A Gravimetric Technique for Determining the

Percentage of Water Vapor in Flue Gas

-

JON PEACY Pioneer Service & Engineering Company

Chicago, Illinois

This paper describes the theory of adsorption and the gravimetric technique and compares them to a standard method of determining the percentage of water vapor in flue gas. The method used is based on the adsorptive powers of various desiccants. These desiccants are com­pared to each other and to the standard method for an evaluation. A simple device is described and its operation is detailed for each desiccant. The standard method used is based on the ASME combustion calculations for deter­mining the percentage of water vapor in flue gas.

I NTRODUCTI ON

The main impetus behind this research effort stems from some of the source testing that has been conducted. It is a matter of significance why there were tests using different methods for determining the water vapor con­tent of flue gases and why they sometimes give different results. The problem appears to be the lack of a standard­ized operating procedure for each humidity measurement method. In addition to the above problem of developing standardized operating characteristics, this research is an attempt to demonstrate a superior meth.od (with standardized operating characteristics) for determining the water vapor in flue gases.

The state-of-the-art on humidity measurements states a variety of measurement devices. When this enormous list of measurement methods is confronted, the universal moisture determining method is not apparent. A reliable method to use in all instances is necessary.

161

The Gravimetric Technique, based on the adsorptive powers of certain desiccants, deals with the problem of determining the percentage of water vapor present in flue gas. The theory is explained, the method is demonstrated by comparing the desiccants to each other, and then compared to the ASME Calibration Method 19-10, the standard method now in operation.

The experiment is described, discussed and results ob­served, concluding that the Gravimetric Technique is reliable and that certain desiccants tested should be incor­porated into this method for determining the percentage of water vapor in flue gas.

THEORY OF ADSORPTION

The theory behind the Gravimetric Technique is based on adsorption. That is, a solid adsorbent (desiccant) has the ability of adsorbing moisture from, or adding moisture to, a gas such as an air-water vapor mixture. This property depends on the vapor pressure difference between the water in the gas and the water in the adsorbent. All gases and vapors are adsorbed to some extent on an adsorbent. surface. In the case of an air-water vapor mixture, the amount of air adsorbed is very small compared to the amount of water adsorbed, and consequently, dehumidi­fication of the air occurs. A figure illustrating this concept appears on page 239 in ASHRAE, Handbook of Funda­

mentals. [1] For some other gases containing moisture, the amount

of the carrier gas adsorbed may be appreciable with a con�

•

sequent decrease in the water adsorbing capacity of the desiccant. Although attempts have been made to correlate the amounts of specific components adsorbed on various , desiccants, no completely reliable means of predicting these have been found. Polar compounds are usually more strongly adsorbed than nonpolar. Within a given chemical family, high molecular weight compounds are adsorbed easier than low molecular weight compounds.

The process of adsorption by solid desiccants is revers­ible. If the vapor pressure of the adsorbed water becomes greater than the partial pressure of the vapor in tj1e sur­rounding atmosphere, water will be released by the adsorb­ent. In most cases, this desorption is accomplished by the application of heat to drive off the adsorbate. Reactivation temperatures for common desiccants are generally in the range of 93°C to 260°C. Hence, these temperatures are a limiting factor in this application of desiccant devices. Page 236 in ASHRAE,Handbook of Fundamentals, [1] has a figure illustrating the effect of these limiting temper­atures. Since no physical or chemical change occurs to the adsorbent in this process, the adsorbent is again ready to extract water from a wet gas after the so-called reactiva­tion. It is this property of reversibility which makes ad­sorption an economical process. Most solid adsorbents are able to operate for thousands of adsorption-reactivation cycles. [1]

Molecular sieves act as physical adsorbents in almost all cases. This means that a molecule is held within the molecular sieve crystal by relatively weak, physical forces of the van der Waals type. When the molecule is desorbed by the application of heat or the displacement by another material more strongly adsorbed, it leaves the molecular sieve crystal in the same chemical state as when it entered. A model of a molecular sieve crystal appears on page 5 of Thomas, "Molecular Sieves in Petroleum and Natural Gas Processing". [2] -

