WO2002004941A2

WO2002004941A2 - On-line deposition monitor

Info

Publication number: WO2002004941A2
Application number: PCT/US2001/021920
Authority: WO
Inventors: Richard M. Irwin; Geary G. Yee
Original assignee: Hercules Incorporated
Priority date: 2000-07-12
Filing date: 2001-07-10
Publication date: 2002-01-17
Also published as: AU2001271988A1; WO2002004941A3; US20020060020A1

Abstract

Online methods of quantitatively and qualitatively monitoring the biofilm growth and deposition organic and inorganic contaminants in paper processing equipment are provided. Spectroscopic methods, and more specifically attenuated total reflectance techniques are disclosed.

Description

ON-LINE DEPOSITION MONITOR

FIELD OF THE INVENTION

The present invention relates to a method and apparatus using spectroscopic analysis for the on-line monitoring of biological and chemical deposition from paper process water. More particularly, the present invention relates to methods and apparatuses using attenuated total reflectance specfroscopy for qualitatively and quantitatively determining contaminants depositing from paper process water, as well as for determining the rates of deposition and growth of such contaminants.

BACKGROUND OF RELATED TECHNOLOGY

Many industrial processes, such as paper making, utilize water and/or other liquid material in processing steps. Such process liquid typically provides an excellent supply of carbon and nutrients which promote bacterial growth. In paper mills, for instance, bacterial films ("biofilms") undesirably and readily form on the steel surfaces of process equipment used during manufacture. Such biofilms typically are accompanied by protective exopolysaccharides ("slime") and occur at the interface of these equipment surfaces and process water streams. Similarly, inorganic contaminants, such as calcium carbonate ("fillers") and organic contaminants often deposit on such surfaces. These organic contaminants typically include pitch (e.g., resins from wood) and stickies (e.g., glues, adhesives, tape, and wax particles).

The growth of biofilm and the deposition of these inorganic and organic contaminants can be detrimental to the efficiency of such equipment causing both reduced product quality, reduced operating efficiency, and general operational difficulties in the systems. Biofilm growth and organic and inorganic contaminant deposition on consistency regulators and other instrument probes can render these components useless, and such growth and deposition on screens can reduce tliroughput and upset operation of the system. Growth and deposition can occur not only on metal surfaces in the system, but also on plastic and synthetic surfaces such as machine wires, felts, foils, Uhle boxes and headbox components. The difficulties posed by these growths and deposits include sloughing off of large particles of the deposit causing sheet holes and breaks which result in reduced production and contaminated sheet surfaces having dirt and other sheet defects that reduce the quality and usefulness of the paper for operations that follow like coating, converting or printing.

Consequently, methods of preventing and removing the build-up of such growths and deposits on paper mill equipment surfaces are of great industrial importance. While paper machines can be shut down for cleaning to remove growths and deposits, this is undesirable as it necessarily results in a loss of productivity. The product which results prior to such cleaning is of poor quality as it is partially contaminated from growths and deposits which break off and become incorporated into product sheets. Preventing biofilm growth and contaminant deposition is thus greatly preferred as it allows for consistently high quality product to be produced in an efficient manner.

Further, the growth of slime on metal surfaces promotes corrosion of such surfaces, and fouling or plugging by slime readily occurs in paper mill systems.

Typically, the slime becomes entrained in the paper produced and causes breakouts on the paper machines with consequent work stoppages and the loss of production time. It also causes unsightly blemishes in the final product, resulting in rejects and wasted output. These contamination problems have resulted in the extensive utilization of biocides in water used in paper mill systems. Agents which have enjoyed widespread use in such applications include chlorine, organo-mercurials, chlorinated phenols, organo-bromines, and various organo-sulfur compounds, all of which are generally useful as biocides but each of which is attended by a variety of impediments. Particularly, the use of compositions comprising gelatin, such as that described in U.S. Patent No. 5,536,363 to Nguyen, have been found to be well suited for regulating the growth and deposition of contaminants in papermaking systems.

It is also known to monitor biofilm growth in papermaking systems, such as through the apparatuses and methods described in U.S. Patent Nos. 5,049,492 to Sauer et al. and U.S. Patent No. 6,017,459 to Zeiher et al., in which water is sampled during the manufacturing process. Such methods typically require that a coupon onto which contaminants have grown and deposited be removed from the fluid stream prior to analysis. Such methods are limited to traditional analysis, such as microscopy, which are laborious, subjective, and do not reliably reveal the dynamics (e.g., effects of pH, system additives, consistency) of the variations in process water parameters as the sampling frequency cannot typically be greater than one sample per hour, whereas the actual time constants of the variations are a matter of a few minutes. Sophisticated analyses to reveal deposit composition are limited to relatively thick deposits and are generally very difficult owing to alteration and aging of surface layers during handling.

