Apparatus For Determining Organic Carbon Content Of Polluted Liquids

Abstract

Apparatus for determining the organic carbon content of a liquid sample whereby the sample is acidified and scrubbed to remove its inorganic carbon content, and then vaporized in a reaction chamber having an air atmosphere which oxidizes to carbon dioxide the total organic carbon content of the sample. Measurement of the amount of carbon dioxide formed from the organic carbon is effected by an infrared analyzer.

Description

BACKGROUND AND SUMMARY OF THE INVENTION

In the measurement of pollution levels in aqueous systems, the amount of organic carbon in a sample taken from the liquid source to be monitored is an important index of the existing pollution level.

Accordingly, there is a need for equipment and methods that enable rapid and accurate determination of the organic carbon content of a liquid on a continuous or quasi-continuous sampling basis. One rather elaborate apparatus for total carbon analysis is described in U.S. Pat. No. 3,296,435 issued on Jan. 3, 1967 to J. L. Teal et al.

The invention provides an improved apparatus and a method for performing total organic carbon analyses more efficiently and rapidly than can be done with either the standard laboratory five-day biochemical oxygen demand test ( B O D ), or the two-hour chemical oxygen demand test, ( C O D ).

In the analytical apparatus of the invention, a sample stream from the aqueous liquid source to be monitored is continuously fed into a mixing chamber together with sufficient acid to react with and remove as carbon dioxide all of the inorganic carbon content of the sample, i.e. the carbonates in the sample. The acidified sample is scrubbed to remove all carbon dioxide produced by the carbonate-acid reaction, and the carbonate-free sample is metered into a reaction chamber. The reaction chamber has an inlet through which the sample and air for oxidizing the organic carbon of the sample are introduced; an outlet for the exit of gaseous and vapor products formed from the sample; and a granular packing material inside that is heated by electric resistor elements disposed outside the chamber in surrounding relation thereto. This packing material is chemically inert, as for example, crushed quartz, and is heated to a temperature at which the organic carbon in the sample is oxidized to carbon dioxide by the air atmosphere in the chamber.

Clogging of the reaction chamber by solids deposited upon the packing material is minimized through a special arrangement of the packing material with respect to the chamber boundaries. In accordance with the invention, the packing material is disposed to define within the reaction chamber an inlet plenum zone communicating with the inlet to accommodate preheating of the sample by the packing material without contact therewith; and an outlet plenum zone. The outlet plenum zone is separated from the inlet plenum zone and communicates with the outlet to collect and deliver thereto the gaseous and vapor products of the sample.

The size of the chamber, its inlet plenum zone and the thermal mass of the packing material are such that the sample is vaporized within the inlet plenum zone, before contact with the packing material itself.

Carbonaceous matter in the sample is quickly oxidized by the hot air atmosphere of the chamber so that the effluent therefrom is a mixture of water vapor and other gaseous products including carbon dioxide, the amount of carbon dioxide corresponding to the amount of organic carbon originally present in the sample. The water vapor portion of the reaction chamber effluent is expediently removed by a conventional gas-liquid separator before delivery to an infrared analyzer for measurement thereby of the carbon dioxide component.

For a better understanding of the invention and its various advantages, reference should be had to the following detailed description and accompanying drawing which together exemplify a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWING

In the drawing:

FIG. 1 is a schematic diagram of an organic carbon content analyzer apparatus according to a preferred embodiment of the invention.

FIG. 2 is an elevation view, partly in section, of the reaction chamber used in the apparatus represented by FIG. 1, as seen in a typical installation arranged for external heating of the reaction chamber and packing material therein.

FIG. 3 is a plan view of the reaction chamber and heating installation shown in FIG. 2.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

In FIG. 1 there is schematically exemplified an analyzer apparatus 10 constructed in accordance with the invention and which is operable to measure, on a continuous flow basis, the total organic carbon content in a sample stream taken from an aqueous liquid source 11, such as a body of water to be monitored for pollution level.