Adsorption on molecular sieves is characterized by a Langmuir type isotherm, where the amount of a given compound adsorbed increases rapidly to a saturation value as its pressure or concentration increases in the ex­ternal bulk phase. Any further increase in the pressure at constant temperatures causes no further increases in the amount adsorbed. With molecular sieves this equilibrium saturation value usually corresponds to completely filling the internal void volume with the material adsorbed. This desorption from molecular sieves shows little hysteresis, that is, the adsorption and desorption are reversible with the respective isothermal curves coinciding. With the pelleted molecular sieve material, however, some further adsorption may occur at pressu,res near the saturated vapor pressure due to the condensation of liquid in the

inter crystalline voids in the pellet. The external surface area of the molecular sieve is

available for adsorption of molecules of all sizes, whereas the internal area is available only to molecules small enough to enter the molecular sieve pores. The external area is only 1 percent of the total surface area. Materials which are too large to be adsorbed internally will com­monly be adsorbed externally to the extent of 0.2 - 1 per­cent by weight. Molecular sieves are capable of separating materials based on their molecular size and configuration. This is illustrated on page 5 of Thomas, Linde Molecular

Sieves Adsorbent Bulletin. [2] This figure shows retention and displacements of molecular sieve 3A, and leads to the conclusion that water will displace the other compounds, at least from the internal surface area of type 3A.

Thus, molecular sieves 3A, 4A, and SA were three of the desiccants chosen for this experiment. Silica gel, alumina gel, and activated alumina are the other three desiccants used. All six have the characteristics necessary for this experiment. That is, they are all inexpensive, easily obtained, safe to handle, nonpoisonous, and have a convenient size and shape.

162

, DESI CCANT TUBE HOLDER DESIGN

After choosing the desiccants for the experiment, it was necessary to design a tube holder. The design was based upon a desirable weight change which would be larger than any inaccuracies due t<} the balance used, the particulate matter collected, or regeneration problems en­countered (residual moisture). A desirable weight change of 50 grams was selected. By using the adsorption data in the literature, [1] 250 grams of desiccant was "necessary to obtain this change in weight.

A convenient container for this amount of material would be a clear plastic tube which is flexible. A search for an inexpensive, high temperature plastic was conducted with the "Tygon" compound R3603 [3] being the final choice. This material was tested for heat stability by an overnight (12 hours) exposure to 110°C heat and it suffered no ill effects. Another "Ty,gon" compound, R44, which was listed [3] as having better temperature character­istics, suffered extreme discoloration, rendering the tubing opaque and therefore disqualifying it.

After selecting the material for the container, the largest inside diameter tubing available was needed. With toUbing of a 1.58cm inside diameter and a desired weight change of 50 grams, a length of tubing equal to 183cm was selected. Twelve tube holding devices of this length were constructed. Each weighed approximately 150 grams, com­plete with handles. The empty test weight, complete with

corks, tubes, handles, and serum caps, was approximately 400 grams before the addition of the desiccan t. The device in Fig. 1 is the desiccant tube holder, which holds the tubes and is convenient for handling.

Several preliminary tests were conducted in the laboratory to ascertain the effectiveness of the 183cm length. During these tests, other tube lengths were tried and a length of IS0cm was chosen as the most practicable. This was later verified during the several hundred tests that were conducted, as the IS0cm tube appeared to "last" for the desired 30 minute test period without breakdown, i.e., passing excessive water vapor so as to affect the meter in­let temperature.

DESICCANT SAMPLE PREPARATI ON

After selecting the tubing, samples of the desiccants were prepared. It was then necessary to develop a drying technique. Each of the desiccants was placed in an open Pyrex tray in a heated oven for approximately 12 hour� before being cooled. The oven was held at 104.SoC for the silica gel regeneration and 20SoC for the regeneration of the other desiccants. They were then placed in the desic­cant tube holder, capped, weighed'on a Mettler P1200 balance, and then exposed to the flue gas at various flow rates for approximately 30 minutes.

Before the above mentioned technique was developed, other techniques were tried, such as passing heated low moisture air through the "full" desiccant tube holder, and also heating the desiccant in a frying pan. Both of these failed.