Spectroscopic means have been used generally in analyzing biofilm growth or chemical contaminants dissolved or dispersed in fluid media. (D.E. Nivens, et al., "Continuous Nondestructive Monitoring of Microbial Biofilms: A Review of Analytical Techniques", Journal of Industrial Microbiology. (1995) 15 : 263-276 ("Nivens"); Tornberg, J. et al., "On-line Measurement Of Organic Substances In Paper Machine Wet End Water Using IR Specfroscopy", Paper and Timber. (1993) 75, 4: 228-232 ("Tornberg"). However, such techniques would appear to be unsuitable for use in on-line analysis of paper machine process water due to the unique characteristics of such process water. For example, as used in Nivens, attenuated total reflection (ATR) specfroscopy, a sampling technique used to examine aqueous environments near the surface of a special substratum called the internal reflection element (IRE), permits analysis of abase layer (approximately 1 micron) of biofilms and only provides an average picture of the chemistry transpiring over the entire area exposed to the aqueous environment. Additionally, as used in Nivens, ATR produces spectra containing vibrational information from all the molecules within the evanescent-wave region (region into which infrared radiation penetrates) resulting in data which is coincidental and convoluted. Further, determinations such as distinguishing dead biomass from living biomass from a single spectrum cannot be done. As used in these references, IR specfroscopy, particularly ATR, is not suitable for use in analyzing paper machine process water. For example, the use of germanium as an IRE, as used in Nivens, is not acceptable in an ATR unit for use with paper machines processes as such this element corrodes in paper process waters. Further, under typical ATR conditions, such as those in these Nivens and Tornberg, the depth of penetration of the infrared radiation, between 0.45 and 1 micron, does not allow for meaningful analysis of the types of growths and deposits found in paper machine process Whitewater, which are typically several centimeters in thickness. Additionally, it has been found that the ATR as used in these references does not permit for the analysis of organic and inorganic contaminants, which typically deposit on paper machines surfaces in the presence of high concentrations of typical paper making additives, such as calcium carbonate, and other suspended solids and fines.

Therefore, there exists a need for a method and apparatus which permits the on-line quantitative and qualitative analysis of biofilm and organic and inorganic contaminants which adsorb onto the surfaces of paper making equipment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIEMENT

The present invention involves the use of infrared specfroscopy, particularly ATR specfroscopy, wherein electromagnetic radiation is absorbed by atoms or molecules to qualitatively and quantitatively study biofilms and chemical contaminants (e.g., cellulose, carbonates, lignins, pitch, stickies) present in paper process water. The interaction of the radiation with the atoms or molecules causes redirection of the radiation and/or transitions between the energy levels of the atoms or molecules. Absorption occurs when a transition from a lower level to a higher level occurs with a transfer of energy from the radiation field to the atom or molecule. When atoms or molecules absorb radiation, the incoming energy excites a quantized structure to a higher energy level. The type of excitation depends on the wavelength of the radiation. For example, in the present invention, vibrations are excited by infrared radiation.

From these absorptions, an absorption spectrum is realized, which is the absorption of radiation as a function of wavelength. The spectrum of an atom or molecule depends on its energy level structure, and absorption spectra are useful for identifying compounds. In the present invention, each organic and inorganic contaminant has a characteristic absorption spectrum in which peaks due to different functional groups (e.g., hydroxyl) can be identified.

In the present invention, an absorption spectrum or absorption values at particular wavelengths are measured through the use of ATR spectrometry in which a beam of infrared light is transmitted through a crystal having the sample to be analyzed adsorbed thereto. Once the beam hits the surface of the sample it measures the active groups on or near the surface of the sample.

ATR specfroscopy, which uses the total internal reflection technique, is typically used in the mid-infrared region of the visible spectrum where absorptions due to molecular vibrations permit the analysis of contaminants in the present invention at the interface of an IRE present in the ATR unit. While the absorptions at each light reflection with the IRE are small, the attenuation of the incident infrared radiation can be increased by multiple reflections along the length of the IRE. The incident radiation is of sufficient intensity so that the light emerging from the IRE crystal after multiple reflections can be measured with good precision. The present invention involves the use of such an ATR technique to sense both the composition and rate of deposition of contaminant substances onto paper machine surfaces from aqueous process fluids.

