CONTINUOUS PRESSURE SWING ADSORPTION (CPSA) FOR NITROGEN REJECTION FROM NATURAL GAS

PHASE II PROGRESS REPORT

6/21/95 - 12/21/95

DOE SBlR Grant No. DE-FG03-94ER81819

January 22,1996

Principal Investigator

Peet M. Soot, PhD

Northwest Fuel Development, Inc. ’ 4064 Orchard Drive

Lake Oswego, OR 97035 - (503) 699-9836

TABLE OF CONTENTS

Pase

SUMMARY

LABORATORY DEVELOPMENTAL ACCOMPLISHMENTS

LABORATORY EQUIPMENT CONSTRUCTION

LABORATORY PREPARATORY TESTS

LABORATORY TEST RESULTS

i

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsi- bility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Refer- ence herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recom- mendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

LIST OF TABLE AND FIGURES

Paae

Table 1. Table 2. Table 3 . Table 4 . Table 5. Table 6 . Table 7. Table 8. Table 9.

Figure 1, Figure 2.

Figure 3. Figure 4. Figure 5. Figure 6. Figure 7, Figure 8. Figure 9. Figure 10. Figure 11.

CPSA LABORATORY ACCOMPLISHMENTS REPEATED TRIAL CONDITIONS FEED CONCENTRATION VARIATION FEED PRESSURE VARIATION TOTAL CYCLE TIME VARIATION FEED STEP TO PRODUCT STEP TIME RATIO EFFECT OF FEED TIME WITH BACK PRESSURE EFFECT OF BACK PRESSURE BACK PRESSURE CONTROL

2 6 8 8 10 10 14 16 19

CPSA LABORATORY FLOW DIAGRAM NORMALIZED PERCENT MAXIMUM PRODUCT ENHANCEMENT vs. FEED PRESSURE FLOW RATES vs. FEED PRESSURE ENHANCEMENT vs. FEED RATIO FLOW RATES vs. FEED RATIO RECOVERY vs. FEED RATIO WASTE CONCENTRATION vs. FLOW RATE FLOW RATES vs. BACK PRESSURE METHANE CONCENTRATION vs. BACK PRESSURE METHANE RECOVERY vs. BACK PRESSURE ENHANCEMENT vs. BACK PRESSURE

3

9 9 11 11 12 15 17 17 18 18

SUMMARY

The work accomplished during the first six-month period of Phase I1 consisted of process laboratory experimentation and computer modeling of the process. Work on demonstration unit design and fabrication has awaited the results of these two tasks. Now that data are available from the laboratory phase, some of the design work can be initiated.

The laboratory work has included equipment development, shakedown operations and actual process runs with the laboratory scale units. logistical issues. Prof. Ruthven, project modeling consultant, moved from the University of New Brunswick to the University of Maine during the early stages of Phase 11. He was still able to take delivery of Prof. Alpay's gProm computer simulation package (from Imperial College in the UK) during that period, but was not able to make any runs with the system. The University of Maine's Sun Workstations were not totally compatible with the gProm program. New Brunswick and Prof. Ruthven will be able to make simulation runs at that University. immediate future.

The computer modeling has been delayed by some

It has now been installed at the University of

Results willbe available in the

LABORATORY DEVELOPMENTAL ACCOMPLISHMENTS

Table 1 outlines some of the milestones accomplished in the Continuous Pressure Swing Adsorption (CPSA) laboratory during this reporting period. considerably from Phase I through many modifications. control features were identified and a firm basis for future laboratory and demonstration scale testing has been developed.

The CPSA equipment has evolved Critical

LABORATORY EQUIPMENT CONSTRUCTION

Several CPSA column designs have been constructed and tested under a variety of operating conditions. are described below and shown in Figure 1.