After each desiccant was dried in the above mentioned manner, they were placed in their special tube, and it was sealed shut with rubber stoppers and serum caps. Figure 2 shows the loading technique applied to one of the desic­cant devices. When the proper number of desiccant tube holders were prepared, they were taken to the balance room to be weighed and then removed to the test site. The loading and weighing operation requires approximately 4S minutes. Figures 3 and 4 show some of the test opera­tions. In both of them, testing is in progress. After being exposed to the flue gas, they were sealed by the serum caps, returned to the balance room and weighed. The desicc'ant material was removed and placed in the ovens. This completed the test cycle.

DI SCUSSION OF EXPERI MENT"

During the first month of the tests, a problem appeared with molecular sieve SA. This particular compound ad­sorbs CO2 as well as H20 as indicated in Thomas. [2]

163

o

I----� - --- -1------1

•

I-----I------�------�

o

F IG. 1 DESICCANT TUBE HOLDER

Several attempts at trying to "field test" the possi.bility of CO2 being adsorbed and to discover the quantity adsorbed, were made. Most of these attempts tried to 'analyze the gas that was passing through the desiccant, meter, and leak­proof (rotary vane) pump. Other attempts were made to' extract the gas sample so it would not become dilluted with any outside air, as Fig. S shows. None of these attempts were successful in conclusively demonstrating that the desiccants were removing CO2 in addition to water vapor. As far as other contaminents; fly ash, dust, methane or other unburned hydrocarbons; were con­cerned, it was assumed they did not exist in sufficient quantity to affect the results. Frequent visual inspection of the probe, constant surveillance of the boiler meter panel and fire box, and frequent discussions with the boiler operators reinforced the above assumptions.

The length of the test for the desiccant devices was 30 minutes and approximately 140 liters of flue gas were

F IG. 2 THE DESICCANT TUBE HOLDERS IN T HE LEFT FOREGROUND ARE LOADED W ITH A MOLECULAR S IEVE COMPOUND, AND ARE READY TO BE WE I G HED PRIOR TO TESTI NG.

F IG. 4 THE DESICCANT DEVICES IN OPERAT ION.

FIG. 3 RECORDING PERTINENT TEST DATA FROM T HE GAS METERS.

164

FIG. 5 ORSAT DEVICE ATTACHED TO PUMP EXHAUST.

sampled during that time, necessitating a sample flow rate of 4.66 LPM. Other flow rates were tried with the result that a high flow rate, greater than 7.08 LPM, led to prob­lems with moisture passing through the desiccant bed un. collected. This was evidenced by a rapid rise in the inlet (meter) thermometer's temperature or by water condens­ing out in the clear (for that purpose) tygon tubing that led from the desiccant tube holder to the meter. Since the tubing holding the desiccant was clear and most of the desiccant had indicating (color change when wet) agents in them, it would have been easy to spot escaping moisture by a color change near the exit of the holder.

The flow rates used for activated alumina and silica gel desiccants were 3.31 LPM to 7.08 LPM, which gave satis­factory results. At these rates, water vapor never passed through the desiccants. It was difficult to operate these at higher flow rates since the packing density interferred with the gas movement. This was not the case with the molecular sieves, whose shapes allowed higher flow rates. Rates in the vicinity of 9.42 LPM were tried, but there was a tendency to pass water vapor at this flow rate. Therefore, the' molecular sieves were tested at 4.66 LPM to 8.50 LPM.

RESULTS OF ADSORBENT EVALUATI ON

Five graphs, Figs. 6-10, are presented to show the results of this test series with desiccants. They are each a

165

plot of the humidity values that were obtained by the test procedure. The indicated percentage of moisture content is derived from the experimental device and plotted along the ordinate. The abscissa in each graph is the percentage of moisture content obtained by ASME calculation technique. A line is drawn in each case to represent an exact agreement between the indicated and calculated values.