Turning to Figure 1, an ATR flow cell 100 of the present invention is shown. Process water to be analyzed flows from paper machine process water source 102 into an input conduit 104, as indicated by arrow 103. The process water then flows fro input conduit 104 into fluid chamber 106, in fluid communication therewith, where it then flows longitudinally. Over time, contaminants 114 which are present in the water will adsorb onto the upper surface of IRE 112 within fluid chamber 106. The water then exits the ATR flow cell 100 as indicated by arrow 107 through an output conduit 108 which is in fluid communication with input conduit 104 and fluid flow chamber 106. After exiting ATR flow cell 100, the process water then re-enters process water source 102 or is discarded. The paper machine process water source which may be analyzed by the present invention may be any water source found in the papermaking industry, such as Whitewater. Elements of ATR flow cell 100 of the present invention are selected such that they do not corrode under conditions associated with such process water.

The top portion of flow cell 100 forms a cover over the IRE crystal 112 and is made of clear plastic, which facilitates access to IRE 112 for cleaning. An O-ring and screws are respectively used to seal and secure the cover to the flow cell 100. Further, a flow channel is machined into the cover which is designed so that the complete volume of fluid flow chamber 106 is swept at nearly the same flow rate and fabricated such that sharp edges and burrs are minimized which may trap fines, paper fibers, and debris. It has been found that a desired rate of process water flow which permits contaminants to adsorb to the surface of IRE 112 occurs when inlet conduit 104 and outlet conduit 108 have minimum diameters of 5 mm, flow chamber 106 has a flow cell volume of at least 7 cm³, and the linear flow velocity of the process water through flow chamber 106 remains constant between 125 and 175 cm/min, parameters which have been found to be uniquely suited for analysis of paper process water contaminants. These parameters permit the study of organic and inorganic contaminant deposition over extended periods of time and allow comparison of deposition rates at various parts of paper machine process systems.

An infrared radiation source 110, from a broadband or discreet light source, provides radiation to an IRE 112, as indicated by arrow 111 in Figure 1. The LRE may be any material that is suitable for use in the present invention so long as the material is non-corrosive under paper machine process water conditions and is non- reactive to components of paper process water streams. An IRE suitable for use in the present invention must be capable of withstanding paper machine process water conditions (e.g., be insoluble in water), must be capable of reflecting internally, and must be transparent to the infrared radiation. The material must be transparent because the IR radiation must reach the detector 116.

Accordingly, it has been found that an IRE of zinc selenide crystal is suitable for use in the present invention while germanium is not. Additionally, for purposes of the present invention, an active area on the IRE which is relatively large, for example 3.8 cm², has been found suitable for permitting the adsorption of contaminants from paper process streams thereon. However, this is in no way meant to be limiting and any active area may be used that permits such adsorption. The IRE may be of any suitable crystalline geometry.

Light propagates through IRE 112 by multiple internal reflections. At the interface between the paper process water and the IRE 112, the reflectance of the light is attenuated variably by partial reflections across the spectrum of the input light in accordance with the optical absorption characteristics of the contaminants. As the process water flows within fluid flow chamber 106, a layer of contaminants 114, particularly organic and inorganic contaminants, such as biofilms and calcium carbonate, form over time on the upper surface of the IRE 112.

As the light passes through IRE 112, a standing wave of radiation penetrates out from IRE 112 into the process water, and the intensity of the radiation decays exponentially with its distance from the IRE 112. The decaying wave, known as an evanescent wave, consists of the same frequencies as the reflected light, and may be absorbed by the contaminant molecules near the outer surface of the IRE.

The radiation is absorbed by a molecule of a contaminant when the energy of the radiation is equal to that required to promote the molecule to an excited vibrational state. Typically, absorption occurs only at discrete frequencies when a molecule is exposed to a continuum of IR radiation and the amount of radiation absorbed is proportional to the number of molecules present. This frequency- dependent absorption results in a unique absorbence pattern (spectrum) that is defined by the structure of the molecule.

In the present invention, for example, complex systems such as biofilms have a spectrum that is the sum of the specfral signature of each biomolecule in the sample. The frequency or wavenumber at which a molecule absorbs radiation is mainly determined by specific groups of atoms (functional groups) within the molecule. The individual wavenumber range at which a specific group of atoms absorbs radiation is referred to as the characteristic frequency.