The current features

The main body of the CPSA column in each design is composed of 1/2 inch stainless steel ( - 3 / 8 " I D ) and associated compression fittings. markedly improve the adaptability of the CPSA laboratory system over the Phase I equipment. Major alterations and changes in column lengths can be accomplished in a minimal amount of time. Surge tanks have been placed into each of the gas stream lines to minimize fluctuations in the flow rates so that flow measurements can be taken more accurately. This also allows gas streams to be maintained at a more constant pressure. A vacuum/compression pump has been installed on the product gas line (not shown in Figure 1) in order to broaden the possible operating pressures for the process.

The compression fittings and associated materials

-1-

Table 1. CPSA LABORATORY ACCOMPLISHMEN"8

Equipment Arrangements :

1 ) 5' column w i t h f e e d c n l e r i n g a t t o p

2 ) 7 ' column w i t h f e e d e n t e r i n g a l o n g column, 2 ' f rom t o p

3 ) 7 ' column w i t h f e e d e n t e r i n g f r o m t h e top

4 ) 3 ' column w i t h f e e d e n t e r i n g from t h e top

A c c e s s o r i e s d e s i g n e d , i n s t a l l e d and tested:

1 ) Dus t t r a p s and f i l t e r s t o p r e v e n t c l o g g i n g

2 ) PLC c o n t r o l l e r f o r a c c u r a t e t i m i n g

3 ) W e t t e s t meters, m a s s flow meters a n d r o t a m e t e r s f o r f l o w measurements

4 ) S u r g e t a n k s on f e e d , p r o d u c t and w a s t e l i n e s t o smooth f low

5 ) Dual methane d e t e c t o r s to e n a b l e c o n s t a n t stream m o n i t o r i n g

6 ) V a c u u m pump on p r o d u c t l i n e to e n h a n c e r e c o v e r y a n d f u l l y c o n t r o l p r e s s u r e p a t t e r n

C o n t r o l F e a t u r e s ( I n d e p e n d e n t V a r i a b l e s ) T e s t e d :

1 ) Feed p r e s s u r e

2 ) Feed c o n c e n t r a t i o n

3 ) C y c l e r a t i o s ( f e e d , 1st d e l a y , p r o d u c t i o n , and 2nd d e l a y p r o p o r t i o n s ) t

4) T o t a l c y c l e t i m e

5 ) B a c k p r e s s u r e on w a s t e stream

6 ) Waste stream f l o w c o n t r o l

Figure 1. CPSA LABORATORY FLOW DIAGRAM

CPSA COLUMN

CH 4 Product

Sarnplesto to Wet Test Gas Analyser Meter

Samples to Gas Analyser

7

Dust Trap

I * Dust Trap

to Gas Analyser

N 2 Product

LEGEND :

O M ? Z Surge Manual Pressure Solenoid Rotameter Tanks Valves Indicators Valves

FMR 1015195

The feed and product gas stream cycles are regulated by solenoid valves. These valves are now controlled by an Allen-Bradley programmable logic controller (PLC) - Model MicroLogix 1000. This unit allows precise timing functions for the solenoid valves. Needle valves are used to control the flow rates of various gas streams in and out of the system. A check valve prevents flow from the waste surge tank back into the CPSA column at times when the bottom of the column experiences low pressures.

A sampling system is in place to direct parts of the various gas flow streams through one of two continuous infrared gas analyzers. methane analyzers. used to verify data from the Horiba instruments. Flow rates can be measured in a number of ways. rotameters, a mass flow meter (with accompanying totalizer), and a Precision Scientific wet test gas meter. have been periodically calibrated against each other in order to verify the accuracy of the data for gas flows.

During the course of this work numerous improvements were designed into the CPSA system, allowing easier operation and more consistent results. of the adsorbent due to bed fluidization during the rapid depressurization step of the cycle. exit the column and clog the 80 mesh screens which had been placed in the lines to prevent valve damage. not totally unexpected since Kadlec's students had experienced similar problems. In their case, the entire CPSA column became clogged with the fines, leading to increased pressure drops in the system. It was apparent that NW Fuel's initial column design did not eliminate this problem. incorporated springs at the top of the column attached to a fine mesh material to hold the adsorbent in place. The needed improvement included higher compression strength springs and longer springs which would keep the adsorbent bed compacted even after some initial settling.