A continuous sample stream from source 11 is delivered by a metering pump 12 into a mixing chamber 13. Another metering pump 14 delivers hydrochloric acid from a reservoir 15 into mixing chamber 13 for the purpose of acidifying the liquid sample therein to a pH of approximately 2.0. The inorganic carbon present in the sample as carbonates is converted to carbon dioxide by reaction with the acid, and the organic carbon content of the sample is substantially unchanged.

The acidified sample stream is expediently fed into a conventional gas scrubber 16 that is supplied with air from a pump 17 to purge from the sample whatever carbon dioxide was formed by the acidification reaction. This carbon dioxide, which corresponds quantitatively to the amount of carbonates in the sample, is by choice vented to a waste zone, but could be delivered to a measuring means (not shown ) should it be desired to measure the amount of inorganic carbon in the sample.

The carbonate-free sample is fed by a metering pump 18 from scrubber 16 into a heated reaction chamber 19, which is also supplied with air from pump 17 to establish an oxidizing atmosphere within chamber 19. This hot oxidizing atmosphere rapidly vaporizes the sample and oxidizes the organic carbon content thereof to carbon dioxide.

The vapor and gaseous mixture effluent of reaction chamber 19 is delivered to a conventional gas-liquid separator 20 that removes by condensation the vapor component of the mixture and passes the gaseous portion containing the carbon dioxide to an infrared analyzer 21.

Infrared analyzer 21 is of conventional construction and serves to measure the amount of carbon dioxide formed by oxidation of the organic carbon in the sample. The total quantity of organic carbon originally present in the sample can be readily established by applying a known proportionality factor to the carbon dioxide measurement. Analyzer 21 is preferrably of a type which has an electrical analog signal presentation of the carbon dioxide measurement data. In such case, the carbon dioxide data signal is applied to the input of a compatible moving chart recorder 22 for direct display of the analysis results, either in terms of carbon dioxide quantity or, in terms of equivalent organic carbon, which can be done by suitable calibration of recorder 22 using techniques well known to those skilled in the art.

For calibration purposes, the inlet of metering pump 12 can be diverted temporarily from source 11 to another source, (not shown ), of liquid having a known concentration of organic carbon sufficiently constant as to be useable as a standard. The gas mixture output of separator 20 can be applied to an oxygen demand analyzer, (not shown ), instead of to the infra-red analyzer 21 where it is desired to measure the oxygen demand level of the sample.

While other means could be employed for effecting oxidation of the organic carbon content to carbon dioxide, the reaction chamber 19, shown in specific detail by FIGS. 2 and 3 offers definite improvements and advantages over prior art counterparts. The Chamber 19 has a peripheral wall 23 joined to a top cover 24 and a bottom cover 25 so as to form a sealed enclosure. Within chamber 19 is an apertured plate 26 which serves to retain a quantity of crushed quartz material 27.

Packing material 27 is so disposed as to define within chamber 19 an inlet plenum zone 28 and an outlet plenum zone 29 which is separated from inlet plenum zone 28. Plenum zone 28 communicates with an inlet opening 30 provided in cover 24 and a conduit 31 extending outside chamber 19. Conduit 31 in turn communicates with both the air supply pump 17 and the outlet of metering pump 18 to accommodate the introduction of oxidizing air and the sample into chamber 19. The outlet of chamber 19 is defined by a conduit 32 that extends through cover 24, inlet plenum zone 28, packing 27 and plate 26 to communicate with the outlet plenum zone 29. Plenum zone 29 thus serves to collect and deliver to outlet conduit 32 the gaseous and vapor products from the sample for exit from chamber 19. Plenum zone 28 is used for preheating the sample by packing 27 without contact therewith.

Pump 17 is selected and operated so as to deliver into chamber 19 several times the stoichiometric volume of air required for complete oxidation of the maximum anticipated carbon content of the sample.

