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[Atmospheric Pollution Technical Bulletin No. 29 of the National Council for Stream

Improvement, Inc., New York, N.Y., June 1966 ]




In February 1956, following an initial recommendation by West Coast mills and general discussions over a two-year period, the Board of Governors agreed that the National Council should undertake research and development in the field of air pollution control. It was recommended that this activity be carried on as a special project and financed separately. National Council members, at their own option, were eligible to join in this activity on payment of an additional assessment earmarked for it. Sufficient support to get started was quickly obtained and the first project got under way at the University of Florida in July of the same year. In the interim, the Council staff assembled a bibliography and library on the subject in the New York office. The first project to get underway, was the l'niversity of Florida in July 1956. This was headed by Dr. E. R. Hendrickson, a specialist in the atmospheric pollution field, and nationally known through his activities with phosphate industry problems. He has since served as Chairman of the Florida Air Pollution Control Commission for several years, and as national president of the Air Pollution Control Association, Dr. Hendrickson was assisted on our project by Admiral A. L. Danis, an eminent meteorologist. The following tasks were included in the project :

(1) To summarize the general principles of meteorolgy as they apply to air pollution and its control by pulp and papermills and show how they could be applied in assessing and combating the problem. Also included was the task of setting forth the technique for collection and tabulation of such information so that it could be of maximum value.

(2) To develop as simple an applicable techniques as possible for measuring flow, sampling, and analysing kraft mill and other pulp and papermill mill stack effluents. A second project was initiated in April 1957 at Washington State University under Prof. Donald Adams. This department was selected because of its northwestern location, an area where air pollution control was very active, and the competence of this research group in the new analytical tool, gas chromatography. The purpose of this project was to :

(1) Develop gas chromatography techniques for identification and measurement of the compounds responsible for the odor of kraft stack eilluents.

(2) Use these techniques to survey the kraft mills in the northwest to determine the discharge level of the major odorous compounds from the various emission sources.

(3) Determine the effectiveness of chlorine oxidation on the major odor sources, mercaptans and sulfides.

(4) Develop gas chromatography techniques suitable for continuous measurement of odorous sulfur compounds for adaptation in mill operating control applications.

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A year later in 1958, an additional project was instituted at New York University under Dr. William Ingraham. This University has been a leader in the field of air pollution resulting from particulate matter, having been employed by a number of large power companies for many years. The job assigned to this project was to prepare a manual dealing with air pollution resulting from fuel combustion. This work was accomplished in a little over one year, and a manual covering legislation, regulations, methods of measurement, combusion control, stack-cleansing techniques and stack-height determination was published as Air Technical Bulletin No. 12.

From 1959 to 1963, Rutgers University conducted specialized studies on aerial sampling and analysis—particularly with regard to hydrogen sulfide and its effect on painted surfaces. Through coordination of knowledge provided by this project and the University of Florida achieved by Dr. N. J. Lardieri of the staff, the methods of aerial survey now recommended by the Council and employed by a number of mills were developed.

The Operating Committee has directed that, insofar as possible, the air pollution control program be integrated with the five National Council Research Centers. The first moves made in this direction were to obtain personnel at Louisiana and Oregon State Universities to start a program. Council research activities at these centers have been largely directed toward laboratory and field studies dealing with methods for reducing kraft mill odors, which appear to be the major immediate problem that cannot be solved with existing techniques. Naturally, attending problems have and will receive further attention.

The body of this report consists of a staff review of progress and the current status of research and technical programs in the following areas:

(1) Analytical methods for source-gas sampling and gas-flow measurement.

(2) Black liquor oxidation.
(3) Absorption and oxidation of sulfur compounds.
(4) Particulate emission control.
(5) Meteorology and ambient-air-sampling techniques.
(6) Cooperative mill service activities.

(7) Staff technical activities. Further details are available by reference to the 28 technical bulletins published since inception of the program. The report concludes with a staff appraisal of identified research needs for the foreseeable future.


1. Analytical methods for source-gas sampling and gas-flono measurement

To evaluate the effect of kraft mill emissions on surrounding areas it was necessary to develop adequate source-sampling and analytical techniques. The first step was a review of the literature on methods of analysis, which subsequently was published in two technical bulletins. The Council then developed and published a wet analytical method for sulfur compounds. Field experience indicated that a major limitation of this method was the determination of total sulfur by combustion to sulfur dioxide. Too high a degree of control was required in this step.