Both of these instruments are Horiba PIR 2000 A portable MSA methanometer has also been

The system is equipped with

These instruments

One initial problem was the abrasion

Fine particles were able to

This effect was

This initial design

As a result of the production of fines, additional safeguards were installed into the equipment. Dust traps were arranged to allow the dust to fall away from gas line screens and out of the gas flow stream. installed to further prevent clogging. With these improvements, the CPSA columns have run through nearly forty trials without interruption.

Additional in-line filters were designed and

LABORATORY PREPARATORY TESTS

Data are currently available for tests with two separate column arrangements under a variety of operating conditions. column is 5 feet in length with the feed stream entering at the top of the column. The second column is 7 feet long and is fed

The first

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from the side at a point two feet from the top. In both configurations, the product stream is generated from the top of the column while the waste stream exits from the bottom.

A four step timed cycle is used during the experiments, First the column is IIfedrr or pressurized with the feed gas while the product line is closed, The second step is a delay where both feed and product valves are closed. gas generated while the feed line valve remains closed. Finally, the fourth step is another delay where both inlet and outlet valves are closed. The waste stream produced from the opposite end of the column is left open throughout the entire cycle. the column and the waste end of the column does not experience a very large fluctuation in pressure. A shorthand notation has been developed for the times allotted to each step of the full CPSA cycle. The time notation lists the time for each step in the cycle in the order they are described above (e.g. 2, 0.1, 3, 0.2 denotes a cycle composed of a 2 second feed, 0.1 second delay after the feed step, 3 second production, and a final 0.2 second delay after the production step and before the feed step for the next cycle) .

The third step has product

This is possible since there is a pressure drop through

The critical dependent variables are as follows:

(1) Percent of product enhancement (the methane concentration in the product minus the concentration in the feed),

(2) Normalized percent of maximum possible enhancement ( % product enhancement divided by the difference between 100% and the feed concentration, expressed in a percentage),

( 3 ) Methane recovery (percentage of feed methane that is recovered in the product gas stream),

( 4 ) Flow rates of each gas stream.

After system shakedown some experiments were run and repeated in order to verify the consistency of results. Table 2 lists several repeated test conditions. In general, the results match very well. Although there is some variation in the last set of runs. The reference to back pressure in the footnote of the Table refers to the pressure at the waste end of the column. Initially, the waste end of the column was allowed to vent gas to atmospheric pressure with no restriction. It was later found that better results woul’d be obtained with the column if the outlet flow at the waste end of the column was restrained - which effectively imparted back pressure on the column at the waste gas end.

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Table 2. REPEATED TRIAL CONDITIONS

Product Flow R a t e s Rri n Enhance men t. Wnste P r o d u c t Waste

# % % of max Conc. (scfh) ( s c f h )

FB1 6.3 16 59.7 5.1 15.1 FC 1 5.3 15 60.7 ‘3.8 15.0 5 ’ top fed column, 62% feed

- Repeats

FD 1 3.1 8 61.0 FE1 3.0 8 60.7 7’ mid fed column, 59% f e e d

FF2 2.4 6 57.8 FG1 2.9 7 57.5 FG7 3.4 8 58.1 7’ mid fed column, 62% f eed

10.0 9.7

9.0 9.5

10.9

15.8 16.0

16.3 15.9 17.5

Methane Recovery

( % )

28 22

41 40

37 39 41

A l l of t h e s e employed 20 p s i g f eed pressure with a 2 , .1, 2 , .1 Cycle without any back pressure.

-6-

LABORATORY TEST RESULTS

A variety of independent variables were tested with the CPSA laboratory system. These variables included feed gas methane concentration, feed gas pressure, and cycle times. The cycle time variations include total cycle time as well as times for the individual steps within any given CPSA cycle. Based on these test results a number of dependent variable effects were also analyzed. These dependent variables included the effects of feed:product step time ratio, feed-step time, and back pressure with constant cycle times.

