METHOD FOR TREATING WATER WITH CHLORINE DIOXIDE

Abstract

A method for treating water with chlorine dioxide wherein the reactor is contained inside of the water supply line being treated and an eductor is used to draw in the chemical precursors. The method offers facilitated chlorine dioxide (ClO .sub.2) generation and safer operation over wider ClO.sub.2 mass flow capacity, thus offering a more adaptable system for CLO.sub.2 treatments. Noise reduction and ease-of-use versus traditional eductor-based ClO.sub.2 generators are additional benefits from using this method.

Claims

1. A method for ClO.sub.2 treatment that uses an eductor-based reactor assembly to expand the ClO.sub.2 flow capacity comprising: an eductor to provide flows of precursor chemicals to generate the ClO.sub.2 a mixing zone to ensure the ClO.sub.2 is generated at safe operating pressures below explosive limits of the ClO.sub.2; a pipe to which the reactor assembly is mounted that allows for containment of the eductor inside the process stream and direct treatment of the process stream with the ClO.sub.2; a means to provide motive water supply for the eductor; a control system that monitors precursor chemical flow rates and process flow rates to ensure that proper dilution and safe ClO.sub.2 dosage is being applied to the process stream being treated.

2. The method according to claim 1 whereby the precursors are acid and sodium chlorite.

3. The method according to claim 1 whereby the precursors are acid, sodium hypochlorite, and sodium chlorite.

4. The method according to claim 1 whereby the precursors are chlorine and sodium chlorite.

5. The method according to claim 1 wherein a flushing zone is an additional component of the reactor assembly that prevents ClO.sub.2 from accumulating within the process line and reactor assembly volume by continuously flushing volume outside of the eductor.

6. The method according to claim 1 wherein the reactor assembly is of modular design to accommodate interchangeable reactor assemblies for variable chlorine dioxide production capacity and turn down ratio.

7. The method according o claim 1 wherein the reactor assembly also comprises: a first-stage reaction chamber located upstream of the eductor wherein neat precursor chemicals mix and react to form the ClO.sub.2, and dilution water can optionally be added to dilute or flush said reaction chamber; a second-stage reaction chamber located downstream of the eductor wherein neat precursor chemicals and the motive water mix and react to form the ClO.sub.2 such that higher conversion of precursor chemicals to the ClO.sub.2 is achieved prior to blending with the process stream being treated; and optionally, additional reactor stages as required for enhancing safety and ClO.sub.2 yield.

8. The method according to claim 1 wherein a baffle is included that supports the reactor assembly and allows for insertion of instrumentation such as thermocouples, probes, and sensors that can monitor the state of the reactor and also be used in the control system.

9. The method according to claim 1 wherein the reactor assembly offers noise reduction as opposed to an eductor-based reactor that is not housed within the process flow.

10. The method according to claim 1 wherein the range of the ClO.sub.2 production and flow capacity can be changed by modifying the eductor, modifying the precursor feed lines, modifying the precursor concentrations, using multiple reactor assemblies, or any combination thereof.

11. The method according to claim 1 wherein the process reduces or eliminates additional water being added to the process.

12. A method for treating a liquid with chlorine dioxide, the method comprising passing a motive fluid through an eductor having an ejector end disposed in the liquid to be treated to draw precursor chemicals for the generation of chlorine dioxide into the eductor, contact the precursor chemicals within the eductor to generate chlorine dioxide, and eject the generated chlorine dioxide directly into the liquid to be treated.

13. The method according to claim 12, further comprising: generating a flow of the liquid to be treated through a passage, wherein the passage comprises a reactor assembly comprising the eductor, and the eductor comprises: one or more inlets for flow of precursor chemicals for the generation of chlorine dioxide into the eductor; a reaction space for contact of the precursor chemicals to generate chlorine dioxide; an entry for introduction of the motive fluid into the eductor for flow of the motive fluid through the eductor and out the ejector end thereof, wherein at least the ejector end is disposed within the passage for ejection of the generated chlorine dioxide directly into the liquid, whereby flow of the motive fluid draws the precursor chemicals into the reaction space via the inlets, and carries the generated chlorine dioxide directly into the passage; and injecting the motive fluid through the eductor to draw the precursor chemicals into the reaction space, generate chlorine dioxide, and carry the chlorine dioxide into the liquid flow,

14. The method according to claim 13, wherein the eductor is disposed internally within the passage for being disposed within the flow of liquid, wherein generating the flow of liquid comprises containment of the eductor assembly within the liquid stream, with ejection of the generated chlorine dioxide directly into the liquid stream for direct treatment of the liquid stream with the generated chlorine dioxide.

15. The method according to claim 13, wherein the reactor assembly further comprises a control system configured for monitoring and adjusting flow rates of the precursor chemicals and flow rate of the fluid stream, and the process further comprises monitoring and adjusting the flow rates of the precursor chemicals and flow rate of the fluid stream to provide a predetermined chlorine dioxide dosage into the liquid.

16. The method according to claim 12, wherein the precursor chemicals comprise acid and sodium chlorite,

17. The method according to claim 12. wherein the precursor chemicals comprise acid, sodium hypochlorite, and sodium chlorite.

18. The method according to claim 12, wherein the precursor chemicals comprise chlorine and sodium chlorite.

19. The method according to claim 12, wherein the reactor assembly has no additional pumps for moving the precursor chemicals.