In Fig. 6, the seven experimental points appear to be grouped slightly below the line when the point A is ex­cluded. Point A should be excluded as it was obtained from the initial test of desiccant 3A. Each of the molecular sieve desiccants exhibited a tendency to yield �xception­ally ·high indicated percentages of moisture by vo�u;ne as a result of the first test. Since their following results were "grouped", a conclusion of an initial "break in" period is unavoidable.

In Fig. 7, four of the five experimental points appear to be grouped. Point B should be excluded from considera­tions. It was obtained from the initial test of desiccant 4A, and appears to result from the "break in" period as mentioned before.

Both of these desiccants, molecular sieve 3A and 4A, appear to yield values of the percentage of moisture con­tent that is close to the calculated value when points A and B are excluded. The conclusion is there are an insuf­

ficient number a/ test points to determine the accept­ability of these desiccants.

Figure 8 illustrates the accuracy of molecular sieve SA. In almost every case, this desiccant indicated a hlgher percentage of moisture content of the flue gas than was calculated by the standard calibration method. From this it is concluded that molecular sieve SA is not an accept­

able desiccant for determining the percentage of moisture content in flue gas.

The silica gel desiccant test results are depicted in Fig. 9. Silica gel appears to be barely adequate for deter­mining the percentage of moisture content of flue gas streams. It is significant that approximately 47 percent of the test points lie within the ± I percent of the moisture content tolerance limit. For this reason, it is concluded that the silica gel desiccant should not be pre/e"ed for use in determining the percentage of moisture content of flue gas streams.

The test results of the activated alumina desiccant are depicted in Fig. 10. It can be seen that approximately 54 per­cent of the test values lie with the ±1 percent of the moisture

- - - -

content tolerance limits. Therefore, it is concluded that the activated alumina desiccant is an acceptable desiccant to use in determining the percentage of moisture content of flue gas streams.

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F IG.6 G RAPH OF THE RESULTS OF THE TEST SERIES W ITH MOLECULAR S IEVE 3A DESICCANT.

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Calculated % of Moisture (by volume)

F IG.7 GRAPH OF THE RESULTS OF THE TEST SERIES W ITH MOLECULAR S IEVE 4A DESICCANT.

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Calculated I of Moisture (by volume'

GRAPH O F THE RESULTS OF THE TEST SERIES WITH MOLECULAR S IEVE SA DESICCANT.

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166

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F IG.9 GRAPH OF THE RESULTS OF THE TEST SERIES WITH THE S IL ICA GEL DESICCANT.

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SAMPLE CALCULATI ONS

The following sample formulae are similar to those used in each test case for computing the percentage of moisture by volume that was experimentally determined during each adsorption test.

Formula (4) yields the volume of sampled flue gas at standard temperature and pressure:

(4)

Formula (5) yields the volume of sampled flue gas at duct temperature and pressure:

. _ V std P std Tduct V

duct - -'--T--"-P-­std duct

(5)

Formula (6) yields the volume of water vapor at duct temperature and pressure based on the amount of water collected by the desiccant:

1 w V

wv = (82.057) Tduct Pduct 18.00

(6)

Formula (7) yields the volume percentage of water vapor as determined by the desiccant weight change method:

V Vol. percent water vapor =

wv X 100 (7) V

duct + VWI'

The following sample calculations use'data gathered on the 6th of October, 1970. This data can be found on Table 8.

Run 1 Formula

(163.4 L) (659mm)(330oK) .:..-----=-::....--�---..:. = 140.2 L

(760mm)(332°K)

(140.2 L)(760mm)(433°K) . = 188.8 L

(761mm)(3300K)

(762mm)(15.24gm)(82.057cc/gm mole.°K)(433°K) =27700cc

(761mm)(l8.00gm/gm mole)

27.7 L """1"7 8-::-' 8.-=- 8-=-L-+

.o.':2:":: 7:-:.7:-:L:- X 100 = 12.8%

(4)

(5) .

(6)

(7)

The same operation was carried out for another set of ex-perimental values and that result was averaged with Run 1. This yielded a value of 12.2 percent. This value represents the percentage of moisture by volume as determined by the desiccant technique. The values were computed for each test done and are found in Table 3.