Trials examining the effects of the feed concentration are shown in Table 3. As expected, the flow rates remain essentially unchanged with variations in feed concentration. While there is no clear trend, it appears that the normalized percent of maximum enhancement remains constant or may even increase as the feed concentration rises. Notice that the 5-foot column yielded twice the enhancement as the 7-foot column with only a modest loss in productivity.

The effects of variations in feed pressure are displayed in Table 4 . including better enhancement, better recovery, and a productivity that was proportional to the feed pressure (see Figures 2 and 3). Trial FA3 yielded the highest enhancement of all the trials covered by this summary with a 10% improvement. This is equivalent to a normalized enhancement of 21% of the maximum possible enhancement from the feed concentration of 52% and a pure 100% methane product.

Higher feed pressures gave consistently better results

Table 5 lists comparisons of cycle time variations. The last two sets of trials show that longer cycle times produced increased enhancement at the expense of lower yields (recoveries) and lower product flow rates. The results from the first set (5-fOOt column; cycle times of 2.5, 0.1, 1.5, 0.1 seconds) appears to peak, butthis is likely an artifact. The product concentration from the 4.2 second cycle varied significantly and the highest value is listed; if the average value was used and the intermediate enhancement would be shown. The variation was much less for the other trials. Note that the cycle with 1, 0.1, 3, 0.1 second step times gave better or equal enhancement with higher recovery rates that the 2.5 0.1, 1.4, 0.1 second step time cycle.' This effect is due to similar product flow rates but lowered waste flow rates.

The feed step:product step time ratio is examined in Table 6. Lower feed percentages gave increased enhancement, recovery and product flow rate (see Figures 4, 5, and 6). This was somewhat unexpected as literature results gave peaks at a value of 1. The tests reported in the literature focused on raffinate purification rather then the adsorbate, as is the case in the present study. The results from the 7-foot column (with feed offset from the end) are similar but less dramatic. As with the

-7-

Table 3. FEED CONCENTRhTION VARIATION

Product Concentrations (%CH4) Enhancement Flow Rates Methane

Run ........................... % Product Waste Recovery ’ # Feed’ Product Waste % of Max. (scfh) (scfh) - ( % ) - - FA2 5 2 . 1 60.4 47 .9 8 .3

FB1 61 .7 68 .0 59 .7 6 . 3 - FCl 6 2 , 3 68,O 60.7 5 .7 5 ’ top fed column, cycle times of 2 , 0.

vs 1 7 8 1 2 4 5

16 15

5 4

15 1 5

28 22

FF2 F G l FG7

58 .6 61.0 57 .8 2 .4 58.1 61 .0 57 .5 2 . 9 58 .9 62 .3 58 .1 3 .4

FD 1 62.0 65 .1 61.0 3 .1 FE1 62.0 65.0 60 .7 3.0

FF1 84 .3 86.5 82 .9 2 .2 7’ mid-feed column, cycle times of 2, 0’

vs

vs

6 7 8

9 9

11

1 6 1 6 18

37 39 41

8 8

1 0 1 0

1 6 1 6

4 1 40

18 14 11 39

9

9

1 2

1 2

44

47

FF8 58.6 61 .0 5 8 . 1 2.4 6

FD6 62.0 66 .6 60 .7 4 . 6 1 2 7 ’ mid-feed column, cycle times of 1, 0 . 1 , 3 , 0 . 1

vs

All trials utilized 20 psig feed without back pressure.