Known characteristic frequencies allow the identification of LR absorbence bands which permit identification of differences in molecular structure of the contaminants and which permit the contaminants to be quantified as well. The correlation of functional groups and wavelengths of absorption bands is known in the art (e.g., Infrared and Raman Specfroscopy. Grasselli, J.G., Brame, E.G., Ed., Marcel Dekker (1977); Siverstein, Bassler and Morrill, Spectrometric Identification of Organic Compounds). Upon exiting IRE 112, as indicated by arrow 115, the attenuated light which is then measured in a conventional manner by a detector, such as a filter, interferometer, or array-based measuring device. Desirably, the detector is part of an optical spectrometer 116 for measuring wavelengths of light emitted from IRE 112. The radiation is monitored by spectrometer 116 at particular frequencies which are chosen to specifically correspond to the frequency values of known molecular absorptions present in the paper process water deposit contaminants of interest. For example, very strong absorbence signals from carbonate between 1600 and 1300 cm^"1, commonly present in paper process waters, must be suppressed to allow observation of weaker signals from other components of interest at nearby frequencies. This is effectively accomplished by measuring the 870 cm^"1 absorption exclusively from carbonate and subtracting this signal, after multiplication with an appropriate factor, from the values obtained at other infrared frequencies. This is possible only with very stable specfrophotometric systems of the present invention.

Spectrometer 116 may be, for example, a Fourier transform-infrared (FTIR) spectrometer which uses an interferometer to measure all light frequencies simultaneously with the light signal modulated over time. An FTIR is desirably used in the present invention because it offers increased analysis speed, improved signal to noise ratios, better wavenumber accuracy, and greater signal throughput at similar resolution, as compared to other known detectors. A solid state array detector, or a spectrometer which measures discreet wavelengths or a range of wavelengths, however, may facilitate lower cost for the apparatus. Such instruments typically incorporating radiation beams can be switched with reflective optics and facilitate measurement of the spectra of deposits on IREs in different flow cells, exposed to different treatments, thereby permitting use of the present invention in experimental designs, such as to test the efficacy of various biocidal agents on the growth of biofilms in paper process water.

As indicated in Figure 1, spectrometer 116 outputs spectral data corresponding to the absorption of light by molecules present in the contaminants to a signal processing algorithm 118 which is used for calculating and reporting changes in absorption over time. The data obtained thereby are output to controllers 120 for regulation of chemical levels (e.g., biocidal levels) present in paper process water source 102 in order to effectively regulate the presence of contaminants in the paper process water. By measuring as a function of time the changes in intensity of radiation transmitted through the IRE as the concentration of particular process components change at the IRE surface, the spectrometer 116 and signal processing algorithms 118 permit monitoring of both the compositions and rates of deposition of those compositions onto paper machine surfaces from aqueous process fluids. The process outputs 120 which are generated can be used to control process parameters, and components resulting from organic and inorganic contaminant deposition can be differentiated and independently monitored.

Claims

WHAT IS CLAIMED IS:

1. A method of monitoring an aqueous paper process medium for the presence of organic and inorganic contaminants, comprising the steps of:

a. providing a paper process water stream to a flow cell containing an internal reflectance element, wherein organic and inorganic contaminants present in said paper process water stream are permitted to be adsorbed onto a surface of said internal reflectance element and wherein said internal reflectance element does not corrode in the presence of the paper process water of said paper process water stream; b. radiating said internal reflectance element with a beam of infrared radiation; c. permitting said infrared radiation to contact a portion of said organic and inorganic contaminants which adsorb onto said surface of said internal reflectance element, wherein molecules present in said organic and inorganic contaminants absorb said infrared radiation at particular wavelengths; d. detecting and measuring transmitted infrared radiation emerging from said internal reflectance element.

2. The method of claim 1 , wherein said radiating step involves an attenuated total reflectance spectroscopic technique.

3. The method of claim 1, wherein said internal reflectance element is zinc selenide.

4. The method of claim 1 , wherein said paper process water stream flows through said flow cell at a rate which permits said organic and inorganic contaminants to be monitored over extended periods of time.

5. An apparatus for monitoring an aqueous paper process medium for the presence of organic and inorganic contaminants, comprising:

a. a flow cell containing an internal reflectance element, wherein organic and inorganic contaminants present in a paper process water stream are adsorbed onto a surface of said internal reflectance element and wherein said internal reflectance element does not corrode in the presence of the paper process water of said paper process water stream; b . an infrared radiation source for providing a beam of infrared radiation to said internal reflectance element; d. a spectrometer for detecting and measuring transmitted infrared radiation emerging from said internal reflectance element, wherein said infrared radiation contacts a portion of said organic and inorganic contaminants which deposit onto a surface of said internal reflectance element and wherein molecules present in said organic and inorganic contaminants absorb said infrared radiation at particular wavelengths.

6. The apparatus of claim 5, further comprising signal processing algorithms for calculating data obtained from said spectrometer and generating process output signals.