Since the assessment of total sulfur is useful in obtaining a loss balance on a kraft mill, the wet analytical method was modified to collect and measure the four major sulfur compounds present in the airborne effluents (hydrogen sulfide, methyl mercaptan, dimethyl sulfide, and sulfur dioxide). A further modification, designed as a check on the total sulfur measured as individual components. involves thermal oxidation to sulfur trioxide, followed by chemical oxidation by hydrogen peroxide, and has eliminated the earlier limitation.

The analysis for individual components has been used to evaluate critically odor control processes, and has clearly pointed up some inadequacies of these processes. The use of these sampling and analytical techniques in the field, has provided data supporting many of the theories about furnace operation, the problems caused by contact evaporation, and the question of sources of sulfur emissions in a mill

. The usefulness of these developed analytical methods in determining emission levels was illustrated in the summary of three years of evaluations presented at our last annual meeting. Development of newer instrumental analytical methods, specifically gas chromatography, suggests erentual replacement of the wet methods by such instruments. Figure 1 shows a gas chromatograph used in our research and development program at Louisiana


State University. Very briefly, this is a device which partitions an unknown gas mixture on the basis of physical or chemical characteristics of its constituents.

In the early application of gas chromatography, the instruments lacked sensitivity. Even for stack gas analysis, the samples had to be concentrated before successful partition could be effected and measured. Therefore, the Council initiated research toward the development of more effective techniques for gas chromatography. As new and more sensitive detector systems were dereloped, they were evaluated on the compounds common to kraft pulping. To date, the most promising chromatographic development is the microcoulometric detector. This instrument is sensitive to 1 ppm of sulfur compounds. Therefore it appears that source sampling using this detector may require only a grab sample at the stack, followed by analysis in the mill laboratory. Several mills are now using gas chromatographs, and others are contemplating their use for routine testing and eventually continuous monitoring. 2. Black liquor oxidation

Black liquor oxidation has been practiced in the kraft industry for a number of years, and its value in the control of hydrogen sulfide in the recovery furnace stack has been well demonstrated. Excessive foaming is encountered when black liquor oxidation is attempted on weak black liquor from the pulping of resinous woods. Considerable research effort has been spent toward developing means of controlling such foam chemically, mechanically, thermally, and sonically without much success. Investigations, however, showed that concentrated black liquor high in soaps could be sucecssfully oxidized without severe foaming.

The Pasadena, Texas, mill of Champion Papers had been oxidizing concentrated black liquor for two years when they reported their results at the Council's 1962 Annual Meeting. Since that date, ten large, heavy black liquor oxidation units have been either installed or planned. The Council acted as liaison between interested mills for the dissemination of information pertinent to the adaptation of the Champion system. Without this cooperation between member companies and the National Council, it is doubtful that concentrated black liquor oxidation would be as widespread today, and it may very well have been more costly for each mill to develop its own oxidizing system.

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Along with the dissemination of design information, the Council also evaluated the effect of oxidation at various mills employing black liquor oxidation. Better than 90 per cent reduction of HS was shown to be effected on all tested furnaces which did not exhibit excessive losses from the firing zone. The benefits of black liquor oxidation with respect to ambient sulfide levels were shown in the results of a 2-year testing program conducted by a member mill with the cooperation of the National Council. The curves shown in Figure 2 indicate the rate of decrease of sulfides at various distances from the mill when half and all the black liquor were oxidized.

Although uncontrolled foam was a serious problem in attempting weak black liquor oxidation, some laboratory mass transfer devices which were designed to minimize foam were evaluated. This research was described in Technical Bulletin No. 165. Fundamental absorption rates were measured at low turbulence in thin film devices which were successful in controlling foam. These, however, were found to be impractical since too much surface area was required for effective oxidation. In a recent study, the foaming tendency of weak black liquor has been put to some use in a proposed foam fractionation process to increase soap yields. 3. Absorption and oxidation of sulfur compounds