Table 4. FEED PRESSURE VARIATION

Product Pressures (psig) Enhancement Waste F l o w Rates Methane

Run Feed N2 % Conc. Product Waste Recovers - % of Max. ( % C H 4 ) (scfh) (scfh) ( X ) - # FP NP -

FA1 10 1 4 . 6 F A 2 20 1 . 5. 8 .3 FA 3 30 2 . 5 9 . 9 5’ top fed column, 52% feed

1 0 1 7 2 1

49 .2 47 .9 46.0

3 8

11

6 1 2 17

4 1 45 46

FE4 10 1 0 .6 2 FE1 20 2 3 .0 8 FE2 30 3 5.3 1 4 7 ’ mid-fed column, 62% CH4 feed

61.0 60 .7 60.7

4 10 1 4

8 1 6 23

3 6 . 40 4 1

-8-

Figure 2. NORMALIZED PERCENT MAXIMUM PRODUCT ENHANCEMENT FEED PRESSURE

22 21 2 0 - 19 18 17 16 IS 14 I3 12

2 9 , 8 - 7 - 6 - 5 - 4 - 3

1 - 0

1 1

&l Product Enhancement vs Feed Pressure

- - - - -

A-

/'- ./ ./ ./ /-/

/ - - - - / O'

/-- /-*

/--- /-*

1 I I I I I I I I I I

Figure 3. FLOW RATES vs. FEED PRESSURE

Flow Rates vs Feed Pressure

40

35

30

25

20

IS

10

5

0 I I I I I I 1 I I I I

10 12 14 16 18 20 22 24 26 28 30

-9-

vs .

Table 5. TOTAL CYCLE TIME VARIATION

T o t a l P roduc t C y c l e Enhancement Waste

Run T ime % Conc. # (sec) % of Max. ( % CH4) --

FC8 2 . 1 4 . 3 11 60.4 FC2 4 . 2 6.0 1 6 59 .7 FC7 8 . 4 5 . 0 1 3 60 .7 5’ t o p f e d column, 63% CH4 f e e d @ cycle f o r m a t 1, 0 . 1 , 3 , 0 .1 .

F l o w R a t e s CH4 J?rod. Waste Recov. ( s c f h ) ( s c f h ) ( % )

6 1 2 36 5 1 0 36 3 9 26

20 p s i g , no back p r e s s u r e ,

- FC5 2 . 1 2 .7 7 61.3 6 18 25 FC4 4.2 4.7 1 2 61.0 4 1 7 21 FC6 8 . 4 5.0 13 61 .3 3 1 6 15 5’ t o p fed column, 63% CH4 f e e d @ 20 p s i g , no back p r e s s u r e cycle f o r m a t 2 . 5 , 0 . 1 , 1 . 5 , 0 .1 ,

FF5 2 . 1 0.8 2 58.4 - 10 20 34 FF3 4 .2 2 .1 5 58 .1 8 1 9 31 FF6 8 . 4 3.4 8 58.1 5 1 7 24

, 7’ mid-fed column, 59% CH4 f e e d @ 20 p s i g , no back p r e s s u r e cycle f o r m a t 2 . 5 , 0 . 1 , 1 . 5 , 0 .1 .

Table 6. FEED STEP TO PRODUCT STEP TIME RATIO

P r o d u c t Feed/ Errhancement Waste F’1.o~ R a t e s CH4

% of Max ( % C H 4 ) ( s c f h ) ( s c f h ) ( % ) Run Produce % Conc. P r o d . Waste Recov.

- - # R a t i o __I

FC2 0 .33 6 . 0 . 1 6 59.7 5 1 0 36 FC1 1 . 0 0 5 . 7 15 60 .7 4 1 5 22 FC4 1 . 6 7 4 . 7 1 2 61.0 4 1 7 21 FC3 7 .00 2 . 7 7 61.7 3 21 11 5’ t o p f e d column, 62% CM4 f e e d @ 20 p s i g , no back p r e s s u r e t o t a l c y c l e t i m e of 4 .2 s e c o n d s , 0 . 1 s e c o n d d e l a y s .