20. A direct treatment system for generating chlorine dioxide and treating a liquid with the chlorine dioxide, the system comprising: a passage for flow of the liquid therethrough; and an eductor comprising: one or more inlets for flow of precursor chemicals for the generation of chlorine dioxide into the eductor; a reaction space for contact of the precursor chemicals to generate chlorine dioxide; an ejector end within the passage for ejection of the generated chlorine dioxide directly into liquid within the passage; and an inlet for introduction of motive fluid into the eductor for flow of the motive fluid through the eductor and out the ejector end thereof, wherein flow of the motive fluid draws the precursor chemicals into the reaction space to generate the chlorine dioxide, and ejects the generated chlorine dioxide into the passage.

Description

DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 shows the schematic for the three-part eductor-based reactor assembly.

[0022] FIG. 2 shows a schematic for a two-part reactor assembly with reaction chamber upstream of the educator.

DETAILED DESCRIPTION

[0023] A novel eductor-based reactor assembly is presented in FIG. 1 that provides a wider range of ClO.sub.2 mass flow capacity while maintaining safe operation. It also provides a compact design that facilitates maintenance, repairs, and overall operation of the ClO.sub.2 generator.

[0024] As shown in FIG. 1, the motive water, 4, for the eductor, 6, is provided by a separate water supply or can be drawn from the primary water supply upstream of the reactor. The dosage can be varied by controlling the process flow influent, 8, as well as the chemical precursor feeds, 1, 2, and 3.

[0025] The reactor assembly is composed of an eductor, 6, housed within the main water pipe, 10. Motive water is sent through the eductor to produce vacuum on the reactant chemical feed lines. Liquid flow controllers and flow meters are used to control and monitor the reactant feed rates.

[0026] A water flush zone, 5, near the base of the reactor assembly prevents ClO.sub.2 accumulation at the low point in the process line. Due to the high density of ClO.sub.2, it is possible that it will descend from the application point 7 and accumulate at low regions if not appropriately mixed into the process stream effluent, 9. Flow for 5 can be provided by the motive water supply or another external water supply.

[0027] The eductor-based reactor can efficiently produce ClO.sub.2 using any combination of generator chemistries. However, in the case of the acid-chlorite generator, a pre-mixing reaction chamber is required upstream from the eductor to achieve suitable conversion. FIG. 2 shows the 2-part acid/sodium chlorite reactor design. Acid and sodium chlorite feeds, 1 and 2, are directly mixed into a reaction chamber, 4, while being siphoned into the eductor, 6. Motive water, 3, is supplied to pull vacuum on the chemical feeds and is also used to flush the zone around the reactor assembly, 5. Process flow inlet, 7, is treated at the application point, 9, before leaving the process pipe, 10, as the treated process flow outlet, 8.

[0028] The invention is further illustrated with the following example.

EXAMPLE

[0029] The range of flow capacity for a given eductor design was determined for standard ClO.sub.2 generators versus novel reactor assembly designs. Using water flows to mimic 25 wt % NaClO.sub.2, 33wt % HCl, and 12.5 wt % NaOCl precursor solutions, maximum and minimum ClO.sub.2 production flows were determined according to fixed hardware, inlet pressure, and motive water flow rate.

[0030] Table I shows that the novel reactor assembly can achieve over an order of magnitude increase in ClO.sub.2 production level for a given eductor design and set of basic operating conditions. In addition, while the turn-down ratio of standard systems is limited to 4:1, the novel reactor assembly can achieve at least 10:1 under most operating conditions.

TABLE-US-00001 TABLE I Flow Capacity Range for Standard versus Novel Reactor Assembly Design Standard System (3,000 ppm max) Novel Reactor Assembly Maximum Maximum Motive capacity, Turndown Motive water capacity, Turndown water flow, kg ClO.sub.2/day Ratio flow, GPM kg ClO.sub.2/day Ratio GPM Eductor size 1: 175 4:1 11 2,800 >10:1 11 1.25 with 0.191 orifice 0.290 throat Eductor size 2: 425 4:1 27 3,200 >10:1 27 1.25 with 0.300 orifice 0.358 throat

[0031] Besides the increased range in ClO.sub.2 flow capacity, the novel reactor assembly was also much quieter on account of smaller motive water pump size and muffled eductor.

[0032] The reactor has a small dilution zone to application point. Because the eductor will be placed inside the main water pipe, it does not need to adhere to the 3,000 ppm maximum ClO.sub.2 concentration at the eductor outlet. Safe operation is preserved as the concentrated ClO.sub.2 stream is immediately diluted into the bulk process water flow. In cases where extended reaction time is required for reactor efficiency, the reactor assembly could include an extended eductor length that promotes higher conversion of reactants to ClO.sub.2. An examination as to the acceptable volume and maximum allowable ClO.sub.2 concentration in this zone would be required on a case-by-case basis. However, for most circumstances, it is expected that conversion will be sufficient and very rapid after the eductor, thus allowing for quick dilution into the main pipe header and safer operation by minimizing the total volume of high concentration ClO.sub.2.

[0033] In the case of high temperature or other reactor malfunction, the reaction chamber can be flushed with water, which may or may not be tied in with the eductor water feed pump. In the case that active flushing is not possible, the reactor assembly flush can be supplied by a pressurized water tank that purges the free volume of the reaction chamber to a safe level of dilution. Some means of volume expansion can also be incorporated to prevent over pressurization of any ClO.sub.2 that has off-gassed. This could include venting to a separate vessel that possibly contains an agent that effectively neutralizes ClO.sub.2.