ASME CALIBRATION METHOD

The theory behind this method involves a combustion theory and it is not the intent of this paper to delve into

167

Device

Method

Number of tests

Range of Deviations • Average Deviation

Average Deviation Without Extremes

Change in Average Deviation

Table 1. Deviation Comparison

5A

18

8.6%

+3.0

+2.4

0.6

Desiccants

4A 3A AA

5 7 1 1

7.6% 6.8% 4.8%

+0.9 -1.0 -1.3

-0.4 -1.5 -0.7

1."3 0.5 0.6

Table 2. In and Out of Tolerance

SG

15

5.1%

-0.8

-0.5

0.3

Tolerance +1.0 Percent of the Moisture Content by Volume

Device

Method

Number of Tests

No. out

No. in

Total

Percentage of Tests

% Out

% In

•

No. Date

1 9/15

2 9/15

3 9/15

4 9/15

5 9/16

6 9/16

7 9/16

8 9/16

9 9/17

10 9/17

5A

15

3

18

83

17

Desiccants

4A

2

3

5

40

60 -

Table 3

3A

6

1

7

86

14

AA

5

6

1 1

46

54

Percentage of Moisture in Flue Gas

CO2 Time % Calc. A.A. S.G.

4:41 8.4 14.7

3:55 6.8 14.0 X

3: 16 X

5:09 7.2

4:20 5.8 11.4 X

4:52 5.6 11.3

5:35 5.2 10.9 X

6: 15 5.2 11.5

2:55 6.8 11.3

3:20 8.4 16.9 X

SG

1 1

4

15

73

27

M.S.

type

5A

5A

5A

•

5A

5A

%

17.2

15.5

13.9

17.5

11.5

15.4

11.7

17.3

19.3

13.9

No.

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

51

52

53

54

55

56

57

Table 3 (Continued) Table 3 (Continued)

Date Time

9/17

9/17

9/18

9/18

9/18

9/18

9/21

9/21

9/21

9/21

9/22

9/22

9/22

9/22

9/23

9/23

9/23

9/23

9/24

9/24

9/24

9/24

9/30

9/30

9/30

10/1

10/1

10/1

10/5

10/5

10/5

10/5

10/6

10/6

10/6

10/6

10/6

10/8

10/8

10/8

10/9

10/9

10/9

10/13

10/19

10/19

10/20

4: 11

5:30

3:48

4:28

5:08

5:47

3:05

3:41

4:40

5:07

2:02

2:47

3:28

4: 18

2:25

2:57

3:38

3:59

3:02

3:47

4:30

5:30

5:20

5:51

6:29

3:03

4:36

5:34

4:20

5:38

6: 1 0

6:55

4: 17

4:48

5:47

6:33

7:57

3:36

4: 14

5:08

2:49

3:40

4:36

6:27

4:30

6:40

5: 18

CO, M.S. CO, M.S. % Calc. A.A. S.G. type % No. Date Time % Calc. A.A. S.G. type %