FF8 0 .33 2 . 4 6 58 .1 9 1 2 44 FF2 1 . 0 0 2.4 6 57 .8 9 1 6 37 FF3 1 . 6 7 2 . 1 5 58 .1 8 1 9 31 FF4 7 .00 0 .8 2 58 .4 5 21 20 7’ mid f e d column, 59% CH4 f e e d @ 20 p s i g , no back p r e s s u r e

-10-

Figure 4. E=CEMEN!L' vs. FEED RATIO

6 -

5 - 4 - 3 -

2 -

1 - 0

Y C

i V

C 0 c C W s s E - X

a. 0

DE

1 I I 1 I I

2 4l \=

FeeJ/Produdlon Time Ratlo

fl

Figure 5. FLOW RATES vs. FEED RATIO

(5' column rosults)

26 I

n 0 [I K Y

z G 8 L 6

01 I I I 1 I 1 I 0 1 2 5 4 5 6 7

Fwd/Productlon Tlmo Ratlo 0 Product + Wasto 0 Total

-11-

Figure 6. RECOVERY vs. FEED RATIO

(5' column results)

38

10 ' I 1 I I 1 1

4 5 6 7 0 1 2 3

Feed/Production Time Rotlo

5-fOot column, this case is giving much lower enhancement but higher product flow rates.

Another view of the CPSA cycle ratio was taken by varying the feed times while leaving the rest of the cycle constant (Table 7). end of the column. needle valve between the end of the column and the waste surge tank. The average pressure was kept close to the average pressure at the feed end of the column. in the cases of very short cycle times.) with this configuration yielded better enhancement but a loss in recovery. To some extent, this type of control is artificial in the fact that the major impact is on the waste flow rate. Higher waste flow rates can maintain the 50% pressure during the long feed times, while shorter times dramatically lower the waste flows to the point where the 50% pressure can not even be achieved. The lower waste flows contain markedly less methane (see Figure 7) while improving the recovery. But the flows are so low that the product enhancement declines. The enhancement is traded roughly equally for recovery, i.e. the enhancement multiplied by the recovery is nearly constant.

In these tests, back pressure was also applied to the waste This is accomplished by partially closing a

(This was not possible The higher feed times

Table 8 explores the use of back pressure with constant cycle times. For the 5-foot column, increasing the average pressure on the waste end of the column decreases the waste flow rate and removes more methane from this stream - which increases the recovery. It also increases the product flow rate. This comes at the cost of lower product enhancement and lower overall flow rates (see Figures 8, 9, and 10). The middle data point in these Figures (from the 5-fOOt column at 30 psig feed) is a bit anomalous. There was probably some logging of the product line during this trial. similar except that there is a peak in enhancement (Figure 11). At higher back pressures, the enhancement matches or beats that from the 5-foot column.

The results from the 7-foot column are

Back pressure can be applied before the waste surge tank, as described above, or by using a needle valve placed in-line after the surge tank. This latter approach allows gas to flow freely between the column and the waste surge tank. Under this arrangement, the surge tank will purge the column during production times and then refill during feeding times. Several tests were performed to see which method was more beneficial - needle valve before or after the waste surge tank. The results shown in Table 9 do not indicate a significant difference under the range of conditions tested with these trials. (not described in this report) show large variations in these results with long total cycle times. this point were apparently too short to allow much back flow from the waste surge tank to the column.

Later tests

The cycles studied up to

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Table 7. EFFECT OF FEED TIME WITH BACK PRESSURE

Ave, Press. Product Feed (3 waste Enhancement Waste Flow Rates CH4

% of Max. ( % CH4) (scfh) (scfh) ( % ) Run Time end % Conc. Prod. Waste Recov.

- - # (set 1 (Psig 1 - FC16 FC12 FC15 FC14 FC13

0 . 5 1

1 . 2 5 1 . 5

2

8 . 5 1 0

10 .25 10 .25

1 0 . 5

4 . 3 4 . 3 5 .0 5 . 7 5 . 7

11 11 1 3 1 5 15

20.1 33.6 47.2 55 .3 57 .5

5’ Top fed column, 62% CH4 feed (3 20 psig 0 .1 second delays, 3 second production step, back pressure controlled before surge tank.