To determine whether any alternatives to burning odorous gases for their ultimate destruction might be feasible, methods for absorption and chemical oxidation came under investigation. Chemical streams inherent in the kraft process, such as chlorine bleach effluents and dilute caustic solutions, were obvious possibilities, since this chemical is effective in absorbing H.S and methyl mercaptan. Laboratory and field studies have shown that the absorption rate is dependent on the pH of the scrubbing solution, a stream with a pH of less than 11.0 being no more effective than plain water. With the use of streams of pH near 14.0, the absorption rate can increase 20- to 30-fold. The effectiveness of an existing scrubber is increased accordingly. The use of caustic in scrubbing mercaptans is of limited odor control value due to the formation of odorous disulfides in the presence of oxygen. These reaction products will be stripped out of the exhausted scrubbing liquor unless handled in a closed system.

The use of chlorine in acid and alkaline solutions has been studied and found to be effective in the oxidation of H.S, methyl mercaptan, and dimethyl sulfide.

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In acid media, reaction is slow, but a stable, innocuous end product results. Reaction of reduced S compounds with chlorine at alkaline pH levels was shown to be more rapid. However, methyl disulfide, an insoluble, odorous compound is formed by partial oxidation and stripped out of solution. Field evaluation of existing odor control scrubbers is currently under way, and the findings will be summarized in a technical bulletin to be distributed shortly.

Fundamental studies on other chemical oxidants and xidation catalysts have been initiated and will be extended as benefits are shown. 4. Particulate emission control

Previously, reference was made to the work of Dr. Ingraham in preparation of the material for Technical Bulletin No. 12. It suffices to say that this comprehensive review illustrates that the air pollution problem associated with fuel burning and related to particulate discharge from such a cause, is usually amenable to reasonably precise definition and solution.

This is in contrast to the knowledge that has been available on reducing particulate emissions from recovery furnaces beyond that achieved in conventional control devices. The Council's West Coast Research Center has been active in this area since initiation of the air pollution program at Oregon State. Interest in this area stemmed from the need of local mills to comply with existing ambient air quality requirements for particulate matter. After cooperation with two mills on pilot studies of secondary scrubbers behind the primary recovery units, an evaluation of field installations was initiated. Seven such units now exist or are under construction, handling flows of from 60,000 to 40,000 cfm. The objectives of this survey are set forth below:

(1) To determine effectiveness on particulate discharge control.
(2) To determine energy and water requirements for scrubbing.

(3) To compile corrosion problems involved and determine suitability of promising materials of construction. The effectiveness of particulate control is being measured by stack sampling, and in most cases can be correlated with ambient-air survey data collected prior to scrubber installation. Energy and water requirements are related both to the economics of operation as well as efficiency. Due to high corrosion rates in early scrubber installations, the suitability of more resistant materials now in use, such as tile and fiberglass, as materials of construction are being documented.

Stack survey and ambient air data confirm that these devices are capable of reducing salt cake fallout in the mill vicinity to a minimum, well within existing ambient air quality requirements. They are also capable of meeting the most rigorous source emission regulations now in force. These devices are not, however, effective in reducing gaseous sulfur emissions unless the pH of the scrubbing solution is above 11. Pilot and one full-scale field investigation has shown that 80 per cent of H.S in relatively high concentration are removed with caustic use amounting to approximately 125 lb/ton pulp produced. 5. Meteorology and ambient air sampling techniques

A significant part of the Council's effort in air pollution work has been related to means of defining the conditions that can, or do, exist in the ambient air surrounding mill environs. Those areas of principal interest where work has been done and technical bulletins have been issued are listed below:

(1) Meteorology.
(2) H2S tile study.
(3) Techniques for high-volume sampling.

(4) Methods for conducting ambient air surveys. The application of techniques for collecting and tabulating meteorological data set forth have constituted the basis for several sampling programs, either now in eristence or since terminated.

There is a need for continuous monitoring of H.s in some areas and work was undertaken to evaluate the simple lead acetate tile technique for this use The research showed that uncontrollable environmental factors limit the effectiveness of the method as a quantitative analytical tool.

A recent bulletin describes sampling and analytical techniques for measuring suspended particulates in the atmosphere. This permits interested mills to collect information and compare local conditions with those in the 250-station, national air-sampling network operated by the Public Health Service. It may also define a mill's contribution to local situations.

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