Disposed outside chamber 19 in surrounding spaced relation thereto are a plurality of electric heater elements 33 that are used to heat the chamber 19 and quartz packing 27 to a temperature of approximately 850.degree.C. At such temperature, and with a mass of packing 27 that occupies at least 50 percent of the volume of chamber 19, the sample is preheated to vaporization almost immediately upon entering plenum zone 28, for sample feed rates up to about 2 percent per minute of the plenum zone 28 volume.

For example, at a packing 27 temperature of 850.degree.C, plenum zone 28 vaporization of an aqueous sample was achieved at a sample feed rate of 4cc/minute into chamber 19 having a plenum zone 28 volume of 500 cc and a total volume of 2,660 cc of which 1,660 cc was occupied by quartz packing 27.

With the plenum zone vaporization afforded by the invention, there is no cold liquid impingement upon the packing, and therefore the packing is not subject to further pulverization by thermal stress action. Consequently, the flow area presented by the voids between the pieces of packing 27 stays relatively constant and is not reduced significantly by clogging due to pulverization compaction of the packing 27.

In plenum zone 28, the sample is converted to a mixture of vapor and suspended solids which then pass the inert packing 27 in heat exchange flow contact therewith, and the organic carbon content of the mixture is completely oxidized to carbon dioxide before passing through plate 26 into the outlet plenum zone 29 at the opposite end of chamber 19.

To aid in controlling the temperature of the packing 27 there is provided in chamber 19 a thermocouple well 34, into which can be inserted a standard thermocouple, (not shown ).

From the foregoing description it will become apparent to the artisan that the invention is adaptable to many specific applications where the carbon content of liquids must be monitored, and that obvious changes in the exemplified apparatus can be made to satisfy particular requirements.

Claims

What is claimed is:

1. In an analytical apparatus for determining the total quantity of organic carbon as a pollutant in an aqueous stream by vaporizing a sample taken from the stream and oxidizing to carbon dioxide the total organic carbon in the sample, the determination being on the basis of the measure of carbon dioxide formed per unit measure of the sample, the improvement which comprises a mixing chamber, a first metering pump disposed to deliver into said mixing chamber a continuous flow sample taken from the stream, a second metering pump disposed to deliver into said mixing chamber a continuous flow of liquid reagent for reaction therein with the sample to remove the inorganic carbron content thereof as carbon dioxide; a reaction chamber, means connected to said mixing chamber and to said reaction chamber to deliver from said mixing chamber into said reaction chamber a continuous flow aqueous sample to be analyzed and which is substantially free of inorganic carbon and carbon dioxide, said reaction chamber having an inlet for introducing the aqueous sample to be analyzed and an outlet for the exit of gaseous and vapor products formed from such sample, means for introducing air into said reaction chamber to establish an oxidizing atmosphere therein, a packing material disposed within said reaction chamber for heating the sample introduced, and means for heating said packing material to a temperature at which the organic carbon in the sample is oxidized to carbon dioxide by said atmosphere, said packing material being disposed to define within the reaction chamber an inlet plenum zone communicating with said inlet to accommodate preheating of the sample by the packing material without contact therewith, and an outlet plenum zone separated from said inlet plenum zone and communicating with the outlet to collect and deliver thereto the gaseous and vapor products from the sample, said outlet plenum zone being communicated with said outlet by a conduit extending through said packing material.

2. The improvement according to claim 1 including a conduit extending outside the reaction chamber and communicating with an air supply means and said inlet for introducing air therethrough along with the sample.

3. The improvement according to claim 1 wherein the means for heating said packing material is disposed outside the reaction chamber.

4. The improvement according to claim 1 wherein said packing material is crushed quartz and occupies at least 50 percent of the reaction chamber volume.

5. The improvement according to claim 1 wherein said inlet plenum zone is at one end of the reaction chamber and said outlet plenum zone is at the opposite end of the reaction chamber, and said packing material contains voids accommodating the flow therethrough to the outlet plenum zone of the gaseous and vapor products of the sample.