mounted, is comparatively low.
Further provided by the invention is the use of the arrangement described for the treatment of water flowing in the pipeline with chlorine dioxide which has been synthesized from the reactants in the reaction chamber. The chlorine dioxide is synthesized more particularly by the sodium chlorite/hydrochloric acid process. The treatment is preferably a biocidal treatment, in other words the killing of microorganisms living in the water, with ClO2. Microorganisms are, in particular, bacteria, viruses, fungi, germs, spores, algae or microbes. The killing of the microorganisms, in other words the disinfection of the water, is untaken from an industrial motivation in the case, for example, of the treatment of cooling waters, or alternatively on medical or veterinary grounds, as in the case of the treatment of drinking water or wash water in the case of interventions in the animal or human body.
The invention is now to be elucidated in more detail by means of exemplary embodiments. For this purpose
a: exit position 180° relative to the reactant lines;
b: exit position 90° relative to the reactant lines;
The external thread 4 is intended for screw connection of the shaft 1 to the cylindrical reaction chamber 5 shown in
In the screwed-on state, the reaction chamber 5 encloses a reaction space, shown with dashed lines in drawing 2, with the reaction volume V. Immediately after the end of the internal thread 6, an exit hole 7 with cross section Q has been made in the shell of the reaction chamber 5. In the screwed-on state, the reaction volume V is in contact with the environment exclusively via the exit hole 7 and via the distal outlets of the two reactant lines 2a and 2b. In operation, the two reactants are passed into the reaction chamber 5 via the coupling sleeves 3a, 3b and along the reactant lines 2a and 2b, and do not intermix until they reach said chamber 5. The reaction of the products to form chlorine dioxide therefore takes place within the reaction volume V. The chlorine dioxide produced by reaction is displaced from the reaction volume V by the continued conveying of reactants, and exits the reaction chamber through the hole 7. The dimensions of the reaction volume V are such that the residence time of the reactants within the reaction chamber amounts to around 5 seconds.
The result achieved through combination of the reaction chamber shown in
It is easy to see that by virtue of the screw connection 4, 6 between reaction chamber 5 and shaft 1, it is possible, using a small number of parts, to construct a sequence of reactors which cover different performance ranges. In this case, in practice, a greater number of performance stages will be provided than the two nominal sizes shown in the examples.
In operation, one reactant is conveyed into the shaft via each sleeve (3a shown, 3b facing away from the viewer in the section in
The entire shaft 1 and the reaction chamber 5 are manufactured wholly from PTFE. Both parts are turned or milled from the solid material.
Table 1 shows technical data for three embodiments of the arrangement in different performance classes, including the structural dimensions and operational parameters necessary for maintaining the short residence time.
In a series of experiments, a combination of pipeline and reactor as shown in
Experiment 06.12.2011-2 was carried out using 2 mm holes. The yield was approximately 100% before the conversion collapses completely and dropped even to below 20%. This is probably attributable to lumps of salt which blocked the two holes.
Experiment 06.12.2011-3 was carried out using 3 mm holes. The conversion yield fluctuates between about 75%-about 90%
Experiment 06.12.2011-1 was carried out using 2 mm holes. The yield fluctuated between about 80% to 100%.
Experiment 06.12.2011-4 was carried out using 3 mm holes. The yield climbs with fluctuation from about 40% to about 90%.
From the results it can be concluded that where possible the position of the exit opening should be made at 90°, i.e. transverse to the longitudinal axis of the pipeline, since higher and more stable conversion rates can be expected.
The intention was to investigate whether the size of the diameter of the hole for product exit in the arrangement shown in
In experiment 11.01.2012-1, the yield fluctuates between about 90% and about 100%.
In experiment 11.01.2012-2, the yield fluctuates between about 90% and about 100%.
In experiment 12.01.2012-1 the yield fluctuates between about 90% and about 100%.
With this experiment, the fluctuations are less strongly pronounced than in the other two experiments.
Experiment 2 shows that small holes can become clogged by salt, that larger holes improve gas removal and hence the conversion rate, and that water, if holes are too large, may wash out and/or dilute the reactor contents, and that the conversion rate may collapse.
The intention was to investigate the effect of the ratio of the cross-sectional area Q of the exit opening to the production performance M of the reactor, and whether this ratio is suitable as a design variable for a series with different reactor performance classes. For this purpose, conversion experiments were undertaken using different hole cross sections and different generational performances; the molar ratio of the reactants and the residence time, were not varied. The results are plotted in Table 5.
In the experiments set out in Table 5 it can be seen that high conversions above 90% are achieved more at a ratio of Q/M of between 30 and 60 than outside this range.
| Number | Date | Country | |
|---|---|---|---|
| 61674022 | Jul 2012 | US |