-14-

89 84 74 7 0 64

F i g u r e 7. WASTE CONCENTRATION Vs. FLOW RATE

(both controllod through back pmwrro)

T I 0 Dc v

C 0 - ” e U C 0 u

s E H ti 0 U

P I I I 1 I

0 1 2 3 4 5 6

Waste Stream Flow Rote (scfh)

-15-

Table 8. EFFECT OF BACK PRESSURE

Run #

Ave. P r e s s . Product @ w a s t e Enhancement Waste Flow R a t . e s

end % Conc. Prod. Waste % of Max. ( % CH4) ( s c f h ) ( s c f h ) - '

(PSi i3)

FB1 2 6.3 16 59.7 5 15 FB2 10.5 5.3 14 57.5 8 6 FB3 13.5- 3.8 10 28.9 9 2 FB4 14.5 3.0 8 15.6 9 1 5' top fed column, 62% CH4 feed 42 20 psig, 2, 0.1, 2, 0 . 1 c y c l e .

FD 1 2 3.1 8 61.0 10 16 FD4 5.5 4 . 2 11 58.6 10 13 FD2 10 4.2 11 58.6 12 7 FD3 14.5 3.0 8 21.3 12 1 7' m i d f e d column, 62% CH4 feed @ 20 psig, 2, 0.1, 2, 0.1 cycle.

CH4 Recov.

( % I

28 60 87 93

41 46 65 96

F i g u r e 8 . FLOW RATES vs. BACK PRESSURE (5' colunn w / 2 0 psl9 feed)

90

80

70

60

50

4 0

30

20

10

n 1: L U U

8 Y 0 II:

- - -

- - - - - -

21

17 - 16 -

1 1 1 0 - 9 - 8 -

6 -

4 - 3 - 2 - 1 - 0

-

5 c-

I I I 1 1 I I I . I I I I 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 6

Buck Prassura (psfq) 0 Product + Wasto 0 Total

F i g u r e 9. METHANE CONCENTRATION VS. BACK PRESSURE

(5' colmn w/20 pdg faad)

100

- 0 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5

Back Pretsura (psig) 0 Product 4. waste

-17-

Figure 10. METHANE RECOVERY vs. BACK PRESSURE (5' column w / 2 0 pslg food)

n

U b!

i? i: (r K 0

f Y

f

100

90

80

70

60

50

40

30

20

10

0 0 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5

Bock Pressure (&d U Product

Figure 11. ENHANCEMENT vs. BACK PRESSURE

Y C 0

fi v C t) L C W

0 3 v Q

U

P

(7' mld fad column)

0 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5

Back Prcssuro (pdg) 0 Prduct + waste

-18-

Table 9. BACK PRESSURE CONTROL

Ave. Press. Product @ w a s t e Enhancement Waste

Run end % Conc. - # ( w i g ) % of Max.(% CH4)

FG1 2 2.9 7 57.. 5 FG2 6 3.9 9 57.0 FG3 10 3.9 9 56.4 FG4 13 '3.6 9 55.6 Back pressure before surge tank.

- 6

FD1 2 3.1 8 61.0 FD4 5.5 4.2 11 58.6 FD2 10 4.2 11 58.6 FD3 14.5 3.0 8 21.3 Back pressure after surge tank.

FG5 15 2.9 7 28.5

Flow R a t e s Prod. Waste ( s c f h ) ( s c f h )

9 16 10 12 11 8 11 4

10 16 10 13 12 7 12 1

12 1

CH4 Recov.

( % I 39 49 63 76

41 46 65 96

94 Back pressure c o n t r o l l e d before and a f t e r surge tank

A l l tr ials performed w i t h a 7 ' mid fed column us ing 58 or 62% CH4 f e e d @ 20 p s i g w i t h a 2 , 0 . 1 , 2, 0.1 c y c l e .