7.1 13.1

6.7 14.0

8.5 14.7

9.0 16.4

8.1 14.0

8.0 14.6

7.8 17.1

8.0 14.9

7.9 13.6

7.6 12.1

7.8 18.4

8.3 15.3

7.4 13.9

7.5 14.8

7.0 15.5

X

X

X

X

7.3 13.7 X 7.4 15.2

8.3 16.4

6.8 13.7 X 6.9 13.1

6.3 11.9

4.3 8.2

4.4 12.1

3.9 9.8

4.6 11.3

7.6 14.9

7.7 14.2

7.6 14.6

7.3 14.0

7.7 13.7

7.3 13.5

7.6 13.6

7.2 13.8

7.7 13.7

7.5 13.5

7.3 14.8

7.1 13.4

7.2 13.8

6.6 13.2

7.5 14.5

7.7 15.2

7.8 13.6

7.0 13.4

7.0 13.6

7.0 13.7

7.1 13.4

X

X

X

X

X

X X

X

X

X

X

X

X

5A 16.6 58

11.8 59

5A 17.2 60

13.4 61

13.7 . 62

5A 16.2 63

14.7 64

15.7 65

5A 16.3

5A 16.4

14.7

5A 14.8

5A 16.0

16.6

14.7

14.7

5A 16.6

5A 19.0

13.3

13.8

5A 14.7

5A 15.0

14.0

4A 16.1

3A 15.0

13.1

4A 15.1

3A 14.6

10.2

11.2

4A 12.9

3A 12.0

3A 12.2

4A 12.9

12.4

11.5

4A 12.1

3A 11.1

12.0

3A 13.4

5A 15.7

13.0

168

66

67

Time

3:46

3:47

3:50

Time

3:53

4: 14

10/20

10/21

10/21

10/23

10/23

10/23

10/30

10/30

10/30

10/30

6:53

4:30

6:00

4:20

5:23

1 :58

11 :44

1 :33

2:43

3:00

7.6 13.2

6.4 13.4

7.6 13.1

7.1 13.9

9.7 13.9

7.9

5.0 10.4

6.2 12.2

6.0 11.6

6.0 11.7

Table 4

X

X

3A

7.2

9.1

5A 11.5

9.1

Summary of Acceptability for Determining Percent of

Moisture Content of Flue Gas

Method

Molecular Sieve 5A

4A

3A

Drierite

Si I ica Gel Activated Alumina

Table 5

Acceptability

No Conditional Cond iti onal

No No Yes

Raw Test Data of 10/6/70

Boiler Number

4

3

6

Duct Temp. of

260

255

Steam Flow 1000 Ib/hr

26

32

85

Dect Press. H,O

-0.60

-0.60

Fuel Integrator Reading Gas % Type

443698

792168

221843

Intake Air Wb Db

61 84

60 83

8.0 0, 7.0 CO, 6.2 0,

•

Table 5 (Continued)

Time CO.%

3:54 7.0

4:03 5.9

4:08

4: 17

4:22

Date

10/6

5.8

7.2

5.7

Container

P

Meter Used No. JA 570251

Sum

13.7

15.0

14.1

0% •

6.7

9.2

6.9

Final Weight, Grams

698.07

Barometric Pressure at Test Location 30.010 "Hg.

Meter Meter Cubic Press. Temp.

Time Feet "Hg. of Cubic FPH

3:58 985.52 4.1 74 12

4:21 4.2 75

4:28 4.2 75

Flue Meters

x

X

x X

X

Initial Weight , Grams

682.78

Desiccant Inlet Temp.

of

92

123

124 •

such matters. A revision of the American Society of Mechanical Engineers will be used.

The ASME method is found in their Performance Test Code 19-10, Flue and Exhaust Gas Analysis. [4] Revision of the method that will be utilized is from the book, Steam, Its Generation And Use. [5] The method involves determining the moisture in the intake air, the moisture in the fuel (from the ultimate analysis), and the moisture due to combustion of the hydrogen bearing compounds in the fuel. Based on the above three items and the Orsat analysis of the flue gases, the water vapor content is calculated. This method requires approximately 30 minutes to compute the percentage of the moisture content of the flue gas. A sample calculation can be found in the appendix.

169

CONCLUSI ONS

The first conclusion to be made concerns tolerance limits. It is of interest to note that the calculated moisture content values are not invariant. They fluctuate with a range of 10.1 percent in the calculated percentage of moisture content with an average daily fluctuation of 1.8 percent. This was determined by an analysis of Table 3.

This daily fluctuation of 1.8 percent in the calculated percentage of moisture by volume formed the basis of choosing the + 1 percent of the moisture content as a tolerance limit. This was for the experimental desiccants that were tested. One half of this daily fluctuation was taken and arithmetically rounded off to form the upper and lower limit of expected error. Each test done on an experimental desiccant was correlated as closely as pos­sible to the calculated percentage of moisture by volume. This was done by obtaining Orsat analysis during the operation of each experimental desiccant.

The last conclusion concerns the adequacy of the de sic-• cants. It appears that all of the tested desiccants will capture water, but that this ability was greater in some of the desiccants than in others. When we consider the number of tests that were within the + 1.0 percent tolerance limit that was set and the comparison of per­cent deviations, molecular sieve 4A stands out. This is especially true when we consider the phenomena of "initial" moisture in the desiccant, which yields the value far out of the tolerance limit, as depicted on Fig. 12, point B. This is reinforced by comparing Tables 1 and 2. One conclusion is that molecular sieve 4A should be pre­treated. The "Runner Up" in the desiccant contest must be activated alumina, and we have rated it acceptable on Table 4 with no pretreatment. It also enjoys �he distinc­tion of having the lowest price. It is therefore concluded that the best desiccants for determining the percentage of water vapor in flue gas are molecular sieve 4A and activated alumina.

ACKNOWLEDGEMENTS

The au thor would like to thank Professors A. T. Rossano and M. J. Pilat of the University of Washington, Depart­ment of Civil Engineering, for their help and support in making this research possible.

REFERENCES

[1) ASHRAE, Handbook of Fundizmentals, pp. 99-110, 235-240, 359-370, American Society of Heatmg, Refrigerating and Air Conditioning Engineers, Inc., New York, 1968.

[2) Thomas, T. L., "Molecular Sieves in Petroleum and Natural Gas Processing," Linde Molecular Sieves Adsorbent Bulletin, Union Carbide Corporation, New York, 1963.

[3) Moulding Compounds, Sec. Tygon, pp. IT-127 ; Universal

Plastics Company, Seattle, 1967. [4) Light, F. H., "Performance Test Codes," Volume 19.10-

1968, Volume 18-1932, Volume.21-1941, Volume 27-1957, Volume 19.3-1961, American Society of Mechanical Engineers, New York.

[5) Steam. Its Generation and Use, p. 4-A9, The Babcock and Wilcox Company, New York, 1963.

[6) Trusell, F., "Efficiency of Chemical Desiccants,"

Analytical Chemistry, Volume 35, (6), pp. 674-677, Pergamon Press, New York, 1963.

170

APPENDIX

COMBUST ION CALCULATIONS MOLAL BASIS

From the fuel analysis, the number of moles of com­

bustibles are determined for each compound in the fuel

and are summarized below.

Fuel Moles C Moles H. Constituent Percentage 1 00 Moles Fuel 1 00 Moles Fuel

CH. 93.32 93.32 186.64

C. H. 3.72 7,44 1",6

C3H. 0.97 2.91 3.88

C. HIO 0.33 1.32 1.65

C, H12 0.05 0.25 0.30

N, 1.47

100.00 105.24 203.63

The Orsat analysis is used to compute the percentage of excess air that existed in the duct. In formula (17) the O2 and CO are given in percentage by volume.

.

7.2%-0 X 100 0.264 (84.2%) - 7.2%

- 48%

Total Air = 100% + Excess Air

- 100%+ 48%

= 148%

The following chart illustrates the method used in determining the pound mole composition of flue gas. This can then be used to ascertain the percentage of moisture by volume of the flue gas. Values computed in the previous calculations are used in the following chart. The sums of the columns titled Moles C and Moles H2 are used in their proper place in the chart. The result of the Excess Air calculation is used where indicated. The interested reader is referred to Steam, Its Generation and Use, page 4-A9. [5]

Excess Air = O2- �CO

0.264(N2) - (Or �CO) X 100 (17)

The percentage of water vapor by volume is determined by taking the total of the sums under the Flue Gas Composition columns. This total is divided into the sum of the H20 column. When this operation is carried out, the percentage of water vapor by volume is 13.8%

•

Moles

Fuel Fuel 0, Constituent Constituent Multiplier

C to CO, 105.24 1

H, 203.63 Yo N, 1.47

CO, 0.14

Sum 310.48

Excess Air x 0" Moles Required

207.10 x 0.48 =

Sum

Nitrogen in Combustion Air

3.76 x 306.40 =

Sum

Moisture in Atmosphere Entering

1458.40 x 0.0009 =

Sum

0. Moles

Required

105.24

101.86

207.10

99.30

306.40

1152.00

1458.40

Flue Gas Composition

CO. 0. N, H. O

105.24

203.63

1.47

0.14

99.30

1152.00

13.10 13.10

1471.50 105.38 99.30 1153.47 216.73

171